JPH08294291A - Ultrasonic motor - Google Patents

Abstract

PURPOSE: To provide a small size and highly efficient ultrasonic motor which is resistive to the influence of load variation, etc., and maintains uniform friction contact between a vibrating body and a moving body to reduce generation of noise. CONSTITUTION: A vibrating body 13 obtained by joining a piezoelectric body 12 to an elastic substrate 11 having a plurality of projections 11a is pressurized in contact with a moving body 16 and the moving body is driven through a friction force between the vibrating body and moving body by energizing the vibrating body with a travelling wave. The surface of a contact area 16b of the moving body 16 provided opposed to the projection 11a of the vibrating body 13 is inclined so that the internal circumference is projected from the external circumference and difference Δt of distances from the contact surface S of the projections of the internal and external circumferences as the inclination degree is set larger than the amplitude value of deflective vibration applied to the vibrating body and smaller than 10 times the amplitude value.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vibrating body in which a piezoelectric body such as a piezoelectric ceramic is coupled to an elastic substrate having a plurality of protrusions, a moving body is brought into pressure contact with the vibrating body, and the vibrating body is bent by the piezoelectric body. The present invention relates to an ultrasonic motor configured to drive a moving body via a frictional force between the vibrating body and the moving body by exciting a traveling wave of vibration.

[0002]

2. Description of the Related Art In recent years, attention has been paid to an ultrasonic motor that excites elastic vibration in a vibrating body formed of a piezoelectric body such as a piezoelectric ceramic and drives a moving body by using this as a driving force.
Hereinafter, a conventional technique of an ultrasonic motor will be described with reference to the drawings.

FIG. 3 is a sectional view showing the structure of the main part of a conventional ultrasonic motor. The vibrating body 3 is configured by bonding the piezoelectric body 2 to the elastic substrate 1 having a plurality of protrusions 1a. The moving body 7 having the output take-out portion 4 is formed by coupling an abrasion resistant friction material 6 to the elastic body 5, and this is installed in pressure contact with the vibrating body 3.

Next, the operation of the ultrasonic motor thus constructed will be described with reference to the operation principle diagram of the ultrasonic motor shown in FIG. First, the piezoelectric body 2 is provided with two sets of drive electrodes. When two AC voltages having a predetermined phase difference are applied to the drive electrodes, stretching vibration is generated in the piezoelectric body 2. Since the elastic substrate 1 acts to resist expansion and contraction of the piezoelectric body 2, the traveling wave of the flexural vibration is excited in the vibrating body 3 by the same action as that of the bimetal. An arbitrary point on the surface of the vibrating body 3 moves so as to draw an elliptical locus by the traveling wave of the flexural vibration. The protrusion of the vibrator (1 in Fig. 3)
In a), the lateral displacement (ζ in FIG. 4) of this elliptical locus is magnified. The moving body 7 placed in pressure contact with the protrusion of the vibrating body 3 is driven by frictional force due to the enlarged lateral displacement to rotate.

In the conventional ultrasonic motor as described above, as shown in the enlarged sectional view of the contact state between the vibrating body 3 and the moving body 7 in FIG. Vibrating body 3
Contacts the contact surface S of the protrusion (1a in FIG. 3) of
The friction material 6 is configured to contact the central portion of the contact surface S with a flat surface narrower than the contact surface S of the protrusion 1a.

[0006]

When attempting to downsize the conventional ultrasonic motor as described above, if the outer diameter of the vibrating body is reduced, the kinetic energy stored in the vibrating body becomes smaller. Along with that, it becomes more susceptible to the load. Therefore, when the pressure contact between the vibrating body and the moving body becomes uneven due to the plane accuracy of the contact surfaces of the vibrating body and the moving body, which depends on the processing accuracy of the vibrating body and the moving body, or Even when uniform pressure is applied to the moving body, when the output of the ultrasonic motor is taken out from the moving body to the outside through the output taking-out portion, the moving body is moved at the central portion of the protrusion of the vibrating body as in the conventional example. In the structure in which the friction material contacts with a flat surface, load fluctuation is likely to occur due to uneven pressure applied between the vibrating body and the moving body. Furthermore, when a force is applied by an external load in the axial direction (pressurizing direction) of the ultrasonic motor or in a direction perpendicular to the axial direction, stress is applied from the protrusion of the vibrating body to the elastic substrate (base portion other than the protrusion), and bending vibration is generated. Receive a disturbance. As a result, unnecessary vibration occurs, the contact state between the moving body and the vibrating body becomes non-uniform, and the motor efficiency decreases and noise is likely to occur.

