JP2532425B2 - Ultrasonic motor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention excites a bending traveling wave in a stator composed of an annular piezoelectric element and a vibrating plate, and the bending traveling wave excites the apex of an elliptical locus on the stator surface. The present invention relates to an ultrasonic motor that rotates a rotor by contacting the rotor.

[Conventional technology]

Recently, an ultrasonic motor has been spotlighted as a new motor replacing the electromagnetic motor. This ultrasonic motor is not only new in principle, but also has the following advantages over a conventional electromagnetic motor.

Does not require a central axis.

It is small, thin, and lightweight.

There is no transfer of magnetic effects.

Simple component structure and high reliability.

Low speed and high torque can be obtained without gears.

There is no backlash and positioning is easy.

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. 6 is a schematic view of a typical conventional rotary ultrasonic motor. The principle of this ultrasonic motor is that a traveling wave is excited by a bending vibration due to an inverse piezoelectric effect in a metal donut-shaped diaphragm 2 integrated with a ring-shaped piezoelectric element 1, and a backward elliptical locus of a surface mass point generated by this is generated. By arranging the rotor 3 so as to be in contact with the apex, the rotor 3 is rotated as shown by arrow A. The method of exciting the traveling wave will be described below.

FIG. 7 shows a piezoelectric element 1 constituting a general ultrasonic motor.
FIG. 7 is a diagram showing a polarization state diagram of FIG. 6 and corresponds to the diagram seen from below in FIG. The ring-shaped piezoelectric body is polarized so that the polarization directions are alternately opposite to each other like +-+ -..., 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. And 3 / 4λ, 1 / 4λ at 180 ° different positions
The long unpolarized portions 1a and 1b are arranged, and nλ pieces of polarizing bodies are arranged symmetrically with respect to the center line connecting them. However, the polarization direction is continuously arranged so that the polarization direction is alternately opposite in the circumferential direction.

Among such polarization arrangements, 3 / 4λ, 1 / 4λ unpolarized parts 1a, 1b
The surface of the left half that is not in contact with the diaphragm is covered by one electrode, and this is used as one common electrode 4a on one side as shown in FIG. 8, and the surface that is not in contact with the diaphragm of the right half is Another electrode is covered, and this is also used as another one-side common electrode 4b as shown in FIG. The electrode 4c on the diaphragm 2 side is the diaphragm 2
And is commonly used as the ground side electrode of all 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,
As shown in FIG. 7, a 90 ° phase shifter 5 is interposed between one of the terminals a and c and one of the terminals b and c so that they are mutually π / 2.
With a phase difference of λ, wavelength λ, inner / outer diameter of the annulus, thickness,
An electric signal having a natural frequency ω determined by the piezoelectric ceramics and the average elastic constant, density, etc. of the diaphragm is input.

Now, as shown in FIG. 9, the diaphragm 2 and the electrodes on the piezoelectric element are arranged.
When an AC voltage having a frequency ω is applied from the AC power source 6 to 4a or 4b, a bending standing wave is excited in the diaphragm 2. When the AC voltage is applied to the left side portion of the piezoelectric element 1 in FIG. 7, a standing wave having a displacement of y ₁ = Asin2π / λ psinωt (1) is generated on the neutral axis of the diaphragm 2. Be excited. Further, when an AC voltage having a frequency ω whose phase is deviated from the AC voltage by π / 2 is applied to the right side portion of the piezoelectric element 1 in FIG. 7, y ₂ = A standing wave having a displacement of Asin2π / λ (p−λ / 4) sin (ωt−π / 2) (2) is excited.

Therefore, when the AC voltages shown in the equations (1) and (2) are simultaneously applied to the right and left halves of the piezoelectric element 1, y = y ₁ + y ₂ = Asin (2πp / λ−ωt) ... (3) A traveling wave with the following displacement is obtained. A surface traveling wave having the same phase as the neutral axis is also excited on the surface of the diaphragm 2. In such a bending traveling wave of a plate, as shown in FIG. 9, the mass point on the surface makes a backward elliptical motion with respect to the traveling direction of the wave. Therefore, when the rotor 3 is pressed and arranged on the surface of the vibration plate 2 with a certain constant pressure as shown in FIG. 6, the rotor 3 rotates in the direction opposite to the traveling direction of the wave due to the frictional force with the vibration plate 2. It will be.

