Research On Phase-shift PWM Driving And Control Of Traveling-wave Ultrasonic Motor

Ultrasonic motor is a new kind of actuator for motion control. Because of its special structure and different operating mechanism, ultrasonic motor has some prominent advantages which are different from the traditional electromagnetic motors. These characteristics make it has broad application prospects in non-continuous and accurate motion control fields. So, the study on ultrasonic motor's motion control technology has drawn greater attention. However, the ultrasonic motor has strong non-linear and time-varying characteristics. In order to make full use of the motor's great performance, the appropriate driving circuit and control strategy must be specifically designed.This paper firstly analyzes the nonlinear of ultrasonic motor driving circuit in detail, and points out the existing of control nonlinear phenomenon and their reasons. This analysis provides the basis of the reasonable design of high-performance driving devices and the improvement of control nonlinearity. Based on this analysis, the H bridge phase-shift PWM driving circuit is designed to weaken the control nonlinearity caused by driving circuit. A kind of phase H bridge phase-shift PWM control signal generator is designed using CPLD, and the SPI communication between DSP and the PWM signal generator is also realized using CPLD to ensure the reliable transmission of control information. This circuit design based on DSP and CPLD not only meets ultrasonic motor's special requirements on control signal, but also provides complete control freedom for the control algorithm design.Based on this digital hardware platform, this paper studies the ultrasonic motor's speed closed-loop control in detail. The closed-loop control of the amplitude of two-phase driving voltages is studied to make the two voltages'amplitude agreed with each other and controllable. This amplitude control strategy improves the operation stability of ultrasonic motor. Then, the ultrasonic motor's high-speed start difficulty is solved using neural network start-up controller. At last, a novel multi- variable control strategy for ultrasonic motor's speed control is designed and implemented. The strategy uses two controllable variables, frequency and voltage amplitude, to realize the harmonious control of speed.Experiments prove that, the designed driving circuit has higher control precision and good stability, and the control strategy is simple and effective.