JP2003111454A - Ultrasonic motor and its stator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ultrasonic motor in which generation of noise can be reduced. SOLUTION: The ultrasonic motor comprises a stator 1 constructed by tightening first and second piezoelectric elements 5 and 6 held between upper and lower metal blocks 3 and 4 by means of a bolt 9 inserted into the piezoelectric elements 5 and 6 and the metal blocks 3 and 4 in the axial direction and vibration upon application of a high frequency voltage, and a rotor 2 coming into pressure contact slidably with one end face of the stator 1 and rotating based on the vibration of the stator 1. The components constituting the stator 1, i.e., the upper and lower metal blocks 3 and 4 and the bolt 9, have natural resonance frequencies set to deviate from the audible frequency region (0.02-20 [kHz]). With such an arrangement, occurrence of a large peak of sound pressure is suppressed in the audible frequency region.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic motor and its stator.

[0002]

2. Description of the Related Art As a conventional ultrasonic motor, there is a standing wave type (so-called bolting Langevin type) as shown in FIG. This ultrasonic motor includes a stator 51 and a rotor 52. The stator 51 includes metal blocks 53 and 54, piezoelectric elements 55 and 56, electrode plates 57 and 58,
And a bolt 59 (indicated by a broken line in the figure). As shown in FIG. 6, the members 53 to 58 are laminated in a substantially cylindrical shape, and the metal blocks 53 and 54 are connected and fixed by being tightened by bolts 59 inserted in the metal blocks 53 and 54 in the axial direction.

A slit 54a for generating a torsional vibration based on a longitudinal vibration is formed on the outer periphery of the lower portion of the stator 51, that is, on the outer periphery of the lower metal block 54. Further, on the outer periphery of the lower metal block 54, the slit 54a
An annular fixing convex portion 54b for fixing to the outside (motor case or the like) is formed below the.

The rotor 52 is formed in a substantially cylindrical shape, and is rotatably press-contacted to the upper surface of the stator 51, that is, the upper end surface of the upper metal block 53 by a pressing mechanism (not shown).

A slit 52a is formed on the outer periphery of the rotor 52 to generate torsional vibration based on longitudinal vibration. In this ultrasonic motor, when a high frequency voltage (for example, 65 kHz) is applied to the electrode plates 57 and 58, longitudinal vibration is generated in the piezoelectric elements 55 and 56. Then, torsional vibration is generated in the slit 54a of the metal block 54.
In the rotor 52, torsional vibration is generated in the slit 52a based on (resonant with) the vibration propagated from the stator 51. Then, the rotor 52 is rotationally driven by the buoyant force due to the longitudinal vibration of the stator 51 and the propulsive force due to the torsional vibration of the stator 51 and the rotor 52.

[0006]

By the way, in the above ultrasonic motor, since the rotor 52 is rotated by vibration, noise (audible frequency range (0.02 to 0.02) due to the vibration is generated.
20 [kHz]) may occur.

Here, the results of measuring the natural resonance frequency of each component of the conventional ultrasonic motor are shown in FIGS.
1 will be described. As shown in FIG. 7, the lowest-order natural resonance frequency of the assembled stator 51 is about 32 k.
It was Hz. As shown in FIG. 8, the lowest-order natural resonance frequency of the rotor 52 was about 30 kHz. As shown in FIG. 9, the lowest-order natural resonance frequency of the upper metal block 53 was about 26.6 kHz. As shown in FIG. 10, the lowest-order natural resonance frequency of the bolt 59 is about 30.
It was kHz. As shown in FIG. 11, the lowest-order natural resonance frequency of the lower metal block 54 is about 17.8 kHz.
It was z. 7 to 11 show the finite element method (FE
It is explanatory drawing which shows the shape of each member at the time of the vibration identified using M: Finite Element Method.

The result (frequency analysis result) of measuring the noise of the ultrasonic motor composed of the above components will be described with reference to FIG. FIG. 12 is a frequency-sound pressure characteristic diagram. As shown in FIG. 12, in the ultrasonic motor, a large peak of the sound pressure occurs at about 17.8 kHz, which is substantially the same frequency as the lowest natural resonance frequency of the lower metal block 54 (maximum about). 63dBA). Therefore,
In the above ultrasonic motor, a large audible frequency range (about 17.
There is a problem that a sound of 8 kHz), that is, a large noise is generated.