[Problems to be solved by the invention]

When the bending traveling wave is excited in the diaphragm 2 as described above, vibration (displacement) in the mode as shown in FIG. 10 occurs on the surface of the stator. The broken line 7 in FIG. 10 shows the displacement in the stationary state, and the solid line shows the displacement in the excited state. As can be seen from FIG. 10, in the above mode, all mass points of the ring are vibrating. In such a vibration mode, the driving efficiency is significantly reduced depending on how the stator is supported. Therefore, conventionally, a vibration-proof rubber or the like is arranged on the side opposite to the rotor contact side of the stator so as not to interfere with the above-mentioned vibration, and the stator is held via the vibration-proof rubber or the like. However, if the stator is held via the anti-vibration rubber or the like, the vibration of the stator will leak to the anti-vibration rubber or the like. As a result, there is a problem that the energy loss is large, the driving efficiency of the ultrasonic motor is significantly reduced, and various harmful effects are caused in practical use. Japanese Patent Laid-Open No. 61-49671 discloses a technique in which a supporting pin is provided at the node of the standing wave and the stator is supported by this supporting pin, but there are various problems in practical use.

Therefore, it is an object of the present invention to provide an ultrasonic motor that does not impede the vibration of the stator, does not leak the vibration, and can drive the rotor extremely efficiently without any practical problems.

[Means for solving problems]

In order to solve the above problems and achieve the object, the ultrasonic motor of the present invention is configured as follows. That is,
An annular piezoelectric element which is divided into two parts in a region having an average diameter of an inner diameter and an outer diameter and which is divided into a plurality of parts in the circumferential direction and subjected to polarization, and an annular part which is joined to the piezoelectric element. A vibrating plate, an annular rotor pressed and held by the vibrating plate, and a supporting member for supporting the piezoelectric element or the vibrating plate in the entire region having the average diameter of the inner diameter and the outer diameter of the annular ring. The vibration plate is configured to excite a bending traveling wave having a node in a region over the entire circumference having an average diameter of the inner diameter and the outer diameter of the annular ring to drive the rotor.

[Action]

As a result of taking the above measures, the following effects occur. That is, the piezoelectric element of the annular stator or the diaphragm is
The diaphragm is supported in a region having an average diameter of an inner diameter and an outer diameter, and the diaphragm is a node having a region having an average diameter of the inner diameter and the outer diameter of the ring. Since the bending traveling wave is excited, there is no fear that the generated vibration will be disturbed by the supporting member, and the vibration will not leak to others. Therefore, the driving efficiency is high. And, in particular, since the annular stator is supported in a region (a region existing along the average radius line) over the entire circumference having the average diameter of the inner diameter and the outer diameter of the annular ring, the annular stator is mechanical. Even so, it will be supported in a well-balanced and stable state.

〔Example〕

1 to 3 are views showing a first embodiment of the present invention, and FIG. 1 is a perspective view showing the appearance of the stator 10. As shown in FIG. 1, this stator 10 is the same in appearance as the conventional one, and an annular piezoelectric element 12 is attached to an annular diaphragm 11.
Are integrally joined by means such as adhesion.

2 (a) and 2 (b) are views showing the polarization arrangement of the piezoelectric element 12 in the stator 10 and the stator support means. As shown in FIG. 3A, the piezoelectric element 12 is polarized and arranged in each region of the annular stator 10 which is divided into two by the average radius line L on the annular ring. The right half 8-divided electrode is connected to one terminal (not shown) by means such as vapor deposition, and the left half 8-divided electrode is the same. Thus, as in the case of FIG. 7, the piezoelectric element 12
By applying an AC voltage whose phase is shifted by π / 2, the traveling wave existing on the line L in the mode node is excited. Further, as shown in FIG. 2B, the stator 10 is the average radius line L on the piezoelectric element 12 side.
It is supported by an L-shaped support member 13 having its tip abutted on top. The support member 13 is fixed on the base 15 with screws 14.

In this embodiment, when an AC voltage having a phase shift of π / 2 is applied to the piezoelectric element 12, a traveling wave in a vibration mode as shown in FIG. 3 is excited. That is, this traveling wave is a traveling wave in which the mode node C exists on the average radius line L. In part A or part B of this traveling wave, the surface mass moves backward elliptical motion in the same direction. Therefore, the rotor (not shown) pressed against the surface of the stator 10 rotates due to the frictional force with the surface of the stator.

