GB1574258A

GB1574258A - Linear ball bearings

Info

Publication number: GB1574258A
Application number: GB2089678A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1978-05-19
Filing date: 1978-05-19
Publication date: 1980-09-03

Description

(54) IMPROVEMENTS IN OR RELATING TO LINEAR BALL BEARINGS (71) I, CONRAD ERWIN FREDER ICKS, a British subject, of 9 Tavistock Terrace, Upper Holloway, London, N19 4BZ, do hereby declare the invention, for which I pray that a patent may be granted to me, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to linear ball bearings of the kind in which a plurality of separate series of bearing balls are recirculatable around corresponding paths whose planes are radially or substantially radially disposed with respect to the axis of linear displacement of the bearing. Linear ball bearings of this kind are sometimes referred to as radial ball bushings. A radial or substantially radial recirculation path is defined as being one in which the "loaded" and "unloaded or return" portions of the path are wholly or principally at opposite sides of a boundary surface between parts of the bearing concerned and there is a distinction between such radial or substantially radial recirculation paths and tangential or substantially tangential recirculation paths in which the "loaded" and "unloaded or return" portions thereof are wholly or principally at the same side of a boundary surface between parts of the bearing concerned. The present invention does not relate to linear ball bearings which comprise tangential or substantially tangential ball recirculation paths. The invention also relates to assemblies of shaft mountings, shafts and linear ball bearings or bushings which are axially displaceable relative to the corresponding shafts. The term "linear ball bearing(s)" will henceforth be used alone for the sake of brevity.

Linear ball bearings of the type referred to above are furnished in three different forms. Firstly, a right-circular cylindrical form which extends through 360" around the axis of linear displacement. Secondly, a cylindrical form in which the bearing, proper, subtends marginally less than 360" around the axis of linear displacement, there being a narrow slot-like gap in the bearing which subtends the balance (only a few degrees) of one complete 360" revolution about the axis of linear displacement of the bearing that is not subtended by the bearing itself. The slot-like gap is provided at its opposite sides with lugs or the like which can be drawn towards one another, against the strong resilient opposition of the parts from which the bearing is made, by bolts or the like to tighten the bearing round various shafts, principally for purposes of adjustment. Thirdly, linear ball bearings take the form of a cylinder in which a segment of significant angular extent around the axis of linear displacement (typically, 90 ) is missing. Linear ball bearings of this third form are particularly useful for linear movement, without angular displacement, along shafts that are fastened to supports at locations between the opposite ends of those shafts, the "missing" segments of the bearings being arranged to register axially with such shaft supports.

An object of the present invention is to provide efficient and long lasting linear ball bearings which are less complicated and expensive to manufacture than are the bearings which have been used heretofore.

According to the invention, there is provided a linear ball bearing of the kind set forth, wherein the paths which contain a plurality of said series of recirculatable bearing balls are substantially radial recirculation paths (as hereinbefore defined) and have their planes inclined to corresponding strictly radial planes which contain the axis of linear displacement of the bearing, and wherein those series of bearing balls which are at one side of a strictly radial datum plane that also contains said axis have the planes of their recirculation paths inclined to said corresponding strictly radial planes in one direction whereas those series of bearing balls which are at the opposite side of said datum plane have the planes of their recirculation paths inclined to the corresponding strictly radial planes in the opposite direction.

For a better understanding of the invention, and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which: Figure I is a combined end view and cross-section through a linear ball bearing in accordance with the invention, Figure 2 is a section taken on the line II-II in Figure 1, Figure 3 is a cross-section through a mounting for a shaft along which is axially displaceable a linear ball bearing in accordance wih the invention, Figure 4 is a side elevation corresponding to Figure 3, and Figure 5 is a plan view corresponding to Figures 3 and 4.

Referring to Figures 1 and 2 of the accompanying drawings, the linear ball bearing which is illustrated therein is shown as being of the first form that is discussed at the beginning of this specification, that is to say, it is illustrated as being of right-circular cylindrical configuration. However, as will be described below. Figure 1 illustrates modifications to the bearing that would be required to provide it in either the second or the third of the three forms which have been referred to. The illustrated linear ball bearing comprises a cylindrical body shell that is afforded wholly or principally by an outer shell 1 and an inner shell 2 that is disposed concentrically (with respect to an axis of linear displacement 4 of the bearing) inside the outer shell 1. A plurality (in this case, fourteen) of guide ribs 3 are provided or ;he inner concave surface of the inner shc:l '.

each guide rib 3 being flanked at its opposite sides by axially extending concave recesses 5 which co-operate to form a corresponding "loaded"ball channel 6 in which, during operation, will recirculate a corresponding series of bearing balls 7.

