A way to understand mechanical characteristics of an ultrasonic motor is presented. First, the vibration mode of a stator is calculated using a finite-element method (FEM) code. The path of the elliptic motion of the stator's teeth is obtained. The computed vibration mode at the surface of the stator is compared with that measured by an electrooptical displacement transducer. Next, the contact condition of the rotor/stator is calculated. The displacement and velocity of the rotor/stator, the distortion of the stick/slip area, the rotational speed of the rotor, and the friction loss of the motor are obtained. The calculated rotor displacement and torque-rotational speed curve correspond closely to the experimentally measured ones. The internal loss of the rotor/stator and the loss of the supporting felt are measured. The total loss of these losses and the calculated friction loss agree with the measured total loss. The calculated and the measured efficiency of the motor also agree.

This paper presents a new method to clarify t h e m e c h a n i c a l c h a r a c t e r i s t i c s of an U l t r a s o n i c Motor. We calculate the vibrat'ion mode of a stator by using the Finite Element Method (FEM.MSC/NASTRAN) . The shape of the elliptic motion at the surface point o f p r o j e c t i o n s i s o b t a i n e d . W e a l s o m e a s u r e the vibration mode o f the projection by using electro optical displacement transducers made by Zimmer KG. Next, w e calculate the dynamic contact condition of a stator and a rotor by using the FEM (JNIKE3D). The stick and slip at the contact surface of the stator a n d t h e r o t o r a r e t a k e n i n t o a c c o u n t . T h e d i s p l a c e m e n t a n d t h e v e l o c i t y o f t h e s t a t o r projection and the rotor spring. the distribution of the stick and the slip area, the rotating speed of the rotor, and the friction loss at the contact area a r e a l l obtained when changing torque, pressure. friction factor. vibration amplitude of the stator. and stiffness of t h e rotor spring. The calculated rotor displacement and T-N curve correspond closelyto the experimental ones. Furthermore, we measure internal loss of the stator. loss of the supporting felt. and internal loss of the rotor. The total loss of the motor obtained by adding the above losses and the calculated friction loss agree with the measured t o t a l l o s s . T h e c a l c u l a t e d a n d t h e m e a s u r e d efficiency of the motor are also similar.