Novel disk type ultrasonic traveling wave motor for high torque

Today most rotary traveling wave motors either have a ring type or a disk type stator. In the ring type usually a mode shape with 3 to 11 nodal lines but without nodal circle is excited by a piezoceramic ring. This ring is bonded on the opposite side of the contact area at the same radial position as the teeth of the stator. Due to manufacturing reasons the maximum outer diameter of piezoceramic rings is limited. Therefore the possibility to obtain higher output by increasing the radial dimension of the motor is limited when using this kind of design. In the disk type stator usually a vibration mode with few nodal lines and one nodal circle is used. To the best of the authors´ knowledge up to now the contact area was always located inside the nodal circle, resulting in a low torque/high velocity characteristic compared to the ring type motor. For many applications, however, high torque is the most important design goal. The present paper is dedicated to the investigation of stator geometries for motors with high torque. First numerical and experimental results obtained for a ring type and a disk type motor of a novel design will be reported. In the disk type motor the piezoceramic excitation is inside the nodal circle and the friction contact zone is outside the nodal circle so that high output torque can be expected. By using piezoceramic rings of 90 mm outer diameter and a vibration mode with one nodal circle and 11 nodal lines a stator diameter of 112 mm was realized. Furthermore a ring type stator with 98 mm outer diameter was built and used for prototyping a new traveling wave motor. In the paper the design and optimization of the stator geometry and first experimental results will be reported