ABSTRACT

Geneva drive or Maltese cross is a indexing mechanism that converts the

continuous motion into intermittent motion. By means of this mechanism the

rotary motion of the driver wheel is converting into intermittent rotary motion

of sprocket. The film passed over the sprocket. Due to the intermittent motion,

the film advanced frame by frame in front of lens for 1/24th second in frequency

of 48 Hz.

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LIST OF FIGURES

FIGURE NO. TITLE PAGE NO.

1 Geneva Mechanism 8

2 External Geneva Mechanism 9

3 Internal Geneva Mechanism 10

4 Spherical Geneva Mechanism 10

5 Moving Of Film Frame By Geneva Mechanism

12

6 Working Stages Of Geneva Mechan-ism

12

7 Dwell Period 15

8 Working Process 15

9 Intermittent Mechanism 17

10 Ball Bearing 20

11 Project Model 22

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LIST OF SYMBOLS Z No. Of Slots R Radius of Geneva Wheel rD Radius of driving wheel r Radius of cam rp radius of pin a Centre distance between Geneva cross & the

centre of cam disc ds Diameter Of Shaft t Slot Width l Slot Length L Shaft Length γ Angle Of Locking Section α Semi Indexing Angle (Driven) β Semi Indexing Angle (Driver) € Gear ratio v Indexing Time Ratio T Time ω1 angular velocity of cam ω2 angular velocity of driven disc

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CHAPTER 1

INTRODUCTION

Geneva mechanism is commonly used indexing mechanism where an

intermittent motion is required.

The Inverse Geneva mechanism, which is a variation of the Geneva

mechanism, is used where the wheel has to rotate in the same Direction as crank. It

requires less radial space and the locking device can be a circular segment attached

to the crank that locks by wiping against a built up rim on the periphery of the

wheel.

The design and fabricating of a conventional Geneva mechanism is gen-

erally simple and inexpensive because there is no specially curved profile on any

of the components except straight lines and circular arcs. However, due to the dis-

continuity of the acceleration at the beginning and ending positions, the shortcom-

ing of using conventional Geneva mechanism is the large impact when the driving

crank engages and disengages with the wheel slot.

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1.1 GENEVA MECHANISM

Fig.1. GENEVA MECHANISM In this mechanism, for every turn of the driver wheel A, the driven

wheel B makes a quarter turn. The pin, attached to driver wheel A, moves in the

slots causing the motion of wheel B. The contact between the lower parts of

driver A with the corresponding hollow part of wheel B retains it in position

when the pin is out of the slot. Wheel A is cut away near the pin as shown, in

order to provide clearance for wheel B as it moves. If one of the slots is closed,

A can make less than one revolution in either direction before the pin strikes the

closed slot and, stopping the motion.

1.2 CLASSIFICATION OF GENEVA MECHANISM

1.2.1 EXTERNAL GENEVA MECHANISM: In this type of mechanism,

the Geneva cross is connected with cam drive externally which is the

most popular and which is represented by the device below fig.

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FIG.2. EXTERNAL GENEVA MECHANISM

1.2.2 INTERNAL GENEVA MECHANISM: In this type of mechanism, the

Geneva cross and cam drive are connected internally in the closed

box, which is also common and is illustrated by below fig.

Fig.3. INTERNAL GENEVA MECHANISM

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1.2.3 SPHERICAL GENEVA MECHANISM: In this type of mechanism

the Geneva cross is in spherical shape and cam drive are connected in

externally, which is extremely rare and is illustrated in below fig

Fig.4. SPHERICAL GENEVA MECHANISM

1.3 ADVANTAGES OF GENEVA MECHANISM

i. Geneva mechanism may be the simplest and least Expensive of all intermittent motion mechanisms.

ii. They come in a wide variety of sizes, ranging from those used in instruments, to those used in machine tools to index spindle carriers weighing several tons.

iii. They have good motion curves characteristics compared to ratchets, but exhibit more “jerk” or instantaneous change in acceleration, than better cam systems

iv. Geneva maintains good control of its load at all Times, since it is provided with locking ring surfaces.

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1.4 DISADVANTAGES OF GENEVA MECHANISM

i. The Geneva is not a versatile mechanism.

ii. The ratio of dwell period to motion is also established Once the no of dwells per revolution has been selected.

iii. All Geneva acceleration curves start and end With finite ac-celeration & deceleration.

iv. This means they produce jerk.

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CHAPTER 2

GEOMETRY OF FILM FRAME

Fig.5. GEOMETRY OF FILM FRAME

In the most common arrangement, the driven wheel has four slots and thus ad-

vances for each rotation of the driver wheel by one step of 90° If the driven

wheel has n slots, it advances by 360°/n per full rotation of the drive wheel.

