JP2683587B2 - Ultrasonic motor - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic motor which can be realized with a relatively small size and low power consumption. Conventionally, as an ultrasonic motor using a piezoelectric vibrator, a standing wave system or a traveling wave system has been known. For example, "New method /
The principle of conventional ultrasonic motors is shown in "Points of New Principle Motor Development and Practical Use" (1984). Further, as shown in FIG. 4, there is known a structure having a ring-shaped vibrating body portion 403 and applying a predetermined voltage to the piezoelectric vibrator 404 to rotate the moving body 405.
Further, as shown in FIG. 5, a structure having a disk-shaped vibrating body portion 503 and applying a predetermined voltage to the piezoelectric vibrator 504 to rotate the moving body 505 has been known. For example, Japanese Patent Laid-Open Nos. 59-96881 and 60-174078 disclose conventional structures. In the conventional ultrasonic motor, in the structure having the ring-shaped vibrating body portion 403 as shown in FIG. 4, the bending vibration excited by the piezoelectric vibrator 404 is used. Waves have no nodes of vibration. Therefore, the support mechanism 406 has a problem that the vibration wave is attenuated and the electromechanical conversion efficiency is reduced. Further, in the structure having the disk-shaped vibrating body portion 503 as shown in FIG. 5, the vibration is performed in the secondary vibration mode in the radial direction of the vibrating body portion 503. Vibrating body 503
Are supported at two positions in the radial direction by the fixed base 502. In this structure, there is a problem in that the electromechanical conversion efficiency is reduced due to variations in the positions of the nodes, variations in the area supporting the vibrating body, and variations in the supporting force supporting the vibrating body. [0007] Such problems are more seriously affected if the size of the ultrasonic motor is reduced. The structure in which the moving body 405 and the central shaft 401 are integrated, and the moving body 5
In the structure in which 05 and the central shaft 501 are integrated, there is a problem that the bearing member 407 such as a bearing and the bearing member 506 are required. Therefore, an object of the present invention is to obtain a small, thin, and highly efficient ultrasonic motor which does not reduce the vibration wave component due to the supporting structure of the vibrating body. In order to solve the problem of reduction in electromechanical conversion efficiency due to the support structure of the vibrating body of the ultrasonic motor, the present invention provides at least a thick shaft portion and a thin shaft portion. A central shaft formed by forming two or more shafts, the thick shaft being fixed to a fixed base, and the central hole being closely fixed in the radial direction to the thin shaft of the central shaft. The vibrating body part with one surface near the center hole closely fixed to the attached part in the axial direction, the piezoelectric vibrator fixed to one surface of the vibrating body part, and the radius of the vibrating body part with the central axis as the rotation guide. The ultrasonic motor is downsized, thinned, and highly efficient, which has a configuration including a moving body that makes pressure contact in the vicinity of the maximum amplitude portion with respect to the direction, and a pressing unit that pressurizes the vibrating body portion and the moving body. Was realized. In a typical construction of the ultrasonic motor of the present invention, as shown in FIG. 1, the central shaft 101 is fixed to the fixed base 102.
Fixed to The vibrating body portion 103 is a thin axis of the central axis 101.
It is tightly fixed to the part 101c in the radial direction, and the central axis 1
Stepped portion 1 between thick shaft portion 101b and thin shaft portion 101c of 01
One surface in the vicinity of the central hole 103a is tightly fixed to 01a in the axial direction . The piezoelectric vibrator 104 is fixed to one surface of the vibrating body 103. The piezoelectric vibrator 104 and the vibrating body portion 103 are driven so as to have a maximum amplitude portion in the radial direction of the vibrating body portion 103. The moving body 105 makes pressure contact with the vicinity of the maximum amplitude portion in the radial direction of the vibrating body portion 103 with the central axis 101 as a rotation guide. The pressing means 106 is the vibrating body section 1.
03 and the moving body 105 are pressurized. In the structure of the present invention, since the support of the vibrating body is fixed support near the center of the central axis, the vibration wave is less attenuated. In addition, it is easy to adjust the pressure applied to the vibrating body and the moving body, and the moving body can be rotated with an appropriate contact pressure.
