Bearings for wave reducers

Abstract

To provide a bearing for wave reduction gear capable of suppressing vibration or sound of a holder.SOLUTION: A bearing 100 for wave reduction gear is a ball bearing applied to a wave reduction gear 102 and comprises: an outer ring 118 disposed inside of a flexible spline 106; an inner ring 120 disposed outside of an elliptical cam 108; a ball 122 as a rolling body which rolls between the outer ring and the inner ring; and a holder 124 including a plurality of pockets 132, of which the inner surfaces are spherical, for storing balls therein. The ball bearing further includes: a first gap 134 between a ball and an opening 146 of the pocket at the side of the inner ring in a breadthwise direction of the cam; a second gap 136 and a third gap 138 between the holder and the inner and outer rings in the breadthwise direction of the cam; a fourth gap 140 between an opening 150 of the pocket at the side of the outer ring and the ball in a long axis direction of the cam; and a fifth gap 142 and a sixth gap 144 between the holder and the inner and outer rings in the long axis direction of the cam. Among the gaps, the first gap or the fourth gap is minimum.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a bearing for a harmonic reducer applied to a harmonic reducer.

Background Art

[0002] Conventionally, a harmonic reducer that applies the deflection of metal has been known. As an example, the harmonic reducer includes a circular spline, a flex spline to which an output shaft is attached, an elliptical cam to which an input shaft is attached, and a bearing. The circular spline is a rigid annular member fixed to the casing and has internal teeth. The flex spline is a member made of a thin-walled cup-shaped metal elastic body, is disposed inside the circular spline, and has external teeth on its outer peripheral surface that partially mesh with the internal teeth of the circular spline. Also, the number of teeth of the external teeth is less than the number of teeth of the internal teeth (for example, two).

[0003] The bearing is disposed between the flex spline and the elliptical cam. The bearing has an outer ring fixed to the flex spline, an inner ring fixed to the cam, rolling elements that roll between the outer ring and the inner ring, and a cage that holds the rolling elements. The outer ring and the inner ring are metal annular members and are thin-walled, so they can be elastically deformed in the radial direction.

[0004] Since the cam of the harmonic reducer has an elliptical shape, the bearing and the flex spline located outside the cam deflect elliptically, so that the external teeth of the flex spline can be partially meshed with the internal teeth of the circular spline. That is, in the harmonic reducer, the teeth mesh with the circular spline in the long axis direction of the elliptically deflected flex spline, and the teeth are separated from the circular spline in the short axis direction.

[0005] By rotating the cam, the position of the long axis of the ellipse of the flex spline, that is, the position meshing with the internal teeth, can be moved with respect to the circular spline. Along with this movement, the flex spline rotates in a state where the teeth are partially meshed with the circular spline.

[0006] Specifically, when the cam is rotated 180° clockwise, the flex plane moves counterclockwise by a distance equivalent to half the difference in the number of teeth between the external and internal teeth (e.g., one tooth), and when the cam is rotated another 180° clockwise, it moves counterclockwise by a distance equivalent to the difference in the number of teeth (e.g., two teeth). Therefore, in a wave-driven gearbox, the rotation of the flex plane, to which the output shaft is attached, is taken as the output in response to the input of the cam, to which the input shaft is attached, and functions as a gearbox.

[0007] However, in bearings used in wave reducers, an elliptical cam is press-fitted and fixed into the inner ring. As a result, the outer and inner rings deform into an elliptical shape, while the cage remains circular without elliptical deformation. Consequently, the gaps between the cage and the inner and outer rings, and between the cage and the rolling elements, become small in the bearing. This can lead to localized stress in the cage, potentially causing it to fail prematurely.

[0008] In contrast, Patent Documents 1 and 2 describe ball bearings for wave reducers. These ball bearings have an elastically deformable inner raceway (inner ring), an elastically deformable outer raceway (outer ring), balls which are rolling elements provided between the inner and outer rings, and a cage. The cage has multiple pockets formed in the circumferential direction for housing the balls which are rolling elements.

