Ring-shaped traveling wave ultrasonic motor for high-output power density with suspension stator

A ring-shaped traveling wave ultrasonic motor with a suspension stator is proposed for improving output power density. Piezoelectric stacks working in d₃₃ mode are involved in the stator, whereas piezoelectric plates employed in classic ring-shaped traveling wave motors often work in d₃₁ mode. Spring-mass systems are used to suspend the stator from the base that supports the motor and provide preload force. The volume of piezoelectric material and the power density of the motor can be easily increased through the suspension structure. Large vibration amplitude of the stator can be generated on the coupling surface. Simulink analysis and finite element analysis are conducted to verify the theory and determine the optimum parameters of the suspension stator with four piezoelectric stacks. The maximum free vibration amplitude of 4.25 µm of the stator is observed, which is nearly 4.7 times of that without suspension. The prototype can work at a maximum no-load speed of 62 rpm and produce a stall torque of 49.5 mN m under a driving signal of 30 V_pp when the mass block is 0.30 g. Furthermore, the higher output power can be expected because more extra stacks can be added in this suspension structure.