Piezoelectric ultrasonic motors are driven by tangential stresses in the interface between stator and rotor. These stresses are generated by the elliptical motion of the material points of the stator or rotor surface and depend on frictional processes in the contact area. The contact mechanics of piezoelectric ultrasonic motors determines the operational characteristics, like rotational speed and torque or transmitted mechanical power and efficiency. Wear properties and lifetime of piezoelectric ultrasonic motors are also determined by contact mechanics. The goal of the present paper is to summarize the state of the art in the understanding of some fundamental processes governing the contact mechanics of piezoelectric ultrasonic motors. After a short introduction, a survey of publications devoted to the subject will be given. Then, an attempt will be made to classify the mechanical models, which were developed in order to explain the contact mechanics of piezoelectric ultrasonic motors, according to the physical effects which have been taken into account in their derivation. Some results concerning the choice of proper contact materials, wear and lifetime of ultrasonic motors will be addressed in a separate section. Finally a summary and outlook will be given and open questions for future research will be formulated.

https://iopscience.iop.org/article/10.1088/0964-1726/7/3/011/pdf

Contact mechanics of piezoelectric ultrasonic motors

This paper deals with the vibration analysis of a circular plate surface bonded by two piezoelectric layers, based on the Kirchhoff plate model. The form of the electric potential field in the piezoelectric layer is assumed such that the Maxwell static electricity equation is satisfied. The validation of the theoretical model is done by comparing the resonant frequencies of the piezoelectric coupled circular plate obtained by the theoretical model and those obtained by finite-element analysis. The mode shape of the electric potential obtained from free vibration analysis is generally shown to be non-uniform in the radial direction in contrast to what is commonly assumed. The piezoelectric layer is shown to have an effect on the frequencies of the host structure. The proposed model for the analysis of a coupled piezoelectric circular plate provides a means to obtain the distribution of electric potential in the piezoelectric layer. The model provides design reference for piezoelectric material application, such as an ultrasonic motor.

https://iopscience.iop.org/article/10.1088/0964-1726/10/2/308/pdf

Analysis of piezoelectric coupled circular plate

A fuzzy neural network (FNN) position controller is proposed to control the ultrasonic motor (USM) servo drive. The FNN controller is trained online using the proposed delta adaptation law. Moreover, a new driving circuit for the travelling-wave type ultrasonic motor (USM), which is a push-pull DC-DC power converter and a two-phase series-resonant inverter combination, is presented. First, the network structure, the online learning algorithm and the proof of convergence of the learning algorithm of the FNN are described. Next, the operating principles of the proposed driving circuit for the USM are described in detail. Then, the FNN position controller is implemented to control the USM drive to reduce the influence of parameter uncertainties and external disturbances. The effectiveness of the proposed driving circuit and FNN controller is demonstrated by some experimental results.

Fuzzy neural network position controller for ultrasonic motor drive using push-pull DC-DC converter

Standing wave brass-PZT square tubular ultrasonic motor.

In this paper, a nonlinear free vibration analysis of thin annular functionally graded (FG) plate integrated with two uniformly distributed actuator layers made of piezoelectric (PZT4) material on the top and bottom surfaces of the annular FG plate is presented based on Kirchhoff plate theory. The material properties of the FGM core plate are assumed to be graded in the thickness direction according to the power-law distribution in terms of the volume fractions of the constituents and the distribution of electric potential field along the thickness direction of piezoelectric layers is simulated by a sinusoidal function such that the Maxwell static electricity equation is satisfied. The differential equations of motion are solved analytically for various boundary conditions of the plate. The analytical solutions are derived and validated by comparing the obtained resonant frequencies of the piezoelectric coupled FG annular plate with those of an isotropic core plate. In numerical study, the emphasis is placed on investigating the effect of varying the gradient index of FG plate on free vibration characteristics of the structure. In addition, good agreement between the results of this paper and those of finite element (FE) analyses validated the present approach. The analytical solutions and findings contribute towards a simplified model for the parametric study and understanding of vibration of piezoelectric-coupled FGM annular plate.

http://admt.iaumajlesi.ac.ir/article_534749_9f2cb2137580747e125c2380934f3bb1.pdf

An Analytical Model for Free Vibration Analysis of Smart Annular FGM Plates Integrated with Piezoelectric Layers

A piezoelectric rotary ultrasonic motor is modeled for the purpose of predicting, a priori, motor performance as a function of design parameters. The Rayleigh-Ritz assumed mode energy method is used to model the distributed piezoceramics and the traveling wave dynamics of the stator. Natural frequencies and modeshapes are obtained for a generally configured motor. Nonlinear normal and tangential interface forces between the rotor and stator are incorporated into the forcing function along with the linear piezoelectric forcing. Given the applied torque, applied axial loading, and piezo drive voltages as inputs to the model, general motor performance measures are obtained-namely speed, input power, output power, and efficiency. The approach presented here provides a general framework for modeling these motors as well as a design tool for optimizing prototypes with the added flexibility of allowing for a wide variety of geometries and materials. >

Modeling of a piezoelectric rotary ultrasonic motor

A piezoelectric rotary ultrasonic motor is modeled for the purpose of predicting, a priori, motor performance as a function of design parameters. The Rayleigh-Ritz assumed mode energy method is used to model the distributed piezoceramics and the traveling-wave dynamics of the stator. Natural frequencies and dynamic modeshapes are obtained for a generally configured motor. Nonlinear normal and tangential interface forces between the rotor and stator are incorporated into the forcing function along with the linear piezoelectric forcing. Given the applied torque, applied axial loading, and piezo drive voltages as inputs to the model, general motor performance measures are obtained--namely speed, input power, output power, and efficiency. The approach presented here provides a general framework for modeling these motors as well as a design tool for optimizing prototypes with the added flexibility of allowing for a wide variety of geometries and materials.

Andrew J. McFarland

Papers

Modeling of a piezoelectric rotary ultrasonic motor

Modeling of a piezoelectric rotary ultrasonic motor

Modeling, design, development, and testing of a piezoelectric traveling wave rotary ultrasonic motor for space applications