Design of 2-DOF pyramid type ultrasonic motor

The design of an ultrasonic motor having 2-DOF is presented. The drive unit consists of four piezoelectric actuators arranged in a pyramid shape. Circular vibration at the apex generates a thrust when a rotor is pressed against the apex. The direction of the thrust within the tangent plane of the rotor is controlled by the displacement and phase differences among the four piezoelectric actuators. The theoretical analysis and design method of this actuator unit is presented. This actuator can rotate a spherical rotor. The orientation of the spherical rotor, which has three degree of freedom, is controlled by solving nonholonomic kinematics equations between the rotor and the drive unit. The solution is given in detail. The experimental results demonstrate that the direction and speed of the rotation of the spherical rotor are controllable