JPS6118369A - Piezoelectric motor - Google Patents

Abstract

PURPOSE:To obtain a piezoelectric motor which has small loss and large torque and speed and in which a piezoelectric unit is bonded on one side surface of a circular elastic unit and a rotor is contacted with the other side surface by increasing the thickness of the elastic unit toward the outer periphery. CONSTITUTION:A circular elastic unit 6 which has one surface being flat and the other surface increasing its thickness toward the outer periphery is formed, a piezoelectric unit 5 is bonded to the flat side to form a piezoelectric driver 11. Further, a rotor 8 which has a surface contacted in coincidence with the other surface (oblique surface) side of the unit 6 is contacted through a slider 12 with the oblique surface. A voltage is applied to the unit 5, a peripheral bending vibration is excited in the driver 11 to form a traveling wave to elliptically move a mass point on the other surface of the unit 6, thereby rotating the rotor 8. Thus, mechanical Q becomes small in the resonance frequency to reduce the loss.

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.

Conventional configurations and their problems In recent years, it has been difficult to use piezoelectric materials such as piezoelectric ceramics to excite single-wave ultrasonic vibrations, but piezoelectric motors that perform rotational, linear, or curved motion have been announced, and the number of component parts has increased. It is attracting attention because of its small size, high efficiency, and ability to be made small.

A conventional piezoelectric motor will be explained below with reference to the drawings.

Figure 1 is an example of a conventional piezoelectric motor published in Nikkei Mechanical (58, 2, 28), etc.A circular elastic body 1
An annular piezoelectric ceramic 2 is bonded to the surface of the annular piezoelectric ceramic 2, and the annular piezoelectric ceramic 2 excites the annular elastic body 1 so that the annular elastic body 1 vibrates as a unit.

The annular piezoelectric ceramic 2 has a division ratio of 22.5° or 11.25°, for example, as shown in FIG.
The polarization is performed so that the direction of polarization is opposite in adjacent regions. Thereafter, the surface of the piezoelectric body is combined into two parts A and B by covering the electrodes with conductive paint or the like as shown in FIG. Here, E in FIG. 2 is a ground terminal. As shown in FIG. 1, a moving body 4 to which a slider 3 is fixed is located above the annular elastic body 1. As shown in FIG.

The operation of the conventional piezoelectric motor configured as described above will be described below. Electrode A on one side of the piezoelectric body 2
K VoSIIl ωt, other electric & B I/CVO
AC signals of cos ωt whose phases are shifted by π/2 from each other are respectively applied. Then, the divided regions alternately expand and contract in the circumferential direction, and bending vibration occurs in the annular elastic body 1. FIG. 3 is a perspective view of a portion of the piezoelectric motor shown in FIG. 2, showing how adjacent portions with opposite polarization directions undergo bending vibration with opposite curvatures due to the above driving. Figure 4 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 is along the long axis 2
w, the vertex where the elastic body drawing an elliptical locus with the minor axis 2u contacts the moving point, and point A is V = 2 in the negative direction of the X axis.
It has a speed of πfu. Here f is the driving frequency and ω=2
It has a relationship of πf. As a result, the moving body is driven by the frictional force with the elastic body in the direction opposite to the direction of wave propagation at a speed of ■. In order to draw an elliptical locus as a thrust on the surface of an elastic body in this way, it is conceivable to excite Rayleigh waves of surface acoustic waves or bending or bending vibrations of the elastic body as traveling waves. However, once the driving frequency is determined, surface acoustic waves have longer wavelengths than bending vibrations. As mentioned above, in the piezoelectric motor, the peak of the elastic wave of the elastic body contacts the moving body and drives the moving body, so the larger the contact area, the greater the torque that can be obtained.

Therefore, it is preferable to use bending vibration for a piezoelectric motor because the contact area is smaller for the same magnitude.

In the conventional example described above, the bending vibration is used as a traveling wave by providing a ground terminal E in a part of the piezoelectric element 2. The progression e is generally ξ=cosωt*coskx+
sinωt*5inky: −−−−=−, (1)(
k: wave number). 0) According to the equation, the traveling wave is COSωt and S! whose phase is temporally shifted by ~~. noJt, and cos k x and sin positionally out of phase by π/2
A traveling wave is obtained by the sum of the respective products with k x, and it can be seen from the above explanation that the conventional piezoelectric motor has such a configuration and driving method.

However, the above configuration has the following drawbacks.

