JPH0697860B2 - Ultrasonic motor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention excites a bending traveling wave in a stator composed of a ring-shaped piezoelectric element and a vibrating plate, and the rotor is located at the apex of an elliptical locus on the stator surface by the bending traveling wave. The present invention relates to an ultrasonic motor that rotates a rotor by touching.

[Prior Art] Recently, ultrasonic motors have been spotlighted as new motors replacing conventional electromagnetic motors. This ultrasonic motor is not only new in principle, but also has the following advantages over conventional electromagnetic motors.

No central axis required.

Thin and lightweight.

There is no exchange of magnetic effects.

The parts configuration is simple and highly reliable.

Low speed and high torque can be obtained without gears.

Positioning is easy with no backlash.

The rotor rotates, chucks, floats,
There are three possible states.

Thus, various application techniques are being researched in order to make use of these advantages.

FIG. 8 is a diagram showing a typical conventional rotary ultrasonic motor. The principle is that a traveling wave is excited in the metallic toroidal diaphragm 2 integrated with the annular piezoelectric element 1 by the inverse piezoelectric effect, and the rotor 3 is brought into contact with the apex of the backward elliptical motion locus of each surface point generated by this. By pressing and arranging, the rotor 3 is rotated as shown by arrow A. The method of exciting the traveling wave will be described below.

FIG. 9 is a diagram showing a polarization state of a piezoelectric element constituting a general ultrasonic motor, and corresponds to a diagram seen from the lower side of FIG. The ring-shaped piezoelectric body is polarized so that the polarization directions are alternately opposite to each other, or a plurality of divided piezoelectric elements are arranged so that the polarization directions are opposite to each other. In such an arrangement, one pair of adjacent polarization directions that are opposite to each other corresponds to one wavelength λ. Then, 3 / 4λ, 1 / 4λ-long unpolarized portions 1a, 1b are arranged at positions different by 180 °, and nλ polarization pairs are arranged symmetrically with respect to the center line connecting them. However, the directions of separation are continuously arranged so that the polarization directions are alternately opposite to each other in the circumferential direction.

Of these polarized arrangements, the surface not in contact with the left half diaphragm sandwiching the 3 / 4λ, 1 / 4λ unpolarized parts 1a, 1b is covered with one electrode as shown in Fig. 10. One side common electrode
4a, and the surface that is not in contact with the right half diaphragm is
As shown in FIG. 10, it is covered with another electrode, and this is used as another one-side common electrode 4b. The electrode 4c on the side of the vibration plate 2 is electrically connected to the vibration plate 2 and is commonly used as the ground side electrode of all the piezoelectric elements.

The electric signal input terminal to the above structure has a structure having three terminals a, b and c as shown in FIG. When driving a structure having such a polarization arrangement and electrode arrangement, there is a π / 2 phase difference between terminals ac and bc, and λ,
An electric signal having a natural frequency ω determined by the inner and outer diameters of the ring, the thickness, the average elastic constant of the piezoelectric ceramics and the diaphragm, and the density is input. Now, when a voltage applied between the terminals a-c and V _o sin .omega.t, so that V _o cos .omega.t becomes voltage is applied between the terminals b-c.

On the other hand, the displacement y at a certain annular point due to the traveling wave is generally represented by y = A _sin (cp-ωt) (1). Where A is the maximum displacement, c is 2π / λ, ω
Is the natural frequency described above, and p is the position of a certain point in the annular shape.

From the formula (1), y = A _sin 2π / λp _cos ωt + A _sin (2π / λp−π /
2) _sin ωt (2) Therefore, if the vibration y ₁ = A _sin 2π / λp _cos ωt and the vibration y ₂ = A _sin 2π / λ (p−λ / 4) _sin ωt are superposed at the point p, a traveling wave can be obtained. . The time terms sin ωt and cos ωt are vibrations whose phase is shifted by π / 2 at point p, and sin 2πp / λ
And sin 2π / λ (p−λ / 4) mean that the position is shifted by λ / 4. In FIG. 9, the electrode arrangement is λ / 4,3λ
The reason for having a / 4 unpolarized portion is based on the above reason.

A traveling wave can be obtained by shifting the electrode arrangement by λ / 4 as described above and by shifting the electrical input signal by π / 2.