The present invention has been made to solve the above problems, and an object thereof is to provide an ultrasonic motor capable of reducing the generation of noise, and a stator thereof.

[0010]

According to a first aspect of the present invention, a piezoelectric element is fastened in a state of being sandwiched between a plurality of metal blocks, the stator vibrating when a high frequency voltage is applied, and the stator. In an ultrasonic motor provided with a rotor that is movably pressure-contacted and rotates based on the vibration of the stator, each component constituting the stator has its natural resonance frequency outside the audible frequency range. Is set.

According to a second aspect of the present invention, in the ultrasonic motor according to the first aspect, each of the components includes a fastening member that fastens the metal block and the stator. According to a third aspect of the invention, in the ultrasonic motor according to the first or second aspect, the natural resonance frequency of the rotor is set outside the audible frequency range.

According to a fourth aspect of the present invention, in the ultrasonic motor according to any one of the first to third aspects, the lowest natural resonance frequency of each component constituting the stator is set to the maximum audible frequency. By setting it larger, the natural resonance frequency of each component was set to be outside the audible frequency range.

According to a fifth aspect of the present invention, in the ultrasonic motor according to the first to fourth aspects, the stator in which the above-mentioned components are assembled has a natural resonance frequency outside the audible frequency range. Is set.

In a sixth aspect of the present invention, the piezoelectric element is fastened in a state of being sandwiched between a plurality of metal blocks, and the constituent elements of the stator of the ultrasonic motor vibrating when a high-frequency voltage is applied constitute the piezoelectric element. The component is set so that its natural resonance frequency is outside the audible frequency range.

(Operation) According to the invention described in claim 1,
Each component constituting the stator is set so that its natural resonance frequency is outside the audible frequency range. With this configuration, when the stator vibrates, generation of a large peak of sound pressure in the audible frequency range is suppressed in the stator. Therefore, the sound in the audible frequency range, that is, noise is reduced,
An ultrasonic motor with high quietness can be obtained.

According to the second aspect of the present invention, each component including the metal block and the fastening member that constitutes the stator is set so that its natural resonance frequency is outside the audible frequency range.

According to the third aspect of the invention, the natural resonance frequency of the rotor is set outside the audible frequency range. With this configuration, it is possible to prevent the rotor from generating a large peak of sound pressure in the audible frequency range when the stator vibrates. Therefore, the sound in the audible frequency range, that is, noise is reduced, and an ultrasonic motor with high quietness can be obtained.

According to the fourth aspect of the present invention, the lowest-order natural resonance frequency of each component forming the stator is set higher than the maximum audible frequency, so that the natural resonance frequency of each component is increased. It is set to be outside the audible frequency range.

According to the fifth aspect of the present invention, the stator to which the components are assembled is set so that its natural resonance frequency is outside the audible frequency range. By doing so, it is possible to further suppress the occurrence of a large peak of sound pressure in the audible frequency range of the stator when the stator vibrates. Therefore, the sound in the audible frequency range, that is, noise is reduced, and an ultrasonic motor with high quietness can be obtained.

According to the sixth aspect of the present invention, each component constituting itself is set such that its natural resonance frequency is outside the audible frequency range. By so doing, it is possible to suppress the occurrence of a large peak of sound pressure in the audible frequency range when the stator vibrates. Therefore, the sound in the audible frequency range, that is, the noise is reduced, and a highly quiet stator can be obtained.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described below with reference to FIGS. As shown in FIGS. 1 and 2, the ultrasonic motor includes a stator 1 and a rotor 2. The stator 1 includes an upper metal block 3, a lower metal block 4, first and second piezoelectric elements 5 and 6, first and second electrode plates 7 and 8, bolts 9 as fastening members, and an insulating collar 10 (see FIG. 2)).