FIG. 6 shows the distribution of the amplitude of the bending vibration excited on the surface of the elastic body 1 of the piezoelectric motor described above, measured in the radial direction, and normalized at the point of the largest amplitude on the outer diameter. As shown in the figure, even if the inner diameter is changed, the function form after normalization of the amplitude distribution is almost the same.・Figure 6 shows the amplitude distribution at the outer diameter at the same drive current density value (current divided by electrode area) when the inner diameter/outer diameter ratio of the elastic body 1 of the piezoelectric motor is changed. be. The displacement shown in Figures 5 and 6 is WK in Figure 4.
It's appropriate. However, in the piezoelectric motor that we are currently dealing with, if the shape and material are determined (the thicknesses of the piezoelectric element 2 and the elastic body, and the materials of each are determined), W and U have a certain relationship. Therefore, from FIG. 5, the drive speed around the outer diameter is high, but the drive speed around the inside diameter is low, and the piezoelectric motor of the conventional type in which the entire annular surface of the slider 3 is in contact with the elastic body 1, It actually rotates at a lower speed than the driving speed at the outer periphery. Furthermore, since the inner circumferential portion acts as a brake while the outer circumferential portion is driving, input energy is consumed and efficiency deteriorates. Furthermore, mechanical damage due to friction becomes large and the life span is shortened. From FIG. 6, if the inner diameter becomes smaller (the width of the ring becomes wider), only a smaller amplitude can be obtained for the same drive current density. In other words, the inner peripheral side of the piezoelectric element 2 does not contribute to displacement, but performs a braking action. For this reason, elastic body 1. The smaller the width of the piezoelectric element 20, the faster a piezoelectric motor can be obtained. However, in the structure of a conventional piezoelectric motor, the contact area becomes smaller and the output torque becomes smaller, so the width of the ring cannot be made smaller. .

As described above, conventional piezoelectric motors have had various problems.

Purpose of the Invention The purpose of the present invention is to eliminate drive loss caused by the difference in amplitude between the inner and outer diameter portions of an annular ring, and to achieve a high output torque, a wide range of rotational speed, high efficiency, and a long service life. Our purpose is to provide piezoelectric motors.

Composition of the Invention The piezoelectric motor of the present invention has a drive body formed by laminating a toroidal piezoelectric body on the flat side of a toroidal elastic body whose thickness increases toward the outer periphery. By bringing a rotor having a surface shape similar to that of the surface into contact with each other, a piezoelectric motor with low loss and high output torque and rotational speed is provided.

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 7 is a sectional view of a piezoelectric motor that is an embodiment of the present invention. In the figure, reference numeral 7 denotes a fixing base, which serves both the role of fixing the driving body 11 made by pasting together the annular piezoelectric body 5 and the annular elastic body 6, and the role of fixing the rotating shaft 9. By applying a voltage to the piezoelectric body 5 and driving it, a vibration as shown in FIG. 8 is excited in the circumferential direction of the driving body 11, and this vibration propagates in the circumferential direction as a traveling wave. As a result, a point on the toric surface of the elastic body 6 of the driving body 11 performs an elliptical motion, and the rotor 8 installed thereon rotates around the rotation axis 9.

A projection is provided at the upper end of the rotating shaft 9, and serves to fix a spring 1o that positions the rotor 8 and keeps the rotor 8 in contact with the elastic body 6 with a constant load.

As mentioned above, in a piezoelectric motor, a point on the surface of the driving body moves in an ellipse, and the rotor placed in contact thereon is moved by frictional force, so the piezoelectric motor has constant speed and constant output torque characteristics. In order to achieve this, it is necessary to keep the rotor 8 and the driving body 11 in stable contact with each other with a constant load using the spring 10. 12 in the figure is a slider that is integrated with the rotor 8. The slider 12 is made of a material with good wear resistance, and exists to reduce wear caused by slight relative movement between the slider 12 and the drive body 11.

The piezoelectric body used in this example is similar to that shown in Fig. 2, in which the entire circumference of the ring is divided into an even number of sizes, and one of them is further divided into two, as shown in Fig. 2. It has a similar configuration and is driven near the resonant frequency such that the length of the large area in the circumferential direction is half a wavelength.

Therefore, the number of divisions can be any number, and the same operation can be achieved by changing the driving frequency. In Fig. 2, the E terminal is set as the ground terminal, and the A and B terminals have Vsinωt, respectively.
V cos ωt --- (2) ■ = Instantaneous value of voltage ω: Drive angular frequency t: When a voltage expressed in time is applied, the driver 11 vibrates as shown in FIG.

However, as described above, the elastic body 6 constituting the driving body 11
If the thickness is uniform, the displacement distribution on the surface of the driving body 11 will be maximum at the outer circumference and minimum at the inner circumference (see Fig. 5).
. The motion direction component of the rotor 8 of the elliptical locus of the point on the surface of the driving body 110 (11214, the component that contributes to the speed at which the rotor 8 rotates) is determined by the material and thickness of the driving body 11, and the long axis of the elliptical locus. Since the ratio of the short axis is determined, the larger the displacement of the surface, the thicker it is. Therefore, if contact occurs near the outer periphery, rotor 8
The 0 rotation speed becomes a dog, and when contact occurs near the inner circumference, the rotation speed of the rotor 9 becomes small. If you try to increase the rotational speed and make contact only near the outer periphery, the frictional force between the drive body 11 and the slider 12 of the rotor 8 will be small and 'f! ,,b output torque becomes smaller. Furthermore, if the inner and outer circumferences are brought into contact in order to increase the output torque, the rotational speed of the rotor 90 will be reduced. Furthermore, since the displacement decreases toward the inner circumference, energy loss is greater in this area, and most of the input energy is converted to heat, making less contribution to rotation.

