horizontalapnj001 en 03

Horizontal Flow Wrapper Machine Automated with next Omron products: Model: R88D-KN@@@-ECT Servo Drive NJ@-@@@ Machine Controller 3G3MX2-A @ -@@ @ E Inverter

APPLICATION NOTE

Doc N APNJ001-EN-03

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Omron ATC-Europe Application Notes


Horizontal flow wrapper machine Page 2 of 48 Version 04

CONTENTS

1. INTRODUCTION 2. MACHINE OVERVIEW: The horizontal flow wrapper.

a. Which kind of package. b. The machine general description. c. The necessities and requirements for the motion control d. The Omron solution with SYSMAC NJ

General overview of the solution How the Omron solution match the machine requirements. Part list and product description.

3. MACHINE SECTIONS: Detailed description.

a. The main conveyor. Description and technical issues. How to solve this with Omron.

b. The longitudinal sealer. Description and technical issues. How to solve this with Omron.

c. The press belt. Optional part. Description and technical issues. How to solve this with Omron.

d. The transversal sealer Description and technical issues How to solve this with Omron

e. The unwinder. Optional device Description and technical issues. How to solve this with Omron.

4. THE MACHINE OPERATION. State diagram and user interface. 5. ADVANCED MACHINE OPERATIONS:

a. No product no feed. b. No gap no seal.

6. SUMMARY AND CONCLUSION.



1. INTRODUCTION The purpose of this document is to provide a description about how a typical horizontal flow wrapper machine operates, to describe the main functional operations of the machine and a possible practical implementation. Later it is explained how Omron can meet the requirements and offer a solution that fits the application. Every part of the machine is discussed in detail, it is explained the operation itself and how to program this operation with the Omron solution. Some example programs are provided too so, this document is an useful tool to help both, to select the suitable Omron products according to your machine, and to program the products as the main subroutines are pre-made.



2. MACHINE OVERVIEW

a. Which kind of goods is packaging.

The horizontal flow wrapper machine is designed to pack:

- Solid individual pieces like cookies, cakes. - Cosmetics & sanitary. - Etc.

The pack is a soft plastic bag made from a roll of plastic film. See some examples in the picture:

The products are solid and they come at a fixed separation on top of a conveyor in the horizontal direction. The plastic film is wrapped around the film while the product is feed at a constant speed. The product flow is continuous and for this reason it is possible to get high production rates.

b. The machine general description. Although there are many variations and every machine has differences from another one due to the OEM technology, the packaging material and the goods to be packed, we can say that the horizontal flow wrapper is one of the most standard machine into the packaging market.

Fig. 1



Here you can see a general diagram of a typical machine:

Some parts of the machine must always be present; some other varies depending on the material used in the bags and on the goods to be packed. BRIEF DESCRIPTION: The bag material comes from a plastic film coil that is unwinded. This plastic film is wrapped around the product by some mechanical elements called formers while the product is moving. This plastic film is fed by the longitudinal sealer in synchronization with the product at the same time that it seals the film creating a tube with the product inside. This tube with the products inside must be sealed transversally (and cutted transversally too) to form the individual bags. This sealing is done on the fly.

* * *

UNWINDER

Sensor for empty coil

Fig. 2

E

PRODUCT INTRODUCTION MAIN CONVEYOR

LONGITUDINAL SEALER

PRESS BELT

TRANSVERSAL SEALER

External encoder for slip compensation

Registration mark



THE MAIN CONVEYOR The main conveyor is the responsible to feed the products to the rest of the machine with a constant separation. Typically consist on a conveyor with some spacers that are running at a constant speed called the line speed. In each spacer there is one product so, the position of every individual product is perfectly known. This part of the machine usually runs at the commanded speed with no corrections. The main conveyor is driven by a servomotor or, in the most simple machines, by an AC motor with an external encoder.

* * * THE PRODUCT INTRODUCTION This part is the responsible to put the products from the production line into the main conveyor. This device puts one product between two spacers in the main conveyor. In most of the cases this product introduction is a separate machine and has been specially designed for a certain kind of product. In fact, in some cases, the product introduction can be even more complex and expensive than the flow wrapper machine itself. One quite common configuration of a product introduction is a series of small conveyors driven by servomotors running at different speeds that separate the products and feeds them in synchronization with the main conveyor. To know the position of the products it is necessary a photocell in each individual conveyor.

Fig. 3

Sensors for product adjustments

PRODUCT INTRODUCTION

Products from the production line

Product separators



You need to have as many of those separators as number of products that fits in one single separator.

