This invention relates to an ultrasonic motor, and more particularly, to the construction of a contact section between a moving element and a fixed element in an ultrasonic motor.
In recent years, ultrasonic motors have been achieved, in which piezoelectric elements, or the like, are used to generate ultrasonic vibrations in a stator (fixed element), and a rotor (moving element) that is in press contact with the stator is made to perform rotational movement or linear movement by the frictional force between the two members. Patent Document 1, for example, describes a vibration actuator (ultrasonic motor) in which a spherical rotor is arranged in a recess section formed on one end of a stator. The rotor is in press contact with a circular ring-shape corner section on an open end of the recess section of the stator, and the rotor is made to perform rotational movement by the frictional force between this corner section and the rotor. Furthermore, a lubricant, such as grease, is accommodated inside the recess section of the stator, and this lubricant is supplied between the stator and the rotor.
Patent Document 1: Japanese Patent Application Publication No. 2008-206251
As a drive force is achieved by using the frictional force between the rotor and stator, the members of the ultrasonic motor wear over time, and it is known that wear occurs in the stator of the piezoelectric actuator described in Patent Document 1. More specifically, in the case of the piezoelectric actuator described in Patent Document 1, the corner sections of the recess section of the stator wear into a shape corresponding to the spherical rotor. In this case, the contact surface area between the rotor and the stator becomes greater as wear progresses, and therefore variations also occur in the drive force of the rotor due to the stator. Furthermore, the vibration actuator described in Patent Document 1 supplies lubricant between the rotor and stator, but since the surface pressure between these members varies with an increase in the contact surface area, it is not possible to maintain an appropriate surface pressure as the wear progresses, and the required drive force can no longer be obtained. In this way, the piezoelectric actuator described in Patent Document 1 has a problem in that large variations in the drive force occur as wear of the stator progresses.
The present invention was devised in order to resolve problems of this kind, an object thereof being to provide an ultrasonic motor which suppresses increases in the contact surface between the moving element and the fixed element, as wear progresses, and which achieves reduction of variations in the drive force.
The ultrasonic motor related to the present invention includes: a moving element which performs rotational movement or linear movement; a fixed element which has a contact surface capable of making surface contact with the moving element and which causes the moving element to move; a pre-loading means which presses the moving element against the fixed element; and a vibration means which causes the moving element to move by generating ultrasonic vibrations in the fixed element, wherein a different level section is formed in the fixed element so as to form a gap between the fixed element and the moving element.
According to this invention, increases in the contact surface area between the moving element and the fixed element as wear progresses are suppressed, and variations in the drive force can be reduced.
Below, embodiments of the invention are described with reference to the accompanying drawings.
The ultrasonic motor 1 causes a rotor 2, which is a moving element having a substantially cylindrical shape, to perform rotational movement about an axial direction (see arrow R) by using ultrasonic vibrations, and includes a stator 3 which is a fixed element that is in contact with the rotor 2, and a piezoelectric element 4, which is a vibration means that generates ultrasonic vibrations in the stator 3. In the present embodiment, the direction of rotation of the rotor 2 corresponds to the direction of movement.
The stator 3 is fixed to the piezoelectric element 4 by a male screw thread 3b formed on a shaft section 3a engaging with a female screw thread 4a formed on an inner circumference section of the piezoelectric element 4. Furthermore, the stator 3 and the piezoelectric element 4 have a substantially cylindrical shape overall, and are arranged in such a manner that the axial direction of the rotor 2 and the axial direction of the stator 3 and the piezoelectric element 4 are mutually orthogonal. The piezoelectric element 4 is formed by laminating together a plurality of piezoelectric element plates, and by applying an AC voltage to these piezoelectric element plates from a drive circuit (not shown), ultrasonic vibrations are generated in the stator 3.
A shaft 5 is provided to pass through the central portion of the rotor 2 along the axial direction, and the shaft 5 is supported rotatably by bearings 6a, 6b provided inside the rotor 2. Furthermore, an opening section 2a which opens to the lower side is formed in an intermediate section of the axial direction of the rotor 2, and a holding member 7 surrounding the outer circumference section of the shaft 5 is accommodated inside the opening section 2a. The holding member 7 is a member for coupling a rod 8 passing through the stator 3 and the piezoelectric element 4, to the shaft 5. The holding member 7 and the rod 8 are fixed by means of a male screw thread 8a formed on the outer circumference section of the rod 8 engaging with a female screw thread 7a formed on the holding member 7, and the upper end portion of the rod 8 is abutted against the outer circumferential surface of the shaft 5.
