Numerical simulation of contact state of ultrasonic motor with gradient friction material

Friction material is one of the most important parts for ultrasonic motor. Due to the special principle of ultrasonic motor, the wear of friction material is inevitable. Output characteristics of ultrasonic motor depend on the contact state between stator and rotor to a great extent. However, the contact state will be changed by wear of friction material, and the properties stability of ultrasonic motor also will be declined. Consequently, attentions of study on friction material with special properties, which can maintain the properties of ultrasonic motor, are attracted. In this paper, a new type of gradient friction material, which normal elastic modulus gradient declined from surface to rotor substrate, was introduced and a simplified contact model of ultrasonic motor was established. The effects of wear of gradient friction material on contact state of ultrasonic motor were studied based on the contact model. Evolution trend of contact state of ultrasonic motor with wear of gradient friction material and homogeneous friction material were compared and analyzed. The results shown that better stability of contact state, stability of output characteristics and longer service life of ultrasonic motor would be obtained by using this type of gradient friction material. Thus, a new field is presented for choosing friction material for ultrasonic motor.