Therefore, the present invention solves the problems of the prior art as described above, suppresses the generation of noise by maintaining a uniform frictional contact between the vibrating body and the moving body, and is small in size with high efficiency. An object is to provide an ultrasonic motor.

[0008]

The ultrasonic motor according to the present invention is characterized by a main body of a moving body which comes into pressure contact with a vibrating body in which a piezoelectric body is coupled to an elastic substrate having a plurality of protrusions. A contact portion having a surface projecting from the outer circumference in the axial direction and facing the protrusion of the vibrating body is integrally formed, and the surface of the contact portion facing the protrusion has a surface with respect to the contact surface of the protrusion. The point is that the surface is inclined in the radial direction.

Preferably, the surface of the contact portion facing the protrusion is inclined in the radial direction so that the inner peripheral side projects from the outer peripheral side, and the inner peripheral end and the outer peripheral end as the degree of inclination are inclined. The distance difference from the contact surface is set to be larger than the amplitude value of the flexural vibration excited by the vibrating body and smaller than 10 times the amplitude value.

Further, it is preferable that the movable body is formed of a resin molded body, and the surface of the contact portion facing the protrusion is finished by polishing to have a maximum surface roughness of 2 μm or less. Furthermore, it is preferable that the moving body is formed of a fiber reinforced resin, particularly a carbon fiber reinforced resin. In this case, the content of the carbon fibers may be in the range of 5 to 50% by weight from the viewpoint of improving the rigidity of the moving body and the wear resistance of the contact portion, and maintaining the moldability and mechanical strength. preferable.

[0011]

[Operation] In the ultrasonic motor according to the present invention, the main body portion of the moving body and the contact portion having the surface projecting from the outer periphery in the axial direction and facing the protruding portion of the vibrating body are integrally formed from a resin molded body or the like. In addition, since the surface of the contact portion facing the protrusion is formed by a surface inclined in the radial direction with respect to the contact surface of the protrusion, a friction material is interposed at the center of the protrusion of the vibrating body. Compared to the case of the conventional example in which the vibrating body and the moving body are in contact with each other on a flat surface, the effect of absorbing the undulation in the contact portion between the vibrating body and the moving body (surface correction effect) is higher.
Therefore, even when a force due to an external load is applied in the axial direction of the ultrasonic motor or in a direction perpendicular to the axial direction, the effect of load fluctuation can be reduced at the moving body contact portion, and the load-bearing characteristic of the vibrating body is improved. That is, the uniform contact state between the vibrating body and the moving body is maintained even when the above-mentioned force due to the external load is applied.

The inclination of the surface of the contact portion is obtained by projecting one of the inner peripheral side and the outer peripheral side of the contact portion from the other, or by projecting at the center and retracting toward the inner peripheral side and outer peripheral side. can get. However, in order to achieve the above-mentioned effects, it is better to project the inner peripheral side from the outer peripheral side, and the difference in distance between the inner peripheral edge and the outer peripheral edge as the inclination degree from the projection contact surface. It has been found from an experiment to be described later that it is preferable to set a value larger than the amplitude value of the flexural vibration excited by the vibrating body and smaller than 10 times the amplitude value.