Fig.6. WORKING STAGES OF GENEVA MECHANISM

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2.1 COMPONENTS

DRIVER GEARThe input is given manually by handle through this

Driver gear. It’s a one type of continuous motion.

CAM & PINIt’s main part of this mechanism. Because it converts

The continuous rotary motion into intermittent motion by guiding the Geneva cross along its circular path. Then it converts this motion as require for the movement of film frame.

GENEVA GEAR OR MALTESE CROSSIt’s also take part as vital role in this mechanism.

Because the rotary intermittent motion produced in this part only. Geneva cross has 4 slots in it, pin goes into along circular movement of cam.

SHAFTShaft holds the all parts of mechanism by horizontally

On its threaded portion. There are 2 shafts are provided in this mech-anism.

SPROCKETIt is provided for hold the film frame according to the

rotary intermittent motion of the Geneva cross. Pressure rollers also provided for perfect movement of film frame.

FILM FRAMEIt’s the component which carries the picture on it and to

slide on the sprockets regularly according to the motion.

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2.2 MATERIALS

Geneva wheel ---------> M S plate

Shaft --------------------> M S rod

Bearings ----------------> deep groove ball bearing

Cam drive --------------> aluminium alloy plate

Geneva cross ----------> steel plate

Sprockets ---------------> acrylic fibre

Pressure roller ----------> polymers

Base, stand --------------> steel

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CHAPTER 3

WORKING PRINCIPLE OF FILM FRAME

According to the principle of Geneva mechanism, the input is given

by motor to the driver gear of the arrangement. In the most common arrange-

ment, the driven wheel has four slots and thus advances for each rotation of the

drive wheel by one step of 90°. If the driven wheel has n `slot.

ELEMENTS

I. Film frame

A commonly-held misconception is that film projection is simply

a series of individual frames dragged very quickly past the projector's intense

light source. If a roll of film were merely passed between the light source and

the lens of the projector, all that would be visible on screen would be a continu-

ous blurred series of images sliding from one edge to the other. It is the shutter

that gives the illusion of one full frame being replaced exactly on top of another

full frame.

A rotating petal or gated cylindrical shutter interrupts the emitted light during

the time the film is advanced to the next frame. The viewer does not see the

transition, thus tricking the brain into believing a moving image is on screen.

Modern shutters are designed with a flicker-rate of two times (48 Hz) or even

sometimes three times (72 Hz) the frame rate of the film, so as to reduce the

perception of screen flickering. Higher rate shutters are less light efficient, re-

quiring more powerful light sources for the same light on screen.

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Fig.8.WORKING PROCESSES OF MOVING OF FILM FRAME

Mechanical sequence when image is shown twice and then advanced.

Outer sprockets rotate continuously while the frame advance sprockets are con-

trolled by the mechanism shown.

II. Feed & extraction of sprockets

Smooth wheels with triangular pins called sprockets engage per-

forations punched into one or both edges of the film stock. These serve to set

the pace of film movement through the projector and any associated sound play-

back system

III. Film loop

As with motion picture cameras, the intermittent motion of the

gate requires that there be loops above and below the gate in order to serve as a

buffer between the constant speed enforced by the sprockets above and below

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the gate and the intermittent motion enforced at the gate. Some projectors also

have a sensitive trip pin above the gate to guard against the upper loop becom-

ing too big.

IV. Film gate pressure plate

A spring loaded pressure plate functions to align the film in a

consistent image plane, both flat and perpendicular to the optical axis. It also

provides sufficient drag to prevent film motion during the frame display, while

still allowing free motion under control of the intermittent mechanism. The

plate also has spring-loaded runners to help hold film while in place and ad-

vance it during motion.

V. Intermittent mechanism

Fig.9. INTERMITTENT MECHANISM

The intermittent mechanism can be constructed in different ways. For

smaller gauge projectors (8 mm and 16 mm), a pawl mechanism engages the

film's sprocket hole one side, or holes on each side. This pawl advances only

when the film is to be moved to the next image. As the pawl retreats for the next

cycle it is drawn back and does not engage the film. This is similar to the claw

mechanism in a motion picture camera.

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In 35 mm and 70 mm projectors, there usually is a special sprocket im-

mediately underneath the pressure plate, known as the intermittent sprocket.

Unlike all the other sprockets in the projector, which run continuously, the inter-

mittent sprocket operates in tandem with the shutter, and only moves while the

shutter is blocking the lamp, so that the motion of the film cannot be seen. The

intermittent movement in these projectors is usually provided by a Geneva

drive, also known as the Maltese cross mechanism.

