AbstractAs a new type of motor, the traveling wave type rotary ultrasonic motors (TRUM) have a wide range of applications. However, the friction between stator and rotor leads to its poor start reliability, which retards the progress of application of ultrasonic motors. Sometimes TRUMs which are widely used cannot start after storage. Height of tooth of the ultrasonic motor’s stator is one of the factors affecting TRUM’s start stabilizing. In this paper, combined with the ultrasonic motor running mechanism, the factors that affect TRUM’s start reliability are studied. Model of ultrasonic motor stator tooth height is analyzed by finite element analysis (FEA). Five TRUMs with different tooth heights are fabricated and measured. A TRUM with 1.85 mm tooth height can start properly in humidity 90%, but ultrasonic motors with 1.8–1.9 mm tooth height cannot start properly under the same conditions.
