WO2000025034A9

WO2000025034A9 - Nested track bearing

Info

Publication number: WO2000025034A9
Application number: PCT/US1999/021267
Authority: WO
Inventors: Allison Ng
Original assignee: Thomson Industries Inc
Current assignee: TGA North America Holdings III Inc
Priority date: 1998-10-27
Filing date: 1999-09-23
Publication date: 2000-09-28
Anticipated expiration: 2001-04-27
Also published as: WO2000025034A1; AU1092000A

Abstract

A linear motion bearing assembly for movement along a shaft which includes rolling element retainer structure having at least a portion of a plurality of substantially parallel, adjacent nested open rolling element tracks formed therein, the rolling element tracks including an open load bearing portion, an open return portion and turnarounds interconnecting the load bearing and return portions; a plurality of bearing rolling elements disposed in the rolling element tracks; and a plurality of load bearing plates positioned adjacent the rolling element retainer structure for receiving load from the rolling elements disposed in the load bearing portion of the rolling element tracks. A ramp is formed at a junction of the load bearing portion and the turnaround portion of the rolling element tracks for providing a transition between the load bearing portion and the turnaround portion. The linear motion bearing may be a closed or an open-type bearing.

Description

NESTED TRACK BEARING

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to linear motion bearing assemblies and, more particularly, to a linear motion bearing having nested race tracks.

2. Description of the Related .Art

The present invention is directed to improvements in linear motion bearing assemblies. In particular, the improvements relate to linear motion bearing assemblies of the type which support a carriage or pillow block for linear movement along a support member such as an elongated shaft, spline, and/or rail.

These bearing assemblies can either be of the open type or the closed type. Bearing assemblies contemplated by the present invention generally include an outer housing and a rolling element retainer dimensioned for insertion into the outer housing. The outer housing of bearing assemblies of the type contemplated by the present invention are typically in the form of a one piece hollow steel cylinder which serves to, inter alia, retain and protect the rolling element retainer and rolling elements. See, for example, U.S. Pat. Nos. 5,046,862 to Ng and 3,767,276 to Henn. The rolling element retainer typically defines a plurality of longitudinal planar faces each having at least one rolling element track in a loop configuration for containing and recirculating bearing rolling element. The rolling element tracks include

open portions which facilitate load transfer from the supporting shaft to load bearing structure such as load bearing plates operatively associated with either the rolling element retainer or the outer housing. Return portions of the rolling element tracks permit continuous recirculation of the bearing rolling elements through the rolling element tracks during linear motion. The rolling element retainer is typically formed as a monolithic element with the rolling element tracks integrally incorporated therein. The load bearing structure may be in the form of integral elements formed on an inner radial surface of the outer housing. Typical bearing assemblies utilizing load bearing structure formed in the outer housing are shown, for example, in commonly owned U.S. Pat. No. 5,046,862 to Ng, the disclosure of which is incorporated herein by reference. In lieu of integral load bearing structure, separate load bearing plates may be utilized to transfer loads from the supporting shaft. These load bearing plates are longitudinally oriented in association with the rolling element retainer so as to engage at least those bearing rolling elements in direct contact with the support shaft or inner race. These load bearing plates may also be configured to be axially self-aligning by providing

structure which permits the plates to rock into and out of parallelism with the longitudinal axis of the rolling element retainer. See, for example, commonly owned U.S. Pat. No.

3,545,826 to Magee et al. Individual load bearing plates may be expanded transversely so as to engage bearing rolling elements in corresponding adjacent load bearing tracks. In this form, parallel grooves are formed in the underside of the plates to guide the bearing rolling elements while they are in the load bearing portion of the rolling element tracks. See, for example, U.S. Pat. No. 5,558,442 to Ng, the disclosure of which is incorporated by reference herein.