* * * THE FILM FEEDER AND LONGITUDINAL SEALER The film feeder, consist in two pre-heated wheels driven by a servomotor that seals the plastic bag longitudinally while, at the same time, it is feeding the plastic film. When the plastic film is of a single color or has a random design, the movement is just a synchronization with the main conveyor but, if the film has an specific design that must be in a defined position on respect on the product, in this case it is necessary to superimpose a correction to the synchronized movement, depending on the detection of a printed mark in the film pattern. Another topic to consider is the slip. When the longitudinal sealer moves one turn, the plastic film usually moves a bit less than the sealer wheel perimeter, and this difference depends on several factors as:

- The adherence of the material to be feed. - The mass of the material to be feed, this factor is very

important when there is no unwinder system. - The line speed. The faster speed, the more slip.

In some machines, this slip is partially compensated increasing slightly the synchronization ratio according to the operation characteristics: The approximate slip is known depending on the plastic material and the speed and, then, it is compensated following a table or a simple mathematical operation like:

speedLinematerial VKRatioSynch _1_ += Where Kmaterial depends on the plastic film material. Another way to compensate the slip is to use an external encoder to measure the real movement of the plastic and to make the

Fig. 4 Design with no Mark

Design with Mark



synchronization considering this external encoder instead of the servomotor encoder. If the slip is compensated in one or other way, the corrections for the mark will be very small. This is the desired behavior. The last comment is that a few machine makers consider this axis as the machine master axis, and the correction is done in the other axes. This is not the most usual way of doing it, anyway.

* * *

THE PRESS BELT The press belt is synchronized with the Main Conveyor. It consists in an upper belt (and sometimes a lower belt too) that guides the bag and the product from the longitudinal sealer to the horizontal sealer. The mission is to guide the product, this is specially important when the machine is packing products that can move or roll easily because of their rounded shape or its low weight.

* * *

THE TRANSVERSAL SEALER The horizontal sealer consists on two rotary cylinders that have one, two or four heated seal heads (in some machines this can be changeable to pack a wider product range). A servomotor drives this cylinder. This axis must be synchronized with the main conveyor during the angle where the sealing is done, and must change the speed in the other angles in such a way that during one sealing cycle of the sealer, the main conveyor has fed one product. This movement changes when the product length changes and/or the number of seal heads changes.

* * *

THE UNWINDER One optional device is the unwinder. For the smaller machines, the longitudinal sealer is, at the same time, unwinding the plastic from the coil. But this system is valid if the plastic coil is not very big and the plastic is rather rigid so, it is not deformed by excessive tension during the acceleration. Usually it exists some kind of accumulator system.



For bigger plastic coils and delicate material it is usual to have some kind of unwinding system and a material accumulator. Those unwinding systems tend to be very simple as no precision is required. Normally it is used an AC motor with a frequency inverter in speed or PID control. Another possibility is to have a servo unwinding tangentially in synchronization with the longitudinal sealer. As the machine is running continuously, that servo has small size and the accumulation system is not needed.

* * * SPECIFICATION EXAMPLE: A typical specification of a horizontal flow wrapper machine can be as it is shown in the table below: ITEM VALUE Bag Width 10 mm minimum up to 300 mm maximum Bag Length 40 mm minimum up to 410 mm maximum Bag high 1 mm min. to 90 mm max. Machine Speed 120 pack/min (Single Horizontal sealer Jaw)

200 pack/min (Double Horizontal sealer Jaw) Power Requirements 220-240Vac single phase, 4.5 KW Film Width 650 mm Maximum Roll Diameter 350 mm Machine Finish Stainless Steel Machine dimensions 4440mm L x 965 mm W x 1820 mm H Available Option Film feed (Unwinder)

Print registration system

c. The necessities and requirements for the motion control.

The machine consist on the next axes

- Main conveyor. - The longitudinal sealer. - The press belt. - The transversal sealer. - The product introduction (necessary, but can be considered a

different machine). - Unwinder (optional)

The unwinder, if it exists, is usually one inverter with an embedded PID. The PID is executed in the inverter and the setpoint is set from the Motion controller (although it tends to be a fixed value). In modern systems, inverter are controlled in similar way than servos using a common motion bus. The movements of the machine are basically synchronized movements, that is, the position of one axis (the slave) depends on the position of



another axis (the master). All the correction must be made On the fly, that is, while the machine is moving. The next diagram shows the sequence of a complete cycle:

The Main conveyor is usually considered as the machine master and is moving at a constant speed defined by the machine operator. Nevertheless, it usually gives better performance to define a virtual axis as master of the machine and to link the Main conveyor to this virtual master with a ratio of 1:1. The rest of the axes will make their movements following the (virtual) master. So, for the virtual master we need

- Speed control And for the main conveyor we need

- Synchronization (to the virtual master)

The longitudinal sealer is working in synchronization with the virtual master, needs to have the possibility to superimpose a correction based in a printed mark and to connect an external encoder to make the synchronization based in the real plastic position. So:

- Synchronization. - Mark correction. - Superimposing movements. - External encoder connection (full closed encoder).

