Design Of Ultrasonic Motor Actuator Control System

The ultrasonic motor is a new type of motor which converts energy by using the reverse piezoelectric effect of piezoelectric ceramics,it has the advantages of quick response,flexible structure and good electromagnetic compatibility.Compared with the same power brushless DC motor,the ultrasonic motor’s output speed is lower and the torque is larger.By using ultrasonic motor in the actuator,the reduction gear can be omitted,which can simplify the actuator structure and avoid the nonlinear factors introduced by the reduction gear to improve the control effect.Based on the structure and working principle of the circular traveling wave ultrasonic motor,this thesis analyzes the vibration of the stator and its friction drive with the rotor,the mathematical model of the motor is established and simulated.The equivalent circuit of the motor is also established from the perspective of energy conversion,which provides a theoretical basis for the design of the ultrasonic motor driver.On the basis of the theoretical analysis,the hardware and software of the actuator control system are designed.According to the driving theory of ultrasonic motor and characteristics of the actuator system,this thesis choose a comprehensive control method of frequency and amplitude modulation,the half-bridge inverter driver controlled by the PWM module,and the proportional operation driver controlled by the DDS module are designed,and verified by circuit simulation and software testing.The actuator digital controller uses FPGA as the core device,its functions include data communications and processing,A/D conversion,PWM and sinusoidal signal generation.Finally,the system is tested.The half-bridge inverter driver and the proportional operation driver can both generate the driving signal that meets the requirement of the motor.The half-bridge inverter driver is simple,reliable and easy to implement.The actuator using this driver has a good control precision of position.The proportional operation driver outputs sinusoidal signal directly which can improve the control effect,but it is difficult to realize in actuator system,so the driver still needs further improvement.