Electrical braking a stepper motor (revisited)

Question

My question is similar, but not identical, to an older question about electrical braking a stepper motor: Can I use electrical braking with stepper motor?

In my application I do not need to brake the motor, but rather hold it steady at its present position. I know that I can do this by keeping the proper coils energized, but for long durations this impacts my battery drain. Empirically, externally shorting the coils makes the motor "harder to turn."

What I'd like to do is actively stop the motor, then (carefully!) remove the driving voltage, and short the coils. Ideally the shaft position should hold within one full step, but some slip may be acceptable. [To re-start the motor, the process should be reversed.]

I'm having difficulty calculating how well this scheme could actually work, and if there are already existing driver controllers and bridges implementing this. Stepper motors sometimes specify open circuit detent torque, but I've not found numbers for different resistive shorting. Also, I'd expect the timing details and circuit transients could be rather intricate, and would hope they have already been incorporated into commercial IC's.

Summary:

1. How much would resistive shorting improve detent torque?
2. Are there any commercial drivers that implement this?

Answer 1

Torque is controlled by current and the velocity that creates the BEMF is not sufficient to add much torque compared to say 25% PWM or even less with a light bias force. But it will retard an impulse disturbance, yet not a slow drag.

• if you are using microstepping, i suggest it is better to use full stepping with a pulley gear reduction on load torque effects then use acceleration and velocity control to increase your seek time and reduce your voltage to manage energy consumption.
• can this be done in your software or controller Zaxis gcode driver to regulate PWM ? Is it hard to do simply, perhaps but that depends on your system.

If you can monitor slip voltage from the open circuit gated logic , you may be able to integrate the current in a burden R and reverse it for short disturbances before it slips a step. But this is getting fancy.

• your best bet is to balance the forces so there is less chance to slip or get a different servo motor that does it automatically with rotor feedback.