Time

Time

Time

Time

Main conveyor

Speed

Longitudinal Seal Speed

Press belt Speed

Transversal sealer speed

1 Prod Fig. 5

Registration Registration

MASTER



The Press belt is running in synchronization with the virtual master axis. So:

- Synchronization. The transversal sealer has the most complex movement. Needs to be synchronized with the products during a certain angle (the angle during which the seal heads are sealing the bag) and speed up or slow down in coordination with the master depending on the bag length. So:

- CAM table - Possibility to change the CAM during program execution.

The product introduction uses to be a separate machine. There are a wide variety of product introductory systems, depending on the product. As an example we will propose a system based in belts and registrations. This introductory consist on three different conveyor belts: The first one is full of products coming from the production line. The second one is running at a higher speed than the first one to separate the products, and the third one detects the product and position it in synchronization with the main conveyor. Nevertheless, product introduction is a separate machine and, so, it out of the scope of this document.



d. The Omron solution with SYSMAC NJ

- General overview of the solution.

This is the proposed Omron solution for horizontal flow wrapper machines.

The proposed solution is based in the SYSMAC NJ motion controller.

- How the Omron solution match the machine requirements.

The solution based in SYSMAC NJ match perfectly the machine requirements.

Regarding the performance, the SYSMAC NJ is an advanced machine controller that supports registration correction, external encoder and advanced movements as synchronization, CAM profiles, virtual axes, etc..

G5-ETHERCAT MAIN CONVEYOR

NJ301-1200

G5-ETHERCAT LONGITUDINAL

SEALER Fig. 6

E

MX2 UNWINDER

G5-ETHERCAT PRESS BELT

G5-ETHERCAT TRANSVERSAL

SEALER

NS5-SQ11B-V2

ETHERCAT

ETHERNET-IP



Besides, the SYSMAC NJ can also handle the machine sequence by the addition of remote I/Os. It has a variety of possible communication interfaces to communicate with any upper controller or other third party components in the machine, although the Embedded Ethernet-IP is the recommended one

The SYSMAC NJ is programmed using IEC61131-3 programming standard, supporting Ladder & Structured Text languages with standard PLC-Open motion blocks.

The SYSMAC NJ controls the servomotors using the high performance Ether-CAT motion bus. EtherCAT sends cyclicaly and deterministically the position reference to the servodrives. The system dramatically reduces the wiring of the machine because the connections to the servodrives is done by using cheap and widely available standard EtherNET cables (Category 5 or higher). That reduces cost of cables and installation manpower compared with the traditional pulse or analogue solutions. In addition, EtherCAT adds additional performance as you can access to all drive features from a single connection point, including read/write parameters, tuning, trace, diagnostics, etc.

The inverter also is connected to the same Ether-CAT network and is handled in the same way than a servodrive (in speed control in this case), this simplifies also the wiring and the engineering hours.

The ACCURAX G5 servodrives with embedded EtherCAT interface (R88D-KNxxxx-ECT) controls the servomotor. The position loop is performed in the servodrive so, it is quick and independent on the number of axes. Besides, it has registration input and connection for the external encoder for the slip compensation. All this without additional boards.

ACCURAX G5 is the servo with the highest bandwidth (faster dynamic response) in the market (at January 2012).

The servodrives also have embedded Safety (STO) to match the safety regulations in a simple way. Up to 8 servodrives can be connected to a single safety relay.

The MX2 Inverter, with the EtherCAT interface module has an embedded PID that is used to control the unwinder so, the motion controller simply gives the PID reference and the sequence commands (run, stop, reset, ) via EtherCAT.



The user interface typically is an NS touch screen HMI that provides a friendly graphic and intuitive environment to the machine operator. Besides we can make all the necessary machine adjustments, have a complete diagnostics and make all the operations from this single point. The HMI is connected to the SYSMAC NJ via Ethernet-IP protocol in a transparent way for the programmer.

- Part list and details about the products:

MOTION CONTROLLER 1x NJ301-1200 Machine controller 1x NJ-PA3001 Power supply

SERVO SYSTEM 4x R88M-K75030H-S2 750W,3000rpm

servomotor 4x R88D-KN08H-ECT 800W, EtherCAT

servodrive 4x R88A-CAKA005SR-E Motor power cable 4x R88A-CRKA005CR-E Motor encoder cable 4x R88A-FIK107-RE Filters 1x R88A-CNW01C IO connector (to

connect the registration)

4x R88A-CSK003S-E Safety connector cable (3m)

INVERTER 1x MX2AB007-E MX2 Inverter 1.1KW 1x 3G3AX-MX2-ECT EtherCAT interface

HMI 1x NS5-SQ11B-V2 HMI with Ethernet

OTHER 1x E3M-VG16 Fast photocell for

registration 1x G9SB-2002A-24V Safety relay



3. MACHINE SECTIONS.

In this section it is described in detail the different sections of the machine and the way of solving it with the Omron products. It includes technical description of the different topics and references to the different program examples.

a. The main conveyor: The main conveyor consists on a belt where the products are traveling in predefined position. In most cases, this distance is guaranteed by some mechanical spacers in the belt (see the picture). That means that, for changing the product format, it is necessary to change those mechanical spacers. In some other cases, a product introduction system is the responsible to do that action. This axis is the machine master, and is working in speed control. The speed of the machine is usually described in bags/minute and is selected in the HMI. The rest of the axes in the machine are making their movement in synchronization with this axis In the more simple machines, this main conveyor is an AC motor with an encoder, in this case, Trajexia reads this encoder, that is the Master encoder. In the more complex machines, the main conveyor is a controlled servodrive. In practice, it is better that the machine has a virtual master and the main conveyor is linked 1:1 to this virtual master.

