JPS62236368A - Ultrasonic motor - Google Patents

Abstract

PURPOSE:To improve the operability of an ultrasonic motor by providing a coupling mechanism which can be suitably connected or disconnected between a first rotor and a second rotor to reduce the operating force at manual operation time. CONSTITUTION:A second rotor 22 is coaxially arranged on the outer periphery of a first rotor 21. The rotor 21 is provided to apply a pressing force to a stator. The rotor 22 is so provided as to apply a driving force to a unit to be driven and integrated, for example, with the lens of a camera. Coupling mechanisms 23, 24 are interposed between the rotors 21 and 22 to connect or disconnect the rotors 21, 22.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention excites a bending traveling wave in a stator consisting of an annular piezoelectric element and a diaphragm, and a rotor is formed at the apex of an elliptical locus on the stator surface caused by the bending traveling wave. This invention relates to an ultrasonic motor that rotates a rotor by touching the rotor.

[Conventional technology]

Recently, ultrasonic motors have been in the spotlight as new motors that can replace conventional electromagnetic motors. This ultrasonic motor is not only new in principle, but also has the following advantages over conventional electromagnetic motors.

■Does not require a central axis.

■Thin and lightweight.

■There is no exchange of magnetic influence.

■The component structure is simple and highly reliable.

■Low speed and high torque can be obtained without gears.

■There is no backlash and positioning is easy.

■The rotor rotates and chucks against the stator.

It can take on three states: floating.

In order to take advantage of these advantages, various applied techniques are being researched.

FIG. 5 is a conceptual diagram of a typical conventional rotary ultrasonic motor. The principle is that a traveling wave is excited by an inverse piezoelectric effect in a metal donut-shaped diaphragm 2 integrated with an annular piezoelectric element 1, and a rotor 3 is moved so as to be in contact with the apex of the backward elliptical trajectory of each point on the surface generated by this. By pressing and arranging the rotor 3, the rotor 3 is rotated in the direction of arrow A. The above traveling wave excitation method will be explained below.

Figure 6 shows the piezoelectric cord 1 that constitutes a general ultrasonic motor.
This is a diagram showing the polarization state diagram of Figure 5, bottom of Figure 5. ka1
■e■e1. .

A 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 set of adjacent polarization directions opposite to each other corresponds to one wavelength λ. and,
Unpolarized portions 1a and lb having lengths of 3/4λ and 1/4λ are arranged at positions different by 180°, respectively, and polarized bodies of nλ pieces are arranged symmetrically with respect to the center line connecting these parts. However, the directions of polarization are arranged continuously in the circumferential direction so that the directions of polarization are alternately opposite to each other.

Of this polarization arrangement, the left half of the surface that is not in contact with the diaphragm, with the 3/4λ and 1/4λ unpolarized parts 1a and 1b sandwiched between them, is covered with one electrode, and this is connected as shown in Figure 7. One side is set as a common electrode 4a, and the right half surface not in contact with the diaphragm is covered with another electrode, which is also set as the other side common electrode 4b as shown in FIG. The electrode 4c on the side of the diaphragm 2 is electrically connected to the diaphragm 2, and is shared as a ground-side electrode for all piezoelectric elements.

The electrical signal input terminal to the above structure has three terminals a, b, and c as shown in FIG. When driving a structure with such polarization arrangement and electrode arrangement, there is a phase difference of π/2 between terminals a and c and between terminals b and c, and the inner and outer diameters of the λ1 ring are , the thickness, the average elastic constant of the piezoelectric ceramic and the diaphragm, the density 1, and the like. Now, if the voltage applied between terminals a and c is V08tnωt, then a voltage Vl)cosωt will be applied between terminals b and c.

On the other hand, the displacement y of a certain point on a circular ring due to a traveling wave is generally y-As i n (cp-ωt) - (1)
It is expressed as Here, A is the maximum displacement ffi, and c is 2π/
λ and ω represent natural frequencies, and p represents the position of a certain point on the ring. From formula (1), y−A sin 2πp/λ cosωt+As i
n (2πp/λ−π/2)sinωt
...(2) becomes. Therefore, if the vibration yl-As in 2πp/λ cosωt and the vibration y2-As in 2yr/λ (p-λ/4) sin ωt are superimposed at point p, a traveling wave will be obtained. The time terms sinωt and cosωt are vibrations with a phase shift of π/2 at point p, and sin 2πp/λ and sin 2π/λ(p-λ/4) mean a positional shift of λ/4. are doing.

This is the reason why the electrode arrangement in FIG. 6 has unpolarized portions of λ/4 and 3λ/4.

