Slide bearing

Abstract

To provide a slide bearing for reducing the weight and the size to suppress an allowable moment load and the function deterioration of moment rigidity while reducing the manufacturing cost.SOLUTION: A slide bearing 1 includes inner and outer rings 2, 3. On the outer peripheral face of the inner ring 2, an annular recessed part 4 is provided which is recessed radially inward. The inner peripheral face of the outer ring 3 is provided on an annular protruded part 5 which is fitted into the annular recessed part 4 and slidable relative to the inner ring 2 in the circumferential direction. The inner ring 2 and the outer ring 3 are each provided to be integrated. One or both of the inner and outer rings 2, 3 include resin having self lubrication property. The slide bearing 1 includes a contact angle for enabling the support of a moment load.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a sliding bearing, and more particularly to a sliding bearing used in a joint of an industrial robot, a service robot or the like, or in a reducer mounted on such a joint. [Background technology]

[0002] Most cross roller bearings for robot reducers are used under moment load conditions, and so the inner and outer rings are of an integral structure (Patent Document 1). In a cross roller bearing, as shown in Fig. 9, a roller 50 is inserted through a roller insertion hole 51a provided in an outer ring 51, and the roller insertion hole 51a is covered with a stopper 52, which is then fixed to the outer ring 51 with a pin (not shown). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 3739056 Summary of the Invention [Problem to be solved by the invention]

[0004] In the industrial robot market, demand for small robots such as collaborative robots and service robots is increasing. Accordingly, there is a trend toward more compact and lightweight robot reducers for robots. A particular challenge is the main bearings in the robot joints, which have traditionally been made up of cross roller bearings, back-to-back combination bearings consisting of back-to-back angular contact ball bearings, or four-point contact ball bearings. In recent years, there has been a demand for cheaper, more compact, and lighter main bearings.

[0005] An object of the present invention is to provide a sliding bearing that is lightweight and compact, suppresses any deterioration in the allowable moment load and moment rigidity, and enables reduction in manufacturing costs. [Means for solving the problem]

[0006] The sliding bearing of the present invention is a sliding bearing equipped with inner and outer rings, The outer peripheral surface of the inner ring is provided with a sliding surface in the shape of an annular recess that is recessed radially inward, the inner peripheral surface of the outer ring is provided with a sliding surface in the shape of an annular convexity that fits into the annular recess and is capable of sliding circumferentially relative to the inner ring, the sliding surface of the annular recess is provided with a pair of inclined surfaces on both axial sides, and a central diameter PCD, which is the diameter dimension of the radial central part of the sliding surface between the inner and outer rings, is located on the outer diameter side of the bearing central diameter Dc. The "bearing center diameter" is the dimension obtained by adding the inside diameter of the inner ring to the outside diameter of the outer ring and dividing the value by 2.

[0007] According to this configuration, since multiple rolling elements are not required, it is possible to reduce the bearing cross section and achieve lighter and smaller size compared to conventional cross roller bearings, and the number of parts can be reduced to reduce manufacturing costs. The outer peripheral surface of the inner ring is provided with an annular recess recessed inward in the radial direction, and the inner peripheral surface of the outer ring is provided with an annular protrusion that fits into the annular recess and can slide circumferentially relative to the inner ring. For this reason, the plain bearing can support moment loads in both directions, and costs can be reduced by making each raceway into a relatively simple integrated shape. In addition, when each raceway is integrated, the rigidity is higher than when the raceway is a split type. Since the central diameter PCD is located on the outer diameter side of the bearing central diameter Dc, the distance between the intersection points of the axis and the load application point (the distance between the application points) can be made wider compared to, for example, when the central diameter PCD and the bearing central diameter are the same, which provides superior rigidity against moment loads and increases the load capacity.

[0008] Because this sliding bearing can support moment loads through surface contact, it has an advantage in terms of rigidity over the line contact of a cross roller bearing or the point contact of a four-point contact ball bearing.As a result, compared to conventional technologies such as cross roller bearings or four-point contact ball bearings, it is lighter and more compact, prevents any decline in performance in allowable moment load and moment rigidity, and reduces manufacturing costs.

