WO2018199016A1

WO2018199016A1 - Ball bearing

Info

Publication number: WO2018199016A1
Application number: PCT/JP2018/016445
Authority: WO
Inventors: 康由林
Original assignee: Ntn株式会社
Priority date: 2017-04-26
Filing date: 2018-04-23
Publication date: 2018-11-01
Also published as: JP2018184996A; JP6846980B2

Abstract

The present invention prevents, when strain wave gearing is used, the occurrence of displacement of a ball bearing (1) that is interposed between a flexspline (3) and a cam (4), the displacement being caused by a thrust force acting on the ball bearing (1), and also prevents an inner ring (5) from being cracked due to interference between the inner ring (5) and the cam (4). The ball bearing (1) is configured such that, when the ellipse circumferential length of an outer periphery (4a) formed into an elliptical shape on the cam (4) is L1, and the circumferential length of an inner surface (5a) of the inner ring (5) is L2, the value of L1/L2 falls within the range from 1.0001 to 1.0007.

Description

Ball bearing

The present invention relates to a ball bearing, and more particularly, to a ball bearing interposed between an elliptical cam and a flexspline provided in a wave gear device.

Conventionally, wave gear devices are used in places where a speed reduction mechanism is required, such as a joint part of an industrial robot. The wave gear device includes a circular spline, a flexspline, a cam, and a ball bearing interposed between the flexspline and the cam. The cam has an elliptical outer peripheral surface. Ball bearings have thin inner and outer rings. The ball bearing is elastically deformed into an elliptical shape by being fitted to the outer peripheral surface of the cam. The flexspline has a cup shape having a cylindrical portion and a bottom portion. The cylindrical portion is elastically deformed into an elliptical shape by an outer ring of an elliptical ball bearing. The flexspline is meshed with the circular spline at two points in the elliptical long axis direction. The cam and the ball bearing constitute a so-called wave generator. That is, when the elliptical ball bearing rotates in unison with the rotation of the cam, the direction of the major axis of the ellipse changes in the direction of rotation, and the meshing position of the circular spline and flexspline moves in the rotational direction. And a relative rotation occurs between the circular spline. The relative rotation is taken out as a deceleration rotation (for example,

Patent Documents

1 and 2 below).

When using a wave gear device, a thrust force acts on the wave generator due to the elastic deformation of the flexspline. This thrust force acts on the ball bearing. When the wave gear device is used as a speed reducer, the thrust force acts in the direction of pushing the ball bearing toward the bottom side of the flexspline (Non-Patent Document 1 below).

Japanese Patent Laid-Open No. 2015-209931 JP 2016-121724 A

In the fitting part between the inner ring of the ball bearing and the cam, when the tightening margin between the cylindrical inner surface formed on the inner ring and the elliptical outer surface of the cam is small, the thrust force causes the outer periphery of the cam There is a possibility that the inner diameter surface of the inner ring is displaced in the axial direction relative to the surface. When the wave gear device is used as a speed reducer, the ball bearing may move to the bottom side of the flexspline with respect to the cam. Thereby, an excessive tensile stress is generated in the tube portion of the flexspline, and the tube portion may be cracked. Further, when the above-described tightening allowance is large, since the inner ring is thin, the tensile stress generated in the inner ring is increased, and the inner ring may be cracked.

In a general bearing fixing structure in which a ball bearing is fixed by fitting an inner diameter surface formed in a cylindrical surface shape on the inner ring and an outer diameter surface formed in a cylindrical surface shape on the counterpart member, the inner diameter surface and the outer diameter A method has been established for selecting the tightening allowance with the surface. However, in a bearing fixing structure in which a ball bearing is fixed to a cam by fitting an inner diameter surface formed in a cylindrical surface shape on an inner ring and an outer peripheral surface formed in an elliptic shape in a cam of a wave gear device, these inner diameter surfaces A method for selecting the tightening allowance between the outer peripheral surface and the outer peripheral surface has not been established.

In view of the above-mentioned background, the problem to be solved by the present invention is to prevent the ball bearing from shifting due to the thrust force acting on the ball bearing interposed between the flexspline and the cam when the wave gear device is used. In addition, the inner ring is prevented from cracking due to the tightening allowance between the inner ring and the cam.