While the above described structure comprises a suitable bearing, a continuing goal of bearing designers and manufacturers is to design and manufacture a bearing having greater load carrying capability. For example, U.S. Pat. No. 5,558,442 to Ng discloses a linear motion bearing assembly having the load bearing portions of two

adjacent race tracks adjacent to each other in an attempt to increase the load bearing capacity of the bearing. However, a need still exists for a bearing having an increased capability of concentrating load bearing tracks at a given orientation to thereby optimize and/or maximize the load performance of the bearing.

SUMMARY OF THE INVENTION

A linear motion bearing is provided having a nested rolling element track geometry which enables the load track location to be advantageously configured to maximize the load carrying capacity of the bearing at a given orientation. Although the advantages of the present invention may be applied to both open and closed type linear motion bearings, the open type linear motion bearings realize an additional advantage wherein the load bearing tracks may be oriented to maximize the bearing pull-off load capacity. In accordance with an embodiment of the present invention, a linear motion bearing assembly for movement along a shaft is provided which includes rolling element retention structure having at least a portion of a plurality of nested open axial

rolling element tracks formed therein, the rolling element tracks including an open load bearing portion, an open return portion and turnarounds interconnecting the load bearing and return portions; a plurality of bearing rolling elements disposed in the rolling element tracks; and a plurality of load bearing plates axially positioned adjacent the retention structure for receiving load from the rolling elements disposed in the load bearing portion of the rolling element tracks. The linear motion bearing may be a closed or an open-type bearing.

Each of the nested axial rolling element tracks in the linear motion bearing assembly includes at least two individual rolling element tracks. In a preferred embodiment, the load bearing portions of two adjacent nested rolling element tracks are adjacent to each other such that the load bearing plates are adjacent to each other to maximize the load bearing capacity of the bearing at a given orientation. In the open-type linear motion bearing assembly the load bearing plates are preferably positioned adjacent an opening formed in the bearing. The load bearing plates are monolithically formed or are individual bearing plates configured and positioned over corresponding load bearing portions of the rolling element tracks. These and other objects, features and advantages of the present invention will become apparent from the following detailed description of illustrative embodiments, which is to be read in connection with the accompanying drawings. BRIEF DESCRIPTION OF THE DR WINGS

For a better understanding of the invention, reference is made to the following description of exemplary embodiments thereof, and to the accompanying drawings, wherein: FIG. 1 is a perspective view of a linear motion bearing assembly in an assembled configuration in accordance with one embodiment of the present invention;

FIG. 2 is an exploded perspective view of the linear motion bearing assembly of FIG. 1;

FIG. 3 is a perspective view of a linear motion bearing assembly in an assembled configuration in accordance with one embodiment of the present invention; FIG. 4 is a perspective view in partial cross-section of the linear motion bearing assembly of FIG. 3;

FIG. 5 is an exploded perspective view of the linear motion bearing

assembly of FIG. 3; FIG. 6 is a perspective view of a monolithic ball retainer structure for use with the linear motion bearing assembly of FIG. 3;

FIG. 7 is a cross-sectional view taken along line 7-7 of FIG. 3; FIG. 8 is a perspective view of an open-type linear motion bearing assembly in an assembled configuration in accordance with another embodiment of the present invention;

FIG. 9 is a perspective view in partial cross-section of the open-type linear motion bearing assembly of FIG. 8; FIG. 10 is an exploded perspective view of the open-type linear motion bearing assembly of FIG. 8;

FIG. 11 is a cross-sectional view taken along line 11-11 of FIG. 8; FIG. 12 is a cross-sectional view of a linear motion bearing assembly having a segmented ball retainer in accordance with another embodiment of the present invention;

FIG. 13 is a cross-sectional view of a closed type linear motion bearing assembly having individual load bearing plates in accordance with another embodiment of the present invention; FIG. 14 is a cross-sectional view of a closed type linear motion bearing assembly in accordance with another embodiment of the present invention;

FIG. 15 is a perspective of an open-type linear motion bearing assembly having a segmented ball retainer in accordance with another embodiment of the present invention; and FIG. 16 is a cross-sectional view taken along line 16-16 of FIG. 15.

