pneumatic clamping

95
Handling Machining Assembly Control Pneumatics Electronics Mechanics Sensorics Software Chinese English French German Russian Spanish Blue Digest on Automation 053 585 Hesse Clamping with compressed air and vacuum

Upload: ragdapattice

Post on 07-Apr-2015

684 views

Category:

Documents


4 download

TRANSCRIPT

Page 1: Pneumatic Clamping

Handling

Machining

Assembly

Control

Pneumatics

Electronics

Mechanics

Sensorics

Software

Chinese

English

French

German

Russian

Spanish

Blue Digest

on Automation

053 585

HesseClamping withcompressed airand vacuum

328,5 mm

160 mm

120 mm 42 mm8,5 mm

47,3

mm

88,5

mm

158,

5 m

m19

5 m

m22

5 m

m

Ha

nd

ling

Pn

eu

ma

ticsE

ng

lishB

lue

Dig

est

He

sseC

lam

pin

g w

ith co

mp

resse

d a

ir an

d va

cuu

m

��

Page 2: Pneumatic Clamping

Hesse

Clamping with compressed air and vacuum

Page 3: Pneumatic Clamping
Page 4: Pneumatic Clamping

Clamping with compressedair and vacuum

Blue Digeston Automation

HandlingPneumatics

Stefan Hesse

Page 5: Pneumatic Clamping

Blue Digest on Automation

© 2001 by Festo AG & Co.Ruiter Strasse 82D-73734 EsslingenTel. +49 (0)711 347-0Fax +49 (0)711 347-2155

All texts, representations, illustrations and drawings included in this book arethe intellectual property of Festo AG & Co., and are protected by copyright law.All rights reserved, including translation rights. No part of this publication may be reproduced or transmitted in any form or by any means, electronic,mechanical, photocopying or otherwise, without the prior written permission of Festo AG & Co.

Page 6: Pneumatic Clamping

Often small and inconspicuous, sometimes large and bulky, but alwaysindispensable – such is the nature of clamping devices. These are used in themetalworking industry for drilling and milling operations and in the automobileindustry for clamping components which are to be welded. Basic assemblycomponents frequently require clamping, as do many types of workpiece in thewoodworking industry. In short-processing or machining needs to be precededby precision clamping. This secures workpieces against the forces generatedduring processing or machining and also the force of gravity. The efficient andreproducible clamping of workpieces naturally also offers considerable potentialfor rationalisation benefits. Many manufacturing companies therefore see anopportunity to optimise costs not only in terms of spindle speeds and feed ratesbut also through improved clamping systems. More and more use is being madeof modular clamping systems.

In the design of clamping systems, compressed air and vacuum have proved tobe excellent working media for powering clamping devices. Pneumatic clampsare efficient, reliable and inexpensive. There are, however, a large number ofvariants. Users therefore need to be well informed concerning the type ofclamping these variants offer, their operating conditions and the pneumaticcomponents involved. The aim of this book is to help provide this information.The main emphasis here is accordingly on the design concepts for clampingdevices which are used in constantly new forms in craft workshops and factories.The wealth of proven pneumatic components which are available creates anexcellent basis which allows users to enjoy an attractive cost/benefit ratio andachieve a high level of standardisation. The field of clamping technology is ofcourse much larger in its entirety than we are able to cover in this short introduc-tion. Notwithstanding this, we hope that the practical users for whom this bookhas been written will be encouraged to work independently to further expandtheir detailed knowledge of clamping technology and make creative use of this.We wish all our readers every success in this endeavour.

Stefan Hesse

Foreword

5

Page 7: Pneumatic Clamping
Page 8: Pneumatic Clamping

Contents

1 Fundamentals of clamping technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 991.1 Clamping as a function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91.2 Definition and positioning as preliminary stages to clamping . . . . . 141.3 Clamping methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

22 RReeqquuiirreemmeennttss ppllaacceedd oonn ccllaammppiinngg ddeevviicceess . . . . . . . . . . . . . . . . . . . . . . . . . . 22662.1 Classification of clamping devices . . . . . . . . . . . . . . . . . . . . . . . . . . . 262.2 Clamping force and clamping reliability . . . . . . . . . . . . . . . . . . . . . . . 272.3 Maintaining clamping force . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 322.4 Amplifying clamping force . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 342.5 Pressure intensifiers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 362.6 Limiting clamping force . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 382.7 Clamping range . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 392.8 Clamping accuracy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

33 TTyyppeess ooff ccllaammppiinngg ddeevviicceess . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44333.1 Lever clamps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 433.1.1 Simple lever clamps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 433.1.2 Toggle-lever clamps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 443.1.3 Toothed-segment clamps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 463.1.4 Swivel clamps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 473.1.5 Welding clamps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 483.1.6 Clamps with a centring action . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 503.2 Hold-down clamps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 523.3 Frame and panel clamps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 533.4 Diaphragm clamps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 553.5 Tubing clamps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 593.6 Vacuum clamps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 623.7 Internal clamps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 643.8 Clamping against conveyor belts . . . . . . . . . . . . . . . . . . . . . . . . . . . . 673.9 Compensating clamps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 683.10 Clamps for automobile bodywork construction . . . . . . . . . . . . . . . . . 70

44 PPnneeuummaattiicc sseeccttiioonn ooff aa ccllaammppiinngg ddeevviiccee . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77664.1 Control of clamping cylinders . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 764.2 Position monitoring using back sensors . . . . . . . . . . . . . . . . . . . . . . 784.3 Control system for a vacuum-operated clamping table . . . . . . . . . . . 80

55 DDeessiiggnn aanndd sseelleeccttiioonn ooff ccllaammppiinngg ddeevviicceess . . . . . . . . . . . . . . . . . . . . . . . . . . . 88115.1 Steps in the design process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 815.2 Selection of clamping devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82

66 SSaaffeettyy wwiitthh ccllaammppiinngg ddeevviicceess . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8844

77 AA bbrriieeff oovveerrvviieeww ooff ccoommppoonneennttss . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8877

LLiitteerraattuurree . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9900

GGlloossssaarryy ooff tteecchhnniiccaall tteerrmmss . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9911

77

Page 9: Pneumatic Clamping
Page 10: Pneumatic Clamping

1 Fundamentals of clamping technology

Clamping technology is an important element in craft workshops and factories,since workpieces, assemblies and semi-finished products need to be held securely to allow work to be carried out on them. Clamping ensures a definedand secure relationship between a workpiece and a machine table (machinecoordinate system) and thus between the workpiece and the tool in question.Clamping devices also have to absorb machining forces, assuming that machin-ing is not being carried out by laser, in which case no motion forces are appliedto the workpiece. Devices which hold workpieces securely in place are known asclamping devices or simply clamps. There are also clamps whose only purpose is to secure workpieces against gravity, for example tack-welding devices. Ingeneral, however, the following principle applies:

Every active force (machining force, processing force) generated by a tool must

be counterbalanced by the reactive force (holding force) of the clamping device

in question.

Clamps should be simple, fast and easy to operate and should be capable ofbeing adapted without difficulty for new clamping tasks. Notwithstanding theneed for flexibility, it is also necessary to maintain close tolerances.Furthermore, workpieces should be easily accessible while clamped, which isoften not easy to achieve, for example with large bodywork components in theautomobile industry. Clamping technology is, among other things, the art of holding a workpiece securely while using the minimum possible force.Pneumatically powered clamps have proved to be an ideal way of achieving this.

If we take a more general view of the clamping process, we find that the use of clamping devices goes far beyond the clamping of workpieces. In the con-struction of containers and apparatus, for example, it is necessary to hold covers closed and/or interlock these, while in mechanical engineering there is a need toclamp tools and jigs securely and durably. There is a similar need in the field ofmetal forming, where press tools, extruder heads and cutting and bending toolsalso need to be held accurately in position. In security zones, access doors mustbe interlocked and secured against unauthorised forcible opening. For theseapplications, too, there is a choice of pneumatics-based solutions, both formanual control and for integration into automatic control sequences.

The term “clamping” is used mainly in the construction of jigs and fixtures, whilein the field of handling technology we speak of “gripping” (Fig. 1-1). The purposeof clamping is to maintain a defined state. In the field of production technology,it is necessary to secure three-dimensional objects only temporarily; in this bookwe will consider only clamping achieved through the pairing of forces. The quali-ty of the result achieved in production and assembly operations will generallydepend directly on precise and dependable clamping.

9

1

Fundamentals of

clamping technology

1.1Clamping as a function

Page 11: Pneumatic Clamping

How is “clamping” defined? Clamping and unclamping are variants of the elementary functions “holding”and “releasing”. “Holding” is the temporary securing of a body in a certain position. This can be achieved through the pairing of materials, the pairing ofshapes (positive locking) or the pairing of forces (force locking). Working on thebasis of the VDI Guideline 2860, we can thus state the following definitions:

Clamping

Temporary holding (securing) of a body in a certain orientation and position

through the use of forces.

Unclamping

The opposite of clamping, which is to say the release of a body through the

removal of clamping forces.

Clamping forces are applied in one or two coordinate directions with the aid ofclamping components. As a general rule, the use of three clamping devices willresult in an unacceptable restriction of the freedom of axis of the tool in ques-tion and should therefore be avoided. The magnitude and direction of clampingforces should be controllable, and clamping forces should in general be alignedat right angles to workpiece surfaces. Clamping forces must furthermore notfluctuate as a function of time. “Clamping” includes the following subfunctions:

Positioning

This comprises the moving of a workpiece within a clamping device from its initial (insertion) position to the desired orientation position for all three coor-dinate axes. In the case of automatic clamping, special positioning componentsare used. These must not, however, impede feeding, processing and grippingoperations.

Definition

Determinate definition of the position and orientation of a workpiece in a clamp-ing device through the contact of the determining workpiece surface with thedefining surfaces of the clamping device.

1 Fundamentals of clamping technology10

Handling functions

Storing Quantitychanging

Moving Securing Controlling

Ordered storing(Magazining)

Sorted partsstoring(Stacking)

Random storing(Binning)

PartingCompilingSeparatingAllocatingBranchingConverging(Collecting)

TurningTransferringSwivellingOrientatingPositioningArrangingGuidingPassing onConveying

HoldingReleasingClamping

Unclamping

Checking– Identity– Presence– Size– Colour– Weight

MeasuringCounting

Fig. 1-1:

Classification of handling

functions in accordance

with VDI 2860

Page 12: Pneumatic Clamping

1 Fundamentals of clamping technology

Support

Support components prevent processing forces from causing undesired defor-mation of the workpiece. These components ensure secure support of the workpiece, free of the risk of tilting (see also Fig. 1-13).

It will be appreciated that it is necessary to take into account a large number offundamental principles and recommendations if we are to obtain favourabledesigns of clamps for every application. We can state some general rules (whichcould be described as rules for “clamping-friendly design”) as follows:

• As far as possible, no clamping forces should act on workpieces duringdefinition. These should be allowed to come into contact with the defining surfaces without external pressure forces, which should be applied onlyduring the clamping operation.

• Force should be applied only when the workpiece has ceased to move, thusavoiding the risk of workpiece deformation.

• The accessibility of clamped workpieces must not be restricted by clampingcomponents. Clamping cannot be carried out at the same place and time asmachining. If there is a need to keep 5 sides of a workpiece clear, it may benecessary to use magnetic or vacuum clamping plates (see also Chapter 3.6).

• Force should as far as possible be applied evenly to all points of the work-piece. If this is not done, the workpiece may revert to a previous shape whenunclamped. This will also mean a distortion of machined surfaces.

• There must be a safety interlock between the clamping device and the ma-chine tool concerned. There must be no possibility of machining starting before the full clamping force has built up. In cases where several indepen-dent clamping components are used, clamping force must be applied in a defined sequence.

• Efforts should be made in mechanical engineering in cases where workpiecesare machined on all sides, to work with the minimum possible number of workpiece clamps. Furthermore, the auxiliary process time for clamping, reclamping and unclamping should also be kept to a minimum.

Clamping devices may be of dedicated or multi-purpose design. In many cases,these devices are created from standard pneumatic components. We shoulddistinguish between standard and special clamping devices. Special devices arejustified in cases of high-volume production where workpiece clamping needs tobe at an optimum level. Special clamping devices are designed and produced onthe basis of workpiece drawings or by studying workpiece reject patterns andwith due regard to the machining operation involved.

11

Page 13: Pneumatic Clamping

Clamps may be fixed, i.e. permanently installed, but may also be mobile, for example if they are installed on workpiece carriers and circulate within trans-fer systems. In the case of mobile devices, these will have a mechanical clamp-ing action (spring force) and a pneumatic unclamping action. This means that a connection to a source of compressed air will be required only briefly at a loading or unloading station within a production line. Fig. 1-2 shows the clampvariants which are theoretically possible, disregarding electrical and electro-magnetic clamps.

Although clamping devices are often extremely simple, we must conduct an analysis of influential factors before deciding on a design. Clamping shouldalways be considered within the context of the relevant working environment.This process is shown in generalised form in Fig. 1-3. Another factor governingthe quality of finished workpieces is the way in which a clamping device is aligned and mounted on the machine table. Further important factors are as follows:

• The way in which workpieces are fed to the clamp, and the time required forthis

• The tendency of the workpiece to deform, and its surface properties• The rise in machining forces as tools slowly become blunt • The need for reliable operation despite the presence of machining swarf and

liquid coolant.

1 Fundamentals of clamping technology12

Clamping Unclamping Example showing design principle

mechanical pneumatic

pneumatic pneumatic

pneumatic mechanical

mechanical mechanical

Fig. 1-2:

The operating principle of

clamping devices is variable

Page 14: Pneumatic Clamping

1 Fundamentals of clamping technology

The workpiece contact points within clamping devices may become dirty afterprocessing only 15 to 20 workpieces. To enable clamping devices to be cleanedeasily, “dirt traps” should be avoided. Clamping systems should also have dirt-repellent surfaces. Clamping devices should continue to operate reliably in allcases even if dirt deposits are present.

Automated sequences must be monitored continuously to ensure that all theconditions are fulfilled for correct clamping operation. Fig. 1-4 shows in detailthe associated subfunctions. Every function which is considered necessary mustbe implemented in the form of some kind of function provider. The exampleassumes that workpieces are inserted by a handling device with a jaws-type orvacuum gripper.

Clamping and machining or shaping are sometimes very closely linked. A case ofthis kind is shown in Fig. 1-5.

13

ClampingUnclamping

Machining process

Workpieces Tool

Machine

Environmental influences

Development ofclamping force

Development ofclamping force

Environmental influences

Monitoring of

Gripperfreedom

Supportfor inser-tion

PresenceIdentity

Correctposition

Clampingand posi-tion status

Clampingand posi-tion status

Clampingstatus Gripperfreedom

Presence Clean-liness

Applica-tion ofclampingforce

Work-piecedefinition

Hold-

ing

Releaseof clamp-ing force

Supportfor re-moval

Cleaning

Chipremoval Chips

Coolant

Workpiece– Machined– In gripper– Over clamp

Workpiece– Unmachined– In gripper– Over clamp

Machining

Fig. 1-3:

Factors influencing

the clamping operation

Fig. 1-4:

Workpiece-related

subfunctions and monitoring

tasks with automatic

clamping devices

Page 15: Pneumatic Clamping

Here, a plywood casing is “clamped” against a heated former. Strictly speaking,this “clamping device” is a press. Clamping must be carried out in a definedsequence. A solution using a pneumatic drive is without doubt highly advan-tageous.

