JP3155339B2 - Ultrasonic motor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic motor, and more particularly, to an ultrasonic motor in which a vibration generated at a rotor contact portion of a stator is improved.

[0002]

2. Description of the Related Art An ultrasonic motor converts vibrational motion generated when a frequency voltage such as AC is applied to a piezoelectric element into rotational motion or one-dimensional motion. Compared with a conventional electromagnetic motor, no winding is required, so that the structure is simple and compact, and there is an advantage that high torque can be obtained even at low speed rotation.

In general, an ultrasonic motor includes a rotor as a moving body, a stator as a vibrating body, and a supporting member for supporting these.

Among them, the stator is formed by laminating a piezoelectric body such as PZT (lead zirconate titanate) to a vibration elastic body made of a copper alloy or the like. Usually, this piezoelectric body is divided into a large number and polarized alternately in positive and negative directions, and two sets of electrode groups are provided correspondingly. By applying a voltage at a resonance frequency having a phase difference of 90 ° to these two sets of electrodes, two standing waves are synthesized and a plurality of peaks moving in a constant direction in the circumferential direction with time. A traveling wave having a wave is excited on the rotor contact surface. Therefore, by bringing the rotor into contact with the rotor contact surface of the stator, the rotor is driven to rotate in a predetermined direction.

[0005] As a conventional ultrasonic motor of this type, for example, a proposal according to Japanese Patent Application Laid-Open No. 59-201685 is known. In particular, in the ultrasonic motor according to this proposal, by dividing the surface of the vibrating elastic body constituting a part of the stator into a large number of parts, the moving speed of the rotor is increased, and an ultrasonic motor with high driving efficiency can be realized. And

[0006]

Incidentally, in many cases, conventional ultrasonic motors generate longitudinally long elliptical vibrations by a traveling wave on a rotor contact surface of a stator and rotate the rotor in many cases. This is because the rotor is driven to rotate at a low speed and a high torque by generating a vertically long elliptical vibration.

However, it has been confirmed that in this type of ultrasonic motor, not only the stator but also the rotor vibrates in accordance with the vibration of the stator. Therefore, as before,
If the rotor contact surface of the stator is made to elongate a vertically long elliptical vibration trajectory, the rotor side contacts not only the top of the elliptical vibration but also points with different vibration speeds at multiple points and moves at each contact point Different speeds cause transmission loss of traveling wave energy.

Therefore, although the conventional ultrasonic motor has an advantage that a high torque can be obtained with a simple structure,
There is a problem that the output efficiency of the motor is not sufficient.

The present invention has been made in view of such conventional problems, and has as its object to reduce the output efficiency to about 40 to 50% without impairing the advantages of the ultrasonic motor.
An object of the present invention is to provide an ultrasonic motor having a high output efficiency of about 50% .

[0010]

In order to achieve the above object, the present invention includes a vibration elastic body having a plurality of projections formed in a ring on a front surface side and a piezoelectric element provided on a back surface side,
A vibrating elastic body including a stator that generates a traveling wave in the vibrating elastic body by applying a predetermined voltage to the piezoelectric element, and a moving body that moves in a predetermined direction by the traveling wave generated in the vibrating elastic body; TB, the thickness of the protrusion
Assuming that the height is tS and the wavelength of the traveling wave is λ, K =
(2π / λ) (tS + tB / 2) is almost 1.
The vibration of the mass on the surface of the rotor contact portion of the stator caused by the traveling wave is formed to have a perfect circle or a locus close to a perfect circle, and the output efficiency is about 40 to 50%.
It is characterized by having been done.

In another invention , a plurality of projections are provided on the surface side.
A vibrator formed in a line in a ring and having a piezoelectric element on the back side
A predetermined voltage is applied to the piezoelectric element including a dynamic elastic body.
For generating a traveling wave in the vibrating elastic body by
In a predetermined direction by the traveling wave generated in the vibrating elastic body.
And a moving body that moves.
B, the height of the protrusion is tS, and the wavelength of the traveling wave is λ
Then, the value of K = (2π / λ) (tS + tB / 2) is formed to be approximately 1, and the state generated by the traveling wave is obtained.
The vibration of the mass on the rotor contact surface of the rotor
Is formed to have a locus close to a perfect circle, and the output efficiency is 50%
It is characterized by the degree .

