JP2645845B2 - Ultrasonic motor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an ultrasonic motor that is relatively small and can be used in the field of low power consumption.

[Summary of the Invention]

The present invention is directed to an ultrasonic motor that frictionally drives a moving body by a vibration wave using the expansion and contraction motion of a piezoelectric vibrator, wherein the center of the vibrating body portion is fixedly supported on a central axis installed on a fixed base, Alternatively, a configuration is adopted in which the vibrating body is excited in a primary vibration mode in the radial direction, and a displacement enlarging mechanism is further provided on the outer peripheral portion where displacement is large so as to contact the moving body. At this time, the rotation center axis of the moving body is disposed outside the outer periphery of the vibrating body, and the outer periphery of the moving body is frictionally driven by being in pressure contact with a part of the outer periphery of the vibrating body.
Further, the rotation speed of the moving body is increased by making the radius from the rotation center axis of the moving body to the frictional force generating section smaller than the radius from the center of the vibrating body to the frictional force generating section.

[Conventional technology]

Conventionally, as an ultrasonic motor using a piezoelectric vibrator, a standing wave system, a traveling system, and the like have been known. For example, the principle of the conventional ultrasonic motor is shown in "New Method / New Principle Motor Development and Practical Points" (1984) published by Japan Industrial Technology Center. The use of the ring-shaped vibrating body 403 shown in FIG.
A traveling wave motor using a disk-shaped vibrating body portion 503,903,1003 as shown in FIG. 10 has been known. For example, JP-A-59-
Such a conventional structure is disclosed in 96881 and JP-A-60-174078.

[Problems to be solved by the invention]

In the structure of the ultrasonic motor as described above, for example, in a structure having a disk-shaped vibrating body 903 as shown in FIG. 9, when the vibrating body 903 is excited in a primary vibration mode in a radial direction. In this case, the vibration amplitude displacement of the vibrating body 903 becomes largest near the outer periphery, but the entire outer peripheral portion of the vibrating body 903 and the moving body 9
Since 05 is in pressurized contact, the amplitude displacement of the vibrating body 903 is attenuated by the external force of pressurization, thereby reducing the electro-mechanical conversion efficiency. Further, since the central axis of the vibrating body 903 and the rotation central axis 901 of the moving body 905 are the same axis, the rotational speed of the moving body 905 is a function of the driving frequency, the longitudinal amplitude of the vibrating body, the vibrating body thickness, and the vibration wave wavelength. Since it is determined, the only factor controlling the rotational speed depending on the shape is the thickness of the vibrating body. For example, when it is desired to reduce the power consumption per rotation by increasing the number of rotations even if the output torque is small, such as the motor for driving the pointer of an electronic timepiece, the conventional motor has a low rotation speed and cannot reduce the power consumption. .

[Means for solving the problem]

In order to solve the above-mentioned problem, in the present invention, the vibrating body or the vibrating body portion is configured to be excited in a primary vibration mode in a radial direction, and in this case, a part of an outer peripheral portion where a large amplitude displacement can be obtained. The displacement enlargement mechanism is provided, and the outer periphery of the moving body having a small diameter having a center axis outside the outer periphery of the vibrator and the displacement enlargement mechanism are brought into pressure contact and driven by friction. At this time, the friction radius of the vibrating body was made sufficiently larger than the friction radius of the moving body.

[Action]

According to the above configuration, since the moving body does not come into pressure contact with the front surface of the vibrating body, the amplitude attenuation of the vibrating body becomes extremely small as compared with the related art, and the rotational movement of the moving body can be efficiently converted. Also, if the friction half ratio of the moving body is made sufficiently smaller than the friction radius of the moving body, the rotational speed of the moving body can be increased by the diameter ratio.

Furthermore, even when a plurality of moving bodies are arranged outside the outer periphery of the vibrating body, the plurality of moving bodies can be rotated by one vibrating body because the outer peripheral front surface of the vibrating body does not come into pressure contact.

〔Example〕

 Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

The present invention is directed to a standing wave type or traveling wave type ultrasonic motor.