[0009] In Patent Documents 1 and 2, the retainer has an annular portion and a plurality of columnar portions extending axially from the annular portion, with pockets between adjacent columnar portions in the circumferential direction. The circumferential gap formed between the ball and the columnar portion, and the radial gap of the annular space formed between the non-circularly deformed inner and outer rings and the retainer are appropriately set in the longitudinal or transverse direction of the inner and outer rings. Patent Documents 1 and 2 state that this prevents localized stress from occurring in the retainer, reduces the stress generated in the retainer, and makes it possible to rotate the retainer stably. [Prior art documents] [Patent Documents]

[0010] [Patent Document 1] Patent No. 6432337 [Patent Document 2] Patent No. 6432338 [Overview of the project] [Problems that the invention aims to solve]

[0011] However, Patent Documents 1 and 2 merely specify that the circumferential gap formed between the ball and the column be greater than or equal to the radial gap of the annular space formed between the non-circularly deformed inner and outer rings and the retainer, and further define the relative sizes of the circumferential gap and the radial gap in the long axis or short axis direction of the inner and outer rings. In Patent Documents 1 and 2, widening the predetermined gap makes it less likely for the retainer to be constrained by the ball, thereby increasing the degree of freedom of the retainer. However, when the degree of freedom of the retainer increases, the ball and retainer can swing freely, which generates vibration and noise.

[0012] In view of these problems, the present invention aims to provide a bearing for a wave reducer that can suppress vibration and noise of the cage. [Means for solving the problem]

[0013] To solve the above problems, a typical configuration of the wave speed reducer bearing according to the present invention is a wave speed reducer bearing applied to a wave speed reducer comprising a circular spline having internal teeth, a flex spline having external teeth that mesh with the internal teeth and are located inside the circular spline, and an elliptical cam, wherein the bearing comprises an outer ring located inside the flex spline, an inner ring located outside the cam, rolling elements that roll between the outer ring and the inner ring, and a cage having a plurality of spherical inner surface pockets that house the rolling elements. The above-described bearing for wave reducer has a first gap between the inner ring opening of the pocket in the short axis direction of the cam and the rolling element, a second gap between the cage and the inner ring in the short axis direction of the cam, a third gap between the cage and the outer ring in the short axis direction of the cam, a fourth gap between the outer ring opening of the pocket in the long axis direction of the cam and the rolling element, a fifth gap between the cage and the inner ring in the long axis direction of the cam, and a sixth gap between the cage and the outer ring in the long axis direction of the cam, characterized in that the first or fourth gap is the smallest of each gap.

[0014] In the above configuration, in the bearing for a wave speed reducer applied to a wave speed reducer, the first gap between the inner ring side opening of the cage pocket and the rolling element in the short axis direction of the elliptical cam, or the fourth gap between the outer ring side opening of the pocket and the rolling element in the long axis direction of the cam, is smaller than the second and third gaps between the cage and the inner and outer rings in the short axis direction of the cam, and the fifth and sixth gaps between the cage and the inner and outer rings in the long axis direction of the cam.

[0015] Therefore, the cage either interferes with the rolling element at the inner ring side opening of the pocket in the short axis direction of the cam, or with the rolling element at the outer ring side opening of the pocket in the long axis direction of the cam, and does not come into contact with the inner or outer ring. In other words, when the cage rotates, it interferes with the rolling element (ball) in the radial direction and always acts as a ball guide. Therefore, with the above configuration, rattle of the cage can be suppressed, and vibration and noise can be suppressed.

[0016] In the above configuration, since the pockets of the cage are spherical pockets with an inner surface that is spherical, the amount of lubricant retained in the pockets is greater than that in cylindrical holes. Furthermore, since the cage is not an inner ring guide, a gap is secured between the inner ring and the cage, resulting in a greater amount of lubricant enclosed on the inner diameter side of the cage than in cylindrical holes. Therefore, the cage can rotate smoothly.

