plc controling drive via encoder

I would like to control a drive from a plc with a pulse train or 4-20 loop. (via pid?) This drive would have to home to another conveyer and match the flites together. Any good ideas or code examples? I thought an encoder on the conveyer to be matched with a prox to sense the flights or sequence of each machine. One machine would have the frequencey drive the other is a belt variable drive. I would use rslogix500.

could you explain your task? i'm not sure how to understand it now.. do you need to run slave drive by encoder at master drive or what?

What kind of drive are you going to use? Some drives will do gearing with an encoder so you would not need a PLC. It depends on what other logic you need to do. You can read an encoder and do the gearing inside of the PLC. Im sure someone here can give you an idea of how to do this with AB.

Use the belt as a master speed control. Use an encoder to monitor the belt speed and feed the pulses to the VFD as its speed reference.

You would need a trim pot to the VFD to "FINE TUNE" the speed matching but rarely need to adjust it once things have run a bit.

that hasn't been dicided yet but, probably a power flex. The machine must be homed so, both conveyers match their flites. Is there a drive that could do home logic? I will still use a PLC for the machine.

It sounds to me like you have two conveyors that run continuously (as opposed to reciprocally). If this is the case you really don't need to perform specific homing function. I am assuming there is some speed relationship that, in a theoretically perfect world, once the flites are 'aligned' they would stay aligned.

Leadfoot is largely correct. Concentrate on getting the baseline speed relationships correct. After that you will need some type of sensor on each conveyor to tell you the position of the flites. Once the flites are 'aligned' there will be some distance relationship between the flite sensor triggers. Your job will be to keep this distance the correct value. You can probably do this by making a single triangular speed correction once you know the error distance.

That's why I said you probably don't need a specific homing function. Just run the conveyors normally and they will very quickly become aligned based on normal control.

The PowerFlex family will probably be able to do what you want depending on the version (4, 40, 70, 700, 700S). As you go up that list the capability increases. I'm pretty sure the 70 and above will take an encoder input as a speed reference but I'm not convinced you would need to use an encoder reference.

As Leadfoot said, designate one of the conveyors as the master. This conveyor just gets a raw speed reference with no correction. The other conveyor gets the same raw speed reference (scaled to get the correct surface speed) but also gets the correction to align the flites.

I'm pretty close geographically. As you get going on this I may be able to help if you get hung up.

Keith

I like CharlesM's suggestion about gearing as opposed to using a velocity reference. Velocity control is not position control and velocity control does not guarantee that the 'flites' remain synchronized.

conveyers

Thanks for the input. With some help I feel challanged to come up with a cost effective sollution for this ongoing problem.