An Equivalent Circuit of a Novel Ultrasonic Motor

This paper presents an equivalent circuit of a novel ultrasonic stator and discusses its applications in evaluation of the stator´s frequency characteristics. The equivalent circuit analysis is based on the principle of ultrasonic motor operations and is conducted from the viewpoint of the mechanic vibration of the piezoelectric ceramic disk. When an external electric field is applied on a piezoelectric ceramic disk, two equivalent vibrations will, one in the thickness direction and the other in the radial direction, be observed. However, when the thickness-to-radius ratio is very small, the extensional vibration in the thickness can be ignored. On the other hand, the tangential vibration and coupling vibration are induced due to the non-equal-triangular boundary condition of the stator. The two-dimensional equivalent circuit model for the new disc-type ultrasonic motor is derived based on the above considerations. The rotor is assumed as a rigid body, and its effect will be separately added into the equivalent circuit model. In this paper, the equivalent circuits are admittance-type expression of a piezoelectric stator and focused on the contacted point between the stator and the rotor with the most significant lateral elliptic motion effect