As described above, a traveling wave can be obtained by shifting the electrode arrangement by λ/4 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 follows an elliptical trajectory as shown in FIG. Explain about drawing. The vibration of the traveling wave is a plate wave obtained by the bending vibration caused by bonding the piezoelectric ceramic and the metal plate, but if the bending is equivalent along the thickness direction of the plate, the displacement component of the surface point p yp is yp-As in (2πxp/λ-ωt)e(1-c
osθp) −(3). However, here, θp is the angle formed between the axis perpendicular to the neutral axis of the annular body at point p and the X axis, and e is 1/2 of the plate thickness. Now, θp
-0, so equation (3) is ypζAsLn (2πxp/λ-ωt) ... (4) 1.1
Tona6・Ma”・Displacement component x p It e py'
0 and 7xp-esin θ p 'i e θ
p, but from equation (4), θp-d 3/I) / d x p-ACcos
(2πxp/λ-ωt), so xp-ACe cos (2πxp/λ-ωt)
...(5) becomes. Therefore, from equations (4) and (5), (λX p/
2 A e yr ) ~ 10 (yp/A) 2-1
...(6), and it can be seen that an elliptical locus is drawn. Since the vertices of this elliptical locus always face in the same direction, the rotor installed at the apex of the elliptical locus will move.

As an application of the ultrasonic motor based on this principle, moving the lens barrel of a camera is being considered. FIG. 9 shows an example of this, in which an ultrasonic motor 10 consisting of a stator consisting of a piezoelectric element 11 and a metal diaphragm 12, and a rotor consisting of a member 13 in pressure contact with the stator is fixed to a lens barrel frame. 14, and by rotation of the rotor, the lens 1
5 is adapted to drive a linear moving element 16 which is integrated with the moving element 5. Note that the V-groove 17 provided on the linear slider 16 engages with a protrusion 18 protruding from the inner wall of the fixed lens barrel frame 14, and the slider 16 moves linearly using this engagement portion as a guide. I will do it. That is, it has a so-called helicoid structure.

[Problem that the invention seeks to solve]

In the system shown in FIG. 9, there is a problem regarding automatic/manual switching. In other words, the purpose of installing an ultrasonic motor in a camera is to perform autofocus, but it is more useful to have a camera that can perform manual focusing as needed, rather than using only autofocus all the time. It can be said. However, since ultrasonic motors hold the rotor under pressure to improve efficiency, simply turning off the drive power of the ultrasonic motor during manual operation will cause the rotor's pressing force to act as resistance, causing a considerable increase in Requires operating power.

As a way to solve this problem, during manual operation,
There is a way to excite standing waves. When a standing wave is excited, a vertical vibration state in which only yp exists instead of the spheroidal motion shown in FIG. 8 is created, and the friction between the rotor and stator becomes small. Therefore, this is a preferable state for manual operation. In addition, to excite the standing wave,
Instead of applying a 90° phase to the ultrasonic motor, voltages of the same phase may be applied.

However, such means using standing wave excitation,
There is a drawback that power consumption increases.

That is, exciting standing waves during manual operation always consumes electrical energy. However, for devices such as cameras that are desired to be small and lightweight, dry batteries with as small a capacity as possible are used as a power source.

Considering the consumption of dry batteries, it is desirable to have a device that does not consume electrical energy during manual operation, similar to conventional manual focusing.

Therefore, the present invention requires less operating force when operating manually, has good operability, and consumes no power during manual operation, making it extremely suitable for equipment that requires automatic/manual switching operation. The purpose is to provide a sonic motor.

[Means for solving problems]

In order to solve the above-mentioned problems and achieve the object, the present invention takes the following measures. That is, in an ultrasonic motor that rotates the rotor by exciting a bending traveling wave in a stator consisting of an annular piezoelectric element and a diaphragm and bringing the rotor into contact with the apex of an elliptical locus on the stator surface caused by the bending traveling wave, The first rotor is arranged so as to exert a pressing force on the first rotor.

(2) A second rotor is provided adjacent to the first rotor to provide a driving force to the driven body.

■ Interposed between the first rotor and the second rotor,
A coupling mechanism is provided that can connect and disconnect the first rotor and the second rotor as needed.

/f,,,,filling machine ti,= L-Ci, 1st
．． ). - A piezoelectric displacement element whose base end is fixed to the second rotor and whose tip part is bent and displaced during automatic operation, and when this piezoelectric displacement element is bent and displaced, a second rotor [
or the first rotor] is preferable.

[Effect]

By taking such measures, the following effects occur. Due to the connection mechanism, the first. When the second rotor is connected, the driven body side is integrated with the drive source side, and automatic operation similar to the conventional one is possible.

