Design and experimental research of a frequency-tracking and amplitude-stabilizing power supply system for robotic ultrasonic machining

Aiming at the problems of resonant frequency drift and amplitude instability caused by dynamic load fluctuations during robotic ultrasonic machining, a frequency tracking and amplitude stabilization power supply system based on STM32 was designed and developed in this work. A compound frequency tracking strategy integrating "variable-step maximum current method for coarse tracking and phase difference method for fine locking" was proposed, and amplitude stabilization was achieved through current feedback. In terms of hardware, the system was constructed with a digital control circuit centered on the STM32F103, a power conversion circuit comprising a front-stage Buck voltage regulator and a rear-stage full-bridge inverter, and high-precision feedback sampling circuits. Experimental results indicated that the frequency tracking error of this system was less than 140 Hz under different static loads, the dynamic response time was less than 15 ms, and the amplitude fluctuation could be suppressed within ±5%. Comparative drilling experiments on Carbon Fiber Reinforced Polymer (CFRP) confirmed that after enabling the amplitude stabilization control, the quality of the hole exit morphology was significantly improved, with a notable reduction in burrs and fiber tear defects, and the cutting force became more stable. This research provides an effective solution for stabilizing ultrasonic energy output in dynamic robotic machining environments and possesses significant engineering application value.