Further, the surface of the contact portion of the moving body integrally formed by molding of the carbon fiber reinforced resin, facing the protrusion, is finished by polishing, and the maximum surface roughness thereof is set to 2 μm or less. By doing so, it is possible to reduce changes with time in the contact state between the vibrating body and the moving body.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to the drawings showing specific embodiments. (Embodiment 1) FIG. 1 is a sectional view showing a structure of a main part of an ultrasonic motor according to Embodiment 1 of the present invention. Multiple protrusions 1
A vibrating body 13 is configured by bonding a piezoelectric body 12 made of piezoelectric ceramic or the like to the bottom surface of an elastic substrate 11 having 1a. The moving body 16 is made of polyetheretherketone (P) containing 30% by weight of carbon fibers (short fibers).
EEK resin is formed by injection molding, and includes a main body portion 16a and a contact portion 16b. This moving body 16 is the output take-out section 1
It is fixed to 4 by a method such as press fitting or adhesion.

FIG. 2 shows an enlarged sectional view of a contact portion between the vibrating body 13 and the moving body 16. The surface (the surface facing the vibrating body 13) of the contact portion 16b of the moving body 16 is formed so as to be inclined in the radial direction, and the inner peripheral side projects from the outer peripheral side. In this way, the vibrating body 13 and the moving body 16 are brought into pressure contact with each other on the surface (that is, the contact surface) of the protruding portion 11a of the vibrating body 13. The specific degree of inclination, that is, the difference in distance between the inner peripheral edge and the outer peripheral edge of the contact portion 16b from the contact surface of the protrusion (Δ in the figure
The following experiment was conducted to properly set t).

That is, small ultrasonic motors having a diameter of 10 mm were produced for several types having different inclination degrees Δt, and the amplitude value of the flexural vibration excited by the vibrating body 13 was set to 1 μm, and the vibrating body 13 and the moving body 16 were set. The contact state with was evaluated.
This evaluation was performed by providing a sensor electrode for detecting the vibration of the vibrating body on the drive electrode portion of the piezoelectric body, measuring the waveform of the sensor electrode output, and evaluating the fluctuation rate. Table 1 shows the results.

[0017]

[Table 1]

In Table 1, the fluctuation rate of the sensor electrode output waveform is defined as the rate at which the peak value of the sensor electrode output waveform fluctuates up and down. It is indicated that the greater the fluctuation rate of the sensor electrode output waveform, the greater the degree of non-uniformity of the contact state between the vibrating body and the moving body.

As shown in the results of Table 1, when the inclination degree Δt of the surface of the movable body contact portion 16b is the same as the flexural vibration amplitude value (1 μm), Δt = 0 (flat).
Although the fluctuation rate of the sensor electrode output waveform is slightly improved compared with the case of 1, the contact state between the vibrating body and the moving body is still non-uniform. This is because when the inclination degree and the amplitude value of the flexural vibration excited by the vibrating body are approximately the same, the moving body contact portion is elastically deformed by the pressurization of the vibrating body and the moving body and approaches a flat state. In addition, it is considered that the effect of providing the contact portion 16b of the moving body with an inclination, that is, the effect of uniformly maintaining the contact between the vibrating body and the moving body is not sufficiently exhibited.

The inclination degree Δt of the surface of the moving body contact portion is set to 3 μm.
It can be seen from Table 1 that the fluctuation rate of the output waveform of the sensor electrode becomes small when it is increased to 8 μm. However, if the inclination degree Δt is further increased, the amplitude value (1 μm) of the flexural vibration excited by the vibrating body is 10 times or more (10 μm, 12 μm).
Similarly, it can be seen from Table 1 that the variation rate of the output waveform of the sensor electrode increases again when m). This is considered to be due to the following reasons.

That is, the degree of inclination is 1 of the amplitude value of the flexural vibration.
When it becomes about 0 times, stress is concentrated on the moving body contact portion due to the pressurization of the vibrating body and the moving body, and the elastic deformation amount of the moving body contact portion increases. This amount of deformation depends on the flatness of the vibrating body and the moving body, and when the vibrating body and the moving body are processed with high accuracy on the order of submicrons (0.1 μm), uniform deformation occurs, In the case of the flatness of the processing accuracy of the actual micron order, the deformation of the moving body contact portion becomes non-uniform. Therefore, it is considered that the load applied to the elastic substrate of the vibrating body from the protruding portion of the vibrating body becomes non-uniform, and the flexural vibration of the vibrating body is disturbed.

