Design of a novel piezoelectric vibrator driven by asymmetrical electric fields for linear ultrasonic motors

This paper presents an ultrasonic linear motor with a novel piezoelectric vibrator driven by asymmetric electric fields. Two driving methods of the vibrator are investigated by single-phase and multiphase respectively for the generation of an oblique line trajectory or an elliptical trajectory. A finite element analysis tool is employed to design the vibrator which can generate coupled longitudinal-bending resonance modes, for a higher coupling factor and a specified oblique angle to achieve high power density in the application of linear ultrasonic motors. A prototype of the proposed vibrator with a volume of 262.5 mm ³ can produce a sliding velocity of 130 mm/s, a maximum force of 2.75 N, and a power density of 0.34 mW/mm ³ from the single-phase drive; while up to 245 mm/s velocity, 4.8 N sliding force and 1.12 mW/mm ³ power density can be obtained from the multiphase drive. Compared to traditional ultrasonic linear motors, the presented piezoelectric vibrator offers a simple structure, easy fabrication and a high power density design.