Abstract: Ultrasonic motor is a new type of motor driven by friction force between the contact interface of rotor and stator. Friction material is an important part of contact interface. Its design and wear control are key problems for ultrasonic motor. A simplified model of ultrasonic motor is established. Effect of wear of friction material on contact parameters and driving friction force is studied. The properties that worn friction material should have are obtained by keeping stable contact width between rotor and stator. Design principle and theoretical structure model of gradient friction material for ultrasonic motor are proposed. The simulation analysis shows that normal elastic modulus of friction material pasted on rotor should gradually decline from the extenior to the interior. This type of friction material can maintain the output properties and increase performance lifetime of ultrasonic motor. And a new field is opened up for choosing and reasearching friction material for ultrasonic motor.

Key words: Contact interface, Friction material, Gradient, Ultrasonic motor, Wear, Content Architecture, Discrete Manufacturing Systems, Energy Efficiency, State of the Art, Manufacturing Systems