Advantages of the Invention

[0017] According to the present invention, it is possible to provide a bearing for a harmonic reducer that can suppress vibration and noise of the cage.

Brief Description of the Drawings

[0018] [Figure 1] FIG. 1 is a diagram showing a schematic configuration of a harmonic reducer to which the bearing 100 for a harmonic reducer according to an embodiment of the present invention is applied. [Figure 2] FIG. 2 is a diagram showing the cage of the bearing for a harmonic reducer of FIG. 1. [Figure 3] FIG. 3 is a diagram showing a main part of the bearing for a harmonic reducer of FIG. 1.

Embodiments for Carrying Out the Invention

[0019] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. Dimensions, materials, and other specific numerical values shown in such embodiments are merely examples for facilitating understanding of the invention and do not limit the present invention unless otherwise specified. In the present specification and drawings, elements having substantially the same functions and configurations are denoted by the same reference numerals to avoid redundant description, and elements not directly related to the present invention are not shown.

[0020] FIG. 1 is a diagram showing a schematic configuration of a harmonic reducer 102 to which the bearing 100 for a harmonic reducer according to an embodiment of the present invention is applied. FIG. 1(a) schematically shows a state of the harmonic reducer 102 viewed from the axial direction. FIG. 1(b) is a longitudinal sectional view of the harmonic reducer 102 of FIG. 1(a).

[0021] The harmonic reducer 102 is a reducer that applies the deflection of metal. As shown in Fig. 1(a), it includes a circular spline 104, a flex spline 106 to which an output shaft is attached, an elliptical cam 108 to which an input shaft is attached, and a bearing for the harmonic reducer (hereinafter, ball bearing 100). The output shaft and the input shaft are not shown in the figure.

[0022] The circular spline 104 is a rigid annular member fixed to a casing (not shown), and has internal teeth 110 on its inner peripheral surface. The inner peripheral surface of the circular spline 104 is circular with the axis O as the center.

[0023] The flex spline 106 is disposed inside the circular spline 104. The flex spline 106 is a member made of a thin-walled cup-shaped metal elastic body, and has a cylindrical portion 112 that can be elastically deformed in the radial direction and a bottom portion (see Fig. 1(b)) to which an output shaft is attached. The cylindrical portion 112 has external teeth 116 on its outer peripheral surface that partially mesh with the internal teeth 110 of the circular spline 104. Also, the number of teeth of the external teeth 116 is, for example, 2 less than the number of teeth of the internal teeth 110. The difference in the number of teeth between the external teeth 116 and the internal teeth 110 is arbitrary.

[0024] The ball bearing 100 is disposed between the flex spline 106 and the cam 108. The ball bearing 100 has an outer ring 118, an inner ring 120, balls 122 as rolling elements, and a cage 124 (see Fig. 2) that holds the balls 122. The outer ring 118 is disposed inside the flex spline 106 and fixed thereto. The inner ring 120 is disposed outside the cam 108 and fixed thereto.

[0025] The outer ring 118 and the inner ring 120 are thin-walled annular members made of metal and can be elastically deformed in the radial direction. The balls 122 roll between the outer ring 118 and the inner ring 120. The cage 124 has the role of maintaining the interval between the balls 122 so that the balls 122 do not rub against each other.

[0026] In the wave speed reducer 102, because the cam 108 has an elliptical shape, the ball bearing 100 located outside the cam 108 and the cylindrical portion 112 of the flexspline 106 deflect in an elliptical shape, allowing the external teeth 116 of the flexspline 106 to partially engage with the internal teeth 110 of the circular spline 104.

[0027] In other words, in the wave reducer 102, as shown in Figure 1(a), the external teeth 116 of the flexus spline 106 and the internal teeth 110 of the circular spline 104 mesh in the long axis direction of the elliptically curved flexus spline 106 (see arrows A and C), while the external teeth 116 and internal teeth 110 are separated in the short axis direction (see arrows B and D).

