Pick and Place Logic

[aussiesurf]

Hi Guys,

I have an application i hope someone can help with.

First of all, all air cylinders are controlled by double acting valves.

I have a machine that picks up material from one pallet, and places it onto a conveyor. The part i am struggling with is working out logic for the pick and place. Pick up and drop off points to not change.

Basically the cylinder goes to the left, gripper goes down, gripper goes up,cylinder goes to the right,gripper goes down,gripper goes up,cylinder goes to the left.....and we just keep cycling like that until the switch is turned off. Need to remember valves are double acting....

Could someone please help me by sending me some handwritten ladder logic? Im not bad at PLC's but for some reason cant nut this out and im sure its pretty basic.......must be getting old!!

Thanks very much

 

[geniusintraining]

Just break it down to small parts, before anyone can write code they would need to know more details such as is there a lift table that lifts the product or does the head lower to the product, are there suction cups or how does it pick?

Anyway as you can see there are a lot of questions... so start small and write our what you need to happen then write the code

1) lift pallet to PE that stops the lift
2) lower head
3) start vacuum
4) check vac suction then lift
5) etc
6) etc

Once you have everything wrote then start with 1) and start the code... then tie 1) to 2)

Hope that helps

 

[Velociraptor]

There has to be a little more to the application than you have listed so far. If you are doing a repetitive pick from one spot and a place on a conveyor, there must be something that is moving a new item to the "pick" position after you have picked the item that was there.

I would suggest flow charting the operation as a state machine. Your application is a natural state machine. There must also be some timing involved to allow for pick, travel and release. After you have your flowchart, you can either translate the flow chart to ladder, or use a PLC that can be programmed in flow charts.

If you are still having trouble, I can see about posting the flow chart & possibly equivalent ladder logic (if I get sufficient time).

 

[ndzied1]

Here is a pick and place simulation I did a while back. Watch this a few times and see if you can come up the sequence or flow chart.

http://youtu.be/MOYGJOpy7zU

 

[aussiesurf]

hi guys thanks for the feedback.

ive got all the other logic sorted, ie, lift table etc, i just need the logic for back and forth and up down. basically just a continuos cycle.

 

[brendan.buchan]

Use a simple state machine.

Step 0 - wait for healthy/preconditions/auto switch, go to step 1.

Step 1 - move back, wait for back feedback, go to step 2.

Step 2 - move down, wait for down feedback, go to step 3.

Step 3 - move up, wait for up feedback, go to step 4.

Step 4 - move forth, wait for forth feedback, go to step 5.

Step 5 - end of cycle, if more cycles required, go back to step 1.

Use a single address to hold your current step number and look at this value to control the process/check for transition to next step. Write new step number to address to change steps.

Pretty basic explanation but should be enough to get you started.

 

[aussiesurf]

thanks for your help. The explanations are great but is someone able to just scribble the ladder logic on paper and email it to me.
I know it may sound like im being lazy but im realy struggling with this section of the code.

my email address is [email protected]

thnakyou

 

[ndzied1]

In case you haven't noticed, everyone is trying to lead you to the answer without giving you the answer. There are a lot of students that try to get their homework answered here and that is not looked upon favorably.

You will get a lot of help and suggestions if you just show what you have, even if it doesn't work or you think it is totally useless.

 

[aussiesurf]

Right Ok...for the record im not a student and sorry if ive offended anyone.

 

[Lancie1]

First of all, all air cylinders are controlled by double acting valves.

Does not that mean that each air cylinder needs 2 solenoid valves for control? How do you know when each cylinder has reached the proper position in each direction (limit switches maybe)?

Here would be a machine-written (sorry, hand-written costs extra) attempt to make your Left-Right Cylinder go first to the Left as you stated it did. Now could you write the rung for the next motion?

 

|  Start/   Right Pos.   Left Position    Move Left      |

|  Stop     L.S.(N.O.)   L. S. (N.C.)     Solenoid Valve |

|--| |----+----| |-----+------|/|--------------( )-------|

|         |            |                                 |

|         | Move Left  |                                 |

|         | Solenoid   |                                 |

|         +----| |-----|                                 |

 

[cwal61]

Maybe this will help get you going in the right direction.

 

[Goody]

You have to realise most of us make our living from writing logic code (or some of our living)

We are here to help - not do.

Pick and place is a very common program but none are identical.

Show us what you have done and people will push each other out of the way to help.

 

[Velociraptor]

There are a lot of details that you have not defined, so I'm going to make some assumptions & show you the start of a flow chart and a section of the equivalent ladder. I'm assuming that the "home" or unactuated position for the head up/down is up, linear travel is over the Pick position and gripper is closed. I'm also assuming that you've got limit switches to detect gripper open/closed, head up/down, and linear position over pick/place.

This is a natural state machine and flow charts are natural for state machines. There is initialization that will be required - that I have left off. Here are the first few steps of a flow chart, based on my assumptions. I did this in Velocio vBuilder.

This is the equivalent of the first couple of steps in Ladder. Again, I used vBuilder Ladder

.

I don't know what PLC you are using, but the basic logic should work with whatever.

 

[Doug-P]

Velocio vBuilder.

Nifty! I didn't know this was out there!

 

[aussiesurf]

Hi again guys.
Firstly thanks for your help so far.
I just realised this site has a free logic simulator....how cool.
I can put my logic into it and run it but when i turn on the inputs they dont highlight in the ladder logic??
Am i doing something wrong? Is there another simulator i could use?