Programming issue

[jchal3 0]

Hello all, I am running a Q-series mitsubishi PLC. Here is what I am trying to accomplish: I have a drying conveyor which has product fed into it on one end by an "infeed" conveyor. When the product comes onto the drying conveyor it indexes. There is a one sensor that starts and stops the index of the drying conveyor based on the rising and falling pulse of the product coming onto the belt. On the outfeed end of the drying coveyor, the product must transfer onto an "outfeed conveyor". The problem I am having is that the indexes are not consistant enough to keep a simple one in - one out rythem going continuously. As the system runs, the index distance changes and causes the oufeed conveyor to recieve two products on one index. The conveyor motors are just normal motors, not steppers or servos. I am sure this is a problem that many poeple have faced. I am a novice programmer, and I would like to know how this problem is best solved. Thanks for the input.

[Goody 5]

No replies so far as I think you have not described your problem properly. as in Try explaining exactly what you would like the machine to do and you will get help

[BobLfoot 302]

I've not used a Mitsi PLC in some years but the basic problem you described is filled with several areas for variation which can add up and cause the accumulated error response youa re describing. The simplest and quickest "knee jerk" solution I can suggest is take the rising edge of the product present on drying belt sensor and start a timer. Set the value of the timer as such that is moves a prodcut as far as you want plus 25 % to 50% more. have the timer timing run the drying conveyor motor. See if this doesn't resolve some of your issues. You will probably want to debounce the Photoeye also so you ignore any rising edges which occur while the motor is running.

[jchal3 0]

I am sorry if I have been unclear. I will Make another attempt at an explanation. I have three conveyor belts all running on the same line. The three are an infeed conveyor, drying conveyor, and outfeet conveyor. The infeed conveyor loads the drying conveyor, and the outfeed conveyor catches the products as they come out of the drying conveyor. The infeed and outfeed conveyors run at a constant rate. When a product on the infeed conveyor reaches the drying conveyor, the drying conveyor indexes. This index is started by the rising edge of the product as it comes up to the belt, and stops upon the falling edge of the product plus a timer. As the product indexes down the drying conveyor, the spacing becomes inconsistant, and they do not always index onto the outfeed conveyor consistantly. You run into the situation where when the drying conveyor indexes you could have two products on the outfeed conveyor, one, or none at all. I need to keep the spacing of the products on the drying conveyor as close as possible to allow for maximum drying time, but I also need the system to work consistantly on a one-in, one-out type of set up. I hope this makes more sense. Thanks

[Inntele 60]

Yes now all is much more clear than in previous time, but not about the task's conditions... I support Goody, to understand in what is your task and what is the problem to solve it, we must understand all without your own slang and controversial ideas. There should be only a clear description of process and a clear question.

[Sergei Troizky 26]

Conflict between input and output sides is a common problem for smart conveyors, and may be very difficult to be resolved. Still, you have not specified: - Which of the infeed/outfeed conveyors is faster? Is it always the same? - Are the products separated on the infeed conveyor? If yes, how consistent is the separation? - What's wrong with two products unload onto the outfeed conveyor? - Can you afford products touching each other, and/or being touched by a mechanical device, and/or sliding on conveyor surface (both before and after drying)? - How responsive is the middle conveyor to speed changes? Is it reversible? Edited 12 Feb 2011 by Sergei Troizky

[Crossbow 296]

Are the conveyors controlled by VFDs? You said normal motors. If there was a VFD, you could add encoders to the conveyors and vary the speed of the belts based on the encoder feedback so that they all ran the same.