The upper and lower metal blocks 3 and 4 are made of a conductive metal and are made of an aluminum alloy in this embodiment. The upper metal block 3 is formed in a substantially cylindrical shape. On the upper part of the upper metal block 3, a horn part 3a for amplifying the vibration generated on the upper end surface is formed by increasing the inner diameter thereof. A female screw 3b is formed on the inner peripheral surface of the upper metal block 3 excluding the horn portion 3a. A thin friction material 3c is attached to the upper end surface of the upper metal block 3.

The lower metal block 4 is formed in a substantially cylindrical shape having the same inner and outer diameters as the upper metal block 3. A slit (recess) 4a is formed on the outer periphery of the upper part of the lower metal block 4 to generate torsional vibration based on the excited longitudinal vibration. A plurality of slits 4a are formed in the circumferential direction,
Each is inclined with respect to the rotation axis direction.

A plurality of fixing projections 4b are formed in the circumferential direction on the outer periphery of the central portion of the lower metal block 4 (the central portion in the direction of the rotation axis) for fixing to the outside (motor case or the like not shown). There is. The fixing convex portion 4b is (continuously) formed on the lower end side of the slit 4a. Also, the fixing protrusion 4
The central position in the circumferential direction at the base end of b is the slit 4a.
Is set to the position on the lower end side of. This fixing convex portion 4b
Are formed for each slit 4a, that is, as many as the number of slits 4a.

The inner peripheral surface of the lower metal block 4 (see FIG. 2)
A female screw 4c is formed in the middle (shown by the broken line).
The first and second piezoelectric elements 5 and 6 are formed in a disc shape, and through holes are formed in the central portions thereof. The inner diameters of the first and second piezoelectric elements 5 and 6 are set larger than the inner diameters of the upper and lower metal blocks 3 and 4.

The first and second electrode plates 7 and 8 are formed in a disc shape, and through holes are formed in the central portions thereof. The inner diameters of the first and second electrode plates 7 and 8 are set to be the same as the inner diameters of the first and second piezoelectric elements 5 and 6.

The bolt 9 has a substantially columnar shape with a male screw 9a formed on the outer periphery thereof, and has the female screws 3b, 4 described above.
It can be screwed into c. The insulating collar 10 is formed of insulating resin into a cylindrical shape. This insulation collar 10
Has an outer diameter of the first and second piezoelectric elements 5, 6 and
And the inner diameters of the second electrode plates 7 and 8 are set to be the same as the outer diameter of the male screw 9a of the bolt 9 (the bolt 9 can be fitted therein).

The upper and lower metal blocks 3 and 4 sandwiching the first and second piezoelectric elements 5 and 6 and the first and second electrode plates 7 and 8 are bolts that penetrate the inside thereof in the axial direction. It is fastened by 9. More specifically, the lower metal block 4, the second electrode plate 8, the second piezoelectric element 6, the first electrode plate 7, the first piezoelectric element 5, and the upper metal block 3 are stacked in this order and inserted into the inside. The bolts 9 (male screws 9a) are fastened by being screwed into the female screws 3b and 4c of the upper and lower metal blocks 3 and 4, respectively. At this time, the first and second piezoelectric elements 5 and 6 are laminated so that their polarization directions are upside down. At this time, the insulating collar 10 is provided between the inner peripheral surfaces of the first and second piezoelectric elements 5 and 6, the first and second electrode plates 7 and 8 and the outer peripheral surface of the male screw 9a of the bolt 9. Is intervened. Therefore, the inner peripheral surfaces of the first and second piezoelectric elements 5, 6 and the first and second electrode plates 7, 8 and the outer peripheral surface of the bolt 9 are electrically insulated. At this time, the second electrode plate 8 is electrically connected to the upper metal block 3 via the lower metal block 4 and the bolt 9.

The rotor 2 is formed in a substantially cylindrical shape having the same outer diameter as the upper and lower metal blocks 3 and 4, and the upper surface of the stator 1, that is, the upper metal block 3 (friction material 3c) is applied by a pressing mechanism (not shown). ) Is in pressure contact with the upper end surface so that it can slide and rotate. On the outer periphery of the rotor 2, a slit (recess) 2 that generates torsional vibration based on the excited longitudinal vibration.
A plurality of a are formed in the circumferential direction. This slit 2a
Are inclined with respect to the rotation axis direction.

