Step-Rate Modulation and Piecewise Linear Control to Adapt Stepping Motors to Low-Bandwidth Servos

Stepping motors provide precise digital control of speed, without tachometer feedback, and have no brushes to wear. This makes them useful in feedback control systems. However, the stepping motor´s natural resonance and its requirement for limited acceleration can cause sustained vibrations and overshoots. Modulating a stream of stepping pulses at twice the resonance frequency with special sequences of ones and zeros overcomes resonance problems. Using a piecewise linear function relating the target stepping rate to the position error prevents saturated overshoots. This function can be generated automatically from more basic parameters of the control system.