Piezoelectric Ultrasonic Traveling Wave Motor

This paper presents several main steps to design and prototype a traveling wave (TW) piezoelectric ultrasound motor (PZUM) for outer space applications. The TW-PZUM stator is a radially polarized PZ cylinder, divided into eight angular sectors, which are powered with a pulse width modulated (PWM) power stage that delivers two harmonic, opposite phased voltages. As will be shown, this powering scheme provides for a flexural traveling wave within the stator, which is transmitted through friction contact to the rotor. As result, the rotor is entrained into motion. In this study we present numerical simulations results used in the design phase to analyze the stator dynamics, which are used then in sizing the power source. Because a resonant mode of vibration is requested for the stator TW torque to reach large amplitude, a modal analysis was performed to find the structural eigenfrequencies of the stator. This information is then used to tune the PWM power stage working frequency with the aim to produce higher rotational speeds, as the stator TW amplitude is proportional to the rotor speed. Then, we provide an overview of the control and power electronics that were developed to power and control the PZUM.