TW202219398A - Cross roller bearing - Google Patents

Abstract

The present invention suppresses the causes of deterioration of the low torque property and rolling life of a crossed roller bearing, while avoiding excessive machining of an inclined raceway surface of the crossed roller bearing. An inclined raceway surface (1a) of an outer ring (1) is provided so as to have a smaller surface roughness Ra than the surface roughness Ra of an inclined raceway surface (2a) of an inner ring (2). The inclined raceway surfaces (1a, 2a) are provided such that the surface roughnesses Ra are smaller than or equal to 0.3 [mu]m.

Description

Crossed Roller Bearings

The invention relates to a cross-roller bearing incorporating rollers between an outer ring and an inner ring in a manner that the oblique directions alternate in the circumferential direction.

A crossed roller bearing is a system in which a plurality of rollers are arranged on a pair of inclined raceways formed on the inner peripheral surface of the outer ring that are orthogonal to each other, and a pair of inclined raceways formed on the outer peripheral surface of the inner ring in such a manner that the inclined direction alternately changes in the circumferential direction of the bearing. between a pair of inclined track surfaces that are orthogonal to each other (for example, Patent Document 1).

In a normal crossed roller bearing, the surface roughness of each inclined raceway surface of the inner ring and the outer ring is the same.

Crossed roller bearings are widely used in industrial machinery because they can support large radial loads, thrust loads, and moment loads, such as reducers for robots that require high rigidity. [Prior Art Literature] [Patent Literature]

[Patent Document 1] Japanese Patent No. 3739056

[Problems to be Solved by Invention]

For crossed roller bearings mounted on reducers for robots, low torque performance or rolling life that can be used continuously and stably is required.

However, in a crossed roller bearing, there is frictional resistance in which the end surfaces of the rollers are in sliding contact with the inclined raceway surfaces. This frictional resistance hinders low torque performance and causes wear, which adversely affects rolling life.

In addition, the cross-roller bearing installed in the reducer for the robot is used in a thin lubrication condition where the oil film parameter between the inclined raceway surface and the roller is small because of the slow rotation speed. Here, the oil film parameter means the ratio of the minimum oil film thickness between the two surfaces of the rolling calculated according to the elastic fluid lubrication theory to the square root of the sum of the squares of the root mean square roughness of the two surfaces.

The smaller the oil film parameter, the higher the possibility of roller peeling. Here, the peeling refers to a dense damage with a size of about 10 μm and a depth of several μm to 10 μm. The peeling of the rollers is the cause of the significant deterioration of the rolling life. It is known that peeling is likely to occur under thin lubrication conditions and when the difference in surface roughness between the two rolling surfaces is large.

In order to suppress the frictional resistance caused by the above-mentioned sliding contact or suppress the occurrence of peeling, it is preferable to reduce the surface roughness of the inclined raceway surface. above.

In view of the above-mentioned background, the problem to be solved by the present invention is to avoid excessive machining of the inclined raceway surface of the crossed roller bearing, and to suppress the cause of deterioration of low moment performance and rolling life. [Technical means to solve problems]

In order to achieve the above-mentioned problem, the crossed roller bearing of the present invention includes: an outer ring having a pair of inclined raceways orthogonal to each other on the inner peripheral surface; and an inner ring having a pair of inclined raceways orthogonal to each other on the outer peripheral surface surface; a plurality of rollers, which are arranged between a pair of inclined track surfaces of the above-mentioned outer ring and a pair of inclined track surfaces of the above-mentioned inner ring in such a way that the inclined directions are alternately changed in the circumferential direction; The surface roughness Ra of the inclined raceway surface is set to be smaller than the above-mentioned constitution of the surface roughness Ra of the inclined raceway surface of the inner ring. Here, the surface roughness Ra refers to the arithmetic mean roughness of the roughness parameters specified in JIS B0601:2013 (corresponding to ISO4287:1997): Ra.

