Scaling of piezoelectric ultrasonic motors at submillimeter range

The scaling of physical effects is of great interest not only to understand the behavior in microengineering but also to design next-generation micromachines. This study presents the scaling of piezoelectric ultrasonic motors using theoretical and experimental methodologies. The motor performance parameters, such as torque, angular velocity, and efficiency, are modeled to predict how they behave at millimeter to submillimeter scales. Two types of ultrasonic motors are examined as case studies: Typical traveling wave ultrasonic motors using a ring stator and micro ultrasonic motors using a cubic stator. Although the miniaturization of the ring stator is limited because of its complicity, the simple cubic stator design enables miniaturization even up to a side length of 0.5 mm, which is the smallest ultrasonic motor reported to date. Using several prototype micro ultrasonic motors, the scaling of the motor performance parameters predicted by the models are experimentally confirmed. It is shown that the ultrasonic motors are advantageous to other driving-principle-based motors at millimeter to submillimeter range.