JPS62196080A - Ultrasonic motor - Google Patents

Abstract

PURPOSE:To enable a stable high speed to be obtained and increase mechanical output, by a method wherein the disc of a large mass in the same occupied space is used, and wherein a higher bending oscillation mode is adopted, and wherein a projection unit is set at the specified position of a driving unit. CONSTITUTION:The disc-formed driving unit 9 of a large mass is composed in the same space by putting a piezoelectric unit 7 together with an elastic unit 8. On the surface of the driving unit 9, a projection unit 10 is concentrically set so that the position of the web of a tertiary or more and diameter-directional secondary bending oscillation mode may be included in the circumferential direction excited by the driving unit 9. An abrasion-proof slider 11 comes in contact with the tip of the projection unit 10 to be arranged, and is put on an elastic unit 12 to compose a mover 13. When a two-phase AC electric field is applied to the piezoelectric unit 7 near the resonance frequency of the bending oscillation of the driving unit 9, then a mover 13 is rotated with a rotary shaft 14 for the center.

Description

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

2. Description of the Related Art In recent years, ultrasonic motors have attracted attention, in which elastic vibrations are excited in a driving body using a piezoelectric body such as a piezoelectric ceramic, and this vibration is used as a driving force.

The principle of the ultrasonic motor will be explained below with reference to the drawings.

Figure 3 shows an example of an ultrasonic motor, with an annular elastic body 1
A toroidal piezoelectric ceramic 2 is laminated on one side of the toric surface.
It constitutes a piezoelectric drive body 3. 4 is a slider made of a wear-resistant material, and 6 is an elastic body, which are pasted together to form the moving body 6. The moving body 6 is in contact with the driving body 3 via the slider 4.

When an electric field is applied to the piezoelectric ceramic 2, a traveling wave of bending vibration is excited in the circumferential direction of the driving body 30, thereby driving the moving body 6. Note that the arrow in the figure indicates the rotation direction of the moving body 6. FIG. 4 shows an example of the electrode structure of the piezoelectric ceramic 2 used in the ultrasonic motor of FIG. 3. In the figure, nine waves of bending vibration are applied in the circumferential direction. In the same figure,
A and B are electrode groups each consisting of a small area equivalent to 1/2 wavelength, and C and D are electrode groups consisting of 3/4 wavelength and 1/4 wavelength, respectively.
It is an electrode with a wavelength length. Therefore, there is a phase shift of one quarter length (=90 degrees) between the electrode group M and the electrode group B in the circumferential direction. Adjacent small electrode portions within B are polarized in opposite directions to each other in the thickness direction. The bonding surface of the piezoelectric ceramic 2 with the elastic body 1 is the surface opposite to the surface shown in FIG. 4, and the electrodes are solid electrodes. When using the electrode group, B
As indicated by diagonal lines in FIG. 4, these electrodes are short-circuited and the peta electrode is used as a common electrode.

The operation of the ultrasonic motor configured as above will be described below. Voltage V = Vq-gin (wt) -... on the electrode group of the piezoelectric body 2
When (1) is applied, the driving body 3 bends and vibrates in the circumferential direction. FIG. 5 is a perspective view of the driving body of the ultrasonic motor shown in FIG. 3 when it is approximated by a straight line. The situation when a voltage is applied to the piezoelectric body 2 is shown.

FIG. 6 is an enlarged depiction of the contact situation between the moving body 6 and the driving body 3. Vo-sin is applied to the electrode group A of the piezoelectric body 2.
(wt), and voltages Vo-cos (wt) whose phases are shifted by π/2 from each other are applied to the electrode group B. A traveling wave of bending vibration can be created in the circumferential direction of the driving body 3.

Generally speaking, if the amplitude of a traveling wave is ξ, then ξ=ξQ−Cog(W
t −kx) −−−−−−(2). (The clever formula is ξ=ξ(,-(cos(wt)-cos Qcx)+s
in (wt)-sin(kx))... (3
), Equation (3) is a traveling wave with waves cog (wt) and sin (Wt) whose phase is shifted by π/2 in time, and cos (kx) whose phase is shifted by π/2 in position. and 5
inQcx). From the above explanation, the piezoelectric body 2 is a group of electrodes whose phases are shifted from each other by π/2 (two λ/4).

