A high-bandwidth frequency tracking method for giant magnetostrictive ultrasonic machining system by valuing dynamic resonance impedance

Rotary ultrasonic machining (RUM) has been regarded as a promising method for processing difficult-to-cut materials due to improved machining efficiency and surface quality. Due to the machining load-induced resonant frequency shift of the RUM system, frequency tracking is a critical function to ensure the RUM system works at a resonance state to output an efficient tool vibration. However, current frequency tracking methods assume that the system's impedance circle is unchanged under load, which is not unsatisfactory, especially for large loads, resulting in a narrow bandwidth of frequency tracking. This study proposes a high-bandwidth resonant frequency tracking method valuing the dynamic resonance impedance characteristics of the giant magnetostrictive RUM system. The resonant frequency of the system is derived from the electrical feedback based on a RUM system's novel electrical model, which assumes a dynamic resonance impedance circle. Control simulation is conducted on the Modelsim software to verify the feasibility of the proposed frequency tracking method preliminarily. Then, an ultrasonic power supply with a new frequency tracking module is built. Loading experiments and machining tests are conducted to evaluate the load response of the RUM system. The results demonstrate that the frequency tracking bandwidth can be improved from 450 Hz to >750 Hz or 200 Hz to >1000 Hz for two different RUM system configurations, verifying the proposed method's efficacy.