[0012]

In the ultrasonic motor according to the present invention, since the mass point on the surface side of the vibrating elastic body is formed so as to have a perfect circle or a locus close to a perfect circle, the moving body vibrates only at the top of the stator and the elliptical vibration. Instead, even in the case of multipoint contact, the moving speed of the mass point at each contact point becomes substantially equal. Therefore, the moving body can be efficiently moved in a predetermined direction using the traveling wave generated on the stator side.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 2 schematically shows an annular ultrasonic motor according to an embodiment of the present invention. The ultrasonic motor according to the embodiment includes a stator 100 and a rotor 200 as a moving body that is rotationally driven by a traveling wave generated in the stator 100.

The stator 100 includes a piezoelectric ceramic 12 as a piezoelectric element formed in a ring shape, and a vibration elastic body 10 to which the piezoelectric ceramic 12 is adhered and fixed on the back side. As shown in FIG. 3, the piezoelectric ceramics 12 is divided into a large number in the circumferential direction and polarized positively and negatively alternately, and two sets of electrodes are provided correspondingly. Then, a sine wave output from the oscillator 30 is applied to these two sets of electrodes via the amplifier 32, and a cosine wave whose phase has been shifted by 90 ° by the phase shifter is applied via the amplifier 36. As a result, two standing waves composed of a sine wave and a cosine wave are synthesized, and a traveling wave having a plurality of peaks moving in a constant direction with time in the circumferential direction is excited. The frequency at this time is determined by detecting the signal of the feedback (FB) terminal provided on the pressed-body ceramics 12 by the frequency tracking circuit 38 and feeding it back to the oscillator 30 so that the generated voltage, that is, the amplitude value becomes constant. Controlled.

The vibrating elastic body 10 is used for efficiently transmitting vibration generated in the piezoelectric ceramics 12 and vibrating. The surface of the vibrating elastic body 10 is provided with a plurality of grooves 16 in a radial manner to increase the amplitude. ing. Therefore, the elliptical vibration in a predetermined direction is efficiently generated on the surface of the convex portion 14 of the vibration elastic body 10.

The rotor 200 comprises a ring 22 and a friction material 2 bonded and fixed to a stator contact surface of the ring 22.
0, and the friction material 20 is formed so as to contact the surface of the vibration elastic body 10 with a predetermined pressure.

As a result, the driving by the traveling wave generated in the vibration elastic body 10 is efficiently performed via the friction material 20 by the rotor 2.
00, the rotor 200 is rotationally driven in a predetermined direction.

At this time, in the conventional ultrasonic motor, FIG.
As shown in (1), the mass point on the stator surface is drawn in a vertically long locus.

Such an elliptical vibration does not cause any problem since it contacts only the top of the vibration when the vibration does not occur on the rotor 200 side.

However, in practice, since vibration also occurs on the rotor 200 side, the rotor 200 comes into multipoint contact not only at the top of the elliptical vibration but also at points other than the top where the vibration speed differs. The difference in the moving speed at each contact point has caused the motor output to decrease as described above.

On the other hand, the vibration of the present invention
As shown in FIG. 5, a perfect circle or a vibration close to a perfect circle is generated on the surface of the stator 100. Thereby, the rotor 2
Vibration also occurs on the side of the stator 100 and the rotor 20.
Even when 0 and multipoint contact other than the top of the vibration,
Since the moving speed of each point is almost the same, the stator 1
The traveling wave generated on the 00 side can efficiently rotate and drive the rotor 200.

Here, as shown in FIG. 4, if the vertical diameter of the ellipse is l ₁ and the horizontal diameter is l ₂ , the shape K of the elliptical vibration is K =
It is represented by l ₂ / l ₁ .