To achieve the above object, the present invention provides an inner ring having an inner diameter surface that fits into a cam of a wave gear device, an outer ring having an outer diameter surface that fits inside a flexspline of the wave gear device, a plurality of balls interposed between the inner ring and the outer ring, the ball bearing with a, an oval peripheral length of the outer peripheral surface formed into an elliptical shape with the cam and L _1, the circumferential length of the inner ring inner diameter surface when was the _{L _2,} the value of L 1 / _{L 2} is obtained by employing the structure is 1.0001 or more 1.0007 or less.

According to the above configuration, the value of the circumferential length ratio L ₁ / L ₂ between the elliptical circumferential length of the outer circumferential surface of the cam and the circumferential length of the inner circumferential surface of the inner ring is set to 1.0001 or more. In use, the inner ring can be prevented from moving in the axial direction with respect to the cam by the thrust force acting on the ball bearing. Further, since the value of the circumference ratio L ₁ / L ₂ is set to 1.0007 or less, it is possible to prevent the inner ring from being cracked due to the tightening allowance between the inner ring and the cam.

T / T, where t is the inner ring wall thickness that is the difference between the inner diameter and outer diameter of the inner ring, and T is the bearing cross-sectional height that is the difference in diameter between the inner diameter surface of the inner ring and the outer diameter surface of the outer ring. Is preferably 0.109 or more and 0.448 or less. This numerical range of t / T is suitable for preventing the inner ring from shifting and cracking.

The value of B / T is 0.789 or more and 1.579, where B is the width of the inner ring and T is the bearing cross-sectional height, which is the difference in diameter between the inner diameter surface of the inner ring and the outer diameter surface of the outer ring. It may be the following. This numerical value range of B / T is suitable for preventing the displacement of the inner ring.

By adopting the above configuration, the present invention eliminates the movement of the ball bearing due to the thrust force acting on the ball bearing interposed between the flexspline and the cam when the wave gear device is used, and tightens the inner ring and the cam. It is possible to prevent the inner ring from cracking due to the bill.

A longitudinal front view showing a wave gear device provided with a ball bearing according to an embodiment of the present invention Cross-sectional view of a wave gear device including a ball bearing according to an embodiment of the present invention FIG. 2 is a partially enlarged view showing the cam shown in FIG. A longitudinal front view showing a ball bearing according to an embodiment of the present invention The side view which shows the inner ring | wheel of FIG. 4 from an axial direction

Embodiments of the present invention will be described with reference to the accompanying drawings. As shown in FIGS. 1 and 2, this ball bearing 1 is for a wave gear device. The wave gear device includes a circular spline 2, a flexspline 3, a cam 4, and a ball bearing 1 interposed between the flexspline 3 and the cam 4.

The ball bearing 1 includes an inner ring 5, an outer ring 6, a row of balls 9 interposed between the raceway groove 7 of the inner ring 5 and the raceway groove 8 of the outer ring 6, and a cage that maintains a circumferential interval between these balls 9. 10. In general, an odd number of balls 9 are arranged between the

raceway grooves

7 and 8.

Hereinafter, the “axial direction” refers to a direction along the bearing central axis (not shown) of the ball bearing 1. The bearing central axis of the ball bearing 1 is designed to be coaxial with the central axes of the race rings of the inner ring 5 and the outer ring 6 and designed to be coaxial with the rotational axis of the wave gear device. Hereinafter, a direction perpendicular to the bearing central axis is referred to as a “radial direction”, and a circumferential direction around the bearing central axis is referred to as a “circumferential direction”.

The cam 4 is rotatable in the circumferential direction integrally with the first shaft S1. The flexspline 3 is rotatable in the circumferential direction integrally with the second shaft S2 disposed coaxially with the first shaft S1.

A predetermined number of teeth 11 are provided in the circumferential direction on the inner periphery of the circular spline 2.

The flex spline 3 has a cup shape formed by a cylindrical portion 12 and a bottom portion 13 continuous with one axial end of the cylindrical portion 12. The inside of the cylinder part 12 is formed in a cylindrical surface shape. The tip of the cylinder part 12 in the axial direction is an opening edge 14 of the flexspline 3. On the outer periphery of the cylindrical portion 12, teeth 15 that mesh with the teeth 11 of the circular spline 2 are provided. The number of teeth 15 of the flexspline 3 is two less than the number of teeth 11 of the circular spline 2. The second shaft S <b> 2 is connected to the center portion of the bottom portion 13.