The program is as simple as a SPEED function (see the program example below).

Fig. 7

Product to be packed

Spacer



The speed is updated via a variable written from the HMI The entire machine is referred to the product position so, it is necessary some kind of homing or start sequence to be sure that the machine start with the products in the right position.

TECHNICAL HINT What is a virtual axis? A virtual axis is one axis that exists internally in a motion controller for computational purposes. You can order any movement to this virtual axis as it was a real one and you can read the position that is updated every motion cycle. In fact, a virtual axis can be considered just a profile generator, based in the motion commands, a command position is generated every motion cycle. As there is no position loop, the feedback position is equal to the command position and the following error is zero. The command position in the virtual axis is used in the program for calculation, to add this profile to a real axes, etc. The actions that require the use of an external input (Latch, Pot/Not, ) are not available in a virtual axis.

MOTION COMMANDS FROM

PROGRAM

MOVE... CAM... JOG...

PROFILE GENERATOR

COMMAND POSITION

FEEDBACK POSITION =

VIRTUAL AXIS



TECHNICAL HINT Why we need a virtual machine master When, in a machine, all the axes make movements linked to another axis that is the master, we have two potential problems that are solved by the use of a virtual axis.

Transmitted vibration If the Master has some undesired vibration, this vibration is transmitted to the slave.

Master Speed

Time

Ratio 1:1 Slave Speed

Time

There is vibration

Vibration is transmitted

The master axis tends to be a low rigid axis (material feed, conveyor) so, the vibration is smoothed but the slave axes tends to be high rigid axis so, a small vibration tends to be amplified. Synchronization delays: When a slave follows a master the slave always has a certain delay due to bus transmissions, conversions and adjustments. The slave is delayed by a number of cycles compared to the master (although this can be minimized by synchronizing with the master command, in case the master is a controlled axis)

Master Speed

Time

Slave Speed

Time

Ra tio 1:1

There is Delay

MAIN CONVEYOR

LONG. SEALER

TRANSV. SEALER

PRESS



TECHNICAL HINT With the use of a virtual axis, Those potential problems can be eliminated.

MAIN CONVEYOR

LONG SEALER

TRANS SEALER

PRESS BELT

VIRTUAL 1

Transmitted vibration. If we use a virtual axis as Master There are no vibration at all!

Master Speed

Time

Ratio 1:1 Real master Speed

Slave Speed

Time

There is no vibration

There is vibration

Vibration is not transmitted Synchronization delays The Real master and the slave have the same delay so, no relative delay

VirtualMaster Speed

Time

Ratio 1:1

Real master Speed

Time

Slave Speed

Time

There is Delay

There is NO Delay



This is the code if we have a Virtual master axis and the Main conveyor follows it

b. Longitudinal sealer The longitudinal sealer has two working modes: Without registration mark and with registration mark. When the plastic film is of a single color or has a random pattern there is no need to position the plastic in a certain position relative to the product, then we are working without registration mark. In this case the movement is simply synchronization 1:1 with the master axis. To compensate the effect of the slip we have two options: to change the synchronization ratio, as explained in section 2.b. or to keep the ratio 1:1 and to use an external encoder in a Full closed loop

Fig. 8

Printed mark

E

External encoder for slip compensation

Plastic film

Mechanical mandrel for bag

forming

Longitudinal sealer.

Bag and product in the right position



configuration. If the plastic film has a certain design we have to put the design in a certain position relative to the product, for this we need:

- To detect the difference between the real position of the design and the expected position.

- To apply the correction while keeping the synchronization A registration mark allows to capture the position of the reference mark exactly in the moment it occurs with microsecond delay. Comparing this position with the expected position (fixed value) we have the error to be corrected. To apply the correction in the fly while keeping the synchronization we have a Motion Function block specially designed for this: MC_PHASING. This block behaves like in Figure 9

Time

Time


Total movement

Phase correction

Registration Registration

COMPOSED MOVEMENT

Time


Synch. With master

SYNCHRONISATION

PTP MOVEMENT

=

+

Fig. 9



In Fig.10 you can see the displacement in the printed pattern when the product is packaged without the print correction.

