Structural parameter study on polymer-based ultrasonic motor

Abstract

Our previous study has shown that traveling-wave rotary ultrasonic motors using polymer-based vibrators can work in the same way as conventional motors with metal-based vibrators. It is feasible to enhance the performance, particularly output torques, of polymer-based motors by adjusting several key dimensions of their vibrators. In this study, poly phenylene sulfide, a functional polymer exhibiting low attenuation at ultrasonic frequency, is selected as the vibrating body, which is activated with a piezoelectric ceramic element bonded on its back surface. The optimal thicknesses of the polymer-based motors are higher than those of metal-based motors. When the same voltages were applied, the maximum torques and output powers available with the polymer-based motors were lower than the values of the metal-based motors with the same structures. The reasons for the lower torque were explained on the basis of vibration modes. First, the force factors of the polymer-based vibrators are lower than those of metal-based vibrators owing to the great difference in the mechanical constants between polymers and piezoelectric ceramics. Subsequently, though the force factors of polymer-based vibrators can be slightly enhanced by increasing their thicknesses, the unavoidable radial vibrations become higher and cause undesirable friction loss, which reduces the output torques. Though the polymer-based motors have rotation speeds comparable to those of metal-based motors, their output power are lower due to the low electromechanical coupling factors of the polymer-based vibrators.

A Traveling-Wave Linear Ultrasonic Motor Driven by Two Torsional Vibrations: Design, Fabrication, and Performance Evaluation

“…The output power and efficiency corresponding to 360 N were higher than those to 240 and 480 N probably because the frictional loss was smaller [40,41]. Most TW motors cannot provide high efficiencies as the vibration velocities differ among the driving feet [21,31,35]. In contrast, only one wave crest exists on each vibrating body; this may suppress vibrationvelocity-difference-induced frictional loss and consequently enhance the efficiency.…”

“…To obtain high thrust force density and high power density, we investigate how the keff/m ratio changes with varying dimension (where keff and m are respectively the effective electromechanical coupling factor and the stator's weight). Here, we focus on keff as it markedly affects USMs' mechanical outputs [2,31,32]. Besides, the resonance frequency f should be in the inaudible range (>20 kHz) to avoid the existence of noise.…”

“…(4) Calculate keff through finite element analysis, of which the detailed procedures are given in refs. [4] and [31]. In the meantime, m is derived by accumulating each part's weight.…”

A Novel Self-Moving Framed Piezoelectric Actuator

“…Sci. 2020, 10, 6682 2 of 12 type piezoelectric actuators utilize single vibration mode or coupling of multi vibration modes to generate micro amplitude elliptical motion of their driving foot, and then the macro motion can be achieved due to the friction coupling effect [16,17]. This accumulation of micro-movement enabled resonant piezoelectric actuators to function with higher output velocity and more considerable movement travel.…”

Velocity Control of Traveling-Wave Ultrasonic Motors Based on Stator Vibration Amplitude

“…A TWUSM is driven by the two-phase sinusoidal waves, which excite elliptical motion on the stator [6,7]. Generally, the velocity of TWUSMs is controlled by the voltage amplitude [8], the driving frequency [9,10,11,12,13], or the phase difference between the two-phase sinusoidal waves [14].…”