As shown in FIG. 3, the cam 4 has an outer peripheral surface 4a formed in an elliptical shape. The outer peripheral surface 4a of the cam 4 has an oval peripheral length _{L 1.} The elliptical circumferential length L1 is the length of _one round at an arbitrary axial position of the outer peripheral surface 4a.

FIG. 4 shows a cross section when the ball bearing 1 is in a natural state. As shown in the figure, the inner ring 5 is composed of a bearing ring having a raceway groove 7 on the outer periphery. The outer ring 6 is a race ring having a race groove 8 on the inner periphery. The inner ring 5 and the outer ring 6 are each composed of one annular part made of bearing steel.

Here, bearing steel refers to high carbon chromium steel containing 0.9% to 1.1% carbon and 0.9% to 1.6% chromium. As the bearing steel, for example, a high carbon chromium bearing steel material defined by JIS standard (G4805: 2008) can be mentioned.

FIG. 5 shows a side view of the inner ring 5. As shown in FIGS. 4 and 5, the inner ring 5 has an inner diameter surface 5a formed in a cylindrical surface shape. An inner diameter surface 5 a of the inner ring 5 defines an inner diameter d of the inner ring 5. The inner diameter d of the inner ring 5 matches the bearing inner diameter of the ball bearing 1.

The outer diameter Di of the inner ring 5 corresponds to the diameter of a virtual cylindrical surface that circumscribes the inner ring 5. The outer diameter Di of the inner ring 5 is defined by the shoulder outer diameter of the inner ring 5. The inner ring wall thickness t is the difference between the inner diameter d and the outer diameter Di of the inner ring 5. The value of the inner ring wall thickness t corresponds to the difference between the outer diameter Di and the inner diameter d of the inner ring 5.

Inner surface 5a of the inner ring 5 has a circumferential length _{L 2.} Circumferential length L ₂ is the length of one round at any axial position of the inner surface 5a.

As shown in FIG. 4, the inner ring 5 has a width B. The width B corresponds to the distance between two parallel virtual planes that contact the inner ring 5 from both sides in the axial direction.

The outer ring 6 has an outer diameter surface 6a formed in a cylindrical surface shape. The outer diameter surface 6 a of the outer ring 6 defines the outer diameter Do of the outer ring 6. The outer diameter Do of the outer ring 6 matches the bearing outer diameter of the ball bearing 1.

The bearing cross-sectional height T of the ball bearing 1 is a diameter difference between the inner diameter surface 5 a of the inner ring 5 and the outer diameter surface 6 a of the outer ring 6. The value of T corresponds to the difference between the outer diameter Do of the outer ring 6 and the inner diameter d of the inner ring 5.

The value of t / T is set to 0.109 or more and 0.448 or less.

The value of B / T is set to 0.789 or more and 1.579 or less.

As shown in FIGS. 1 and 2, the inner ring 5 of the ball bearing 1 is elastically deformed into an elliptical shape by being fitted to the outer peripheral surface 4a of the cam 4 at the inner diameter surface 5a. By this fitting, the ball bearing 1 is fixed to the outer peripheral surface 4 a of the cam 4. In addition, along with the elliptical deformation of the inner ring 5 at this time, the outer ring 6 is elastically deformed into an elliptical shape by being pushed through the ball 9. In this state, the outer diameter surface 6a of the outer ring 6 of the ball bearing 1 is press-fitted inside the cylindrical portion 12 of the flexspline 3, so that the cylindrical portion 12 of the flexspline 3 is also elastically deformed in an elliptical shape.

The cam 4 and the ball bearing 1 fitted together constitute a wave generator. That is, when the first shaft S1 rotates and the elliptical ball bearing 1 rotates integrally with the rotation of the cam 4 fixed to the first shaft S1, the direction of the elliptical major axis direction is changed in the rotational direction. As a result, the meshing position of the teeth 11 of the circular spline 2 and the teeth 15 of the flexspline 3 moves in the rotation direction, and relative rotation of two teeth occurs between the flexspline 3 and the circular spline 2 in one rotation. . The relative rotation is extracted as a deceleration rotation. During this use, a thrust force F acts on the wave generator due to the elastic deformation of the flexspline 3. This thrust force F acts on the wave generator from the contact portion (on the long axis) between the outer ring 6 of the ball bearing 1 and the flex spline 3.

