JPH09172790A - Ultrasonic motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the abrasion of a relative motion member caused by the ridge of an oscillator so as to enhance the durability of an ultrasonic motor, by bringing a circular relative motion member into compression-contact with an oscillator so that it may not contact with at least one ridge of the oscillator. SOLUTION: A rotor 3 is rotated, with its center eccentric from that of an oscillator S. The frictional contact face with which the rotor 3 is contacting of the surface 1a of the oscillator S shifts within the range of δ in quantity of eccentricity in diametrical direction on the surface by the rotation of the rotor 3, and every hour the contact face with the oscillator S changes. This way, the contact face of the rotor 3 on the surface of the oscillator S changes, so one place of the oscillator S is never shaved by abrasion, and the whole of the surface 1a of the oscillator S can be used efficiently.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic motor that uses vibration to obtain a driving force.

[0002]

2. Description of the Related Art A conventional ultrasonic motor has a structure in which a vibrator composed of a piezoelectric body and an elastic body and a rotor are in pressure contact with each other, as described in, for example, Japanese Patent Application Laid-Open No. 59-204477. have. The piezoelectric body causes the elastic body to vibrate to rotate the rotor.

[0003]

Since the ultrasonic motor drives the rotor by the frictional force between the vibrator and the rotor,
There has been a phenomenon that the rotor is severely worn at the portion that contacts the ridge of the vibrator. Therefore, the desired performance of the ultrasonic motor cannot be obtained, which is one of the causes of lowering the durability. The present invention aims to solve such conventional problems.

[0004]

To achieve the above object, according to the present invention, a ring-shaped oscillator and a ring-shaped relative device that makes a relative motion by being in pressure contact with the oscillator. An ultrasonic motor comprising a moving member, wherein the relative moving member is pressure-contacted so as not to contact at least one ridge line portion of the vibrator.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1A is a plan view of an ultrasonic motor according to an embodiment of the present invention, and FIG. 1B is a sectional view of the ultrasonic motor. FIG. 2 is a sectional view when the ultrasonic motor is unitized. FIG. 3A and FIG. 3B are structural views showing the shape of the rotor of the ultrasonic motor. FIG. 4 is an explanatory diagram showing the driving principle of the ultrasonic motor. FIG. 5 is a graph showing a characteristic curve of the input frequency and the amplitude of the ultrasonic motor.

As shown in FIGS. 1A and 1B, a vibrator S is a piezoelectric element 2 as an electromechanical conversion element and an elastic body that is excited by the piezoelectric element 2 to generate a traveling wave (surface wave). It consists of 1. Then, the elastic body 1 is placed on the vibrator S.
A ring-shaped rotor 3 that is in pressure contact with
And the ring-shaped rotor 3 constitute an ultrasonic motor. The ring-shaped rotor 3 is a ring having a constant width,
The center O ′ is provided so as to be eccentric with respect to the center O of the vibrator S. The ring-shaped rotor 3 is arranged so as to rotate about the center O of the vibrator S as a rotation center. At this time, the ring-shaped rotor 3 rotates on the fixed vibrator S, but swings around the vibrator S with an arbitrary eccentricity δ. In this way, the rotor 3
When the rotor 3 is rotated with the center of the vibrator S and the center of the vibrator S eccentric to each other, in the cross-sectional view shown in FIG.
The contact portion 1b between the vibrator S and the rotor 3 on the surface 1a of
With the rotation of the rotor 3, a single vibration with a single amplitude of the eccentricity amount δ with respect to the rotation center O is performed. That is, the frictional contact surface with which the rotor 3 is in contact on the surface 1a of the vibrator S moves radially within the range of the eccentricity amount δ on the surface 1a by the rotation of the rotor 3 and vibrates momentarily. This means that the contact surface with the child S has changed. Therefore, unlike the conventional case, in which the contact surface between the rotor 3 and the vibrator S is always in frictional contact without changing, unlike the conventional case, the contact surface of the rotor 3 on the surface 1a of the vibrator 3 is constantly changing. Therefore, one portion of the vibrator S is not shaved by abrasion, and the entire surface 1a of the vibrator S can be efficiently used. The eccentricity δ is arbitrarily determined within a range satisfying the following condition.