FIG. 2 is a diagram showing an example of a traveling wave generation principle in a traveling wave type ultrasonic motor. 201 is a piezoelectric ceramic,
This is a piezoelectric vibrator made of a piezoelectric crystal, and is polarized at equal intervals with a width b as shown in the figure, and the directions of polarization between adjacent directions are opposite to each other. A conductive material such as silver or nickel is deposited on each piezoelectric vibrator by a method such as evaporation or plating.
Are formed, and they are connected to the signal lines 203 and 204.
, And high-frequency voltages from different signal sources are applied. A gap having a width c is provided between the electrode groups connected by the signal lines 203 and 204, respectively. At this time, the gap having the width c may be either polarized or non-polarized. here,
For convenience of explanation, the distance between the centers of the electrodes sandwiching the width c is a. The mechanism of generation of a traveling wave will be described below with reference to the above figures and symbols. Considering the midpoint of the electrode portion in the figure, a bending vibration wave composed of a traveling wave and a backward wave can be expressed as follows.

Asin (ωt−kx) + Asin (ωt + kx) Equation (1) Here, Equation (1) indicates a so-called standing wave. On the other hand, the bending vibration wave caused by the electrode portion shown in FIG.

Bsin (ωt−k (x + a) + φ) + Bsin (ωt + k (x + a) + φ) Expression (2) where k = ω / ν = 2π / λ λ: wavelength, phase difference angle with respect to φ: expression (2) At In other words, equation (2) can be expressed as follows.

Bsin (ωt−kx + απ) + Bsin (ωt + kx + βπ)
Equation (4) Therefore, the bending vibration wave to be more excited is represented by a type obtained by adding the equations (1) and (4). Here, considering the condition for the presence of only the traveling wave component from the expansion formula of equation (4), it can be seen that α is an even number and β is an odd number. Here, from the equation (3), a and φ can be expressed by the following equations using α and β.

That is, when (α, β) = (0,1), (2,3) When (α, β) = (2,1) When (α, β) = (0,3) As a result, when both a and φ are simultaneously satisfied, only the traveling wave component exists. To give an example, Considering the case (1), the expression (1) + the expression (2) is as follows.

Asin (ωt−kx) + Asin (ωt + kx) + Bsin (ωt−kx) −Bsin (ωt + kx) Equation (6) Here, the oscillation width A of the high-frequency voltage signal output from the drive circuit.
If A and B are A = B, equation (6) becomes 2Asin (ωt−kx)
It turns out that only the traveling wave component remains. In order to drive the motor in the reverse direction, only the backward wave component needs to be left. Therefore, α and β in the equation (5) may be reversed so that α is an odd number and β is an even number. Considering the solid line as a reference, the phase of the signal to be applied should be shifted by 180 ° as compared with the time of forward rotation driving.

FIG. 3 is a view showing the principle that a traveling wave type ultrasonic motor rotates by a traveling component. Numeral 301 denotes a vibrator, which generates bending vibration because the piezoelectric vibrator is bonded to the elastic member. Here, when a traveling wave in the right direction is generated according to the principle shown in FIG. 2, one point on the surface of the vibrating body 301 draws an elliptical trajectory in the left direction. Moves in the opposite direction. The above is described in Nikkei Mechanical (1985.9.23) or the like, and a detailed description on that one point on the surface of the vibrating body 301 draws an elliptical locus is also described in the same document.

