A RETAINERLESS LINEAR MOTION BEARING

Abstract: A ball holder (1) for a retainerless saddle (6) having an elongated shaft (2) and a plurality of contact surfaces (3) therearound to hold steel balls (7) in cooperation with a bearing body (4) only when the saddle (6) is withdrawn from a rail (R). The shaft can be made of a hollow tube (41) or a pair of cantilever projections (52 or 62) so that the size of its cross-sectional area can be adjusted. Due to this adjustability, the size of the raceways can also be adjusted to enable to reassemble the steel balls (7) into the saddle (6) at a working site.

Description: Title of the Invention A Retainerless Linear Motion Bearing Background of the Invention A conventional linear motion bearing shown in USP 4,253,709 has a large rigidity and can sustain a heavy load at a high speed with a high accuracy. Due to those excellent properties, it has been widely used especially in a field of machine tools. One of the main features of the linear motion bearing is that it can provide a preload in the steel balls since the diameter of the steel ball is slightly larger than that of the raceway formed between the complementary grooves of the bearing body and the rail. Due to the preload, the assembled rigidity of the structure becomes larger which, in turn, enables to attain high accuracy. On the other hand, one of the shortcomings of the linear motion bearing is in the usage of a retainer which holds or maintains the steel balls from falling off from the bearing body when it is withdrawn out of the rail. The shape of the retainer can be either a plate structure as shown in Figure 8 in USP 4,253,709 or a piano wire-like structure extending along the grooves as shown in USP 4,929,095. These retainers are attached either to the bearing body or to the end caps. Because of this, the structure of the linear motion bearing becomes more complicated and more difficult to assemble a saddle from bearing body with steel balls by an automatic process. Further, if the retainer dislocates its position, it may contact the steel balls and increases the friction. The retainer will be damaged or destroyed eventually. It also increases the cost of the linear motion bearing. Another problem of the retainer lies in that the size of the radius of the curvature of the groove is inevitably limited due to existence of the retainer in the narrow raceway and so is the load rating. It is well known that the retainer loses its function and becomes useless once the saddle is fit onto the rail since the steel balls are held solely by the complementary grooves. Nevertheless, there must be a retainer since if the retainer is eliminated from the linear motion bearing, there is no way to maintain the steel balls within the bearing body of the saddle when it is withdrawn from the rail. Yet another problem is how to fit the saddle onto the rail while maintaining the loose steel balls. Summary of the Invention This invention is directed to a retainer-less linear motion bearing in which a retainer is completely eliminated from a bearing body. Instead, a ball holder independent of the bearing body, or a saddle, is used only when the saddle is withdrawn from the rail to retain the steel balls within the bearing body so as to prevent them from falling off when it is withdrawn from the rail. This invention is also directed to a method for automatically assembling a complete saddle from a bearing body, end caps, steel balls and a ball holder. Another object of the invention is to provide an adjustable ball holder which enables to reassemble the saddle at a working site without using any special devices. Brief Description of the Drawings Figure 1 illustrates a cross-sectional view of a saddle 6 with a ball holder 1 of the present invention. Figure 2 illustrates a perspective view of saddle 6. Figure 3 illustrates a perspective view of ball holder 1. Figure 4 illustrates a method to assemble saddle 6 onto rail R. Figure 5 illustrates a cross-sectional view of retainer-less linear bearing along X-X in Figure 4. Figure 6 illustrates a perspective view of ball holder 1 ' made of rubber. Figure 7 illustrates a process to automatically assemble a saddle 6 from bearing body 4, end caps 5, 5, steel balls 7... , and ball holder 1. Figure 8 illustrates a ball holder 11 provided with end plate 15. Figure 9 illustrates a detachable end plate 12. Figure 10 illustrates a ball holder 11' with a friction plate 14'. Figure 11 illustrates a ball holder 11" with an end plate 15" and a step portion 14". Figure 12 illustrates an adjustable ball holder 21. Figure 13 