Multi-phase stepping motor controller

Abstract

A disc rotatable with the motor shaft has circumferentially equally spaced slots formed therethrough between the motor step positions. A light source and receiver assembly are operatively arranged relative to the slots to produce position pulses when the motor shaft is positioned between steps. Since the motor shaft varies during operation, the widths of the position pulses also vary in proportion to the motor shaft speed. Timing pulse generators are arranged to generate timing pulses of fixed duration at various motor shafts spacings before the desired stopping position. The coincidence between the timing pulses and the position pulses is sensed, and the motor phases are switched to apply reverse torque to the motor shaft during the intervals of coincidence or non-coincidence of the timing pulses and position pulses. The intervals of coincidence or non-coincidence are proportional to the speed of the motor shaft since the pulse widths of the position pulses are proportional to the motor shaft speed and the pulse widths of the timing pulses are fixed. Reverse torque is thereby applied to the motor shaft in proportion to the motor shaft speed. The excitation power of the motor may be increased during the reverse torque periods, and also for a predetermined number of steps after the motor is initially excited.