Among the preliminary considerations in the process of designing a clampingdevice is the question of what defining surfaces and components are to be used.Lack of attention here may mean that the resulting clamping device does notwork correctly. The aim of the process is to ensure that the machining operationcan be carried out to the required tolerances. In order to achieve this, referencesurfaces must be defined on the workpiece drawing when dimensions are enter-ed. Following this, we must select the defining surfaces for clamping. 6 contactpoints are required in order to determine a V-shaped body and thus prevent thisfrom moving in all 3 dimensions. This applies to both gripping and clamping. Theprinciple is shown in Fig. 1-6.

1 Fundamentals of clamping technology14

3

4

1

2

5

6

7

8

Fig. 1-5:

Shaping device for casings

1 Mounting plate

2 Foot mounting

3 Pneumatic cylinder

4 Pressure jaw

5 Plywood casing

6 Heater

7 Heater plate

8 Former

1.2Definition and positioning as pre-liminary stages toclamping

Page 16: Pneumatic Clamping

1 Fundamentals of clamping technology

The term “defining surface” is used to describe the plane on which definition isactually carried out. The defining surface is governed by production factors. Thedefining surfaces, on the other hand, are the contact surfaces present on theworkpiece and used for determining. In defining these contact points, we mustpay attention to the following points:

• The contact points for a defining surface should be as far apart as possible.• The defining components must be capable of absorbing clamping, weight and

machining forces.• Clamping forces should always be applied at right angles to the contact points

(the centre of lines linking these points of the centre of a clamped triangle).• The defining surfaces should be available on the workpiece in the form of

machined surfaces, since it may otherwise not be possible to maintain unam-biguous and reproducible positional relationships.

With regard to the last requirement, additional machined shaped componentsare often fitted to the workpiece to prevent the possibility of undefined positiondetermination. An example is shown in Fig. 1-7. If side contact surfaces are usedwith an undulating blank workpiece, this will lead to an imprecise and non-reproducible position in the clamp. The workpiece has accordingly been pro-vided with a finish-machined hole which is used for definition purposes in thefirst and subsequent clamping devices. The centre of the hole can be used as a reference point for precise positioning.

15

1

2

3

4

Fig. 1-6:

Defining a body

with 6 contact points

1 Contact point

2 Workpiece

3 Supporting force

4 Defining surface

Page 17: Pneumatic Clamping

A number of examples now follow which illustrate the choice of defining surfaces. Fig. 1-8 shows the possibilities in the case of a panel-type workpiece.Correct selection and shaping of defining surfaces helps to prevent machining errors.

Example: A drilling jig is to be designed for the workpiece shown in Fig. 1-9a.Which defining surfaces should be chosen?

1 Fundamentals of clamping technology16

Poor Good

1

2

a b c

F

Workpiece

a b

Fig. 1-7:

A finish-machined hole

ensures precise definition for

an otherwise unmachined

casting.

Fig. 1-8:

The various possible

determining surfaces with

a panel-type workpiece.

a) Contact edge

b) Fixed corner

c) Hole

1 Defining surface

2 Clamping-force generator

Fig. 1-9:

Clamping device for drilling

panels

a) Workpiece drawing

b) Clamping-device concept

F Manual force

Page 18: Pneumatic Clamping

1 Fundamentals of clamping technology

As dimensioning is carried out from one corner, this will also be used as a defining corner. In the example, clamping is carried out diagonally via a handlever and a self-locking clamping cam. It would of course also be possible to usea pneumatic cylinder as a force generator.

If we go too far with the defining process, the result is over-definition, whichmust be avoided at all costs, since it will lead to operational problems. Over-definition is present when there is more than one defining surface in a givendirection for a reference plane. The easiest way to understand this is through anexample. Fig. 1-10 shows a panel which is to be determined with the aid of twoholes. It is unfortunately possible to produce the holes to a high degree of accu-racy either not at all or only at an unacceptable cost. The definition process musttherefore be made less critical, for example by using an elongated hole torestrict the rotary freedom of movement of the workpiece.

Instead of the elongated hole, we could select suitable jig components – in thiscase, a locating pin with a pair of flats. Pins of this kind provide a definingfunction in only one direction. Fig. 1-11 shows an example.

17

1 2 3

Over-defined Possible correct solution

a b

Fig. 1-10:

Defining components

should be selected in such

a way that over-definition

is avoided

1 Defining component

2 Workpiece

3 Clamp baseplate

Fig. 1-11:

Examples of determining pins

a) Round defining pin

b) Defining pin with pair

of flats

Page 19: Pneumatic Clamping

The defining operation is generally carried out by activating clamping components, for example by precise insertion of a workpiece into a clampingdevice. It can, however, also be carried out during the clamping process itself, as shown by a number of examples in Fig. 1-12. This is not recommended whenprecision clamping is required. The defining surfaces can be seen clearly, andthe defining operation also provides a centring function.

Workpieces do not always have regular surfaces. Castings in particular may exhibit major forming discrepancies. Support components should be providedwithin the jig body to act as contact points and ensure that the casting is notclamped at “hollow” points. There are three kinds of support components:

• Support components with a fixed non-adjustable support height, such as support pins

• Precisely-adjustable components such as support screws• Self-adjusting support components

This last type itself generates a defined support force, for example via a springassembly. It is, however, also possible to use pneumatic cylinders, which areactivated after clamping is complete and generate a certain supporting force tocounterbalance the machining force, for example during drilling. Fig. 1-13 showsan example. The projecting end of the workpiece rests on a further supportwhich compensates for the tilting moment generated by the machining force.

1 Fundamentals of clamping technology18

Fig. 1-12:

Defining through

a centring operation

Page 20: Pneumatic Clamping

1 Fundamentals of clamping technology

To sum up, we can state that the characteristic features of support componentsare their contact force against the workpiece, their support stroke to compen-sate for position deviations, their steady-state rigidity and the maximum possi-ble support force which they can provide.

19

6

1

2

3

3

4

5

FS FB

Fig. 1-13:

Swivel clamp system with

pneumatically-activated

support component

1 Clamp lever

2 Workpiece

3 Support

4 Clamp block

5 Support cylinder

6 Swivel clamp

FS Clamping force

FB Machining force

Page 21: Pneumatic Clamping

The “clamping method” describes the way in which a clamping force is appliedto a workpiece and the number of defining surfaces planes. Clamping methodscan be classified on the basis of the following criteria:

• Ability to react to workpiece changesThese changes may include, for example, expansion due to heat generated bymachining. We make a distinction between rigid and flexible clamping devices.Wedges, screws and cams are rigid and do not provide compensation, in contrast to clamps operating with spring and magnetic force and fluid-powerclamping devices (pneumatic and hydraulic).

• Clamping actionWe can distinguish between clamping from one side and from both sides. Theformer type can be carried out directly against the body of the jig, as shownby the examples in Fig. 1-14. Clamping from both sides, with a jig componentbetween the workpieces, is shown in Fig. 1-15.

1 Fundamentals of clamping technology20

F

F

1/4 F 1/4 F 1/4 F 1/4 F

F

1/2 F1/2 F

F

1/2 F 1/2 F

F1/2 F

FF F

F F

1/2 F 1/2 F 1/2 F

1/2 F 1/2 F

1.3Clamping methods

Fig. 1-14:

Examples of clamping from

one side with and without

mechanical distribution

of the force F

Fig. 1-15:

Some examples of double-

sided clamping

Page 22: Pneumatic Clamping

1 Fundamentals of clamping technology

• Alignment during clampingIn the case of centred clamping, clamping is carried out from several direc-tions in order to bring the workpiece into a desired position on a symmetricalplane without additional positioning components. Fig. 1-16 shows the princi-ple of this, while Fig. 1-17 shows a practical example in which the force of apower cylinder is distributed via 3 or 4 angle levers. The clamping centre isalways reached precisely, even in the case of diameter deviations.

21

1

2

3

4

5

Fig. 1-16:

Principle of centred clamping

Fig. 1-17:

Centred lever clamp

1 Workpiece

2 Angle lever

3 Lifting component

4 Short-stroke cylinder

5 Jig body

Page 23: Pneumatic Clamping

We distinguish between single and multiple clamps on the basis of the numberof workpieces which can be clamped simultaneously in a device. Particularlywith milling and grinding operations, it is possible to reduce both machining andauxiliary process times considerably through the use of multiple clamps, thusmaking auxiliary motions and the approach and transfer paths of tools shorter. A force compensator is required in order to ensure that the clamping force actingon all the workpieces in the jig is the same. This compensator is made necessaryin particular by workpiece tolerances. Examples with mechanical force distribu-tion are shown in Fig. 1-18. The compensation effect is provided by floating pressure pieces. The clamping force per workpiece is reduced as a function ofthe number of workpieces to be clamped, for example to F/4 in the case of clamping as shown in Fig. 1-18a.

It is of course possible to work without force distribution. In this case, directly-acting force generators are used, as shown in the example in Fig. 1-19. Thegenerators in this case are pneumatic cartridge cylinders. Often, however, theresulting clamping force is insufficient, and hydraulic cartridge cylinders areused instead. A pneumohydraulic pressure converter can also be used as apower source.

1 Fundamentals of clamping technology22

1/4 F

F

1/4 F 1/4 F 1/4 F F/8

F

F/8 F/8 F/8 1/4 F 1/4 F

a b

1

2

3

4

5

F

F

F

Fig. 1-18:

Distribution of force F

with a multiple clamp

a) Identical clamping forces

b) Non-identical clamping

forces

Fig. 1-19:

Multiple clamping device

1 Upper part of device

2 Cartridge cylinder

3 Pressure cap

4 Workpiece

5 Support strips

with V grooves

F Clamping force

Page 24: Pneumatic Clamping

1 Fundamentals of clamping technology

Another method of achieving multiple clamping is layered clamping. This isshown by the example, in which slots are cut in pins. Fig. 1-20 shows two clamping solutions. The first of these is a lever clamp in which the selected leverarm ratios provide a force boost at the pressure point. It is also possible toarrange V-shaped workpiece holders in layers (Fig. 1-20b) and apply the pistonforce directly. For example, 6 workpieces can be clamped simultaneously andslots cut with a multiple milling cutter (Fig. 1-20c). The V-shaped holders are inserted loose. All workpieces are clamped with a force F/2. The V-shaped holders must of course be manufactured to close tolerances and must fit intothe jig body with only a very slight lateral play.

There are still further examples of multi-layered clamping. Fig. 1-21 shows anumber of examples. In this case, the workpieces (semi-finished products) alignone another during clamping. This type of clamping is useful when, for example,it is desired to cut a large number of workpieces to length at the same time orwhen the end faces of the workpieces are to be milled. The clamp is well able tocope with variations of diameter or square cross-section. Solutions of this kindare, however, suitable only for workpieces with a simple geometry.

23

1/4 F

F

P

P

a b c

Fig. 1-20:

Clamping device for cutting

slots in pins

a) Clamping with mechanical

distribution of force F

b) Layered clamping

(plan view)

c) Multiple milling cutter

to cut slots in groups of

workpieces arranged in

layers

p Compressed air

Page 25: Pneumatic Clamping

Multi-layered clamping can also be implemented using fluid pressure transmis-sion. The principle of a device of this kind is shown in Fig. 1-22 and is based onPascal’s Law:

When a pressure acts on a fluid in one direction, this pressure is propagated

unchanged throughout all parts of the fluid and in all directions.

The clamping device in this case includes a suitable pressure chamber into thewall of which a number of small pistons are fitted. These must be fitted to closetolerances to prevent pressure leaks. Gelatinous plastics are used as pressuremedia.

1 Fundamentals of clamping technology24

1

2

3 4

5

6

F F

F F

Fig. 1-21:

Examples of multi-layered

clamping

F Clamping force

Fig. 1-22:

Clamping with hydraulic

pressure transmission

1 Jig body

2 Workpiece

3 Coupling

4 Power cylinder

5 Clamping piston

6 Plastic medium

Page 26: Pneumatic Clamping

1 Fundamentals of clamping technology

Thanks to their operating principle, clamping devices of this kind are able tocompensate without difficulty for variations in workpiece dimensions. In manycases, the return of the small pistons into their initial position is assisted bybuilt-in springs. To sum up, we can state that a multiple clamping device is cost-effective in caseswhere the cost of workpiece changing is higher than the extra cost for a multipleclamp in comparison with a single clamp. In certain cases, multiple clamps areused in order to allow better exploitation of large machine table workpiece clamping areas.

25

Page 27: Pneumatic Clamping

2

Requirements placed

on clamping devices

2.1Classification of clamping devices

Fig. 2-1:

Method of classifying

clamping devices

Clamping devices can be classified on the basis of numerous criteria. Modulardevices, for example, are those which can be assembled in accordance with specifications from a component system. The components in this system includebasic, expansion, stop and clamping modules. The mechanical interfaces aredesigned to allow countless variants to be created.

Even using standard modules, it is possible to assemble a clamping device forthe generation of a clamping force in the form of either a dedicated or multi-purpose device. Dedicated devices are usually special clamps which have beencreated for use with a particular product and which lie idle in a storeroom whenever this product is not being manufactured. Multi-purpose clamping devices are created using a basic clamping system unit and workpiece-specificclamping inserts which can be interchanged. They are less expensive overallthan individual dedicated clamping devices.Clamping devices can be classified as shown in Fig. 2-1 on the basis of themethod used to generate the clamping force.

Clamping devices with pneumatic force generation are relatively simple and ofrobust construction. They are used mainly to clamp smaller workpieces. In orderto distribute forces and also to amplify these, various transmission devices,generally of simple design, are introduced into the force flow. In special cases,clamping devices can even be actuated via pull-rods, which allows one pneumatic cylinder to provide the power for up to 8 clamping points.

Vacuum is primarily used for gripping tasks. Vacuum is also used successfully asa clamping force medium for parts with smooth, non-porous or slightly poroussurfaces and also flat parts. Rotating and tilting work surfaces are available formanual workstations which are constructed in the form of a suction area.

2 Requirements placed on clamping devices26

Permanent magnets

Electromagnets

Permanent/electromagnet

Clamping devices

Mechanicalclamps

Magneticclamps

Vacuumclamps

Othersolutions

Electrical

Hydraulic

PneumaticPistonLeverWedgeScrew

Suction cup

Nozzle plate

Grid plate

Slotted plate

Adhesive foils

Piezoelectricactuators

Rheological fluids

Memory-metalactuators

Page 28: Pneumatic Clamping

2 Requirements placed on clamping devices

Standard clamping devices consist of standard components and are suitable to a greater or lesser degree for universal use in clamping workpieces. Standardclamping devices allow a clamping function to be provided quickly and inexpen-sively without the need for major design work beforehand. The reproducibility ofthe workpiece position within these devices is adequate for many applications.

In the manufacturing of workpieces, the cutting forces of the tool are transmittedto the workpiece and thus to the clamping device. The forces are then dissipatedfrom here into the machine frame. These forces must be opposed by other forceswhich are large enough to ensure that the workpiece is not able to change itsposition. These are referred to as clamping forces. If rotary or tilting torque ispresent the clamping torque should be regarded as a countertorque.

