JPH10323063A - Vibration actuator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide vibration actuator which obtains degeneracy, creates vibration with a large amplitude, is high in Q-value, and generates less heat. SOLUTION: The actuator is provided with a rotating member 13 which is rotatable on a specified rotary shaft; an elastic member 4 which creates longitudinal vibration in the direction of the rotary shaft and torsional vibration around the rotary shaft, thereby producing elliptic motion at the end face in the direction of the rotary shaft; and a piezoelectric element which is installed on the elastic member in a position where there is a node of torsional vibration, and excites torsional vibration in the elastic member 4. In this case, the rigidity of the elastic member 4 varies along the rotary shaft, so that the maximum degree of sharpness does not become 0 or above when the distribution of the shearing strain is observed in terms of the direction of the rotary shaft.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vibration actuator for generating a driving force on a rotating member by utilizing the vibration of an elastic member.

[0002]

2. Description of the Related Art Conventionally, a vibration actuator of this type has been disclosed in, for example, Japanese Patent Application Laid-Open No.
There is a vibration actuator disclosed in 140377. FIG. 9 shows a vibration actuator disclosed in JP-A-8-140377 (hereinafter referred to as "conventional vibration actuator").
FIG. 10 is a sectional view showing the stator of the vibration actuator shown in FIG.

As shown in FIG. 9, a conventional vibration actuator has a stator 107 and a moving element 106 mounted on a shaft 107.
Is attached, and the moving element 106 is brought into pressure contact with the stator 101. The mover 106 is a mover base material 1
06-1 and a sliding member 106-2 provided on a surface of the moving element base material that comes into contact with the stator 101 and sliding with the stator 101. Further, as shown in FIG. 10, the stator 101 has an elastic body 10 obtained by dividing a thick-walled cylindrical member into two parts.
2 and 103, and two types of plate-like piezoelectric bodies (electromechanical energy conversion elements 104 and 105). The stator 101 includes the piezoelectric bodies 104 and 105 between the elastic bodies 102 and 103. It is sandwiched and assembled so as to have a substantially cylindrical shape as a whole.

Here, the piezoelectric body 104 is an element that expands and contracts along the central axis A1 of the stator 101 when a voltage is applied in the plate thickness direction, while the piezoelectric body 105 similarly applies a voltage. When applied, the element undergoes shear deformation along the central axis A1. In a conventional vibration actuator, a predetermined frequency voltage is applied to the piezoelectric bodies 104 and 105 with a phase difference of 90 degrees, and a longitudinal vibration in a direction along the center axis A1 and a direction of twisting about the center axis A1 are applied to the stator 101. Excites torsional vibration. As a result, the end face (hereinafter referred to as “driving face”) D1 of the stator 101 performs an elliptical motion, and a part of the elliptical motion is transmitted to the moving element 106, and the moving element 106 rotates in a certain direction. .

As described above, the conventional vibration actuator employs a configuration in which a piezoelectric body is disposed on the divided surfaces of the elastic bodies 102 and 103. Therefore, a large-area plate-like piezoelectric body is used. It has made it possible to realize an actuator with a high torque and a high rotational speed.

[0006]

In the conventional vibration actuator, in order to efficiently generate an elliptical motion on the driving surface D1, the natural frequency of the torsional vibration of the stator 101 and the natural frequency of the longitudinal vibration are required. Must match. This means that if these natural frequencies do not match,
This is because so-called degeneration of the vibration does not occur. However, when the stator 101 has a simple columnar shape or the like, the natural frequencies of the stators do not match, and there is a problem that it is difficult to efficiently drive the vibration actuator. In response to the above problems, the applicant of the present application
By providing grooves on the outer periphery of the stator to adjust and match the magnitudes of the above natural frequencies, and invented a vibration actuator with improved driving efficiency, this is disclosed in Japanese Patent Application No. 7-2416.
No. 23 and the like.

On the other hand, the vibration actuator causes a stator to vibrate in a desired mode by using a force generated by an electromechanical energy conversion element such as a piezoelectric body. Therefore, it is extremely important to place the electromechanical energy conversion element on the elastic body.
The present applicant has already disclosed in Japanese Patent Application No. 7-241623 and the like. According to this, it is most preferable that the electromechanical energy conversion element is arranged at a position of a node (a portion where strain is concentrated) of the vibration to be excited. Get higher.

