JPS63173378A - Polalization of ultrasonic motor element - Google Patents

Abstract

PURPOSE:To prevent the generation of spark discharge and fine cracks, by applying alternately a half-wave rectification voltage rectified via a rectifier to series-connected positive and negative polarization electrodes, in the case where a voltage is applied to the positive direction and the negative direction of a polarizion power source using an alternating current. CONSTITUTION:One side of the ring of a piezoelectric ceramics 1 is a common electrode 4, and the other side is composed of an electrode groups 2 and 3 polarized by a positive and a negative voltages. Each electrode is radially arranged around a ring center and separated with constant angle intervals. Neighbouring electrodes are so constituted that each of them has a polarization of different direction from each other. As to a power source for polarization, the half-wave rectification voltage of an alternating current 8 by, for example, rectifier diodes 91 and 92 is used, and the voltage is alternately applied to the electrode groups 2 and G of positive and negative directions. Thereby, potential difference between the electrodes is maximized under the same condition as the case where the voltage is applied only in one direction, and the polarization can be simultaneously progressed in both directions. Therefore, the equiblium of polarization in the positive and the negative directions is sufficiently maintained, and a high reliable element for a motor wherein spark discharge and cracks do not generate between the electrodes can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of polarizing a piezoelectric ceramic plate for an ultrasonic motor, which efficiently converts the vibrational energy of an ultrasonic vibrator into rotational energy and is used as a drive source for an apparatus.

There are various ideas for ultrasonic motors, but the one related to the present invention is called a surface wave type, in which a thin plate ring of piezoelectric ceramics is bonded to one side of a metal ring, electrodes are formed on the piezoelectric ceramic ring, and the voltage is applied. A rotating motion is obtained using a traveling wave generated on the surface of a metal ring by a combination of signals.

The piezoelectric ceramic ring used here generally consists of two groups of electrodes, one with a common electrode on one side and one with positive and negative voltages polarized on the other side.Each electrode group is separated from the other at a constant angular interval radially from the center of the ring. The polarization directions between adjacent electrodes are different from each other.

Conventionally, the polarization direction of this type of element has been determined by raising the piezoelectric ceramic element to a temperature of 100°C or higher in oil, applying a predetermined voltage in one direction to perform polarization treatment, and then polarizing the piezoelectric ceramic element in the opposite direction in the remaining direction. A method has been used in which polarization is performed in two directions by applying voltage.

In this method of polarization processing, after complete polarization in one direction, the polarization of the electrode polarized in the previous step is attenuated due to the influence of the temperature that rises during polarization in the process of applying voltage in the other direction. However, there was a drawback that the positive and negative electrodes caused an imbalance in the polarization level, which significantly deteriorated the performance of the motor.

A further improved example is a method in which polarization is performed by simultaneously applying both positive and negative voltages extracted from two power supplies or one power supply using a resistance element to each electrode surface. In this case, there is no need to worry about polarization imbalance as in the method described above, and this is the method that is currently commonly used. As a result, a potential difference twice the applied voltage occurs between the electrodes, and spark discharge is likely to occur during polarization through dirt, foreign matter, etc. on the electrode separation line, and also at the boundary of the electrodes of the ceramic ring. It has the disadvantage of generating fine racks. If cracks occur, the reliability of the motor will be significantly impaired, especially when the thickness of the thin electrode is thin.

In order to eliminate these drawbacks, the present invention uses an alternating current half-wave rectified voltage as a polarization power source to provide electrode groups in two directions, positive and negative.
By applying voltage alternately, the potential difference between the electrodes is at most the same as when applied in only one direction, and polarization can proceed in both directions simultaneously, so polarization in both positive and negative directions is sufficiently balanced. It is an object of the present invention to provide a highly reliable motor element that does not cause spark discharge or cracks between electrodes.

In the polarization process of an ultrasonic motor element, the present invention is configured to apply voltage alternately in both directions using an alternating current half-wave rectified voltage to the polarization power supply. It is characterized by good balance, no spark discharge between electrodes during polarization, and a highly reliable device.