[0028] In the wave reducer 102, by rotating the cam 108 about the axis O, the position of the major axis of the ellipse of the flexspline 106, that is, the position where the external teeth 116 and internal teeth 110 mesh with the circular spline 104, can be moved. As a result of this movement, the flexspline 106 rotates with the external teeth 116 and internal teeth 110 partially meshing with the circular spline 104.

[0029] Specifically, when the cam 108 is rotated 180° clockwise, the flexspline 106 moves counterclockwise by a distance equivalent to half the difference in the number of teeth between the external teeth 116 and the internal teeth 110, which is equivalent to one tooth. When the cam 108 is rotated another 180° clockwise (i.e., a full rotation), the flexspline 106 moves counterclockwise by a distance equivalent to the difference in the number of teeth (for example, two teeth).

[0030] Therefore, the wave reducer 102 functions as a reducer by taking the rotation of the flexspline 106, to which the output shaft is attached, as an output in response to the input of the cam 108 to which the input shaft is attached.

[0031] Figure 2 shows the cage 124 of the ball bearing 100 in Figure 1. The cage 124 is a one-piece molded part made of resin and is crown-shaped as shown in the figure. The cage 124 has an annular portion 126 centered on the axis of the ball bearing 100, a base portion 128 protruding axially from the annular portion 126, and claw portions 130 protruding from both sides of the base portion 128 in the circumferential direction.

[0032] Furthermore, the retainer 124 has a plurality of pockets 132 formed between adjacent bases 128 and opening in the axial direction, as shown in the figure. The pockets 132 are spherical pockets that accommodate the balls 122 (see Figure 1) and have a spherical inner surface.

[0033] Figure 3 shows the main parts of the ball bearing 100 shown in Figure 1. In the figure, two pockets 132 of the cage 124 are shown as representative examples, located in the short axis and long axis directions of the elliptical cam 108 (see Figure 1), and containing the balls 122.

[0034] The ball bearing 100 further has a first clearance 134, a second clearance 136, and a third clearance 138 in the short axis direction of the cam 108, and a fourth clearance 140, a fifth clearance 142, and a sixth clearance 144 in the long axis direction of the cam 108.

[0035] The first gap 134 is the gap between the opening 146 (see Figure 2) on the inner ring 120 side of the pocket 132 in the short axis direction of the cam 108 and the ball 122, and its size is given by dimension La.

[0036] The second gap 136 is the gap between the retainer 124 and the inner ring 120 in the short axis direction of the cam 108, and its size is dimension Lb. The third gap 138 is the gap between the retainer 124 and the outer ring 118 in the short axis direction of the cam 108, and its size is dimension Lc.

[0037] The fourth gap 140 is the gap between the opening 150 (see Figure 2) on the outer ring 118 side of the pocket 132 in the longitudinal axis direction of the cam 108 and the ball 122, and its size is given by dimension Ld.

[0038] The fifth gap 142 is the gap between the retainer 124 and the inner ring 120 in the longitudinal direction of the cam 108, and its size is dimension Le. The sixth gap 144 is the gap between the retainer 124 and the outer ring 118 in the longitudinal direction of the cam 108, and its size is dimension Lf.

[0039] In the ball bearing 100, among the dimensions of each of the above-mentioned gaps, the dimension La of the first gap 134 or the dimension Ld of the fourth gap 140 is the smallest. As a result, the cage 124 does not come into contact with the inner ring 120 and the outer ring 118. Rather than the first gap 134 and the fourth gap 140 being equally narrow, it is preferable that when one gap is narrow, the other gap is looser.

[0040] When the dimension La of the first gap 134 is at its minimum, the retainer 124 interferes with the ball 122 between the opening 146 on the inner ring 120 side of the pocket 132 in the short axis direction of the cam 108. In this case, in the long axis direction, the ball 122 moves toward the outer ring 118 side relative to the retainer 124, but since the fourth gap 140 is larger than the first gap 134, the retainer 124 acts as a ball guide at the opening 146 on the inner ring 120 side.