illustrates the unassembled state of adjustable ball holder 21. Figure 14 illustrates a contracted state of adjustable ball holder 21. Figure 15 illustrates a stop cover 28 for adjustable ball holder 21. Figure 16 illustrates second shaft 22' having fit plate 14'. Figure 17 illustrates adjustable ball holder 21" having tapered recess 24" and tapered projection 25". Figure 18 illustrates adjustable tubular ball holder 33 having a slit 35. Figure 19 illustrates adjustable tubular ball holder 43 made of a metal. Figure 20 illustrates adjustable tubular ball holder 43' having slits 46. Figure 21 illustrates a state when adjustable tubular ball holder 33 is placed within bearing body 4. Figure 22 illustrates insertion member 40 for adjustable tubular ball holder 33. Figure 23 illustrates insertion member 42 having recess 43 for adjustable ball holder 33 or 53 or 65. Figure 24 illustrates adjustable ball holder 53 having end plate 55. Figure 25 illustrates adjustable ball holder 53 having fit plate 65. Figure 26 illustrates another insertion member 70 with tapered recess 73. Figure 27 illustrates short insertion member 80 with recess 83. Description of the Preferred Embodiments The first embodiment is directed to a ball holder 1 in which the raceway space formed by bearing body 4 and ball holder 1 is not adjustable. Figure 1 illustrates a cross-sectional view of a retainerless saddle 6 with a ball holder 1 according to this invention. Figure 2 shows a perspective view of saddle 6. Figure 3 shows a perspective view of ball holder 1. The cross- section of ball holder 1 is almost identical to that of track shaft part T, which is a top part of the rail R as shown in Figures 4 and 5. Ball holder 1 is formed by elongated shaft 2 and a plurality of grooves 3... at about four corners of elongated shaft 2. The number of the grooves 3... can be two or more depending upon that of track shaft part T or that of saddle 6. The material of shaft 2 is preferably an elastic one such as soft plastic as shown in Figure 3. When saddle 6 is withdrawn from rail R, steel balls 7 are maintained by ball holder 1. The diameter of the raceway formed by a complementary groove 8 of bearing body 4 and a complementary grooves 3 of ball holder 1 is slightly smaller than that of a steel ball 7. Therefore, the grooves 3... of ball holder 1 are slightly compressed by steel balls 7... such that ball holder 1 is press fitted within saddle 6. Also, since ball holder 1 is smaller than the cavity within bearing body 4 of saddle 6, in storing a plurality of saddles 6... each having ball holder 1 therein, they can be placed one upon another. Thus, the storage of a plurality of saddles 6... is very convenient and occupies less space according to this invention. As shown in Figure 4, in order to assemble saddle 6 onto rail R, saddle 6 is held by one hand of an operator while fitting the inner opening of end cap 5 onto track shaft part T of rail R and is moved toward rail R. As saddle 6 moves leftward in Figure 4, steel balls 7... are successively held within the raceways between the complementary grooves 8... of saddle 6 and those of rail R, thus are preloaded since the " diameter of each raceway is smaller than that of steel ball 7. Eventually ball holder 1 is completely removed from saddle 6 since it is stopped by the end surface of track shaft part T. Thus, steel balls 7... are maintained between rail R and bearing body 4 without a retainer as shown in Figure 5. In order to remove saddle 6 from rail R, ball holder 1 is first positioned at the end surface of track shaft part T. Then saddle 6 is moved rightward in Figure 4 from rail R over ball holder 1 such that steel balls 7... are successively held between the complementary grooves of saddle 6 and ball holder 1. If shaft 2 is made of a material with a plenty of elasticity such as rubber, grooves 3 may be eliminated and instead they can be flat surfaces 3' as shown in Figure 6. Also shaft 2 can be made of a transparent material such that the steel balls 7 can be observed through the transparent body of shaft 2. The length of ball holder 1 is at least the same to that of bearing body 4 or longer. Figure 7 illustrates the process for assembling saddle 6 from bearing body 4, end caps 5, steel balls 7... and ball holder 1. The process proceeds as follows: Step 1. End cap 5 is attached at one end, preferably at a bottom end, of bearing body 4. Then it is fed, with, preferably, the attached end cap facing downward and an open end of bearing body 4 facing upward. Step 2. Raceway Spacer A is inserted into the open cavity within bearing body 4 