Clamping forces and clamping torques or the forces generated by these must

be in static equilibrium with machining forces and torques, including an allow-

ance for safety factors.

In addition to machining forces, we must also consider the following forces:

• Piston forceForce which a power cylinder develops at a given operating pressure, e.g. 6 bar. The force on the piston-rod side is smaller due to the piston-rodcross section.

• Clamping forceThis is the sum of all forces which are applied to the workpiece when clamping components, such as pressure screws, jaws or pressure bars, areclosed. The clamping force should act as close to the machining point as possible in order to minimise any lever effects caused by machining forces.

• Holding forceForce which the closed clamping device applies to the workpiece without permanent deformation as a reactive force in order to oppose the machiningforces acting on the workpiece. Frictional forces play an important role here.

• Release forceThis is the force which a pneumatic drive must develop in order to returnclamping devices to their original position. Particularly in the case of toggle-lever clamps, this force may be high if it is necessary to overcome a leverdead-centre point starting from over-dead centre.

• Surface forceThis is a force which does not act on a point but a two-dimensional area. Thisis the case with vacuum clamping devices, and the force is also referred to asa holding force. Surface forces also occur with magnetic clamping devices andsome diaphragm clamping devices.

27

2.2 Clamping force andclamping reliability

Page 29: Pneumatic Clamping

Let us consider an example which illustrates how the clamping force is deter-mined. A block-shaped workpiece is being clamped and the clamping surfaceslie parallel to and opposite the defining surfaces. As can be seen in Fig. 2-2, a slot is to be milled in the workpiece.

The main cutting force Fmain, the impact factor C (between 1.2 and 2.0, de-pending on the work operation concerned) and a safety factor S are used tocalculate the machining force Fmach as follows:

Fmach = C · S · Fmain

The workpiece must be held securely against these forces. The clamping forces Fclamp generate the frictional forces Ffrict on each surface. The result in the example is:

Ffrict = 2 · Fclamp · µ

In the above, µ is the coefficient of friction between the workpiece and definingor clamping components. Guide values for the static coefficient of friction withdry materials are as follows:

• Steel/PTFE 0.08• Steel/steel 0.15 (0.10 if lubricated)• Steel/oak 0.56 (0.11 if lubricated)• Steel/cast iron 0.19 (0.10 if lubricated)• Brass/oak 0.62 (0.16 if lubricated)

2 Requirements placed on clamping devices28

1

2

3

a4

1

5

FS FS

1/2 FS µ

1/2 FS

FB

FRFRei

FRei

FRei

Fig. 2-2:

Forces acting on a workpiece

aligned by 3 determining

planes

1 Pneumatic cylinder

2 Base plate

3 Workpiece

4 Determining component

5 Tool

FS Fclamp

FRei Ffrict

FB Fmach

FR Freturn

Page 30: Pneumatic Clamping

2 Requirements placed on clamping devices

Coefficients of friction are subject to certain fluctuations, rather like the bloodpressure of human beings. In cases of doubt, tests can be carried out in which a workpiece is placed free of forces on an inclined plane and allowed to slidedown this. The angle of inclination Ú of this inclined path is increased graduallyuntil the workpiece begins to move. Since tan Ú = µ, it is possible in this way tocalculate the coefficient of friction. In our example, we can ignore certain finepoints of geometry if we choose a safety factor S = 3. Simplified for equilibriumreasons, we thus obtain

Freturn = S · Fmain

Freturn + Ffrict = Fmach

in which the defining component a also absorbs a certain return force Freturn. Bysubstitution and restatement of the above equations, we obtain an expressionfor the required clamping force Fclamp as

Fclamp = S · Fmain (C – 1)/(2µ)

In other clamping situations, of course, other mathematical relationships apply.In all cases, however, the following remains true:

Pneumatic clamping has the advantage that clamping force can be infinitely

varied as a function of pressure over a wide range.

In practical situations, we often have little idea of the possible order of magni-tude of machining forces. Let us consider this question. In cutting-type manufac-turing processes, the machining force is the cutting force. This can be deter-mined with the aid of the specific cutting force kc (N/mm2) for a given material.Assuming a chip with a thickness and width of 1 mm in each case, we can assume specific cutting forces kc1.1 as follows:

• Steel (St50) 1,780 N/mm2

• Chill castings 2,060 N/mm2

• Brass 780 N/mm2

A guide value for the machining force can accordingly be taken as

Fmach = kc1,1 · A in N

in which A is the chip cross section in mm2.

In the case of the peripheral routing of wooden workpieces with an average chipthickness (arc-shaped chip) of 0.3 mm, the following kc0.3 values apply:

• Red beech (with grain) 22 N/mm2

• Red beech (cross-grain) 60 N/mm2

• Pine (with grain) 20 N/mm2

29

Page 31: Pneumatic Clamping

Example: An underhand routing machine is to be used to cut a slot 6 mm wideand 12 mm deep in pine workpieces with an average chip thickness of 0.3 mm.What is the value of the cutting force (machining force)?

Fmach = kc0.3 · A

Fmach = 20 · 6 · 12 = 1,440 N

In the cases we have studied up to now, the pneumatic motors used have acteddirectly on the workpieces. We are using the word “motor” here for any type ofdrive, no matter whether it is of rotary or linear type.

In order to produce higher clamping forces, transmission devices are often inter-posed. The most common types of devices are

• Clamping cam• Clamping wedge• Clamping screw

In these cases, the clamping force Fclamp comprises a drive force F in accordancewith the equations shown in Fig. 2-3. In all cases, the force F may be producedby manual, pneumatic (linear, rotary) or hydraulic means.

2 Requirements placed on clamping devices30

Self-locking whentan · ≤ tan Ú ≤ Ì

Clamping cam Clamping wedge Clamping screw

F

FS FS FS

F

F

Ì

L

h

Ì

·

d

D

fL

e Ì1

Ì2

Self-locking whenD ≥ 15 · e

F · 2 · L · FS =

h

FFS =

tan ·

F · LFS =

e + Ì1 · f + Ì2 · d/2

Fig. 2-3:

Common types of force

transmission components

F Applied force

Length of lever arm

e Eccentricity

f Distance to pressure point

h Pitch

· Pitch angle

Ú Friction angle

Ì Coefficient of friction

Ì11 Coefficient of friction

between spiral and

workpiece

Ì22 Coefficient of friction

between pivot pin and

bearing

Page 32: Pneumatic Clamping

2 Requirements placed on clamping devices

In cases where, for example, a clamping wedge with self-locking is used, itshould be noted that the return force is higher than the clamping force. It shouldbe noted that clamping cams, wedges and screws require only short clampingpaths. In the case of clamping devices on rotary tables or workpiece carriers, it is customary to use pressure springs to produce clamping force. These may becoil springs or also cup spring assemblies. Only in the clamping/release positiondoes a coupling component connect with a compressed air supply to release theworkpiece. An example of this is shown in Fig. 2-4. A single-acting short-strokecylinder is used in this case.

Clamping with spring force must be designed in a such a way that adequateclamping security is achieved. But what do we mean by “clamping security”?

The clamping security value is the quotient of the holding force produced by

the application of a certain clamping force divided by the maximum occurring

machining force which has a tendency to force the workpiece out of the

clamping device in question.

Clamping security can be enhanced by installing an automatic pressure monitor.For reasons of cost, however, users often content themselves with standard non-return valves.

31

1

2

3

4

5

Fig. 2-4:

Mobile clamping device

on a workpiece carrier

1 Base assembly workpiece

2 Single-acting compact

cylinder

3 Twin-belt conveyor

4 Guide profile

5 Workpiece carrier plate

Page 33: Pneumatic Clamping

A clamping force maintenance system has the function of maintaining force evenin the case of a power supply failure (due, for example, to tubing rupture) andthus protecting the clamped workpiece. Clamping force maintenance systemsmay take numerous forms:

• Clamping with spring force, release with compressed air• Maintenance by means of piloted non-return valves• Maintenance by means of mechanical self-locking (screw, cam, wedge)• Locking the piston rod in the clamping position• Over-dead centre position with toggle-lever clamping systems

Systems of this kind must also ensure that, if the shape of the workpiece changes during clamping or leakages occur, the clamp force or clamping components are adjusted to compensate for any loss of clamping force.

The most common method is to use non-return valves, as shown in theschematic circuit diagram in Fig. 2-5.

Mechanical solutions are, however, also possible. Fig. 2-6 shows a clampingdevice in which the generation of a clamping force Fclamp also produces a leverforce Flever. The force is divided by the slotted link into the force componentsFleverY and FleverX, due to the fact that the piston rod can move only along theX axis. The force FleverX intensifies the closing force and locks the clampinglever, creating a self-locking effect. This diagram ignores the effect of frictionaltorque and frictional forces within the system. The most important functional criterion is the angle between the lever pivot point and the roller contact pointon the slotted link.

2 Requirements placed on clamping devices32

1

2

3

2.3Maintaining clampingforce

Fig. 2.5:

Basic control system,

with maintained clamping

force by means of non-return

valve

1 Non-return valve,

pneumatically piloted

2 5/2-way valve

3 3/2-way valve for

emergency-stop function

Page 34: Pneumatic Clamping

2 Requirements placed on clamping devices

It is also possible to lock the piston rod of a pneumatic cylinder clamping systemin order to maintain clamping force. In order to achieve this, a suitable locking brake must be installed. Fig. 2-7 shows two possible solutions. In the first ofthese, a clamping-force piston is used to provide pneumatic locking by applyingthe force of this piston to a clamping collet. A release function is provided by abuilt-in pressure spring. In the second solution, the clamping action begins whenthe compressed-air supply fails (Fig. 2-7b) and clamping pieces then wedgeagainst the piston rod. In this case, the pneumatic piston is used to release theclamping action produced by spring force.

33

1 2

xlock

FHyFH

FHx

FH

FS

y

1 2 3

4a b

5

6

7

3

Fig. 2-6:

Clamping device with

mechanical self-locking

via a slotted link

1 Connection for opening

function

2 Connection for clamping

function

Fig. 2-7:

Locking brakes for piston-rod

systems

a) Clamping collet brake

b) Spreader clamping system

1 Clamping-force piston

2 Clamping collet

3 Piston rod

4 Friction lining

5 Manual release button

6 Release piston

7 Clamping piece

Page 35: Pneumatic Clamping

In certain cases, directly-generated clamping force will be insufficient, or else nospace will be available to install larger higher-performance pneumatic drivers. In these cases, special devices must be used. Fig. 2-8 shows a number of theo-retical possibilities. Another method is to boost the force provided by the com-pressed air by means of a pressure amplifier (see Fig. 2-12). While a “normal”pneumatic cylinder (Fig. 2-8a) is able to deliver the force

F = p · A · Ë a tandem cylinder as shown in Fig. 2-8b is able to deliver

F = p · Ë (2A – A1)

In the above:

p Operating pressureA Piston cross sectionA1 Piston-rod cross sectionË Efficiency, approx. 0.9

The design of a tandem cylinder, in which 4 piston systems are combined to forma single system, is shown in Fig. 7-1.

The configuration shown in Fig. 2-8c utilises the wedge principle. A practicalapplication of this principle is shown in Fig. 7-2. Toggle-lever mechanisms (Fig. 2-8d) can deliver higher final forces, but only within a very short distancebefore the fully-stretched position. In the interest of longer service life, pneu-matic drives should in any case not be subject to more than 70% of the maximum values quoted in the relevant data sheet.

In order to allow high forces to be generated within a confined space, the driveshown in Fig. 2-9 has an integrated wedge linkage. The piston travel is utilised todrive an angle lever. To prevent lateral forces from acting on the piston rod, the

2 Requirements placed on clamping devices34

1

a

b

c d

23

4

5

6

2.4 Amplifying clamping force

Fig. 2-8:

Possible ways of amplifying

clamping force

a) Normal cylinder,

direct-acting

b) Tandem cylinder

c) Indirect action with

wedge boost

d) Toggle-lever principle

1 Piston area

2 Tandem piston

3 Toggle-lever linkage

4 Sliding wedge

5 Workpiece

6 Pressure roller

Page 36: Pneumatic Clamping

2 Requirements placed on clamping devices

suspended wedge is in contact with 3 points at all times. The stroke of the clamping stem is of course significantly smaller than the piston stroke of thepneumatic cylinder. It is favourable for the design of the clamping device in thiscase that the advance-stroke direction of the pressure stem is the same as thatof the pneumatic piston. There are also other types of “amplifier” solutions, forexample with wedge pieces which run one over another.

The clamping device shown in Fig. 2-10 uses the wedge principle in a slightly different way. If a curved slot is created instead of a straight one, the motioncharacteristics of the clamping arm can be modified in virtually any desired wayby appropriate shaping of this curve. For example, a rapid swivel motion can beprovided at the end of the opening motion, or a self-locking action at the end ofthe clamping motion. The clamping operation here is one-dimensional.

By clever choice of the kinematic properties of the moving components con-cerned, it is also possible to obtain a two-dimensional clamping action with one drive. This is shown in Fig. 2-11. The clamping linkage is a combination of acircular cam and an angle lever. Clamping forces are operative on two surfaces atright-angles, without regard to any workpiece tolerances. High clamping forcescan be achieved, but with the disadvantage that the top face of the workpiece isno longer completely unobstructed.

35

1 2

3 4 5 6 7

F

Fig. 2-9:

Clamping-force amplification

with wedge and toggle-lever

transmission

1 Support roller

2 Wedge slide

3 Compressed air connection

4 Cylinder

5 Piston with spring return

6 Toggle lever

7 Pressure stem

F Clamping force

Fig. 2-10:

Clamping via a slotted link

Page 37: Pneumatic Clamping

In certain clamping applications, the jig used does not offer enough space toinstall large cylinders. One convenient solution is to use small hydraulic cylin-ders for example of cartridge type. The required fluid pressure can be generatedwith the aid of a pneumohydraulic pressure intensifier. The principle of this isshown in Fig. 2-12. The intensifier converts a given air pressure from the com-pressed air supply network into a higher hydraulic-fluid pressure. Intensifiershave two pressure chambers of different cross section and volume. The pistonrod of the pneumatic cylinder enters the oil chamber and acts as a pressurepiston. A facility is also provided for topping-up with hydraulic fluid.

The secondary pressure at the hydraulic cylinder is higher than the primary pressure at the compressed air input in accordance with the boost ratio of theintensifier, which may range from 1:4 to 1:80.

2 Requirements placed on clamping devices36

1

23

4

1

2

3

d D

2.5Pressure intensifiers

Fig. 2-11:

Lever clamp with clamping

cam

1 Cam lever

2 Compressed air connection

3 Pneumatic cylinder

4 Frame

Fig. 2-12:

Transportable pneumatic

pressure intensifier

1 Secondary pressure pout,

hydraulic fluid at 160 bar

2 Primary pressure pin,

compressed air at 6 bar

3 Carrying handle

Page 38: Pneumatic Clamping

2 Requirements placed on clamping devices

In accordance with the principle of equilibrium:

D2 · · 1/4 · pin = d2 · · 1/4 · pout

The hydraulic fluid pressure is accordingly as follows:

pout = D2 · pin/d2

If we assume diameters of D = 200 mm and d = 50, then with a nominal primarypressure of 6 bar we obtain a secondary pressure of 96 bar. With this and aclamping piston diameter of 16 mm, we obtain a clamping force of approxi-mately 2 kN, disregarding frictional losses and spring forces.

