JPS63140680A - Drive circuit of ultrasonic motor - Google Patents

Abstract

PURPOSE:To decrease the number of switching elements and to improve the characteristic of a motor, by connecting electric input terminals of a piezoelectric substance to the secondary terminals of a transformer and by turning ON and OFF the DC power source at the frequency of mechanical vibration. CONSTITUTION:An ultrasonic motor drive circuit is constituted by connecting the secondary terminals of transformers 21 and 22 made up in a ratio of number of turns 1:n each to the electric input terminals of piezoelectric substances 2 and 3 sticking to a stator. One terminals of the primary winding of these transformers 21 and 22 are connected respectively to the contacts of two pairs of switching elements 11 & 12 and 13 & 14 operating in opposite phase. These switching element couples are driven and controlled so that the high-frequency voltage with a phase difference of 90 deg. may be applied to the piezoelectric substances 2 and 3. The voltage by a factor of n on the primary side is thereby induced to the secondary side of transformers 21 and 22, which is applied to the piezoelectric substances 2 and 3 with which the ultrasonic motor is driven.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a driving circuit for an ultrasonic motor that generates driving force using a piezoelectric body.

BACKGROUND OF THE INVENTION In recent years, ultrasonic motors that perform rotational or linear motion by exciting ultrasonic vibrations using a piezoelectric material such as a piezoelectric ceramic have attracted attention because of their small size and high torque.

FIG. 4 shows an example of a conventional ultrasonic motor, in which a stator A is constructed by pasting piezoelectric bodies 2 and 3 on one of the disk surfaces of a disk-shaped elastic body 1 and mounting it on a fixing base 4. There is. Reference numeral 5 denotes a lining made of a wear-resistant material, which is bonded to an elastic body 6 to constitute a rotor B. The rotor B is in contact with the projection 1a of the stator A via the lining 5. Further, a shaft 7 provided on the elastic pair 6 is supported by a bearing 8, and is fastened with a nut 9 so that the lining 5 comes into frictional contact with the protrusion 1a. FIG. 5 shows an example of the shape and electrode structure of the piezoelectric bodies 2 and 3 used in the ultrasonic motor of FIG. 4. In the figure, the bending vibration is arranged to have four wavelengths in the circumferential direction.

Adjacent small electrode portions are polarized in opposite directions. The piezoelectric bodies 2 and 3 polarized in this manner are bonded together with a positional phase shift of a quarter wavelength (90'). Incidentally, the surfaces of the piezoelectric bodies 2 and 3 opposite to the surface shown in FIG. 5 are electrodes all over.

In the ultrasonic motor configured as described above, the piezoelectric body 2 has vo-5 in (wt), and the piezoelectric body 3 has vo-cO8 (
wt) whose phases are shifted by π/2, a traveling wave of bending vibration is excited in the stator A, and the circumferential component of the vibration is amplified by the protrusion 1a, and the rotor B is driven. Ru.

Problems to be Solved by the Invention When trying to obtain a motor output of, for example, IW to 10W with such a motor configuration, due to the characteristics of the ultrasonic motor,
A high voltage of about 30 to 50 V is required as voltage (0). Conventionally, a driving method as shown in FIG. 6 has been used. That is, two switching elements 11, 12, 15, 16, 13, 14, 17, and 18, which operate in opposite phases to each other, are added to each of the electrical input terminals of the piezoelectric body 2 (the same applies to the piezoelectric body 3). , Furthermore, these switching element pairs are each connected to a high voltage DC power supply 19, and a voltage of 30V to
Each switching element is switched at a specific frequency while a high voltage of 50V is applied. However, such a driving method has problems in that a high voltage DC power source is required, the piezoelectric bodies 2 and 3 must be electrically insulated from each other, and the number of switching elements is large.

Means for Solving the Problems The present invention solves the above-mentioned drawbacks of the prior art by connecting the electrical input terminal of the piezoelectric body to the secondary terminal of a transformer configured with a turns ratio of 1:n. A switching element is connected to the primary terminal of the transformer, and the DC power source is turned on and off at the frequency of mechanical vibration.In this way, a high-voltage, high-frequency voltage is applied to the piezoelectric body, and the ultrasonic motor is activated. It is intended to be driven.

In this configuration, even if a low-voltage DC power supply (for example, 5VDC or 12VDC) is used, a high voltage (for example, 30 to 50V) can be applied to the piezoelectric body by appropriately selecting the turns ratio of the transformer.
op) high frequency voltage can be applied. In addition, since the secondary side of the transformer can be completely insulated from the primary side, it is possible to configure the ultrasonic motor with the joint surface of the two piezoelectric bodies serving as a common electrode. No need for insulation. This is very advantageous in manufacturing the motor, improving the characteristics of the motor, and making it possible to construct an ultrasonic motor drive circuit with a small number of switching elements.

In addition, since the switching frequency is high (20kHz to 1
00kHz) The shape of the transformer can be made compact.