Here, the natural resonance frequency of each component of the ultrasonic motor is in the audible frequency range (0.02 to 2).
0 [kHz]). Specifically, the lowest-order natural resonance frequency of the assembled stator 1 is set to about 32 kHz. The lowest natural resonance frequency of the rotor 2 is set to about 30 kHz as in the conventional technique (see FIG. 8). Upper metal block 3
The lowest natural resonance frequency of is set to about 26.6 kHz as in the prior art (see FIG. 9). The lowest natural resonance frequency of the bolt 9 is set to about 30 kHz as in the conventional technique (see FIG. 10). The lowest natural resonance frequency of the lower metal block 4 is set to about 45.9 kHz, as shown in FIG. That is, each component is set so that its lowest resonance frequency is set higher than the maximum audible frequency (20 kHz) so that the natural resonance frequency is outside the audible frequency range. Incidentally, the first and second piezoelectric elements 5, 6, the first and second piezoelectric elements
Since the electrode plates 7 and 8 are sandwiched between the upper and lower metal blocks 3 and 4 by a large force, their natural resonance frequency can be ignored (the element that causes a large peak of sound pressure is extremely small). small). Further, FIG. 3 shows the finite element method (FE
It is explanatory drawing which shows the shape of the lower metal block 4 at the time of the vibration identified using M: Finite Element Method.

In the ultrasonic motor thus constructed,
When a high frequency voltage having a first resonance frequency (for example, about 64 kHz) is applied between the first and second electrode plates 7 and 8, the first
And longitudinal vibration is generated in the second piezoelectric elements 5 and 6. Then, torsional vibration is generated in the slit 4a of the stator 1 based on the vibration. At this time, the upper surface of the stator 1,
That is, the vibration of the upper end surface of the upper metal block 3 (friction material 3c) is a composite vibration that is a combination of torsional vibration and longitudinal vibration. Then, the rotor 2 rotates in one direction by the buoyant force of the longitudinal vibration component of the stator 1 and the propulsive force of the torsional vibration component (stator main mode).

In addition, a second electrode is provided between the first and second electrode plates 7 and 8.
When a high frequency voltage having a resonance frequency (for example, about 67 kHz) is applied, longitudinal vibration is generated in the first and second piezoelectric elements 5 and 6. Then, torsional vibration is generated in the slit 4a of the stator 1 based on the vibration. At this time, the upper surface of the stator 1, that is, the upper metal block 3 (the friction material 3
The vibration of the upper end surface of c) is a composite vibration in which the torsional vibration twisted in the opposite direction of the torsional vibration of the stator main mode and the longitudinal vibration are combined. Here, the resonance frequency of the rotor 2 is set so as to overlap with the second resonance frequency. In the rotor 2, the vertical vibration (composite vibration)
Based on (resonant), torsional vibration is generated in the slit 2a. At this time, the torsional vibration generated in the slit 2a moves in the other direction (opposite direction of the stator main mode).
It is a vibration that works to rotate. Therefore, the rotor 2 rotates in the other direction by the buoyant force due to the longitudinal vibration component of the stator 1, the propulsive force due to the torsional vibration component, and the torsional vibration component of the rotor 2 itself (rotor main mode).

The result (frequency analysis result) of measuring the noise of the ultrasonic motor composed of the above components will be described with reference to FIG. FIG. 4 is a frequency-sound pressure characteristic diagram. As shown in FIG. 4, in the above ultrasonic motor, a large peak of sound pressure is not generated as compared with the conventional technique (up to about 33 dBA).

Next, the characteristic effects of the above embodiment will be described below. (1) Each component of the stator 1 (upper and lower metal blocks 3, 4 and the bolt 9) has its natural resonance frequency outside the audible frequency range (0.02 to 20 [kHz]). It is set. In this way, when the stator 1 vibrates, the occurrence of a large peak of sound pressure in the audible frequency range is suppressed in the stator 1. Therefore, the sound in the audible frequency range, that is, noise is reduced, and an ultrasonic motor with high quietness can be obtained. Also, the motor efficiency of this ultrasonic motor can be improved.