In the example which is being described, there are fourteen separate series of the recirculatable bearing balls 7 and each such series recirculates, during the use of the bearing, through a path which comprises the corresponding "loaded" channel 6 and a spaced but parallel "unloaded" or return channel 8. The opposite ends of each "loaded" ball channel 6 and of the corresponding "unloaded" or return channel 8 are interconnected bv curved transfer channels 9 each of which subtends an angle of 1800 at its own centre of curvature ad each of which channels 9 is formed in one of two end caps 10 of the hearing, said end caps 10 being made partly of metal and partly of a synthetic plastics material, such as a polyamide material, and being of the same cross-sectional shape as the body shell of the bearing which shape, in the case of the example that is illustrated in Figures 1 and 2 of the drawings, is circular. In this connection, it is noted that, although the outer shell 1, the inner shell 2 and the guide ribs 3 will usually be formed from at least one metallic material, this is by no means always the case and any one or more of those three parts can be formed from a synthetic plastics material, such as a polyamide material, having regard to the particular purpose for which the linear ball bearing concerned is intended. The "unloaded" or return channels 8 are formed in the inner concave surface of the outer shell 1 by machining in the case of a metallic outer shell or by moulding and a finishing step in the case of a polyamide or other synthetic plastics outer shell 1. The channels 8 are, it will be noted, themselves strictly radial and can thus be very easily formed by conventional machining or moulding techniques. The inwardly directed mouths of the return channels 8 are closed, to complete those channels 8, during the manufacture of the bearing, by bonding the outer cylindrically curved surface 11 (Figure 1) of the inner shell 2 to the matchingly curved concave inner surface of the outer shell 1. Although it is possible for the guide ribs 3 to be formed integrally with the inner surface of the inner shell 2, it is preferred that the individually formed guide ribs 3 should have their outer surfaces bonded to the inner cylindrically curved surface 12 (Figure 1) of the inner shell 2.

The bonding medium which is used at the surfaces 11 and 12 will, of course, depend to some extent on the particular materials from which the parts exhibiting said surfaces 11 and 12 are formed. Epoxy resin adhesive has been found to be suitable as the bonding medium for many applications but it is emphasised that the use of an epoxy resin adhesive for this purpose is by no means essential and that other known bonding media may be emploved where compatible with the requirements of the bearing that is being constructed. Either surface 11 or 12 of the inner shell 2 may be considered as affording the "boundary surface" which is referred to near the beginning of this specification. It will be noted that the "loaded" ball channels 6 that are formed between the successive guide ribs 3 all extend parallel to the axis of linear displacement 4 and that the slot-like openings which face inwardly towards said axis 4, and through which the balls 7 will partially project to perform their function when the bearing is in use, have widths which are less than the diameters of the balls 7 themselves so that said balls 7 cannot become lost from the corresponding channels 6 through these openings when the bearing is not in surrounding relationship with a shaft.

Figure 1 of the drawings illustrates a vertical datum plane X-X which contains the axis of linear displacement 4 of the bearing and which is thus a strictly radial plane.

Although the longitudinal axis of each "loaded" ball channel 6 and each "unloaded" or return channel 8 is parallel to the axis 4 and thus to the datum plane X-X, the centre lines of the curved transfer channels 9 that are formed in the end caps 10 are not contained in corresponding planes that extend radially from the axis 4 but are contained in planes which are inclined to such radial planes. Thus, each series of recirculatable bearing balls 7 is effectively contained in a corresponding plane Y-Y (Figure 1) and each such plane Y-Y is acutely inclined to a corresponding strictly radial plane Z-Z, each plane Z-Z, of course, containing the axis of linear displacement 4.