Accordingly, providing the groove in the stator not only obtains the degeneration but also concentrates the strain on that portion, mounts the minimum necessary electromechanical energy conversion element, and applies electric energy only to it. It is a very effective means in the sense that it becomes possible. Provision of the groove is also effective in increasing the amplitude of vibration generated in the stator. However, the extreme concentration of distortion, on the other hand, greatly increases the generation of heat. Such heat generation causes a shift in the resonance frequency, and also impairs the stability of the operating characteristics of the vibration actuator. Furthermore, extreme concentration of distortion also causes a decrease in the Q value.

Here, the Q value is a value used for evaluating the vibration characteristics of the vibrator, and is generally a value that increases as local distortion does not concentrate. The higher the Q value, the better the vibration characteristics. The higher the Q value, the higher the upper limit value of the maximum number of rotations of the moving element can be. Furthermore, when the Q value is high, heat generation is also suppressed, and as a result, low-voltage driving of the vibration actuator becomes possible.

By the way, the shape of the vibrator having the highest Q value is a round bar shape or a plate shape having no groove or the like and having a constant cross-sectional shape in the main axis direction. However, considering the use of the vibration actuator as a stator, as described above, the resonance frequency of the torsional vibration does not coincide with that of the longitudinal vibration in such a round bar shape, and so-called degeneration does not occur. Further, there is a problem that the amplitude of the excited vibration becomes small. For this reason, in the conventional vibration actuator, a groove is required, and it is difficult to make the shape of the stator such that the Q value has the highest value. That is, in the conventional vibration actuator, a major problem in development is that the contradictory requirements of degenerating the vibration generated in the stator to obtain a large amplitude and improving the Q value are simultaneously satisfied. Was.

Accordingly, an object of the present invention is to provide a vibration actuator which has so-called degeneration and performs vibration of a large amplitude while having a high Q value and low heat generation.

[0012]

According to a first aspect of the present invention, there is provided a rotating member rotatable about a predetermined rotation axis, a longitudinal vibration in the direction of the rotation axis, and a rotation about the rotation axis. An elastic member that generates an elliptical motion on the end face in the rotation axis direction by performing torsional vibration of the torsional vibration, and the elastic member is installed at a position where a node of the torsional vibration is present, and excites the torsional vibration to the elastic member. In a vibration actuator having a piezoelectric element, the rigidity of the elastic member is such that a maximum kurtosis does not become 0 or more when a strain distribution of shear generated due to the torsional vibration is viewed in the rotation axis direction. In addition, the vibration actuator is characterized by changing along the rotation axis. According to a second aspect of the present invention, in the vibration actuator according to the first aspect, the elastic member changes the rigidity by changing a shape of a cross section perpendicular to the rotation axis along the rotation axis. A vibration actuator characterized in that:

According to a third aspect of the present invention, in the vibration actuator according to the second aspect, the elastic member changes a shape of the cross section along the rotation axis by providing a groove on an outer peripheral surface. A vibration actuator characterized by the following. According to a fourth aspect of the present invention, in the vibration actuator according to the first aspect, the elastic member has two or more members or portions having different elastic coefficients to change the rigidity. This is the vibration actuator. The invention according to claim 5 is the vibration actuator according to any one of claims 1 to 4, wherein the vibration generation source is a piezoelectric element.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION

(First Embodiment) Hereinafter, an embodiment of the present invention will be described in detail with reference to the accompanying drawings. In the following description of each embodiment, an ultrasonic motor using an ultrasonic vibration region as a vibration actuator will be described as an example.

FIG. 1 is a longitudinal sectional view showing the structure of the ultrasonic motor 1 according to the first embodiment. In FIG.
Is a piezoelectric body 3, which is an electromechanical transducer that is excited by input of a drive signal, and holds the piezoelectric body 3 in a state of being sandwiched therein in a direction parallel to the axial direction and excites the piezoelectric body 3. As a result, a primary longitudinal vibration (first vibration) and a secondary torsional vibration (second vibration) are generated, so that the drive surface 4c
And an elastic body 4 that generates a driving force.

