Performances of resonant frequency tracking methods and compensation strategies for rotary ultrasonic machining device with contactless energy transfer

•Series-Series compensation topology has stable impedance features under loading.•Mechanical loads affect the selection of resonant frequency tracking method.•Series-Series topology using the phase-locked method is recommended. As the core component of rotary ultrasonic machining (RUM) device, the ultrasonic transducer is subjected to mechanical loads during processing, leading to variations in its equivalent electrical parameters. For RUM device with contactless energy transfer (CET) system, this phenomenon can cause the mismatch between the compensation parameters and the transient electrical parameters of the transducer, which will further degrade the resonant frequency tracking (RFT) accuracy and the output performance. In this study, bilateral compensation parameters and coil turns of the CET were first calculated for no-load RUM device to gain optimal transfer efficiency and achieve tuning matching and impedance matching. After that, the drift of the transducer electrical parameters under load conditions was quantified by loading experiments. Based on electrical model, the influences of mechanical loads on the impedance characteristics of RUM equipment were revealed. For the four compensation topologies, different RFT methods were employed according to the above analysis. Finally, theoretical analyses and verification experiments were conducted to investigate the performances of various driving configurations for the transducer considering the load effects. The results demonstrate that inappropriate selection of RFT method and compensation strategy can introduce considerable error between the tracking frequency and the resonant frequency of the transducer, causing poor output performance of RUM device. The Series-Series (SS) topology combined with the phase-locked method can gain stable transfer efficiency and high power factor with excellent RFT accuracy. Furthermore, this configuration has load adaptive capability, meaning that the power obtained by the transducer increases as the load increases, which is beneficial to suppress the output amplitude decay during machining. The conclusions presented in this research can provide references for the design of RUM device.