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from the department...
PWM output within Micrologix 1500
Motion control, servos, steppers, etc. topic
Posted by Andy on 28 September, 2000 - 8:21 pm
I have a Feed and Cut application and I'm planning to use a Stepper Motor with its Stepper Drive.

I will like to use an Allen Bradley Micrologix 1500 PLC and control the pulses to the motor via the two 20 KHz Pulse Width Modulation output found within Micrologix 1500.

Does any of you have a sample file or perhaps some comments on how to use this two High Speed outputs?

Any reply will be highly appreciated.

Thanks

Andy

Puerto Rico


Posted by Curt Wilson on 3 October, 2000 - 2:39 pm
While I am not familiar with the details of the Micrologix PWM output, it strikes me that it is fundamentally the wrong type of output for a stepper drive. PWM is fundamentally a fixed-frequency output, with the duty cycle (% on time, or pulse width) varying with the command value. What a stepper drive expects is "pulse frequency modulation" (PFM), a variable-frequency signal, typically with fixed pulse width, and the frequency of pulses varying with the command value.

With the 20kHz PWM output, you will always be commanding the stepper drive to move at 20,000 steps (or microsteps -- whatever it is set up for) per second. The drive does not care (within limits) how wide the pulses are.

Unless you have access to a register that programmatically controls the PWM frequency, I don't see how you can do this. Even if you could do this, a cut-and-feed application is fundamentally a positioning application, so you would somehow need to keep track of the exact number of pulses generated, or you will drift away from your desired trajectory.

Curt Wilson
Delta Tau Data Systems


Posted by Bill Sturm on 4 October, 2000 - 9:17 am
>While I am not familiar with the details of the Micrologix PWM output, it
>strikes me that it is fundamentally the wrong type of output for a stepper
>drive. PWM is fundamentally a fixed-frequency output, with the duty cycle
>(% on time, or pulse width) varying with the command value.

The Micrologix 1500 has a pulse train output, PTO (I think), that seems to be designed for stepper motors. It has adjustable accel/decel and the ability to put out a predetermined number of pulses.

I have not used it, but it actually looks fairly simple.

Bill Sturm


Posted by sarosero on 8 October, 2000 - 11:20 am
Hi Andy....
I made the application... is so easy. If you want I have a document about my experience. You can contact me paeo98@hotmail.com

Is important that micrologix have output by transistor... no by rele! I don't remember the reference just now.....

To programmer you must use RSlogix500. Read the user manuals of micrologix 1500 at www.ab.com.
Will be so usefull!


bye

sarosero

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