The elastic body 4 is made of a metal material such as stainless steel or an aluminum alloy or an elastic material such as a plastic material. The elastic body 4 is composed of a hollow cylindrical elastic member and
Two semi-elastic bodies 4a obtained by dividing into two
4b is again assembled in a columnar shape. The elastic body 4 has three small diameter portions 5a, 5b, and 5c formed by providing peripheral grooves 5d, 5e, and 5f on the outer peripheral surface. In addition, four large-diameter portions 5A, 5B, 5C, and 5D are formed on the outer peripheral surface of the elastic body 4 by being partitioned by these small-diameter portions 5a to 5c. Small diameter part 5
a, 5b, and 5c represent the primary longitudinal vibration generated in the elastic body and 2
It is arranged to degenerate the next torsional vibration.

As shown in FIG. 2 to be described later, piezoelectric members 3a, 3b and 3c are provided on two divided surfaces of the elastic member 4, respectively.
It is held in a state sandwiched by layers. The piezoelectric body 3b is
A piezoelectric element using a piezoelectric constant d _31, is disposed at one position near the section of the primary longitudinal vibration generated in the elastic body 4 (substantially longitudinal center portion of the vibrator 2). Also, the piezoelectric bodies 3a, 3c
Are piezoelectric materials using a piezoelectric constant d ₁₅ ,
It is arranged at two places near the node of the secondary torsional vibration generated in the elastic body 4.

4 is formed on the outer peripheral surface of the elastic bodies 4a and 4b.
Through holes 6a, 6b, 6c, 6d are provided substantially at the centers of the large diameter portions 5A to 5D in the length direction thereof in a direction substantially parallel to the laminating direction of the piezoelectric bodies 3a to 3c. Bolts 7a, 7b, 7c, 7d are inserted into these through holes 6a to 6d, and nuts 8a, 8b, 8c, 8d are screwed to both ends of each of the bolts 7a to 7d, so that elastic members 4a, 4b are formed. Are fastened and fixed in a state where two piezoelectric bodies 3a to 3c are laminated on each of the two divided surfaces.

A through hole 9 is provided near the node of the primary longitudinal vibration in the small-diameter portion 5b. On the other hand, a hollow portion is formed in the longitudinal direction at the center of the elastic bodies 4a and 4b fixed and fastened, and the fixed shaft 10 is installed in a state having a gap with the hollow portion. A through-hole 11 having the same inner diameter as the through-hole 9 is formed at a position corresponding to the position where the through-hole 9 is formed in the longitudinal direction of the fixed shaft 10. Through hole 9 and through hole 11
Is fitted with a support pin 12 which is a support member having an outer diameter to be fitted therein. The elastic members 4 a and 4 b are fixed and supported on the fixed shaft 10 by the support pins 12.

The moving element 13 as a relative moving member is in contact with the moving element base material 13a, which is a hollow cylindrical body, and the end face of the moving element base material 13a on the vibrator 2 side, and comes into contact with the driving surface 4c of the vibrator 2. Annular sliding member 13b. The moving element base material 13a is made of, for example, a light alloy material such as an aluminum alloy or a steel material such as stainless steel. The sliding member 13b is made of, for example, a sliding resistance reducing material such as PTFE. A groove 14 is formed in an annular shape on the inner peripheral portion of the end face of the movable element base material 13a on the anti-vibrator side, and a bearing 15 as a positioning member is fitted in the groove 14. The bearing 15 is mounted and positioned on the fixed shaft 10, whereby the moving member 12 is fixed to the fixed shaft 1.
It is rotatably mounted with respect to 0.

A nut 16 serving as a pressing force adjusting member is screwed to the end of the fixed shaft 10. A disc spring 17 serving as a pressing member, a pressing force is applied between the nut 16 and the movable element 13. A washer 18 as a transmission member is attached to the fixed shaft 10. The moving element 12 is pressed toward the vibrator 2 by the spring force of the disc spring 17. The displacement of the disc spring 17 is adjusted by adjusting the screwing position of the nut 16, thereby adjusting the pressing force. The disc spring 17 is
The applied pressure can be changed continuously. Thus, in the ultrasonic motor 1 of the present embodiment, the fixed shaft 10
The vibrator 2 is fixedly supported, the mover 13 is rotatably supported, and the disc spring 17 is further supported to press the mover 12 toward the vibrator 2.