by Raceway Spacer Moving Device B. Raceway Spacer A is provided with a plurality of grooves 30... each corresponding to each of grooves 8... of bearing body 4. The diameter of each raceway space 9 formed by complementary grooves 30 and 8 is same or slightly larger than that of steel ball 7. Step 3. Steel balls 7 are fed into raceway spaces 9... and escape-ball through holes 10... Due to end cap 5 attached at the bottom of bearing body 4, steel balls 7... are easily fed by Ball Feed Device C into raceway spaces 9... , escape-ball through holes 10... and ball-recirculating grooves in end cap 5. Step 4. Close top open end surface of bearing body 4 by a second end cap 5. It is preferable that ball-recirculating grooves in second end cap 5 are previously filled with steel balls 7... At this stage saddle 6 is formed by bearing body 4 and a pair of end caps 5, 5, Raceway Spacer A, and a plurality of steel balls 7... , however, there is no preload provided in any of steel balls 7... yet. Step 5. Ball holder 1 is positioned at beneath of bottom end cap 5 and then saddle 6 is slid down onto ball holder 1. Since the material of ball holder 1 is much softer than that of steel balls 7 and of bearing body 4, ball holder 1 is slightly compressed without imparting much preload in steel balls 7... so that it is firmly maintained within saddle 6 by friction. It is preferable that ball holder 11 is further provided with end plate 15 at its one end as shown in Figure 8 . End plate 15 has a peripheral configuration substantially identical to the overall configuration of end cap 5. Shaft 2 of the ball holder 2 can be made longer than that of saddle 6 and be provided at both distal ends with detachable end plates 12, 12 as shown in Figure 9. Each of end plates 12, 12 has a shape substantially identical to the size of overall configuration of end cap 5 and is provided with a window 13 through which the distal end of shaft 2 fits with friction. Then the ball holder 1 can be maintained within saddle 6 with certainty since end plates 12, 12 holds saddle 6 therebetween. One of end plates 12, 12 can be permanently fixed at a distal end of shaft 2. Further, as shown in Figure 10, a fit plate 14' can be provided at one end of shaft 2. Or step portion 14" can be provided between end plate 15" and shaft 20" as shown in Figure 11. Fit plate 14' or step portion 14" abuts within the inner opening of end cap 5 in order to reinforce the frictional gripping. One advantage of the embodiments shown in Figure 10 and 11 is that it is easy to align the shaft with accuracy within the bearing body due to friction plate 14' or step portion 14" such that it makes it easier to reassemble saddle 6, the steel balls 7... and ball holder 11' after saddle 6 was accidentally removed from the rail R without using ball holder 11' and steel balls 7... fell off to the ground. Next embodiments shown in Figures 12 through 20 are directed to the ball holder capable to provide adjustable raceway spaces. Figure 12 illustrates adjustable ball holder 21 composed of a pair of independent first and second shaft parts 22 and 23. First shaft part 22 is provided with a concave 24. Concave 24 is provided with a inclined bottom surface 28. On the other hand, second shaft 23 has inclined projection 25 which fits into concave 24. When first and second shaft 22 and 23 are assembled with both end surfaces flushing each other, they rest with a small clearance 26 therebetween and their combined end surfaces form a configuration substantially identical to that of track shaft part T of rail R. As first and second shaft parts 22 and 23 are slightly dislocated from each other along their axial direction, clearance 26 is eliminated. Adjustable ball holder 21 of this contracted state is first inserted into the cavity of bearing body 4 and steel balls 7... are fed into enlarged raceway spaces 9.... Each of raceway spaces 9... formed by grooves 31... of adjustable ball holder 21 and grooves 8... of bearing body 4 is slightly larger than steel balls 7... so that filling of steel balls 7... is easily accomplished. After all raceway spaces 9... and escape-ball through holes 10... and ball-recirculating grooves in end cap 5 are filled with steel balls 7... , another end cap 5 is fixed to cover the opening end of bearing body 4. Then first and second shaft parts 22 and 23 are axially slid until both end surfaces flush each other. The relative position of first and second shaft parts 22 and 23 is maintained by friction, or preferably by detachable screw 27. Alternatively, stop cover 28 as shown in Figure 15 can be used instead