Frequency Modulation based microstepping of stepper motor for real time position tracking applications

Microstepping drive for stepper motor is a well-known technique to improve stepper motor performance. Normally microstepping is carried at fixed pulse width planned. But this method is suitable only when motors are driven at fixed pre-defined speeds for non-real time applications. The problem discussed in this paper considers an application where motors need to track a given reference position profile in real time whose speed is varying at every interval of time. In such scenario fixed speed microstep drive does not meet the high pointing requirements and leads to poor system performance. For such applications, an innovative Frequency Modulation (FM) based microstep drive algorithm is developed which meets high degree of motor pointing even at higher output angular rates. As per this scheme, pulse width and number of steps motor supposed to move are derived from the reference position itself in a given amount of time and motor is actuated with corresponding number of steps in real time. FM based microstep drive is implemented with PWM based chopper current controller in an optimized way without compromising on the motor torque margins. The experimental results obtained are very encouraging. The paper presents the design, analysis, simulation and experimental results of FM based microstep drive.