Abstract:
A linear motion bearing assembly ( 20 ) as provided for movement along a splined shaft ( 10 ). The rolling element retainer of the bearing assembly ( 20 ) is assembled from a plurality of arcuate interengageable self-contained rolling element retainer segments ( 22 ). Each of the rolling element retainer segments ( 22 ) includes at least one rolling element track ( 30 ) having a load bearing portion ( 34 ) and a return portion ( 36 ). At least one load bearing plate ( 44 ) is axially positioned in each segment and serves to receive and transmit loads from the bearing rolling elements ( 32 ) in the load bearing portion ( 34 ) of the ball tracks ( 30 ). An extended housing retainer structure encloses all of the exposed exterior surfaces of the rolling element retainer segments ( 22 ) and is configured and dimensioned to maintain the rolling element retainer segments ( 22 ) in position and to receive a load either directly or indirectly from the load bearing plates ( 44 ).

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   The present application claims priority to U.S. provisional application Ser. No. 60/242,850 filed on Oct. 24, 2000, the entire contents of which are hereby incorporated by reference. 

   BACKGROUND 
   1. Technical Field 
   The present invention relates to linear motion bearing and, more particularly, to linear motion bearing assemblies made up of bearing segments for longitudinal movement along a splined shaft. 
   2. Background of Related Art 
   The present invention is directed to an improved linear motion bearings assembly for use on a splined shaft. In particular, the improvements relate to biased linear motion bearing assemblies of the type which support a carriage or a pillow block for linear movement along an elongated splined shaft. These bearing assemblies can either be of the open type or the closed type. 
   Typical linear rolling bearing assemblies include a series of rolling elements moving about a circulation path which circulation path is formed in the periphery of a track member and a surrounding and enclosing bearing cover confining the rolling elements in their recirculation path. In order to achieve an accurate linear motion, the axis of the bearing assembly must be precisely aligned with the desired direction of motion along the supported structure. In addition this precise alignment also minimizes skewing forces acting on the bearing assembly, which skewing forces tend to reduce the load/life performance of the bearing assembly. 
   Installation of such bearing assemblies on a supporting structure (i.e., shaft, splined shaft, guideway or rail) typically involves precision machining of locating surfaces in order to properly align the bearing assembly on the supporting structure. Such bearing assemblies are typically installed in sets, each comprised of a number of variously facing bearings such as to engage a series of surfaces on the supporting structure (i.e., such as above and below a supporting surface and/or along a lateral edge of a supporting surface). In such instances it is usual to provide a bearing adjustment for enabling precision adjustment of the bearing assembly on the supported structure and also for establishing a proper bearing pre-load by adjusting an opposing bearing assembly for reasons well known to those skilled in the art. In such installations, considerable precision machining of the supported structure is necessitated which is difficult and expensive to accomplish on the supporting structures. 
   Additional prior art bearing assemblies typically include an outer housing and at least one ball retainer dimensioned for insertion into the outer housing. The rolling element retainer has at least one ball track in a loop configuration for containing and recirculating bearing balls therein. The ball tracks typically include open portions which facilitate a load transfer from a supporting shaft to a load bearing structure such as load bearing plates operatively associated with either the ball retainer or the outer housing while return portions of the ball tracks permit continuous recirculation of the bearing balls through the ball tracks during linear motion. 
   In some embodiments, the ball retainer is formed as a monolithic element with the ball tracks integrally incorporated therein. See, U.S. Pat. No. 3,767,276 to Henn. This structure, however, is difficult to efficiently manufacture because of the complex molds required. Also, these ball retainers, prior to insertion into a mounting carriage or outer housing are necessarily open and thus exposed to ambient conditions and contaminants such as dust and dirt. Such exposure could deleteriously affect the operation and life of the bearing assembly as well as the support structure on which it moves. 
   Self-contained linear bearing units are also known in the art. See, e.g. U.S. Pat. No. 4,815,862 to Mugglestone et al. This unit, while representing a marked improvement in the art, still requires the use of end caps to engage the load bearing plates of the bearing segments. Further, the load bearing plates must be precisely machined to properly inter-fit with the end caps. This configuration adds to the expense and complexity of the bearing. 
   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 structures 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 used to transfer loads from the supporting shaft. These load bearing plates are longitudinally oriented in association with the ball retainer so as to engage at least those bearing balls in direct contact with the support shaft. 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 ball 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 balls in corresponding adjacent load bearing tracks. In this form, parallel grooves are formed in the underside of the plates to guide the bearing balls while they are in the load bearing portion of the ball tracks. See, for example, U.S. Pat. No. 3,951,472 to Schurger et al. 