The relevant pneumohydraulic circuit is shown in Fig. 2-13 as a simple basic cir-cuit. As the pneumatic piston is reset by spring force, which also scavenges thehydraulic fluid, it is not absolutely necessary to equip the individual clampingpistons with return springs.

37

1

2

3

4

5

Fig. 2-13:

Example of control system

with pressure intensifier

activated by hand lever

1 Clamping device

2 Hydraulic cylinder

3 Workpiece

4 Pressure intensifier

5 Control cam with hand

lever

Page 39: Pneumatic Clamping

There are also pressure boosters which operate without hydraulic components,since they are designed as air/air intensifiers. These take the form of differentialpiston systems or twin or multi piston devices, with the same piston diameterson the low- and high-pressure sides. Fig. 4-3b shows a circuit diagram for a booster of this kind. The secondary pressure lies between the primary supplypressure and a value equal to twice this.

Air/air pressure intensifiers are used when the available supply pressure is notsufficient to allow the desired forces to be attained using the available drives(actuators). In the field of clamping technology, this method can also be used toprovide the necessary reserves of force. Boosters are also of interest for applica-tions in which hydraulic components are not desirable, such as the woodworkingindustry. They also provide a simple solution in the occasional cases in whichpneumatic drives have been accidentally undersized in terms of force delivery. Itis then possible to obtain higher force without modifications; in many cases ofthis kind, there will in any case not be the space available, for example, to installa larger power cylinder.

One of the great advantages of fluid-power clamping systems is that clampingforce can be infinitely adjusted as a function of pressure. It is necessary to limitclamping force in order to restrict the load acting on the workpiece and thusavoid excessive pressure per unit area and deformation. In the case of toggle-lever clamps, variations on workpiece dimensions may lead to considerable fluctuations in clamping force. The maximum permissible pressures per unit areawith pulsed loads are approximately as follows:

• Steel 3,000 to 5,000 N/cm2

• Hardened steel 4,000 to 6,000 N/cm2

• Brass 1,000 to 1,500 N/cm2

In general, the maximum permissible values will be governed by the hardnessand surface properties of the material concerned.

Clamping force can be limited by means of a pressure regulator, as shown in Fig. 2-14.

2 Requirements placed on clamping devices38

1 2

3 4

2.6Limiting clamping force

Fig. 2-14:

Limitation of clamping force

by means of a pressure

regulator

1 Clamping cylinder

2 Workpiece

3 Pressure regulator

4 Directional control valve

Page 40: Pneumatic Clamping

2 Requirements placed on clamping devices

If force-boosting linkages are also present between the pneumatic drive andclamping component, for example a toggle lever or spindle mechanism, purelymechanical limitation of the torque may be a practical way of limiting the clamp-ing force. This could take the form of adjustable overload protection devices. In the case of toggle-lever clamps with a cantilever clamping arm, it would bepossible to install a torque-limiting torsion device in the force flow, as shown in Fig. 2-15. This torsion device incorporates rubber components with a choiceof Shore harnesses or else takes the form of an integral rubber/metal device. The rubber hardnesses used are 70 Shore A (hard), 60 Shore A (medium) and 45 Shore A (soft). The dimensions are governed by the desired maximumpermissible steady-state torque. Rubber/metal components provide electricalinsulation between the clamping arm and housing and store energy whichassists the return stroke. Furthermore, they do not require precise adjustment to the height of the object to be clamped. On the other hand, the maximumclamping force which can be attained is significantly lower.

The stroke which the clamping components (clamping jaw carriers) are able toexecute is referred to as the clamping range. Strictly speaking, this applies onlyto clamp jaws with a translatory closing motion. In the case of swivelling clampjaws, we could specify a swivel angle. Clamps with a small clamping range aresufficient for series production. For universal clamping, on the other hand, alarge clamping range is advantageous. Base plates are available with a hole andslot system on which clamp blocks can easily be repositioned. This allows work-pieces of different size to be clamped without the need to vary the clampingstroke. A very small clamping range, for example, is provided by the lateral pressure pieces shown in Fig. 2-16. These components admittedly have nothingto do with pneumatics but are simple and inexpensive. They have internalsprings made of wire or elastomer but no controlled drive. These componentsmust be placed into jigs accurately, since the excursion angle of the clampingpins is small.

39

Fig. 2-15:

Limitation of clamping force

of a toggle-lever clamp by

means of a rubber/metal

component

1 Metal core of torsion

component

2 Vulcanised-on rubber

3 Metal ring

2.7Clamping range

1

2

3

Page 41: Pneumatic Clamping

Large clamping ranges and high clamping forces, on the other hand, can beattained with spindle drives. Fig. 2-17 shows a machine vice driven by a pneu-matic motor. The air pressure can be varied to control the clamping force andensure that the workpiece is held securely but not distorted. Lamellar motorsare available with clamping torque ratings from 0.1 to 20 Nm. This includes thenecessary gearing to reduce speed. This type of motor can, incidentally, be over-loaded down to a standstill without damage.

2 Requirements placed on clamping devices40

Fig. 2-16:

Example of very small

clamping range – clamping

with lateral pressure pieces

FS Clamping force

Fig. 2-17:

Machine vice driven

by a pneumatic motor

1 Clamping jaw

2 Body

3 Lamellar pneumatic motor

4 Milling cutter

5 Clamped workpiece

S Clamping range

4

51

2

S

3

FS

Page 42: Pneumatic Clamping

2 Requirements placed on clamping devices

The precision of a machine tool can be fully exploited only if it is not cancelledout by inaccuracies of the associated clamping system. Clamping devices musttherefore be produced to the same level of accuracy as machine tools them-selves.

What are the factors which may impair clamping accuracy?

• Insufficient accuracy of stop (determining) components.• Inaccurate holes and hole pattern for stop components.• Machining forces which are too high and at times overcome

the holding forces.• Stop, support and clamping components whose accuracy is affected by dirt.• Defining components which are worn or insufficiently durable.• Fluctuations in clamping force.• Excessive workpiece tolerances which lead to axial position shifts.• Excessive clamping forces which cause workpiece deformation.

“Clamping accuracy” is always used to mean repetition accuracy. This is the

distribution of the differences between the attained positions and the average

attained position.

In general, it can be said that clamping accuracy is a function of the tolerances ofthe relevant workpiece, jig, workpiece shape and workpiece position, and also ofthe properties of the workpiece surface.

As Fig. 2-18 shows, friction-locking clamping may lead to deformation, partic-ularly with thin-walled workpieces. Workpieces may become flattened at thepoints at which forces act and may develop clamping marks. Workpiece defor-mation can be counteracted by increasing the number of force action points.Plastic inserts on the clamping jaws protect workpieces against clamping marks.

41

2.8Clamping accuracy

Fig. 2-18:

Deformation of a cylindrical

workpiece as the result

of uneven distribution of

clamping force

Page 43: Pneumatic Clamping

The following principle applies:

Clamping forces must be distributed across as large a contact area as possible.

Clamping errors can also result if the body of the clamping device deforms asthe result of the clamping force. Strictly speaking, this always happens, but thepractical effect is small, provided that the device has sufficient rigidity. Thiseffect can also be minimised by making the path of clamping force as short aspossible. Fig. 2-19 shows an example to illustrate this. The clamping force actsboth in a pulling direction and in a pushing direction. In the case of a clampingmotor with a pushing action, the deformation of the jig varies in proportion tothe distance H and in inverse proportion to the cross-section A on which theclamping force acts. In the configuration shown in Fig. 2-19b, the clamping-forcepath is short, preventing the jig from distorting. The pneumatic cylinder has apulling action in this case.

Clamping forces produce deformation of clamping devices which result in

slight shifts in the positions of the components in the workpiece/clamping

jaws system.

In order to ensure precise clamping, the contact deformation between the work-piece and the clamping, support and determining components should also bekept as small as possible. The following therefore applies:

• The surface roughness of contact areas should be as small as possible.• The number of components and connections through which clamping forces

flow should be as small as possible.• Clamping forces should be routed in such a way that they do not cause

positional changes.

2 Requirements placed on clamping devices42

Fig. 2-19:

Clamping-force path

in a clamping device

a) Clamping force with

pushing action

b) Clamping force with

pulling action

1 Workpiece carrier

2 Pressure disk

3 Jig body

4 Slip-in disk

5 Workpiece

6 Tie rod

7 Pneumatic cylinder

8 Support

FS Clamping force

A Cross-section subject

to clamping force

H Effective distance

1 2

3

7654

8

Aa

b

FS

FS

H

Page 44: Pneumatic Clamping

3

Types of clamping

devices

3.1 Lever clamps

3.1.1Simple lever clamps

Fig. 3-1:

Use of clamping cylinders

in lever clamps of the type

frequently installed on

vehicle bodywork welding

production lines

a) Mounting via integrated

clevis foot

b) Fixed foot mounting

c) Installation above actual

clamping point

d) Adaptation to meet local

requirements

1 Claw clamp

2 Workpiece

3 Compressed air connection

4 Pneumatic cylinder

43

Clamping devices are characterised first and foremost by the requirements of agiven work or clamping operation. The wide range of applications is reflected inthe large number of clamping devices of more or less specialised design. Thecurrent trend is away from custom-built clamping devices and towards modularclamping systems. Modular workpiece clamps are generally based on a smallnumber of basic components and product-specific clamp jaws. The basic compo-nents can be used in all cases.

Clamping using a lever principle can be regarded as a technical variant of hold-ing workpieces with the hand or fingers. Levers, in both straight and angle form, can also be used to intensify force on the basis of the lever relationshiprule:

Force x force arm = Load x load arm

The levers in question are generally driven by pneumatic power cylinders, whichare widely used in clamping technology, due to the numerous mounting optionswhich they offer. Examples of these are shown in Fig. 3-1. The cylinders shownhere have integrated clevis foot mountings on their bearing caps. This allowseasy connection and any desired mounting position. The cylinders can also beequipped with an integrated flow control system, which saves space and money.

3 Types of clamping devices

a b

c d

2

1 34

Page 45: Pneumatic Clamping

44 3 Types of clamping devices

This type of clamp is very widely used and very effective. It is distinguished byits force-intensifying action close to the fully-stretched position of the togglelever. Certain types of toggle-lever clamps require a relatively large amount ofinstallation space at the clamping point. Fig. 3-2 shows the design principles oftwo toggle-lever clamps.

These are “half” toggle-lever clamps, so called because their lever arms haveone fixed pivot point. Fig. 3-3, on the other hand, shows a “full” toggle-leversystem. The theoretically usable clamping force Fclamp of the device can be calculated as follows:

Fclamp = p · A · Ë [( 1/tan · + ‚) – tan Ú]

In the above, ‚ is defined as follows:

‚ = arc sin (2 · R · Ì/L)

The coefficient of friction Ì is also defined as Ì = tan Ú. The tangent of the frictional angle is the equal to the coefficient of friction.

ba

R

p

A

αFS FS

F

L

3.1.2Toggle-lever clamps

Fig. 3-2:

Toggle-lever clamps

with concealed pneumatic

cylinders

a) Horizontal clamping,

pulling clamping action

b) Vertical clamping,

pushing clamping action

Fig. 3-3:

Forces operative within a

“full” toggle-lever system,

shown by the example

of an internal clamp

A Piston cross section

F Piston force

FS Clamping force

L Arm length

R Pivot pin radius

p Operating pressure

Ë Efficiency

Ì Coefficient of friction

Page 46: Pneumatic Clamping

45

The example assumes that the two lever arms have the same length L. If thiswere not the case, it would be necessary to incorporate the ratio of the two leverlengths into the equation.

For practical applications, it should be noted that approximately identical clamping forces for each workpiece are obtained only within a narrow clampingrange. The examples in Figs. 3-4 and 3-5 show that the use of the toggle leversand pneumatic cylinders in combination opens up a wealth of possible applica-tions. The choice of variant for a particular application depends on a number offactors. One of these is freedom of access to the clamping point and the ques-tion of whether workpieces need to be inserted from the side or can also be inserted from above, by automated means if necessary.

Toggle-lever clamps are frequently used in automobile factories to clamp sheet-metal workpieces, particularly on bodywork production lines. Chapter 3.10 willdeal with this type of clamp in detail. For present purposes, we will confine ourselves to the clamp shown in Fig. 3-6. We see that the numerous connectionpoints allow a wide choice of mounting options. If the fishplate pin is extended(Fig. 3-6b), it is even possible to arrange for the entire clamp housing to swivelaway as the clamp opens. This creates a large space in which a gripper can operate.

3 Types of clamping devices

Fig. 3-4:

Push-rod clamp with toggle-

lever mechanism

Fig. 3-5:

Vertical clamping with a

toggle-lever system.

The piston rod is supported

by the base plate via a roller

Page 47: Pneumatic Clamping

46

Fig. 3-6:

Examples of mounting

toggle-lever clamps

a) Use of a connection

surface to attach

a workpiece support

b) Use of a guide linkage

to swivel away the

complete clamp

c) Connection

to a clamping station

3.1.3Toothed-segmentclamps

Fig. 3-7:

Toothed-segment clamps

1 Clamp jaw

2 Rod clevis

3 Piston rod

4 Mounting bracket

5 Pneumatic cylinder

6 Stop to limit opening angle

7 Basic plate

8 Clamping jaw

3 Types of clamping devices

These clamps can centre workpieces to a constant clamp jaw mid-point. In orderto achieve this, the clamp arms are linked together via toothed segments. An example is shown in Fig. 3-7. Clamps of this kind can be used to good effectin a multiple parallel configuration to clamp long semi-finished products such as rails, bars, system profiles and piping. The material to be clamped can be inserted axially or horizontally. It is also possible to make the clamp jaws inter-changeable. The motion sequence can be monitored via electrical inductivesensors on the power cylinder or on the clamp arms.

Toothed-segment clamps are also a good way of clamping panel material. A clamp of this kind is shown in Fig. 3-8. A major advantage is that the clampclaw swings fully away, thus ensuring that the insertion of panels from above isnot impeded. This principle is also used in various underclamping systems

1

2

3

4 5 6 7 8

a b c

Page 48: Pneumatic Clamping

Fig. 3-8:

Clamping panels

1 Workpiece

2 Clamp segment

3 Gear rack

4 Pneumatic cylinder

3.1.4Swivel clamps

Fig. 3-9:

Design of a pneumatic

swivel clamp

1 Clamp claw

2 Workpiece

3 Spiral slot

4 Piston

47

These are generally standard clamping devices which execute a lifting/rotarymotion. After the clamp claw opens, it swivels to the side, allowing unimpededremoval of the workpiece from above. This is an important factor if the clampingdevice is to be fed by program-controlled handling devices. As Fig. 3-9 shows,the 90° swivel motion is achieved by means of a spiral-slot guide in the pistonrod.

