JPH0480632B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a motor that generates driving force using a piezoelectric material.

Configuration of conventional examples and their problems In recent years, by exciting various ultrasonic vibrations using electro-mechanical transducers such as piezoelectric ceramics,
Piezoelectric motors that obtain rotational or running motion are attracting attention because they have high energy density.

A conventional piezoelectric motor using these ultrasonic vibrations will be described below with reference to the drawings.

FIG. 1 shows an example of a conventional piezoelectric motor published in Nikkei Mechanical 58, 2, 28, etc., in which a piezoelectric element ring 2 is bonded to the surface of an elastic ring 1 and integrated. As shown in FIG. 2, the piezoelectric element ring 2 is polarized by dividing the ring into 17 regions in the circumferential direction at a division ratio of, for example, 22.5 degrees or 11.25 degrees, and attaching electrodes thereto. The directions of polarization are opposite in adjacent regions. Thereafter, the surface of the piezoelectric element is covered with conductive paint and the electrodes are combined into two as shown by diagonal lines. E is a ground terminal. A moving body 4 to which a slider 3 is fixed is located above the elastic ring 1.

The operation of the piezoelectric motor configured as above will be described below. An alternating current signal of V _O sinωt is applied to one electrode C of the piezoelectric element 2, and an AC signal of V _O cosωt is applied to the other electrode D. Then, the divided regions alternately expand and contract in the circumferential direction, and bending vibration occurs in the elastic body 1. Figure 3 is an enlarged depiction of the contact situation between a moving body and an elastic body, which is well known as the elliptical motion of particles accompanied by surface waves (for example, see Nobuo Mikoshiba's "Sonic Properties", published by Sanseidosha in 1972). . Focusing on one point A on the surface of the elastic body, point A draws an elliptical locus with a major axis 2w and a minor axis 2u. At the vertex where the elastic body contacts the moving body, point A waits for a velocity of V = 2πfu in the negative direction of the x-axis. As a result, the moving body is driven at a speed V in the direction opposite to the wave propagation due to the frictional force with the elastic body. In order to draw an elliptical locus as a thrust on the surface of an elastic body in this way, it is possible to use Rayleigh waves of surface acoustic waves or bending vibration of the elastic body. For example, the wavelength of surface acoustic waves is 10 cm.
However, by using the bending vibration of an elastic body, the wavelength can be reduced to several millimeters, so the number of vertices that serve as contact points can be increased to several. The driving principle of Rayleigh waves, which are surface acoustic waves, is realized by propagating waves using bending vibrations in a partial region of an elastic body, and creating an elliptical trajectory on the surface of the elastic body. In this surface wave type piezoelectric motor, the top of the wave, which is the contact point, is always in contact with the moving object, so the speed of the moving object is equal to the top speed. Further, the magnitude of the output torque is determined by the contact area, load weight, and friction coefficient of the contact portion. Further, this piezoelectric motor can easily switch the rotation direction using a phase-shifted power supply based on the same principle as a two-phase or three-phase motor.

However, in the above configuration,
There are the following drawbacks.

(1) Energy is consumed in repeatedly bending an elastic body with a large Young's modulus, which induces heat generation, resulting in extremely poor linearity. In addition, in order to extract thrust from a minute amplitude of approximately 0.25 μm or less, the moving object uniformly contacts the peaks and troughs of different amplitudes in the stator, and the moving object speed is close to the integral value and has a low speed. It's getting old. Therefore, in order to obtain practical torque, rotation speed, etc., it is necessary to use conventional motors.
It required 10 to 100 times more power.

(2) The vibration amplitude when the surface waveform piezoelectric motor is actually driven is:
The maximum vertical component is about 0.5 μm, and the horizontal component that becomes thrust is about 0.25 μm, and compared to the vibration generation energy required for thrust, more than twice the useless energy is consumed. , it has a structure with extremely poor power efficiency.

(3) In the conventional piezoelectric motor with a surface waveform described above, the drive electrodes are separated into two sets, and the wave excited by the C electrode is propagated to the D electrode, or conversely, the wave excited by the D electrode is propagated to the C electrode. It is propagated as a wave with a longitudinal wave component and a transverse wave component, generating an elliptical trajectory on the surface of the elastic body. Due to this driving principle, the effective driving area is always as low as 50%. For this reason, the elastic ring becomes an infinitely free vibration system, and unnecessary higher-order modes within the ring plane are excited at the same time, which becomes a source of unpleasant audible noise. Furthermore, since the drive principle is based on the configuration of a surface wave device, the stator must have an endless configuration, and the design range is extremely narrow.