   Accordingly, it is an object of the present invention to provide a linear motion bearing segment which can be easily and efficiently manufactured. 
   It is another object of the present invention to provide a linear motion bearing assembly having a rolling element retainer and outer housing which are easily fabricated using engineering polymers, powder metal or insert molding. 
   It is a further object of the present invention to provide a low cost linear motion bearing assembly having a high load bearing capacity and having self-aligning capability. 
   It is yet another object of the present invention to provide a bearing assembly which eliminates the need for extremely high precision rolling element/guideway (rail) bearing assemblies and their resultant expensive manufacturing costs. 
   These and other highly desirable objects are accomplished by the present invention in a linear motion bearing assembly having a plurality of rolling element tracks and individual bearing plates arranged in a rolling element retainer and enclosed by a low cost outer housing which serves to protect the rolling elements, rolling element tracks and load bearing plates without having to transmit loads from the bearing rolling elements to the carriage block into which the bearing assembly is mounted. 
   Objects and advantages of the invention are set forth in part herein and in part will be obvious therefrom, or may be learned by practice with the invention, which is realized and attained by means of instrumentalities and combinations pointed out in the appended claims. The invention comprises the novel parts, constructions, arrangements, combinations, steps, processes and improvements herein shown and described. 
   SUMMARY OF THE INVENTION 
   The present invention provides for a linear motion bearing segment configured and adapted for movement along a splined shaft, guideway or rail. A rolling element retainer structure of the bearing assembly can be either monolithically formed or, alternatively, assembled from multiple elements. In a first multi-element embodiment, the rolling element retainer structure is made up of a pair of quarter arcuate rolling element retainer segments and a half arcuate rolling element retainer segment. In an alternate multi-element embodiment, the rolling element retainer structure is made up of a pair of half arcuate rolling element retainer segments. At least a portion of the axial rolling element bearing tracks are formed in the rolling element retainer structure and, preferably, the complete rolling element bearing tracks are formed therein. 
   The linear motion bearing assembly further includes an outer housing sleeve which substantially encloses all of the rolling element retainer structure. The housing sleeve is preferably formed of an engineering polymer and serves to protect the rolling element retainer and bearing rolling elements contained therein from ambient contamination. 
   A plurality of load bearing plates are axially positioned within the outer housing and serve to receive and transmit loads from the bearing rolling elements to the load bearing portion of the rolling element bearing tracks. Each load bearing plate is at least partially retained in the linear motion bearing assembly by retaining features which are disposed at least partially around the rolling element retainer structures and which retain at least a portion of the load bearing plates. Preferably, the load bearing plates and/or plate retaining features are configured and dimensioned such that the linear motion bearing assembly is substantially self-aligning on the shaft. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings, referred to herein and constituting a part hereof, illustrate the preferred embodiments of the linear motion bearing segment of the present invention and, together with the description, serve to explain the principles of the invention. 
       FIG. 1  is an exploded perspective view of a linear motion bearing segment, with the housing removed, in accordance with one embodiment of the present invention; 
       FIG. 2  is a transverse cross-sectional view of an assembled linear motion bearing segment shown in  FIG. 1 ; 
       FIG. 3  is an exploded perspective view of a half bearing segment of the linear motion bearing segment shown in  FIG. 1 ; 
       FIG. 4  is a perspective view of the linear motion bearing segment with the housing removed and in place in a splined shaft; 
       FIG. 5  is an end elevational view of the linear motion bearing segment showing the internal elements of the bearing segment in phantom; 
       FIG. 6  is a transverse cross-sectional view of a linear motion bearing segment in accordance with a second embodiment of the present invention; and 
       FIG. 7  is an exploded perspective view of the half bearing segment of the linear motion bearing segment shown in FIG.  6 . 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
   Referring now to the drawings, wherein like reference numerals identify similar structural elements of the subject invention, there is illustrated in  FIGS. 1-5  a closed-type linear motion bearing segment constructed in accordance with a preferred embodiment of the present invention and designated generally by the reference numeral  20 . As used herein, the term ball and rolling element are intended to be used interchangeably and encompass namely, ball bearings, roller bearings, needle bearings, axle bearings, etc. While a closed-type linear motion bearing segment is disclosed, it is envisioned that an open type linear motion bearing segment can be constructed in accordance with the present disclosure. 