Furthermore, since the moving body comes into contact with the vibrating body portion in the vicinity of the maximum amplitude portion in the radial direction, even if the vibrating body portion is made of a thin flat elastic member, the component of the traveling wave excited in the vibrating body portion is Is uniformly transmitted to the moving body. Further, the ultrasonic motor can be driven in a primary vibration mode having no nodes in the radial direction of the vibrating body so that the outer circumference of the vibrating body is located at the maximum radial displacement. The ultrasonic motor of the present invention can also be driven in a secondary vibration mode having one node in the radial direction of the vibrating body. Embodiments of the present invention will be described below 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 the principle of traveling wave generation in a traveling wave type ultrasonic motor. The piezoelectric vibrator 201 is composed of a piezoelectric crystal body such as a piezoelectric ceramic. The piezoelectric vibrator 201 is polarized at equal intervals with a width b. The polarization directions of adjacent parts of the piezoelectric vibrator 201 are opposite to each other. The electrode 202 of the piezoelectric vibrator 201 is made of a conductive material such as silver or nickel and is formed by vapor deposition or plating. Electrode 2
02 is connected by the signal line 203 and the signal line 204. A high frequency voltage is applied to the electrode 202 of the piezoelectric vibrator 201 via the signal line 203 and the signal line 204. A gap portion having a width c is provided between the electrode groups connecting the signal line 203 and the signal line 204. The void portion having the width c may be polarized or not polarized, and may or may not have electrodes.
The distance between the centers of the electrodes sandwiching the void portion having the width c is a.
The principle of generation of the traveling wave of the ultrasonic motor will be described below. Consider the midpoint of the electrode portion of FIG. 2 as a reference. A bending vibration wave in which a traveling wave is a backward wave is expressed by the following equation. Asin (ωt−kx) + Asin (ωt + kx) (1) Here, the equation (1) represents a standing wave. The bending vibration wave of the electrode portion of FIG. 2 is expressed by the following equation. Bsin (ωt−k (x + a) + φ) + Bsin (ωt + k (x + a) + φ) (2) where k = ω / ν = 2π / λ λ: phase difference angle with respect to wavelength φ: , −ka + φ = απ ka + φ = βπ (3), the equation (2) is expressed as Bsin (ωt−kx + απ) + Bsin (ωt + kx + βπ) (4) Therefore, and the more excited bending vibration wave,
It is expressed by adding equations (1) and (4). Here, considering the condition for the existence of only the traveling wave component from the expansion of equation (4), α is an even number,
It is when β is an odd number. Here, from the equation (3), a = λ (β−α) / 4 φ = π (α + β) / 2 (5) That is, when (α, β) = (0,1), (2,3) , A = λ / 4 φ = π / 2 (α, β) = (2,1), a = −λ / 4 φ = 3π / 2 (α, β) = (0,3), a = 3λ / 4 φ = 3π / 2. Therefore, when the respective a and φ are satisfied, only the component of the traveling wave exists. For example, when a = 3λ / 5, b = λ / 2, and φ = 3π / 2, the sum of equations (1) and (2) is Asin (ωt −kx) + Asin (ωt + kx) + Bsin (ωt − kx) −Bsin (ωt + kx) (6) Here, if the amplitudes A and B of the high frequency voltage signal output from the drive circuit are A = B, the equation (6) becomes 2Asin (ωt −kx), Only the traveling wave component remains. Further, in order to reverse the rotation of the ultrasonic motor, it is sufficient to leave only the backward wave component. Therefore, α in equation (5) may be an odd number and β may be an even number. In particular,
In FIG. 2, when the portion (2) is used as a reference, the phase of the signal applied to the portion (2) may be shifted by 180 degrees compared with the case where the ultrasonic motor is driven in the normal direction. FIG. 3 is a diagram showing the principle of the traveling wave type ultrasonic motor rotating by the traveling wave component. Vibrating body 301
Is formed of an elastic member. Since a piezoelectric vibrator is bonded to the vibrating body 301, bending vibration occurs. When a traveling wave to the right in FIG. 2 is generated in the vibrating body 301, one point on the surface draws an elliptical locus to the left. The rotor unit 302 moves in the direction opposite to the traveling direction of the traveling wave. The principle of operation of the ultrasonic motor described above is described, for example, in "Nikkei Mechanical (September 23, 1985)" and the like. FIG. 1 is a vertical sectional view of an embodiment of the ultrasonic motor of the present invention. The central axis 101 is
A thick shaft portion 101b and a thin shaft portion 101c having different diameters are formed.