(4) Half of the total area always functions as a forced oscillator, but the other area is open as an infinitely free oscillating system, so the distribution of vertical strain becomes noticeable, especially under heavy loads at the level of actual driving. becomes uneven, resulting in uneven rotation.

Purpose of the Invention The purpose of the present invention is to solve the above-mentioned various drawbacks by focusing on highly efficient spatial waves excited by piezoelectric ceramic vibrators, and by using this as a driving force, it is possible to achieve extremely efficient practical use. The purpose of this invention is to provide a piezoelectric motor with a unique design.

Composition of the Invention A piezoelectric motor according to the present invention includes a stator including four piezoelectric vibrators and an acoustic material stacked in the thickness direction, and a sliding member that is stacked in the thickness direction and makes surface contact with the stator. Has children. Said 4
Each piezoelectric vibrator has thickness direction polarization consisting of one or more pairs of divided regions divided in the slider movement direction, and the directions of these polarizations are opposite to each other in adjacent regions. Two of the four are stacked one on top of the other so that the regions with different polarization directions face each other to form a pair, thereby making two identical sets. The two sets of piezoelectric vibrators configured as described above are arranged so that the vicinity of the boundary of each polarization region on one side is located near the center of each polarization region on the other side. When the piezoelectric vibrators configured as described above are driven with voltages at predetermined forced excitation frequencies that are out of phase with each other, the maximum amplitude position of the combined vibration of the stator caused by both piezoelectric vibrators moves in a constant direction over time. The slider in contact with the apex receives a driving force in that direction.

DESCRIPTION OF EMBODIMENTS Details of embodiments of the present invention will be described with reference to the drawings. The stator has a structure as shown in FIG. 4, for example. Disc-shaped first piezoelectric vibrators 11 and 1
For example, on the surface of 2, there are 8 areas divided into 45° areas.
electrodes 11a and 12a are provided. The electrodes 11a, 12a are formed on the surfaces of the first piezoelectric vibrators 11, 12 by printing, vapor deposition, plating, or other methods using a conductive material such as silver, silver palladium, rhodium, or nickel. The electrode (not shown) provided on the back surface may or may not be divided like the front electrode.
First piezoelectric vibrator 11, 1 configured as above
Polarization is performed so that the polarization directions of two adjacent electrodes are different from each other in the thickness direction. As a result, the fourth
As shown in the figure, 8 poles, 4 poles consisting of regions with alternately positive or negative polarity
A set of forced excitation oscillators is constructed. electrode 11a,
12a does not need to be divided after polarization,
Connected so that voltage can be applied all at once. The disk-shaped second piezoelectric vibrators 13 and 14 have the same structure as the first piezoelectric vibrators 11 and 12, and have positive polarity or negative polarity 8 alternately.
It consists of four sets of forced excitation vibrators.

The minimum amplitude position of the first piezoelectric vibrators 11, 12 or the second piezoelectric vibrators 13, 14 is near the boundary between adjacent electrodes, and the maximum amplitude position is near the center of each electrode. And both piezoelectric vibrators 11, 12, and 13, 14
The second piezoelectric vibrators 13 and 14 are placed near the center of the electrode, which is the maximum amplitude position of the first piezoelectric vibrators 11 and 12.
The electrodes are superimposed so that the boundary between adjacent electrodes is located at the minimum amplitude position.

Electric 1 piezoelectric vibrator 11 configured as above,
12 and second piezoelectric vibrators 13 and 14 are laminated together with thin metal plates 15, 16, and 17, which are electrical terminals, respectively. Further, at the top of the piezoelectric vibrator, a rib 18 and a coupling shaft 19, which are vibration transmitting members, are attached in an overlapping manner.
The rib 18 of the member is made of acoustic material or friction material made of aluminum, brass, iron, stainless steel, hardened steel, synthetic resin material such as nylon, ceramic material, glass material, rubber material, or a composite material made of these materials. It is formed using etc.

Further, the rib 18 may be formed as an integral structure with the piezoelectric vibrator 11. The coupling shaft 19 is also formed using a similar structure or an acoustic material.