of screw 27. Figure 16 shows another embodiment of second shaft 22' provided with fit plate 14' which fits into the inner opening of end cap 5. Figure 17 shows still another embodiment of first and second shaft 22" and 23" in which concave 24' and projection 25' are both tapered in their cross-sections. Figure 18 illustrates still further embodiment in which shaft 33 is somewhat tubular and has a cross-sectional configuration almost identical to that of track shaft part T of rail R except it has a cut opening 35 at its bottom formed by a pair of lips 34, 34. Provided at the four corners of ball holder 33 are grooves 35... substantially identical to those of track shaft part T of rail R. Figures 19 and 20 show different embodiments of such ball holder which are here made of metal. In Figure 20, ball holder 43' is provided with windows 46 which enable easy holding of the steel balls 7... In each of those embodiments, the outer configuration of ball holder 33... is substantially identical to that of track shaft part T, however, becomes smaller when lips 34 and 34 are held to contact each other as shown in Figure 21 such that the diameter of each raceway space 9 formed therein becomes slightly larger than that of steel ball 7. After steel balls 7... are filled in the raceway spaces, lips 34 and 34 are released so that ball holder 33 springs back to its original shape and steel balls 7... are held between bearing body 4 and ball holder 33. Figure 22 illustrates insertion member 40 to be inserted into clearance 35 between lips 34 and 34. Since the width of projection 41 of stop member 40 is slightly larger than clearance 35 between lips 34 and 34 after the steel balls 7... are filled, ball holder 33 is even more firmly held in saddle 6 when stop insertion 40 is inserted. Further, insertion member 40 prevents ball holder 33 from being deformed due to the resistance from preloaded steel balls 7... when saddle 6 slides onto rail R and thus also prevents steel balls 7... from falling off due to the possible deformation. Figure 23 illustrates another insertion member 42 having recess 43 and projection 44. Recess 43 works to hold lips 34 and 34 to contact each other. Figure 24 illustrates another embodiment of adjustable ball holder 53 having end plate 55 and a pair of separated cantilever projections 52, 52 projecting therefrom. The outer configuration of end plate 55 is substantially identical to that of end cap 5 or of bearing body 4. Therefore, when ball holder 53 is inserted into saddle 6, with the position of side plate 55 exactly coincides with end cap 5, the positions of separated cantilever projections 52 and 52 are also determined in the exact locations to provide the raceways 9... each slightly smaller than the diameter of steel balls 7... Then the central clearance 57 between separated cantilever projections 52 and 52 is narrowed by holding lips 54 and 54 to contact each other in order to fill the steel balls 7... into the slightly widened raceways 9.... After completion of filling steel balls 7..., lips 54 and 54 are released so that separated cantilever projections 52 and 52 hold steel balls 7... against the grooves 8... of bearing body 4. Figure 25 illustrates another embodiment of ball holder 63 provided with fit plate 65 which abuts with the inner opening of end cap 5 with friction. Also, cantilever projections 62, 62 are separated from fit plate 65 with clearance 66 such that cantilever projections 62 and 62 can be easily inclined. Figure 26 illustrates insertion member 70 having a projection 71 and tapered recess 73. The outer cross-section of insertion member 70 is identical to the inner cross-section of the inner cavity between cantilever projections 52 and 52 or 62 and 62. First, clearance 57 or 67 is narrowed by moving tapered recess 73 onto lips 54 and 54 or 64 and 64. After steel balls 7... are supplied, insertion member 70 is withdrawn from the lips. Then whole insertion member 70 is inserted into the inner cavity of cantilever projections 52 and 52 or 62 and 62 such that ball holder 53 or 63 hold steel balls 7... more firmly. Figure 27 illustrates short insertion member 80 with recess 83. The length L of recess 83 is much shorter than the distance between the outer edges of the lips 54 and 54 or 64 and 64 in order to close clearance 57 or 67. The width W of short insertion member " 80 is slightly substantially identical to clearance 57 or 67. Thus when saddle 6 is assembled, short insertion member 80 is inserted into narrowed clearance 57 or 67 by steel balls 7... so as to push the cantilever projections outwardly.