The central shaft 101 is the thick shaft portion 101b and the fixed base 102 is
It is fixed to the hole portion 102a. The vibrating body portion 103 has a hole portion 10.
3a is closely attached to the thin shaft portion 101c of the central shaft 101 in the radial direction.
It is fixed, and the thick shaft portion 101b and the thin shaft of the central shaft 101 are fixed.
In the stepped portion 101a between the portions 101c, in the vicinity of the hole 103a
One side is fixed in close contact with the axial direction. Here, as the material of the vibrating body portion 103, an elastic material such as stainless steel, brass, or duralumin is used. The piezoelectric vibrator 104 is at least one or more piezoelectric ceramics having a hole formed in the center or a plurality of piezoelectric ceramics divided in the circumferential direction. The piezoelectric vibrator 104 has a plurality of electrode portions in the circumferential direction and is polarized. The piezoelectric vibrator 104 is fixed to one surface of the vibrating body 103. The moving body 105 has a guide hole at the center. The moving body 105 has the central axis 101 as the center of rotation.
The pressure adjusting mechanism includes a spring member 106, a washer 107, a stopper 108, and the like. The pressure adjusting mechanism is the moving body 105.
The vibrating body portion 103 is pressurized. The pressure regulating mechanism is the vibrating body section 1.
The vibration pressure generated in 03 is efficiently transmitted to the moving body 105 to set the predetermined pressure so as to rotate the moving body 105. For adjusting the pressure applied by the pressure adjusting mechanism, the shape of the spring member 106 such as a leaf spring or a cross spring may be changed, or the number of washers 107 used may be changed. As the pressure adjusting mechanism, a C ring or E ring stopper may be used, or a double nut may be used. Further, a ball bearing and a coil spring may be used as the pressure adjusting mechanism. Further, the moving body 105 is structured so as to come into contact with the vibrating body portion 103 in the vicinity of the maximum amplitude portion in the radial direction. Even if the vibrating body portion 103 is made of a thin flat elastic member, the components of the vibration wave excited in the vibrating body portion 103 are uniformly transmitted to the moving body 105. In addition, a contact-tooth-shaped displacement magnifying mechanism is provided at the contact portion between the moving body 105 and the vibrating body portion 103 so as to form unevenness in the circumferential direction as shown in the conventional structure of FIG.
The performance of the motor can also be improved. By adopting the structure of this embodiment, the vibrating body portion 103 and the moving body 105
Can be made thinner and smaller. Further, since the outer peripheral portion of the vibrating body portion 103 is set as the location where the maximum displacement in the radial direction is generated, the ultrasonic motor can be excited by the driving frequency which resonates in the primary vibration mode. With this configuration, the ultrasonic motor can be driven at a low frequency, and the current consumption of the oscillation circuit and the drive circuit can be reduced. FIG. 6 is a vertical sectional view of another embodiment of the ultrasonic motor of the present invention. The central shaft 601 is fixed to a fixed base 602. The vibrating body portion 603 is supported by the central shaft 601. The piezoelectric vibrator 604 is fixed to the surface of the vibrating body portion 603 away from the fixed base 602. The outer diameter of the piezoelectric vibrator 604 is the vibrating body portion 603.