3 Types of clamping devices

1

2

3

4

1

2

3

4

Page 49: Pneumatic Clamping

48 3 Types of clamping devices

There are various types of swivel clamps (Fig. 3-10), generally designed to provide higher clamping forces than hydraulic cylinders. Pneumatic swivelclamps generate clamping forces from 0.2 to 1.6 kN, which is usually sufficient,for example, to clamp workpieces for welding. The advantages of swivel clampsare their smooth outer surfaces and favourable deflection angles, which ensurethat swarf and drilling emulsion slide off easily and do not accumulate in trappoints. The swivel area of the clamps must at all times be kept free of collisionhazards. Clamping forces must be used only during the vertical lifting phase.Versions are available which swivel to the right or to the left. In the case of twin-arm types, the clamping force available for each workpiece is half the total.

Workpieces to be welded must be held by hand or by means of a robot in a suitable position for tack and finish welding. The clamping devices used must be robust and unaffected by the stress resulting from the application of heat. Inview of the fact that work with welding torches or spot-welding tongs requires agreat deal of space, the interference contours created by the clamping compo-nents should be kept as small as possible. Consideration must also be given tothose components of the clamping device which are susceptible to dirt. Powercylinders are equipped with a special wiper ring which prevents welding spatterfrom damaging the piston rod. Another way of achieving this would be to fit gaiters, but these are costly. It is always advantageous to position the driveunits slightly away from the working area (Fig. 3-11) or install these under coverif possible (Fig. 3-12).

a b c

Fig. 3-10:

Common types of com-

mercially-available swivel

clamps

a) Table-mounting type

b) Screw-in swivel clamp

c) Double-arm swivel clamp

3.1.5Welding clamps

Page 50: Pneumatic Clamping

49

In conclusion, let us look at a type of clamp for very high clamping forces (Fig. 3-13). The top-fitted clamping plate is driven via an angle-arm device which forms a toggle-lever linkage. The end position is limited by an adjustablestop bolt.

3 Types of clamping devices

1

2

3

2

1

3

4

Fig. 3-11:

Wide-opening lever clamp

for workpieces to be welded

1 Workpiece to be welded

2 Clamp arm

3 Frame

Fig. 3-12:

Welding workstation with

pipe clamping device

1 Workpiece

2 Pull-down stop

3 Clamp lever

4 Pneumatic cylinder

with rod eye

Page 51: Pneumatic Clamping

50 3 Types of clamping devices

The requirements of production technology often mean that workpieces must be clamped with centring action, which ensures that, despite dimensional tolerances, workpieces are always centre-aligned. This is necessary in caseswhere machine-tool operating program are based on this centre point (symmetrical axes, reference point). From the point of view of the clampingdevice, this means that there can be no fixed clamping block and that the clamp-ing components must move towards each other equally. To achieve this, theclamp jaws must be coupled together in one way or another. In the solutionshown in Fig. 3-14, this is achieved by means of a lever mechanism. It wouldalso be possible to introduce force at another point within the system. Thisprinciple of synchronous mechanical clamping allows high clamping forces to be achieved. The clamp jaw inserts are interchangeable, permitting adaptationto different shapes of workpieces or semi-finished products.

1

2

3

4

5

6 7

Fig. 3-13:

Clamping station with

toggle-lever clamp system

1 Pressure plate

2 Workpiece support

3 Stop bolt

4 Fishplate

5 Bracket

6 Device body

7 Power cylinder

3.1.6Clamps with a centring action

Page 52: Pneumatic Clamping

51

It is also possible to use cams, the simplest of which have a conical form. Motionand force characteristics can be controlled by the choice of cam shape. It is evenpossible to select an angle of inclination at the end of the clamping operationsuch that the clamping device automatically locks. An example of this is shownin Fig. 3-15.

The design of clamping device shown in Fig. 3-16 can be used for workpieceswith either a round or rectangular cross section. A centring action on 2 planes is,however, obtained only when an appropriate number of jaw pairs (more than 2)are provided. The transmission levers are then connected to the piston rod via a star linkage, for example for 3 clamp arms in the case of the clamping of rota-tionally symmetrical workpieces.

3 Types of clamping devices

1

2

3

4

5

6

7

8

4

5

6

1 2

3

Fig. 3-14

Jaw clamping device with

coupled lever mechanism

1 Clamp jaw

2 Support and guide

3 Angle lever

4 Jaw guide

5 Base plate

6 Power cylinder

7 Toggle lever

8 Clamping edge

Fig. 3-15:

Claw clamp drive via a cam

1 Cam

2 Clamping cylinder

3 Foot mounting

4 Workpiece

5 Clamp claw

6 Workbench

Page 53: Pneumatic Clamping

52 3 Types of clamping devices

The clamp jaws of the variants shown in Figs. 3-14 and 3-16 cannot open verywide, which may be a disadvantage.

I am sure all my readers will have experience of using a rubber hammer to taphome workpieces in a machine vice. This takes time and is not possible at all in automated production sequences. The aim of tapping home is to ensure thatworkpieces are pressed not only against clamp jaws or positioning bars but alsoagainst the support surface on which they lie. This can be achieved by arrangingfor the force-generating components to act on the workpiece at a slightly inclined angle. Examples are shown in Fig. 3-17. The angle a need be no morethan 3 to 5°. It is also possible to install clamp claws and pressure screws to actin this direction. In certain cases, it may be sufficient to have clamp componentswith inclined pressure surfaces which divide the available force into 2 compo-nents. Clamps of this kind are also referred to as hold-down clamps, reflectingthe action which they produce.

1

2

3

Fig. 3-16:

Pneumatic toggle-lever clamp

for centred clamping

1 Rotationally symmetrical

workpiece

2 Clamp jaw

3 Toggle-lever mechanism

3.2Hold-down clamps

Page 54: Pneumatic Clamping

53

A hold-down action is also produced by the clamping device shown in Fig. 3-18.The action is obtained through appropriate design of the clamping block and bymeans of a ribbed clamp jaw which acts on the workpiece (a casting) in an arc.

Frames and panels are geometrically simple bodies. Typically, they can be clamped not via their main faces but only at the sides. It will generally be thecase that machining operations will be carried out on the main faces and thatclamp jaws would interfere with these. Fig. 3-19 shows some well-proven solu-tions. Precise positioning is achieved by means of defining components, which incertain cases can be inserted into a hole matrix as appropriate to the size ofpanel concerned. The resulting clamping force is directed towards the “fixed cor-ner” or is generated to act in this direction.

3 Types of clamping devices

a b

dc

1

2

3

4

5

6

Fig. 3-17:

With these clamps, there is

also a force component which

acts downwards towards the

support surface

a) Direct inclined force action

b) Clamping via taper

c) Inclined clamp claw

d) Clamping via wedge

Fig. 3-18:

Clamp with hold-down

action for castings

1 Workpiece

2 Clamp block

3 Clamping device body

4 Pneumatic cylinder

5 Clamp lever

6 Clamp claw with ribbed

jaw

3.3Frame and panelclamps

Page 55: Pneumatic Clamping

54 3 Types of clamping devices

A similar solution, for clamping frames, is shown in Fig. 3-20. In this case, theclamping force is directed at the gluing points of the wooden battens. Here, too,it is advantageous to have defining bars with locating pins which allow be re-positioning. The pressure components are able to move to a certain degree toallow them to make full contact with workpieces with a slight angle deviation.The clamping cylinders can be re-positioned as desired along the side of thedevice.

1

2

34a b

c d

5

6

7

8 9

10

2

1

3

4

5

Fig. 3-19:

Devices for clamping panels

a) Cam as intermediate

mechanism

b) Direct-acting

pneumatic drives

c) Diagonal clamp slide

d) Angle lever as pressure

component

1 Lever

2 Clamp slide

3 Clamp cam

4 Base plate

5 Workpiece

6 Pressure piece

7 Pneumatic cylinder

8 Determining pin

9 Pressure roller

10 Angle lever

Fig. 3-20:

Clamping a frame using

direct-acting pneumatic

drives

1 Base plate with hole grid

2 Stop bar

3 Wooden batten

4 Pressure jaw

5 Clamping cylinder

Page 56: Pneumatic Clamping

55

Diaphragm systems are pneumatic devices whose shape and stability are provided or significantly influenced by pressure differences. The characteristic feature of these devices is their flexible tensile-stressed envelope (diaphragm),which can also be combined with a meshed fabric. Diaphragm clamps exploit the flexible properties of a two-dimensional component. Diaphragms can also bemade (spun) from metal or produced from rubber or elastomer materials.Elastomer clamping modules of the kind shown in Fig. 3-21 have only a smallclamping stroke but offer a direct action. The pliable surface of diaphragmclamps means that they are able to hold even workpieces with uneven surfacessecurely. The modules are very low and can be installed easily in devices withlimited installation space. Pressure surfaces can be stabilised by means of a clipped-on metal pressure plate, which prolongs the service life of the elastomerdiaphragm. A return force is produced by the elasticity of the stressed dia-phragm. If we regard the pressure plate as a “piston rod”, we can equally regarda diaphragm clamping module as a single-acting pneumatic cylinder.

A great advantage of these devices is their modular design, which makes it easyto arrange a number of modules in parallel to form a clamping system.Configurations can be adapted to suit different shapes of workpieces. Fig. 3-22shows examples of configurations. Clamping forces are cumulative when mod-ules are arranged in series or parallel. Modules can, however, also be arrangedin opposition to provide external or internal clamping. The principle of these two basic applications is shown in Fig. 3-23. We should, however, note that inthe example shown all the contact points have a certain flexibility, which meansthat precise centre alignment cannot be expected.

3 Types of clamping devices

Symbol

b

3

1

a

Stroke

1

2

3.4 Diaphragm clamps

Fig. 3-21:

Pneumatic clamping modules

with clamping forces ranging

from 95 to 1690 N for each

individual module, depending

on size

a) Rectangular clamping

module

b) Circular version

1 Rubber diaphragm

2 Clipped-on pressure plate

3 Clamping module housing

Page 57: Pneumatic Clamping

56 3 Types of clamping devices

Clamping modules can also be used to obtain an indirect clamping action. In this case, they form part of a mechanical structure, as shown in Fig. 3-24. The clamping path is very short, and the very flat design of the modules is agreat advantage if only a small amount of installation space is available. Theoverall clamping force can be increased by arranging several modules in series.In this case, the clamp claw would be equipped with a pressure bar which extends over several modules. As the clamp is of single-acting design, its airconsumption for a clamping operation is only half that of a double-acting cylinder.

a

b e f

c d

1

2

a b

2

1

3

Fig. 3-22:

Combinations of clamping

modules

a) Single module

b) Parallel configuration

c) Clamping curved

mouldings

d) Vice-type configuration

e) Combination for internal

clamping

f) In-line configuration

Fig. 3-23:

Typical clamping methods

for rotationally symmetrical

workpieces

a) Internal clamping

b) External clamping

1 Workpiece

2 Jig body

3 Clamping module

Page 58: Pneumatic Clamping

57

Finally, there are also metal diaphragms, which are however installed in clamping devices in a completely different way. As Fig. 3-25 shows, diaphragmsare produced precisely to a required clamping diameter and machined down insuch a way that a spring clamping force of a defined magnitude is obtained. The edge of the diaphragm is used for clamping. The example shown involvesinternal clamping. A drive is required only for unclamping. When the diaphragmis arched, its diameter is slightly reduced, and the workpiece in question can be removed. The clamp has a centring action, and the pressure per unit area at the contact points is low. There is very little tendency to produce pressuremarks. Due to the fact that the clamping (spring) path is small, only workpiecesproduced to close tolerances can be clamped.

3 Types of clamping devices

4

3

2

1

21 3

4

5

67

8

Fig. 3-24:

Lever clamp based on a round

clamping module with a

rubber diaphragm

1 Clamping module

2 Clamp arm

3 Workpiece

4 Clamping device

Fig. 3-25:

Metal diaphragm clamp

(RINGSPANN design)

1 Puller bolt

2 Metal diaphragm

3 Workpiece

4 Support ring

5 Base plate

6 Jig plate

7 Compressed air connection

for release

8 Power cylinder

Page 59: Pneumatic Clamping

58 3 Types of clamping devices

A special type of clamping function can be obtained by using “Fluidic Muscles”.These are pneumatic drives which operate on the same contraction principle as natural muscles, such as the ones we use to bend or stretch our arms. A fluidic muscle consists of a rubber tube whose walls are fitted along thesheath axis with strong reinforcing fibres in rhomboidal form. When the tube ispressurised by compressed air, the lattice type fibre structure stretches in theperipheral direction, accompanied by a longitudinal contraction of the fluidicmuscle by approx. 20% of its length. This creates a tensile force in the axialdirection. A fluidic muscle as shown in Fig. 3-26 with a length of 150 mm and an internal diameter of 20 mm can generate a force of 1,730 N with 6 bar inter-nal pressure and a 10 mm stroke. The mass of this type of drive is relatively low,and its reaction time is very fast. The force generated and available stroke arelargely dependent on the

• length and expandability of the pneumatic sheath • the strength and elasticity• the level of the internal pressure and• the type of mounting used.

1

2

3Stroke

relaxed contracteda

4

5

3

6b

73

8c

Fig. 3-26:

Fluidic muscle (Festo)

a) Configuration

b) Example of use

for clamping

c) Changing the direction

of force action

1 Locking nut

2 Flange

3 Contraction diaphragm

4 Workpiece

5 Clamping device

6 Clamp arm

7 Pushrod

8 Mounting bracket

Page 60: Pneumatic Clamping

3.5 Tubing clamps

Fig. 3-27:

Tubing used as a pneumatic

drive

a) Pressure-plate unit

b) Pressure-pin clamp

c) Lever clamp

d) Double-acting rocker lever

1 Pressure tube

2 Rocker arm

3 Pressure spring

4 Tensile spring

5 Lever

59

Fluidic muscles are also of interest as drives for clamping devices (Fig. 3-26b). If the contraction motion of the muscle is transmitted via an internal rod to theopposite end (Fig. 3-26c), it is also possible to generate thrust forces, whichoften allows a simpler connection to be made to clamping devices, such asbeam-type clamp bars.

In physical terms, tubing clamps are also pneumatic devices utilising a dia-phragm principle. This type of device is, by the way, also found in nature. Water frogs, for example, are equipped with resonating sacs consisting of high-strength cellular material. When these are subject to internal pressure, theyswell to a spherical shape. Tubing also expands under pressure and generates a radial force. Tubing can accordingly be used in clamping technology as a pneu-matic drive. In earlier times, firefighting hoses were popular in joinery and furniture-making workshops as the basis for frame presses. Clamping devices of this kind are simple and robust. Fig. 3-27 shows the principles of a number of applications.

Hoses are, however, rather makeshift clamping devices, particularly for large andlong workpieces. Today, standard components are available which can be usedwith little need for adaptation, are more robust and deliver more performance.Nonetheless, there may well be special cases where it is useful to recall the principle of “tubing drives”, which are able to provide interesting solutions forclamping round workpieces, as shown in Fig. 3-28. Workpieces such as slightlyconical containers made of plastic can be clamped gently all round. A length oftubing is fitted into the clamp housing in the form of a coil and generates a clamping force when pressurised. The natural elasticity of the tubing means that it resumes its initial shape when depressurised, allowing the workpiece inquestion to be removed.

