Just come across a stepper motor behaving in a strange way and feel at a loss for an explanation of how it might be able to do this.
The stepper motor is rated at about 1kW is a bipolar device with two pairs of windings (four isolated coils) connected in series. All eight flying leads are connected as per the motor manufacturers guidance and is driven from a stepper driver package recommended by the motion controls company from which the stepper, controller and linear thrust unit were supplied. The installation seems to be connected in accordance with the installation instructions. The whole assembly is expected to provide a significant linear compressive force to the material that the end of the linear thrust unit contacts.
Our investigations so far have stripped the equipment down to just the stepper motor itself (removed from the linear thrust unit) driven from the stepper drive unit. The stepper drive unit takes a direction and step signal from a PLC and translates that into the appropriate motor coil power sequence. We still have a few things to measure on Monday when we return but here is what we have so far.
I will concentrate on the stepper motor part only as this exhibits the behaviour by itself without the lnear thrust unit attached.
When commanded to continuously step, in one direction only, the motor operates smoothly (for the 400 of steps per revolution it is expected to do) and continuously.
We have provided a mechanical stop to the motors ability to rotate at one position in the rotational arc. When this position is encountered the stepper motor slips back in the opposite direction before resuming to rotate up to the stop again. The expectation was that the motor would torque up and hold hard against the stop. The slip back is almost like a cog slipping (only there aren't any). The effort applied before slippage occurs is near maximum torque (as far as can be determined).
Any ideas or explanations for this behaviour?