The other end of the fixed shaft 10 is fixed to a fixing portion 19 of the ultrasonic motor mounted device, whereby the ultrasonic motor 1 is mounted on the mounted device. FIG. 2 is an explanatory view showing the arrangement of the piezoelectric bodies 3a to 3c mounted on the vibrator 2 in the ultrasonic motor 1 of the present embodiment. FIG. 2A is a cross section of a left half from the center line. FIG. 2 is a side view showing FIG.
FIG. 2B is an explanatory diagram showing an AA section, a BB section, and a CC section in FIG. 2A together with a control block.

In the vibrator 2 of this embodiment, the piezoelectric body is roughly composed of three groups of piezoelectric bodies 3a to 3c. Each group of the piezoelectric bodies 3a to 3c is composed of two layers. As described above, one group of piezoelectric 3b of the piezoelectric body 3 group is a piezoelectric element using a piezoelectric constant d _31, the elastic member 4a, 4b the primary longitudinal vibration nodes near that occur It is arranged in one place. On the other hand, the remaining two groups of piezoelectric bodies 3a, 3c
Is a piezoelectric body using a piezoelectric constant d ₁₅ ,
a, 4b, are arranged at two locations near nodes of secondary torsional vibration generated.

As shown in FIG. 2 (b), the piezoelectric body 3a, 3c using a piezoelectric constant d ₁₅ generates a shear displacement with respect to the longitudinal direction of the elastic body 4a, 4b. A in FIG. 2 (b)
-Two groups of piezoelectric bodies 3 in each of the A section and the CC section
a, 3c are arranged such that the shearing deformation that occurs is alternately in the direction toward and away from the circumferential direction. Further, the piezoelectric bodies 3a and 3c are arranged such that the twisting directions are opposite in the AA section and the CC section, respectively. The piezoelectric bodies 3a and 3c are arranged in the directions as shown in FIGS.
When c undergoes shear deformation, a second-order torsional displacement occurs in the vibrator 2 having two nodes. On the other hand, the piezoelectric 3b using a piezoelectric constant d ₃₁ generates the elastic displacement with respect to the longitudinal direction of the elastic body 4a, 4b. 1 in the BB section
All of the longitudinal vibration piezoelectric bodies 3b of the group are arranged such that displacement occurs in the same direction when a certain potential is applied.

[0025] Thus, the piezoelectric constant d ₁₅ to use torsional vibration piezoelectric member 3a, and 3c, arranged a piezoelectric 3b using a piezoelectric constant d _31, the torsional vibration piezoelectric member 3a, to 3c By inputting the sine wave voltage, torsional vibration is generated in the vibrator 2 in response thereto. On the other hand, the piezoelectric body 3b for longitudinal vibration
, A longitudinal vibration is generated in the vibrator 2 accordingly.

As shown in FIG. 2B, the driving circuit 20
Is an oscillator 21 for oscillating a drive signal, and a phase shifter 2 for dividing the oscillated drive signal into signals having a (1/4) λ phase difference.
2, a T amplifier 23 for amplifying the drive signal input to the torsional vibration piezoelectric bodies 3a and 3c, and an L amplifying section 24 for amplifying the drive signal input to the longitudinal vibration piezoelectric body 3b. . In addition, as shown in FIG.
b is grounded.

According to the configuration described above, the oscillating section 21 oscillates the drive signal, and the oscillated drive signal is divided by the phase shift section 22 into two signals having a (１ ／) λ phase difference.
The signals are amplified by the T amplifier 23 and the L amplifier 24, respectively. The drive signal amplified by the T amplifier 23 is input to the torsional vibration piezoelectric bodies 3a and 3c, while the drive signal amplified by the L amplifier 24 is input to the longitudinal vibration piezoelectric body 3b. The torsional vibration piezoelectric bodies 3a, 3 to which the drive signal is input
c and the piezoelectric body 3b for longitudinal vibration cause vibration, respectively,
The secondary torsional vibration and the primary longitudinal vibration are generated in the vibrator 2.

