Patent ID: 7944129

Claim:
An ultrasonic actuator, comprising: a vibrating member having a substantially triangular shape with three vertices; the vibrating member includes: three piezoelectric deformation portions each of which includes each of the vertices and deforms when a voltage is applied thereto; a moving member which is provided so as to be pressure contacted to the three vertices of the vibrating member, the moving member being caused to move relative to the vibrating member by elliptical motions of the three vertices caused by deformations of the piezoelectric deformation portions; and three pairs of A-phase electrodes and B-phase electrodes, each pair of the A-phase electrode and B-phase electrode being disposed on each of the three piezoelectric deformation portions, and either of the A-phase electrodes or the B-phase electrodes being selectively supplied with a driving voltage, wherein the three piezoelectric deformation portions have a same shape; wherein the vibrating member is configured to be driven in an expansion and contraction vibration mode in which the three vertices of the vibrating member radially and reciprocally move in phase due to expansion and contraction deformations of the three piezoelectric deformation portions, and in a bending vibration mode in which each of the three vertices of the vibrating member reciprocally moves in a direction substantially perpendicular to a direction of each of the expansion and contraction deformations; wherein two resonance frequencies of the vibrating member in the expansion and contraction vibration mode and the bending vibration mode are different from each other by a predetermined value; and wherein the expansion and contraction vibration mode and the bending vibration mode are simultaneously resonantly excited at a same frequency when the driving voltage containing an AC component of a frequency between the two resonance frequencies is selectively supplied to either of the A-phase electrodes and the B-phase electrodes, and thereby causing the three vertices of the vibrating member to elliptically vibrate in phase in a same rotational direction.