Design and Investigation of a Sandwich-Type Two-Degree-of-Freedom Ultrasonic Motor for Robotic Arms

In this paper, a novel two-degree-of-freedom ultrasonic motor is designed.By employing the principles of longitudinal-bending and bending-bending composite vibrations, the basic structure and dimensions of the ultrasonic motor are determined.A finite element model was established to investigate the effects of various structural parameters on the resonance frequency through simulation analysis.This ultimately enabled the superposition of multiple modes.Elliptical motion trajectories corresponding to different composite motions were acquired via transient analysis.An experimental platform is set up to test the output performance of the prototype.Under the longitudinal-bending composite vibration mode, the optimal working frequency is 40.00 kHz.At an excitation voltage of 150 Vp-p, the velocity reaches 330.56 mm/s, and under an output force of 35 N, the velocity is 40.10 mm/s.Under the bending-bending composite vibration mode, the optimal frequency is 40.60 kHz, with a velocity of 317.06 mm/s, and under an output force of 30 N, the velocity is 66.85 mm/s.A closed-loop control system is established, and based on PID control, taking the bending-bending vibration mode as an example, the maximum error in sin displacement signal tracking is less than 0.1 mm.The ultrasonic motor achieves two-degree-of-freedom motion, characterized by high speed and high precision, providing significant support for the research on ultrasonic motor-driven robotic arms.