From the above experimental results, the inclination degree Δt of the surface of the moving body contact portion is larger than the amplitude value of the flexural vibration, and
It can be seen that a uniform contact state between the vibrating body and the moving body can be realized by setting the amplitude value to be smaller than 10 times.

Next, with the same small ultrasonic motor, the noise and the motor (driving) efficiency when the amplitude value of the flexural vibration excited by the vibrating body was also set to 1 μm were measured. The results are shown in Table 2.

[0024]

[Table 2]

In Table 2, the noise is 1 from the ultrasonic motor.
The measurement was performed with the A characteristic (L _A ) closest to the auditory characteristic at a position separated by cm. From the results of Table 2, when the inclination degree Δt is the same as the amplitude value (1 μm) of the flexural vibration excited by the vibrating body, or when it is 10 times or more (10 μm, 12 μm), the noise level is large and the motor efficiency is high. It turns out that is low. When Δt = 3 or 8, the noise level is low and the motor efficiency is high. Therefore, the moving body contact portion 16b
By setting the inclination degree Δt of A to be larger than the amplitude value of the flexural vibration excited by the vibrating body and smaller than 10 times the amplitude value, it is possible to realize a small ultrasonic motor with low noise and good efficiency. I understand. (Second Embodiment) Next, an ultrasonic motor according to a second embodiment of the present invention will be described. The structure of the main part is the same as that of the example 1 described with reference to FIGS. 1 and 2, but in this example, the moving body 16 is formed by injection molding a polyphenylene sulfide (PPS) resin containing 30% by weight of carbon fiber. It is formed. The contact portion 16b of the moving body 16 is formed by polishing, as in the first embodiment, so that the inner peripheral side protrudes from the outer peripheral side. The inclination degree Δt of the contact portion 16b is equal to that of the flexural vibration excited by the vibrating body. It is set to three times the amplitude value.

A small ultrasonic motor having a diameter of 10 mm having the above-mentioned structure was produced, and when the amplitude value of the flexural vibration excited by the vibrating body 13 was set to 1 μm, the vibrating body 13 and the moving body 1 were moved.
The contact state with 6 was evaluated from the viewpoint of change with time. This evaluation is performed by measuring the change in the rotation speed of the ultrasonic motor when the operation of forward rotation for 1 second, reverse rotation for 1 second, and stop for 2 seconds is repeated 300,000 cycles using a drive circuit. Experiments were performed with different surface roughness. Table 3 shows the results.

[0027]

[Table 3]

As can be seen from the results of Table 3, when the surface roughness of the moving body contact portion is larger than 2 μm (3 μm, 4 μm), the rotational speed changes greatly and the rotational speed increases with the passage of time. . This is because when the surface roughness of the surface of the moving body contact portion is rough at the initial stage, the contact state having the same uniformity as that of the contact surface between the vibrating body and the moving body after being driven for a long time is set to the driving state. It is difficult to achieve in the initial stage, and gradually changes to a uniform contact state due to the projection surface (contact surface) of the vibrating body and the surface of the contacting portion of the moving body becoming familiar with each other over time. It is thought to be due to.

Therefore, by setting the maximum surface roughness of the surface of the moving body contacting portion to 2 μm or less, it is possible to realize a uniform contact between the vibrating body and the moving body from the initial state, which makes it possible to achieve long contact. It is possible to realize a small-sized ultrasonic motor in which the change in motor characteristics is small even when driven for a long time.

Although specific embodiments have been described above, it is possible to make various modifications to these embodiments when implementing the present invention. For example, the moving body may be formed by cutting from a resin block instead of injection molding. In addition, the carbon fiber content of the carbon fiber reinforced resin forming the moving body can be adjusted according to the pressure applied to the ultrasonic motor and the like.