Next, in such a traveling wave excited state, each point on the surface in contact with the rotor is as shown in FIG. 11 in the traveling direction displacement component x _{P of} the traveling wave and the displacement component y _P perpendicular to the surface. Drawing an elliptical locus will be described. The vibration of the traveling wave is a plate wave obtained by bending vibration due to the bonding of the piezoelectric ceramic and the metal plate. If the bending is the same bending along the plate thickness direction, the displacement component of the surface point p
y _P is y _P = A _sin (2π / λ x _P −ωt) −e (1− _cos θ _P ) ...
It is expressed as (3). Where θ _P is the angle between the x-axis and the axis perpendicular to the neutral axis of the annular body at point p, and e is 1 / th of the plate thickness.
Is 2. now, , And the thus equation (3) becomes _{y P ≒ A sin (2π /} λx P -ωt) ... (4). Also, the displacement component x _P is As _{X P = e sin θ P ≒} eθ is a _P, (4) from equation _{θ P = dy P / dx P} = A ccos (2π / λX P -ωt) x P = Ace cos (2π / λt P - ωt) (5) Therefore, it can be seen from equations (4) and (5) that (λx _P / 2Aeπ) ² + (y _P / A) ² = 1 (6), and an elliptical locus is drawn. Since the vertices of this elliptical locus are always oriented in the same direction, the rotor grounded at the vertices of the elliptical locus moves.

Here, as can be seen from the above description, the stator obtained by joining the piezoelectric element and the metal plate needs to be fixed to a specific portion of a device using the ultrasonic motor. For example, considering a camera barrel as a device to be used, the stator needs to be fixed to a portion that is not involved in the movement of the barrel.

FIG. 12 is a model diagram in which the ultrasonic motor 10 is incorporated in the camera. The ultrasonic motor 10 has a stator in which a piezoelectric element 11 and a vibrating plate 12 are joined together, and is bonded and fixed to an ultrasonic motor mount portion 15 integrated with a lens barrel 14, and the rotor 13 contacts the surface of the vibrating plate 12. It has become like. In FIG. 12, 16 is a taking lens and 17 is a linear moving element.

[Problems to be Solved by the Invention] As described above, the vibrating portion of the ultrasonic motor 10 is a bimorph in which a piezoelectric element and a vibrating plate are integrated. That is, the bending displacement is used as the traveling wave of the plate wave, not the Rayleigh wave. Therefore, the traveling wave moves along the entire thickness direction of the annular plate, and the surface on the mount portion 15 side in FIG. 12 also vibrates similarly. That is, as also shown in FIG. 11, the y _P component of the spheroidal motion has the same magnitude as the surface even on the mount side surface. Therefore, when the surface having such a state contacts the mount portion 15, the ultrasonic motor 10 and the mount portion 15
Depending on the difference in acoustic impedance from 15, the vibration energy will escape. For example, when the ultrasonic motor 10 is fixed to the aluminum mount portion 15, most of the vibration energy escapes, the efficiency is significantly reduced, and the mount portion 15 is also deformed. Thus ultrasonic motor 10
Efficiency depends on which material is fixed to the mount portion 15. Ideally, it is desired that vibration energy does not leak to the mount side at all.

Therefore, the present invention prevents ultrasonic vibration from leaking to the mount portion side such as the lens barrel regardless of the material of the mount portion,
An object of the present invention is to provide an ultrasonic motor having a holding structure capable of driving the ultrasonic motor with high efficiency.

[Means for Solving Problems] The ultrasonic motor of the present invention is configured as follows in order to solve the above problems and achieve the object.

In an ultrasonic motor that excites a bending traveling wave in a stator composed of an annular piezoelectric element and a vibration plate, and contacts the rotor with an apex of an elliptical vibration locus on the stator surface due to the bending traveling wave to rotate the rotor, Hemispherical recesses provided in at least three locations on the outer peripheral surface of the stator, where the displacement component in the traveling direction of the bending traveling wave is zero, and on the outer peripheral side of the stator, provided on the stator. A holding member having a hemispherical concave portion at a position facing the hemispherical concave portion; and a spherical member housed in the hemispherical concave portions of the stator and the holding member facing each other. .

[Operation] By taking such means, it is possible to suppress the leakage of ultrasonic vibration energy as much as possible.