[0009] Each of the inclined surfaces of the inner ring and the outer ring may have an inclination angle that inclines toward the outer diameter side from an axial center or a portion near the axial center toward the outside in the axial direction. The axial center portions of the inner and outer wheels may extend a predetermined distance on both sides of the axial center of each drive wheel. The "predetermined distance" is determined appropriately according to the required distance between the load points. In this case, a large distance between the points of application can be ensured, roughly the same as in the back-to-back combination of a duplex bearing, even though the bearing is a single plain bearing. This means that, compared to a rolling bearing with the same main dimensions, it has superior rigidity against moment loads, and the load capacity can be increased.

[0010] Either or both of the inner and outer rings may contain a self-lubricating resin. In this case, lubricants such as grease can be eliminated, improving maintainability compared to those that require grease.

[0011] The sliding bearing may have a contact angle capable of supporting a moment load. In this case, the sliding bearing alone can reliably support the moment load.

[0012] A surface treatment layer that serves as a sliding resistance reducing member may be provided on either or both of the inner circumferential surface of the outer ring and the outer circumferential surface of the inner ring. In this case, friction on the sliding surfaces between the inner and outer rings can be reduced compared to a structure not provided with a surface treatment layer. This can reduce power loss in the drive source.

[0013] The resin may have a core metal, which makes it possible to improve the durability of the resin against elongation, peeling, and breakage when a load is applied, compared to a resin without a core metal. Effect of the Invention

[0014] The sliding bearing of the present invention is a sliding bearing with an inner and outer ring, wherein the outer peripheral surface of the inner ring is provided with a sliding surface in the shape of an annular concave that is concave radially inward, the inner peripheral surface of the outer ring is provided with a sliding surface in the shape of an annular convex that fits into the annular concave and is capable of sliding in the circumferential direction relative to the inner ring, the sliding surface of the annular concave is provided with a pair of inclined surfaces on both axial sides, the sliding surface of the annular convex is provided with a pair of inclined surfaces on both axial sides, and a central diameter PCD, which is the diameter dimension of the radial central part of the sliding surface between the inner and outer rings, is located on the outer diameter side of the bearing central diameter Dc. This allows for lighter and more compact bearings, suppresses deterioration in allowable moment load and moment rigidity, and reduces manufacturing costs. [Brief description of the drawings]

[0015] [Figure 1] FIG. 1 is a partial perspective view showing a longitudinal section of a sliding bearing according to a first embodiment of the present invention. [Diagram 2] FIG. 2 is a partially enlarged view of a main part of FIG. [Diagram 3] FIG. 4 is an explanatory diagram showing the relationship between the PCD of the sliding surface of the sliding bearing and the bearing center diameter. [Figure 4] FIG. 11 is a partial perspective view showing a longitudinal section of a sliding bearing according to a second embodiment of the present invention. [Diagram 5] FIG. 11 is a longitudinal sectional view of a sliding bearing according to a third embodiment of the present invention. [Figure 6] FIG. 13 is an explanatory diagram illustrating a difference in the point of action. [Figure 7] FIG. 11 is a partial perspective view showing a longitudinal section of a sliding bearing according to a fourth embodiment of the present invention. [Figure 8] FIG. 11 is a partial perspective view showing a longitudinal section of a sliding bearing according to a fifth embodiment of the present invention. [Figure 9] FIG. 11 is a vertical sectional view of a main portion of a conventional cross roller bearing. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] [First embodiment] A sliding bearing according to an embodiment of the present invention will be described with reference to Figures 1 to 3. The sliding bearing according to the embodiment is a sliding bearing used in, for example, a joint of an industrial robot, a service robot or the like, or in a reducer mounted on such a joint.

[0017] <Schematic configuration of a sliding bearing> As shown in FIG. 1, the sliding bearing 1 is provided with an inner ring 2 and an outer ring 3, and is a sliding bearing with a contact angle that enables the bearing alone to support a moment load, and is not provided with rolling elements. The contact angle is the angle of the load action lines Lf, Lf relative to the axial center C, as shown in FIG. 3. As shown in FIG. 1, the outer peripheral surface of the inner ring 2 is provided with an annular recess 4 that is recessed radially inward at or near the axial center. The inner peripheral surface of the outer ring 3 is provided with an annular protrusion 5 that fits into the annular recess 4 and is capable of sliding relative to the inner ring 2 in the circumferential direction. The inner ring 2 and the outer ring 3 are each provided as a single unit.