The structure constructed as described above is used as the stator 20 shown in FIG. As shown in FIG. 5, the output signal oscillated by the oscillator 21 at the forced excitation drive frequency determined by the stator 20 is branched, one is directly sent to the amplifier 22, and the other is sent to the phase shifter 23.
The signal is inputted to the amplifier 24 via. The phase shifter 23
Then, a signal whose phase is shifted within the range of ±10° to ±170° is shaped to be used for forward rotation or reverse rotation as described later. The output signal of the oscillator 21 is directly input to the amplifier 22 and the amplified signal is sent to the first piezoelectric vibrator 1 through lead wires 25 and 26.
1 and 12. As a result, the stator 20 has eight poles, corresponding to four sets of forced excitation vibrators, with each pair of regions having mutually different positive polarity or negative polarity in the polarization direction of the first piezoelectric vibrators 11 and 12 as one wavelength. Four wavelengths of forced excitation waves are generated. The second piezoelectric vibrators 13 and 14 are similarly driven by applying the output of the amplifier 24 via lead wires 27 and 28.

Figure 6 shows the strain in the vertical direction when an electric signal is applied to the first piezoelectric vibrators 11, 12 and the second piezoelectric vibrators 13, 14 at a circumferential position of about 70% of the maximum diameter. The results are shown as changes in direction and position. The measurement was performed by irradiating the measurement location with a He-Ne gas laser beam and using an interference method between the incident light and reflected light. Figure 6a shows lead wires 25 and 2.
The measurement results obtained when the first piezoelectric vibrators 11 and 12 were driven by applying a signal to the piezoelectric vibrator 6 are shown. ± when applying 50V
It showed an amplitude of about 0.8 μm. The minimum amplitude position is located near the boundary between adjacent electrodes, and the maximum amplitude position is located near the center of each electrode. Figure 6b shows the results of vertical strain measured when the second piezoelectric vibrators 13 and 14 were driven in the same manner.
It was shown to. When 50V was applied, the amplitude was about ±0.8μm. The minimum amplitude position is located near the boundary between adjacent electrodes, and the maximum amplitude position is located near the center of each electrode.

Next, the measurement results when the first piezoelectric vibrators 11, 12 and the second piezoelectric vibrators 13, 14 were simultaneously driven using the configuration shown in FIGS. 4 and 5 are shown in FIG. 6c. In the strain distribution in the vertical direction, the position where the amplitude is maximum has moved to an intermediate position between a and b. Furthermore, the maximum amplitude of vertical strain is approximately 1.3 times larger. Here, as described above, the second piezoelectric vibrators 13 and 14 are ±
Because it is driven with a phase shift of 10° or ±170°,
The maximum amplitude position of the composite wave C moves in a constant direction with time.

A slider 29 is in contact with the top of the stator 20. The slider 29 is composed of an elastic body 30 made of a friction material or an elastic material, and an acoustic material 31 coupled thereto.

When the stator 20 is driven as described above, the apex of the vibration on the side of the stator 20 facing the slider 29 comes into contact with the slider 29, and since the apex moves with time, the slider 29 A force having a lateral component is applied to the In this way, the slider 29 repeats positional movement in the lateral direction with the drive frequency determined by the stator 20, and as a result, it is possible to obtain rotational motion in the range of approximately several to 1,000 rotations per minute. The generated torque varies depending on the acoustic materials that make up the stator, the friction coefficient and contact area of the slider that makes surface contact with the stator, or the magnitude of the load received, but it ranges from several decimal grams to several centimeters. It was possible to obtain torque in the range of 1,000 gcm. Regarding the direction of rotation, if the rotation obtained when driving the second piezoelectric vibrator by applying a signal whose phase is shifted in the range of +10° to +170° with respect to the reference signal is, for example, positive rotation, then the reference signal When driving by simultaneously applying signals with a phase shift in the range of -10° to -170°, the rotation direction obtained is rotation in the opposite direction.
Further, the rotation speed can be arbitrarily selected by selecting the magnitude or phase of the applied signal, or the magnitude of the load received by the contact portion.

Further, according to the configuration shown in FIGS. 4 and 5, the heavy load of distorting metal having a large Young's modulus in the conventional method is eliminated. Furthermore, since each piezoelectric vibrator has an active parallel bimolk structure, the mechanical displacement is doubled when driven by a constant voltage. Furthermore, since the capacitance is quadrupled and the AC impedance is reduced to one-fourth, effective driving can be achieved. Furthermore, a piezoelectric motor with extremely good linearity can be realized without generating a large amount of heat during application. Furthermore, since the effective drive area is always 100%, unnecessary vibrations, noise, and uneven rotation will not occur.