FIG. 3 is an explanatory diagram showing a waveform example of the secondary torsional vibration (T2 mode) and the primary longitudinal vibration (L1 mode) generated in the vibrator 2. As shown in the figure, the vibrator 2 to which the drive signal has been input is the torsional vibration piezoelectric bodies 3a, 3b.
Excitation of c and the piezoelectric body 3b for longitudinal vibration generates a first-order longitudinal vibration (L1 mode) and a second-order torsional vibration (T2 mode) having antinodes and nodes of the vibration. At this time, if the phase difference of the periodic voltage applied to each of the torsional vibration piezoelectric bodies 3a and 3c and the longitudinal vibration piezoelectric body 3b is set to be shifted by (1/4) λ (λ: wavelength), the primary longitudinal Vibration (L1 mode)
An elliptical motion is generated on the drive surface 4c, which is a composite vibration of the vibration and the secondary torsional vibration (T2 mode).

At this time, the torsional vibration (T2 mode) is
Knots are formed at the two small-diameter portions 5a and 5c having low torsional rigidity, and the drive surface 4c becomes an antinode. On the other hand, in the longitudinal vibration (L1 mode), a node occurs near the small diameter portion 5b, and the driving surface 4c becomes an antinode. The moving element 13 that comes into pressure contact with the driving surface 4c receives a driving force from the vibrator 2 frictionally and is driven.

FIG. 4 shows a longitudinal vibration (L1) generated in the vibrator 2.
FIG. 9 is an explanatory diagram showing, over time, generation of an elliptical motion on the drive surface 4c by combining the torsional vibration (T2 mode) and the torsional vibration (T2 mode). In FIG. 4, for convenience of explanation, the moving element 13 that comes into pressure contact with the vibrator 2 via the driving surface 4c is not shown. When the phase difference between the period of the torsional vibration generated in the vibrator 2 and the period of the longitudinal vibration is set to be shifted by (1/4) λ, an elliptical motion is generated at a point on the drive surface 4c.
At this time, if the frequency of the drive signal is set to a value close to the natural frequency of the primary longitudinal vibration and the natural frequency of the secondary torsional vibration, resonance occurs and both the longitudinal vibration amplitude and the torsional vibration amplitude are changed. It is enlarged. As a result, a large elliptical motion occurs on the drive surface 4c.

In FIG. 4, if the drive frequency is f and the angular frequency of the drive signal at this time is ω, the displacement of the torsional vibration is maximum on the left side when t = 0. On the other hand, the displacement of the longitudinal vibration is zero. In this state, the moving element is pressed against the vibrator 2 by the pressing member, and thus comes into contact with the driving surface 4c of the vibrator 2 in a pressed state. t =
From 0 to t = (4/4) · (π / ω), the torsional vibration is displaced from the maximum on the left to the maximum on the right. On the other hand, the longitudinal vibration is displaced from zero to an upper maximum and returns to zero again. Therefore, the driving surface 4c of the vibrator 2 rotates rightward while pressing the mover, and the mover is driven to rotate rightward.

Next, from this time, t = (6/4) · (π /
ω), until t = (8/4) · (π / ω), the torsional vibration is displaced from the maximum on the right to the maximum on the left. On the other hand, the longitudinal vibration is displaced from zero to a lower maximum and returns to zero again. Therefore, since the driving surface 4c of the vibrator 2 rotates leftward while moving away from the moving element, the moving element is not driven. At this time, the moving element is pressed by the pressing member, but since the natural frequency of the pressing member is lower than the ultrasonic vibration range, the moving element does not follow the contraction of the vibrator 2.
In the ultrasonic motor 1 of the present embodiment, since the torsional resonance frequency and the longitudinal resonance frequency can be matched with the transducer 2 alone, the shape of the moving element 13 can be set relatively freely. There is an advantage.

Next, the form of the vibrator will be described in more detail. FIG. 5 is a comparative diagram showing the performance of five types of vibrators having different positions and widths of the small diameter portion. The uppermost part of FIG. 5 shows a schematic diagram of each vibrator and a distribution of strain generated in the vibrator when longitudinal vibration or torsional vibration is excited. In the second and lower stages, the performance such as the Q value of the vibrator is shown in the form of a star chart. The five types of vibrators are a constriction-free type, a uniform groove width A type, a uniform groove width B type, an L groove-wide type, and a T groove-wide type in order from the left in the figure. FIG. 6 is a diagram illustrating dimensions of an A-type vibrator having a uniform groove width and a T-groove-wide type vibrator.