[0018] <Inner circle> As shown in FIG. 2, the inner ring 2 is made of, for example, bearing steel. On the outer peripheral surface of the inner ring 2, inclined surfaces 4a, 4a are provided on both axial sides of the axial center or near the axial center. The inclined surfaces 4a, 4a are formed on a sliding surface with a V-groove cross section that forms an annular recess 4 that inclines toward the outer diameter as it moves from the axial center or near the axial center toward the axial outside. The "near the axial center" is a portion of the outer peripheral surface of the inner ring 2 that is separated from the axial center by a length determined in the axial direction C1. The axial direction of the central axes of the inner ring 2 and the outer ring 3 is defined as the "axial direction" C1. The determined length is set appropriately according to the conditions of use of the plain bearing 1. When inclined surfaces 4a, 4a are provided on both axial sides of the axial center of the outer peripheral surface of the inner ring 2, a difference occurs in the moment load that can be supported in both directions, so the mounting direction of the plain bearing 1 is uniquely determined according to the conditions of use. The inclination angle α of each inclined surface 4a with respect to the axial direction C1 is determined as appropriate in accordance with the conditions of use of the sliding bearing 1. The inclination angles α of the inclined surfaces 4a, 4a on both axial sides are set to be the same or may be set to different angles. The axially outer edge of each inclined surface 4a is connected to the inner ring end face 2a.

[0019] <Outer ring> The outer ring 3 is made of, for example, a resin having self-lubricity. Resins having self-lubricity are, for example, fluororesins, high molecular weight polyethylene resins, etc. Examples of high molecular weight polyethylene resins include Beary NY5000 manufactured by NTN Corporation, polyacetal resin (POM), etc. In this example, the entire outer ring is formed by injection molding. Specifically, with the inner ring 2 supported by an injection molding machine (not shown), the entire outer ring is formed by injection molding into the cavity on the outer peripheral side of the inner ring 2.

[0020] On the inner peripheral surface of the outer ring 3, inclined surfaces 5a, 5a are provided on both axial sides of the central portion in the axial direction or the vicinity of the central portion in the axial direction. These inclined surfaces 5a, 5a are fitted into the annular recess 4 and are formed on a sliding surface having a V-shaped cross section that forms an annular convex portion 5 that is slidable relative to the inner ring 2 in the circumferential direction. The outer axial edges of each inclined surface 5a are connected to the outer ring end face 3a. The inclination angle of the inclined surface 5a with respect to the axial direction C1 is set to be the same as the inclination angle α of the inclined surface 4a of the corresponding inner ring 2.

[0021] <Regarding the relationship between PCD and the bearing center diameter> As shown in FIG. 3, the central portion diameter PCD, which is the diameter dimension of the radially central portion of the sliding surface Fs between the inner and outer rings, is located on the outer diameter side with respect to the bearing center diameter Dc. The "bearing center diameter Dc" is, as described above, the dimension obtained by dividing the value obtained by adding the inner ring inner diameter and the outer ring outer diameter by 2. The intersections of the load action lines Lf, Lf of the two sliding surfaces Fs, Fs and the shaft center C correspond to the distance L between the action points. Since the central portion diameter PCD is located on the outer diameter side with respect to the bearing center diameter Dc, the distance L between the action points can be widened compared to, for example, the case where the central portion diameter PCD and the bearing center diameter Dc are the same, resulting in superior rigidity against moment loads and an increase in the load capacity.

[0022] <Function and effect> The sliding bearing 1 shown in FIG. 1 described above does not require multiple rolling elements, so compared to conventional cross roller bearings and the like, it is possible to reduce the bearing cross section, making it lighter and more compact, and also to reduce the number of parts and manufacturing costs. The outer peripheral surface of the inner ring 2 is provided with an annular recess 4 that is recessed radially inward at or near the axial center, and the inner peripheral surface of the outer ring 3 is provided with an annular protrusion 5 that fits into the annular recess 4 and can slide circumferentially relative to the inner ring 2. As a result, the sliding bearing 1 can support moment loads in both directions, and costs can be reduced by making each of the raceways 2, 3 into a relatively simple one-piece shape. Furthermore, when each of the raceways 2, 3 is one-piece, it has higher rigidity than if the raceways were split.