Here, considering the tightening allowance when the outer peripheral surface 4a of the cam 4 shown in FIG. 3 and the inner diameter surface 5a of the inner ring 5 shown in FIG. 5 are fitted as shown in FIGS. Is equivalent to the difference between the major axis length of the outer peripheral surface 4a and the inner diameter d (see FIG. 4) of the inner diameter surface 5a. The minimum value of the tightening allowance corresponds to the difference between the short axis length of the outer peripheral surface 4a and the inner diameter d of the inner diameter surface 5a.

The fastening allowance between the outer peripheral surface 4a of the cam 4 and the inner diameter surface 5a of the inner ring 5 includes a virtual outer diameter surface 4av (see FIG. 3) when the outer peripheral surface 4a is virtualized and an inner diameter surface 5a (see FIG. 3). 5)). Here, the virtual circle is that of a circle having an oval peripheral length L ₁ the same circumference and the outer peripheral surface 4a. The relationship between the virtual outer diameter surface 4av of the outer peripheral surface 4a of the cam 4 and the inner diameter d of the inner diameter surface 5a of the inner ring 5 corresponds to L ₁ / L ₂ .

When the fastening allowance between the virtual outer diameter surface 4av of the outer peripheral surface 4a of the cam 4 and the inner diameter surface 5a of the inner ring 5 is determined, the fitting surface pressure between the virtual outer diameter surface 4av and the inner diameter surface 5a can be obtained. The pulling force of the inner ring 5 necessary for pulling out the inner ring 5 from 4 is also known. When the obtained pulling force of the inner ring 5 is larger than the above-described thrust force F, the inner ring 5 does not move in the axial direction with respect to the cam 4 due to the thrust force F. Therefore, you are possible to determine a virtual outside diameter surface 4av the outer peripheral surface 4a of the cam 4, interference of the lower limit of the inner diameter surface 5a of the inner ring 5, i.e. the lower limit of the value of L _{1 /} L _2. When the value of L ₁ / L ₂ is 1.0001 or more, it is possible to prevent the ball bearing 1 from moving with respect to the cam 4 due to the thrust force F in practical use of the wave gear device.

Further, when the tightening allowance between the virtual outer diameter surface 4av and the inner diameter surface 5a and the inner ring wall thickness t described above are known, the tensile stress applied to the cross-sectional area of the inner ring 5 is known. If this tensile stress exceeds the allowable value, the inner ring 5 may break and break. In the case of the inner ring 5 and the outer ring 6 made of bearing steel, the upper limit value of the tightening allowance that allows the ball bearing 1 to be used stably without breaking the inner ring 5 is that the maximum value of the tangential stress of the inner ring 5 is approximately 13 kgf / mm. ^The value should not exceed ² (127 MPa). Therefore, it is possible to determine a virtual outside diameter surface 4av the outer peripheral surface 4a of the cam 4, interference of the upper limit of the inner diameter surface 5a of the inner ring 5, namely the upper limit of the value of L _{1 /} L _2. When the value of L ₁ / L ₂ is 1.0007 or less, the wave gear device can be practically prevented from cracking the inner ring 5 due to a tightening margin between the inner ring 5 and the cam 4.

As described above, since the value of L ₁ / L ₂ of the ball bearing 1 is 1.0001 or more and 1.0007 or less, the ball bearing 1 is interposed between the flex spline 3 and the cam 4 when the wave gear device is used. As a result, the thrust force F acting on the ball bearing 1 prevents the ball bearing 1 from being displaced relative to the cam 4, and the inner ring 5 can be prevented from cracking due to the interference between the inner ring 5 and the cam 4.

Further, the ball bearing 1 has a t / T value of 0.109 or more and 0.448 or less and a B / T value of 0.789 or more and 1.579 or less. It is suitable for preventing cracking.

Examples are oval peripheral length _{L 1} of the outer peripheral surface 4a of the cam 4 is 78.66Mm (hereinafter, referring to FIGS. 1, 3, 5). The generated thrust force F is 10 kgf (however, the maximum output torque is 46 Nm at the moment). This example is based on the HDS model number 14 on page 052 of Non-Patent Document 1. The thrust force F can be obtained by 2 × T / D × 0.07 × tan 30 ° (where T: output torque, D: HDS model number × 0.00256).

