controlling a stepper motor via PWM of the PCI7334 motion controller

[Rani]

Hi,
I have the PCI-7334 motion controller and i need to control a fifth axis stepper motor via the PWM output of the Motion I/O module.How can this be done?That is generating the required number of pulses and send them to the motor.
Any exemples or references would be quiet helpfull.
Waiting for your reply and thanks you in advance.

[Jochen]

Sorry but this is not possible. The PWM output of the 7334 is not intended to do any motion control. It's a static PWM output. You can set the frequency and the duty cycle programmatically within some given ranges and that's it. The output is free running and you can't output a determined number of steps. It's also not possible to generate any trajectory profiles on these outputs.

There are several use cases for the PWM outputs. Here are some examples:

- Laser pulse control
- current limiting for motion drives (some drives provide a PWM input for this purpose)

I can think of two solutions:

1. use another 7334
2. If you don't need to move the fifth axis in parallel to the other four you could design a little circuitry with some SPDT relays on it in order
to switch the motion signals from one amplifier input to the next. You would need one SPDT relay for each of these signals: step, direction, FWD, REV and Home limit switch inputs, inhibit output.
You could control the SPDT (single pole double throw) with the digital outputs of your 7334.

Best regards,

Jochen Klier
National Instruments Germany

[Jochen]

Sorry but this is not possible. The PWM output of the 7334 is not intended to do any motion control. It's a static PWM output. You can set the frequency and the duty cycle programmatically within some given ranges and that's it. The output is free running and you can't output a determined number of steps. It's also not possible to generate any trajectory profiles on these outputs.

There are several use cases for the PWM outputs. Here are some examples:

- Laser pulse control
- current limiting for motion drives (some drives provide a PWM input for this purpose)

I can think of two solutions:

1. use another 7334
2. If you don't need to move the fifth axis in parallel to the other four you could design a little circuitry with some SPDT relays on it in orde
r to switch the motion signals from one set of amplifier I/Os to the next. You would need one SPDT relay for each of these signals: step, direction, FWD, REV and Home limit switch inputs, inhibit output.
You could control the SPDT (single pole double throw) relays with the digital outputs of your 7334.

Best regards,

Jochen Klier
National Instruments Germany

[Buechsenschuetz]

Any relay (with the exception of very expensive ones) will cause more or less contact bounce which might be received as valid step signals by a stepper motor driver and might cause unwanted motion. Instead of using relays I would recommend using a digital multiplexer which is available as dedicated IC or can be built with a couple of TTL gates or a programmable device (GAL).

When switching the INH signals, too, take care that the driver which currently is NOT connected to the 73x4 INH output receives proper level at its INH (or ENABLE) input. If a driver is switched off by accidentally supplying an INH signal the motor will have no holding torque.

[Rani]

Dear Buechsenschuetz,
Thank you for your reply.As a mechanical engineer I need you to explain a little more 'if there is no much trouble' what I must do.
Thank you.
Rani.

[Rani]

Dear Buechsenschuetz,
Thank you for your reply.As a mechanical engineer I need you to explain a little more 'if there is no much trouble' what I must do.
Thank you.
Rani.

[Buechsenschuetz]

I don't know about your background with digital electronics but to design such an interface circuit you need at least some knowledge about designing circuits with standard TTL ICs.

If you don't have the necessary experience a skilled technician or engineer in that field will be able to help you. I have seen more than one mechanical engineer with some electronic background, maybe there is someone around at your site. I think the hints I gave will point him/her into the right direction.

Sorry, I am not a consultant or running my own business so I can't design circuits in detail for other companies.