Figure 1 shows a conventional circuit configuration when applying positive and negative DC voltages simultaneously. Polarization is performed by setting the common electrode to zero potential using one DC power supply and the potential difference due to the voltage drop in the resistor circuit, and applying either positive or negative DC voltage to the positive and negative electrode groups. , is a circuit configuration in which the AC half-wave rectified voltage of the present invention is applied alternately to positive and negative electrodes. 1
Polarization is performed by applying a sinusoidal half-wave voltage rectified using two variable voltage AC power supplies and two rectifiers to the positive and negative electrodes, respectively.

Figure 3 shows the shape and electrode pattern of the piezoelectric ceramic element for an ultrasonic motor used in this experiment. The annual cost is a three-component system whose main components are lead zirconate and lead titanate, and its basic material constants are shown in Table 1.

Table 1 Basic Constants of Ceramic Element Materials As a method of applying an AC half-wave voltage to an element, a jig with pins arranged in a shape that matches the electrode pattern of the ceramic element is used, and a constant load is applied to the bottle and the electrode surface maintain contact with. The ceramic plate to be polarized was placed in a temperature-adjustable silicone oil bath.

Next, examples according to the present invention will be shown. Regarding polarization conditions,
The tests were carried out using the conventional DC voltage method shown in Figure 1 and the half-wave rectified voltage method according to the present invention shown in Figure 2.

a. DC voltage method sample temperature 150±5℃ Applied voltage ±2. OKV (reading of Vl, V2) Application time: 30 minutes, half-wave rectification method Sample temperature: 150±5℃ Applied voltage: IKV, 1.5KV, 2.0KV (effective value of output terminal of AC power supply) Application time: 30 minutes The completed device was left at room temperature for 24 hours or more after the polarization treatment, and then evaluated as follows.

・Using a polarization direction hot air dryer and a galvanometer, we observed and confirmed the polarity of the voltage generated on the electrode surface at the moment the hot air hit it.

・Degree of polarization Separate each electrode part of the ring. ・Regarding each as one thickness oscillator, measure the resonant frequency and anti-resonance frequency using the constant voltage method, and calculate the electromechanical coupling coefficient in the thickness moat using the following formula. I asked for it.

The above experimental results are shown in Table 2.

As is clear from the experimental results in the margins below, when AC voltage is directly half-wave rectified and polarized, the effective value of the output terminal of the power supply is 1.5.
It has been shown that if the voltage is KV or higher, polarization can be achieved at the same level as in the conventional DC voltage application method. In addition, the IKV, 1.5KV, and 2KV in polarization by AC half-wave rectification of the present invention
Under these voltage conditions, no spark discharge between the electrodes was observed, proving the effectiveness of the present invention.

[Brief explanation of the drawing]

Figure 1. How to polarize piezoelectric ceramic plates for ultrasonic motors using the DC voltage method. Figure 2. Method for polarizing piezoelectric ceramic plates for ultrasonic motors using the AC half-wave rectified voltage method. Figure 3. Piezoelectric ceramic plate for ultrasonic motor. DESCRIPTION OF SYMBOLS 1... Piezoelectric ceramic plate (ring shape), 2... Positive electrode, 3... Negative electrode, 4... Common electrode, 5... DC power supply, 61.62.63... Resistor, 71.72...
- DC voltmeter, 8... AC power supply, 91.92... Semiconductor guide for rectification, 10... AC voltmeter, 21.
22... Positive electrode, 31.32... Negative electrode. Patent applicant: Tohoku Metal Industry Co., Ltd. Figure-1 Figure-2 =10- Figure-3

Claims (1)

[Claims] In the polarization process for manufacturing ultrasonic motor elements, in which electrodes are applied to both sides of a ring-shaped ceramic plate, the electrodes are divided radially, and the polarization direction is alternated for each section, alternating current is used as the polarization power source to differentiate the positive and negative voltage directions. A method for polarizing an ultrasonic motor element, characterized in that a half-wave rectified voltage rectified through a rectifier is applied alternately in series to positive and negative polarized electrodes as a voltage applied in the voltage direction.