allan bradley PLC using ladder programming to control a servo motor


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I would like help on connecting an allan bradley PLC to a servo motor, interfacing , ADC , DAC etc. and using Ladder programming to use PID control when a load is added the angular velocity will remain at a constant spped. any general help would be helpfull.

James Ingraham

I doubt that this is technically possible, though if your requirments are low enough you might get away with it. I say this because no PLC vendor does it. Arguably, this is because they want to charge you for a motion control card. But really it's because motion control almost always requires a high-speed DSP.

Considering the vast array of options for speed control, why would you even WANT to do this? An indexing servo can maintain a pre-set constant velocity with an on-off signal from the PLC. A-B makes servo motion controllers for most of their product line; the ControlLogix motion controller is excellent. For that matter, the Ultra 3000 drives from A-B (and many other people's drives, as well) can follow a pulse count, which again the A-B PLC's have options for.

If money is the factor, I would caution you that you'll burn an awful lot of time trying to accomplish this.

-James Ingraham
Sage Automation, Inc.

Is this a new installation using new hardware??
If so there are easier ways to deal with this other than PID hardcoding ... AB has some off the shelf devices and programming packages that can do exactly what your looking to do easier!!

If not a new install what are the component details

Bob Peterson

If the drive is set for velocity control a constant analog signal to it will produce a constant speed. You may need to tweak the velocity control loop in the drive itself.

Bob Peterson

Indramat dkc's have a motion controller built into them. You can send strings or hardwire i/o in a bunch of different ways. It will close its own loop after you set the running conditions up. It will also provide you with status info as well as aknowledgments.

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