PET AH ZED DESCRIPTION OF PREFERRED EMBODIMENTS

Referring initially to FIGS. 1-2, there is shown a linear motion closed-type bearing assembly 50 in accordance with a prefeπed embodiment of the present invention. As illustrated more clearly in FIG. 2, bearing assembly 50 generally includes five rolling element retainer segments 54, load bearing plates 56, bearing rolling elements (not shown), five outer sleeve segments 60, which combine to form an outer housing, load ring 62 and end rings 64.

The five rolling element retainer segments 54 combine to define a bore therethrough configured and dimensioned to receive a shaft. Each of the segments 54 has an outer radial surface and an inner radial surface. In accordance with an embodiment of the present invention, a nested rolling element track 70 is formed in each of the five segments 54. Each of the nested rolling element tracks includes two individual tracks, each having a load bearing portion 72, a return portion 74 and a pair of turnaround portions 76. The outer radial surface of segments 54 is preferably shaped to confirm to an inner radial surface of outer sleeve segments 60. Furthermore, protrusions 66 extend

from corner portions of segments 54 and are configured to mate with coπesponding holes 68 in sleeve segments 60. A longitudinal channel 80 extends through the inner radial surface of the load bearing portions 72 to permit bearing rolling elements 58 access to a shaft. A ramp 81 is formed at a junction of the load bearing portion 72 and the turnaround portions 76 of the nested rolling element tracks (i.e., at the ends of

longitudinal channel 80) for providing a transition between the load bearing portion and the turnaround portion. Both the load bearing portions 72 and the return portions 74 of the rolling element tracks of this embodiment of the present invention are substantially open to facilitate loading of the bearing rolling elements therein. Retainer segments 54 may be molded from an appropriate engineering plastic using known materials and molding techniques. It is also within the scope of the present invention to fabricate the rolling element bearing segments from an engineering metal using known fabrication techniques.

A plurality of bearing rolling elements are disposed in nested rolling element tracks 70, with those bearing rolling elements positioned in the load bearing tracks 72 extending at least partially into longitudinal bores 80 to contact a support shaft. In this embodiment of the invention, as is discussed in further detail below with reference to FIG. 7, the load bearing portions 72 of two adjacent sets of nested rolling element tracks 70 may be oriented in substantially parallel adjacent relation. This orientation facilitates enhanced load capacity capability and maximizes space utilization for a more compact and efficient bearing arrangement.

Referring again to FIG. 2, a plurality of load bearing plates 56 are incorporated into the linear motion bearing assembly 50 and serve to receive load from the bearing rolling elements which are in contact with a shaft. Load bearing plates 56 are elongated along the longitudinal axis of the bearing assembly and include an outer radial surface and an inner radial surface. The outer radial surface is substantially arcuate having a curvature coπesponding to the inner radial surface of outer sleeve segments 60. The inner radial surfaces of the load bearing plates 56 are advantageously provided with a plurality of axial grooves which serve as the upper surface of load bearing portions 72 of the nested rolling element tracks. The number of axial grooves in the inner radial surfaces are determined by and coπespond to the number of load bearing^* tracks in each of the adjacent nested rolling element. Load ring 62 is illustrated in a C-ring configuration having an inner diameter coπesponding in dimension to the outer diameter of the bearing plate 56 to effectively transfer the load from the bearing plate to a bearing housing bore, and fit into a circumferential channel 58 formed in the outer radial surface of outer sleeve segments 60 to form a single unit.

End rings 64 are configured and dimensioned having slots 63 which engage arcutate tabs 65 extending from the ends of retainer segments 54. End rings 64 thereby enclose and protect the internal components of the bearing assembly while holding the retainer segments 54 in place. End rings 64 typically do not transmit load from a support shaft. Therefore, end rings 64 may be fabricated from less expensive and lighter engineering plastics such as, for example, polyurethane, polyester elastomer or nylon. It is also envisioned that various other seals and/or wiper structure may be incorporated into the bearing assembly to inhibit the ingress of dust, dirt or other contaminants. Referring now to FIGS. 3-7, there is shown a linear motion closed-type bearing assembly 150 in accordance with another embodiment of the present invention. In FIG. 3, bearing assembly 150 is illustrated mounted on a support shaft 152 for relative linear motion therewith. Although support shaft 152 is illustrated as a substantially

cylindrical shaft, one skilled in the art will appreciate that support members of other configurations are within the scope of this invention. FIGS. 4 and 5 progressively illustrate further details of the components of bearing assembly 150. Bearing assembly 150 generally includes ball retainer structure, shown generally at 154, load bearing plates 156, bearing balls 158, an outer housing sleeve 160, retention structure 162 and end seals 164.

