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 work was supported in part by the National Natural Science Foundation of China under Grants 61329301,
61374039, 61473163, and 61374127, the Hujiang Foundation of China under Grants C14002 andD15009, the Engineering and Physical Sciences Research Council (EPSRC) of the UK, the Royal Society of the UK, and the Alexander von Humboldt Foundation of Germany.

/pdf/fuzzy-logic-based-control-filtering-and-fault-detection-for-39yg6917y8.pdf

Fuzzy-Logic-Based Control, Filtering, and Fault Detection for Networked Systems: A Survey

Piezoelectric ultrasonic motors are a new type of actuator. They are characterized by high torque at low rotational speed, simple mechanical design and good controllability. They also provide a high holding torque even if no power is applied. Compared to electromagnetic actuators the torque per volume ratio of piezoelectric ultrasonic motors can be higher by an order of magnitude. Recently various types of piezoelectric ultrasonic motors have been developed for industrial applications such as cameralens drive or as actuator in the head restraint of automobile seats. This paper describes several types of piezoelectric ultrasonic motors. In the first part the working principle of the travelling wave motor is explained. In the second part other types of piezoelectric ultrasonic motors are described and classified with respect to the vibration modes and contact mechanisms used in their design. Finally some open problems in piezoelectric ultrasonic motor research are addressed.

Piezoelectric ultrasonic motors

In this study, a recurrent fuzzy neural network (RFNN) controller is proposed to control a piezoelectric ceramic linear ultrasonic motor (LUSM) drive system to track periodic reference trajectories with robust control performance. First, the structure and operating principle of the LUSM are described in detail. Second, because the dynamic characteristics of the LUSM are nonlinear and the precise dynamic model is difficult to obtain, a RFNN is proposed to control the position of the moving table of the LUSM to achieve high precision position control with robustness. The back propagation algorithm is used to train the RFNN on-line. Moreover, to guarantee the convergence of tracking error for periodic commands tracking, analytical methods based on a discrete-type Lyapunov function are proposed to determine the varied learning rates of the RFNN. Then, the RFNN is implemented in a PC-based computer control system, and the LUSM is driven by a unipolar switching full bridge voltage source inverter using LC resonant technique. Finally, the effectiveness of the RFNN-controlled LUSM drive system is demonstrated by some experimental results. Accurate tracking response and superior dynamic performance can be obtained because of the powerful on-line learning capability of the RFNN controller. Furthermore, the RFNN control system is robust with regard to parameter variations and external disturbances.

Recurrent fuzzy neural network control for piezoelectric ceramic linear ultrasonic motor drive

A fuzzy adaptive model following mechanism for the position control of a traveling-wave-type ultrasonic motor (USM) is described in this study. Since the dynamic characteristics of the USM are difficult to obtain and the motor parameters are time varying, fuzzy adaptive control is applied to design the position controller of the USM for high-performance applications. The driving circuit for the USM, which is composed of a high-frequency boost DC-DC chopper, a two-phase series-loaded resonant inverter and an inner speed loop, is built first. Next, the control algorithm for fuzzy adaptive control is discussed. Then, a simple linear position control loop is designed and augmented by the model-following error-driven fuzzy adaptive mechanism to reduce the influence of parameter variations. The effectiveness of the proposed controller is demonstrated by some experimental results.

Fuzzy adaptive model-following position control for ultrasonic motor

The basic driving and control principles and the operating characteristics of a newly-developed ultrasonic motor (USM) are described. The two-phase resonant inverter for driving the USM, which includes a variable-frequency PWM (pulse width modulation) control scheme and a phasor control function between inverters, is discussed. A novel automatic resonant frequency tracking strategy using the PLL (phase-locked loop) technique is presented. It uses both sensor and sensorless interfaces to operate at a certain optimum point. The two-phase high-frequency inverter using parasitic resonant impedances incorporated in the ultrasonic motor, which is represented in terms of an electrical resonant tank circuit model, is proposed as a high-power density switching mode ultrasonic power amplifier. Experimental results obtained with this inverter-drive USM system with frequency timing control are illustrated. >

Load-adaptive frequency tracking control implementation of two-phase resonant inverter for ultrasonic motor

A high-performance servo control scheme using compact ultrasonic motors (USMs) as actuators has not yet been practically realized in modern industry and office automation systems because the dynamic and steady-state modeling of USMs is almost impossible from a theoretical point of view. A high-performance speed/positional servo control scheme based on modern fuzzy reasoning concepts and featuring a traveling wave-type USM with high torque at low speed range is presented. The control method of the USM servo system using inverter frequency and voltage control strategies for the speed and amplitude of the traveling wave on the USM stator and the phase difference control scheme between two-phase high-frequency inverters are demonstrated and evaluated using experimental results. In particular, the control implementation is described from a practical viewpoint. >

New fuzzy reasoning-based high-performance speed/position servo control schemes incorporating ultrasonic motor

This paper presents the latest significant developments of ultrasonic motor (USM)-actuated servo drives suitable for direct-drive motion systems, which effectively introduce the practical fuzzy-reasoning controller with speed and positional state-variable feedback schemes. The USM-actuated servo control system is schematically composed of the commercially-available travelling-wave type USM, mechanical loads, high-frequency DC-DC chopper regulator, two-phase high-frequency resonant inverter using parasitic piezo-electric load resonance parameters, pulse-encoder and its processing interface, and newly-developed fuzzy-reasoning software controller. The experimental breadboard is feasibly implemented and the software of the fuzzy-reasoning controller is designed for the specific USM characteristics and USM-related control loops. The experimental verifications are illustrated and their results are evaluated using a one-axis servo motion drive system from a practical point of view. It is proved that a new compact servo motion drive system using USM which incorporates the microprocessor-based two-input and one-output fuzzy-reasoning controller is cost-effective and more acceptable for certain direct drive applications. >

Y. Izuno

Papers

Load-adaptive frequency tracking control implementation of two-phase resonant inverter for ultrasonic motor

New fuzzy reasoning-based high-performance speed/position servo control schemes incorporating ultrasonic motor

High performance and high precision ultrasonic motor-actuated positioning servo drive system using improved fuzzy-reasoning controller