Miniature Ultrasonic Motor Using Shear Mode of Potassium Sodium Niobate-Based Lead-Free Piezoelectric Ceramics

A miniature piezoelectric ultrasonic motor (USM) using the shear mode of (K,Na)NbO 3 (KNN)-based lead-free piezoelectric ceramics was developed. The motor can be driven in the shearing and bending vibration modes. By using the finite-element method, the motor vibration modes and driving mechanism were modeled. Both the "soft-type" (high- d USM) and "hard-type" (high- Q m USM) KNN-based lead-free piezoelectric ceramics were employed to clarify the characteristics of USMs. The experimental results reveal that the high- d USM widens the band of operational frequency in both vibration modes. In the shearing vibration mode, the high- d USM showed a revolution speed of 416 rpm, a torque of 41.5 µN m, and an efficiency of 0.6%, whereas the high- Q m USM showed the same characteristics of 313 rpm, 19.6 µN m and 1.6%, respectively. In the bending vibration mode, the characteristics of the high- Q m USM were 376 rpm, 51.4 µN m and 0.4%; however, the characters of the high- d USM deteriorated owing to the shift in resonance frequency caused by heat generation.