COMMUTATION AND CONTROL OF STEP MOTORS.

Abstract

Most current 'control' schemes for step motors use sequencing logic to position at cardinal step locations. Using this approach it is difficult to control the motor 'smoothly' or at high speed or with varying loads. Futhermore, positioning between cardinal steps or commanding forces (torques) is impossible using this approach and very limited and complex using a second approach of current modulation of the motor coils. The problems above are solved using a new electronic commutation method which determines the correct enabling of the motor coils based on position sensing of the motor's phase. Using electronic commutation for step motors transforms the problem of control of a step motor to the one of controlling a standard dc motor. This way one can achieve high positional accuracy, high speed and force (torque) control of linear or rotary step motors which is independent of the motor cardinal step positions.