Investigation to Dual-Frequency Direct Digital Synthesis and Resonance Frequency Tracking in Power Ultrasonic Generator

We propose a novel dual-frequency direct digital synthesis (DDS) module and dual-frequency resonant frequency tracking (RFT) algorithm which can be applied to the power ultrasonic such as micro hole drilling applications. To attain the M-type vibration trajectory of the drilling tool, the dual frequency, which the first and the third order frequency of the transducer, is excited at the same time, and the vibration amplitude of the transducer is controlled in independent or coupling mode. Due to the resonant frequency of the transducer is shifted during the drilling process, the resonant frequency tracking (RFT) of the first-order frequency is developed. In order to accurately achieve the phase between the voltage and current, we propose a fourth order Butter-worth low pass filter to the zero-crossing circuits to realize RFT of the first-order frequency of the transducer. Moreover, a dual-frequency direct digital synthesis (DDS) which can generate a mixed signal output with independent frequency and vibration amplitude control is proposed. Finally, a 100 Watt prototype of dual-frequency ultrasonic generator is established to verify the proposed dual-frequency DDS and RFT.