Stability of a stepping motor

The stability of a 2-phase step motor subjected to a multiple step input is analysed, taking into account the effect of winding inductance, load torque and damping forces. The time interval between input steps is assumed constant. With this assumption, the voltage appearing across each phase of the motor will be a square wave. To obtain some insight into the synchronising behaviour of the motor, the square-wave voltage is replaced by a sine-wave voltage, and the approximate stepping rates are determined using a phase-space approach. The critical response of the motor for a square-wave input is also examined, and the criteria for synchronisation are established. The results of the analysis are normalised and can be used to determine the maximum stepping rate of a permanent-magnet or constant-field-current step motor. The experimental results obtained show reasonable agreement with the theory.