In the above operation, the stator 10 has the traveling wave mode node C.
Is supported by the portion of the average radius line L, the vibration of the stator 10 is not hindered by the support member 13, and the vibration energy of the stator 10 may leak to the outside through the support member 13. Nor. Therefore, efficient rotor driving can be performed.

FIGS. 4 (a) and 4 (b) are views showing a second embodiment of the present invention. This embodiment is different from the first embodiment in that a band-shaped zone R is provided on the average radius line L of the stator 20 as shown in FIG. The support member 23 integrally provided with the diaphragm 21 is projected from the zone R by polarization, and the projecting end is screwed.
It is a point fixed on the base 25 at 24.

According to this embodiment, since the diaphragm 21 and the supporting member 23 are integrally provided, they can be easily obtained by bending the same plate material. Therefore, there is an advantage that the structure is simple and the manufacture is easy.

FIG. 5 is a diagram showing a third embodiment of the present invention. The present embodiment differs from the first and second embodiments in that the stator 30 is provided with piezoelectric elements that are polarized and arranged in a diagonally cut state as shown in the figure. It was experimentally confirmed that even the piezoelectric element provided with the polarization arrangement as described above can achieve the same effect as that of the above-mentioned embodiment.

The present invention is not limited to the above embodiment.
For example, the piezoelectric elements 12, 2 shown in FIGS. 2 (a) and 4 (a)
The polarization direction inside 2 may be opposite to that shown. However, in this case, the four right inner electrodes and the four left outer electrodes were driven by the same AC power source, and the four right outer electrodes and the four left inner electrodes were 90 ° out of phase with the power source. Must be driven by AC power supply. In addition, there is no problem even if the polarization direction is completely opposite to that shown in the drawings. Further, the shape of the diaphragm is not limited to the shape shown in the embodiment, but may be any shape. The present invention can also be applied to an ultrasonic motor having an amplitude in the radial direction. Of course, various modifications can be made without departing from the scope of the present invention.

〔The invention's effect〕

According to the present invention, the piezoelectric element or the vibration plate of the annular stator is supported in the region over the entire circumference having the average diameter of the inner diameter and the outer diameter of the annular ring, and the diaphragm has the inner diameter of the annular ring and Since it is configured so that a bending traveling wave having a node over the entire circumference having an average diameter with the outer diameter is excited,
The generated ultrasonic waves are not likely to be disturbed by the supporting members, and the vibrations do not leak to other parts, resulting in high drive efficiency, and ultrasonic waves that support the annular stator in a mechanically balanced and stable manner. A motor can be provided.

[Brief description of drawings]

1 to 3 are views showing a first embodiment of the present invention.
FIG. 2 is a perspective view showing the appearance of the stator, FIGS. 2 (a) and 2 (b) are views showing the polarization arrangement of the piezoelectric elements and the stator support means in the stator, and FIG. 3 is a mode node on the average radius line of the stator. It is a figure which shows the surface displacement state of a traveling wave. 4 (a) and (b) are diagrams showing a second embodiment of the present invention, and FIG. 5 is a diagram showing a third embodiment of the present invention. Sixth
FIG. 10 to FIG. 10 are views showing a conventional technique, FIG. 6 is a schematic view of an ultrasonic motor, FIGS. 7 and 8 are views showing a configuration of a piezoelectric element, and FIG. 9 is a view showing a principle of rotation. FIG. 10 is a diagram showing a surface displacement state of a traveling wave. 10,20,30 …… stator, 11,21 …… vibration plate, 12,22 …… piezoelectric element, 13,23 …… supporting member, 14,24 …… screw, 15,25…
… Base, L… average radius line of ring, R… zone.

Claims (1)

(57) [Claims] 1. A ring-shaped piezoelectric element, which is divided into two parts in a region having an average diameter of an inner diameter and an outer diameter over the entire circumference, and is divided into a plurality of pieces in the circumferential direction, and the piezoelectric element is joined. A ring-shaped vibration plate, a ring-shaped rotor pressed and held by the vibration plate, and an area around the entire circumference having an average diameter of the inner diameter and the outer diameter of the ring, supporting the piezoelectric element or the vibration plate. And a driving member for driving the rotor by exciting a bending traveling wave having a node in a region over the entire circumference having an average diameter of the inner diameter and the outer diameter of the annular ring in the vibration plate. An ultrasonic motor characterized by the above.