Modeling the optimal compensation capacitance of a giant magnetostrictive ultrasonic transducer with a loosely-coupled contactless power transfer system

The giant magnetostrictive rotary ultrasonic processing system (GMUPS) with a loosely-coupled contactless power transfer (LCCPT) has emerged as a high-performance technique for the processing of hard and brittle materials, owing to its high power density. A capacitive compensation is required to achieve the highest energy efficiency of GMUPS to provide sufficient vibration amplitude when it works in the resonance state. In this study, an accurate model of the optimal compensation capacitance is derived from a new electromechanical equivalent circuit model of the GMUPS with LCCPT, which consists of an equivalent mechanical circuit and an electrical circuit. The phase lag angle between the mechanical and electrical circuits is established, taking into account the non-negligible loss in energy conversion of giant magnetostrictive material at ultrasonic frequency. The change of system impedance characteristics and the effectiveness of the system compensation method under load are analyzed. Both idle vibration experiments and machining tests are conducted to verify the developed model. The results show that the GMUPS with optimal compensation capacitance can achieve the maximum idle vibration amplitude and smallest cutting force. In addition, the effects of magnetic conductive material and driving voltages on the phase lag angle are also evaluated.