Development of a stabilisation scheme for the suppression of parametric instability in stepping motors

A scheme for stabilising the dynamic performance of a stepping motor is described. When the motor operates unstably, the velocity varies cyclically about the synchronous speed. A signal proportional to this velocity oscillation is used to frequency modulate the command pulses, which control the switching of the motor phases. Stable operation is achieved by suitable adjustment of the phase displacement between the velocity signal and the modulating signal. The approach is derived from an analysis which provides a physical understanding of the mechanism of dynamic instability.