Pid Control

Hello: I need if someone can tell me how do I make a lader program using a PID control,to control the clamp movement of a injection molding machine.I am new in this so please go easy with me. The plc that I use is a cutler hammer D32LT and the software is WINGPC.THANK YOU

JAVY-

You must first determine IF this PLC has PID functions in it.

IF it does, then you must identify the INs and OUTs for this control loop.

The INs would be the ACTUAL POSITION of the clamp (Measured Variable)
Is it an encoder?

The OUTs would be the output signal to whatever it is thats makes this clamp move, it could be an hydraulic proportionnal valve, a servo, a VFD drive... what is it? (Controled variable)

TheN you just have to link those 2 data to your PID function or block.

Then, in your program, you have to send this block a TARGET or Set Point which is the main concern. Thats where you want the clamp to be.

After this, you must give 3 arbitrary values: P, I and D

Say you give P a 50% band, I a 2 seconds repeat rate and D is set at 0... thats ZERO (don't need this and 0 should cancel it off)

After you have done this, COME BACK and ask "How to tune a PID controler"

Also, give A LOT MORE DETAILS.

Remeber, a what wize man said: Nothing can be at two position at one time.

The PLC will control Setpoint handling in the sequence. The PID will sorta work by itself... being slave to your ladder sequence.

Why use close loop?

JAVY, open loop is MUCH easier. Getting the position PID done is just the beginning.

Steve, why not post a link to the PID infomation on your site. This is what I do and it avoids the negative feedback. I have posted many links to example programs on our site.

To the rest, some of the best information is on manufacturer's web sites. If I want to know how to make a brushless motor controller I would go to the TI, Motorola and Analog Devices sites just to get their application notes. Each company puts a lot of effort into these application notes that explain how to user THEIR products. These application notes are also very educational because the companies WANT you to be able to use their product.

I think it is OK do post links application notes. However, I too have refused fill out infomation and just left the site if I don't need the information that badly.

So why not help JAVY with his PID? You know I can detail him to death about PIDs, but I don't know anything about Cutler Hammer PIDs and I don't have documentation for it. If JAVY really wanted help he would have posted a link to a .pdf file on the PID. ( Oh, this may be on a Cutler Hammer web site ).

In addition, if JAVY did figure out the PID, there are many other important questions that must be answered. Without having all the answers one will just be slamming clamps and molds together. The molds cost more than the machines.

My advice, go open loop or find someone that has some experience with injection molding machines or similer machines.

The Cutler Hammer site doesnt make it easy to find things. I havent found manuals etc for the D32LT but have for the D320 and since both are programmed by GPP Win they may be close.
D320 PLC Manual

PID Loop Control Cutler Hammer D320

I am having problems with net at work, maybe I can find more on this subject when I get home. See if this may help to get you started.

Basic PID examples which usually cover temperature control are going to be of minimal use in devising control of clamp movement, because that is position control.
Clamp position is normally tracked with a linear sensor (Temposonics, Baluff, etc.).

The goal is rapid movement until nearly closed, then slow down and stop smoothly at the fully closed position so that you only hear a very soft thud. On opening, it might be slow break, rapid retract, slow & stop at fully open position. All positions need to be variable to accommodate different moulds.

A simple method for achieving this would be to give a series of fixed outputs to the clamp's proportional hydraulic valve as clamp position crosses appropriate setpoints. Two or three levels are probably sufficient. Some machines don't use proportional valves but instead two on-off valves in parallel with individual flow restrictors for fast/slow speed control. I'm guessing that Peter's reference to open loop is about this type of control.

As Peter said, making a position controller with PID blocks is just the beginning. It will need to be a cascade loop (position & velocity), it will need to compensate for the differing characteristics of the ram when opening and closing. Finally, a 'profile generator' is required to supply the setpoint so that accel, peak velocity, and decel are controlled.
And then, of course, it would have to be tuned...

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