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Fig. 7. DWELL PERIOD FOR MECHANISM

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CHAPTER 4

DESIGN CALCULATION4.1 SPECIFICATIONS

o Number of Slots, Z= 4

o Radius of Geneva wheel, R = 40 mm

o Distance between centres of Geneva Wheel &driven

wheel, a= 56.5 mm

o Radius of driving Wheel, rd= 60 mm

o Radius of cam, r= 40mm

o Radius of pin, rp=2.5mm

4.2 DESIGN CALCULATION FOR CAM DRIVE

o Angle of locking section, γ= π/2 (Z+2) =270˚

o Semi-indexing angle(driven) α= π/Z = 45˚

o Semi-indexing angle (driver) β= π(Z-2)/(2Z) =45˚

o Gear ratio є=1 for Z=4

o Radius ratio, µ= R/r =1.000

o Indexing time ratio, ν= β/π =0.2500

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4.3 DESIGN CALCULATION FOR BEARING & GENEVA CROSS

FOR GENEVA CROSS:o Slot width, t = 5 mm

o Length of Slot, l= 25 mm

o Shaft diameter, ds= 15 mm

o Thickness, b = 5m

FOR BEARINGS:

Fig.10

Here we used ball bearings.o Bearing of basic design no. (SKF) = 6000

o Inner diameter of bearing, d = 10 mm

o Outer diameter of bearing, D = 26 mm

o Static capacity, Co= 19 KN

o Dynamic capacity, C = 36 KN

o Assume :

Time T=0.166 sec

Speed N=360 rpm (N=60/T)

Angular velocity of driving crank ω1= 2πN/60 =37.7rad/sec Angular velocity of driven disc

ω2 =λ/ (1-λ) ω =91.012rad/sec

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CHAPTER 5

FABRICATING PROCEDURE

GENEVA WHEEL DESIGN The basic design criteria of a Geneva wheel is that the centrelines of the

slot and crank are mutually perpendicular at engagement and at Disengagement.

The crank, which usually rotates at a uniform angular Velocity carries a roller to

engage with the slots. During one revolution of the crank the Geneva wheel ro-

tates a fractional part of the revolution, the amount of which is dependent upon

the number of slots. The Circular segment attached to the crank effectively

locks the wheel Against rotation when the roller is not in engagement and also

positions the wheel for correct engagement of the roller with the next slot.

The design of the Geneva mechanism is initiated by specifying the Crank

radius, the roller diameter and the number of slots. At least 3 slots Are neces-

sary but most problems can be solved with wheels having from 4 to 12 slots.

The angle (β) is half the angle subtended by adjacent slots I.e. where n is the

number of slots in the wheel. Then, defining r2 as the crank radius we have,

Where c is the centre distance. Note that the actual Geneva wheel radius is more

than that which would be obtained by a zero-diameter roller. This is due to the

difference between the sin and the tangent of the angle subtended by the roller,

measured from the wheel centre.

The final step in the design process is to choose a convenient radius for

the circular pert of the Geneva wheel, which meshes with the input wheel lock-

ing the Geneva wheel.

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Fig.11. GENEVA WHEEL DESIGN

A ball bearing used for fix the shaft on stand on base. The bearing se-

lected according to the diameter of the shaft. The shaft was threaded on its both

ends. The driver gear And cam are inserted to the shaft on threaded end. Then

the Maltese cross also fitted with sprockets on its end. Sprockets are designed

according to the film frame width. Pressure rollers are provided for regular

movement of film frame. A handle is fitted to the driver gear manual input. Fi-

nally all these arrangements are fit on the base.

Fabricating process

The Geneva Wheel Mechanism, which was manufactured, had 9 parts.

They were the two Geneva wheel pieces, two circular locking slots, a Crank

Pin, a spacer plate, two Shaft Pins to carry the Geneva wheel and the input shaft

and a Base plate.

The Geneva wheel was manufactured by turning a 10 mm thick MS Plate

to the external dimensions. Then the profile was punch marked on the plate. The

plate was put in a indexing milling machine and the Profile was milled to the re-

quired dimensions including the cutting of slots.

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The locking wheel was also punch marked and milled to the required di-

mensions. The crank pin was made by gas cutting the required shape and the

roller pin was fitted at the required distance of 50 mm from the crank centre. All

the other components were turned to the required dimensions. The Base plate

as cut out of a 4 mm thick transparent acrylic plate. The holes for carrying the

shafts were then drilled by using a 16mm drill taking care of the distance

between the centres.

