Life prediction model of friction material for traveling wave ultrasonic motor

Traveling wave ultrasonic motor (TWUSM) relies on friction force for torque transmission. Wear often exists on friction material (FM) inevitably, and largely affects life of TWUSM. A new life prediction model of FM for TWUSM was proposed. Compared with standing wave USM, wear of TWUSM FM was resulted from scratching of traveling wave crests on stator. Considering motion of a particle in contact interface between stator and rotor, visco-elastic polymer contact model was used to calculate normal pressure distribution and relative sliding speed, which were introduced to traditional wear law of Archard. In the model, special relation between time and distance for traveling wave was used to analyze contact intervals. The change of thickness of FM during service which made decrease of preload was also taken into account. Parameters of common disc-type TWUSM were used to compute life prediction curve, and meanwhile the experimental investigation was carried out. The life prediction result found out to be consistent with the test.