A Traveling Wave Ultrasonic Motor For High Power Density With Suspension Stator

Traveling wave ultrasonic motors are based on the concept of driving the rotor by a mechanical vibration excited on the stator via the piezoelectric effect.The rotor produces motion of rotation or straight line through friction coupling between the stator and the rotor,so as to output power to drive the load.They exhibit merits such as compact structure,high torque with low speed,low noise,self-locking when the power is off,and high position accuracy.The motors are widely used in aerospace,biomedical engineering,robots,business,and other fields.This dissertation focus on optimizing the structure of the stator to increase the output power of the motor.Several kinds of stator structures of traveling wave motors were analyzed,including the classic bonded-type stator,the sandwiched-type stators excited by Langevin-type longitudinal vibration transducers and the sandwiched-type stators excited by piezoelectric stacks.The advantages and disadvantages of the stators were summarized by analyzing the vibration characteristics of the stators and the working modes of the piezoelectric materials.A kind of suspension structure of the stator excited by piezoelectric stacks was proposed to improve its output power.The structure includes springs,which are used to isolate the vibrator from the base that supports the motor,and mass blocks,which are used to provide active force for the vibrator.The vibrator is excited by piezoelectric stacks and its vibration amplitude is not limited by the vibration amplitude of the piezoelectric stacks.The piezoelectric stacks work in the d33 mode with a larger electromechanical coupling coefficient compared with the d31 mode.Moreover,the volume of the excitation material and the power density of the motor of the suspension structure are increased.The key parts of the structure were designed with the help of COMSOL finite element simulation analysis.The whole structure of the motor was designed meanwhile.The mechanical model of the suspension stator was modeled and simulated with Simulink.The effect of structural parameters on the vibration amplitude of the stator was analyzed quantitatively.The vibration process of the stator was analyzed as well.The vibration modes of the stator were simulated by COMSOL finite element simulation analysis and were selected according to some proposed principles.The vibration response of the stator was simulated and analyzed.The resonant frequency,the vibration modes and the vibration amplitude of the stator were measured,and the results were compared with the simulation results.The no-load speed and the stall torque of the motor were tested.The output performance of the motor was compared with that of the traveling wave ultrasonic motor used in Nikon AFS50-1.4g camera lens.The experimental results show that the suspension vibrator with four piezoelectric stacks with dimensions of 1.68× 1.68 ×5.0 mm3 has a maximum free peak to peak vibration amplitude of 4.25 ?m with an excitation voltage of 30 Vpp,which is nearly 4.7 times that without suspension.The prototype motor can work with a maximum no-load speed of 62 rpm and produce a stall torque of 49.5 mN·m with an excitation voltage of 30 Vpp when the mass block is 0.30 g.Higher output power can be expected because additional piezoelectric stacks can be used in this suspension structure.