FIG. 1 is a sectional view of an ultrasonic motor according to the present invention.
The central shaft 101 is integrated with the fixed base 102 by driving, and the vibrating body portion 103 has an integral structure with the central shaft 101 at a central portion. The vibrating body 103 is made of an elastic member such as stainless steel, brass, and duralumin, and is supported by the central shaft 101 at a substantially central portion. In addition, the mechanical resonance frequency of the central axis 101 and the fixed base 102 is sufficiently higher than the resonance frequency of the vibrating body including the vibrating body portion 103, the piezoelectric vibrator 105, and the like. There is no support structure. The piezoelectric vibrator 105 is a piezoelectric ceramic having a hole at the center, or several pieces of piezoelectric ceramic divided in the circumferential direction. It is joined to the side of the unit 103 opposite to the surface on which the output extraction unit 104 is provided. The moving object is a mobile vehicle 106
And the moving body rotation 107, and the moving body axis center is disposed outside the outer periphery of the vibrating body. The moving body shaft 107 and the moving body wheel 106 are supported and fixed by driving, and the fixed base 10 is fixed.
2. It is rotatably supported by the moving body receiver 107. The outer periphery of the moving vehicle 106 is in contact with the output extraction unit 104 of the vibrating body. The pressing force of the contact portion is determined by a pressure adjusting spring 108 pressing the moving body shaft 105. At this time, the pressure applied to the moving body 106 by the pressure adjusting spring 108 is N, the friction coefficient between the vibrating body output extraction unit 104 and the moving body 106 is μ, and the friction of the moving body from the center axis of the moving body is generated. Assuming that the distance to the part is a, the torque T generated in the moving body can be approximately T = μNa. The output position 104 of the vibrating body is set in order to efficiently convert the minute flexural vibration amplitude of the vibration wave component excited by the vibrating body including the vibrating body portion 103 and the piezoelectric vibrator 105 into the rotational motion of the moving body. Thus, a protrusion is provided on the vibrating body 103 so that the vibrating body and the movable vehicle 106 contact only at a part of the vibrating body portion 103 in the radial direction. FIG. 7 is a plan view showing the relationship between the vibrating body and the moving body according to the present invention.
This figure is a diagram showing a planar relationship between the vibrating body and the moving body in FIG. As can be seen from FIG. 7, an output take-out section 704 for the vibrating body is provided on a part of the outer periphery of the vibrating body section 703 so as to be in contact with the moving vehicle. Distance r ₂ as compared to the distance r ₁ to the output extraction portion 704 of the vibrating body from the central axis of the vibrating body from the central axis of the moving body to the frictional force generating portion of the mobile is sufficiently small. By the way, the most characteristic features of the present invention are that the output take-out position 704 of the vibrating body is not on the entire circumference of the vibrating body portion 703, and the center of the moving body is shifted from the center of the vibrating body to compare the diameter r _1.
/ r ₂ is set to be larger than 1. I want to say a little about why we do this. The field of application of the present invention is relatively small and low power consumption applications. Because of the small diameter structure, the mechanical resonance frequency of the vibrating body necessarily increases. In general, if the drive frequency exceeds 100 kHz, the circuit efficiency of the drive system is inevitably reduced. Therefore, the drive system must be excited in the primary vibration mode in the radial direction. When the excitation is actually performed at a driving frequency such that the primary vibration mode is set in the radial direction, the vibration amplitude increases toward the outer diameter, and the amplitude becomes maximum at the outermost periphery. Therefore,
It is thought that the output take-out part 704 of the vibrating body should be set at the outermost periphery of the vibrating body and should be brought into contact with the moving body at this position. The state of the amplitude vibration of the vibrating body changes depending on whether the part is in pressure contact with the entire circumference or in part. Eleventh
The figure shows the difference in the amplitude of the vibrating body due to the difference in pressurizing the vibrating body. The method for measuring the frequency characteristic of the vibration body amplitude amount utilizes the fact that the piezoelectric element is composed of two circuits, and a frequency voltage is swept to one side to excite the vibration body with a standing wave. In addition, a technique is used in which a back electromotive voltage generated by the piezoelectric effect on the other circuit side is Fourier-transformed by a spectrum analyzer. 11a shows a case where only the vibrating body is excited, b shows a case where a part of the outer peripheral portion of the vibrating body comes into pressure contact with the moving body as in the present invention, and c shows an outer peripheral portion of the vibrating body. The case where the entire periphery of the unit and the moving body are in pressure contact with each other is shown. Here, the pressures b and c are the same. Since the back electromotive voltage due to the piezoelectric effect on the vertical axis increases in proportion to the vibration amplitude, it can be said that the vertical axis indicates the magnitude of the vibration amplitude. In the conventional method (c in the drawing) in which the entire outer periphery of the vibrating body is brought into pressure contact with the moving body, the attenuation of the amplitude near the mechanical resonance point of the vibrating body is smaller than that in the method of the present invention (b in the figure). It can be seen that is larger. As a result, according to the present invention, the amplitude displacement in the friction drive unit is large, and a more efficient rotational movement can be realized even at a lower voltage than the conventional structure.