(2) The natural resonance frequency of the rotor 2 is set outside the audible frequency range (0.02 to 20 [kHz]). By doing so, it is possible to prevent the rotor 2 from generating a large peak of sound pressure in the audible frequency range when the stator 1 vibrates. Therefore, the sound in the audible frequency range, that is, the noise is reduced, and it is possible to obtain an ultrasonic motor with high quietness.

(3) In the stator 1 in which the respective components are assembled, its natural resonance frequency is in the audible frequency range (0.02).
.About.20 [kHz]). In this way, when the stator 1 vibrates, the occurrence of a large peak of sound pressure in the audible frequency range of the stator 1 is further suppressed. Therefore, the sound in the audible frequency range, that is, the noise is reduced, and it is possible to obtain an ultrasonic motor with high quietness.

The above embodiment may be modified as follows. In the above-described embodiment, the lowest-order natural resonance frequency of the lower metal block 54 of the conventional technique (see FIG. 6) is within the audible frequency range (0.02 to 20 [kHz]) (about 1).
Therefore, the lower metal block 4 whose shape and the like have been changed is used, but each component (excluding the first and second piezoelectric elements 5 and 6, and the first and second electrode plates 7 and 8). The natural resonance frequency of is in the audible frequency range (0.02 to 20 [kHz])
The shape of each component may be appropriately changed as long as it is set to be other than the above.

For example, the lower metal block 4 of the above embodiment may be changed to the lower metal block 21 shown in FIG. The lower metal block 21 is formed in a substantially cylindrical shape having the same inner and outer diameters as the upper metal block 3. A slit (recess) 21a is formed on the outer periphery of the upper portion of the lower metal block 21 to generate torsional vibration based on the excited longitudinal vibration. A plurality of slits 21a are formed in the circumferential direction, and each slit 21a is inclined with respect to the rotation axis direction.

An annular fixing convex portion 21b for fixing to the outside (a motor case (not shown) or the like) is formed on the outer periphery of the central portion (central portion in the rotation axis direction) of the lower metal block 21. The fixing convex portion 21b is formed (separated) on the lower end side of the slit 21a. Further, the fixing convex portion 21b is set to have a smaller width (thickness) in the rotation axis direction and a smaller protrusion amount than those of the conventional technique (see FIG. 6). The lowest natural resonance frequency of the lower metal block 21 is set to about 46 kHz.
Even in this case, the same effect as that of the above-described embodiment can be obtained.

In the above embodiment, two metal blocks are used.
Although the ultrasonic motor (stator 1) is provided with three (upper and lower metal blocks 3, 4), it may be changed to one having three or more metal blocks. For example, the lower metal block 4 may be changed to one that is divided in the axial direction.
That is, even if the portion of the lower metal block 4 in which the slit 4a is formed is changed to a portion of the lower metal block 4 below the fixing convex portion 4b, which is a separate metal block. Good. In this case as well, the natural resonance frequency of each divided metal block is in the audible frequency range (0.02 to 20).
It must be set to a value other than [kHz]). Even in this case, the same effect as that of the above-described embodiment can be obtained.

In the above embodiment, the bolt 9 is used as the fastening member, but it may be changed to another fastening member (for example, one which is fastened by caulking). In this case, the natural resonance frequency of the other fastening member is in the audible frequency range (0.02 to 20).
It must be set to a value other than [kHz]). Even in this case, the same effect as that of the above-described embodiment can be obtained.

In the above-described embodiment, the rotor 2 is embodied as an ultrasonic motor capable of rotating in both directions, but it may be embodied as an ultrasonic motor exclusively for unidirectional rotation. In this case, it is necessary to appropriately change the shape of the slit 2a of the rotor 2 and the like. Even in this case, the same effect as that of the above-described embodiment can be obtained.

Although the stator 1 of the above-described embodiment has two piezoelectric elements (first and second piezoelectric elements 5 and 6), the number of piezoelectric elements may be changed appropriately. For example, one or three piezoelectric elements may be provided.
Even in this case, the same effect as that of the above-described embodiment can be obtained.