F

F

F

1

34

F

F

2 F

F5

a b c d

3 Types of clamping devices

Page 61: Pneumatic Clamping

60 3 Types of clamping devices

In the device shown in Fig. 3-29, the clamp jaws are driven by tubing pieces. Thisdevice is easy to produce and the drive is highly compact, which is a particularadvantage. The clamping forces are lower than with other types of clamp but willbe adequate for special cases.

An interesting holding device, albeit not a clamp, is shown in Fig. 3-30. This isfor irregularly-shaped castings. The workpiece contour is temporarily mirroredby a matrix of support rods as the workpiece is laid onto these. In a sense, thematrix is programmed by this action. The workpiece is now in a stable positionand can be worked on by hand, for example to trim moulding joins. Before thiscan be done, however, the rods must be locked into place. This is achieved by

1 2 3 4

1

2

3

4

Fig. 3-28:

Tubing clamp for lightweight

round workpieces

1 Compressed air supply

2 All-round clamp housing

3 Workpiece

4 Pressure tube

Fig. 3-29:

Holding device for piping,

using an inflatable tubing

drive

1 Clamp jaw

2 Workpiece

3 Pressure tube

4 Jaw pivot axis

Page 62: Pneumatic Clamping

61

means of a piece of tubing threaded through the matrix in an S shape. This is avery inexpensive solution, notwithstanding that the forces holding the rods inplace are not very high. Other types of rod locking devices involve considerablygreater mechanical complexity. This device is admittedly a special solution butits principle may provide the answers to other applications.

A simple and interesting solution is offered by pneumatic cushions, a kind ofmodern ready-made version of the “tubing motors”. Fig. 3-31 shows one of themany possible applications. “Pneumatic clamp bars” are available in lengths from 0.1 to 20 metres and can be used to clamp even very large workpieces ofthe type encountered in the woodworking industry. Pneumatic cushions are produced as cylindrical convoluted bellows and of course also in square form.

3 Types of clamping devices

12

3

4

Fig. 3-30:

Programmable holding

device for castings

1 Workpieces

2 Holding device (plan view)

3 Spring-loaded

displaceable support rod

4 Pressure tube

Page 63: Pneumatic Clamping

62 3 Types of clamping devices

The advantage of vacuum clamping technology is the gentle non-damagingclamping action which it provides. Workpieces do not suffer any of the scratchesor clamping marks associated with mechanical clamping. Demand for vacuumclamping systems is rising due to the increased use of thin-walled light metalworkpieces, those made of composite materials and flat plastic workpieces,which cannot be clamped by magnetic means. Vacuum clamps develop a holdingforce which is spread across the entire workpiece area, making them ideal forflat thin-walled workpieces.

The components of a vacuum clamp are the vacuum generator, clamping tool,seal components in the case of grid plates, and a control valve. Vacuum clampsthemselves do not require any power transmission components and thus be produced in lightweight materials (aluminium). To make vacuum clamps easierto use, they can be provided with positioning crosses or full-area carrier tem-plates for workpieces. Even chucks are produced in the form of vacuum clamps.Fig. 3-32 shows an overview of the most important types of vacuum clamps.

1

2 3

4

4

5 6

Fig. 3-31:

Clamping with pneumatic

cushions (PRONAL)

1 Support structure

2 Workpiece

3 Clamp block

4 Pneumatic cushion or bar

5 Compressed air connector

6 Vulcanised-on

threaded pin

3.6Vacuum clamps

Page 64: Pneumatic Clamping

63

In the case of slotted grid systems, the working area must be sealed againstatmosphere by a neoprene bead. There are also clamping plates whose unusedsuction-air openings are sealed by plugs. With sintered metal plates, the sur-faces of these must be sealed by a foil with a cut-out aperture only in the area where the workpiece is placed. The level of clamping force which can beachieved is governed by the size of the workpiece contact area, together in certain cases with the workpiece shape and the flatness of the contact area. The maximum vacuum which can be achieved depends on the instantaneous at-mospheric pressure, which can vary from approximately 0.930 bar to 1.013 bar.We can thus assume a clamping force of only around 9.3 N/cm2, which may be reduced still further as the result of clamping conditions. If we take 98% vacuumas being the most that can be achieved, we shall obtain a clamping force of only9.1 N/cm2. If we then allow for a safety factor of around 1.5 to 2 and for leakagelosses due to unevenness and roughness, the maximum force will fall still fur-ther. For rough calculation purposes, the following applies:

Fclamp = 0.01 · V · po · A · S–1 in N

In the above:

V Maximum relative vacuum in percentpo Atmospheric pressure in hPa A Effective workpiece support area in cm2

S Safety factor

The required suction power depends on the size of the grid (or slotted) clampplates. The following can be taken as a guide:

• Grid clamp plate with an active area of 800 cm2 – approx. 7.5 m3/h • Grid clamp plate with an active area of 2,400 cm2 – approx. 21 m3/h

3 Types of clamping devices

5

d

1 2

a

1 7

8e

1

9

Vacuum f

4

c

3

b

Fig. 3-32:

Vacuum-operated clamping

plates for holding workpieces

a) Suction plate

b) Carrier plate

c) Round vacuum-

operated chuck

d) Slotted suction plate

e) Sintered metal clamp

plate (SAV)

f ) Vacuum-operated clamping

table with rubber suction

cups

1 Workpiece

2 Suction air plate

3 Carrier template

4 Suction air openings

or slot system

5 Suction slot

6 Vacuum connection

7 Cover foil

8 Sintered metal plate

9 Disk suction cup

Page 65: Pneumatic Clamping

64 3 Types of clamping devices

Fig. 3-33 show a vacuum-operated clamp plate in which the suction area hasbeen limited to the dimensions of the workpiece. This is achieved by inserting abead seal into the slots in the plate. There is only one row of suction holes in thecentre of the plate; vacuum is distributed via the grid slots. This system is evenable to deal reliably with holes and slots in the workpiece in question. If theentire area is used, measuring 300 x 300 mm, the resulting holding force, with a 3x safety factor, is approximately 2,000 N.

In addition to vacuum clamp plates, there are also dice-shaped 5-sided vacuumcomponents which can, for example, be used to clamp angle workpieces. Ifworkpieces held by vacuum clamp plates are separated, the vacuum collapses.To deal with this problem, ingenious people have come up with a plastic matwhich can be laid under the workpiece. This contains a large number of micro-distributed vacuum points in the form of vacuum suction cups of various sizeswith flexible lips at the top and a fine hole in the centre. The undersides of thecups are equipped with plastic lugs which can be inserted into the vacuumclamp plate. This allows clamped workpieces to be separated, and it is evenpossible to mill into the plastic mat.

The main use of internal clamps is to pick up workpieces via drilled holes. This can be achieved with jaw-type clamps if the holes in question are largeenough, but spreading and expanding devices can also be used. Fig. 3-34 showsa number of practical examples. A cup-spring assembly has a relatively precisecentring action during clamping, but this cannot be expected with elastic rubberclamping devices. These devices also develop less holding force.

1 2

Fig. 3-33:

Vacuum-operated clamp plate

with grid slot system

(Swisstool)

1 Grid suction plate

2 Bead seal insert

3.7Internal clamps

Page 66: Pneumatic Clamping

65

In jig construction, we also find numerous other solutions, for example equippedwith inclined pull-action slides or wedges which use the pulling or pushingaction of a drive to generate a spreading or expanding clamping action.Expanding tapered mandrels used in this way generate high holding forces andalso maintain the axis centre of the clamped workpieces to a high standard ofaccuracy.

For ring- and tyre-shaped workpieces, it is possible to construct a clamping device as shown in Fig. 3-35. In this case, the force of a pneumatic cylinder isdistributed among a number of clamping rods. The power cylinder can be in-stalled below the table plate. The rod guides are suspension-mounted to ensurethat the rods do not jam. As all the rods advance at the same time, the work-piece is always correctly aligned to the centre.

3 Types of clamping devices

12

a

P

3 4 5 6

P

b

Fig. 3-34

Internal clamp

with pneumatic drive

a) Clamp with cup spring

assembly

b) Clamping with elastomer

device

1 Workpiece

2 Cup spring assembly

3 Barrel-shaped rubber

component

4 Tie rod

5 Clamping support

6 Bracket for pneumatic

cylinder

Page 67: Pneumatic Clamping

66 3 Types of clamping devices

Fig. 3-36 shows a design which is both simple and interesting. Although original-ly intended as a gripper, this rubber-pin device can also be used for stationaryclamping tasks. The rubber pins which “advance” when pressure is applied offer a high coefficient of friction, ensuring that workpieces are held securely. With adiameter D of 100 mm, 6 bar operating pressure, and a safety margin of 20%, a total force of 2,800 N is developed.

1

2

3

4

1

2

P

F F

D

Fig. 3-35:

Device for internal clamping,

with force distribution

(plan view)

1 Clamping cylinder

2 Workpiece

3 Pressure roller

4 Clamp block

Fig. 3-36:

Rubber-pin gripper used as

workpiece holder (Sommer)

1 Body

2 Rubber-pin diaphragm

F Pin force

p Compressed air

Page 68: Pneumatic Clamping

67

The task of clamping stationary workpieces presents requirements which arefundamentally different from those in the case of moving workpieces, such asturned components rotating in a chuck or clamping against conveyor belts.There are various ways of achieving the latter function, including suction air (Fig. 3-37). Vacuum conveyor belts hold moving workpieces securely in place,producing a ‘clamping’ function by means of air pressure. This method can beused, for example, to hold lengths of foil and at the same time draw this awayfrom a roll. Operations of this kind are of great interest, for example, in pack-aging technology. A holding function is provided only above the suction airchamber.

Particularly in the woodworking industry with panel-cutting machines, it isimportant to generate the pressure of the workpiece against the conveyor beltwhich is necessary to ensure that the workpiece is transported by friction. In thesolution shown in Fig. 3-38, the pressure rollers operate directly on the work-piece. The pressing force is produced by a pneumatic cylinder. Good use is madehere of the spring action of the compressed air and the facility for infinite pressure adjustment.

3 Types of clamping devices

4

3 2

1

1

2

3

4 5

3.8Clamping against conveyor belts

Fig. 3-37:

Vacuum conveyor belt

1 Perforated conveyor belt

or toothed belt with

perforations between teeth

2 Suction air chamber

3 Vacuum connection

4 Vacuum

Fig. 3-38:

Clamping against a conveyor

belt using pneumatic

cylinders

1 Pneumatic cylinder

2 Pressure roller

3 Workpiece passing

through machine

4 Belt support

5 Conveyor belt

Page 69: Pneumatic Clamping

68 3 Types of clamping devices

It is also possible to apply clamping force to the conveyor belt, as shown in Fig. 3-39. The roller pressure segments are able to swivel through a smallangle, ensuring that all the pressure rollers within a segment are in contact withthe belt. The pressure force can be adjusted easily as a function of the com-pressed air pressure. Differences in workpiece heights can be managed withoutdifficulty. The compressibility of the air once again offers the advantage of aspring-loaded effect, allowing the travelling conveyor belt to conform well to theworkpiece.

We have already considered the principle of compensatory clamping. This in-volves the even distribution of clamping force among several workpieces, eventhough these may have different shapes and dimensions. Fig. 3-40 shows a so-lution in which force is applied via wedge pieces. These are inserted loose andtheir position can be varied by small amounts from a central control point. Theforce F initially acts on the first sliding wedge and is then propagated throughany desired number of wedge-shaped pressure and compensator pieces until thelast wedge piece, whose position is fixed. The pressure pins are returned to their initial position by return springs. The required stroke H at the point of forceapplication is made up of the individual clamping strokes a of the various pres-sure pins. In this case, its value is:

H = 4 · a

1 2 3

45 6

Fig. 3-39:

Pressure device

with pneumatic cylinders

1 Guide roller

2 Pneumatic cylinder

3 Conveyor belt

4 Incoming workpiece

5 Roller pressure segment

6 Lateral belt guide roller

3.9Compensating clamps

Page 70: Pneumatic Clamping

69

There are certain cases where it is necessary to clamp a workpiece securelyagainst another but without allowing any forces to act on the inboard workpiece(Fig. 3-41) due to the risk of bending. These cases require a facility for positionadjustment between the individual clamps. This is called “floating” clamping. The pneumatic cylinders are fitted in pairs on a clamping bridge which is able to move freely and undriven within a guide. This produces a closed-loop flow of force via the bridge at each clamping point. This system is comparable toclamping with 4 individual screws clamps. At each point, the force and counter-force are in equilibrium.

3 Types of clamping devices

1

2

8

7

6

5

4

3

F

Ha

Fig. 3-40:

Compensatory clamping

with the aid of wedge pieces

(plan view)

1 Clamp arm

2 Pressure piece

3 Pneumatic cylinder

4 Compensator piece

5 Pressure pin

6 Workpiece

7 Determining pin

8 Jig body

Page 71: Pneumatic Clamping

70 3 Types of clamping devices

Toggle-lever clamps have become particularly important in the automobile in-dustry and are used for the temporary clamping of sheet metal, profiles or large-volume workpieces such as seat, suspension and chassis components. Fig. 3-42shows a typical design of a toggle-lever clamp. The decisive advantage of thistype of clamp is the good accessibility it provides with large bodywork compo-nents. Toggle-lever clamps operate quickly and reliably and require no mainte-nance even after long periods of service. Their opening angle is large, and theirwidth should be kept as small as possible. Flat oval-piston cylinders are there-fore often used as force generators. The end position on the opening stroke iscushioned. The heavily-loaded clamp shaft usually runs in plain bearings, butneedle bearings are also used. Clamps should offer a service life of at least 5 million strokes.

2

3

5 4

6

1

2

3

4

5

Fig. 3-41:

Clamping mouldings with

floating clamping bridges

1 Clamping device for basic

component

2 Pneumatic cylinder

3 Bridge

4 Additional clamped

workpiece

5 Basic component

6 Bridge guide

3.10Clamps for automobilebodywork construction

Page 72: Pneumatic Clamping

71

Automobile production lines require torque values at the clamp arm rangingfrom 20 to 400 (500) Nm. The toggle-lever clamps used are thus often referredto as power clamps. Their housings should have as many mechanical interfacesas possible to allow connections to be made as required on any of 4 sides (sideand end faces). Clamps are also made with integrated valve systems (attachedto the base of the cylinder) and with integrated sensing of operational status. A distinction can be made between the following 4 types, based on the design of the clamp arm:

• Clamp arm with open head• Clamp arm with enclosed head• Clamp arm connected at one side only• Double clamp arms

These variants are shown in Fig. 3-43. The toggle lever of the open-head designis susceptible to dirt (welding spatter), while the enclosed-head design avoidsthis, the encapsulated head providing secure protection. Enclosed-type clampsare thus becoming more and more widespread in the mechanical-engineeringand automobile industries. Clamp arms connected at one side only are easier toremove, but both right- and left-hand versions are then required. Double-armclamps are used as large grippers.