[0041] When the dimension Ld of the fourth gap 140 is at its minimum, the retainer 124 interferes with the ball 122 between the opening 150 on the outer ring 118 side of the pocket 132 in the long axis direction of the cam 108. In this case, in the short axis direction, the ball 122 moves toward the inner ring 120 side relative to the retainer 124, but since the first gap 134 is larger than the fourth gap 140, the retainer 124 acts as a ball guide at the opening 150 on the outer ring 118 side.

[0042] In other words, when the cage 124 rotates, it interferes with the balls 122 in the radial direction, and always acts as a ball guide. Therefore, with the ball bearing 100, rattling of the cage 124 can be suppressed, and thus vibration and noise can be suppressed.

[0043] Furthermore, in the ball bearing 100, by making the pocket 132 of the cage 124 a spherical pocket with a spherical inner surface, the amount of lubricant that can be held in the pocket 132 is greater than that of a cylindrical bore. In addition, in the ball bearing 100, since the cage 124 is not an inner ring guide, a gap is secured between the inner ring 120 and the cage 124, so the amount of lubricant that can be sealed into the inner diameter side of the cage 124 is greater than that of a cylindrical bore. Therefore, with the ball bearing 100, the cage 124 can rotate smoothly.

[0044] Preferred embodiments of the present invention have been described above with reference to the attached drawings, but it goes without saying that the present invention is not limited to these examples. It will be obvious to those skilled in the art that various modifications or alterations can be conceived within the scope of the claims, and these will naturally also fall within the technical scope of the present invention. [Industrial applicability]

[0045] This invention can be used as a bearing for wave reducers applied to wave reducers. [Explanation of Symbols]

[0046] 100...Bearing for wave reducer, 102...Wave reducer, 104...Circular spline, 106...Flex spline, 108...Cam, 110...Internal teeth of circular spline, 112...Cylindrical section of flex spline, 114...Bottom section of flex spline, 116...External teeth of flex spline, 118...Outer ring, 120...Inner ring, 122...Ball, 124...Cage, 126...Ring section, 128...Base, 130...Claw section, 132...Pocket, 134...First gap, 136...Second gap, 138...Third gap, 140...Fourth gap, 142...Fifth gap, 144...Sixth gap, 146, 150...Opening

Claims

[Claim 1] A bearing for a wave reducer, which is applied to a wave reducer comprising a circular spline having internal teeth, a flex spline having external teeth disposed inside the circular spline and meshing with the internal teeth, and an elliptical cam, An outer ring positioned inside the flexply, An inner ring positioned on the outside of the cam, A rolling element that rolls between the outer ring and the inner ring, The system comprises a retainer having multiple spherical inner surface pockets for housing the rolling elements, The bearing for the wave reducer is, The first gap between the opening on the inner ring side of the pocket in the short axis direction of the cam and the rolling element, The second gap between the retainer and the inner ring in the short axis direction of the cam, The third gap between the retainer and the outer ring in the short axis direction of the cam, The fourth gap between the opening on the outer ring side of the pocket in the longitudinal axis direction of the cam and the rolling element, The fifth gap between the retainer and the inner ring in the longitudinal direction of the cam, The cam has a sixth gap between the retainer and the outer ring in the longitudinal direction, Of the aforementioned gaps, the first gap or the fourth gap is the smallest, The aforementioned retainer is, When the first gap is at its minimum, the inner ring side opening of the pocket in the short axis direction of the cam interferes with the rolling element, and the rolling element is guided by the inner ring side opening. A bearing for a wave reducer, characterized in that when the fourth gap is at its minimum, the opening on the outer ring side of the pocket in the longitudinal axis direction of the cam interferes with the rolling element, and the rolling element is guided by the opening on the outer ring side.

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