Experimental study of contact state between stator and rotor in a traveling wave ultrasonic motor

An electric contact method to measure contact state of stator and rotor in traveling wave type ultrasonic motor(TWUSM) is presented. The effects of preload and exciting voltage (amplitude) of stator on contact state between stator and rotor are studied with this method. By a simulated tester of friction properties of TWUSM, the variations of stalling torque and no-load speed of TWUSM against the preload and the exciting voltage have been measured. The relative contact length that describes the contact characteristic of stator and rotor is proposed. The relation between the properties of TWUSM and the contact state of stator and rotor are presented. Additionally, according to a theoretical contact model of stator and rotor in TWUSM, the contact lengths in given condition are calculated and compared with the experimental results. The result can provide theoretical guidance for design of TWUSM.