B, a traveling wave of bending vibration can be created in the driving body 3 by applying voltages with a phase difference of π/2 to each of the electrode groups.

Figure 6 shows that the surface entry point of the driving body 3 is moving in a circular motion with the long axis 2w and the short axis 2u due to the excitation of the traveling wave, and the moving body 6 placed on the driving body 3 is shaped like an ellipse. It shows how the waves move at a speed of V=W-U in the opposite direction to the traveling direction of the waves due to contact at the apex. That is, the moving body 6 is pressed against the driving body 3 with an arbitrary static pressure, comes into contact with the surface of the driving body 3, and is driven at a speed V in the direction opposite to the direction of wave propagation due to the frictional force between the moving body 6 and the driving body 3. be done. ``When there is slippage between the two, the velocity becomes smaller than the above V.

Problems to be Solved by the Invention FIG. 7 is a diagram showing the displacement distribution of an annular driving body. From the figure, the displacement increases toward the outer diameter. The speed of the ultrasonic motor can be expressed as v=w@uocw-ξoIIh (4). Therefore, when using a bending mode of 3rd order or higher in the circumferential direction of an annular shape and 1st order in the radial direction as shown in Fig. 7, if the moving object is installed so that it is in contact with the outer periphery, the speed will be maximized. big. However, since the outer periphery is a free end, placing a moving object there as a load will have a significant effect on vibration. Also,
Since toric-shaped moving objects have a small volume within the same occupied space,
The energy of the driving body cannot be increased.

Therefore, there are drawbacks such as large fluctuations in motor characteristics due to load and inability to obtain large mechanical output.

Means for solving the problem A disk with a hole in the center or a disk without a hole is used as the drive body, and the drive body has three or more orders in the circumferential direction and a second order in the radial direction. Excite the traveling wave in the next bending imaging mode, provide a protrusion so as to include the antinode of the bending vibration on the contact surface side of the driving body with the moving body, and transmit power via the protrusion. .

By using a disk that can increase the mass in the same space as the action driving body and by adopting a high-order bending vibration mode, the accumulated energy within the driving body is increased, and the energy accumulated in the driving body is increased, and
By providing the protrusion so as to include the antinode position of the next bending vibration mode, high speed can be stably achieved and mechanical output can be increased.

EXAMPLE An example of the present invention will be described below with reference to the drawings.

The first factor is a cutaway perspective view of an ultrasonic motor according to an embodiment of the present invention. In the figure, a piezoelectric body 7 is bonded to an elastic body 8 to form a disc-shaped driving body 9 with a large mass in the same space. Reference numeral 10 denotes a protrusion provided on the surface of the driving body 9, which is arranged concentrically so as to always include the antinode of the third or higher order bending vibration mode in the circumferential direction and the second order in the radial direction excited by the drive member 1o. It is set up. Reference numeral 11 denotes a wear-resistant slider, which is disposed in contact with the tip of the projection 1o, and is attached to the elastic body 12 to constitute a moving body 13. Reference numeral 14 denotes a rotating shaft, and when a two-phase alternating current electric field is applied to the piezoelectric body 7 near the resonance frequency of the bending vibration of the driving body 9, the moving body 13 rotates around the rotating shaft 14. Note that the bending vibration mode can be selected by appropriately setting the external drive frequency in relation to the electrode configuration.

FIG. 2 1 is a diagram of the embodiment shown in FIG. 1 when the driving body 9 is straightened, and the increase in bending rigidity of the driving body 9 due to the protrusion 10 is small, and the change in the position of the neutral plane NL is also small. Because it is small,
As shown in the figure, the distance hHh' becomes large, a large lateral component is obtained for the same drive, and the speed of the moving body 13 becomes large according to equation (4). In addition, in order to maximize the speed of the moving body 13 at this time, it is only necessary to ensure that the antinode of the bending vibration having a large amplitude ξ0 is located within the protrusion 1o.

