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cmarcus

PWM and Stepper Motors

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Hello All,

I have a simple 1-axis stepper motor application that I'd like to use a Vision 130-33-T2 PLC and control the motor using the +24V DC PWM outputs. The problem I'm having is finding a decent low cost motor controller that supports sourcing inputs for step control. I seem to keep coming across ones that only accept sinking inputs or the fully programmable ones.

So I guess my question is two fold: 1) Does anyone know any low cost stepper conrollers that accept the +24 VDC pulse train from the PWM outputs on the PLC. 2) Is there a simple way to convert the Unitronics output to sinking?

Thanks in advance,

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First off, you don't want to use a -T2. You'll find the outputs won't be fast enough. Depending on your I/O needs, a -TR20 or -TR34 is a much better choice. Been there.

The high speed outputs on the -TR20 and -TR34 are NPN (sinking) out of the box. They go to 200 kHz which should be way faster than you need.

If you look at the actual circuit for a stepper control, it is usually an isolated opto-coupler and really doesn't care whether the output is sinking or sourcing; it's just a matter of how you hook it up. You want to limit your current to about 10 ma, so if you put a 2.2K resistor in series between your 24V supply and the (+) stepper input you can drop the voltage down to the 5V the control is looking for. Connect the (-) stepper input to the PLC output and you've completed the circuit.

As far as low cost stepper controls, I've never seen any cheaper than these:

http://www.mpja.com/Step-Motor-Driver-5A-Max-Wide-Range-CW250/productinfo/17452+MS/

This unit is limited on its micro-stepping options. This may or may not matter to you. If you need precise positioning (< 1.8 deg), you need to use micro-stepping and hence a higher frequency to drive it at a decent speed

If you look at its little brother (3A rated) on the website it has many more micro-stepping choices.

Joe T.

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