FIG. 7 shows the results of measuring the strain in the vertical direction when the stator 20 is driven with an electric signal applied thereto, as a change in the cross-sectional direction of the stator 20 shown by the imaginary line. The measurement was carried out using the interferometry method using laser light, similar to the measurement in the circumferential direction. When 50V is applied, 1.8μm near the rib 18 shown in Figure 4
The maximum amplitude of the degree was shown. The amplitude phase shift turning point, the so-called vibration node, is 80% if the diameter is 100%.
~85%, and changed almost linearly, with an amplitude of about 2.5 μm at the end. 11th to be described later
As shown in the figure, a buffer body 33 is provided at the bottom of the stator 20. Since the stator 20 is curved based on the buffer body 33 as shown in FIG. 7, the apparent amplitude is increased. Furthermore, if the support position is located near the vibration node, a drive with less loss can be realized. As a result, the lateral component which becomes the thrust force of the slider 29 increases in the rib 18, and the slider 29 is driven in a constant direction very efficiently.

FIG. 8 shows the relationship between the drive voltage and rotation speed of the piezoelectric motor according to the present invention. For comparison, Figure a shows the characteristics of a conventional surface waveform piezoelectric motor. b is the characteristic of the piezoelectric motor according to the present invention without ribs,
c shows the characteristic when the vertical length of the rib of the piezoelectric motor according to the present invention is 2 mm, and d shows the characteristic when the vertical length of the rib of the piezoelectric motor according to the present invention is 4 mm. By changing the vertical length of the rib 18 of the stator member in this manner, a desired running speed could be obtained. From these facts, it can be seen that the piezoelectric motor according to the present invention is extremely efficient. In FIG. 8, the maximum speed is 360 rpm, but in a prototype machine with a larger diameter or a model with a smaller diameter rib 18, a speed of about 1000 rpm could be measured. Moreover, the power consumption at this time was about 1/10 to 1/100 of that of conventional piezoelectric motors. Furthermore, the power efficiency was also relatively better than that of DC micromotors.

FIG. 9 shows an example of the structure of the rib 8 of the stator member. The contact surface of the rib 18 with the slider 29 has a plurality of grooves, for example, 1° or Etched or machined knife-etch grooves 32 are provided every several tens of degrees. The precipitated powder resulting from rotational wear of the ribs 18 and the slider 29 can be effectively cleaned by the grooves 32. The precipitated powder is guided within the grooves 32 and carried to the outside. As a result, both the contact surfaces of the rib 18 and the slider 29 were able to maintain the initial friction coefficient and contact area, and the generated torque was always constant.

FIG. 10 shows changes in operating time when the materials of the ribs 18 and the elastic body 30 of the slider 29 are changed.
a indicates the operating time when the elastic body 30 is made of a composite material such as asbestos with a rubber binder. b indicates the operating time when a structural material such as hardened steel is used as the material of the rib 18. c is an elastic body 3 made of a composite material such as pulp and silica with a synthetic resin binder.
It shows the operating time when configuring 0. d
9 shows the operating time when the rib 18 is provided with a knife-etch groove for cleaning precipitated powder due to rotational wear,
Initial characteristics can be guaranteed even after approximately 1000 hours of actual rotation.

FIG. 11 shows a more specific embodiment of a piezoelectric motor using a stator etc. as shown in FIGS. 4 and 5. The same parts as in FIG. 5 are given the same numbers. Lead wires 25, 26, 27, 28
The stator 20 is attached to a frame (not shown) via a buffer 33 so as to be able to vibrate freely. A slider 29 is in contact with the top of the stator 20 via a bearing 34 made of a bearing inserted into the coupling shaft 19. The pressing force adjustment screw 35 is attached to the upper end of the coupling shaft 19, and when it is tightened, the chrysanthemum-shaped leaf spring 36 is bent, and the stator 20 and the slider 29 can be brought into contact with each other with an arbitrary pressing force. can. The result is a few decimal grams/cm to several thousand grams/cm.
It was possible to obtain torque in the range of . Further, a fixed ring 37 is fixed on the slider 29, and rotation is transmitted to the rotated body by sandwiching the rotated body between it and a guide ring 38 shown by a phantom line. .