Smaller than the outer diameter of According to this configuration, the piezoelectric vibrator 60
The capacitance of No. 4 is small, and low current consumption can be realized. When the piezoelectric vibrator 604 is made thin, the electric field strength becomes strong and it can be driven at a low voltage. On the other hand, when the piezoelectric vibrator 604 is made thin, the electrostatic capacity is increased. Therefore, reducing the diameter of the piezoelectric vibrator 604 is effective in reducing the current consumption. The pressure adjusting mechanism of this embodiment utilizes the repulsive forces of a plurality of permanent magnets. A threaded portion is provided on the outer circumference of the central shaft. The guide member 607 supports the vibrating body portion 603 and guides the rotation of the moving body 605. The magnet portion 608 and the magnet portion 609 are assembled via a washer 610. The stopper 611 pushes the magnet portion 609 toward the magnet portion 608. The magnet portion 608 and the magnet portion 609 repel each other due to the magnetic force of each other. The moving body 605 includes a magnet unit 608 and a magnet unit 60.
The repulsive force of 9 makes contact with the vibrating body portion 603 at a predetermined pressure. FIG. 7 is a diagram showing the behavior of the vibrating body portion in the radial direction of the embodiment of the ultrasonic motor of the present invention. Vibration part 70
The central portion of 2 is fixed to the central shaft 701. Piezoelectric vibrator 7
03 is fixed to one surface of the vibrating body portion 702. The vibrating body portion 702 operates in the primary vibration mode so that the outer peripheral portion has the maximum displacement. FIG. 7A is a view showing a structure in which the vibrating body portion 702 and the piezoelectric vibrator 703 have the same outer diameter. The vibrating body portion 703 and the piezoelectric vibrator 703 are transformed into the shape shown by the dotted line in the figure. This deformation is substantially arcuate. FIG. 7B is a diagram showing the configuration when the outer diameter of the vibrating body portion 702 is larger than the outer diameter of the piezoelectric vibrator 703. The portion of the vibrating body portion 702 to which the piezoelectric vibrator 703 is fixed deforms into a substantially arc shape. The portion of the vibrating body portion 702 to which the piezoelectric vibrator 703 is not fixed deforms linearly. A portion of the vibrating body portion 702 where the piezoelectric vibrator 703 is not fixed serves as a displacement magnifying mechanism. Comparing the displacements of FIGS. 7A and 7B, Xa is larger than Xb. On the other hand, in order to reduce the current consumption of the ultrasonic motor, a displacement magnifying mechanism is provided in FIG.
The structure of is effective. Further, the configuration of the ultrasonic motor of the present invention is the same even when the vibration is excited in the secondary vibration mode in the radial direction of the vibrating body. FIG. 8 is a diagram showing the relationship between the shape of the vibrator and the mechanical resonance frequency in the embodiment of the ultrasonic motor of the present invention. FIG. 8 shows a case where the vibrating body portion 103 is brass and three waves are generated in the circumferential direction of the vibrating body portion. The outer diameter of the vibrating body in which the piezoelectric vibrator is fixed to the vibrating body portion is plotted on the horizontal axis, and the mechanical resonance frequency is plotted on the vertical axis. The parameters in the figure are 0.2, 0.4, and 0.6 as the thickness of the vibrating body.
And 0.8 mm are illustrated. When the vibrating body portion 103 is supported at the center and the outer diameter of the vibrating body portion is reduced, the mechanical resonance frequency increases. Therefore, a low mechanical resonance frequency of 20 kHz or more of so-called ultrasonic waves is good for low power consumption. Therefore, it is preferable to make the vibrating body thin, but considering the state of flexural vibration and the occurrence of cracks, 0.1 to 0.2 mm is preferable.