3 Types of clamping devices

1

2

3

4

5

6

7

8

9

10

4

Fig. 3-42:

Pneumatic clamp with single

toggle lever (Festo)

1 Pressure screw

2 Clamp arm

3 Aluminium housing

4 Clamp shaft

5 Fishplate

6 Guided rod head

7 Bushing

8 Pneumatic cylinder

9 Piston rod

10 Washer

Page 73: Pneumatic Clamping

72 3 Types of clamping devices

The clamp arms can be equipped with pressure screws, pressure bars or pres-sure pieces shaped to match the workpiece in question, as the examples in Fig. 3-44 show. The fitting by which the arms are attached to drive shafts may besquare, hexagonal or octagonal.

ba

c d

12 3

4

5

6

Fig. 3-43:

Clamp arm variants

a) Open head, opening

angles 40°, 90°, 135°, 180°

b) One-sided clamp arm

c) Enclosed head,

opening angle 135°

d) Double clamp arm

Fig. 3-44:

Some designs of clamp arms

1 Contour of machine tool

2 Sheet metal workpiece

3 Clamp jaw

4 Toggle-lever clamp

5 Pressure screw

6 Clamp arm with octagonal

fittings

Page 74: Pneumatic Clamping

73

With certain clamps, it is even possible to modify their kinematic properties byadding supplementary components. For example, the motion path of a clawclamp can be changed to allow insertion into sheet-metal workpieces even in confined spaces. Moreover, it can be arranged for support components to moveinto contact with the workpiece contour as the clamp closes. Fig. 3-45 showssome examples. It can be seen that the clamp housing is prepared with a seriesof holes to allow the fitting of supplementary components. Clamps of this kindhave been used for the last 40 years in the American automobile industry. Theinventor L. Blatt designed these clamps so that they are self-locking at an angleof 12 to 2° before dead centre. “Self-locking” means that the workpiece will continue to be securely held even if the compressed air supply fails.

A particular problem with toggle-lever clamps is to achieve precise setting of the pressure point. As we know, at dead centre the resulting force tends towardsinfinity. If the mechanism is moved beyond dead centre, a self-locking effect is produced. We call this an “over dead centre interlock”. The travel of the mechanism is often halted 8° before dead centre. If it is allowed to pass beyonddead centre, there is the risk that the power cylinder may not be able to deliverenough force for the return stroke. How is it then possible to adjust the pressurepoint precisely to the relevant workpiece thickness? The following methods canbe used:

• After the clamp has been fitted, spacers can be placed under the pressurepiece to correct the height of this. These spacers are available in thicknessesof 4 to 6 mm in steps of 0.2 mm.

3 Types of clamping devices

Fig. 3-45:

Examples of applications

of standard clamps for sheet-

metal workpieces based on

toggle-lever systems

(IMI-NORGREN)

Page 75: Pneumatic Clamping

74 3 Types of clamping devices

• Clamps are available with a diagonally split housing, allowing precisionadjustment of the upper part of the housing and thus facilitating height adjustment.

• The generated clamping force can be limited in the vicinity of dead centre by(patented) mechanical means, such as a slight hollowing-out of the guide slotfor the guide roller. This causes the piston rod to shift slightly to the side,reducing the high terminal force in the fully-stretched position.

• The generated torque can be limited by resilient (elastomer) intermediatecomponents. These may, for example, be rubber torsion components of thekind already shown in Fig. 2-15.

It is often necessary in vehicle bodywork construction to carry out clampingthrough holes and other openings which may be distributed over a wide area.The clamping devices used for this are adapted accordingly. Fig. 3-46 shows the clamp claws of the devices known as under-clamps. The clamping mandrelholders have diameters of 18 to 40 mm, strokes range from 25 to 100 mm andthe devices can clamp sheet metal components up to 2.5 mm thick. Clamps with a centring mandrel provide the functions of aligning the workpiece to beclamped (centring) and holding it securely in this position. In the case of pull-action and swivel hook systems, the hooks are retracted fullyinto the centring mandrel as the clamp opens.

a b

c

D2

D1

Clamped

Open

Fig. 3-46:

Under-clamp systems

for shaped sheet-metal

workpieces

a) With centring mandrel and

pull-action hook,

D1 = 20 to 40 mm

b) With centring mandrel and

swivel hook

c) With retracting hook,

D2 = 40 mm

Page 76: Pneumatic Clamping

75

An interesting clamp which can also be used as a gripper is shown in Fig. 3-47. It recalls the “Devil’s claw”, a tongs-type gripper for use with wooden beams,which was used as far back as the 19th century. The operating principle can beseen clearly. As the gripper arms close, their inner sides act in the same way ascams over which a roller travels, with high force being achieved at the end of the‘clamping curve’. During the opening phase, on the other hand, the roller drivesthe clamp arms apart. As the point of action of the roller now lies close to thepivot axis of the arms, a large opening angle is produced, with a choice of 60°,90° and 150°. The unusual shape of the arms is dictated by their function. A large range of different clamp arms is available, together with interchangeablejaws, which are mounted in a floating manner. The gripper will continue to hold aworkpiece securely even in the case of a sudden failure of the compressed airsupply.

3 Types of clamping devices

1

±5°

2

1

3

Fig. 3-47:

Clamp or gripper system for

sheet metal workpieces (BTM)

1 Clamp jaw

2 Clamp arm

3 Sheet metal workpiece

Page 77: Pneumatic Clamping

76 4 Pneumatic section of a clamping device

It is in principle easy to control a clamping cylinder, and a 5/2-way valve can beused for this purpose. One-way flow control valves are usually fitted externally,as close as possible to the relevant cylinder. The control process becomes morecomplicated if the clamping operation is part of a complex functional sequence,in which case the opening and closing of the clamp jaws are only individualsteps in a sequence chain. In this case, in addition to automatic operation, provision must also be made for manual actuation of the clamp to allow func-tional testing.

Fig. 4-1 shows a control circuit for single-acting clamping cylinders. The clampingpistons are reset in this case by spring force.

If there is a requirement for clamping of the piston rod in order to maintain clamping force, the control circuit shown in Fig. 4-2 can be used. The clampingfunction can be provided by a pneumatic clamping unit. These are available insingle- and double-acting versions.

If the clamping cylinder is powered via a pressure intensifier, it can be connectedup as shown in Fig. 4-3. This is a pneumohydraulic system.

Fig. 4-3b shows a schematic circuit diagram for a pressure booster which oper-ates in the air/air system as a twin-piston pressure intensifier. The power pis-tons are fed with compressed air via a pneumatically-actuated directional control valve. The piston direction is reversed each time a stroke end position is reached, thus producing the required oscillating action.

4

Pneumatic section

of a clamping device

4.1Control of clampingcylinders

Fig. 4-1:

Schematic control circuit

for pneumatic clamping

with several drives

Page 78: Pneumatic Clamping

77

Typical piston diameters are 63 and 100 mm. Not shown are the pressure gauges used to indicate the primary and secondary (high-pressure side) pressures.

It is also possible to fit the clamping cylinder with inductive sensors which generate an electrical signal by contactless means when the cylinder pistonreaches a certain position. This signal is triggered by a permanent magnet fittedto the piston of the cylinder. The magnetic field passes through the cylinder wall.Sensors of this kind may not operate reliably in a working environment wherestrong magnetic fields are present, for example in the case of resistance weldingmachines. There are, however, special sensor circuits which can detect whether

4 Pneumatic section of a clamping device

a

b

Fig. 4-2:

Clamping cylinder

with clamping of piston rod

Fig. 4-3

Boosting force through

pressure intensification

a) Clamping cylinder with

air/hydraulic fluid

pressure intensifier

b) Air/air pressure intensifier

Page 79: Pneumatic Clamping

78 4 Pneumatic section of a clamping device

the sensor in question is being triggered by a constant magnetic field (the fieldof the switching magnet) or an alternating magnetic field such as a thyristor-con-trolled welding machine. It is therefore necessary to consider whether inductivesensors should be fitted which are resistance to magnetic fields (welding-proof ).Fig. 4-4 shows a circuit for a reed switch which includes operational status in-dicators for the clamp. These are in the form of LEDs which together with theballast resistor R also provide a protective circuit function.

In automated production systems, workpieces to be clamped are fed into therelevant clamping devices automatically. Before clamping, a check must be car-ried out to see that the workpiece is correctly in contact with the determiningsurfaces. This can be achieved by various means, including pneumatic backpressure sensors. Fig. 4-5 shows a schematic circuit diagram for the clampconcerned. The status of the sensors D1 to D7 is evaluated in a logic circuit. Thesensors monitor the horizontal plane on the clamp slide side (D1, D2, D3), thehorizontal plane on the clamp block side (D4, D5) and the vertical plane on theclamp block side (D6, D7).

Load

0 V

24 V DC

R

E1

E2

D6

D7

D1 D2 D3

D4 D5

Fig. 4-4:

Schematic circuit diagram

for a reed switch with LED

indicators used as a cylinder

switch (end-position sensing)

4.2Position monitoringusing back pressuresensors

Fig. 4-5:

Schematic circuit diagram

for an automatic workpiece

clamping device

E1 Sensor to monitor

clamping cylinder stroke

E2 Pressure switch

Di Back pressure sensors

Page 80: Pneumatic Clamping

79

Fig. 4-6 shows the defining components, which are equipped with integrated airnozzles. These reflex nozzles are used as a pneumoelectrical sensor system toverify that the workpiece is correctly positioned and in contact with the correctsurfaces. This system does, however, require every defining component to be fitted with tubing, and the generated signal must be converted and evaluated.Reflex sensors can detect distances of ≥ 0.1 mm. The maximum switchingdistance of pneumoelectrical sensors is governed by the following factors:

• Nozzle diameter• Throttle diameter• Switching pressure of threshold switch• Properties of contact surfaces of workpiece

With fully-automatic operation of clamping devices, for example for a millingmachine, the equipment required for signal detection and evaluation may behighly complex. The steps in the sequence are as follows:

- Workpiece clamping device free?- Insert workpiece.- Workpiece inserted? Correct position reached?- Position and clamp workpiece.- Is workpiece in contact with vertical defining surfaces?- Is workpiece in contact with horizontal defining surfaces?- Is the required clamping pressure present?- Workpiece is machined.- Is machining complete?- Open clamp slide.- Is clamp slide open?- Remove workpiece.

4 Pneumatic section of a clamping device

1

2

3

4

5

Fig. 4-6:

Determining components

with pneumatic monitoring

of position and contact

1 Workpiece

2 Defining component

for vertical reference

surfaces

3 Reflex sensor

4 Jig baseplate

5 Compressed air connection

Page 81: Pneumatic Clamping

80 4 Pneumatic section of a clamping device

If the answer to any question is “no”, the sequence is interrupted and an errormessage is generated. Even with this relatively simple clamping task, there is aneed for logic processing of a number of signals.

In conclusion, let us take at look at clamping with vacuum. We will choose as our example a clamping table which is used to hold workpieces for manual work operations. In most cases, tables of this kind will offer a 3-dimensional tiltfacility to allow the worker concerned to assume an ergonomically favourableposture. They may also feature a pneumatic lifting axis, which is very useful. A possible variant for the control system is shown in Fig. 4-7. In this case, everysuction cup is connected up via a flow control valve. When a workpiece makescontact with the suction cups, these are automatically activated. The flow controlvalve of each suction cup shuts off the air supply to the cup if it is not coveredby a workpiece. This not only makes it easier to work with the device but alsohelps maintain the vacuum circuit. An ejector pulse is all that is required toremove workpieces from the suction cups. It can also be advantageous to arrange for the workpiece first to come into contact with the suction cups, becarefully positioned and then be clamped only after this, controlled by a manualswitch.

1

2

3

4

5

6

Vacuum

4.3Control system for a vacuum-operatedclamping table

Fig 4-7:

Vacuum-operated

clamping table

1 Workpiece

2 Suction cup

3 Clamping table frame

4 Flow control valve

5 Vacuum control valve,

pneumatically piloted

6 Ejector valve

Page 82: Pneumatic Clamping

5

Design and selection

of clamping devices

5.1Steps in the designprocess

81

Clamping devices are never used in isolation. They always form part of theequipment of a particular workstation. They are thus incorporated into the work-piece/tool/machine system. Any evaluation of solutions must therefore alwaysbe based on a study of the wide-ranging requirements and parameters whichcharacterise the point at which the clamping device in question is being used.

Every clamping application is different and must therefore be thought throughfrom the beginning. Standard solutions are not appropriate. It is, however, possible to describe a standard procedure in general terms. It is necessary towork through the following steps:• Definition of task

- Detachment of clamping task from the technical operating sequence- Definition of object to be clamped- Definition of accuracy criteria- Definition of safety criteria

• Definition of clamping geometry details- Definition of defining surfaces based on technological factors- Definition of reference and contact points- Definition if appropriate of any necessary support points

• Study of force relationships- Calculation or estimation of relevant machining (cutting) forces and torques- Derivation of necessary holding force- Determination of coefficients of friction- Determination of clamping force- Check of existing and maximum possible pressures per unit area

• Selection of function units- Defining and positioning components- Clamping unit- Support modules- Monitoring, sensor and control modules- Support or base modules- Cleaning accessories, such as flushing nozzles

• Combination to form overall solution- Overall assembly- Comparison with requirement profile (functional, geometrical, safety-related,

mechanical with regard to overload, economics)- Check for collision hazards.

Collision analysis is an important aspect of planning work, especially in the caseof flexible devices which are to be used with several different workpieces. Thiswill involve different clamp jaw positions and possibly also different tools.Objects which may collide include the following:• Components of the clamping device with other components• The workpiece and clamp components

5 Design and selection of clamping devices

Page 83: Pneumatic Clamping

82 5 Design and selection of clamping devices

• The clamp and a gripper (in the case of automatic feed)• The clamp and the workpiece.

In cases where conditions are complicated, CAD systems are also used.The design process can be considerably shortened in the case of comparativelysimple applications. In more demanding mechanical-engineering applications,on the other hand, clamping becomes a science. The clamping operation mayeven have effects on the workpiece in the sense of requiring an easy-to-clampworkpiece design. In order to achieve this, it may be necessary to provide spe-cial clamping recesses in castings, support shoulders and centring and clampingpoints.

The decisive factor in the design process is to provide resistance to process forces while at the same time ensuring the necessary accuracy.

Many suppliers offer clamps which can be used without the need for custommodifications. In these cases, users must determine which products are mostsuitable for their requirements. The 10 most important factors can be stated asfollows:1. Where can the workpiece be clamped?

Accessible surfaces will often be small or already finish-machined. It is best to mark impermissible areas on the relevant drawing. It is important to achieve an appropriate positional relationship between the areas of the workpiece which are to be machined, the areas which are to be leftunmachined and the machine coordinate system.

2. How can the workpiece be clamped?The decisive factor here is the workpiece geometry. Clarification is necessaryof the surfaces on which the workpiece can lie and by which it can be sup-ported and how machining forces can be dissipated into the machine.Clamping points should be limited to a minimum. The form elements whichare suitable for the positional definition for subsequent clamping operationsmust be assigned the relevant quality parameters.

3. What clamping force is required?This must be high enough to hold the workpiece securely in every possiblesituation. Machining forces should not act against clamping forces butagainst fixed jig components. The required clamping force should be kept as low as possible.

4. Will the workpiece be able to withstand the clamping force?It is not possible to apply clamping force to every type of workpiece. In somecases, this may result in clamping marks and deformation. Both of these willgenerally not be acceptable. Furthermore, clamping forces must not causedistortion of the workpiece. Allowance must be made for workpiece strengthand the maximum permissible pressure per unit area. Defining and clamping areas must therefore be dimensioned sufficiently large.