TECHNICAL HINT Why the registration is needed? When we have a design that must be centered in the pack, showing the brand logo, etc, we can never guarantee that the design length is exactly same that the product length. Note that we use the word product length but it includes the gap between products too. Of course, both lengths are nearly same, but the precision is never infinite And the error is accumulative!! For example, if the product length is 100mm (guaranteed by the spacers) but the real pattern is 100.1 mm and we have no correction, we are accumulating an error of 0.1mm per pack. Of course, in a few packs we will not note the difference but, after 500 packs, we will have an error of 50 mm!!! Using the mark, every pack we correct the difference between the desired position and the real position of the mark respect on the product. The correction is very small and do not affect to the dynamics. And besides, if we loose one mark some other time, nothing happens, the error in one bag is very small and will be corrected in the next one.

d 50d 500d

After 1 pack After 50 packs After 500 packs

When the mark is detected here...

the product is supposed to be here. Any

difference must be corrected.

WITHOUT CORRECTION

Fig. 10



In all the cases, there is a synchronized movement to the master axis. When the registration is used, we register the position of the longitudinal sealer axis in the moment that the mark is detected by the sensor. It is not necessary to correct against the product because it comes in a known position.

The difference between the registered position (Where the mark is) and the theoretical position of the mark (where the mark was supposed to be) gives the phase that we must advance (or delay). MC_PHASING superimposes a point-to-point movement that correspond with that phase. Many times we correct just a percentage of this phase for stability reasons. See the program below.

The correction is expected to be small so, we put limits to the maximum correction distance and also to the speed of this correction (not included in the example in order to keep the code simple). Sometimes some parts of the bag design are detected as marks. To distinguish between the design patter and the real mark it is possible to use windowing, that means that every mark detected outside a set window position is ignored.

TECHNICAL HINT How the G5 captures the registration? The G5 has three fast registration inputs with a delay of about 7s and two hardware latch circuits (that means that we can capture two of them at the same time). This latch captures in real time the position of the axis in the moment that the latch input has a rising edge. The encoder in the motor is a serial encoder that sends its position every 82s to the drive. The position of the motor in the precise moment in which the mark arrived is the result of the interpolation between two consecutive samples. The result is very accurated. This value is sent to the motion controller via EtherCAT to apply the correction in a transparent way for the user.

Position

Time 82s

T



Note: All the pieces of code in this document have been tested and are supposed to be correct but in order to guarantee a good



understanding of the main movements, the programs have been simplified. In a real machine, the user must add the necessary sequence handling, HMI interface, manual modes, stop/start sequence, etc.

As the axis is counting always in the same direction, the position counter is always counting up. If the mark, for any reason, does not arrive, the feeder moves the theoretical bag distance with no correction. One missing mark does not affect to the operation of the machine because the error is small so it continues working. But if we start missing many consecutive marks, that means that something goes wrong (broken paper, dirty photocell, ) and the machine must stop. For this, we keep a counter of missed consecutive marks that is resetted when a valid mark is received. As the position is always counting-up, the expected mark position and the window are increased by the bag length (including correction) every cycle. We also consider the case where the position overflow occur when the axes reaches the maximum modulo.

Connecting the external encoder is very easy. The G5 has connector CN4 encoder.

TECHNICAL HINT How the Full closed encoder works? In many application we have a servomotor that is moving the material via a mechanical transmission. Due to this mechanical transmission, the movement in the material do not corresponds with the movement in the motor so we want to put an external encoder that is measuring the real position of the material, and to make the positioning using this external encoder as feedback. The position loop uses the external encoder, but the other loops (speed loop and torque loop follows the motor encoder, as it is shown in the drawing. As a recommendation, if the slip is quite big, it is recommended to decrease the gains in the position loop.

E

Position Loop

Speed Loop Torque Loop

P +

- +

- PI

Position Reference

Motor Encoder

External Encoder



Fig. 10

To activate the Full closed encoder in the G5, you have to change next parameters: Pn001 (Object 3001.00hex)=6 Enable Full closed control Pn323 to Pn328 for the external encoder setup

See the G5 manual for details. There is no necessary to make changes in the application program. Note, to change from/to Full closed control and other modes is necessary to power off-on the drive after changing Pn001 parameter The program is exactliy same than using the motor encoder.

c. The press belt. The press belt is moving simply synchronized with the virtual master at a ratio of 1:1. The mission is to keep the shape of the bag and to avoid that the product is moving on respect on the paper, as at this point of the machine there is no spacers that keeps the product in the right position. This is especially important with products with round shape that can roll. The high of this axis is mechanically adjustable to adapt to the bag high. As in the longitudinal sealer, it is better to synchronize with the virtual master to eliminate the synchronization delay due to the motion bus. The final program is as simple as a single MC_GearIn command:

Fig. 12

Press belt

Product Plastic film tube



An improved version will be to use a MC_PHASING instead so, apart from keeping the synchronization we can make small advancements or delays in order to keep the right tension in the plastic firm. Of course it is necessary to add all the sequence to start, stop, etc, but the motion part is just this one.

d. The transversal sealer.