Hereinafter, the shape and performance of the vibrator will be described with reference to FIG. The constriction-free type vibrator is a vibrator having no small diameter portion. In a constrictorless vibrator, the rigidity against torsional vibration and the rigidity against longitudinal vibration are uniform throughout the vibrator. For this reason, when torsional vibration and longitudinal vibration are excited in a non-constriction type vibrator, distortion is dispersed, and the Q value of longitudinal vibration (hereinafter referred to as “QL value”) and the Q value of torsional vibration (hereinafter “Q value”). QT value) is high. Therefore, the constrictionless vibrator has good performance as a resonator. However, since the resonance frequencies of the longitudinal vibration and the torsional vibration are different, it is difficult to reduce a different mode (longitudinal torsion) by the vibrator alone. In order to cause the degeneracy, the vibrator must always be combined with the moving element. . As described above, since the strain is dispersed, heat generation in the vibrator is small.

An A-type vibrator having a uniform groove width has a circumferential groove (hereinafter referred to as an "L groove") provided at a position corresponding to a node portion of the longitudinal vibration.
And two peripheral grooves (hereinafter, referred to as “T grooves”) provided at positions corresponding to the nodes of the torsional vibration on the outer peripheral surface. As shown in FIG. 6A, all three circumferential grooves have the same groove width. Each circumferential groove is provided at a position where the center in the width direction coincides with the node of vibration. The B-type vibrator having the uniform groove width has one L groove and two T grooves having the same groove width, similarly to the A-type vibrator having the uniform groove width. However, the T-groove is provided such that the center in the width direction is located closer to the end face of the vibrator than the node portion of the torsional vibration. It is different from the type of vibrator.

In these vibrators, by providing a circumferential groove, the resonance frequencies of the longitudinal vibration and the torsional vibration are matched. Therefore, these vibrators can be degenerated by the vibrator alone. Further, in a portion having a circumferential groove, vibration distortion is concentrated because the rigidity of the vibrator is low. FIG.
FIG. 4 is a distribution diagram of shear strain in the vicinity of an outer diameter generated in a uniform groove width B-type vibrator, showing respective distributions of a strain generated based on a longitudinal vibration and a strain generated based on a torsional vibration. As shown in FIG. 7, the concentration of distortion due to torsional vibration is remarkable in the T groove. In FIG. 7, the strain distribution in the T-groove is a positive value having a kurtosis exceeding 0, which indicates that the strain distribution has a sharper shape than the normal distribution. Note that the kurtosis refers to a value obtained based on Expression (1).

[0037]

(Equation 1)

In the resonator of the uniform groove width, since the strain is concentrated as described above, both the QL value and the QT value are relatively low (see FIG. 5). Further, in a portion where the strain is concentrated, heat is also large due to a large internal loss of the member.
This is remarkable in a T-groove where distortion is particularly concentrated. By the way, the piezoelectric body is an element that also has the property of a capacitor. The capacitance is proportional to the area. Therefore, when the area of the piezoelectric body is large,
The capacitance is increased, and the loss of electric energy generated in the piezoelectric body is also large. On the other hand, in the uniform groove width type vibrator, since the distortion is concentrated on the small diameter portion, there is an advantage that the longitudinal vibration and the torsional vibration can be efficiently excited by disposing the piezoelectric body having a small area in the small diameter portion. .

The L-groove-wide vibrator is a vibrator having three circumferential grooves, like the vibrator of the uniform groove width type. However, the width of the L-groove is wider than that of the vibrator of the uniform groove width. The L-groove-wide oscillator is the same as the oscillator having the uniform groove width in that the small-diameter portion is provided so that the resonance frequencies of the longitudinal vibration and the torsional vibration are matched. Therefore, L
The groove-wide transducer can be contracted by itself as in the case of the uniform-groove-width transducer. On the other hand, in the L-groove-wide type vibrator, since the L-groove is wide, the QL value is higher than that of the uniform groove width type vibrator. However, since most of the heat generated in the vibrator is generated in the T-slot where the concentration of distortion is large, the heat generated during driving is large as in the case of the oscillator having the uniform groove width.