This condition is set so that when the rotor 3 is eccentrically rotated, the ring of the rotor 3 always rotates on the surface 1a of the vibrator S without protruding. At this time, the rotor 3 comes into contact with the vibrator S without making contact with the ridge lines on the inner circumference side and the outer circumference side of the vibrator S. Therefore, abrasion of the rotor 3 due to contact with the ridge portion can be prevented, and the durability of the ultrasonic motor is improved.

Here, the outer diameter of the vibrator S is D, the inner diameter is d, the outer diameter of the rotor 3 is D ', and the inner diameter is d'.
Is a and the ring width of the ring-shaped rotor 3 is b. At this time, the conditions are:

[0009]

[Equation 1]

The amount of eccentricity δ is set as follows. FIG.
FIG. 2 is a structural diagram in which the ultrasonic motor of FIG. 1 is configured in a unit. The ultrasonic motor has cylindrical cases 10a and 10b.
Is housed inside. A biasing means (for example, an elastic member such as rubber) 6 is arranged on the bottom of the case 10a, and a disc 5 for evenly transmitting the biasing force of the biasing means 6 is provided on the biasing means. A transducer S of the ultrasonic motor is placed on the disk 5.
A cushioning material 4a for protection that absorbs the vibration is fixedly provided.
Then, the transducer S of the ultrasonic motor is placed on the protective cushioning material 4a.
Is installed.

The center of the vibrator S is located at the cases 10a and 10
It is arranged so as to coincide with the center of b. Further, on the inner diameter side of the vibrator S, there is provided a support portion 7 configured to prevent the vibration of the ultrasonic motor from propagating to the case 10a even when fixed to the inner cylinder of the case 10a. This support part 7
Is formed in a tubular shape so as to project from the inside of the vibrator S and fit into the inner cylinder of the case 10a as shown in FIG. The support portion 7 positions and fixes and supports the vibrator 3 with respect to the case 10a, and may be formed integrally with the vibrator S or may be formed as a separate member.

A rotor 3 whose center is eccentric by an eccentricity δ is arranged on the vibrator S, a cushioning material 4b for absorbing the vibration is provided on the rotor 3, and a ring is further provided on the cushioning material 4b. The member 8 is fixed. The ring member 8 is the rotor 3
It is arranged in the case 10b through a ball race 9 for smoothly rotating. This ring member 8
Has a guide groove provided concentrically with the center of the case 10b such that the centers of the cases 10a and 10b are the centers of rotation. The ball race 9 arranged around the center of the case 10b is fitted into the guide groove so that the ball race 9 is rotatable. That is, the shape of the ring member 8 is an eccentric ring in which the side fixed to the rotor 3 is eccentric, and the side in contact with the case 10b coincides with the center of the vibrator S. Therefore, in order to extract the power from the unitized ultrasonic motor, the power of the ring member 8 rotated by the ultrasonic motor may be appropriately extracted according to the device using the unit. For example, if this unit is used as a taking lens barrel of a camera, it can be used for driving diaphragm blades and lenses.

As an embodiment of the present invention, the case where the center of the rotor 3 is eccentric with respect to the center of the vibrator S has been described, but in addition to this, FIG. 3A and FIG. The ring-shaped rotor shown in B) is conceivable. FIG.
As shown in (A), the ring-shaped rotor 31 may be formed in a ring shape in which the centers of the outer diameter and the inner diameter are eccentric. Further, as shown in FIG. 3 (B), the ring-shaped rotor 32 is
It may be formed in an elliptical shape.

FIG. 4 shows the operating principle of the vibrator S and the rotor 3. The vibrator S causes bending vibration by the piezoelectric element 2 and a traveling wave is generated on the surface. At this time, the traveling wave of the oscillator S advances in the direction of arrow P, and the particle P1 on the surface makes an elliptic motion. When the rotor 3 is pressed against the oscillator S, the rotor 3 generates a surface wave by the oscillator S, the traveling direction thereof is the direction of arrow Q, and the particle Q1 on the surface similarly performs an elliptic motion. Here, the oscillator S and the rotor 3 change the amplitude of the vibration that generates the surface wave depending on their materials and shapes, and consider the following three cases of the amplitude of the oscillator and the rotor.