Further, the pulling force of the inner ring 5 can be obtained by 0.12 × P × π × d × B (where P: surface pressure of the outer surface of the inner ring, d: inner diameter of the inner ring, B: width of the inner ring).

For each example in which the outer ring Di is fixed to 26 mm, the inner ring 5 width B is fixed to 7 mm, and the inner diameter d of the inner ring 5 is varied to vary the circumferential ratio L ₁ / L ₂ , the pulling force of the inner ring 5 Table 1 shows the results of calculating the maximum stress of the inner ring 5 (the maximum value of the tangential stress) together with the values of t / T and B / T.

For each example in which the outer diameter Di of the inner ring 5 is fixed to 29 mm, the width B of the inner ring 5 is fixed to 3.5 mm, and the inner diameter d of the inner ring 5 is changed to make L ₁ / L ₂ different, Table 2 shows the results of calculating the maximum stress of the inner ring 5 (the maximum value of the tangential stress) together with the values of t / T and B / T.

When the maximum stress in Tables 1 and 2 exceeds 13 kgf / mm ² , the inner ring 5 may be cracked. Therefore, in Tables 1 and 2, an example in which the inner diameter d of the inner ring is 25.02 mm (circumferential length ratio L ₁ / L ₂ is 1.0008) is not an appropriate fastening allowance.

Further, when the pulling force of the inner ring 5 in Tables 1 and 2 is a thrust force F: 10 kgf or less, the inner ring 5 moves in the axial direction with respect to the cam 4. Therefore, in Tables 1 and 2, an example in which the inner diameter d of the inner ring is less than 25.038 mm (L ₁ / L ₂ is 1.0001) is not an appropriate tightening allowance.

That is, it can be seen from Tables 1 and 2 that if 1.0001 ≦ L ₁ / L ₂ ≦ 1.0007, an appropriate margin is obtained.

Further, from Tables 1 and 2, focusing on the t / T of each example in which the pulling force of the inner ring 5 is superior to the thrust force F, if 0.109 ≦ t / T ≦ 0.448, the displacement of the inner ring 5 It turns out to be suitable for preventing movement.

Further, from Tables 1 and 2, focusing on the B / T in each example where the pulling force of the inner ring 5 exceeds the thrust force F, if 0.789 ≦ B / T ≦ 1.579, the displacement of the inner ring 5 It turns out to be suitable for preventing movement.

Further, from Tables 1 and 2, when focusing on B / T in each example where the maximum stress does not exceed 13 kgf / mm ² , if 0.789 ≦ B / T ≦ 1.579, the inner ring 5 is cracked. It turns out to be suitable for prevention.

The embodiments and examples disclosed this time should be considered as illustrative in all points and not restrictive. Therefore, the scope of the present invention is defined by the terms of the claims, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

DESCRIPTION OF SYMBOLS 1 Ball bearing 2 Circular spline 3 Flex spline 4 Cam 4a Outer surface 5 Inner ring 5a Inner ring surface 6 Outer ring 6a Outer surface 9 Ball t Inner ring wall thickness B Inner ring width L ₁ Elliptical circumference L ₂ Circumference length T Bearing cross section height

Claims

An inner ring having an inner diameter surface that fits into a cam of a wave gear device, an outer ring having an outer diameter surface that fits inside a flexspline of the wave gear device, and a plurality of intermediate rings interposed between the inner ring and the outer ring A ball bearing comprising a ball,
An oval peripheral length of the outer peripheral surface formed into an elliptical shape with the cam and L 1, when the circumferential length of the inner ring of the inner surface was L 2, the value of L 1 / L 2 is 1.0001 or more 1 A ball bearing characterized by being no more than 0007.
T / T, where t is the inner ring wall thickness that is the difference between the inner diameter and outer diameter of the inner ring, and T is the bearing cross-sectional height that is the difference in diameter between the inner diameter surface of the inner ring and the outer diameter surface of the outer ring. The ball bearing according to claim 1, wherein the value of is 0.109 or more and 0.448 or less.
The value of B / T is 0.789 or more and 1.579, where B is the width of the inner ring and T is the bearing cross-sectional height, which is the difference in diameter between the inner diameter surface of the inner ring and the outer diameter surface of the outer ring. The ball bearing according to claim 1 or 2, wherein:
The ball bearing according to any one of claims 1 to 3, wherein the inner ring is formed of bearing steel.