The T-groove-wide transducer is a transducer used in the ultrasonic motor according to the present invention, and corresponds to the transducer 2 in FIG. As shown in FIG.
The T-groove-wide oscillator is a uniform-groove-width oscillator (FIG. 6).
(A) A vibrator in which the width of the T-groove is increased. Therefore, in the T-groove-wide type vibrator, the degree of concentration of distortion at the node of the torsional vibration is low, and the distribution of distortion is flatter than that in the uniform groove width type vibrator. FIG. 8 shows a T-slot.
It is a distribution diagram of the shear strain near the outer diameter part which arises in a wide type vibrator. The distribution of strain related to torsional vibration shown in FIG.
The kurtosis obtained based on the equation (1) is about -0.13.
That is, in the T-groove-wide type vibrator, the distribution of the strain related to the torsional vibration is flatter than the normal distribution.

Here, the respective roles of longitudinal vibration and torsional vibration in the ultrasonic motor according to the present invention will be considered.
First, the longitudinal vibration plays a clutch-like role to intermittently contact the vibrator and the moving element. Therefore, the longitudinal vibration only needs to be able to produce a force that does not lose the preload applied from the moving element, and the amplitude itself does not need to be large. Rather, an unnecessary amplitude of the longitudinal vibration does not appear as an output of the ultrasonic motor, and as a result, the efficiency of the ultrasonic motor is reduced.

On the other hand, the torsional vibration plays a role of giving a rotational force to the moving element. Therefore, if the amplitude of the torsional vibration is large, the output rotation speed of the ultrasonic motor is increased accordingly, and the characteristic as a high-speed rotation motor can be provided. For this reason, in the ultrasonic motor, in order to increase the amplitude of the torsional vibration, a high voltage is applied to the piezoelectric body for the torsional vibration, or the diameter of the vibrator at the node of the torsional vibration is reduced, and so on. The amplitude of torsional vibration is further expanded. However, such a treatment, at the node of torsional vibration,
This causes a larger concentration of strain as compared with the node part of the longitudinal vibration, and causes a large current to flow into the piezoelectric body for torsional vibration and a large amount of heat generation. In addition, a large amount of heat generated from the nodes of the torsional vibration causes a change in the resonance frequency of the vibrator.

Here, in the T-groove-wide type vibrator, as described above, the T-groove is made wider than before so as to avoid excessive concentration of distortion. As a result, as shown in FIG. 5, heat generation in the vibrator is reduced, and the QT value is also improved. Further, in the T-groove-wide type vibrator, not only the QT value but also the QL value are better than those of the uniform groove width type vibrator. This is because the enlargement of the T-groove also contributes to appropriate dispersion of distortion due to longitudinal vibration.

On the other hand, an increase in the width of the T-groove leads to an increase in the surface area of the heat generating portion of the vibrator. Therefore, in the case of the T-groove-wide type vibrator, the radiation efficiency is also improved. In addition, since the improvement of the Q value lowers the resonance resistance value, it is possible to increase the maximum inflow current near the resonance point to the piezoelectric body, and as a result, the ultrasonic motor having the maximum rotation speed of the moving element is large. Is realized. Further, due to the improvement in the Q value, the ultrasonic motor using the T-groove-wide transducer is driven at a lower voltage than the conventional one. This means that the ultrasonic motor can be driven using a small booster circuit or can be directly driven by a battery. Therefore, the actuator using the T-groove-wide transducer is suitable for a portable small device operated by a battery, and can maximize the essential advantages of the ultrasonic motor, such as small size and high torque.

In the vibrator of the present embodiment, the shear strain caused by the torsional vibration is greater on the outer diameter side than on the inner diameter side near the axis of the vibrator. Therefore, when looking at the kurtosis of the shear strain distribution in the axial direction of the vibrator, when comparing the inner diameter side and the outer diameter side of the vibrator, the kurtosis obtained based on the strain distribution near the outer diameter part is smaller. It is thought to be the largest. In the present embodiment, when the strain distribution of the shear of the vibrator is viewed in the axial direction of the vibrator, the kurtosis is set to be less than 0 near the outer diameter portion of the vibrator where the kurtosis is maximum. Thus, advantages such as large amplitude, high Q value, heat generation and low drive voltage are obtained.