However, as shown in FIG. 8, even if the driver 9 is used in the second order in the radial direction, the position of the antinode of vibration changes depending on the order in the circumferential direction. Figure 8 shows the state of vibration of the drive body 9 and its radial displacement distribution when the disc is 3rd order in the circumferential direction and 2nd order in the radial direction, and the displacement distribution when the circumferential order becomes 6th order. changes, and the position of the antinode of vibration moves toward the outer circumference. Generally, as the order in the circumferential direction increases with secondary fixation in the radial direction, the position of the antinode of vibration moves outward. Therefore, if you try to always obtain the maximum speed for any order in the circumferential direction, the position of the protrusion 1o will increase as the order in the circumferential direction increases so that the antinode of vibration is within 1° of the protrusion. must be placed in concentric circles.

The drive body in the above embodiment uses a disk without a hole, and the center of the disk hardly vibrates, so that the rotation axis can be adjusted.
Although it is taken from the center of the moving body, the same result can be obtained by drilling a hole in the center of the driving body, fixing it to a base with something like felt that does not inhibit mechanical vibration, and then taking out the rotating shaft from the base. Effects can be obtained.

FIG. 9 is a plan view showing the electrode structure of the piezoelectric material used in this example. In the figure, A/ and B/ are electrodes whose phase differs from each other by π/2 in the circumferential direction, and both electrodes h/ ,
B/ each has a length equivalent to 1/2 wavelength in the circumferential direction,
Adjacent small electrode portions are composed of small electrodes polarized in opposite directions in the thickness direction. c/ and D/ are regions each having a length of 3/4.174 wavelength in the circumferential direction. During driving, electrodes A/ and B/ are short-circuited, and sine wave and cosine wave alternating current voltages are applied, respectively. In other words, according to equation (3), a traveling wave of bending vibration is excited in the driving body.

In the above embodiment, the third order was used in the circumferential direction, but any order higher than the third order may be selected without any problem in operation.

Effects of the Invention As described above, in the present invention, by employing a disk as the driving body, the mass of the driving body is increased within the same occupied space, and the bending of the disk is tertiary or higher in the circumferential direction and secondary in the radial direction. By exciting the vibration mode as a traveling wave, and by providing the protrusions concentrically on the driving body so that the antinode of the vibration is always within the protrusion, the lateral component is expanded, and the velocity becomes large. Moreover, it is possible to provide an ultrasonic motor with a large mechanical output.

[Brief explanation of drawings]

Fig. 1 is a cutaway perspective view of an ultrasonic motor according to an embodiment of the present invention, Fig. 2 is a linear model diagram for explaining the operation of the protrusion, and Fig. 3 is a cutaway perspective view of a conventional ultrasonic motor. Figure 4 is a plan view of the piezoelectric body used in the conventional example shown in Figure 3, Figure 5 is a model diagram showing the vibration state of the driving body of the ultrasonic motor, and Figure 6 is a diagram explaining the principle of the ultrasonic motor. , FIG. 7 is a plan view of a piezoelectric body used in the embodiment of the annular ultrasonic motor shown in FIG. 7...Piezoelectric body, 8...Elastic body, 9...
...Driver, 10...Protrusion, 11...
...Slider, 12...Elastic body, 13...
...Moving object, 14...Rotation axis, M', B'...
····electrode. Name of agent: Patent attorney Toshio Nakao and 1 other person
1 Figure 2 Figure 3 Figure WJ4 Figure 5 Figure 6 Figure 7

Claims (1)

[Claims] In an ultrasonic motor that moves a moving body placed in contact with the driving body by exciting an elastic traveling wave in the driving body made of an elastic body and a piezoelectric body, a disk is used as the driving body, and the The driving body has three or more orders in the circumferential direction and two orders in the radial direction.
A traveling wave in the next bending vibration mode is excited, and a protrusion is provided concentrically at a position including the antinode of the bending vibration on the contact surface side of the driving body with the moving body, and the traveling wave is transmitted to the moving body via the protrusion. An ultrasonic motor characterized by power transmission.