Study On Unidirectional Stepping Ultrasonic Motor And Its Drive Control System

Unidirectional stepping ultrasonic motor is a new type of standing wave motor,which not only has special advantages such as simple driving,stepping operation,but also has the advantages of compact structure,low speed and high torque.In this thesis,the working characteristics of the ultrasonic motor are studied and its drive and control system is designed,which is based on DSP.The characteristics,development history and application of ultrasonic motors are briefly introduced,and the research status of stepping ultrasonic motor,impedance characteristic testing of stator and driving technology are summarized.According to the novel structure,the operation principle of ultrasonic motor is analyzed,and the analytical model for radial vibration of the stator,the thrust model of the motor and electrical equivalent model are presented.Meanwhile,the impedance characteristics testing platform in operating voltage of stator is established,and the output performance of the motor is tested.The impedance characteristics and the amplitude of the stator under different conditions are analyzed on the basis of theoretical model.The results show that the impedance characteristics vary greatly under different voltages,and the resonant and antiresonant frequencies decrease with the increase of voltage amplitude.In addition,the optimal operating frequency of the motor is 74 kHz,and the stator amplitude reaches the maximum value of 0.47 μm under an operating voltage of 100 Vpp.Finally,the driven control strategy is determined according to the test results of output performance.For the design of drive circuit,the push-pull transformer is mainly studied.The transformer model is stablished in Ansoft Maxwell software,and the equivalent circuit of the motor is connected for simulation.The simulation results show that changing the air gap of transformer core has no effect on the leakage inductance,while different turns ratio and winding air gap have great effect on the leakage inductance.Besides,the series inductance in the circuit should be used to meet the matching requirements because the leakage inductance of PQ2020 type transformer cannot reach 1.24 mH which is the inductance required by the impedance matching of USM.DSP TMS320F28335 is applied to design the driving control system of unidirectional stepping ultrasonic motor,including PWM wave generation module,voltage and current sampling module,as well as stepping control and auto-frequency tracking module.The experimental test results show that the motor can realize stepping operation with a step angle of 45°without miss-step.At the same time,the system can track the frequency drift so that the speed of USM can be controlled within a certain range and the whole system has good stability.Compared with the same type of stepper motor,the proposed motor has advantages of high torque density,simple drive and high scalability.The research of its driving control system provides the foundation for the further development and application of the new USM.