When the carbon fiber content is less than 5% by weight, the effect of improving the rigidity of the moving body is insufficient, and the wear resistance of the contact portion of the moving body is insufficient. On the other hand, if the carbon fiber content exceeds 50% by weight, the molding becomes difficult and the mechanical strength of the molded moving body becomes brittle, although it depends on the molding method or the fluidity of the resin. Therefore,
The carbon fiber content is preferably in the range of 5 to 50% by weight. Furthermore, the material properties required for the moving body,
When comprehensively judging the moldability of the moving body, the cost of the moving body, etc., it is more preferable that it is within the range of 15 to 35% by weight.

The resin used for the carbon fiber reinforced resin is not limited to PEEK resin or PPS resin, but polyimide, polyamide or the like can be used. Further, the moving body may be formed using not only carbon fiber reinforced resin but also reinforced resin such as glass fiber or metal fiber.

[0033]

As described above, according to the present invention, by devising the structure of the moving body, in particular, the shape of the surface of the contact portion facing the protrusion of the vibrating body, the influence of the external load can be reduced. It is difficult to receive the vibration, and it is possible to maintain a uniform contact state between the vibrating body and the moving body. As a result, it is possible to provide a small ultrasonic motor that suppresses the generation of noise and is efficient. . Further, by polishing the surface of the contact portion to have a maximum surface roughness of 2 μm or less, it is possible to reduce a change with time in the contact state between the vibrating body and the moving body.

[Brief description of drawings]

FIG. 1 is a sectional view showing a configuration of a main part of an ultrasonic motor according to an embodiment of the present invention.

FIG. 2 is a partially enlarged sectional view showing a contact state between a vibrating body and a moving body of the ultrasonic motor of FIG.

FIG. 3 is a cross-sectional view showing a configuration of a main part of a conventional ultrasonic motor.

FIG. 4 is an explanatory diagram showing the operation principle of the ultrasonic motor.

5 is a partially enlarged cross-sectional view showing a contact state between a vibrating body and a moving body of the ultrasonic motor of FIG.

[Explanation of symbols]

 11 Elastic Substrate 11a Projection Part 12 Piezoelectric Body 13 Vibrating Body 14 Output Extraction Section 16 Moving Body 16a Main Body Section 16b Contact Section S Contact Surface

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Osamu Kawasaki 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (6)

[Claims] 1. A vibrating body formed by coupling a piezoelectric body to an elastic substrate having a plurality of protrusions is brought into pressure contact with a moving body, and a traveling wave of flexural vibration is excited in the vibrating body, whereby the vibration is generated. In an ultrasonic motor for driving the moving body via a frictional force between the body and the moving body, the main body of the moving body and the protruding portion of the vibrating body projecting in the axial direction from the outer periphery of the main body. A contact portion having a surface is integrally formed, and a surface of the contact portion facing the protrusion is a surface inclined in a radial direction with respect to the contact surface of the protrusion. Sonic motor. 2. The surface of the contact portion facing the protrusion is inclined in the radial direction so that the inner peripheral side protrudes from the outer peripheral side, and the contact degree between the inner peripheral end and the outer peripheral end as the inclination degree thereof. The ultrasonic motor according to claim 1, wherein the distance difference from the surface is set to be larger than the amplitude value of the flexural vibration excited by the vibrating body and smaller than 10 times the amplitude value. 3. The moving body is formed of a resin molding, and the surface of the contact portion facing the protrusion is finished by polishing to have a maximum surface roughness of 2 μm or less. Ultrasonic motor. 4. The ultrasonic motor according to claim 3, wherein the moving body is made of fiber reinforced resin. 5. The ultrasonic motor according to claim 4, wherein the moving body is made of carbon fiber reinforced resin. 6. The carbon fiber content of the carbon fiber reinforced resin is in the range of 5 to 50% by weight.
The described ultrasonic motor.