On the other hand, a pre-load nut 9 is attached to the lower end section of the rod 8 which extends to the lower side of the piezoelectric element 4, and a pre-load spring 10 is provided between the piezoelectric element 4 and the pre-load nut 9. The pre-load spring 10 is held between the piezoelectric element 4 and the pre-load nut 9 in a state of compression by a prescribed load, whereby the rotor 2 is impelled towards the lower side and is pressed against the stator 3. More specifically, the rotor 2 relating to this embodiment rotates while rubbing against the stator 3, and the direction of rubbing of the rotor 2 and the direction of rotation indicated by arrow R match. Here, the holding member 7, rod 8, pre-load nut 9 and pre-load spring 10 constitute a pre-loading means in the ultrasonic motor 1.
As shown in
Here, the composition of the contact section between the rotor 2 and the stator 3 is described in detail with reference to
As shown in
The different level section 23 is provided so as to have a clearance of approximately 0.1 mm, for example, from the outer circumferential surface 2b of the rotor 2, in such a manner that the peripheral shape of the contact surface 21 of the stator 3 does not vary greatly. Consequently, by forming the different level section 23, effects on the vibration mode of the ultrasonic motor 1 can be avoided. Furthermore, the side wall surface 23b, which links the bottom forming surface 23a of the different level section 23 with the contact surface 21, is formed so as to extend along the direction in which the rotor 2 is pressed against the stator 3, in other words, along the vertical direction.
By providing this different level section 23, the contact surface 21 of the stator 3 makes contact with the outer circumferential surface 2b of the rotor 2 between the edge portion A positioned on the outer side (upper side) and the edge portion B positioned on the inner side (lower side). Here, if the different section 23 is not provided, then the outer circumferential surface 2b of the rotor 2 and the contact surface 21 of the stator 3 make contact between the edge portion A and the virtual edge portion C shown in
A different level section 25 in which a portion positioned to the outer side from the edge portion A is cut away is formed in the contact surface 21 on the side far from the central axis of the stator 3, in other words, on the outer side thereof. The side wall surface 25a forming this different level 25 is formed along a direction towards the lower side from the edge portion A of the contact surface 21, in other words, the direction in which the rotor 2 is pressed against the stator 3, and the bottom forming surface 25b is formed so as to extend towards the outer side from the lower end portion of the side wall surface 25a. Here, the direction in which the rotor 2 is pressed against the stator 3 is a direction towards the lower side. Consequently, if the contact surface 21 of the stator 3 wears with the rotation of the rotor 2, then the wear proceeds towards the lower side as indicated by the single-dotted line shown by reference numeral 21′ in
Next, the operation of the ultrasonic motor 1 relating to the first embodiment of the invention will be described.
As shown in
When the rotor 2 rotates, the lubricant with which the supply body 14 in the recess section 13 of the stator 3 is impregnated adheres to the outer circumferential surface 2b of the rotor 2, and is supplied in between the outer circumferential surface 2b and the contact surface 21 of the supporting part 11 and between the outer circumferential surface 2b and the contact surface 22 of the supporting part 12. Here, a minimal different level section 23 and a minimal different level section 24 are formed respectively on the inner side of the contact surface 21 and the inner side of the contact surface 22. These different level sections 23, 24 function as oil grooves for drawing in the lubricant supplied from the lubricant supply body 14, in between the outer circumferential surface 2b of the rotor 2 and the contact surfaces 21, 22, and therefore lubricant can be supplied efficiently to the rotor 2 and the stator 3, in addition to which the friction between the members is reduced and durability can be improved. Furthermore, since the lubricant is supplied to the contact surfaces 21, 22 by the supply body 14, then the rubbing motion of the rotor 2 is smooth and variations in the drive force due to friction can also be suppressed.
In an ultrasonic motor 1 which operates in this way, the rotor 2 rotates due to frictional force with the stator 3, and therefore these members wear over time, in which case wear occurs in the stator 3. Furthermore, when manufacturing the rotor 2 and the stator 3, the members are processed within a prescribed range of dimensional accuracy, and hence variations occur in the respective dimensions. To give a more concrete explanation, the contact surface 21 and the contact surface 22 of the stator 3 are formed so as to have a shape following the outer circumferential surface 2b of the rotor 2, but due to variations in the dimensions during manufacture, there are differences in the state of contact between the outer circumferential surface of the rotor 2 and the contact surface 21 and the contact surface 22 of the stator 3 immediately after assembly of the ultrasonic motor 1.
More specifically, if the diameter of the rotor 2 is greater than the diameter of the contact surface 21 and the contact surface 22 of the stator 3, then the rotor 2 immediately after assembly contacts the contact surface 21 and the contact surface 22 on the upper side, that is, the side of the edge portion A shown in
Here, as shown in
Moreover, in the different level section 23 and the different level 25 of the contact surface 21, the side wall surface 23b and the side wall surface 25a are formed to extend towards the lower side, which is the direction in which the rotor 2 is pressed against the stator 3. Therefore, even if the contact surface 21 wears as indicated by the single-dotted broken line 21′, in accordance with the rotation of the rotor 2, there is no change in the contact distance between the rotor 2 and the contact surface 21, in other words, the distance from edge portion A to edge portion B, and consequently, there is no great variation in the contact surface area or the contact angle α2. Consequently, no great variation occurs in the drive force of the rotor 2 due to the stator 3, or the surface pressure between the rotor 2 and the contact surfaces 21, 22 of the stator 3, and therefore even if wear progresses on the contact surfaces 21, 22, it is possible to reduce variations in the drive force of the ultrasonic motor 1.
As described above, since a different level section 23, a different level section 24, a different level section 25 and a different level section 26 are provided in the contact surface 21 and the contact surface 22 of the stator 3, and the contact distances between the outer circumferential surface 2b of the rotor 2 and the contact surfaces 21, 22 are limited, then even if the contact surfaces 21, 22 wear, increases in the contact surface area with the rotor 2 are suppressed. Consequently, there is little variation in the drive force of the ultrasonic motor 1.
Moreover, if the side wall surfaces 23b, 24b of the different level sections 23, 24 and the side wall surfaces 25a, 26a of the different level sections 25, 26 are formed to extend in the direction in which the rotor 2 is pressed against the stator 3 as in the ultrasonic motor 1, then there is little increase in the contact surface area between the rotor 2 and the contact surfaces 21, 22, due to the progress of wear of the contact surfaces 21, 22. More specifically, it is possible to make variations in the drive force of the ultrasonic motor 1 even smaller.
Next, an ultrasonic motor 31 relating to a second embodiment of the invention is described with reference to
As shown in
In these contact surfaces 41a to 43a, different level sections 41b to 43b similar to the different level sections 23, 24 in the first embodiment are formed respectively in positions on the side near the central axis of the stator 33, in other words, on the inner circumferential side. Furthermore, different level sections 41c to 43c similar to the different level sections 25, 26 in the first embodiment are formed in positions on the side far from the central axis of the stator 33, in other words, on the outer circumferential side. More specifically, the supporting parts 41 to 43 of the stator 33 are circular ring-shaped portions having a cross-sectional shape similar to that of the supporting parts 11, 12 in the first embodiment. The remainder of the construction is similar to the first embodiment.
As described above, even if the ultrasonic motor 31 is composed so as to include a spherical rotor 32, then it is possible to achieve beneficial effects similar to the first embodiment, and more specifically, to reduce variation in the drive force as a result of wear of the contact surfaces 41a to 43a of the stator 33.
The stators according to the first and second embodiments are constructed in such a manner that different level sections are provided on the inner side and the outer side of the contact surfaces, but the positions where the different level sections are provided are not limited to this. It is also possible to adopt another cross-sectional shape, provided that the shape of the stator is not altered greatly, and it is also possible to provide an additional different level section 23′ in an intermediate section of the contact surface 21, as shown in
Furthermore, in the different level sections of the stators according to the first and second embodiments, the side wall surfaces are formed so as to extend in a direction in which the rotor is pressed against the stator, in other words, the vertical direction, but it is also possible to form the side wall surfaces so as to form a prescribed angle with respect to the vertical direction, as in the side wall surface 23b′ and the side wall surface 25a′ shown in
In the stator 3 of the first embodiment, as shown in
Moreover, as shown in
Furthermore, as shown in
Moreover, as shown in
In the first and second embodiments, the moving element is a rotor which performs rotational movement, but the moving element may be used in an ultrasonic motor which performs linear movement.
In the first embodiment, the shape of the rotor is a cylindrical shape, but may also be an elliptical cylindrical shape.
In the second embodiment, the shape of the stator is a circular ring shape, but may also be an elliptical ring shape.
Number | Date | Country | Kind |
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2011-245673 | Nov 2011 | JP | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/JP2012/069321 | 7/30/2012 | WO | 00 | 5/8/2014 |