Power Transfer Performance and Cutting Force Effects of Contactless Energy Transfer System for Rotary Ultrasonic Grinding

In rotary ultrasonic grinding (RUG), a rotating transformer can be used to replace the established slip ring technology and provide a contactless power supply to the revolving transducer. Such contactless energy transfer (CET) is safe, and high rotation speeds are possible. Compared with a closely coupled transformer, the transfer efficiency of the rotating transformer is lower. Compensation of the windings is necessary to improve efficiency. In addition, the cutting force in RUG is not constant; this will influence the power transfer performance, which in turn affects the vibration amplitude of the tool. In this paper, by considering the distinct capacitive and mechanical behavior of the transducer and the equivalent series resistances (ESRs) of the compensation elements, mathematical models are developed to identify the transfer efficiency and the output power of the rotating transformer. A general mathematical compensation model is developed for maximum transfer efficiency. The effects of the cutting force on the transfer efficiency, the output power, and the power factor are also researched. The experimental results basically agree with the calculated results. A CET system that can produce high efficiency, a high power factor and adaptive output power that adapts to the variations of cutting force in the RUG is therefore possible.