Viscoelastic analytical model and design of polymer-based bimodal piezoelectric motor

Polymers have attracted enormous attention due to their characteristics of low density and high energy density for potential applications in low weight piezoelectric motors. However, the viscosity of polymers presents a challenge to match two resonance frequencies of the longitudinal and bending modes of the bimodal piezoelectric motor. In this paper, polyphenylene sulfide (PPS)-based bimodal piezoelectric motor is researched. Concerning the viscoelasticity of PPS, the electromechanical coupling analytical model is established to describe the dynamics of the PPS-based motor by using the Kelvin-Voigt viscoelastic model. Based on the proposed model, the Taguchi method is adopted to match the resonance frequencies of the longitudinal and bending vibration. A PPS-based prototype motor is fabricated with optimized parameters. The frequency response characteristics, displacement response and electromechanical coupling coefficients are computed and compared to the finite element method and experimental results to validate the effectiveness of the model. The comparisons show that the proposed model is valid. The performance test demonstrates that the PPS-based motor can yield the maximal torque of 2 mNm with the stator weight of 5.4 g. Compared with the same volume of phosphor bronze material, 75% of weight reduction can be achieved.