The transversal sealer has to seal the bags in the transversal direction while the packs are moving in the conveyor so the pack is completely sealed (and, normally, cutted at the same time). Some machines allow a variable number of sealing Jaws: 1, 2 or 4 Jaws, increasing the number of Jaws allows the machine to go faster when the bag length is small. The movement of the horizontal sealer is rotatory and has a natural length that is the perimeter of the horizontal sealer, divided by the number of Jaws, that is:

JawsNJawRadiuslenghtsealerNatural_

2__ =

The conditions that the movement must match are:

- While the main axis moves one bag length, the sealer moves one natural length (that is, one turn in case of using one Jaw).

- During the angle where the Jaw is sealing the bag, the movement must be synchronized 1:1.

Fig. 13 Transversal sealer

Sealer with two seal jaws installed

Pack completely finished



So, if the product length is longer than the natural length of the sealer, after the synchronization area the sealer must decrease its speed or even stop. If the product length is shorter than the natural length of the sealer, after the synchronization area, the sealer must increase its speed. And if the product length is equal to the natural length, the movement is a synchronization 1:1. See that graphically in the next figure:

The limit condition between the last two cases (decreasing speed to completely stop depends on the selected ramps but, in the limit, considering linear ramps it is:

Fig. 14

Time

Speed

Time

Speed

Time

Speed

Time

Speed

Time

Speed

Area: Product lenght

Master Speed Sealer Speed

Area: Sealer natural length

Synchronization during sealing angle

Natural_Lenght > Product Length

Natural_Lenght = Product Length

Natural_Lenght < Product Length

Natural_Lenght



LenghtoductareaationSynchronisLenghtNatural _Pr__2 =

To make this kind of complex calculation we will use CAM movements. The different CAMs will be pre-calculated but a scaling will be necessary to adjust to the different bag lengths. In practice, the shapes are not trapezoidal but S-shaped for smooth movement. We draw trapezoidal profile just for the simplicity of the explanation The program that perform that operation is something like:

As the Bag length can be whatever and can be changed depending on the production needs, the CAM cannot be fixed and needs to be re-calculated everytime the bag length is changed. We do not show here the complete calculation, but we will give a couple of hints about the best way to do it (a complete example is available on request. Contact your Omron representative for it):

Fig. 15 Time

Speed 2*Natural_Length-Synch = Product Length



As in the longitudinal sealer, the strategy is to separate one complex movement in two simple ones. One movement is the synchronization, and another one is the difference between natural length and product length:

In the calculation of the CAM we can sum 2 curves, one that is SLAVE=MASTER and the other that is the correction. In the program we distinguish three different situations

a) Product length>sealer perimeter b) Product length



e. The unwinder.

The unwinder is an optional device that not all the machines have. If this device is not existing, it is the longitudinal sealer who is unwinding, at the same time that feeds the plastic film. An unwinding is convenient when the plastic film is delicate and can stretch due to the tension or when the coil diameter is very big. There are different possibilities for the unwinder:

- One servodrive running synchronously with the longitudinal sealer. Although a servodrive is more expensive than an AC motor, the advantage of this system is that does not need any accumulation system so you save in the mechanics price.

- One inverter with an accumulation system, running with a PID system or other similar.

Next diagram shows a diagram of a MX2 inverter working with a PID System. Here you can see a diagram showing this last configuration: Unwinding with a PID.

+

P gain A72

I gain A73

D gain A74

+

Setpoint

Error

PID Calculation Inverter

Motor

External Process

Sensor

Process Variable (PV)

Freq.

Fig. 12



PID diagram in MX2 drive

The principle of operation is next: - You adjust a potentiometer in the dancer arm in the accumulation in such a way that when the accumulator is empty (arm in the top in Fig. 12) the voltage is zero and when the accumulator is full (arm in the bottom in Fig. 12) it gives 10Vdc. We connect this input to an analogue input in the MX2 inverter and we configure it as PID feedback. - We adjust the PID target to a fixed value, for example, 50%. If the potentiometer gives less than 5V, the accumulator is becoming full, the error is negative and that means that we have to decrease speed. - If the potentiometer gives more than 5V, the accumulator is becoming empty, the error is positive and that means that we have to increase speed to fill it again. - As that process uses to be slow, we will program small gains to have smooth movements without sudden speed changes. The advantage of one configuration like this one is that the unwinder works independently of the rest of the machine. In addition, all system, independently if they have unwinder system or not, have a sensor to detect if the coil is empty. The machine stops the operation if the coil finishes. The control of the inverter in Trajexia is like an axis in speed mode (SERVO=0 so, the position loop is disabled). We will program the inverter to activate the PID so, the speed reference is not taken as speed but as PID setpoint. The settings in the MX2 are: A.71=1 to enable the PID A.76=1 to select the feedback signal as Voltage analogue input

Setpoint via EtherCAT and application program.