5.2Selection of clamping devices

Page 84: Pneumatic Clamping

83

5. What motions are the clamping components required to execute?This is a question of clamping range, which must be variable if differentworkpieces are to be clamped. The clamping range may be significantly larger than the workpiece dimensions if space is required for the insertionand removal of workpiece, for example to provide the necessary workingspace for the gripper jaws of a handling device. Clamping and feed pathsshould be short to ensure that the time required for motions is kept to aminimum.

6. What kind of power supply is required?Manual clamping is still a viable option for working processes with longcycles. If powered operation is required, it will depend on the clamping devices used as to whether the drive power is pneumatic, pneumatic with a booster, electrical, magnetic or hydraulic.

7. Are custom-made clamping devices necessary?These will be used only if universal or standard clamps and components are not adequate. A further factor is the scale of the production operation involved. For very long production runs, a more expensive customer-builtclamping device may be more cost-effective, since its design can be opti-mised for a specific task. The general rule, of course, is to make clamps asnon-specific to particular workpieces as possible.

8. What installation space is available?The objective here is to install a clamping device on a workstation or ma-chine in such a way that collisions do not occur. It may be the case that multiple clamps cannot be used at all, due to lack of space. The interferencecontour of the clamping device must not impede tool motion and must alsopermit automatic feed, for example by means of industrial robots.

9. Are accuracy requirements met?Accuracy requirements (for repetition accuracy) must be met in order toensure consistent workpiece quality. A centring clamping action can be animportant factor here, as can a facility for easy replacement of wearing partswhich affect accuracy. Clamping devices should also be easy to clean.Special attention should be paid to ensuring that jigs are sufficiently rigid.

10. Is it intended to automate the clamping operation?This must be considered from both the technical and economic point of view.Automation will generally mean more sensors, which will in turn mean a greater volume of data for processing. Automation is appropriate if work-piece changing directly requires the machine tool in question to be at astandstill. Any automatic monitoring system should include the clampingforce.

From the point of view of users of industrial pneumatics, it is also important tosource components as far possible from a single supplier, since this simplifiesservicing, training and the maintenance of stocks of spare parts.

5 Design and selection of clamping devices

Page 85: Pneumatic Clamping

6

Safety with

clamping devices

84 6 Safety with clamping devices

The devices used for power clamping can be regarded as miniature presses.There is the risk of crushing injuries as the clamping components close and alsoduring the manual insertion of workpieces. It must be ensured that it is not possible to activate clamping power accidentally, for example by means of a footswitch, at any time when operators’ hands are within hazardous zones. In order to make workpiece insertion easier, it may be advantageous to provideworkpieces with grip recesses and thus ensure that it is not necessary to inserthands directly into jigs. Any sharp edges of jigs must be rounded off. To preventfingers from entering the gap between a workpiece and the clamp jaws, this gapshould not be larger than 8 mm (fingertip width) when the clamping device isopen.

We have already dealt at some length with clamping security. Under no circum-stances must it be possible for a failure of clamping force to occur during ma-chining, since this may cause workpieces to be thrown out of machines in anuncontrolled manner. It is thus advantageous to fit monitoring devices for pres-sures and clamping paths. Arrangements must be made for machine tools toswitch off automatically if the clamping pressure falls by more than 20%.

All linkages used with clamping devices to transmit force and motion must becovered in such a way as to eliminate any risk to operators of crushing injuriesand cuts.

It must be possible to install and uninstall clamping devices without risk. If necessary, the devices must be provided with eye bolts to allow hoisting. Manual raising and lowering is permissible with weights of up to 20 kg.Clamping devices are often heavier than the workpieces which they are used to clamp. The same weight limit applies to workpieces in cases where these are inserted manually. If workpieces are heavier than this, the workstation con-cerned should be equipped with hoists.

The main danger with powered equipment driven by mechanical, pneumatic,

electrical or hydraulic energy is motions which may result in injury.

It is also important to select the correct types of tubing, hoses and valves whichare able to resist the pressures and pressure fluctuations occurring in the appli-cation in question. Tubing and hoses should be protected as far as possible from the effects of heat, due to the risk of premature ageing and consequentweakening which this poses. Tubing and hoses must be laid in such a way thatthey are protected from falling workpieces and impermissible bending, com-pression and torsional loads.

If it is not possible by other means to eliminate all risk of injury to operators’hands during clamping operations, a two-hand control unit should be provided.This obliges operators to keep both hands on the two pushbuttons, which mustbe pressed within 0.2 to 0.5 seconds of each other and kept pressed until avisual signal appears, indicating the completion of the clamping operation. A system of this kind does not, however, provide protection for any secondmachine operator who may be present. It is therefore nonetheless important for

Page 86: Pneumatic Clamping

85

operating personnel to observe all applicable accident-prevention regulations. Fig. 6-1 shows the control logic for a pneumatic two-hand control block. Thepneumatic cylinder connected to the output A is fed with pressure only whenthe two inputs P1 and P2 are pressurised simultaneously. The compressed airsupply is fed to a dual-pressure valve with an AND function. This opens onlywhen pressure is present at both inputs.

An interesting contribution to working safety is made by the toggle-lever clampshown in Fig. 6-2. This develops its full clamping force only a few millimetresbefore the end of its stroke (during the last 5° of the clamp arm motion). If theclamp claw encounters an obstacle before this, this will cause a pressure reliefvalve to open and the clamp arm will come to a stop. This pressure relief valve isbuilt into the piston and is operative at all times except at the end of the stroke,at which time the outlet duct in the piston rod is closed. The overall motion ofthe clamp is thus subdivided into a non-hazardous rapid traverse followed bythe actual power stroke. The motion of the clamp arm is cushioned startingapproximately 30 mm before the point at which actual clamping starts.

6 Safety with clamping devices

1

2

A

3

P1 P2 4

Fig. 6-1:

Schematic circuit diagram

for a two-hand control block

1 Shuttle valve (OR function)

2 Two-hand control block

3 Dual-pressure valve

4 Start valve

Page 87: Pneumatic Clamping

86 6 Safety with clamping devices

1

2

3

Fig. 6-2:

Toggle-lever clamp

with integrated safety

function (Tünkers)

1 Clamp claw

2 Clamp block

3 Non-return

(pressure relief ) valve

Page 88: Pneumatic Clamping

7

A brief overview

of components

Fig. 7-1:

Cylinder combination

to provide higher thrust

(Festo)

Available diameters:

25, 40, 63 and 100 mm

87

In this book, we have considered many ways of creating clamp points by usingpneumatic energy. It would therefore seem appropriate to list once again thecomponents which can be used for this purpose. These components are com-mercially available and allow clamping devices to be assembled quickly andreliably.

Compressed-air force generators

- Pneumatic cylinders, single- and double-acting - Power cylinders with integrated suspension mounting- Tandem cylinders- Bellows cylinders, pressure cushions and bars- Rotary vane drives- Swivel clamps with lifting/turning action- Toggle-lever clamps and other power clamp cylinders- Diaphragm cylinders and fluidic muscles- Clamping modules- Pneumatic motors.

This list of components does not of course indicate the possible ways in whichthey can be combined. As Fig. 7-1 shows, tandem cylinders, for example, can be connected in series, producing a multiple of the thrust of one cylinder. This is an alternative to fitting a cylinder with a larger diameter. Designers thus havethe choice of making their clamp drives “wide and short” or “narrow and long”.There are of course also numerous piston diameters available, which provides anumber of intermediate solutions as well. In this configuration, the entire forceis transmitted by a single piston rod. The cylinder caps are equipped with heavy-duty bearings which are able to absorb higher lateral forces. For applicationsinvolving harsh environments, cylinders are also available with heat-resistantseals (for temperatures up to 150°C) and/or corrosion- and acid-resistant pistonrods.

7 A brief overview of components

Page 89: Pneumatic Clamping

88 7 A brief overview of components

Vacuum-based force generators

- Vacuum grid plates with bead edge seal- Suction cup arrays- Circular vacuum clamp plates- Sintered-metal vacuum clamp plates- Slot-type vacuum clamp plates

Accessories

- Mounting components- Compensating couplings- Tubing and piping, with connector components- Piston-rod clamp units- Pressure intensifiers- Vacuum reservoirs- Bead seals, sealing mats and foils- Compressed-air and vacuum generators

Measuring equipment and sensors

- Pressure gauges- Proximity sensors, cylinder switches- Vacuum and pressure switches- Back pressure sensors- LED indicators

Control components

- Directional control valves and operator controls- Vacuum flow control valves- Pressure regulators- Non-return and one-way flow control valves- Two-hand start blocks- Soft start valves- Logic control components (AND and OR functions)

Basic components for jig construction

- Guide components- Rigid support components- Springs and system spring units - Base plates and supplementary plates (smooth or with hole or slot grids)- Clamp jaws and clamp jaw attachments- Support components and auxiliary supports- Support bars, workpiece stops- Pairs of clamp vees- Spindles- Clamp cam profile bars- Auxiliary materials from modular jig systems- Clamping collets, e.g. in accordance with DIN 6343.

Page 90: Pneumatic Clamping

89

Fig. 7-2 shows how a clamping collet can be used to produce a high-power pneumatic clamp. We have already seen the operating principle involved, in Fig. 2-8c. During the clamp operation, the clamp sleeve is pushed upwards by a combination ball/wedge device. The return stroke of the pneumatic pistonis powered by pressure springs. This device offers economical air consumptioncombined with high clamping forces. With a primary pressure of 6 bar, clampingforces of up to 70 kN can be achieved.

A final word of advice: When assembling clamping devices, always try to use a high proportion of well-proven and easily-obtainable components. This raisesthe level of standardisation and reliability of the clamping devices concernedand means that only relatively simple planning work is required instead of laborious design from first principles.

7 A brief overview of components

Fig. 7-2:

Collet clamping device (Festo)

1 Compressed air connection

2 Ball bearing

3 Lock nut

4 Clamping collet

5 Piston

6 Return spring

1

2

3

4

5

6

Page 91: Pneumatic Clamping

90 Literature

Literature

Leiseder, L.M.: Pneumatische Spanntechnik (Pneumatic Clamping Technology),published by verlag moderne industrie, Landsberg 1989

Deppert, W.; Stoll, K.: Pneumatische Steuerungen (Pneumatic Control Systems),10th edition, published by Vogel Verlag, Würzburg 1994

Krahn, H.; Nörthemann, K.-H.; Stenger, L.; Hesse, S.: Konstruktionselemente –Beispielsammlung für den Vorrichtungs- und Maschinenbau (Design Com-ponents – A Collection Of Examples For Jig And Machine Construction), 2nd edition, published by Vogel Verlag, Würzburg 1994

Krahn, H.; Nörthemann, K.-H.; Eh, D.; Hesse, S.: Konstruktionselemente 3 –Beispielsammlung für Montage- und Zufuhrtechnik (Design Components 3 – A Collection Of Examples For Assembly And Feed Technology), published by Vogel Verlag, Würzburg 1999

Trummer, A.; Wiebach, H.: Vorrichtungen der Produktionstechnik (Production Technology Equipment), published by Vieweg Verlag, Wiesbaden 1996

Page 92: Pneumatic Clamping

Glossary of technical terms

AA Active force . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9Air/air pressure intensifier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38Amplifying clamping force . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34Area force . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

B Back pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78

C Cartridge cylinder . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22Clamp arm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72Clamping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10Clamping accuracy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41Clamping application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81Clamping cam . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30, 36, 54Clamping collet brake . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33Clamping device . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43Clamping error . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42Clamping force . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27Clamping force maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32Clamping mark . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82Clamping method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20Clamping module . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55Clamping moulding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70Clamping range . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39Clamping screw . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30Clamping security value . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31Clamping technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9Clamping torque . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27Clamping unit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76Clamping wedge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30, 31Clamping with wedge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53Clamping-device concept . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16Clamping-force piston . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33Claw clamp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43, 73Claw clamp drive . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51Coefficient of friction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28, 44Collet clamping device . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89Collision analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81Compensatory clamping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68Contact deformation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42Contact monitoring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79Control process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76Custom-made clamping device . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83Cutting force . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

D Dedicated device . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26Deformation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41Definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10Defining bar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54Defining pin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

91

Glossary

of technical terms

Page 93: Pneumatic Clamping

Defining plane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15Defining surface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15Diaphragm clamp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55Distribution of clamping force . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41Double-arm swivel clamp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

E End-position sensing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78External clamping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56

F Floating clamping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69Flow control valve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80Flow of force . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69Fluidic muscle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58Force compensator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22Force distribution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22, 66Frame clamp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53Frictional force . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

G Grid clamp plate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63

H Handling function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Hold-down clamp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52Holding force . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27, 64

I Impact factor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28Inflatable tubing drive . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60Interference contour . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83Internal clamp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64Internal clamping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56

J Jaw clamping device . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51

L Lamellar pneumatic motor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40Lateral pressure piece . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39Layered clamping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23Lever clamp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23, 36, 43, 57Limiting clamping force . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38Locking brake . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

M Machine vice . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40Machining force . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30Maximum permissible pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38Metal diaphragm clamp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57Monitoring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13Multi-layered clamping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23Multiple clamp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22Multi-purpose device . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

Glossary of technical terms92

Page 94: Pneumatic Clamping

Glossary of technical terms

N Non-return valve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

O Over dead centre interlock . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73Over dead centre . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27Over dead centre position . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32Over definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17Overload protection device . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

P Panel clamp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53Path of clamping force . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42Peripheral routing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29Pipe clamping device . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49Piston force . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27Pneumatic cushion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61Pneumatic motor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40Position monitoring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78Positioning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10Power clamp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71Power stroke . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85Precisely adjustable component . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18Pressure booster . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38Pressure device . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68Pressure intensifier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36, 77Pressure per unit area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38Pressure regulator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38Pressure roller . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67Pressure transmission . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24Pressure pin clamp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59Pressure plate unit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59Push-rod clamp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

R Reactive force . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9Reed switch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78Reference point . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15Reflex sensor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79Release force . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27Repetition accuracy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41Roller pressure segment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68Round vacuum-operated chuck . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63Rubber clamping device . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64Rubber diaphragm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57Rubber/metal component . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39Rubber pin gripper . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66Rubber pin diaphragm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66

S Safety . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84Safety factor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28, 63Self-locking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31, 32Sensor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77

93

Page 95: Pneumatic Clamping

Sheet-metal workpiece . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73Sintered metal plate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63Slotted link . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32, 35Spiral-slot guide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47Spreader clamping system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33Standard clamping device . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27Static coefficient of friction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28Suction cup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80Suction plate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63Support . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11Support component . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18Swivel clamp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47Swivel hook system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74

T Tandem cylinder . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34Toggle-lever clamp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39, 44, 70Toggle-lever mechanism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34Toothed-segment clamp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46Torsion component . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39Tubing clamp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59Twin-piston pressure intensifier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76Two-hand control block . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85

U Under-clamp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74

V Vacuum-operated clamping plate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64Vacuum-operated clamping table . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63, 80Vacuum clamping technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62Vacuum conveyor belt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67

W Wedge linkage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34Welding clamp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48Workpiece carrier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

Glossary of technical terms94