As illustrated in FIGS. 5 and 6, ball retainer structure 154 comprises a monolithic structure having a substantially square cross-section and defining an axial bore therethrough configured and dimensioned to receive shaft 152. Ball retainer structure 154 includes four planar faces, each having an outer radial surface 166 and an inner radial surface 168. In accordance with an embodiment of the present invention, a nested ball track 170 is formed in each of the four faces. Each of the nested ball tracks includes three individual tracks, each having a load bearing portion 172, a return portion

174 and a pair of turnaround portions 176. The outer radial surface 166 is preferably shaped to conform to an inner radial surface 178 of outer housing sleeve 160. A longitudinal channel 180 extends through the inner radial surface 168 of the load bearing portions 172 to permit bearing balls 158 access to shaft 152. A ramp 181 is formed at a junction of the load bearing portion 172 and the turnaround portions 176 of the nested ball tracks (i.e., at the ends of longitudinal channel 180) for providing a transition between the load bearing portion and the turnaround portion. Both the load bearing portions 172 and the return portions 174 of the ball tracks of this embodiment of the present invention are substantially open to facilitate loading of the bearing balls 158 therein. Ball retainer structure 154 may be molded from an appropriate engineering plastic using known materials and molding techniques. It is also within the scope of the present invention to fabricate the ball bearing segments from an engineering metal using known fabrication techniques. A plurality of bearing balls 158 are disposed in nested ball tracks 170, with those bearing balls positioned in the load bearing tracks 172 extending at least partially into longitudinal bores 180 to contact support shaft 152. In this embodiment of the invention, as is discussed in further detail below with reference to FIG. 7, the load bearing portions 172 of two adjacent sets of nested ball tracks 170 are oriented in substantially parallel adjacent relation. This orientation facilitates enhanced load capacity capability and maximizes space utilization for a more compact and efficient ball bearing aπangement. It is also contemplated that roller elements may be utilized instead of bearing balls 158. Referring now to FIGS. 4 and 5, a plurality of load bearing plates 156 are incorporated into the linear motion bearing assembly 150 and serve to receive load from the bearing balls 158 which are in contact with shaft 152. Load bearing plates 156 are elongated along the longitudinal axis of the bearing assembly and include an outer radial surface 182, an inner radial surface 184 and a pair of side wall surfaces 186. The outer radial surface 182 is substantially arcuate having a curvature coπesponding to the inner radial surface 178 of outer housing sleeve 160. The inner radial surfaces 184 of the load bearing plates are advantageously provided with a plurality of axial grooves which serve as the upper surface of load bearing portions 172 of the nested ball tracks. The number of axial grooves in the inner radial surfaces 184 are determined by and coπespond to the number of load bearing tracks in each of the adjacent nested ball tracks. It is also contemplated that side wall surfaces 186 of load bearing plates 156 have longitudinal grooves formed therein to guide bearing balls 158 as they move through the return portion 174 of the nested ball tracks.

Retention structure 162 is illustrated in a C-ring configuration. End seals 164 are configured and dimensioned to engage outer housing sleeve 160 to thereby enclose and protect ball retaining structure 154 and the associated components. End seals 164 typically do not transmit load from the support shaft 152 to the outer housing sleeve 160. Therefore, end seals 164 may be fabricated from less expensive and lighter engineering plastics such as, for example, polyurethane, polyester, elastomer or nylon. It is also envisioned that various other seals and/or wiper structure may be incorporated into the bearing assembly to inhibit the ingress of dust, dirt or other contaminants.