[0023] Because this sliding bearing 1 can support moment loads through surface contact, it has an advantage in terms of rigidity over the line contact of a cross roller bearing or the point contact of a four-point contact ball bearing. Therefore, compared to conventional cross roller bearings or four-point contact ball bearings, it is lighter and more compact, prevents any deterioration in performance of the allowable moment load and moment rigidity, and reduces manufacturing costs.

[0024] As shown in Figure 2, inclined surfaces 4a, 4a are provided on both axial sides of the outer peripheral surface of the inner ring 2, and these inclined surfaces 4a, 4a of the inner ring 2 are formed into a groove-shaped sliding surface that forms the annular recess 4. Furthermore, inclined surfaces 5a, 5a are provided on both axial sides of the inner peripheral surface of the outer ring 3, and these inclined surfaces 5a, 5a of the outer ring 3 are formed into a sliding surface that forms the annular protrusion 5 that fits into the annular recess 4. As a result, the moment load can be supported by surface contact at the inclined surfaces 4a, 5a, which makes it more advantageous in terms of rigidity than rolling bearings in which the raceway surfaces are in line or point contact. Therefore, the sliding bearing alone can support a moment load.

[0025] The inclined surfaces 4a, 5a of the inner ring 2 and the outer ring 3 each have an inclination angle α that inclines from the axial center or near the axial center toward the outer diameter as it moves axially outward. As a result, even though it is a plain bearing alone, a large distance between the load points can be ensured, roughly the same as in the back-to-back combination of a duplex bearing. This means that, compared to rolling bearings with the same main dimensions, it has superior rigidity against moment loads and can increase the load capacity.

[0026] As shown in Figure 3, the load action lines Lf, Lf of the sliding surfaces Fs, Fs between the inner and outer rings are at opposite angles to the shaft center C, so both moment loads can be supported. Since the central diameter PCD is located on the outer diameter side of the bearing central diameter Dc, the distance L between the shaft center C (axis) and the load action point can be made wider than when the central diameter PCD and the bearing central diameter are the same, resulting in superior rigidity against moment loads and an increased load capacity. Since the outer ring 3 is made of a self-lubricating resin, it is possible to eliminate the need for lubricants such as grease, thereby improving maintainability compared to those that require grease or the like.

[0027] <Other embodiments> In the following description, parts corresponding to matters previously described in each embodiment are given the same reference numerals, and duplicated description is omitted. When only a part of the configuration is described, the other parts of the configuration are the same as the previously described embodiment unless otherwise specified. The same configuration has the same action and effect. It is possible to combine not only the parts specifically described in each embodiment, but also partially combine embodiments together, provided that there is no particular problem with the combination.

[0028] [Second embodiment: surface treatment, FIG. 4] 4, a surface treatment layer Sf serving as a sliding resistance reduction member for lowering friction of the sliding surfaces Fs, Fs may be provided on either or both of the inner circumferential surface of the outer ring 3 and the outer circumferential surface of the inner ring 2. In this example, a surface treatment layer Sf such as chrome plating, shot peening, diamond-like carbon (DLC), or hairline (HL) treatment is provided on the inner circumferential surface of the outer ring 3, which is the metal side. However, it is not necessarily limited to these surface treatments, and other surface treatments may also be applied depending on the conditions of use of the sliding bearing 1A. This configuration allows the friction of the sliding surface Fs between the inner and outer rings to be lower than in a structure without a surface treatment layer, which can reduce power loss in a drive source such as a motor.

[0029] [Third embodiment: trapezoidal shape, FIG. 5] As a means for making the distance L between the load centers wider than that of the first embodiment, the axial center portion 3b on the inner peripheral surface of the outer ring 3 may be provided so as to extend a predetermined distance in the axial direction C1, as shown in Fig. 5. The predetermined distance is appropriately determined according to the required distance L between the load centers.