   Linear motion bearing segment  20  is fabricated from a pair of individual quarter arcuate interengageable self-contained ball retainer segments  22  and a half arcuate interengageable self-contained ball retainer segment  24  all of which are supported in interengageable association within a housing  26 . The housing  26  includes a longitudinal groove  18  formed along an inner surface thereof for engaging the half arcuate retainer segment  24 . Stated differently, the linear motion bearing segment  20  is fabricated from a pair of 90° arcuate interengageable self-contained ball retainer segments  22  and a single 180° arcuate interengageable self-contained ball retainer segment  24 . When fully assembled, the quarter segments  22  and the half segment  24  for a linear motion bearing segment  20  are adapted and configured to move on a splined shaft  10  without rotational motion of the bearing segment  20  relative to a longitudinal axis of the splined shaft  10 . Further, although shown as a closed-type bearing, an open-type bearing could be readily fabricated using such self-contained segments. 
   Each quarter segment  22  includes an inner portion  28  having an inner surface configured and adapted to be in clearance to the adjacent quarter arcuate portion of the outer surface of the splined shaft  10 , the inner portion  28  defining a ball bearing track  30  formed therein and which ball bearing track  30  retains a plurality of bearing balls  32 . The ball bearing track  30  is made up of a load bearing portion  34  and a return portion  36  interconnected by turnarounds  38 . An outer lid portion  40  is adapted and configured to engage the inner portion  28  and includes a load bearing plate mounting aperture  42 . By way of example only, the outer lid portion  40  can be snap fit into engagement with the inner portion  28 . However, other engagement mechanisms, such as pins, grooves, adhesives, etc. are also contemplated and are within the scope of knowledge of one skilled in this art. 
   A load bearing plate  44  is dimensioned and configured to fit into aperture  42  of outer lid portion  40  of each quarter bearing  22 . A pair of longitudinal grooves  46  are formed in the side walls of each load bearing plate  44 , which grooves  46  receive projections  48  formed in the periphery of aperture  42 . Each load bearing plate  44  preferably includes at least one longitudinal track  50  formed in an inner surface thereof. This longitudinal track  50  serves as the upper surface of the load bearing portion  34  of the ball track  30 . The plurality of bearing balls  32  are positioned in ball track  30  and, when in the load bearing portion  34 , serve to transmit loads from the load bearing plates  44  to the splined shaft  10  as well as to facilitate reciprocal longitudinal motion therealong. 
   As seen in  FIGS. 1 and 2 , and in particular in  FIG. 3 , the half arcuate ball retainer segment  24  includes a base portion  52  having an inner surface configured and adapted to be in substantial clearance of spline  12  formed along a longitudinal length of the shaft  10 . The base portion  52  includes an outer surface defining a pair of independent ball bearing tracks  54  formed therein and which ball bearing tracks  54  retain a plurality of bearing balls  56 . Each ball bearing track  54  is made up of a load bearing portion  58  and a return portion  60  interconnected by turnarounds  62 . The respective load bearing portions  58  are located adjacent to one another and are spaced from one another by a retaining member  64  formed longitudinally along the base portion  52 . 
   The half arcuate ball retainer segment  24  further includes a single load bearing plate  66  having an inner surface configured and adapted to be disposed over both load bearing portions  58  of each ball bearing track  54  and an outer surface defining a pair of longitudinally extending convergent flat portions  68  and  70 . Each convergent flat portion  68  and  70  is configured and adapted to engage a biasing spring  72 . In addition, the half arcuate ball retainer segment  24  further includes a pair of lids  74  and  78 , which lids  74  and  78  serve to close the half retainer segment  24 . Each lid  74  and  78  includes a window  80  for receiving one of the convergent flats  68  and  70  respectively of the of the load bearing plate  66  and through which window  80  each biasing spring  72  can extend to contact the inner surface of the housing  26 . (See  FIG. 4 ) 
   In use, each biasing spring  72  applies a pre-load to the bearing balls  56  through each convergent flat  68  and  70  of the load bearing plate  66 . The pre-load being applied against opposite sides  14  and  16  of the spline  12  at an angle “θ” in a range of between about 25° to about 75°. (See FIG.  2 ). While the biasing spring  72  is shown as a corrugated leaf spring, it is envisioned that other biasing springs may be substituted including resilient plastic filler, coil springs, torsion springs, etc., with corresponding adaptations to the housing and bearing plates. 
