Windmill-type ultrasonic micromotor fabricated by thermoplastic green machining process

A miniaturized windmill-type piezoelectric ultrasonic motor (USM) was developed using a thermoplastic green machining process. A thermoplastic body, consisting of 60 vol% piezoelectric material and 40 vol% thermoplastic binder, was CNC-machined to create windmill-type blades at the center of a green disk. After the binder burnout and sintering processes, the disk was poled in the thickness direction. By applying an AC field in the thickness direction, the inward blades at the center of the disk converted the radial displacements into tangential ones, causing the shaft at the center to rotate. When the USM stator with dimensions of 5.2 mm (diameter) × 0.6 mm (thickness) was operated in the principal radial vibration mode (260 kHz) at 20 Vp–p, the displacements of the blades in the x- and y-directions were 40 and 20 nm, respectively. The characteristics of the USM, monitored by using a non-contact method with a moment of inertia of 3.6 kg mm2, consisted of a maximum torque of 22 μN m, a maximum speed of 16.4 rad/s, and a maximum efficiency of 12%.