FIG. 6 shows a schematic cross section of the elastic vibrating body 10. The base plate thickness of the elastic vibrating body 10 is t _B ,
The depth (referred to as a slit depth) of the groove 16 sandwiched between the protrusions 14 is represented by t _S, and the wavelength of the generated traveling wave is represented by λ.
In this case, the distance T from the neutral axis of the vibration of the vibration elastic body 10 to the stator surface (the rotor contact surface) is approximately represented by the following equation.

T = t _S + t _B / 2 The shape of the elliptical vibration locus generated on the rotor contact surface is given as a composite wave of the sine wave standing wave and the cosine wave standing wave. Is given by the following equation.

K = (2π / λ) × (t _S + t _B / 2) In FIG. 1, two types of vibration wave motors were measured, and the output efficiency of the motor with the value of K varied was measured. Values are shown. In the actual measurement data, the position where K = 1 is a true circular vibration, and a region where K is smaller than 1 is a vertically long elliptical vibration and a region where K is larger than 1 is a horizontally long elliptical vibration.

As is clear from the experimental data shown in FIG. 3, the rotor 200 can be driven to rotate efficiently by making the mass of the contact surface of the stator of the rotor 100 scribe the vibration locus in a perfect circle or a perfect circle. It will be understood that there is.

The present invention is not limited to the above embodiment, and various modifications can be made within the scope of the present invention.

Further, in the above embodiment, the case where the moving body is formed as a rotor has been described as an example. However, the present invention is not limited to this. It can also be applied to the ultrasonic motor.

[0030]

As described above, according to the present invention,
The rotor contact surface of the stator, the mass point, by generating so as to draw a substantially true circle vibration trajectory can be moved mobile efficiently in a predetermined direction, 40-50%
There is an effect that an ultrasonic motor with high efficiency of about 50% or about 50% can be provided.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a change in motor output efficiency measured by changing a shape of an elliptical vibration locus generated on a rotor contact surface of a stator in an ultrasonic motor.

FIG. 2 is a schematic perspective explanatory view of the ultrasonic motor of the present embodiment with a part cut away.

FIG. 3 is an explanatory diagram of a drive circuit of the ultrasonic motor shown in FIG.

FIG. 4 is an explanatory view showing the principle of operation of a conventional ultrasonic motor.

FIG. 5 is an explanatory diagram illustrating the operation principle of the ultrasonic motor according to the present embodiment.

FIG. 6 is a schematic cross-sectional explanatory view of a vibration elastic body of the ultrasonic motor shown in FIG. 2;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Vibration elastic body 12 Piezoelectric ceramic 14 Convex part 16 Groove part 20 Friction material 22 Ring 100 Stator 200 Rotor

Claims (2)

(57) [Claims] 1. A vibration elastic body in which a plurality of protrusions are formed in a row in a ring on a front surface side and a piezoelectric element is provided on a back surface side,
A stator that generates a traveling wave in the vibrating elastic body by applying a predetermined voltage to the piezoelectric element; and a moving body that moves in a predetermined direction by the traveling wave generated in the vibrating elastic body. Is tB, and the height of the protrusion is tS.
When the wavelength of the traveling wave is λ, the value of K = (2π / λ) (tS + tB / 2) becomes substantially 1.
The vibration of the mass on the surface of the rotor contact portion of the stator caused by the traveling wave is formed to have a perfect circle or a locus close to a perfect circle, and the output efficiency is about 40 to 50%.
An ultrasonic motor characterized in that it has a degree . 2. A method according to claim 1, wherein a plurality of projections are formed in a row on the front surface side in a ring shape, and a pressure is formed on the rear surface side.
A vibration elastic body provided with an electric element, wherein the piezoelectric element
A traveling wave is applied to the vibrating elastic body by applying a predetermined voltage.
A stator for generating a movement in a predetermined direction by the traveling wave generated on the vibration elastic member
Comprising: a movable body that, the, tB the plate thickness of the vibrating elastic member, wherein the height of the projection and tS, and the wavelength of the traveling wave and lambda, K = the (2π / λ) (tS + tB / 2) The value of the stator row generated by the traveling wave
Vibration of the mass on the contact surface
And the output efficiency is about 50%.
An ultrasonic motor characterized in that: