The present invention relates to an ultrasonic motor.
Conventionally, there have been proposed various ultrasonic motors in each of which a stator is vibrated by a piezoelectric element. Japanese Patent Application Laid-Open No. S61-106076 (hereinafter “Patent Document 1”) discloses an example of a piezoelectric motor. In this piezoelectric motor, a slider is rotated by vibration of a fixed element being transmitted to the slider. Moreover, a protrusion for transmitting vibration is provided only on a portion of the fixed element that is in contact with the slider.
Conventionally, in order to increase a torque of a motor, it is necessary to increase the size of the fixed element, in other words, the size of the stator needs to be increased. Therefore, it is necessary to make the whole motor larger. In recent years, downsizing of a device has progressed, but it has been difficult to achieve both of increasing the torque of a motor and contribution to downsizing of the device.
Accordingly, it is an object of the present invention to provide an ultrasonic motor with increased torque without increase in size.
In an exemplary aspect, an ultrasonic motor is provided that includes a stator having a plate-shaped vibrating body including a first main surface and a second main surface that face each other; a piezoelectric element provided on the first main surface of the vibrating body; and a rotor in direct or indirect contact with the second main surface of the vibrating body. Moreover, in accordance with an axial direction that connects the first main surface and the second main surface of the vibrating body and is along a rotation center, the piezoelectric element is disposed along a circumferential direction of a traveling wave. The piezoelectric element vibrates the vibrating body to generate the traveling wave circulating around the axial direction, the piezoelectric element vibrates the vibrating body in a vibration mode including a nodal line extending in the circumferential direction, and a mass addition portion is disposed along the circumferential direction on at least one of the first main surface and the second main surface of the vibrating body, and is located outside the nodal line in a direction perpendicular to the axial direction.
The ultrasonic motor of the present invention provides for increased torque compared with conventional motors without an increase in size.
Hereinafter, the present invention will be clarified by describing specific embodiments of the present invention with reference to the drawings.
Note that each of the embodiments described in the present specification is an exemplary embodiment, and replacement of some part or combination of configurations is possible between different embodiments as would be appreciated to one skilled in the art.
As shown, an ultrasonic motor 1 is provided includes a stator 2 and a rotor 5. The stator 2 and the rotor 5 are in contact with each other. A traveling wave generated in the stator 2 rotates the rotor 5. Hereinafter, a specific configuration of the ultrasonic motor 1 will be described.
The stator 2 includes a vibrating body 3 that has a disk shape in the exemplary aspect. The vibrating body 3 has a first main surface 3a and a second main surface 3b. The first main surface 3a and the second main surface 3b face each other (e.g., are opposing surfaces of the vibrating body). In the present exemplary aspect, an axial direction Z is a direction that connects the first main surface 3a and the second main surface 3b, and is a direction along a rotation center, for example, in the vertical direction of
The rotor 5 has a rotor body 6 and a rotation shaft 7. The rotor body 6 has a through-hole 6c that is located at the center of the rotor body 6. The rotation shaft 7 is inserted in the through-hole 6c. However, the position of the through-hole 6c is not limited to the above. The through-hole 6c only needs to be located in a region including the axial direction center. The rotation shaft 7 is also inserted in the through-hole 3c of the vibrating body 3. The through-hole 3c of the vibrating body 3 and the through-hole 6c of the rotor body 6 do not need to be provided. In this case, for example, one end of the rotation shaft 7 may be connected to the rotor body 6. Furthermore, the shape of the rotor body 6 is not limited to the above described configuration. For example, the shape of the rotor body 6 viewed from the axial direction Z may be a regular polygon such as a regular hexagon, a regular octagon, or a regular decagon in alternative aspects.
In the present specification, a direction viewed from the axial direction Z is referred to as plan view or bottom view in some cases. Note that plan view is a direction viewed from above in
As illustrated in
When the number of the nodal lines extending in the circumferential direction is assumed to be M and the number of the nodal lines extending in the radial direction is assumed to be N, the vibration mode can be represented by an (M, N) mode. In the present embodiment, a (1, 3) mode is used. However, the vibration mode is not limited to the (1, 3) mode. M only needs to be a natural number, and N only needs to be an integer greater than or equal to 0.
As illustrated in
According to the present embodiment, the mass addition portion 3d is provided on the first main surface 3a of the vibrating body 3 along the circumferential direction, and the mass addition portion 3d is located outside the nodal line in a direction perpendicular to the axial direction Z. This configuration increases the torque without increasing the size of the ultrasonic motor 1. Details of this arrangement will be described below together with a configuration of the piezoelectric elements and a driving method of the ultrasonic motor of the present embodiment.
The first piezoelectric element 13A has a piezoelectric body 14. The piezoelectric body 14 has a third main surface 14a and a fourth main surface 14b. The third main surface 14a and the fourth main surface 14b face each other. Moreover, the first piezoelectric element 13A has a first electrode 15A and a second electrode 15B. As shown, the first electrode 15A is provided on the third main surface 14a of the piezoelectric body 14, and the second electrode 15B is provided on the fourth main surface 14b of the piezoelectric body 14. The second piezoelectric element 13B, the third piezoelectric element 13C, and the fourth piezoelectric element 13D are also configured similarly to the first piezoelectric element 13A. Each of the above piezoelectric elements has a rectangular shape in a plan view. It should be appreciated that the shape of each piezoelectric element in a plan view is not limited to the above, and may be, for example, an elliptical shape.
Here, the first electrode 15A is attached to the first main surface 3a of the vibrating body 3 with an adhesive. The thickness of the adhesive is very thin. Therefore, the first electrode 15A is electrically connected to the vibrating body 3.
