Manabu Aoyagi

Ultrasonic Motors Using Longitudinal and Bending Multimode Vibrators with Mode Coupling by Externally Additional Asymmetry or Internal Nonlinearity

The present paper deals with some ultrasonic motors using longitudinal and bending multimode vibrators with their mode couplings caused by externally additional asymmetry or internal nonlinearity. A rectangular plate vibrator with two corners on one diagonal line cut to make its resonance modes couple with each other was used, along with a rectangular plate vibrator under the condition that two resonance frequencies are obtained, for example, as fL/fB=2.0, because internal nonlinear coupling of parametric vibration between two resonance modes is generated under this condition. Using these vibrators with mode couplings, it was found that some ultrasonic motors of simple form can be constructed. The ultrasonic motor using the phenomenon of mode-coupling vibrations dealt with here is not completely new, and a few trial constructions have already been reported [Jpn. J. Appl. Phys. 24 (1985) Suppl. 24-2, p. 739]. However, their motions were not reversible in ordinary driving with an electrical signal of a constant frequency. In contrast, the motors that the authors proposed in this paper can be expected to have a reversible motion.

High power characteristics at antiresonance frequency of piezoelectric transducers

First in this paper, the loss in piezoelectric ceramics is described. Antiresonance is the vibration under constant D (electric displacement) driving, and therefore electro-mechanical loss becomes almost zero: resonance is the vibration under constant E (electric field) driving, and then there exists large electro-mechanical loss. The relations between antiresonance and the constant D driving are explained. Next, a method of measuring the high-power characteristics is described for antiresonance frequency. Experimental results for the quality factor and temperature rise and other equivalent constants are then shown as high-power characteristics obtained at the antiresonance frequency. Finally, some considerations for the stable-state driving of the high-power piezoelectric devices are described.

Some constructions and characteristics of rod-type piezoelectric ultrasonic motors using longitudinal and torsional vibrations

Ultrasonic motors using longitudinal and torsional motions of rod vibrators have previously been proposed. Several motor constructions, whose forms are different from the previous ones, are proposed and their characteristics are experimentally examined in order to develop the ultrasonic motors of this type; that is, they are expected to have much different uses, according to how their forms are modified. Two groups of motor are dealt with: one contains motors basically suited to the relatively high torque of 2-3 kgf-cm and the other contains motors for small or medium torque below about 1.0 kgf-cm. As the result, operational characteristics of motors are totally revealed. These are useful in developing the rod type ultrasonic motors and in their practical applications.<<ETX>>

Dielectric Loss in a Piezoelectric Ceramic Transducer under High-Power Operation; Increase of Dielectric Loss and Its Influence on Transducer Efficiency

Dielectric loss in a piezoelectric ceramic transducer is related to the vibration, and increases markedly under high-power operation. When PZT ceramics is used over the vibration velocity of about 0.25 (m/s), the dielectric loss becomes larger than the mechanical vibration loss. In this paper, the values of the resistances indicating the dielectric loss and mechanical vibration loss in the equivalent circuit are shown. If an equivalent electric circuit including these resistances is utilized, efficiency of the transducers operating at a high-power level may be calculated with more accuracy. By calculation of the efficiency, the maximum efficiency was obtained at the anti-resonance frequency, not at the resonance frequency. These facts cannot be explained by the ordinary equivalent circuit which does not involve dielectric loss related to the vibration.

High-Speed Thin Ultrasonic Spindle Motor and Its Application

In this paper, we report an ultrasonic motor capable of high-velocity revolution applicable for long continuous high operation as a microfan. This study is a response to the new challenge of developing a new field of applications for an ultrasonic motor. Ultrasonic motors using a longitudinal-flexural coupling-vibration mode of a thin plate with a vibrating piece or step-horn are considered. A stator vibrator consists of a metal plate sandwiched by two thin unipoled piezoelectric ceramic plates, the electrodes of which are not divided, and this ultrasonic motor can be driven by a single ac source. Not only the coupling between a longitudinal vibration and flexural one but also the transformation of a longitudinal vibration velocity by a vibrating piece λ/4 long and step-horn λ/2 long are used. They will be effective at making the rotary speed fast. As a result, an ultrasonic motor 0.55 mm thick rotated a shaft 1.5 mm in diameter over 8,000 rpm under conditions of an applied voltage of 30 Vp-p and an input power of only 0.16 W.

