Kazumasa Ohnishi

Wear properties and life prediction of frictional materials for ultrasonic motors

The characteristics and life of an ultrasonic motor are strongly related to the frictional material used on the sliding surface, because the motor is driven by frictional force and its life is limited to that of the frictional material. Hence wear evaluation of the frictional material is necessary for life prediction of the ultrasonic motor. In this experiment, the wear of carbon-fiber-reinforced plastics (CFRP) used as frictional material in ultrasonic motors is evaluated. The specific wear rate is derived from a simple wear test and is applied to estimate the wear of the CFRP used in the ultrasonic motor. The life of the ultrasonic motor, as well as that of frictional material, can be estimated using the equation derived from the experiment.

Presentation of a New Equivalent Circuit of a Piezoelectric Transformer under High-Power Operation

In this paper, the power transmission characteristics of a piezoelectric transformer are considered. As a result, the following has been clarified: the frequency of the maximum step-up voltage ratio coincided with the resonance frequency, and the frequency of maximum efficiency approximately coincided with the intermediate frequency between the resonance and anti-resonance frequencies. However, conventional equivalent circuits cannot represent these phenomena. In this paper, we have proposed an improved equivalent circuit that was useful for presenting the tendency of the experimental results. The specific future of this circuit is that the series and parallel resistances that present high-power operation loss are included. The method used to derive the proposed equivalent circuit is described and some experimental and calculated results are shown.

Characteristics of Ultrasonic Motors Driven in a Vacuum

Ultrasonic motors are driven by the frictional force between a rotor and a stator, and therefore, the contact surfaces are affected by ambient atmosphere. One example of severe driving conditions is a vacuum. First, friction materials, carbon fiber reinforced plastics and carbon metal, which have already been used for ultrasonic motors driven under atmospheric pressure conditions were tried out under two different vacuum pressures. Ceramic materials such as Al2O3, Si3N4 and SiC, have recently been tried out under two different vacuum pressures. The characteristics of motor, friction and wear such as rotor speed, maximum torque, friction coefficient and wear height, were measured and the feasibility of using the ultrasonic motor in vacuum was discussed.

Experimental Investigation of a Piezoelectric Ceramic Transformer Using Radial Vibration of Disks Combined with a Coupling Element

In this paper a new type of piezoelectric ceramic transformer using radial vibration of disks, combined with a coupling element is proposed. The specific merit of this piezoelectric ceramic transformer is that its electrical input impedance is effectively reduced by the radial vibration of disks with a high electromechanical coupling factor. First, the structure of the new piezoelectric ceramic transformer is presented. Next, the experimental results of the input admittance characteristics, gain of step-up voltage and power transmission efficiency of the piezoelectric ceramic transformer which were measured by varying the length of the coupling element are presented. The experimental results proved that the newly proposed piezoelectric ceramic transformer possessed a vibration mode that could realize a low input impedance and power transmission with efficiency of not less than 90% for a high-voltage step-up application.

Piezoelectric Vibratory Gyro-Sensor Using a Trident-Type Tuning Fork Resonator

This paper deals with a piezoelectric vibratory gyro-sensor using a trident-type tuning fork resonator. It is expected that the vibratory gyro-sensor has a high stability as an angular rate sensor. In order to develop such a gyro-sensor, the authors have focused on applying a trident-type tuning fork resonator that is independent of its support condition. In this paper, the vibrational analysis of a trident-type tuning fork resonator and its measured characteristics as an angular rate sensor are described.

Finite-Element Analysis of Trident-Type Tuning Fork Resonator for Vibratory Gyroscope.

We have investigated the possibility of producing a highly stable piezoelectric vibratory gyroscope. In order to achieve such a gyroscope, a trident-type tuning fork resonator was adopted, because it has good inherent vibrational characteristics for its support conditions. However from a practical viewpoint, the tuning fork must be studied with the aim of achieving very high stability, and high performance as an angular rate sensor. Therefore, we investigated the detailed vibrational displacement characteristics using finite-element methods and showed that unnecessary vibration of the tuning fork influenced the sensitivity of the gyroscope. That is, this paper concerns the dimensional conditions of the tuning fork for decreasing vibrational displacements at its base portion. We also report the measured characteristic of the angular rate sensor using such an improved tuning fork.

Experimental Considerations on the Piezoelectric Vibratory Gyrosensor Using a Trident Tuning-Fork Resonator

This paper concerns the piezoelectric vibratory gyrosensor using a trident tuning-fork resonator characterized by high stability. In the first part of this paper, the methods of adjusting the resonance frequencies are discussed. Then the investigations to compensate the imbalance in a trident tuning-fork resonator are shown. Moreover, we constructed an experimental gyrosensor based on these results, using differential detection to eliminate the leakage output signals. A miniature piezoelectric vibratory gyrosensor with superior linearity could be achieved.

Stepped-Cantilever Piezoelectric Actuator Using Anisotropic Composite Material

This paper deals with a vibrational analysis of a stepped-cantilever piezoelectric actuator for the purpose of magnifying its end displacement. The piezoelectric actuator used here is a bimorphic type. As a basic bar of the bimorphic cantilever, we have investigated three kinds of carbon-fiber-reinforced plastic (CFRP) bars. Vibrational analysis has been performed using an electrical circuit analogy of the mechanical vibration system. As a result of simulation and experiment, it was proven that the end displacement could be increased by selecting an appropriate form of stepping.

Characteristics of a Bidirectional Rotary Ultrasonic Motor Using Obliquely Polarized Piezoelectric Transducers

Obliquely polarized piezoelectric ceramic transducers are newly employed to an ultrasonic motor. Since the direction of polarization is neither parallel nor perpendicular to the applied electric field, the longitudinal and the torsional vibrations are excited simultaneously. In addition, the direction of rotation can be switched by changing the driving frequency. Thus, this motor rotates in both clockwise and counterclockwise directions in spite of a single-phase input signal. The principle and the characteristics of the ultrasonic motor are described.

DUMBBELL-SHAPED SMALL-SIZED HYBRID ULTRASONIC MOTOR

A dumbbel-shaped torsional vibrator is studied in the construction of a small hybrid transducer type ultrasonic motor whose stator consists of a Langevin type torsional vibrator and a longitudinal piezoelectric actuator. Two kinds of stators 20 mm in diameter are designed by FEM for this construction. These motors proved to operate successfully as expected and maximum torque of 1kgfcm.