I want to eliminate the wrong direction torque of stepper motor during super fast decelerating.
The wrong direction torque is that: When you suddenly decelerate the input pulses of stepper motor's controller, and if the load on the shaft exceeds the maximum electrical torque, the stepper motor will "slip"(lost sync with the drive circuit). Once the motor has rotated past the current "step"(the motor slips), the current driven into the coils will try to push the rotator ahead toward the next step, at this time the torque is in the wrong direction as you want to decelerate the motor. If the motor is turning rapidly, the torque in the wrong direction may cancel out some of the effect of torque that would be in the right direction(which is to decelerate the motor), so you should not suddenly decelerate the stepper motor controller's input pulses.
But I think with positional feedback, the controller can eliminate this wrong direction torque of the stepper motor in super fast decelerating.
The positional feedback can tell the controller the absolute position of the rotator. Once the motor has rotated past the current "step"(the motor has slipped), the controller can change the current driven into the coils so it won't push the rotator ahead toward the next step, it can only continue to stop the rotator when it has passed the so called "current step", it will continue to try to stop the rotator with its electrical torque even the motor has slipped.
There are many closed-loop stepper motor in the market, the vendors didn't explain the details of operating principle, only said:
- Due to closed loop control, the ES series easy servo systems can always implement 100% torque of the motor, and do not need the huge 50% torque reservation in normal open-loop stepper systems.
- The built-in rotor position detection sensor constantly monitors the motor movement. If synchronism is about to be lost, closed loop control is used, eliminating concern over loss of steps.
Can those closed-loop stepper motor in the market eliminate the wrong direction torque during super fast decelerating?
Best Answer
The torque on the motor is a function of the current through the coils. Back EMF created by the rotor moving causes a voltage. Whether this voltage turns into a torque depends on what is connected to the coils. If left largely on its own, like if the coils are shorted, the back EMF causes current that opposes the rotor motion. For example, electronic braking of permanent magnet motors is often done exactly this way, by shorting the coils. Your premise, and therefore your question, make no sense.