Real-Time Precise Position Tracking With Stepper Motor Using Frequency Modulation Based Microstepping

Microstepping drive for a stepper motor is a well-known technique to improve the stepper motor performance. Normally, microstepping is carried at fixed pulse width planned. However, this method is suitable only when motors are driven at fixed predefined 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 precisely in real time, whose speed is varying at every interval of time. In such a 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 that meets the high degree of motor pointing even at higher output angular rates. As per this scheme, pulse width and the number of steps that motor is supposed to move are derived from the reference position itself in a given amount of time, and the motor is actuated with a corresponding number of steps in real time. FM-based microstep drive is implemented with pulse-width modulation based chopper current controller in an optimized way without compromising on the motor torque margins. Transient error plots obtained through experiments clearly show the advantages of FM-based microstepping over fixed rate. This paper presents the design, analysis, simulation, and experimental results of FM-based microstep drive.