Enhancement of torque density and power density of polymer-based ultrasonic motors via flexible usage of anisotropy in elastic property

Abstract

The carbon-fiber-reinforced poly phenylene sulfide (PPS/CF), which exhibits low density, low energy dissipation, and relatively high elastic modulus among polymers, is a promising material as the vibrating body of lightweight ultrasonic motors (USMs). Interestingly, the flexible usage of the anisotropy in PPS/CF’s elastic property (induced by carbon fibers’ reinforcement) offers a new idea to enhance the torque densities and power densities of the polymer-based USMs. As the key issue of flexibly using the anisotropy, this study aims to accomplish the optimal arrangement of the carbon-fibers’ filling direction according to the structure, the vibration mode, and the piezoelectric material’s polarization direction of the PPS/CF-based motor by performing model construction, structural optimization, and experimental verification. Initially, the dynamic model capable of setting PPS/CF’s anisotropically elastic moduli with the changeable filling direction is established to analyze the vibration characteristics. Subsequently, to increase the vibration velocity, the stiffness, and the electromechanical coupling factors, the optimization is carried out for the PPS/CF-based ring-shaped vibrators, where the optimal angle between the filling direction and the vibrator’s bottom surface is estimated as 60°. Finally, a prototype of the PPS/CF-based vibrator 30 mm in diameter and 8.5 mm in height is fabricated to form a rotary motor, whose movement and load characteristics are investigated through experiments. At 250 V voltage and 24.42 kHz frequency, the motor yields the no-load rotation speed, the maximal torque, and the maximal output power of 99.3 r/min, 29.8 mNm, and 72 mW, respectively. Moreover, its torque density and power density reach respectively 7.1 Nm/kg and 17.1 W/kg, relatively high among the rotary motors with polymer vibrating bodies. This study validates the effectiveness of our idea and also provides a basic approach to design lightweight USMs that employ newly-developed materials with anisotropically elastic properties and good vibration characteristics.