Referring now to FIG. 7, a cross-sectional view of linear motion bearing 150 is shown to illustrate a prefeπed configuration of nested ball tracks 170. Although three individual tracks are illustrated within each nested ball track, the number of individual ball tracks may vary depending on the size and geometry of the bearing. Similarly, the number of nested ball tracks may vary depending on the size and geometry of the bearing.

Support shaft 152 is centrally located within the linear motion bearing and is in contact with the bearing balls 158 which access shaft 152 through longitudinal channel 180 extending through load bearing portions 172, as discussed above. Load bearing plates 156 are positioned along a longitudinal axis of the load bearing portions 172 such that the load is effectively transfeπed from outer housing sleeve 160 to load bearing plates 156 and through bearing balls 158 to support shaft 152. In accordance with an embodiment of the present invention, the nested ball track configuration includes three load bearing tracks which are directly adjacent each other to maximize the load carrying capability of the bearing. Furthermore, in the prefeπed embodiment illustrated

in FIG. 7, the load bearing portions 172 of two adjacent sets of nested ball tracks 170 are oriented in substantially parallel adjacent relation. Thus, six load bearing tracks are adjacent each other on each of an upper and lower portion of linear motion bearing 150, to thereby maximize the load carrying capability thereof in the vertical direction. It is contemplated that the load bearing portions may be oriented for any anticipated vertical, horizontal, or combination thereof, load. Alternative embodiments associated with the components of a closed-type linear motion bearing are illustrated in FIGS. 12-14. The first difference between the embodiments of FIGS. 12-14 and the linear motion bearing assembly 150 illustrated in FIGS. 3-7 is the number of tracks within each of the nested race tracks. Each nested race track comprises two load bearing portions, two return portions and two sets of turnaround portions. Although a reduced number of tracks within the nest may be typical of a bearing having a smaller geometry, it also permits the incorporation of more than one nested track on each face of the ball retainer structure. Furthermore, the nested race track configuration having two load bearing portions and two return portions may be prefeπed since it is easier to control and incorporate self-aligning features such as crowned load bearing elements and sleeves (not shown). See, e.g., U.S. Patent No. 5,558,442, the disclosure of which is incorporated herein by reference. It is also contemplated that integral housing features may be utilized in order to avoid the need for an outer sleeve. In this configuration, the load is transmitted from the load bearing elements directly to the carriage once the bearing is installed. See, e.g., U.S. Patent No. 5,613,780 also incorporated herein by reference. Referring now to FIG. 12, a cross-sectional view of a closed-type linear motion bearing assembly 190 is illustrated which generally includes ball retainer structure 192, load bearing plates 194 and 196, bearing balls 198, and outer housing sleeve 200. In this embodiment of the linear motion bearing assembly, ball retainer structure 192 is made up of six individual retainer segments thus resulting in a hexagonal cross-section. By individually forming each of the ball retainer segments, the molding process is greatly simplified and thus results in a lower cost to produce. The individual ball retainer segments are easily molded from an appropriate engineering plastic using known materials and molding techniques. It is also within the scope of the present invention to fabricate the ball retainer segments from an engineering metal using known fabrication techniques.

Ball retainer structure 192 defines an axial bore therethrough configured and dimensioned to receive shaft 202. The ball retainer structure 192 includes six planar faces, each having an outer radial surface and an inner radial surface. Four of the six planar faces include nested ball tracks, while the remaining two faces include two conventional single axial ball tracks formed therein. Each ball track includes a load bearing portion, a return portion and a pair of turnarounds. Thus, the embodiment

illustrated in FIG. 12 combines the use of conventional race track configurations with the nested race track geometry of the present invention to symmetrically orient a maximum number of load bearing tracks about a six sided ball retainer structure in a linear motion bearing for maximum load bearing capacity.