The sliding contact between the end face of the roller and the raceway surface that occurs in the operation of the crossed roller bearing mainly occurs between the outer ring and the roller, and hardly occurs between the inner ring and the roller. Therefore, if the surface roughness Ra of the inclined raceway surface of the outer ring is set to be smaller than the surface roughness Ra of the inclined raceway surface of the inner ring, the cause of the deterioration of low moment performance and rolling life, that is, the end surfaces of the outer ring and the rollers The frictional resistance between them is reduced, and on the other hand, the surface roughness of the inclined track surface of the inner ring can be avoided to be too small.

The surface roughness Ra of the inclined raceway surface of the outer ring and the surface roughness Ra of the inclined raceway surface of the inner ring can be set to be 0.3 μm or less, respectively. In this way, peeling of the roller can be suppressed.

From the viewpoint of reducing the processing cost of the inclined raceway surface of the inner ring, the surface roughness Ra of the inclined raceway surface of the outer ring and the surface roughness Ra of the inclined raceway surface of the inner ring are preferably set to 0.1 μm or more, respectively.

It is preferably provided in a full roller form. In this way, in particular, it can be used as a crossed roller bearing with high rigidity. [Effect of invention]

By adopting the above-described configuration, the present invention can avoid excessive machining of the inclined raceway surface of the crossed roller bearing, and can suppress the cause of deterioration of low moment performance and rolling life.

Hereinafter, an embodiment as an example of the present invention will be described based on the drawings.

The crossed roller bearing shown in FIG. 1 includes an outer ring 1 , an inner ring 2 , and a plurality of rollers 3 arranged in a single row between the outer ring 1 and the inner ring 2 . This crossed roller bearing system is especially assumed to be incorporated in a reducer for a robot.

The outer ring 1 has a pair of inclined track surfaces 1a on the inner peripheral surface that are orthogonal to each other. The inner ring 2 has a pair of inclined track surfaces 2a orthogonal to each other on the outer peripheral surface.

The rollers 3 include cylindrical rollers.

The outer ring 1, the inner ring 2 and the roller 3 are made of steel, respectively. The material is, for example, bearing steel.

As shown in FIG. 1 and FIG. 2 , a plurality of rollers 3 are arranged between a pair of inclined raceway surfaces 1a of the outer ring 1 and a pair of inclined raceway surfaces 2a of the inner ring 2 in such a manner that the inclination directions are alternately changed in the circumferential direction. between.

The crossed roller bearing is provided in full roller form. Here, the so-called full-roller type means that the sum of the gaps between the rollers 3 arranged in a line between the inclined raceways 1a and 2a does not exceed the diameter of the rollers 3, and does not have the ability to separate the adjacent rollers 3 between the rollers 3. The spaced bearing parts (retainers, spacers, etc.) are arranged so that adjacent rollers 3 can contact each other in order to function as a bearing.

A pair of inclined track surfaces 1a of the outer ring 1 is in its axial cross-section, extending linearly from a relief groove 1b formed in the axial center portion of the inner peripheral surface of the outer ring 1 to both sides in the axial direction, and one of the inclined track surfaces The surface 1a is in linear contact with the rotating surface of the roller 3 . Similarly, a pair of inclined track surfaces 2a of the inner ring 2, in its axial cross section, extend linearly from the escape groove 2b formed in the axial center portion of the outer peripheral surface of the inner ring 2 to both sides in the axial direction, one of which is inclined The raceway surface 2a is in linear contact with the rotating surface of the roller 3 .

The evaluation test was carried out under normal use conditions for samples in which the surface roughness Ra of the inclined raceway surfaces 1a and 2a of the crossed roller bearing was changed. The evaluation contents are rotational inspection by touch, the presence or absence of peeling, and abrasion.