Embodiments Hereinafter, embodiments of the present invention will be described based on the drawings. FIG. 1 shows an ultrasonic motor drive circuit according to a first embodiment of the present invention. In the figure, 2 and 3 indicate the piezoelectric bodies bonded to the stator of the ultrasonic motor, and the bonded surfaces of the piezoelectric bodies 2 and 3 are electrically conductive and have the same potential. show. Electrical input terminals of these piezoelectric bodies 2 and 3 are connected to secondary terminals of transformers 21 and 22, respectively, configured with a turns ratio of 1:n. One of the primary side terminals of the transformer 21, 22 is connected to a connection point of a pair of switching elements 11, 12, 13, and 14, which operate in opposite phases to each other. The other primary terminals of transformers 21 and 22 are both connected to a common potential level. Switching element pairs 11 and 12, 13 and 14 are connected to DC power supplies 19 and 20.
is connected between the positive and negative terminals of. The DC power supplies 19 and 20 have the same voltage magnitude, and their connection point is connected to a common potential level. A high frequency voltage with a phase difference of 90'' is applied to the piezoelectric bodies 2 and 3, and the switching element pairs 11, 12, 13, and 14 are switched with a phase difference of 90''. Note that the switching elements 11, 12, 13, and 14 are constructed of devices with low switching loss, such as bipolar power transistors or power MO3FETs.

The operation of the ultrasonic motor drive circuit configured as above will be explained.

Since switching element pair 11 and 12 operate in opposite phases to each other, when switching element 11 is on, element 12 is off. At this time, the positive terminal of the DC power supply 19 is connected to the primary side terminal of the transformer 21, and voltage v1 is applied thereto.

Conversely, when switching element 12 is on, element 1
1 is off and is the primary end of the transformer.

The negative terminal of the DC power supply 20 is connected to the terminal, and the same voltage Vl of opposite polarity is applied thereto. In this way, the transformer 21
Since positive and negative voltages are applied alternately to the primary terminal of
Due to the induced voltage action, a voltage is induced on the secondary side of the transformer 21, and if the turns ratio of the transformer is 1:n, a voltage that is 0 times the primary side voltage V+ will be induced. The circuit composed of the switching element pair 13 and 14, the transformer 22, and the piezoelectric body 3 operates in exactly the same manner, and the switching elements 11.
By switching 12, 13, and 14, the ultrasonic motor can be driven.

FIG. 2 shows an ultrasonic motor drive circuit according to another embodiment of the present invention. The difference from the first embodiment is that transformers 23 and 24 with intermediate taps are used as transformers. The primary intermediate tabs of transformers 23 , 24 are connected to the positive terminal of DC power supply 19 .

Switching elements 11, 12, 13 and 14 are connected to the other two terminals on the primary side of the transformer 23, 24, respectively. The secondary side of the transformer 23.2.4 is a piezoelectric body 2 constituting an ultrasonic motor, similar to the first embodiment of the invention.
, 3 are connected to the electrical input terminals. Furthermore, transformer 23.
The turns ratio of 24 is 1:1: as shown in the figure.
It is n.

Switching elements 11 and 12 operate in opposite phases to each other. Similarly, switching elements 13 and 14 also operate in opposite phases. The switching element pairs 11, 12, 13, and 14 are switched with a phase difference of 90 degrees so that a high frequency voltage with a phase difference of 90 inches is applied to the piezoelectric bodies 2 and 3.

The operation of the ultrasonic motor drive circuit configured as above will be explained.

Since the switching element pair 11 and 12 operate in opposite phases to each other, when the switching element 11 is on, the element 12 is off, and at this time, the voltage v1 of the DC power supply 19 is applied to the primary winding 23a of the transformer 23. is applied. Conversely, when the switching element 12 is on, the element 11 is off, and the primary winding gland 23a' of the transformer 23 is
Voltage v1 of DC power supply 19 is applied. -Next winding 23a
.

23a' are wound in the same direction, so by alternately applying the DC voltage v1 to the primary windings 23a and 23a' as described above, the magnitude of the amplitude is nV+ on the secondary side of the transformer 23. AC voltage can be induced. Switching element pair 13 and 14. Transformer 24. The circuit made up of the piezoelectric body 3 operates similarly. And switching element 1
By switching 1.12 and 13.14 at the characteristic frequency of the ultrasonic motor, power can be supplied to the piezoelectric bodies 2 and 3 to drive the ultrasonic motor.

In this way, in this configuration, a high voltage (for example, 30 to 50Vo-p) can be applied to the piezoelectric body by appropriately selecting the turns ratio of the transformer and the low-voltage DC power supply (for example, 5VDC or 12VDC). A high frequency voltage can be applied. In addition, since the secondary side of the transformer can be completely insulated from the primary side, it is possible to configure the joint surface of the two piezoelectric bodies that make up the ultrasonic motor as a common electrode, thereby insulating each of the two piezoelectric bodies. There's no need to. This is very advantageous in terms of motor manufacturing, improving the characteristics of the motor, and configuring a simple ultrasonic motor drive circuit with fewer switching elements (half of the conventional example) and one of them all in common. can. Furthermore, the switching frequency is high (20KHz).
~100 KHz), the shape of the transformer can be made small.