Referring now to FIG. 13, a linear motion bearing assembly 210 is illustrated which generally includes ball retainer structure 212, load bearing plates 214, bearing balls 216 and outer housing sleeve 218. Bearing retainer structure 212 is illustrated as the segmented type described above with reference to FIG. 12, however, it is contemplated that it also may be monolithically formed. Ball retainer structure 212 has a substantially square cross-section and defines an axial bore therethrough configured and dimensioned to receive shaft 220. Ball retainer structure 212 includes four planar faces, each having an outer radial surface and an inner radial surface. Two nested ball tracks are formed in each of the four faces. Each nested ball track includes two individual tracks formed therein each having a load bearing portion, a return portion and a pair of turnarounds. The load bearing portions of two adjacent sets of nested ball tracks are advantageously oriented in substantially parallel adjacent relation.

As illustrated in FIG. 13 and in accordance with another embodiment of the present invention, load bearing plates 214 are formed as individual bearing plates such that each load bearing track has an individual load bearing plate positioned axially

thereon. Referring now to FIG. 14, a linear motion bearing assembly 220 is illustrated having a ball retainer structure 222 configured similar to ball retainer stπicture 212 illustrated in FIG. 13. The embodiment of FIG. 14 illustrates load bearing plates 224 which are formed as monolithic units and are positioned above load bearing portions of adjacent nested ball tracks.

Referring now to FIGS. 8-11, there is shown an open-type linear motion bearing assembly 250 in accordance with a prefeπed embodiment of the present invention. In FIG. 8, bearing assembly 250 is illustrated mounted on a support shaft 252 for relative linear motion therewith. Although support shaft 252 is illustrated as a spline shaft, one skilled in the art will appreciate that support members of other configurations are within the scope of the invention. FIGS. 9 and 10 progressively illustrate further details of the components of bearing assembly 250. Bearing assembly 250 generally includes ball retainer structure, shown generally at 254, load bearing plates 256, bearing balls 258, an outer housing sleeve 260, and plate retainer structure 262.

As illustrated in FIG. 10, ball retainer structure 254 comprises a monolithic structure having a substantially pentagonal cross-section (with the bottom side missing) and defining an axial bore therethrough configured and dimensioned to receive shaft 252, with an opening at the bottom to receive the spline of shaft 252. Ball retainer structure 254 includes four planar faces, each having an outer radial surface 266 and an inner radial surface 268. In accordance with an embodiment of the present invention, a nested ball track 270 is formed in each of the four faces. Each of the nested ball tracks includes two individual tracks, each having a load bearing portion 272, a return portion 274 and a pair of turnaround portions 276. The outer radial surface 266 ϊs preferably shaped to conform to an inner radial surface 278 of outer housing sleeve 260. A longitudinal channel 280 extends through the inner radial surface 268 of the load bearing portions 272 to permit bearing balls 258 access to shaft 252. Both the load bearing portions 272 and the return portions 274 of the ball tracks of this embodiment of the present invention are substantially open to facilitate loading of the bearing balls 258 therein. Ball retainer structure 254 may be molded from an appropriate engineering plastic using known materials and molding techniques. It is also within the scope of the present invention to fabricate the ball bearing segments from an engineering metal using known fabrication techniques.

A plurality of bearing balls 258 are disposed in nested ball tracks 270, with those bearing balls positioned in the load bearing tracks 272 extending at least partially into longitudinal bores 280 to contact support shaft 252. In this embodiment of the invention, as is discussed in further detail below with reference to FIG. 11, the load bearing portions 272 of two adjacent sets of nested ball tracks 270 on the upper portion of the bearing are oriented in substantially parallel adjacent relation, and the load bearing portions of the nested ball tracks adjacent to the opening of the bearing are located adjacent to the opening. This orientation facilitates enhanced load capacity capability and maximizes the pull-of load capacity of the open-type bearing. It is also contemplated that roller elements may be utilized instead of bearing balls 258.

