A new stepping motor servo system for improved precision profiling performance

Abstract

The highly nonlinear torque-current-position characteristics make the servo control of hybrid stepping motors very complicated, especially under low operating speed. This thesis focuses on the development of simple and efficient control algorithms for the high-precision tracking control of hybrid stepping motors. The principles of several control schemes have been exploited to minimize the motor's torque ripple, which is periodic and nonlinear in the system states, with specific emphasis on low-speed conditions. The proposed control algorithms are al based on a modular control strategy where the feedback control module is designed to ensure global stability and achieve bounded tracking accuracy, while the feedforward control module is added to compensate for the effect of the torque ripple for improved tracking performance. The interactions between the feedforward and feedback control module have been explored and they have been shown to be complementary to each other. The stability and convergence performance of the control schemes are presented. It has been revealed that all the error signals in the control system are bounded and the motion trajectory converges to the desired value asymptotically. Simulations and experimental results demonstrate the effectiveness and performance of the proposed algorithms. These impressive results pave the way for stepping motors to be used in many applications previously not suitable for open loop steppers such as in low-speed direct-drive systems.