In one embodiment of the present invention, as shown in FIG. 7, the driving body is composed of an elastic body 6 that becomes thicker toward the outer periphery. Thereby, the amplitude ratio between the inner diameter part and the outer diameter part can be changed as shown in FIG. A in Fig. 9 is the driver 1
Amplitude distributions when the thickness of the elastic body 6 constituting the elastic body 1 is uniform.

This is the characteristic when the thickness at the outer diameter portion becomes thicker relative to the inner diameter portion as D increases. Note that A in Figure 9.

B, C, and D are all normalized by the amplitude of the outer diameter portion.

In one embodiment of the present invention, the thicknesses of the inner diameter portion and the outer diameter portion of the driving body 11 are determined as follows. If inner diameter r1 + outer diameter r2, the contribution of a point at radius r to the rotation speed of rotor 8 is the circumferential length of radius r divided by the speed, n=2πr/K·ξ−f − --(3)K
: Proportionality constant ξ : Displacement f : Drive frequency n : Can be expressed as the number of rotations. Therefore, the rotor at each point8. In order to make the contribution to the rotation speed the same, the thickness is increased toward the outer periphery so that the equation (3) always has the same value for r, r, and any r between them.

In another embodiment, it is determined as follows. When the width of the ring is very small, its thickness is 19. The length of one wavelength in the circumferential direction is 4. For example, if the order of vibration is n, then the resonance frequency is ft-1. If the formula (4) is made to hold between the inner diameter r and the outer diameter r2 of the driving body 11, the thickness t at the radius r can be expressed as t2: the thickness at the outer diameter. As can be expressed by, if the thickness is increased toward the outer periphery, the mechanical Q at the resonant frequency, which is the driving frequency, becomes large and the loss becomes small. FIG. 101 shows the frequency characteristic A of the admittance seen from the electric terminal of the piezoelectric body 5 of the driving body 11 when the thickness of the driving body 11 is uniform, and (6)
This is the frequency characteristic of admittance when the thickness of the driving body 11 is increased toward the outer periphery so that the formula holds true.

FIG. 11 is a comparison of characteristics between a piezoelectric motor according to an embodiment of the present invention and a conventional piezoelectric motor. In the figure, C is a conventional motor, and D is a characteristic of the piezoelectric motor of the embodiment.

Effects of the Invention In the present invention, as described above, by increasing the thickness of the driving body toward the outer periphery, it is possible to increase the mechanical Q at the driving frequency and to increase the displacement near the inner periphery. Therefore, it is possible to provide a piezoelectric motor with low loss and high output torque and rotational speed.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view of a conventional piezoelectric motor, Figure 2 is a plan view showing the shape and electrode structure of the piezoelectric body used in Figure 1, and Figure 3 is a vibration of the drive body of the piezoelectric motor. A model diagram showing the state, Figure 4 is an explanatory diagram of the principle of a piezoelectric motor, Figure 5 is a radial displacement distribution diagram of an annular layered moving body (after normalization), Figure 6
The figure shows the amplitude characteristics at the outer diameter part with the same driving current density when the inner diameter/outer diameter ratio of the annular layered moving body is changed. Fig. 7 is a cross-sectional view of a piezoelectric motor according to an embodiment of the present invention. Fig. 8 is a diagram showing the vibration state of the driving body, and Figure 9 is a radial amplitude distribution diagram when the radial thickness of the driving body is changed (normalized by the amplitude of the outer diameter part).
FIG. 10 is a class showing the frequency characteristics of the admittance of the driving body according to an embodiment of the present invention, and FIG. 11 is a graph comparing the rotation speed-output torque characteristics between the conventional example and the embodiment of the present invention. 5...Piezoelectric body, S...Elastic body, 7...
Fixed base, 8... Rotor, 9... Rotating shaft, 1
Q... Spring, 11... Drive body, 12...
·Slider. Name of agent: Patent attorney Toshio Nakao and one other person No. 4 B Fig. 3 + - 15 Radial direction Tato Pancreatic Fig. 6 Inner side / Tatone Mitsu Fig. 8 Fig. 9 Radial direction

Claims (3)

[Claims] (1) A piezoelectric drive body is constructed by bonding a toroidal piezoelectric body whose outer diameter is approximately equal to the outer diameter of the elastic body to one of the principal surfaces of the annular elastic body so that the outer diameters match. By applying a voltage to the piezoelectric body, the driving body is excited to bend in a circumferential direction to create a traveling wave, and the mass point on the other main surface of the elastic body is caused to move in an elliptical manner. In a piezoelectric motor that rotates a rotor placed on the main surface of the piezoelectric motor, the surface of the annular elastic body constituting the drive body that is in contact with the rotor has a shape that becomes thicker toward the outer diameter, and A piezoelectric motor characterized in that a surface of the rotor that contacts the elastic body has the same shape as the surface of the elastic body. (2) The thickness of the annular elastic body is set so that the amplitude of the surface of the driving body is equal to the radius ratio between the inner circumference and the outer circumference. Piezoelectric motor. (3) A patent claim characterized in that the thickness of the annular elastic body constituting the driving body is increased toward the outer periphery so that the value obtained by dividing the thickness by the square of the radius of the annular ring becomes constant. A piezoelectric motor according to range 2.