The piezoelectric motor with the above configuration not only does not take up much of its apparent storage space, but also allows forward and reverse rotation at will by simply changing the phase of the drive signal. Torque within about gcm can be generated. Further, the rotation speed can be arbitrarily selected up to about 1000 rotations by selecting the magnitude or phase of the applied signal, the magnitude of the load received by the contact portion, the length of the ribs, etc. Therefore, there is no need for a speed reducer or the like. Moreover, since it always forms a contact friction pair, there is no moment of inertia, it is rich in minute pulse operation, and is excellent in compactness. Furthermore, since the structure is extremely simple, the price is low.

Effects of the Invention As described above, the piezoelectric motor according to the present invention includes a stator and four piezoelectric vibrators, and these piezoelectric vibrators alternately have at least one pair of regions in which the direction of polarization is reversed in the slider movement direction. It consists of two pairs stacked one on top of the other so that the polarization directions are different from each other, and both pairs are shifted by approximately half an area from each other, and the slider is in contact with the stator. By applying voltages of predetermined frequencies out of phase with each other to both piezoelectric vibrators, a vibration wave moving in a fixed direction is generated in the stator, and the slider is driven. Therefore, the motor can be constructed with an extremely simple structure, and a small motor with good response can be realized.

Moreover, since the above-mentioned pair of piezoelectric vibrators has an active parallel bimorph structure to obtain a lateral component that becomes thrust,
At a constant voltage, the mechanical displacement is doubled and the entire deflection in the cross-sectional direction is output, so it is possible to extract the peak speed without averaging the speed.

[Brief explanation of the drawing]

1 and 2 are a sectional view and a plan view showing the configuration of a conventional piezoelectric motor, respectively, FIG. 3 is a perspective view showing its operation, and FIG. 4 is a fixing of the piezoelectric motor in an embodiment of the present invention. Figure 5 is an exploded perspective view of the stator, Figure 5 is a cross-sectional view showing an outline of a piezoelectric motor using the stator and its drive circuit, Figures 6 and 7 are strain distributions in the piezoelectric motor stator of Figure 5. 8 is a graph showing the characteristics of the rotation speed versus the driving voltage of the piezoelectric motor according to the present invention, FIG. 9 is a perspective view of the main part of the stator of the same motor, and FIG. 10 is a graph showing the operating time characteristics of the same motor. The graph and FIG. 11 are partially sectional front views showing a more specific structure of a piezoelectric motor according to an embodiment of the present invention. 11, 12, 13, 14...piezoelectric vibrator, 11
a, 12a... Electrode, 15, 16, 17... Metal thin plate, 18... Rib, 20... Stator, 29...
Rotor, 21... Oscillator, 23... Phase shifter, 2
2, 24...Amplifier.

Claims (1)

[Scope of Claims] 1. Two piezoelectric vibrators are divided into at least one pair of regions and the polarization directions of each region are alternately reversed, and the polarization directions of the opposing regions are different from each other. The piezoelectric vibrators are stacked one on top of the other to form one set, and another set of similarly configured piezoelectric vibrators are placed so that the boundaries of the respective regions of the other piezoelectric vibrator are located near the center of the respective regions of one of the piezoelectric vibrators. A piezoelectric motor comprising: a stator configured with a group of piezoelectric vibrators arranged one on top of the other; and a slider that makes surface contact with the stator. 2. The piezoelectric motor according to claim 1, wherein the stator includes a vibration transmission member disposed to be interposed between the slider and the piezoelectric vibrator. 3. The piezoelectric motor according to claim 2, wherein the vibration transmitting member is located near the maximum longitudinal displacement of the stator. 4 Claim 2 in which the slider contacting surface of the vibration transmission member has a plurality of grooves with a depth of several μm to several mm.
Piezoelectric motor as described in section. 5. The piezoelectric motor according to claim 2, wherein the thickness of the vibration transmission member is equal to or about 100 times that of the piezoelectric vibrator. 6. The piezoelectric motor according to claim 1, wherein voltages of predetermined frequencies are applied to two sets of piezoelectric vibrators with phases shifted from each other. 7. The piezoelectric motor according to claim 1, wherein the slider comprises an elastic body located on the stator side and an acoustic material bonded to the elastic body. 8. The piezoelectric motor according to claim 1, wherein both piezoelectric vibrators are equally divided. 9. The piezoelectric motor according to claim 1, wherein both piezoelectric vibrators are disk-shaped. 10. The piezoelectric motor according to claim 1, wherein the piezoelectric motor has a shaft at the center of the stator.