Fig. 13



A.78=100 (or other value) to select the limit level of PID effect

And the Variable name is defined in the IO map in Sysmac Studio:



4. THE MACHINE OPERATION AND CONFIGURATION: To program and configure the application you need to use Sysmac Studio. With this software tool you can make your application programs and also you can access to the servodrives and inverter parameters from a single connection point. It is also possible to make tuning, traces and even frequency analisi in the servodrives. We have EtherCAT connection for the servodrives, inverter and, if necessary, IOs and EtherNET connection for the HMI, software tool and possible upper controller. All parameter in the application like: operation speeds, lengths of the movements, wait times, photocell offsets, etc are programmed as global variables that can be set and read from the HMI (those selected as Publish Only).



THE MACHINE OPERATION AND FLOW DIAGRAM. To control the sequence of the machine we propose the next simplified machine state:

As you can see from section 3, making an application program for a Flow wrapper machine is not complicated. Sometimes it is more time consuming to program all the sequence around the cyclic machine operation, that is:

To make the necessary configuration after power-up. To take care of the fault handling: stop the machine in the

right way and report alarms properly. Change from different modes smoothly (manual

automatic). In order to simplify this operation it is necessary that the machine flow diagram is very clear. We propose the flow diagram shown in Fig14. The state machine we propose consists on next 5 states:



- Initialization: Only one time after power on to make sure

that all variables have right values and make the initial checkings that the application requires..

- Stop without alarms: No movements and no alarms. Machine is waiting for commands.

- Stop with Alarm: No movements, no Power in servos and one or more alarms. If it is necessary some diagnostic routine, include it here.

- Automatic mode: Machine working according to the receipe. The data of the receipe is usually entered via the HMI or via factory supervision system.

- Manual mode: Manual movements or individual movements like manual feed to adjust and prepare the machine

And the next transitions:

From Stop without alarm to Automatic mode: Consist in enabling the servos, activate the unwinder and, when ready, change to automatic mode. This transition is enabled if we match some conditions.

From Automatic mode to Stop without alarm. Wait until the cycle of movements is finished and disable the servos

From Stop without alarm to Manual mode: Enable manual movements if the conditions for this are matched.

From Manual mode to Stop without alarm: Cancel all manual movements and disable servodrives.

From any state to Stop with alarm: Cancel any movement and disable all servos.

From Stop with alarm to Stop without alarm: Reset all alarms.

Then, you can focus all your efforts in the machine operation itself. Of course, the details change from one machine to another. After power on, the machine goes to Standby mode, that is, all the motors stopped and no movement. The machine operator can select either to go to manual mode or automatic mode. Manual mode is the mode used to prepare the machine (for example, to pass the plastic film through all the machine) the operations that can be done in this mode are:

- Homing the transversal sealer and the main conveyor. - Jog the longitudinal sealer (forward & reverse) and stop

after the mark (not explained in the examples) and the rest of the axes

- Make an individual bag operation



- Return to start position - Start/stop the unwinder manually

All those axes movements can be commanded from the HMI just by setting the suitable bits, or can be commanded internally from an NJ program. Automatic mode is the automatic operation explained in detail in this document. This automatic operation is programmed in NJ. If the machine operator push the stop button or other stop condition occurs (as the empty coil sensor), the machine returns to Standby. If any error occurs, the machine performs an emergency stop and goes to alarm status. When the error is corrected and resetted the machine returns to Standby.



5. ADVANCED MACHINE OPERATION

In this section we are going to discuss two advanced functions that the most advanced machines have, that improves the performance of the machine and add more functionality. That functionality is rather easy to implement with SYSMAC NJ.

a. No product no feed.

Packaging certain products, the wrapping material can be even more expensive that the product to be packed. In order to save material, if one product is not coming in the main conveyor, we do not want to feed the plastic film corresponding to this product and have an empty bag without product. A product can be missed for several reasons: An error in the product introduction, a rejection during the quality checking, etc.

A product missed in the main conveyor means an empty bag after the

longitudinal sealer.

A product missed in the main conveyor but all the bags are full after the

longitudinal sealer.

NORMAL OPERATION

NO PRODUCT NO FEED OPERATION

Fig. 22



There are 2 possible strategies:

- The main conveyor speeds up for a moment to advance the lost product.

This strategy is valid if only one product is missing (so we do not have to advance a big space in a short time) and the machine is not going to full speed (so we have a margin to accelerate and speed up the main conveyor.

- The rest of the machine stops and waits that the empty product passes and re-start when the new one is coming.