   Although shown herein in a half bearing segment configuration, it is also contemplated that other sizes can be used including quarters or thirds and that the segments can be arranged to accommodate multiple splines on an elongate shaft. 
   Referring now to  FIGS. 6 and 7 , there is illustrated a closed-type linear motion bearing segment constructed in accordance with a further embodiment of the present invention and designated generally by the reference numeral  100 . The linear motion bearing segment  100  is fabricated from a pair of individual half arcuate interchangeable self-contained ball retainer segments  102  supported in interengageable association within a housing  104 . When fully assembled, the half segments  102  are adapted and configured to move on a splined shaft  106 , having a substantially “I” shaped cross-section, without rotational motion of the bearing segment  100  relative to a longitudinal axis of the splined shaft  106 . Further, although shown as a closed-type linear bearing, an open-type linear bearing could be readily fabricated using such self-contained segments. 
   Each half segment  102  includes an inner portion  108  having an inner surface configured and adapted to be in substantial clearance of a lateral half of the splined shaft  106  and an outer surface defining a pair of independent ball bearing tracks  110  formed therein. Each ball bearing track  110  is made up of a load bearing portion  112  and a return portion  114  interconnected by turnarounds  116 . The respective load bearing portions  112  of each inner portion  108  are located adjacent to one another and are spaced from one another by a dividing member  118 . 
   Each half segment  102  includes an outer lid portion  120  configured to engage inner portion  108  and includes a load bearing plate aperture  122 . In the embodiment depicted in  FIGS. 6 and 7 , engagement of each outer lid portion  120  to each inner portion  108  is accomplished by through holes  124  formed in the outer lid portion  120  and pegs  126  extending from an outer surface of the inner portion  108  configured and adapted to engage the through holes  124 . Other engagement mechanisms, such as pins, grooves, adhesives, etc. are also contemplated and are within the scope of knowledge of one skilled in the art. 
   Each half segment  102  includes a load bearing plate  128  dimensioned and configured to fit into the load bearing plate aperture  122  of outer lid portion  120  and adapted to be disposed over both load bearing portions  112  of each ball bearing track  110 . The load bearing plate having a central body portion  132  and a pair of longitudinally extending divergent flat portions  134 . An inner surface  130  of the load bearing plate preferably includes a pair of longitudinal tracks  136  which serve as an upper surface of the load bearing portion  112  of the ball track  110 . 
   Meanwhile, the outer surface  132  of the load bearing plate  128  is configured and adapted to engage a biasing spring  138 . The biasing spring  138  includes a elongate body portion  140  and a pair of elongate diverging corrugated leaf portions  142 . The diverging leafs  142  of the biasing spring  138  are configured and oriented such that each leaf portion  142  engages a respective divergent flat portion  134  of the load bearing plate  128 . A plurality of bearing balls  144  are positioned in each ball bearing track  110  and, when in the load bearing portion  112 , serve to transmit loads from the load bearing plates to the splined shaft  106  as well as to facilitate reciprocal longitudinal motion therealong. The housing  104  includes a pair of opposed “V” shaped protrusions  146  extending inwardly from an inner surface thereof and configured and adapted to engage an outer surface of the elongate body portion  140  of each biasing spring  138 . The “V” shaped protrusion presses the biasing spring  138  such that the diverging leaf portions  142  press against the divergent flat portion  134  of the outer surface of load bearing plate  128 . 
   In use, each biasing spring  138  applies a pre-load to the bearing balls  144  through each diverging flat portion  134  of the load bearing plate  128 . The pre-load being applied at each juncture  148  of the “I” shaped shaft  106  between the pair of horizontal portions  150  and the interconnecting web portion  152  at an angle “φ” in a range between about 25° to about 75° and more preferably about 45°. (See FIG.  6 ). Once again, while the biasing spring  138  is shown as having a pair of corrugated leaf springs, it is envisioned that other biasing springs may be substituted including resilient plastic filler, coil springs, torsion springs, etc. 
   It is envisioned that both the base portion  52  and the lids  74  and  78  of the half bearing segment  24  of the first embodiment and the inner portion  108  and outer lid portion  120  of the second embodiment are preferably formed from an engineering polymer to facilitate ease of manufacture. 
   To the extent not already indicated, it also will be understood by those of ordinary skill in the art that any one of the various specific embodiments herein described and illustrated may be further modified to incorporate features shown in the other specific embodiments. 
   The invention in its broader aspects therefore is not limited to the specific embodiments herein described but departures may be made therefrom within the scope of the accompanying claims without sacrificing its chief advantages.