Electrical Equivalent Circuit Model And Driving Technology Of Traveling Wave Type Rotary Ultrasonic Motor

Traveling wave type rotary ultrasonic motor (TRUM), featuring small size, high torque at low speed, and no electromagnetic interferences, has been widely used in precise instruments and devices, astronautics, medical treatment, and robots. Modeling by electrical equivalent circuit is a very useful method to analyze the characteristics of TRUM. Most of the present electrical equivalent circuit models merely focus on the stator of TRUM, and the mechanical and electrical coupling characteristics and fictional coupling characteristics between the stator and the rotor are not taken into consideration, so theses models are not accurate enough for the design of the motor driving circuit. A completed model is proposed in this thesis to solve the problems above.The vibration characteristics of piezoceramics and the frictional force transmission process are analyzed in detail in this thesis, based on which, the movement Lagrange equations of the stator and the rotor and the current equation of the piezoceramics are derived. Through electrical analogy, the completed electrical equivalent circuit model of TRUM is derived. The proposed model can reflect the inverse piezoelectric effect and dielectric characteristics of the piezoceramics, mechanical characteristics of the stator and the rotor, and frictional characteristics, and it can explain the energy transfer process clearly. In order to identify the parameters of the model, the admittance of the single stator is measured to identify stator parameters, the parameters of the frictional layer and the rotor are calculated with the relevant material characteristics, and the output power and frictional loss are calculated and modified to make sure the veracity of the model.Based on the model, the parameters design in driving circuit including the turns ratio of the transformer and the resonant inductance are discussed, and the experimental results verify the validity of the derived model and the parameter identify method. The driving circuit is improved by adding an inductor in parallel with the transformer to realize soft switching for the switches, thus eliminate the current spikes, and improve the efficiency. The added inductor can be substituted by the magnetic inductor of the transformer. A speed regulation system is constructed to make the speed constant at different load torque. A prototype with PI regulator which adjusts the driving frequency is accomplished, and the experimental results verify the validity of the system.