The outline of the present invention will be described below. FIG. 1 (a) is a diagram showing a circular ultrasonic motor 20 and a part of it cut out, and an ellipse whose displacement at the apex is opposite to the traveling direction of ultrasonic waves. The locus of motion and the rotor mounted on it are drawn. Further, FIG. 3B shows a state in which a part thereof is further cut out. Since the traveling wave is a plate wave as shown in FIG. 6B, each point of the vibrating body draws the same elliptical locus on both front and back surfaces. Incidentally Focusing on the central portion of the thickness direction line, as shown in FIG. (B), although the displacement y _P in the vertical direction has a size not different from the front and back end portions, of the horizontal displacement x _P Is zero.

In the present invention, the portion N where the horizontal displacement x _P is zero is used as the holding portion of the stator in the ultrasonic motor 20.

On the other hand, FIG. 2 is an enlarged view of a part of the polarized arrangement of the piezoelectric element 1 shown in FIG. What should be noted here is that the bimorph formed by the piezoelectric element 1 and the diaphragm 2 has an arc shape. As is well known, the bending displacement amount Δy of the piezoelectric bimorph is expressed by the following equation.

Δy = 3l ² · d ₃₁ / 2t ² · V Here, 1 is the length of the bimorph, t is the thickness, d ₃₁ is the piezoelectric constant, and V is the applied voltage. As can be seen from this equation, when the bimorph has an arc shape, l in the above equation differs between the inner circumference and the outer circumference. Therefore, it can be seen that there is a difference in amplitude if d ₃₁ , t, and V do not change. Such a situation occurs over the entire circumference of the annulus, and since the mounted rotor is in contact with only the outer peripheral portion, conventionally, the efficiency was remarkably adversely affected. However, in the present invention, since the central portion N is held as described above, the amplitude difference between the inner and outer circumferences is reduced, the contact area between the rotor and the stator is increased, and as a result, the efficiency is improved.

[Embodiment] FIGS. 3 to 5 are views showing a first embodiment of the present invention.
As shown in FIGS. 3 and 4, a stator (S) in which a piezoelectric element 21 having a polarization arrangement as shown in FIG. 9 and a metal vibrating plate 22 of brass, stainless steel, titanium, aluminum or the like are joined. Are plural (3 in this example) on the inner circumference of the lens barrel 24.
It is mounted through the micro ball (ball bearing) 25 of. The mounting method is the metal diaphragm of the stator (S).
The N portion of the outer peripheral surface of 22 shown in FIG. 1 (b), that is, there is the amplitude in the vertical direction y _P , but the diameter is approximately equal to w around the point where the amplitude in the horizontal direction x _P is zero. 3 recesses
Provide more than one. Then, the ball 25 is put in the recess so that the ball 25 engages with the recess of the stator holding portion of the lens barrel 24.

FIG. 5 shows the stator (S) shown in FIGS. 3 and 4.
It is the figure which mounted the rotor 23 (R) on the top. Rotor 23
(R) is pressed toward the stator (S) side by applying the tightening force of the screw 26 attached to the stator mount portion of the lens barrel 24 to the outer peripheral tapered surface via the pressing element 27 and the ball bearing 28. ing. It should be noted that the structure is such that a screw lock 29 is provided and fixed in a state where the screw pressure is optimized.

With this structure, the stator (S) is prevented from moving in the circumferential direction, that is, the x _P direction, and the stator (S) is prevented.
And the rotor (R) can be reliably rotated by pressure contact with the rotor (R).

On the other hand, conventionally, the displacement in the y _P direction was larger in the outer peripheral portion than in the inner peripheral portion, so that the rotor and the rotor (not shown) were not effectively contacted over the entire surface. However, in the case of the stator (S) like this structure, the displacement in the y _P direction is suppressed, so the displacement difference between the inner and outer circumferences becomes smaller, and the rotor (R) and the stator (S) are in full contact. Produces the effect. Thus, vibration leakage is prevented and efficiency is significantly improved.

FIG. 6 shows a second embodiment of the present invention. This embodiment differs from the first embodiment, 1 / 2w in y _P direction on the inner peripheral surface of the lens barrel 24
mm or less, with integrally provided with protrusions 31 having a size of 0.5~2mm in x _P direction, the outer peripheral surface of the vibration plate 22 of the stator (S), about w mm in y _P direction, the x _P direction 0.5 The point is that a recess 32 of about 2 mm is provided, and the projection 31 fits into the recess 32. The rotor installation status is the same as in FIG. The effect is almost the same as that of the first embodiment.

