Reducing Position Errors by Vibration Optimization of Stepper Motor Drive Waveforms

Open-loop control of stepper motors reduces system cost and complexity for positioning systems. To produce a precise current waveform, a novel open-loop control implementation of a hysteresis current controller is presented and compared to the existing pulse-width modulation method. The new method extends the resolution available for a given sampling rate, allowing finer control of the motor current. Applications for precision positioning minimize external disturbances but a real, nonideal, motor introduces vibration, and nonuniform motion. Microstepping of the drive waveform approximates a continuous motion to reduce these effects but they are not fully modeled or understood. The proposed current controller is assembled with a hybrid stepper motor to verify the method experimentally. A differential evolution optimizer is applied with the complete physical system in the loop. To measure vibration, a low cost contact microphone is used, eliminating the requirement for expensive rotational sensors. This method is shown to reduce vibration across different speeds. Comparing the microstep positions of a standard sinusoidal waveform and the waveform optimized to reduce vibration, an improvement in position accuracy is also found.