Although the stator 1 of the above-mentioned embodiment has two electrode plates (first and second electrode plates 7 and 8), the number of electrode plates may be changed appropriately. For example, it may be provided with no electrode plate (the metal block itself serves as an electrode plate) or may be provided with three electrode plates.
Even in this case, the same effect as that of the above-described embodiment can be obtained.

[0045]

As described in detail above, according to the invention described in claims 1 to 5, it is possible to provide an ultrasonic motor capable of reducing the generation of noise.

According to the invention described in claim 6, it is possible to provide the stator of the ultrasonic motor capable of reducing the generation of noise.

[Brief description of drawings]

FIG. 1 is a perspective view of an ultrasonic motor according to the present embodiment.

FIG. 2 is a sectional view of a main part of the ultrasonic motor according to the present embodiment.

FIG. 3 is a schematic diagram of the shape of the lower metal block in the present embodiment specified by FEM analysis.

FIG. 4 is a frequency of the ultrasonic motor according to the present embodiment-
Sound pressure characteristic diagram.

FIG. 5 is a perspective view of an ultrasonic motor according to another example.

FIG. 6 is a perspective view of an ultrasonic motor according to a conventional technique.

FIG. 7 is a schematic diagram of the shape of a stator identified by FEM analysis.

FIG. 8 is a schematic diagram of the shape of a rotor identified by FEM analysis.

FIG. 9 is a schematic diagram of the shape of the upper metal block identified by FEM analysis.

FIG. 10 is a schematic diagram of the shape of a bolt identified by FEM analysis.

FIG. 11 is a schematic diagram of the shape of a conventional lower metal block identified by FEM analysis.

FIG. 12 is a frequency-sound pressure characteristic diagram of the ultrasonic motor according to the related art.

[Explanation of symbols]

1 ... Stator, 2 ... Rotor, 3 ... Upper metal block (metal block), 4, 21 ... Lower metal block (metal block), 5, 6 ... 1st and 2nd piezoelectric element (piezoelectric element),
9 ... Bolt (fastening member).

Continued front page    (72) Inventor Masafumi Ishikawa             Asumo Corporation, 390 Umeda, Kosai City, Shizuoka Prefecture             In the company F term (reference) 5H680 AA18 BB04 BB16 CC06 DD02                       DD14 DD23 DD35 DD44 DD65                       DD87 EE04 FF04 FF26 GG01

Claims (6)

[Claims] 1. A piezoelectric element (5, 6) is fastened while being sandwiched between a plurality of metal blocks (3, 4, 21),
An ultrasonic wave including a stator (1) vibrating by applying a high-frequency voltage, and a rotor (2) slidably press-contacted with the stator (1) and rotating based on the vibration of the stator (1). In the motor, each component (3, 4, 4) that constitutes the stator (1)
9, 21) is an ultrasonic motor characterized in that its natural resonance frequency is set outside the audible frequency range. 2. The ultrasonic motor according to claim 1, wherein each component is the metal block (3, 4, 21).
And an ultrasonic motor comprising a fastening member (9) for fastening the stator (1). 3. The ultrasonic motor according to claim 1, wherein the natural resonance frequency of the rotor (2) is set outside the audible frequency range. 4. The ultrasonic motor according to claim 1, wherein each component (3, 4, 4) that constitutes the stator (1).
By setting the lowest-order natural resonance frequency of (9, 21) above the maximum audible frequency, each of the components (3, 4, 4)
An ultrasonic motor characterized in that the natural resonance frequency of (9, 21) is set outside the audible frequency range. 5. The ultrasonic motor according to any one of claims 1 to 4, wherein the stator (1) to which the respective components (3, 4, 9, 21) are assembled has a natural resonance frequency in an audible frequency range. An ultrasonic motor characterized by being set to be other than. 6. A piezoelectric element (5, 6) is fastened in a state of being sandwiched between a plurality of metal blocks (3, 4, 21),
In the stator of an ultrasonic motor that vibrates by applying a high frequency voltage, each component (3, 4, 9, 21) that constitutes itself is set so that its natural resonance frequency is outside the audible frequency range. Characteristic ultrasonic motor stator.