Also, the first connection mechanism. When the second rotor is uncoupled, the driven body is separated from the drive source, and the operating force required to manually operate the driven body is reduced, making it easier to operate. . Furthermore, there is no need to supply power at all during the manual operation.

〔Example〕

FIG. 1 and FIG. 2 are diagrams showing a first embodiment of the present invention.
The figure is a sectional view showing the structure of the rotor section 20, and FIG. 2 is an enlarged sectional view showing the main part B of FIG. 1. As shown in FIGS. 1 and 2, a second rotor 22 is disposed coaxially around the outer periphery of the first rotor 21. As shown in FIGS. The first rotor 21
is provided so as to be able to apply a pressing force to the stator (not shown). Further, the second rotor 22 is provided so as to be able to apply a driving force to a driven body (not shown), such as a linear slider integrated with a camera lens, for example.

A coupling mechanism 23, 24 is interposed between the first rotor 21 and the second rotor 22, so that the two rotors can be coupled or separated. The coupling mechanisms 23 and 24 have the same configuration and are connected at 180° on the rotor circumference.
Although they are disposed oppositely at different positions, they are provided so that they are engaged in opposite directions with respect to the rotational direction, as will be described later.

The above connection mechanism is! As shown in FIG. 2, a piezoelectric transducer (piezoelectric bimorph) 25 that generates bending displacement is housed in a recess 26 provided on the inner peripheral surface of the rotor 22 of i2, and its base end 25a is inserted into the four parts 26. The tip 25b is fixed, and when energized, the tip 25b bends and displaces as shown by the broken line.

Note that from the viewpoint of mechanical strength, the piezoelectric displacement element 25 is
A metal plate laminated with piezoelectric ceramics is preferable.

On the other hand, an engaging portion, that is, a notch portion 27 is provided on the outer circumferential surface of the first rotor 21 so that the bent tip portion 25b of the piezoelectric displacement cord 25 can enter into an engaged state.

It is necessary to supply electricity to the piezoelectric displacement element 25 through a sliding electrode when the driven object is continuously rotated, but when performing autofocus of a camera, for example, Since the rotor rotation angle is usually one rotation or less, there is no problem even if the rotor is connected directly with a lead wire. However, in this case, since it is a reciprocating rotation operation,
As shown in FIG. 1, it is necessary to provide a pair of coupling mechanisms 23, 24 with opposite directions of engagement.

As is well known, the piezoelectric displacement cord 25 has an applied voltage of V, a displacement amount of ΔX, a bimorph length of 0, a thickness of t, and a piezoelectric constant of d31.The displacement amount ΔX is Δx=312d31 V.
/12 It can be expressed by the formula.

The ultrasonic motor configured in this way operates as follows. For automatic operation, the piezoelectric displacement element 25 is energized. Then, the element 25 is bent and displaced as shown by the broken line in FIG. Thus, the first and second rotors 21, 22 are connected to each other.

Therefore, when the stator of the ultrasonic motor is energized in this state, the first rotor 21 rotates and the second rotor 21 rotates.
The rotor 22 also rotates. The driven body is thus driven by the rotational force of the ultrasonic motor. Note that in the initial state, if the relative positions of the piezoelectric displacement element 25 and the notch 27 are shifted, the ultrasonic motor is operated while the piezoelectric displacement element 25 is energized. Then,
The first rotor 21 rotates slightly and the piezoelectric displacement element 25-
The distal end 25b of the cutout 27 becomes invaginated into the notch 27.

When performing manual operation, the power to the piezoelectric displacement cable 25 is cut off. Then, the element 25 returns to its original state. Thus, the first. The second rotors 21 and 22 are disconnected, and the drive source side (the stator and the first rotor 21
) and the driven body side (the driven body and the 20th motor 22) are separated.

Therefore, when the driven body is manually driven, only the driven body rotates, and the drive source side does not rotate at all. Therefore, the drive operation force for the driven body is small, and the drive body is easy to operate. Moreover, in this case, it is not necessary to supply the same electric power to the ultrasonic motor, and power consumption becomes zero.

Note that since the piezoelectric displacement element 25 is used in a DC manner, a current flows at the moment of bending displacement, but once the piezoelectric displacement element 25 is displaced, the displacement state is maintained even if almost no current flows, similar to a capacitor, so power consumption is reduced. It only takes a small amount. Of course, during manual operation, the applied voltage is zero, so
There is no power consumption. Furthermore, the piezoelectric displacement cable 25 currently costs about several thousand yen, and has a simple circuit configuration, so it can be manufactured at low cost, and has the advantage of being small and taking up little space.

FIG. 3 is a diagram showing a second embodiment of the present invention.