[0030] <Differences in point of action P> In Fig. 6(a), a reference comparative example, the axial central portion of the outer peripheral surface of the inner ring 2 is formed into an inner ring convex shape that protrudes radially outward. In this example, the distance between the centers of application L is smaller than in the structures of the first and second embodiments shown in Fig. 6(b). According to the configuration of a sliding bearing 1B in Fig. 6(c), which is a third embodiment, compared to the structure of Fig. 6(b), in which the axial central portion does not extend, and the structure of Fig. 6(a), which is a reference comparative example, the sliding surface Fs can be positioned further outboard in the axial direction C1, making it possible to widen the distance between the centers of application L and providing superior rigidity against moment loads.

[0031] [Fourth embodiment: resin outer ring sliding surface type, FIG. 7] As shown in FIG. 7, a portion of the inner peripheral surface of the outer ring that has a predetermined radial thickness may be made of the aforementioned self-lubricating resin 6. The remaining portion of the outer ring 3, the outer ring body 3A having a rectangular cross-sectional shape, is made of, for example, bearing steel. With the inner ring 2 and the outer ring body 3A supported by an injection molding machine (not shown), resin is injection molded into the cavity between the inner ring 2 and the outer ring body 3A through a gap or the like provided between the end faces 2a, 3a of the inner ring 2 and the outer ring body 3A, or through a radial through-hole or the like provided in advance in the outer ring body 3A. In this way, the outer ring 3 is integrally formed with the outer ring body 3A and the resin 6 that forms the outer ring sliding surface Fs.

[0032] [Fifth embodiment: mandrel type, FIG. 8] As shown in Fig. 8, a mandrel 7 may be provided inside the resin 6 of the outer ring 3. The mandrel 7 is, for example, a metal ring or a wire mesh or thin plate ring, which is inserted into the cavity during the above-mentioned injection molding to provide the mandrel 7 inside the resin 6. In this case, it is possible to increase the durability of the resin against elongation, peeling, and breakage when a load is applied compared to a case in which the resin does not have a mandrel provided.

[0033] Both the inner and outer rings may be configured to contain a resin having self-lubricating properties, which can be made lighter than a bearing equipped with a metal raceway. The resin outer ring or the resin inner and outer rings may be manufactured using, for example, a 3D printer. Either or both of the inner and outer rings may be made of, for example, sintered oil-impregnated metal, ceramic, or the like.

[0034] Although the embodiment of the present invention has been described above, the disclosed embodiment is illustrative in all respects and is not restrictive. The scope of the present invention is indicated by the claims, not by the above description, and is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0035] 1, 1A, 1B... sliding bearing, 2... inner ring, 3... outer ring, 4... annular recess, 5... annular protrusion, 6... resin, 7... core metal, Sf... surface treatment layer

Claims

1. A sliding bearing having inner and outer rings, a sliding bearing in which the outer peripheral surface of the inner ring is provided with a sliding surface in the shape of an annular concave portion that is concave radially inward, the inner peripheral surface of the outer ring is provided with a sliding surface in the shape of an annular convex portion that fits into the annular concave portion and is capable of sliding in the circumferential direction relative to the inner ring, the sliding surface of the annular concave portion is provided with a pair of inclined surfaces on both axial sides, and the sliding surface of the annular convex portion is provided with a pair of inclined surfaces on both axial sides, and a central diameter PCD that is the diameter dimension of the radial central portion of the sliding surface between the inner and outer rings is located on the outer diameter side of a bearing central diameter Dc.

2. 2. The sliding bearing according to claim 1, wherein the inclined surfaces of the inner ring and the outer ring each have an inclination angle that inclines toward the outer diameter side as it moves axially outward from or near the axial center.

3. 3. The sliding bearing according to claim 1 or 2, wherein one or both of the inner and outer rings contain a self-lubricating resin.

4. 3. The sliding bearing according to claim 1 or 2, which has a contact angle capable of supporting a moment load.

5. 3. The sliding bearing according to claim 1 or 2, wherein a surface treatment layer serving as a sliding resistance reduction member is provided on either or both of the inner circumferential surface of the outer ring and the outer circumferential surface of the inner ring.

6. 4. The sliding bearing according to claim 3, wherein the resin has a core metal.

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