Referring now to FIGS. 9 and 10, a plurality of load bearing plates 256 are incorporated into the linear motion bearing assembly 250 and serve to receive load from the bearing balls 258 which are in contact with shaft 252. Load bearing plates 256 are elongated along the longitudinal axis of the bearing assembly and include an outer radial surface 282, an inner radial surface 284 and a pair of side wall surfaces 286. The outer radial surface 282 is substantially arcuate having a curvature which is related to the inner radial surface 278 of outer housing sleeve 260. The inner radial surface 284 of the load bearing plates is advantageously provided with a plurality of axial grooves which serve as the upper surface of load bearing portions 272 of the nested ball tracks. The number of axial grooves in the inner radial surfaces 284 are determined by and coπespond to the number of load bearing tracks in each of the adjacent nested ball tracks. It is also contemplated that side wall surfaces 286 of load bearing plates 256 have longitudinal grooves formed therein to guide bearing balls 258 as they move through the return portion 274 of the nested ball tracks. Plate retainer structure 262 is illustrated in a C-ring configuration having an inner diameter conforming in dimension to the outer diameter of ball retainer structure 254.

Referring now to FIG. 11, a cross-sectional view of linear motion bearing 250 is shown to illustrate a prefeπed configuration of nested ball tracks 270. Although two tracks within the nested ball tracks are illustrated, the number of nested ball tracks may vary depending on the size and geometry of the bearing.

Support shaft 252 is centrally located within the linear motion bearing and is in contact with the bearing balls 258 which access shaft 252 through longitudinal channel 280 extending through load bearing portions 272, as discussed above. Load bearing plates 256 are positioned along a longitudinal axis of the load bearing portions 272 such that the load is effectively transfeπed from outer housing sleeve 260 to load bearing plates 256 and through bearing balls 258 to support shaft 252. In accordance with an embodiment of the present invention, the nested ball track configuration includes two load bearing tracks which are directly adjacent each other on the upper portion of the bearing to maximize the load carrying capability of the bearing, and load bearing portions of the nested ball tracks adjacent to the opening of the bearing are located adjacent to the opening to maximize the pull-offload capacity. Furthermore, in the prefeπed embodiment illustrated in FIG. 11, the load bearing portions 272 of two adjacent sets of nested ball tracks 270 are oriented in substantially parallel adjacent relation. Thus, four load bearing tracks are adjacent each other on an upper portion of linear motion bearing 250, to thereby maximize the load carrying capability thereof in the vertical direction. An alternative embodiment associated with the components of an open- type linear motion bearing is illustrated in FIGS. 15-16. A difference between the embodiments of FIGS. 15-16 and the linear motion bearing assembly 250 illustrated in FIGS. 8-11 is that the ball retainer structure is of the segment type rather than a monolithic structure as described above.

Referring now to FIG. 16 a cross-sectional view of an open-type bearing assembly 290 is illustrated which generally includes ball retainer structure 292, load bearing plates 294, bearing balls 296, and outer housing sleeve or band 298. In this embodiment of the linear motion bearing assembly, ball retainer structure 292 is made up of four individual retainer segments thus resulting in a pentagonal cross-section (with the bottom portion missing to form the open-type bearing). By individually forming each of the ball retainer segments, the molding process is greatly simplified andlhus results in a lower cost to produce. The individual ball retainer segments are easily molded out of an appropriate engineering polymer such as acetal or nylon using known materials and molding techniques. It is also within the scope of the present invention to fabricate the ball retainer segments from an engineering metal such as steel or brass using known fabrication techniques.

Ball retainer structure 292 defines an axial bore therethrough configured and dimensioned to receive shaft 300, with an opening at the bottom to receive the spline of shaft 300. The ball retainer structure 292 includes four planar faces, each having an outer radial surface and an inner radial surface. Each of the four planar faces includes a nested ball track. Each ball track includes a load bearing portion, a return portion and a

pair of turnarounds. The embodiment illustrated in FIG. 16 includes load bearing plates on the upper portion of the bearing for maximum load bearing capacity and adjacent the opening in the bearing for maximum pull-offload capacity.