Geneva wheel analysis

The Analysis of Geneva wheel is done by drawing the position of the pin

and the Geneva wheel at the required position. The position of the Geneva

wheel is given by, Differentiating this with respect to time we get, Differentiat-

ing again with respect time we get, These equations are valid only in the region

– (90-b) to (90-b) of the input crank angle. At all other angles the Geneva wheel

is stationary and hence both angular velocity and acceleration are zero. Both the

angular and acceleration are plotted as a function of input angle in the accompa-

nying plot for an input angular velocity of 1 rad/sec.

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APPLICATIONS & USES

STEPPER MECHANICAL WATCHES PLOTTERS CNC MACHINE IRON RING CLOCK

Modern film projectors may also use an electronically controlled index-

ing mechanism or stepper motor, which allows for fast-forwarding the

film.

Geneva wheels having the form of the driven wheel were also used in

mechanical watches, but not in a drive, rather to limit the tension of the

spring, such that it would operate only in the range where its elastic force

is nearly linear.

Geneva drive include the pen change mechanism in plotters, automated

sampling devices

Indexing tables in assembly lines, tool changers for CNC machines, and

so on.

The Iron Ring Clock uses a Geneva mechanism to provide intermittent

motion to one of its rings.

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MERITS

o The sequence of slides can be altered to meet specific needs.

o May be adopted to group or to individual user

o One can control the length of time each one is shown to allow for explan-

ation, questions from the audience, or discussion of the problem at hand.

The audience will focus its attention on the one slide being shown.

o Easily handled, stored and rearranged for various uses.

o The room need not be extremely dark for projection.

DEMERITS

o The fixed sequence does not permit easy flexibility.

o Can get out of sequence and be projected incorrectly if slides are handled

individually use of the never automatic projectors will alleviate this prob-

lem as the sequence can be worked out and loaded into the special car

bridge before presentation.

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CHAPTER 6

CONCLUSION

Geneva drive indexing mechanism converts the continuous motion of

the driver wheel into intermittent rotary motion of the sprocket. According to

the film length, the cam wheel diameter was chosen. Cam with pin

arrangement integrated with Geneva drive. Input shaft having driver wheel at

one end and cam drive at the other end. Geneva drive and sprocket are mounted

on the output shaft. By cam with Geneva drive arrangement the continuous

motion of the driver wheel converts into intermittent motion of sprocket. Due to

sprocket rotation the film advances frame by frame in front of the lens. Thus the

slide show of the film was obtained successfully.

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BILL OF MATERIALS:

Driver wheel ---------------------> ₨ 150/-

Cam drive ---------------------> ₨ 250/-

Geneva cross --------------------> ₨ 200/-

Sprockets ------------------------> ₨ 150/-

Shafts ----------------------------> ₨ 200/-

Bearings -------------------------> ₨ 100/-

Base & stand --------------------> ₨ 300/-

Bolts & nuts ---------------------> ₨ 50/-

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PHOTOGRAPHS

MOVIE PROJECTOR

KODAK 35mm SLIDE

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PROJECTOR

AUTOMATED SLIDEPROJECTOR

FILM SLIDE PROJECTOR

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SLIDE PROJECTOR

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LCD PROJECTOR

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KODAK FILM PROJECTOR

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BIBLIOGRAPHY

C.Y. Cheng, Y. Lin, Improving dynamic performance of the Geneva mechanism using non-linear spring elements, Mechan-ism and Machine Theory 30(1995) 119–129.

E.A. Dijksman, Jerk-free Geneva wheel driving, Journal of Mechanisms 1 (1966) 235–283.

E.A. Fenton, Geneva mechanisms connected in series, ASME Journal of Engineering for Industry 97 (1975) 603–608.

E.A. Sadek, J.L. Lloyd, M.R. Smith, A new design of Geneva drive to reduce shock loading, Mechanism and Machine Theory 25 (1990) 589–595.

F.L. Litvinov, Gear Geometry and Applied Theory, Prentice-Hall, New Jersey, 1994.Fig. 12. Embodiment of the design and operation sequence.

F.L. Litvinov, Theory of Gearing, NASA, Washington, DC, 1989.

G. Figliolini, J. Angeles, Synthesis of conjugate Geneva mech-anisms with curved slots, Mechanism and Machine Theory 37 (2002) 1043–1061.

H.P. Lee, Design of a Geneva mechanism with curved slots us-ing parametric polynomials, Mechanism and Machine Theory 33 (3) (1998) 321–329.

J.J. Lee, K.F. Huang, Geometry analysis and optimal design of Geneva mechanisms with curved slots, Journal of Mechanical Engineering Science, Proceedings of the Institution of Mechan-ical Engineers, Part C 218 (4) (2004) 449–4540–45.

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