Common case packer program

mdeltat

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Join Date
May 2007
Location
Los Angeles, Ca
Posts
84
In writing logic for a casae packer that has the follwing functions;
1 - place bottles in rows
2 - apply brake to waiting bottles
3 - load box into lift with conveyor
4 - raise lift
5 - actualte slide to drop bottles
6 - lower lift
7 - activate conveyor to discharge filled box

What would standard logic for a case packer of this type look like?
Should a sequencer be used?
Does anyone have a program of this type that I could review to get the basic idea? I have written logic that works (for the most Part) however, i feel it is poorly written and would like to be more efficient and less convoluted on my programming approach.
Thank You
 
I'd approach this with a simple step routine. I'm partial to Grafcets, others not so much. No matter the processor (TI, Siemens, AB, or others), it's very easy to emulate in standard ladder logic.

In essence, you have logic that examines the current step, waits for the condition(s) to go to the next step, and when that condition is met, step to the next step and out of the current step. Each Step performs the actions necessary while in that step. So, in psuedo code:

XIC Step 0 AND XIC Start PB -> SET Step 1, Reset Step 0
XIC Step 1 -> Run Lift Up
XIC Step 1 AND XIC Lift Up Limit -> SET Step 2, Reset Step 1
XIC Step 2 -> Move Pusher Forward
XIC Step 2 AND XIC Pusher Limit -> SET Step 3, Reset Step 2
XIC Step 3 -> Run Timer
XIC Step 3 AND XIC Timer Done -> SET Step 4, Reset Step 3
XIC Step 4 -> Retract Pusher
XIC Step 4 AND XIC Pusher Back -> SET Step 5, Reset Step 4

Etc...

You can also have unconditional moves to a safe step:

XIC Fault -> Reset All Steps, Set Step 0

You can use MOV of values into a word to numerically represent your steps or you can use bits of a single word to represent steps 0 to 15 of a particular process.

This methodology makes it very easy for technicians to troubleshoot as they can immediately see the state of all processes by examining the current step that it is in.
 
Thanks RobertMee. I'm a little embarrassed of posting what I have but if it will get you all to help me then here it is. Note: the only sensors the equipment has are one on the lift to verify that a box is in the lift (this sensor doesnot move with the lift so when the box arrives it is on but as soon as the box lifts it is off again until the lift comes down and then its on again. That's why I used the latch and the counter).
One that says the lift is in the up position,
one that says the bottles are in place and ready to drop.
 
use WINzip, etc. to zip the .RSS file ... then use the "Attach Files" button at the bottom of the "Reply to Thread" page ...

note: it's always better to paste the entire file ... that way we can get a better idea of your I/O, etc. ...
 
Does anyone have a program of this type that I could review to get the basic idea?
No, I don't have one for a Case Packer.

Should a sequencer be used?
Only if you find it easy to understand and troubleshoot. Upon studying your program, I would say hold off on Sequencers for now.

What would standard logic for a case packer of this type look like?
Well, guess what? It would be organized just like this:

Steps.........Action
1 - Place the bottles in rows.
2 - Apply brake to waiting bottles.
3 - Load box into lift with conveyor.
4 - Raise the lift.
5 - Actuate the slide to drop bottles.
6 - Lower the lift.
7 - Activate the conveyor to discharge a filled box.

I tried to organize your program to match what you said it was doing, by dividing it into 7 Steps or Stages. I wound up with 5 rungs left over that do nothing! I moved those to the end of the program, leaving 20 good rungs. You should delete those 5 "Do Nothing" rungs, including 2 timers and 1 counter, unless you know for what they are going to be used.

I also found many unused records in the Symbol database. I deleted the ones that I was sure were not going to be needed. I notice that the program now has dropped from 29 Kbytes down to 26 Kbytes.
 
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Thank you for the assistance Lancie. Your version is way more organized than mine. Can you explain why I don't need to unlatch the "BOX IN LIFTER?" If there is no OTU, when will the bit box have a zero in it to indicate that there is no box in the lifter? Also, will changing the scan sequence affect the execution of this logic?
 
If you are referring to B3:0/7, then there is an OTU on rung 20. The address has an OTU instruction comment assigned which makes its comment appear slightly different from the OTL, which displays the normal address comment.
 
Can you explain why I don't need to unlatch the "BOX IN LIFTER?"
You do need to unlatch it, and as Okie said, the new Rung 20 (the last "necessary rung" of your original rungs) does that.
Also, will changing the scan sequence affect the execution of this logic?
The best I can tell from this remote distance, the way I organized your rungs will allow the program to work correctly. If you notice, a "Step" latches the bits needed during it's turn, then at the end of the step unlatches any that it is possible to unlatch, leaving the others latched until the last Step 7, which unlatches the rest and allows a new cycle to start.

I gather that this program is not finished, and it may not work as is because of missing logic.

However, changing the order of rungs MOST OFTEN will change the way that many programs execute.
 
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