First, after assembling the sample, a spin inspection by touch is performed. As a result, the smaller the surface roughness of the inclined raceway surfaces 1a and 2a, the smoother the rotation. However, the size of the surface roughness Ra of the inclined track surface 2a of the inner ring 2 will hardly affect the result of the rotation inspection of the touch feeling, and the size of the surface roughness Ra of the inclined track surface 1a of the outer ring 1 will affect the result of the rotation inspection. The result of the rotation inspection of the tactile sensation has a great influence. The reason for this is that during operation, as shown in FIG. 2 , the roller 3 is close to the outer ring 1 side, and the end surface 3 a of the roller 3 on the outer ring 1 side is opposed to the inclined raceway surface 1 a pressed against the roller 3 in the traveling direction. , sliding contact in the narrow contact area P, on the other hand, at this time, the end surface 3a of the inner ring 2 side of the roller 3 hardly contacts the inclined raceway surface 2a of the inner ring 2.

In fact, in the wear evaluation test, in the center portion of the inclined raceway surface 1a of the outer ring 1, as shown in FIG. 1, although the contact mark Iw caused by the initial wear occurred, it hardly occurred in the inclined raceway surface 2a of the inner race 2. Contact marks due to initial wear. FIG. 3 illustrates the generatrix shape of the inclined raceway surface 1a of the outer ring 1 in which the wear evaluation test was performed. As is clear from FIG. 3 , in the inclined raceway surface 1a in the initial wear state, initial wear due to contact with the vicinity of the edge of the end surface 3a of the roller 3 was observed in the vicinity of the center portion of the generatrix shape. In addition, in FIG. 1, the contact trace caused by the initial abrasion is greatly exaggerated and drawn.

Next, Table 1 shows the evaluation results of the presence or absence of peeling. In each sample, the inclined raceway surface 1a of the outer ring 1 and the inclined raceway surface 2a of the inner ring 2 were finished to have the same surface roughness Ra. The difference in surface roughness Ra of the inclined track surfaces 1a and 2a between the samples was set to 0.05 μm.

Ra of track surfaces 1a and 2a 0.4 0.35 0.3 0.25 0.2 0.15 Peeling of Roller 3 occur occur none none none none

From the evaluation results in Table 1, it is considered that the rough surfaces of the inclined raceway surfaces 1a and 2a are more likely to cause peeling of the rollers 3. Therefore, setting the surface roughness Ra of the inclined raceway surfaces 1a and 2a to 0.3 μm or less is effective in preventing peeling. .

In addition, from the results of the rotational inspection of the tactile sensation conducted in the above-mentioned wear evaluation test, it can be considered that reducing the surface roughness Ra of the inclined raceway surface 1a of the outer ring 1 is to suppress the gap between the outer ring 1 and the end surface 3a of the roller 3 The contact resistance is particularly effective in reducing the moment and suppressing the deterioration of rolling life due to wear, but it is not effective in reducing the surface roughness Ra of the inclined raceway surface 2a of the inner ring 2 .

On the other hand, the smaller the surface roughness Ra of the inclined raceway surfaces 1a and 2a, the more difficult the processing and the higher the cost.

In view of the above test results and considering the burden of the machined surface, the surface roughness Ra of the inclined raceway surface 1a of the outer ring 1 is set to be smaller than the surface roughness Ra of the inclined raceway surface 2a of the inner ring 2 .

In addition, the surface roughness Ra of the inclined raceway surface 1a and the surface roughness Ra of the inclined raceway surface 2a are set to be 0.1 μm or more and 0.3 μm or less, respectively. In Table 1, although the evaluation results of 0.15 μm or more are described, it is set to 0.1 μm or more in consideration of the unevenness of the processed surface.

In this crossed roller bearing, as described above, since the surface roughness Ra of the inclined raceway surface 1a of the outer ring 1 is set to be smaller than the surface roughness Ra of the inclined raceway surface 2a of the inner ring 2, the low moment performance and rolling life are deteriorated. The reason is that the frictional resistance at the sliding contact portion between the inclined raceway surface 1a of the outer ring 1 and the end surface 3a of the roller 3 is reduced, and on the other hand, the surface roughness Ra of the inclined raceway surface 2a of the inner ring 2 is avoided. too small. Therefore, in this crossed roller bearing, excessive machining of the inclined raceway surface can be avoided, and the causes of deterioration of low moment performance and rolling life can be suppressed.

