Ultrasonic motors are compact actuators with high precision and high stall torque. They feature a friction-based actuation principle and offer an alternative to standard actuators such as direct current motors. However, their nonlinear dynamics, the presence of load-dependent dead zones and the difficulty to control low speeds often prohibit their use. Those issues can be overcome by proper design of a controller. In this work, a novel model for a rotary traveling wave ultrasonic motor, the USR60 from Shinsei, is presented. The novel discontinuous model takes into account the dependency of the motor's velocity on the frequency of the traveling wave, the phase difference of the underlying standing waves and the load-dependent dead zone width. The model is identified with data obtained from a testbed and may serve as a foundation for the design of a variety of controllers.
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