A LOW-COST STEPPER MOTOR POSITIONING SYSTEM WITH MINOR CLOSED-LOOP CONTROL

Stepper motors are commonly used in low-cost open-loop positioning control systems. However, acceleration and deceleration are limited and operating open-loop can cause the loss of steps and stalling of the motor. To overcome these inherent problems, a low-cost minor closed-loop position control system was developed to optimise the torque output, maximise acceleration and deceleration rates and avoid the loss of steps. Two different minor closed-loop position controllers were designed and tested. Both systems employ an optical incremental encoder and both contain two feedback loops: a minor closed-loop (MCL) feeding back a step angle signal and a major closed-loop for position feedback. The first system uses a fixed advance angle MCL control whereas the second uses a fixed advance time MCL control involving a time-based interpolator. Details of these control strategies employed and the results obtained from the prototype systems are presented.