Can I control a stepper motor by a time varying velocity input?

[Kevin_Mayo]

I want to control the motion of the stepper motor by a velocity input that looks something like a Sine wave.The velocity is changing as a function of time. Can I change the velocity of the motor at a prescribed time interval?
Thanks in advance
Kevin

[Buechsenschuetz]

I do not completely understand what you want to do. Do you want to use the sine wave as an 'input' to a 73xx motor controller board, or do you want to use the sine wave as input to a motor driver unit?

Motor drivers typically need step pulses as an input. You can built (or use) a voltage-to-frequency converter, plus a trigger circuit detecting whether your sine wave is in the positive or negative range (frequency cannot have negative values). The latter device should generate the direction input of the motor driver.

Maybe you can use the analog inputs of the 73xx motor controllers and generate the step pulse and direction signals via software but sampling time will not be deterministic.

[Kevin_Mayo]

Thanks for getting back to me on this. The controller card that I have is the PCI-7342 controller card. The time of a cycle is about seven minutes. I want to ramp the RPM of the motor from zero up to a max value then return it to zero and then go in the opposite direction . A graph of the RPM vs Time is attached.

I thought that I could input an array of velocities into a Load RPM VI and specify the time for each input.I have not been able to do this as of yet, because the load RPM VI will not take an array input.

All these inputs would be made in labview so they are inputs for the controller card. I was under the impression that the controller card generates the steps and direction from the data entered in labview and sends the step and direction impulses to the driver. Do I have the method of operation right?
Do you think this is possible?
Thanks again

[Buechsenschuetz]

> I was under the impression that the controller card generates the steps and direction from the data entered in labview and sends the step and direction impulses to the driver. Do I have the method of operation right?

This is correct. But I am rather a hardware guy, and we do not use LabView in our company. I have no experience whether it is possible to change the velocity of a drive controlled by a NI board via software when the motor is already moving other than the automatic ramp generation. The latter, however, does not allow anything else but a constant or a s-curve acceleration.

[Rodj]

Kevin,

I think that the PVT (position,velocity,time) support in Motion Assistant 1.2.x will help you. Motion Assistant will take your PVT array and convert it into a contour array that the 7342 card can understand. You could also try using contour moves directly.

You can get a free 30 day evaluation copy of Motion Assistant from the web www.ni.com/motion.

In your case you can test you system using Motion Assistant as an application. Then when you get your system working, you can leverage the Motion Assistant API to get the same functionality programmatically in LabVIEW.

Rodger S.

[Kevin_Mayo]

Rodger,
Thanks for the reply, it sounds good
Kevin