The difference between this embodiment and the first embodiment is that in the first embodiment, a piezoelectric displacement element 25 is attached to the second rotor 22 side, and a notch 27 is provided to the first rotor 21 side. In this embodiment, the piezoelectric displacement element 3 is provided on the first rotor 31 side.
5 is attached, and a notch 37 is provided on the second rotor 32 side. In addition, 30 is a rotor part, 33.
34 is a connecting mechanism, and 36 is a recess for accommodating an element. This embodiment also has the same effects as the first embodiment.

FIGS. 4(a) and 4(b) are diagrams showing a third embodiment of the present invention. This embodiment differs from the first embodiment in that a first rotor 41 and a second rotor 42 are arranged adjacent to each other in the axial direction of the lens barrel frame 40 of the camera, and a connecting mechanism is provided at the adjacent portion. 4
4.

Therefore, as the coupling mechanism 44 in this case, a piezoelectric displacement cord 45 that bends and displaces in a direction parallel to the axis is attached within the four parts 46 provided on the inner peripheral surface of the second rotor 42, and A notch 47 that engages with the element 45 is provided on the inner circumferential surface of the first rotor 41 in a shape whose depth changes in a direction parallel to the axis. In the figure, 43 is a stator, 48 is a projection for fixing the second rotor, and 49 is a linear slider. This embodiment also provides the same effects as the first embodiment.

Note that the present invention is not limited to the above embodiments. For example, in the above embodiment, a bimorph type piezoelectric displacement element was used as the actuator of the coupling mechanism, but if the required displacement amount is 101a or less, such as in a precision machined product, a laminated type piezoelectric displacement element may be used. may also be used. It goes without saying that various other modifications can be made without departing from the gist of the present invention.

〔Effect of the invention〕

According to the present invention, the first rotor provided to apply a pressing force to the stator and the second rotor provided to apply a driving force to the driven body are arranged adjacent to each other. , a connecting mechanism is provided between the first rotor and the second rotor that can connect and disconnect the first rotor and the second rotor at the appropriate time, so that when the driven body is manually operated. 1st by connecting mechanism. If the second rotor can be uncoupled, the driven body will be separated from the drive source side, and the operating force required for manual operation will be small, resulting in good operability. It is possible to provide an ultrasonic motor that consumes no power during operation and is extremely suitable for equipment that requires automatic/manual switching operation.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing the configuration of the first embodiment of the present invention, and FIG.
The figure is an enlarged sectional view showing the main part of FIG. 1, FIG. 3 is a sectional view showing the configuration of the second embodiment of the present invention, and FIGS. 4(a) and (b).
FIG. 2 is a vertical cross-sectional view and a cross-sectional view of main parts of a third embodiment of the present invention. Figures 5 to 9 are diagrams showing the prior art,
Fig. 5 is a conceptual diagram of an ultrasonic motor, Figs. 6 and 7 are piezoelectric elements, Fig. 8 is a diagram showing the structure of the piezoelectric element, Fig. 8 is a diagram showing the principle of rotation, and Fig. 9 is a sectional view showing an example of application. It is. 1... Piezoelectric element, 2... Vibration plate, 3... Rotor,
20°30...Rotor part, 21, 31.41...First rotor, 22.32.42...Second rotor, 2
3゜24.33, 34.44...Connection mechanism, 25,3
5゜45...piezoelectric displacement element, 26,36.46...
Recessed portion, 27.37.47... cut-in portion (engaging portion). Applicant's agent Patent attorney Jun Tsuboi Figure 1￥! Figure 2 @ Figure 3'' ra) (b)?R4 Figure, 1 Figure 5 fRG Figure Figure 7

Claims (2)

[Claims] (1) An ultrasonic motor that rotates the rotor by exciting a bending traveling wave in a stator consisting of an annular piezoelectric element and a diaphragm, and bringing the rotor into contact with the apex of an elliptical locus on the stator surface caused by the bending traveling wave. a first rotor disposed so as to exert a pressing force on the driven body; a second rotor disposed adjacent to the first rotor so as to apply a driving force to the driven body; An ultrasonic wave device characterized by comprising a coupling mechanism interposed between the first rotor and the second rotor and capable of coupling and disconnecting the first rotor and the second rotor as appropriate. motor. (2) The coupling mechanism includes a piezoelectric displacement element whose base end is fixed to the first rotor [or the second rotor] and whose distal end is bent and displaced during automatic operation, and this piezoelectric displacement element which is bent and displaced. and an engaging portion provided on the second rotor [or the first rotor] so as to engage with the tip of the piezoelectric displacement element when
Ultrasonic motor as described in section.