Compensation modeling and optimization on contactless rotary transformer in rotary ultrasonic machining

Rotary ultrasonic machining (RUM) is an effective solution to cut, grind, or drill the advanced brittle hard materials. Contactless rotary transformer, with the advantages of high-power transmission efficiency and reliability, is a potential structure to transmit electric power in RUM. In this study, an impedance model of rotary ultrasonic holder (RUH) is established to find that there exist deviations for the resonant frequency and impedance between the RUH and the ultrasonic transducer, indicating that without compensation the ultrasonic transducer cannot find precisely its own resonant frequency by sweeping frequency. To match the resonant frequency and impedance, four compensation topologies are compared and the Series-Series (SS) topology is discovered as the most suitable option. The compensated capacitance values are determined by visualized solution from the contour line method. Both simulation (from MATLAB-SIMULINK) and experimental results validate that with compensation elements, the resonant frequency and impedance can be matched precisely between the RUH and ultrasonic transducer and the output voltage and current are with better dynamic performance. Moreover, with the same input voltage, the received power of ultrasonic transducer with compensation capacitors is 7.4 times than the one without compensation. Results verify that the compensation optimization of contactless rotary transformer can improve the vibration amplitude in RUM.