Although the illustrative embodiments of the present invention have been described herein with reference to the accompanying drawings, it is to be understood that the invention is not limited to those precise embodiments, and that various other changes and modifications may be affected therein by one skilled in the art without departing from the scope or spirit of the invention. All such changes and modifications are intended to be included within the scope of the invention as defined by the appended claims.

Claims

WHAT IS CLAIMED IS:

1. A linear motion bearing assembly for movement along a shaft or rail comprising: ball retainer structure having at least a portion of a plurality of substantially parallel adjacent nested ball tracks formed therein, said ball tracks including a load bearing portion, a return portion and turnarounds interconnecting said load bearing and return portions; a plurality of bearing balls disposed in said ball tracks; and a plurality of load bearing plates axially positioned adjacent said ball retainer structure for receiving load from said balls disposed in said load bearing portion of the ball tracks.

2. The linear motion bearing assembly as recited in claim 1, wherein the linear motion bearing is a closed-type bearing.

3. The linear motion bearing assembly as recited in claim 1, wherein the linear motion bearing is an open-type bearing.

4. The linear motion bearing assembly as recited in claim 3, wherein the

ball retainer stπicture is configured such that load bearing portions of the nested ball tracks adjacent to an opening formed in the open-type bearing are adjacent to said opening.

5. The linear motion bearing assembly as recited in claim 1, wherein each of the plurality of nested ball tracks comprises at least two individual ball tracks.

6. The linear motion bearing assembly as recited in claim 1, wherein the ball retainer structure is configured such that load bearing portions of two adjacent nested ball tracks are adjacent to each other.

7. The linear motion bearing assembly as recited in claim 1, wherein said

load bearing plates are monolithically formed.

8. The linear motion bearing assembly as recited in claim 1, wherein said

load bearing plates are individual bearing plates configured and positioned over coπesponding individual load bearing portions of said ball tracks.

9. The linear motion bearing assembly as recited in claim 1 , wherein said nested axial ball tracks have an open outer portion to facilitate loading of the plurality of bearing balls therein.

10. The linear motion bearing assembly as recited in claim 1, wherein the ball retainer structure is formed of a plurality of individual segments.

11. The linear motion bearing assembly as recited in claim 1 , wherein the ball tracks further include a ramp formed at a junction of the load bearing portion and the turnaround for providing a transition between the load bearing portion and the turnaround.

12. A linear motion bearing assembly for movement along a shaft comprising: rolling element retainer structure having at least a portion of a plurality of parallel, adjacent nested rolling element tracks formed therein, said rolling element tracks including a load bearing portion, a return portion and turnarounds interconnecting said load bearing and return portions; a plurality of rolling elements disposed in said rolling element tracks; and a plurality of load bearing plates axially positioned adjacent said rolling element retainer structure for receiving load from said rolling elements disposed in said load bearing portion of the rolling element tracks.

13. The linear motion bearing assembly as recited in claim 12, wherein the linear motion bearing is an open-type bearing.

14. The linear motion bearing assembly as recited in claim 13, wherein the rolling element retainer structure is configured such that load bearing portions of the nested rolling element tracks adjacent to an opening formed in the open-type bearing are adjacent to said opening.

15. The linear motion bearing assembly as recited in claim 12, wherein the rolling element retainer structure is configured such that load bearing portions of two adjacent nested rolling element tracks are adjacent to each other.

16. The linear motion bearing assembly as recited in claim 12, wherein said load bearing plates are monolithically formed.

17. The linear motion bearing assembly as recited in claim 12, wherein

said load bearing plates are individual bearing plates configured and positioned over coπesponding individual load bearing portions of said rolling element tracks.

18. The linear motion bearing assembly as recited in claim 12, wherein said nested axial rolling element tracks have an open outer portion to facilitate loading of the plurality of rolling elements therein.

19. The linear motion bearing assembly as recited in claim 12, wherein the rolling element retainer structure is formed of a plurality of individual segments.

20. The linear motion bearing assembly as recited in claim 12, wherein the rolling element tracks further include a ramp formed at a junction of the load bearing portion and the turnaround for providing a transition between the load bearing portion and the turnaround.