FIG. 7 shows a third embodiment of the present invention. This embodiment is different from the first embodiment in that a pin 41 is inserted into a hole provided in a lens barrel 24, and the tip of this pin 41 is inserted into an insertion hole 32 of a diaphragm 22 to obtain an appropriate insertion amount. By the way, the point is that the lock member 43 is used for fixing.

This embodiment has the following effects. Forming the protrusions 31 integrally with the mount portion as in the second embodiment makes it difficult to process the mount portion, but in this embodiment there is no difficulty in processing. The amount of protrusion of the protrusion with respect to the diaphragm 22 determines the degree of reduction in the difference in y _P amplitude between the inner and outer circumferences described in the first embodiment. However, the difference between the inner and outer circumferences of the stator varies depending on the stator. Therefore, it is desirable to adjust the protrusion amount for each stator, but this embodiment has an advantage that the adjustment can be easily performed. Note that FIG. 7 shows a structure in which the tip of the pin 41 is penetrated to the inner peripheral portion of the stator (S) to extremely reduce the amplitude difference between the inner and outer circumferences. The rotor installation status is the same as in FIG.

All of the above three embodiments have the effect of preventing the leakage of vibration energy and improving the efficiency, and also have the advantage that they can be mounted in a smaller space than the conventional mounting method.

It should be noted that the present invention is not limited to the above-mentioned embodiments, and can be variously modified without departing from the gist of the present invention.

EFFECTS OF THE INVENTION According to the present invention, among the vibration components of the plate wave traveling wave of the stator, the portion where the circumferential component amplitude x _P is zero is coupled to the stator mount portion such as the lens barrel. , Plate wave traveling wave vibration does not leak to the mount side, and the inner and outer peripheral surfaces y _P
It is possible to provide an ultrasonic motor that can reduce the directional amplitude difference and increase the contact area with the rotor, resulting in high efficiency and space saving.

[Brief description of drawings]

1 (a) (b) and FIG. 2 are views for explaining the outline of the present invention, FIGS. 3-5 are views showing a first embodiment of the present invention, and FIG. 3 is a mirror. The front view which shows the attachment structure of the stator with respect to a cylinder, FIG. 4 is sectional drawing of the arrow line view of FIG. 3, 5th
The drawing is a sectional view in which the rotor is combined with FIG. Sixth
FIG. 7 and FIG. 7 are partial sectional views of the second and third embodiments of the present invention, respectively. 8 to 12 are diagrams showing a conventional technique, FIG. 8 is a conceptual diagram of a rotary ultrasonic motor, FIGS. 9 and 10 are diagrams showing a structure of a piezoelectric element, and FIG. 11 is a diagram showing rotation. FIG. 12 is a diagram showing the principle, and FIG. 12 is a diagram showing an example of mounting an ultrasonic motor. 20 ... Ultrasonic motor, 21 ... Piezoelectric element, 22 ... Vibration plate,
23 …… rotor, 24 …… barrel, 25 …… ball, 26 …… screw, 27 …… presser, 28 …… ball bearing, 29 …… screw lock, 31 …… protrusion, 32 …… recess, 41… ... pin, 42 ...
… Insertion hole, 43 …… Lock material.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takashi Kodama 2-43-2 Hatagaya, Shibuya-ku, Tokyo Inside Olympus Optical Co., Ltd. (56) Reference JP-A-59-213286 (JP, A) JP 61-49672 (JP, A) JP-A-61-262091 (JP, A)

Claims (1)

[Claims] Claim: What is claimed is: 1. A stator comprising a ring-shaped piezoelectric element and a vibrating plate is excited by a bending traveling wave, and the rotor is rotated by contacting the apex of an elliptical vibration locus on the surface of the stator by the bending traveling wave. In the sonic motor, hemispherical recesses provided in at least three places where the displacement component in the traveling direction of the bending traveling wave on the outer peripheral surface of the stator is zero, and the outer peripheral side of the stator, A holding member having a hemispherical recess at a position facing a hemispherical recess provided in the stator; and a spherical member housed in the hemispherical recesses of the stator and the holding member facing each other. An ultrasonic motor characterized by the above.