Ultrasonic Rotary Motor Using Longitudinal and Bending Multimode Vibrator with Mode Coupling Caused by External Additional Asymmetry

The present paper deals with the ultrasonic rotary motor using a longitudinal and bending multimode vibrator constructed so that the mode coupling is caused by external additional asymmetry. It is well known that on a rectangular piezoelectric plate vibrator with its two corners cut diagonally or a parallelogram-shaped piezoelectric plate vibrator, the first longitudinal and second bending vibration modes are coupled under a certain dimensional condition. The motor mentioned above is to use this phenomenon; that is, a one-channel drive, reversible rotary motor can be achieved. From results of measurement and calculation of such a trial vibrator, it was found that there were two new resonance vibration modes in the neighborhood of degenerate resonance frequencies of original longitudinal and bending vibrations; hence, the directions of rotor revolution were different at both new modes when the mode-coupled vibrator was used to construct an ultrasonic rotary motor. The trial motor has proven that a simple ultrasonic motor could be easily constructed and it was suitable for light-load use because of its small contact area to the rotor.

Examination of disk-type multidegree-of-freedom ultrasonic motor

A multidegree-of-freedom (MDOF) ultrasonic motor using the multimode of a disk vibrator is realized. A spherical rotor can rotate around arbitrary axes. However, at the beginning of research on the MDOF ultrasonic motor, the MDOF ultrasonic motor did not have any mechanisms for supporting a spherical rotor. Since the preload was given by only the rotors own weight, the friction between the rotor and the stator vibrator was very small, but the torque characteristics of the MDOF motor were insufficient for practical use. The purpose of this study is to improve the motor performance further. In this paper, some support and preload mechanisms using a support plate were examined for the improvement of the motor performance. In addition to these methods, a sandwich structure in which two stator vibrators hold a spherical rotor is proposed. This structure has both a rotor support mechanism and a preload mechanism, and high torque by the torque composition of two stator vibrators can be obtained.

Simplified Equivalent Circuit of Ultrasonic Motor and Its Application to Estimation of Motor Characteristics

This present paper deals with a simplified equivalent circuit of an ultrasonic motor and its application to the estimation of motor characteristics. Investigation of this equivalent circuit is conducted from the viewpoint of systematization of research on ultrasonic motors. The equivalent circuit must show the principle of motor operation and must be expressed simply. In this paper, we propose simplified equivalent circuits of two types of ultrasonic motors which have different combinations of vibrations used. As a result, it has been proven that these equivalent circuits are similar to each other in spite of the difference in the vibrations used. In this paper, moreover, measurement points of an ultrasonic motor for estimation of its characteristics are clarified.

Measuring Methods for High–Power Characteristics of Piezoelectric Materials

Two kinds of measuring method of the high-power characteristics of piezoelectric transducers are described. One is the measurement method at the resonance frequency and another is the measurement method at the antiresonance frequency. The vibrational velocity dependences of the equivalent circuit constants and the temperature rise were measured by using each measurement method under the constant vibrational velocity control. These results are useful for designing the ultrasonic power devices such as the ultrasonic motor, and also useful for investigating the new advanced piezoelectric materials for high power use. Especially, by using the results obtained at the antiresonance frequency, a stable state driving method, named as antiresonance driving, with high-efficiency and low-temperature rise can be achieved.

Examination of Sandwich-Type Multidegree-of-Freedom Spherical Ultrasonic Motor

A sandwich-type multidegree-of-freedom (MDOF) spherical ultrasonic motor (SUSM) is newly proposed. The motor consists of a spherical rotor and two stator vibrators holding the rotor. This structure has both a rotor support and a preload mechanism. The stator excites five vibration modes, and the rotor can rotate on three axes. An experiment of a torque composition of two stators was carried out. The contact surface between the rotor and the stators forms a spherical surface. Moreover, a displacement magnification mechanism, which was used in the former model to rotate on the Z-axis, is no longer necessary. Hence the stator is simpler in construction than the former model. In this paper, we describe the construction and the operating principle of the MDOF ultrasonic motor, modal analysis results for the stator, and some measurement results from trial manufacturing. The miniaturization of the motor and increase in torque were successfully realized.