At this time, when the outer diameter of the vibrating body is 10 mm, the thickness of the entire vibrating body is preferably about 0.3 to 0.6 mm. That is, the thickness of the vibrating body portion 103 is preferably equal to or slightly thicker than the thickness of the piezoelectric vibrator 104. As for the number of bending vibration waves generated in the circumferential direction of the vibrating body, in a configuration in which the vibrating body has the same shape, the mechanical resonance frequency increases as the number of exciting waves increases. 4 is suitable for stably rotating the moving body 104. As described above, according to the present invention, the vibrating body portion closely fixed to the stepped portion of the central axis fixed to the fixing base and the piezoelectric vibration fixed to the vibrating body portion. Since the configuration has the child and the moving body that makes pressure contact in the vicinity of the maximum amplitude portion in the radial direction of the vibrating body portion, the following effects are obtained. (1) The size of the ultrasonic motor can be reduced. (2) The ultrasonic motor can be made thin. (3) The efficiency of the ultrasonic motor can be increased. (4) Since the vibrating body portion is closely fixed to the stepped portion of the central shaft, there is almost no inclination in mounting the vibrating body portion, and the vibrating body portion can be firmly fixed. Therefore, it becomes possible to apply the ultrasonic motor to the field of precision equipment.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a vertical sectional view of a first embodiment of an ultrasonic motor according to the present invention. FIG. 2 is a principle diagram of generation of a traveling wave of an ultrasonic motor. FIG. 3 is a rotation principle diagram of a traveling wave type ultrasonic motor. FIG. 4 is a vertical sectional view (1) of a conventional ultrasonic motor. FIG. 5 is a vertical sectional view (2) of a conventional ultrasonic motor. FIG. 6 is a vertical sectional view of a second embodiment of the ultrasonic motor according to the present invention. FIG. 7 is a diagram showing behavior in a radial direction of a vibrating body portion of the ultrasonic motor according to the present invention. FIG. 8 is a diagram showing a relationship between a shape of a vibrating body of an ultrasonic motor according to the present invention and a mechanical resonance frequency. [Explanation of reference numerals] 101 central shaft 102 fixed base 103 vibrating body portion 104 piezoelectric vibrator 105 moving body 106 spring member 107 washer 108 stopper

Claims (1)

(57) [Claims] In an ultrasonic motor in which a moving body is frictionally driven by an oscillating wave using expansion and contraction motion of a piezoelectric vibrator, a fixing base (102) for fixing the ultrasonic motor, a thick shaft portion (101b) having a different outer diameter, and a thin shaft portion (101b) are used. Shaft (101c)
Forming at least two or more shafts of the thick shaft (101
The central axis (101) which fixed b) to the fixed stand (102)
And a central hole (103a), and the central hole (103a) is closely attached to the thin shaft portion (101c) of the central axis (101) in the radial direction.
The central axis (101) and the thick shaft (101
A vibrating body part (103) in which one surface in the vicinity of the central hole (103a) is axially adhered and fixed to the stepped part (101a) between the b) and the thin shaft part (101c), and a vibrating body part (103). 103) A piezoelectric vibrator (104) fixed to one surface of the moving body, and a moving body which pressurizes and contacts the vicinity of the maximum amplitude portion in the radial direction of the vibrating body portion (103) with the central axis (101) as a rotation guide. An ultrasonic motor comprising: (105); a pressurizing unit (106) for pressurizing the vibrating body section (103) and the moving body (105). 2. In an ultrasonic motor that frictionally drives a moving body by an oscillating wave using expansion and contraction motion of a piezoelectric vibrator, a fixing base (602) for fixing the ultrasonic motor, a thick shaft portion (601b) having a different outer diameter, and a thin shaft portion (601b). Shaft (601c)
Forming at least two or more shaft parts of the thick shaft part (601
Central axis (601) with b) fixed to a fixed base (602)
And has a central hole (603a), the central hole (603a) is fixed to the thin shaft portion (601c) of the central shaft (601), and
The thick shaft portion (601b) and the thin shaft portion (60) of the central shaft (601)
Center hole (603a) in the stepped portion (601a) between 1c)
A vibrating body part (603) in which one surface in the vicinity is closely attached and fixed.
And a piezoelectric vibrator (604) fixed to one surface of the vibrating body portion (603), and a central hole (607a), and the central hole (607a) is a thin shaft portion (601c) of the central axis (601). Fixed to the guide member (60) whose one end surface contacts the vibrating body portion (603).
7), a moving body (605) that is in pressure contact with the vibrating body portion (603) in the vicinity of the maximum amplitude portion in the radial direction, and a pressing body that applies pressure to the vibrating body portion (603) and the moving body (605). An ultrasonic motor comprising: pressure means (608, 609). 3. The guide member (607) is used as a rotation guide, and the vibrating body (6
The ultrasonic motor according to claim 2, further comprising a moving body (605) that is in pressure contact with the vicinity of the maximum amplitude portion in the radial direction of (03).