In order to generate a traveling wave, the stator 2 only needs to include at least the first piezoelectric element 13A and the second piezoelectric element 13B. Alternatively, one piezoelectric element divided into a plurality of regions may be included. In this case, for example, each region of the piezoelectric element may be polarized in different directions.
In the stator 2, a structure in which a plurality of piezoelectric elements are dispersedly disposed in the circumferential direction and driven to generate a traveling wave is disclosed in WO 2010/061508 A1, for example. Not only the structure for generating a traveling wave is described in the following description, but also the configuration described in WO 2010/061508 A1 is incorporated by reference into the present specification, and the detailed description is omitted.
In
Note that, although an example of three waves has been described, the present invention is not limited thereto, and also in the case of six waves, nine waves, twelve waves, or the like, two standing waves having a phase difference of 90° are similarly excited, whereby a traveling wave is generated by combination of the two standing waves.
It is also noted that in the present invention, the configuration for generating a traveling wave is not limited to the configuration illustrated in
As illustrated in
In general, the torque depends on the radius of the motor. In the case of the ultrasonic motor 1, the radius corresponds to the radius of a circle connecting points of action of the stator 2. More specifically, the points of action are portions that are in contact with the rotor 5 and rotate the rotor 5. In the present embodiment, the balance point of mass in the radial direction is closer to the outer side in the radial direction as compared with the case where the mass addition portion 3d is not provided. As a result, the points of action shift radially outward as compared with the case where the mass addition portion 3d is not provided. Therefore, the radius can be increased, and the torque of the ultrasonic motor 1 can be effectively increased. As described above, the torque can be increased without increasing the size of the ultrasonic motor 1.
As described above, in the present embodiment, the (M, N) mode is used. More specifically, M=1 and N=3. In the case where M is 2 or greater, there are generated a plurality of nodal lines extending in the circumferential direction. In this case, it is preferable that the mass addition portion 3d be located on the outside of the outermost nodal line in the radial direction. This arrangement makes it possible to dispose the points of action more reliably on the radially outer side, and the torque can be more reliably increased.
Hereinafter, there will be described first to third variations of the first embodiment in which only the disposition of the mass addition portion is different from the first embodiment. Also in the first to third variations, similarly to the first embodiment, the torque can be effectively increased without increasing the size of the ultrasonic motor.
In the first variation illustrated in
In the second variation illustrated in
However, as in the first embodiment illustrated in
In addition, as illustrated in
Note that the mass addition portion 3d of the first variation can be provided by press working, for example. The mass addition portion 3d of the second variation can be provided by cutting work, for example.
In the third variation illustrated in
The present variation is different from the first embodiment in that a plurality of protrusions 24 are provided on a second main surface 3b of a vibrating body 23D. The protrusions 24 protrude in the axial direction Z from a second main surface 3b. The plurality of protrusions 24 are disposed along the circumferential direction of the traveling wave. In the present modification, the plurality of protrusions 24 are arranged in an annular shape as viewed from the axial direction Z. The plurality of protrusions 24 are located radially inside the nodal line when the traveling wave is excited. A stator 22D is in contact with a rotor 5 at the plurality of protrusions 24.
As described above, the protrusions 24 of the stator 22D protrude in the axial direction Z from the second main surface 3b of the vibrating body 23D. Therefore, when a traveling wave is generated in the vibrating body 23D, the tips of the protrusions 24 are displaced more greatly. As a result, the rotor 5 can be efficiently rotated by the traveling wave generated in the stator 22D.
In the first embodiment illustrated in
In the ultrasonic motor 1, the material of the mass addition portion 3d is the same as the material of the vibrating body 3, and the mass addition portion 3d is integrated with the vibrating body 3. However, the mass addition portion 3d may be a separate body from the vibrating body 3. This example will be described in a second embodiment below.
The present embodiment is different from the first embodiment in that a mass addition portion 33d is not integrated with a vibrating body 33. Instead, the material of the mass addition portion 33d is different from the material of the vibrating body 33. However, other than the above points, the ultrasonic motor of the present embodiment is configured similarly to the ultrasonic motor 1 of the first embodiment.
Moreover, the mass addition portion 33d has an annular shape. The mass addition portion 33d includes, for example, a metal different from the material used for the vibrating body 33, ceramics, or the like. The mass addition portion 33d may be bonded to the vibrating body 33 with, for example, adhesive, solder, or the like.
Also in the present embodiment, similarly to the first embodiment, the mass addition portion 33d is located radially outside the nodal line. As a result, the energy density of vibration in the stator 32 can be effectively increased. In addition, the radius of the circle connecting the points of action of the stator 32 can be increased without increasing the size of the vibrating body 33. As a result, the torque can be increased without increasing the size of the ultrasonic motor.
The density of the material of the mass addition portion 33d is preferably larger than the density of the material of the vibrating body 33. With that arrangement, also in the case where the volume of the mass addition portion 33d is small, the mass can be effectively increased on the radially outside the nodal line. As a result, downsizing of the ultrasonic motor is less likely hindered.
In general, it is noted that throughout this description, the embodiments and examples shown should be considered as exemplars, rather than limitations on the apparatus and procedures disclosed or claimed. Although many of the examples presented herein involve specific combinations of method acts or system elements, it should be understood that those acts and those elements may be combined in other ways to accomplish the same objectives. Elements and features discussed only in connection with one embodiment are not intended to be excluded from a similar role in other embodiments.
Number | Date | Country | Kind |
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2020-189590 | Nov 2020 | JP | national |
This application is a continuation of PCT Application No. PCT/JP2021/041397, filed Nov. 10, 2021, which claims priority to Japanese Patent Application No. 2020-189590, filed Nov. 13, 2020, the entire contents of each of which are hereby incorporated by reference in their entirety.
Number | Date | Country | |
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Parent | PCT/JP2021/041397 | Nov 2021 | US |
Child | 18194775 | US |