(Other Embodiments) The present invention is not limited to the above embodiment. The above embodiment is an exemplification, and has substantially the same configuration as the technical idea described in the scope of the claims of the present invention. It is included in the technical scope of the invention. For example, in the above-described embodiment, the torsional secondary mode, particularly the torsional secondary mode in the case of the deformed mode degenerate type vibrator in which the torsional secondary mode vibration and the longitudinal primary mode vibration occur, has been described according to the present invention. The technical idea can be applied to an actuator that vibrates in another vibration mode as long as it is an actuator using a vibration wave.

In the above-described embodiment, the rigidity of the elastic body is locally changed by providing the circumferential groove. For example, the elastic body is formed of two or more members having different elastic coefficients. Thus, the rigidity may be locally changed. Alternatively, the elastic body may be composed of one type of member, but the elastic body may be composed of two or more parts having different elastic coefficients by locally annealing the member.

Further, in the above embodiment, the case where the piezoelectric body is used as a vibration source for exciting torsional vibration or longitudinal vibration in the elastic body has been described as an example. It is not meant to limit the type of source in any way. The vibration source may be any element that can apply a predetermined vibration to the elastic body, and is an element that excites the elastic body by converting magnetostriction and other electric energy, magnetic energy or heat energy into mechanical displacement. There may be.

[0049]

As described above in detail, according to the present invention, the maximum kurtosis does not become 0 or more when the shear strain distribution caused by the torsional vibration is viewed in the rotation axis direction. As described above, since it changes along the rotation axis, so-called degeneration can be obtained. Further, it is possible to obtain a vibration actuator having a high Q value, a low heat generation and a low driving voltage while performing vibration of a large amplitude. became.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing a structure of an ultrasonic motor according to the present invention.

FIG. 2 is an explanatory view showing an arrangement of a piezoelectric body mounted on a vibrator.

FIG. 3 is an explanatory diagram showing a waveform example of a secondary torsional vibration (T2 mode) and a primary longitudinal vibration (L1 mode) generated in a vibrator.

FIG. 4 is an explanatory diagram showing, over time, generation of an elliptical motion on a drive surface by combining longitudinal vibration and torsional vibration generated in a vibrator.

FIG. 5 is a comparative diagram showing the performance of five types of vibrators having different positions and widths of the small diameter portion.

FIG. 6 is a diagram exemplifying dimensions of an A-type vibrator with a uniform groove width and a T-groove-wide type vibrator.

FIG. 7 is a distribution diagram of distortion generated in a B-type vibrator having a uniform groove width.

FIG. 8 is a distribution diagram of distortion generated in a T-groove-wide oscillator.

FIG. 9 is a sectional view showing a vibration actuator disclosed in Japanese Patent Application Laid-Open No. 8-140377.

FIG. 10 is a perspective view showing a stator of the vibration actuator disclosed in Japanese Patent Application Laid-Open No. 8-140377.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Ultrasonic motor 2 Vibrator 3 Piezoelectric body 4 Elastic body 5d, 5e, 5f Peripheral groove 10 Fixed axis 13 Moving element

Claims (5)

[Claims] A rotating member rotatable about a predetermined rotation axis; and an elastic member for generating an elliptical motion on an end face in the rotation axis direction by performing longitudinal vibration in the rotation axis direction and torsional vibration about the rotation axis. A vibration source having a member and a vibration source installed on the elastic member at a position where a node of the torsional vibration is present and exciting the torsional vibration to the elastic member. When viewing the shear strain distribution caused by the rotation axis direction,
A vibration actuator characterized by changing along the rotation axis so that the maximum kurtosis does not become 0 or more. 2. The vibration actuator according to claim 1, wherein the elastic member changes the rigidity by changing a shape of a cross section perpendicular to the rotation axis along the rotation axis. Vibration actuator. 3. The vibration actuator according to claim 2, wherein the elastic member changes a shape of the cross section along the rotation axis by providing a groove on an outer peripheral surface. . 4. The vibration actuator according to claim 1, wherein the elastic member is configured by two or more members or portions having different elastic coefficients to change the rigidity. Actuator. 5. The method according to claim 1, wherein:
The vibration actuator according to claim 1, wherein the vibration generation source is a piezoelectric element.