FIG. 3 shows another embodiment of the invention, which is a modification of the second embodiment. Inductances 25, 26 are connected in series with the piezoelectric bodies 2, 3 to the secondary side of the transformer 23, 24, and switching elements 11, 12 . .

Diodes 27, 28, 29° 30 in parallel with 13.14
is connected. Incidentally, the inductance 25°26 weakens the magnetic coupling between the primary and secondary sides of the transformers 23 and 24.
A leakage inductance can be created by incorporating the transformer 23, 24.

The operation of the ultrasonic motor drive circuit configured as described above is almost the same as that of the second embodiment, and only the differences in operation will be explained. The piezoelectric bodies 2 and 3 are electrical to mechanical conversion elements, and since they are made of ceramic, they always have electrical capacitance.

The swing elements 11, 12, 13, and 14 are switched at high speed in order to minimize switching losses. Therefore, the rise and fall of the voltage on the secondary side of the transformers 23 and 24 becomes steep. When such a steep voltage is applied, a large surge current flows through the piezoelectric bodies 2 and 3 to charge the capacitance described above. (This current is a reactive current that does not contribute to the output of the ultrasonic motor.) The inductances 25 and 26 increase the impedance against steep changes as described above, and the piezoelectric body 2,
3, a sinusoidal voltage with a gradual change is applied. When the inductance 25.26 is inserted, there is a delay in the current flowing to the primary side of the transformer 23.24, and it is necessary to create a path for current to flow even after the switching element is turned off, so the diode 27,2
8°29.30 are connected in parallel to switching elements 11, 12, 13°14.

In addition to the effects of the invention, the ultrasonic motor drive circuit using a transformer has the following advantages:
Even with a low-voltage DC power supply, by appropriately selecting the turns ratio of the transformer, high voltage (for example, 30 V) can be applied to the piezoelectric body.
It is possible to apply a frequency radio wave having a frequency of 0-p to 50V 0-p. In addition, since the secondary side of the transformer can be completely insulated from the primary side, it is possible to configure the joint surface of the two piezoelectric bodies that make up the ultrasonic motor as a common electrode, insulating each of the two piezoelectric bodies. There is no need to do so. This is very advantageous in manufacturing the motor, and the characteristics of the motor can be improved, and an ultrasonic motor drive circuit can be configured with a small number of switching elements, which has great practical effects.

[Brief explanation of the drawing]

FIG. 1 is an ultrasonic motor drive circuit diagram of a first embodiment of the present invention, FIG. 2 is an ultrasonic motor drive circuit diagram of a second embodiment of the present invention, and FIG. 3 is a diagram of a third embodiment of the present invention. An ultrasonic motor drive circuit diagram of the embodiment, FIG. 4 is a sectional view showing an example of a conventional ultrasonic motor, and FIG. 5 shows the shape and electrode structure of the piezoelectric body used in the ultrasonic motor of FIG. 4. FIG. 6 is a conventional ultrasonic motor drive circuit diagram. 1...Elastic body, 2,3...Piezoelectric body, 1
1.12゜13.14,15,16.17.18...
...Switching element, 19.20...DC power supply, 21°22.23.24...Transformer, 2
5.26...Inductance, 27,28,2
9.30...Diode. Name of agent: Patent attorney Toshio Nakao and one other person 23.24
--Ikhenheki Fig. 2 25.26 ---1 Ridafurus Fig. 4 Fig. 5 Fig. 6

Claims (4)

[Claims] (1) Electrical input terminal to the piezoelectric body of an ultrasonic motor that has an elastic body and a piezoelectric body that excites the elastic body, and drives a moving body with mechanical vibrations generated by applying a high frequency voltage to the piezoelectric body. is connected to the secondary terminal of a transformer configured with a turns ratio of 1:n, a switching element is connected to the primary terminal of the transformer, and the DC power is input to the transformer at the frequency of the mechanical vibration. an ultrasonic motor drive circuit configured to apply the high frequency voltage to the piezoelectric body by turning on and off the ultrasonic motor drive circuit; (2) One end of the primary side of the transformer is connected to a switching element, the other end is connected to a common terminal, and the positive and negative DC power sources are turned on and off at the frequency of the mechanical vibration, as claimed in claim 1. Ultrasonic motor drive circuit described. (3) The primary side of the transformer is equipped with an intermediate tap, a DC power source is connected to the intermediate tap, a switching element is connected to each of the other two terminals on the primary side of the transformer, and the frequency of the mechanical vibration is The ultrasonic motor drive circuit according to claim 1, which turns on and off the input primary side DC power supply of the transformer. (4) The ultrasonic motor drive according to claim 1, 2, or 3, wherein the magnetic coupling between the primary side and the secondary side of the transformer is weakened, and the transformer has a leakage inductance. circuit.