In this document we will study the second alternative. The easier way to implement this function is to use a new intermediate virtual axis. The main conveyor synchronizes with the new virtual master, the rest of the axes synchronizes with the old virtual master, and the new virtual is slave of the old virtual master. So, if the products comes normally, the new virtual is synchronized with the old virtual and the machine works normally as before. If the product is not coming, the new virtual axis disengage from the old (and then, all the axes connected to it will also disengage). When a new product comes we establish the connection again. The distance without synchronization must correspond with one product length.

MAIN CONVEYOR

AUXILIARY VIRTUAL

VIRTUAL MASTER

LONG. SEALER

TRANSV. SEALER

PRESS BELT

Fig. 23



The best way to establish and disconnect a synchronization controlling exactly the point and distance is by using CAMS.

- During normal running the CAM is 1:1 - During disengagement the CAM is deceleration & Stop - While no product is coming we keep stopped - During engagement the CAM is acceleration to synchronization.

The CAMs are scaled by the length of one bag. In the program we add a new auxiliary axis

Time

Time

Time

Time

Main conveyor

Speed

VIRTUAL MASTER Speed

AUXILIARY VIRTUAL

Speed


1 Prod Fig. 24

No product

SYNCHRONIZATION



The Main conveyor part remains as before. The code for theTransversal sealer and press belt is the same with the only difference that, now, the Master is the new Auxiliary Virtual master. This is just one illustrative part of the changed previous code.

b. No gap no seal

It is possible that, occasionally, the product can move inside the pack before the horizontal sealing is done. The reason why this may happen can be, for example, that the product is defective, that the press belt is not properly adjusted, etc. If, in that situation, the sealing is done, the machine will be stopped because the sealer crashes with the product. The possible effects depends on the machine and the products to be packaged, but can be serious like:

- The sealer motor will trip by an overload and stop. - The seal jaw will be dirty with the product and you have to

clean it. Considering that the jaw is warm and the product can be burn or melted, this represent quite a big mess.

- If the Jaw is delicate and the product hard, you can even damage the Jaw.

It is clear that, although this effect is not likely to occur, if this happens, it is a big trouble that can stop the production during a long time so, it is clever to find a way to avoid the situation.



The solution is to detect the gap via the suitable sensor. That mean, to verify that in the space dedicated to the sealing there is no product. In this case the standard sealing is done. On the contrary, if the gap is not detected, that mean that there is a product in the sealing zone and we must skip one sealing operation:

For programming that, we will follow similar strategy that for the no product, no feed functionality, that is, we execute a certain CAM table that, normally is the normal cycle for the cut and, depending on the information from the gap sensor when the current cycle finishes, we will change the current CAM by a new one. The different possible cases are:

Time

Time

Main conveyor

Speed


1 Prod Fig. 26

MASTER

Detection of next product inside the

GAP

The next movement must be a stop

during a product length

Go to Stop position Wait

Accelerate to synchronization

STOP !

If it is detected that there is a

product in the gap, the transversal sealer must skip

one sealing cycle. Fig. 25



- Gap OK: CAM for normal cut cycle - Cutting and next product has no gap: CAM for

Deceleration to stop. - Current product has no gap and next one also has no gap:

STOPPED during a bag length. - Current product has no gap but next one has: Accelerate

to continue normal cut.



In the example above the signal for the gap detection is a local variable. Use the suitable signal in your machine. When designing the different CAMS, the sequence and the start position of the sealer, consider that in the Stop position, the sealer does not have mechanical contact with the product. When a bag with no gap is coming we stop to a safe position and keep stopped while products without gaps are coming. When the gap comes again, we start a new movement considering the current stop position and continue the cycle normally. In fig 27 you can see a drawing with the movements in case of a no gap no seal movement. In the example we draw a sealer with two Jaws so, the natural length corresponds with 180 of the sealer cylinder.


1 Prod

End of sealing synchronizatio

Go to Stop position

Wait for next product.

Accelerate to synchronizatio

Fig. 27



6. SUMMARY AND CONCLUSION

Omron is the right partner to support you in automating your horizontal flow wrapper machine.

The system is easy to install and to program. This shortens the machine production time and simplifies the commissioning. Omron has a deep knowledge an experience in the packaging industry and we will use this to support you. The program examples are available and can be used freely with the understanding that are simply examples and the code can be used as a guideline but needs to be adapted to the particular machine needs.



NOTES



REVISION INFORMATION Rev. Date Remarks 1 April 2012 Original version 2 August 2012 Small errata corrige 3 January 2013 Change fonts in Technical hints in section 3.a

Changing example in section 3.b (longitudinal sealer). Remove MC_SET_POSITION and calculate new expected mark position and windows. Small text improvements.


January 2013

Omron ATC-Europe Josep Pla 2, Building B2, 10th Floor. E-08019 BARCELONA Spain

Cover Flow wrapperOmron Horizontal Flow Wrapper Machine with NJ V2 (January2013)

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Documents

machine overview

machine requirements

machine general description

standard machine

machine sections

omron solution

advanced machine operations

machine controller 3g3mx2