First, when the amplitude AS of the vibrator S is larger than the amplitude A3 of the rotor 3, that is, in the state of FIG. 4, the contact between the vibrator S and the rotor 3 is caused by the wave peak of the vibrator S. And the wave trough of rotor 3. In this case, at the contact point between the oscillator S and the rotor 3, the respective particles P1 and Q1 are
The movement of the motor is in the opposite direction, and the driving force of the ultrasonic motor is increased.

Secondly, when the amplitude AS of the vibrator S and the amplitude A3 of the rotor 3 are equal, the vibrator S and the rotor 3 are in contact with each other over the entire surface. In this case, since the motions of the particles in the peaks and the troughs of the waves of the oscillator S are opposite to each other, the driving forces cancel each other out. Thirdly, when the amplitude AS of the vibrator S is smaller than the amplitude A3 of the rotor 3, the contact between the vibrator S and the rotor 3 is caused by the wave troughs of the vibrator S and the wave peaks of the rotor 3. become. In this case, at the contact point between the oscillator S and the rotor 3, the movements of the respective particles P1 and Q1 are in opposite directions, the driving force of the ultrasonic motor becomes large, and the movement direction is opposite to that in FIG. Become.

Considering the vibration isolation between the vibrator S and the rotor 3, the rotor 3 must transmit its rotation to an external mechanism, and it is more difficult to perform the vibration isolation than the vibrator S. Therefore, considering which one of the first case and the third case where the driving force is large is selected, in the first case where the amplitude A3 of the rotor 3 is smaller than the amplitude AS of the vibrator S, It would be better. Therefore, a method of making the amplitude A3 of the rotor 3 smaller than the amplitude AS of the vibrator S will be described below.

FIG. 5 shows the relationship between the respective frequencies and amplitudes, where fS is the resonance frequency of the vibrator S and f3 is the resonance frequency of the rotor 3. However, it is assumed that the vibrator S and the rotor 3 have the same amplitude at the resonance point. When the rotor 3 is vibrated at the resonance frequency fS of the vibrator S, the amplitude A3 of the rotor 3 is equal to the amplitude A of the vibrator S.
It is smaller than S. Therefore, when the amplitude of the oscillator S is 1, the amplitude A3 of the rotor 3 is 1
The resonance frequency f3 of the rotor 3 may be designed so as to be / X.

In this embodiment, the center O of the vibrator S is
The ultrasonic motor having a configuration in which the center of the rotor 3 and the center O ′ of the rotor 3 are eccentric has been described, but the present invention is not limited to such a configuration. Also in the ultrasonic motor having a configuration in which the center O of the vibrator S and the center O ′ of the rotor 3 are coincident with each other,
The same effect can be obtained by configuring the relative motion member so that it does not come into contact with the ridge line portion of the vibrator, and it does not relate to the presence or absence of the eccentricity.

[0020]

As described above, according to the present invention, since the relative motion member is in pressure contact with at least one ridge line portion of the vibrator so as not to contact, the relative motion caused by the ridge line portion of the vibrator is achieved. Wear of the parts is reduced. Therefore, the durability of the ultrasonic motor can be improved.

[Brief description of the drawings]

1A is a plan view of an ultrasonic motor according to an embodiment of the present invention, and FIG. 1B is a sectional view of the ultrasonic motor.

FIG. 2 is a cross-sectional view of a unitized ultrasonic motor.

FIG. 3 (A) and FIG. 3 (B) are structural views showing the shape of a rotor of the ultrasonic motor.

FIG. 4 is an explanatory diagram showing a driving principle of an ultrasonic motor.

FIG. 5 is a graph showing a characteristic curve of an input frequency and an amplitude of the ultrasonic motor.

[Description of Signs of Main Parts]

 1 ... Elastic body 2 ... Piezoelectric element 3, 31, 32 ... Rotor S ... Oscillator

Claims (1)

[Claims] 1. An ultrasonic motor comprising: an annular oscillator; and an annular relative motion member that is brought into pressure contact with the oscillator to perform relative motion with the oscillator, wherein: The ultrasonic motor, wherein the relative motion member is pressure-contacted so as not to contact at least one ridge line portion of the vibrator.