Flow pack Machine Program

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I'm working on a flow pack machine, it has got all the mechanical parts and the sensors and the actuators with an HMI/PLC Which I can't access, and it's working,
but I want to change the hmi and to add a Siemens S7-1200 plc And I have to make a program  to have the same function ,
I managed to make a little plc program to read all the sensors and the encoder value and to cmd all the motors, but I don't know how to synchronize between the film cutter and the film.

I have a VFD that runs the film cutter (it's a rotary resistor which cuts and seals the product package) and a potentiometer to adjust the speed of the VFD and an encoder attached to the chain of the film cutter
and I also have a servo motor which pulls the film and I control the position and speed of this Servo from the plc
I don't know how to synchronize between the speed of the film cutter (VFD) and the speed of the
film (Servo drive) so I could have the same length of the product in all speeds

I also have an eye color sensor, and I don't know what to do when the eye color sensor detects the eye mark in the film.

Any help appreciated ,

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i have not done one of those but from what i know flow pack machines run conveyor continuously at some more or less constant speed (which can be adjusted) and cutter cuts and seals the pouches (like bags of candy).

if the film to make pouches has marking etc, there need to be registration mark of some sort to be a reference point. this is used to start tracking position so that cuts are always in same place relative to label. 

when ever there are two axes to be synchronized (coordinated motion), there has to be a master/slave setup between the two so one axis can follow the other. 

you need to understand the process before you can control it. this will dictate choices and decisions around particular setup.

it sounds like VFD is running at some preset speed feeding the film. you track position of the VFD by counting pulses output by VFD or encoder with position reset by registration sensor. using this info servo can bring next product to be packaged. 

i guess i would start by bringing first product on a conveyor to a known initial position (positioning without sync) then wait for registration mark and start tracking the film (synced).





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@panic mode has described it perfectly. This us how I have done at one of the machines :-

encoder gives you a fixed PPR > u set electronic gear ratio of servo to feed the exact amount of film required per revolution of encoder. > make the servo in external position mode.

The above had one cutter roller (VFD controlled) , connected to encoder  , driving a servo which pulls the film.

that project didn't had eye sensor. However, delta ASDA-A2 servo has a "capture" function. The document they made for this has a detailed explanation for how to use this function.

Hope it helps.  


Edited by sho19

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This is very much like pouches we used in an earlier job of my life.

What I propose is one possible solution.

The Film VFD will run at whatever production rate you want produce product.

Each given product will have a known distance between eye color mark and the pouch seal.  {let's assume that distance is 3 inches and each pouch is 12 inches long}.

Once you see the mark you'll start tracking two things. 

     1.     The 3 inches of film travel point where you'll fire the knife.

     2.     The 11.9 to 12.1 inches of film travel where you'll expect to see the next new film mark.

               A.  If you see the film mark you repeat watching for your two points.

              B.  If you don't see the second mark, you'll need to eitehr auto fire and count up a missed mark and fail when the missed mark count reaches some number.  Or you'll fail immediately.

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