Miniaturized drive and operational stability of ultrasonic micromotors: A study based on self-oscillating technology

Ultrasonic micromotors, characterized by their compact size, high speed, and high accuracy, are promising actuators for minimally invasive surgical tools and other space-constrained precision systems. However, their application is hindered by bulky drive circuits and resonance drift during prolonged operation. To address these challenges, this paper focuses on capacitive micromotors with resonance frequencies exceeding 100 kHz and proposes a novel miniature drive system based on self-oscillating technology. The motor is integrated into the feedback loop, achieving a compact design that unifies signal generation, signal amplification, and real-time dynamic frequency tracking. Furthermore, this study investigates the fundamental mechanism of resonance frequency shift in ultrasonic motors and the frequency tracking principle of self-oscillating circuits. During prolonged operation, the motor experiences power loss, resulting in temperature rise and changes in material properties, which ultimately cause resonance frequency drift. The self-oscillating circuit effectively tracks these frequency variations through a feedback mechanism, maintaining system stability and reliable performance. Experimental results demonstrate that the proposed system achieves effective frequency tracking with a maximum deviation of 0.20 kHz and a maximum relative deviation of 0.15%. The system, with dimensions of $15\text{mm}\times 12\text{mm}\times 0.6\text{mm}$, operates at a 10 V power supply, delivering a 5 V peak-to-peak output with 14 mA current and 24.88 mW power. It achieves a maximum speed of 6300.20 rpm and a holding torque of 14.59 $\mu$N m with a high linearity torque–voltage relationship ($R_T^2=0.9998$). This study significantly advances the development of compact drive systems, enabling ultrasonic micromotors to operate reliably in space-constrained environments.