Next, the reason why the rotation speed of the moving body increases when r ₁ / r ₂ is made larger than 1 will be described. In general the maximum value of the transverse velocity component of the contributing elliptical trajectory in the rotational movement of the moving body U _max is ^{_{U max = -2π 2 ρδ (T}} / λ) ...... (7) ρ: drive frequency [delta]: Vertical amplitude T: Vibration The body thickness λ: represented by the vibration wave wavelength, the number of revolutions can be increased by increasing the thickness of the vibrating body in terms of shape. However, simply increasing the thickness extremely increases the mechanical hardness and increases the resonance frequency. Therefore, it is advisable to provide a comb-shaped output extraction unit 704 that becomes uneven in the circumferential direction on the vibrating body as a displacement enlarging mechanism. What can be further considered in terms of shape is the diameter r of the output extraction portion of the vibrating body.
_1, is to change the ratio of the diameter r ₂ of the output transmission portion of the moving body (the portion that contacts the vibrator output members pressurization).
Since _{Umax in the} equation (7) is determined only by the vibrating body, if the diameter ratio changes, the rotational angular velocity changes. The rotational angular velocity can be increased by r ₁ / r ₂ as compared with the conventional r ₁ / r ₂ = 1.

The embodiment of the present invention has been described above mainly with reference to the structure of FIGS. 1 and 7, but FIGS. 6 and 8 will be described as another embodiment. FIG. 6 is another embodiment showing a plan view of the vibrating body and the moving body according to the present invention. Vibration body part 80 without displacement enlargement mechanism
3 and the moving body 806 are brought into direct pressure contact and driven by friction. FIG. 8 is another embodiment showing a plan view of the vibrating body and the moving body according to the present invention. Mobile vehicle with one vibrating body part 803 with four vibrating body output extraction parts (with displacement enlargement mechanism)
806, 807, 808, 809 are brought into contact with each other under pressure to simultaneously rotate four moving bodies.

〔The invention's effect〕

According to the ultrasonic motor according to the present invention, in a small motor that is excited in the primary vibration mode in the radial direction of the vibrator, the ultrasonic motor moves without attenuating the amplitude displacement at the outer peripheral portion where the displacement of the vibration amplitude becomes maximum. Since the rotating speed of the moving body can be increased by changing the diameter ratio between the moving body and the vibrating body, it can be transmitted to the body and the output torque can be low enough to drive the hands like a motor in an analog electronic watch. In the case where low power consumption per rotation angle is required, the effect is very large in that high efficiency can be obtained with a small-diameter ultrasonic motor structure. Furthermore, the ability to drive a large number of motors with one vibrating body is very effective for increasing the functionality of an analog electronic timepiece.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of an ultrasonic motor according to the present invention, FIG. 2 is an example of a principle diagram of traveling wave generation, and FIG. 3 is an example of a principle of rotation of a traveling wave ultrasonic motor. , FIG.
FIG. 5 is a cross-sectional view of a conventional ultrasonic motor (1), FIG. 5 is a cross-sectional view of a conventional ultrasonic motor (2), FIG. 6 is a plan view of a vibrating body and a moving body according to the present invention (2), and FIG. FIG. 1 is a plan view of a vibrating body and a moving body according to the present invention (1), FIG. 8 is a plan view of a vibrating body and a moving body according to the present invention (3), and FIG. 9 is a cross-sectional view of a conventional ultrasonic motor. (3), FIG. 10 is a plan view of a displacement enlarging mechanism of the conventional ultrasonic motor used in FIG. 2, and FIG. 11 is a diagram showing a difference in amplitude of a vibrating body due to a difference in pressure. 101,401,501,901 ... Center axis 102,402,502,902 ... Fixing base 105,404,504,904,201 ... Piezoelectric vibrator 103,903,403,503,1003,803,703,603 ... Vibrating body part 104,1004,704,804 105, 605, 705, 805 Moving body rotating shaft 107 Moving body receiver 405, 505, 905 Moving body plate 108, 907 Pressure regulating spring 507… Pressure regulating mechanism 506, 407… Bearing 202… Electrode section

Claims (2)

(57) [Claims] A superconducting device that frictionally drives a moving body by causing an oscillating wave to occur in the vibrating body by using an expansion and contraction motion of a piezoelectric vibrator that is made of an elastic member and that is joined to a vibrating body portion having a central axis at the center. In the acoustic wave motor, the moving body has a rotation center axis disposed outside an outer peripheral portion of the vibrating body, and the vibrating body comes into contact with the moving body to take out an output for frictionally driving the moving body. An ultrasonic motor having a portion, wherein a distance from a central axis of the vibrating body to the output extracting portion is larger than a distance from a central axis of the moving body to a contact portion with the extracting portion. 2. The ultrasonic motor according to claim 1, wherein a plurality of said moving bodies are arranged around said vibrating body, and said respective moving bodies are individually driven by friction by said vibrating body. .