In addition, since the surface roughness Ra of the inclined raceway surface 1a of the outer ring 1 and the surface roughness Ra of the inclined raceway surface 2a of the inner ring 2 of the crossed roller bearing are set to be 0.3 μm or less, respectively, it is possible to suppress the roller 3 Peeling occurs.

In addition, since the surface roughness Ra of the inclined raceway surface 1a of the outer ring 1 and the surface roughness Ra of the inclined raceway surface 2a of the inner ring 2 of the crossed roller bearing are respectively set to 0.1 μm or more, the above-mentioned rolling can be suppressed. The frictional resistance of the sliding contact portion between the end surface 3a of the roller 3 and the inclined raceway surface 1a is reduced to reduce the moment, and the wear caused by the friction and the peeling of the roller 3 are suppressed to improve the rolling life, and the inclined raceway surface 1a, 2a's excessive processing, which can inhibit the offer price.

In addition, since this crossed roller bearing system is provided in an all-roller type, it can be particularly highly rigid. Since the full-roller form has no retainers or spacers, and the maximum number of rollers 3 that can be accommodated is incorporated between the inclined race surfaces 1a and 2a, the adjacent rollers 3 are in contact with each other, and the root of the rollers 3 The number increases. Therefore, the rotation speed of the all-roller type crossed roller bearing is slow, and it is easy to be under the condition of thin lubrication, and the number of sliding contact points between the end surface 3a of the roller 3 and the inclined raceway surface 1a also increases. As described above, by properly normalizing the surface roughness Ra of the inclined raceway surfaces 1a, 2a, low moment performance and improved rolling life can be achieved, and by adopting the full-roller type, high rigidity of the bearing can be achieved, thereby , it can become a crossed roller bearing especially suitable for reducers for robots.

It should be understood that all points of the embodiments disclosed this time are illustrative rather than limiting. Therefore, the scope of the present invention is disclosed by the scope of the patent application rather than by the above description, and is intended to include the meaning equivalent to the scope of the patent application and all changes within the scope.

1: Outer ring 1a: Inclined track surface 1b: Backoff slot 2: inner ring 2a: Inclined track surface 2b: Backoff slot 3: Roller 3a: end face Iw: contact mark P: Contact area

FIG. 1 is a cross-sectional view showing a crossed roller bearing according to an embodiment of the present invention. FIG. 2 is a partial cross-sectional view showing the running state of the crossed roller bearing by the section taken along the line II-II of FIG. 1 . FIG. 3 is a diagram showing an example of measurement of the shape of the generatrix in the initial wear state of the inclined raceway surface of the outer ring of FIG. 1 .

1: Outer ring

1a: Inclined track surface

1b: Backoff slot

2: inner ring

2a: Inclined track surface

2b: Backoff slot

3: Roller

3a: end face

Iw: contact mark

Claims (4)

A crossed roller bearing, comprising: an outer ring having a pair of inclined track surfaces orthogonal to each other on an inner peripheral surface; an inner ring having a pair of inclined track surfaces orthogonal to each other on an outer peripheral surface; and a plurality of Rollers, etc. are arranged between a pair of inclined raceway surfaces of the outer ring and a pair of inclined raceway surfaces of the inner ring in such a way that the inclination directions are alternately changed in the circumferential direction; and it is characterized in that: The surface roughness Ra of the inclined raceway surface of the outer ring is set to be smaller than the surface roughness Ra of the inclined raceway surface of the inner ring. The crossed roller bearing of claim 1, wherein the surface roughness Ra of the inclined raceway surface of the outer ring and the surface roughness Ra of the inclined raceway surface of the inner ring are respectively set to 0.3 μm or less. The crossed roller bearing of claim 2, wherein the surface roughness Ra of the inclined raceway surface of the outer ring and the surface roughness Ra of the inclined raceway surface of the inner ring are respectively set to 0.1 μm or more. The crossed roller bearing of any one of claims 1 to 3, which is provided in the form of full rollers.

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