from the Forum department...
Fine torque control
Motion control, servos, steppers, etc. topic
Posted by Henry on 3 December, 2011 - 12:14 pm
I need variable torque control from zero (no power) up to 2Nm. The speed is close to zero, or negative (opposite direction due to load).
I wired my brushed 200W motor, no encoder, no gears, to a controller. The controller says it can work with armature feedback.

In torque configuration I get a very raw control. Is this primarly due to:
- lack of encoder?
- brushed instead of brushless or stepper?
- bad controller?

Please don't say: all of them :)


Posted by William Sturm on 3 December, 2011 - 5:50 pm
It sounds more like a mechanical or electrical design issue to me; (friction, tuning, lack of resolution...) It could also be that you need a better amplifier. You should not need an encoder for torque control of a brush motor. I don't think a brushless motor or stepper would help either.

Check for friction issues and make sure that you do not have way more torque than you need at max signal. You will probably need to tune the torque loop also, some drives do not allow for this. I used to use Copley analog drives and there was a procedure for tuning the current loop.

Bill Sturm

Posted by Henry on 4 December, 2011 - 1:41 pm
By raw I mean: torque ripple (strong vibration) at minimum torque, and sudden jump to max torque as I increase the voltage to the torque control input.
I "measure" it by hand, on the shaft, so no friction issues.

Also, my driver cannot be tuned on the current loop. It is very basic, so I guess it's the guilty.


Posted by Leon on 15 December, 2011 - 2:57 am
Do you use 4-quadrant PWM amp? And if Yes, what is its PWM frequency and motor's inductance?

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