Stepper motor driving frequency

[ATMA]

Hi guys, if some of you still remember from my other posts i was trying drive a couple of motors using a DAQ card (and yes, next time i'll use a motion control card )

Now, this stepper motor of mine i'm driving it using step pulses generated from my 6221 AO and using its DO to control DIR, EN etc (the reason i didn't use counter to generate the step pulse because both of them are already used for other purposes). My motor runs fine between the frequencies around 500Hz - 1500Hz. But now, when i try to run it at a lower frequency (say 50Hz) of higher frequency (2200Hz) it just stalls or just makes lots of noise without moving.

My default signal is a 50% duty cycle, TTL pulse train. No motion trajectory is implemented.

This is what i've done:
1) Probed the step signals: They are ok, 50Hz is 50Hz
2) Modified the duty cycle of my 50Hz signal to have the HIGH pulse width same as that of 1000Hz: Doesn't work
3) Added extra grounding between my driver and DAQ card: Doesn't work
4) Tried running at half step (my driver supports full and half) with double the freq: Doesn't work
5) Tried running at half step (my driver supports full and half) without doubling the freq: Doesn't work either

What else can be wrong?

[jaced]

Hi,

Without knowing you driver specs it will be difficult to offer suggestions, is your drive capable of operating outside of that range? Also what is your system load compared to the motor’s max load? Did you probe while the signal was connected or just coming out the card without a load? Have you found the exact limit that the motor operates correctly at and is it sporadic at the limit? Please post back with the answers to these questions along with any other information you feel would be useful.

[Buechsenschuetz]

Do you use the motor with a mechanical load, or just with the bare shaft? Depending on inertia of the rotor of the motor, motors have a resonant frequency which will cause stalling or noisy operation with certain stepping speeds. This usually is not a certain well-defined speed but a speed range since the Q factor of the "damping system" of the motor is rather low. You should try to apply some mechanical load to the motor. Some stepper motor vendors have special "damper disks" to be applied to the shaft to avoid stalling/noise around the resonant frequency.

[ATMA]

Sorry for the late reply. Well, the driver i'm using is a bipolar stepper motor driver which uses a ST L297 and L298 controller and IC. I've looked at the L297 datasheet and i did not see any operating frequency range (i'm not sure how fast is the motor able to step at max, i'm guessing around 3k-4k steps/sec)

Anyway, i've managed to run the motor at lower frequencies now. I just added a 1sec delay after i turn on my power supply output before enabling the driver. I don't know the reason behind it but it moves at lower freqs now (albeit the noisy stepping of the motor). At higher frequencies, i'm now also able to drive the motor by ramping up the freq instead of supplying it 3/4k Hz directly.

However, this leads to another question. How do i determine a good velocity trajectory for the motor ramp up? I know i'm not using a NI motion controller so it ain't gonna be perfect, at the moment i'm just having my loop keep incrementing my stepping freqeuncy.

[jaced]

 Hi,

I’m happy to hear that everything is working. I have limited experience with motor control, could you explain a little more about velocity trajectory for motor ramp up. Maybe then I could help to determine the best way to perform this with a DAQ card. It sounds like you are performing this in a valid way by incrementing it with a loop but perhaps with a little more understanding of what exactly you wish to happen I could be of more help.

[ATMA]

Thanks JaceD. I've gotten things sorted out. The ramp issue was resolved through a series of trial and error and finding the suitable increments.