Claims: What is claimed is; 1. A retainerless linear motion bearing assembly having a bearing body, a pair of end caps, a rail, and rows of steel balls; characterized in that said bearing body has a substantially C-shaped recess provided with a plurality number of grooves therein and same number of through holes in. said bearing body; each of said pair of end caps is fixed at each end surface of said bearing body and provided with same number of ball-recirculating grooves; said rail is provided with same number of grooves positioned adjacent to said plurality number of grooves of said bearing body so as to form raceways such that said raceways, said ball-recirculating grooves and said through holes form same number of independent recirculating loop channels; each of said same number of rows of steel balls is placed within each of said independent recirculating loop channels; and a diameter of each of said balls is slightly larger than a diameter of each of said raceways such that said balls within said raceways are preloaded. 2. A ball holder for a retainerless saddle having a bearing body, a pair of end caps attached to said bearing body, an elongated shaft, and a plurality of contact surfaces; characterized in that said elongated shaft has an axial length at least equal to that of the bearing body; said plurality of contact surfaces is provided at the circumstantial surface of said elongated shaft along the axis thereof; each of said contact surfaces positioned adjacent to each of grooves provided within the bearing body such that each of said contact surfaces of said shaft and each of said grooves of the bearing body form an independent raceway, and the outer configuration of the cross- section of said ball holder is substantially identical to that of the cross-section of a track shaft part of a rail. 3. The ball holder of claim 2, characterized in that each of said contact surfaces has a groove. 4. The ball holder of claim 2, characterized in that each of said contact surfaces has a slit. 5. The ball holder of claim 3, characterized in that a material of the ball holder is an elastic member. 6. The ball holder of claim 4, characterized in that a material of the ball holder is a metal. 7. The ball holder of claim 2, characterized in that the diameter of said raceway is substantially identical to that of a steel ball. 8. The ball holder of claim 2, characterized in that the diameter of said raceway is slightly smaller than that of the steel ball. 9. The ball holder of claim 2, characterized in that said shaft is provided with an end plate at one distal end thereof, and that said end plate has an outer configuration substantially identical to the overall outer configuration of said end cap. 10. The ball holder of claim 2, characterized in that said shaft is provided with a fit plate at one distal end thereof, and that said fit plate has an outer configuration substantially identical to the inner peripheral configuration of an opening of said end cap. 11. The ball retainer of claim 10, characterized in that said fit plate is provided with an end plate. 12. The ball holder of claim 2, characterized in that said shaft is composed of a plurality of shaft parts. 13. The ball holder of claim 12, characterized in that said plurality of shaft parts are a pair of first and second shaft parts, and that said first and second shaft parts are engageable with each other. 14. The ball holder of claim 13, characterized in that said first shaft part is provided with an open recess and said second shaft part is provided with a projection, and that the cross-sectional configurations of said open recess and said second shaft are substantially identical. 15. The ball holder of claim 14, characterized in that said open recess has an inclined bottom surface, and that said projection has an inclined top surface. 16. The ball holder of claim 14, characterized in that each of said open recess and said projection has a tapered cross- section. 17. The ball holder of claim 14, characterized in that said first and second shaft parts are attached with a detachable screw. 18. The ball holder of claim 14, characterized in that said second shaft part has a fit plate. 19. The ball holder of claim 14, characterized in that said first and second shaft part are held by a stop member. 20. The ball holder of claim 2, characterized in that said shaft is a hollow tube having a pair of lips with a slit therebetween. 21. The ball holder of claim 20, characterized in that said shaft is made of a metal. 22. The ball holder of claim 21, characterized in that each of said contact surfaces is provided with a window. 23. The ball holder of claim 20, characterized in that said slit between the pair of lips have an " insertion member inserted thereinto. 24. The ball holder of claim 12, characterized in that said plurality of shaft parts are a pair of cantilever projections connected at the root thereof. 25. The ball holder of claim 24, characterized in that each of said cantilever projections is provided with a lip. 26. The ball holder of claim 24, characterized in that a space between said lips accommodate therein an insertion member inserted therein. 27. The ball holder of claim 26, characterized in that said ball holder further has a recess. 28. The ball holder of claim 26, characterized in that said insertion member has a projection at one side and a recess at the other side, and that said insertion member has a cross- section substantially identical to a space between said cantilever projections and said lips. 29. The ball holder of claim 28, characterized in that the width of said recess is tapered. 30. The ball holder of claim 24, characterized in that at least said lips are directly connected to a common plate. 31. The ball holder of claim 30, characterized in that said common plate is an end plate having an outer configuration substantially identical to that of said end cap. 32. The ball holder of claim 30, characterized in that said common plate is a fit plate having an outer configuration substantially identical to the inner configuration of an open cavity of said end plate. 33. The ball holder of claim 30, characterized in that each of said cantilever projections is separated from said common plate. 34. A process for assembling a retainerless saddle for a linear motion bearing having a bearing body, steel balls, a pair of end caps and a ball holder; characterized in that said assembling process attaches one of said end caps at one end surface of said bearing body; provides raceways within said bearing body, the diameter of the raceway being slightly larger than that of the steel ball; feeds said steel balls into said raceways and escape-ball through holes in said bearing body; covers an open end of said bearing body by the other end cap so as to form a saddle; and holds said balls between said saddle and said ball holder.

Inventors: HATTORI KENICHI, HATTORI, KENICHI
Applicants: HATTORI KENICHI, HATTORI, KENICHI
Application year: 1995
Main classification: F16C41
IPC codes: F16C29, F16C33, F16C41, F16C43