Reference to Figure 1 of the drawings will show that there are seven series of recirculatable bearing balls 7 at one side of the datum plane X-X and also seven series of the bearing balls 7 at the opposite side of that plane X-X. It will also be seen that the plane Y-Y which corresponds to each series of bearing balls 7 at one side of the datum plane X-X is acutely inclined to the corresponding strictly radial plane Z-Z in one direction whereas the plane Y-Y that corresponds to each series of bearing balls 7 that is at the opposite side of the datum plane X-X is acutely inclined to the corresponding strictly radial plane Z-Z by the same angle but in the opposite direction. In fact, in the example which is being described with reference to Figures 1 and 2 of the drawings, the seven series of recirculatable bearing balls 7 at one side of the datum plane X-X is symmetrical with respect to the seven series of bearing balls 7 at the opposite side of that plane X-X. It is noted that such a symmetrical disposition of the fourteen series of bearing balls 7 would not be present in relation to a strictly radial plane (not illustrated) that contains the axis 4 but that is perpendicular to the datum plane X-X. The particular inclinations of the planes Y-Y to the corresponding strictly radial planes Z-Z can be determined, in any particular case, by appropriate formation of the curved transfer channels 9 in the end caps 10 and correspnding dispositions of the "loaded" ball channels 6, the latter being readily variable for individual bearings when a bonding medium is used at the surface 12 merely by changing the angular dispositions of the guide ribs 3 relative to the inner shell 2. It has been found that linear ball bearings constructed in this way are effective and long lasting and can be manufactured less expensively than known linear ball bearings of the kind discussed at the beginning of this specification. The end caps 10 are releasably secured to the opposite ends of the body shell of the bearing by employing bolts or screws 13 whose shanks cooperate with internally screw-threaded blind bores in the outer shell 1, between the channels 8, that are parallel to the axis 4.

Figures 3 to 5 of the drawings illustrate the use of a linear ball bearing of the kind which has been described above in supporting an article, such as a machine tool table 14, for linear displacement with respect to a relatively fixed member such as, for example, a machine frame 15. The machine frame 15, which is shown only diagrammatically in Figure 3 of the drawings, carries a shaft support 16 that is of basically square cross section, one corner (in cross section) of the square being formed with a recess 17 which receives a hardened shaft 18 of circular cross section. There will usually be at least two linear ball bearings for the axially slidable support of the machine tool table 14 but only one such linear ball bearing, which is generally indicated by the reference 19, is diagrammatically illustrated in Figures 3 to 5 inclusive. The bearing 19 is, of course, of the third form that is discussed at the beginning of this specification inasmuch as a complete segment thereof, which subtends an angle that is marginally in excess of 90" at the axis of the shaft 18, is entirely missing. Figure 1 of the drawings shows two radial lines 20 which delimit the opposite sides of the "missing" segment of the bearing when, in its finished state, it is to be a bearing such as the bearing 19 that is diagrammatically illustrated in Figures 3 to 5 inclusive. It is noted that the shaft 18 is retained in the recess 17 of the shaft support 16 by at least one, and preferably at least two, studs 21, the or each stud 21 having a screwthreaded shank that is entered into a matchingly screwthreaded radial blind bore in the shaft 18. The shank of the or each stud 21 projects by a considerable distance radially from the shaft 18 and has a head 22 at its outermost end, the shape of the or each head 22 being illustrated in Figure 3 of the drawings and being such that it exhibits a 90" frusto-conically tapering surface which is convergent in a direction towards the end of the stud shank which is remote from the head 22. The head 22, and the part of the shank of each stud 21 which is outside the bore or corresponding bore in the shaft 18 is entered into a substantially cylindrical cavity 23 in the shaft support 16, the frustoconically tapering surface of the head 22 being engaged by two perpendicularly opposed set screws 24 that are received in corresponding internally screwthreaded bores in the shaft support 16. It is advantageous for the shaft 18 to be supported by the two perpendicularly opposed surfaces of the recess 17 since high lateral loading upon the shaft 18 can then be tolerated and the formation of the recess 17 itself is facilitated because the motions of standard machine tools can be used to the best effect when producing the two relatively perpendicular supporting surfaces of the recess 17. The use of at least one stud 21 and at least two perpendicularly opposed set screws 24 to connect the shaft 18 rigidly to the support 16 is also simple and convenient since the shaft 18 can be offered up to the support 16 in a direction that is parallel to the length of the or each stud 21, it being unnecessary to have access to the machine frame 15 or other fixed member from beneath. It will be appreciated that the arrangement which can be seen best in Figure 3 of the drawings constitutes, in effect, a "secret" fixing of the shaft 18 relative to the support 16. It is only necessary temporarily to loosen the or each pair of perpendicularly opposed set screws 24, after first moving the machine tool table 14 or other linearly displaceable article to an appropriate position, when it is desired to disconnect the shaft 18 from its support 16.

The "missing" segment of the or each linear ball bearing 19 has a magnitude that is marginally in excess of 90" in order to permit the shaft 18 to bear against the two perpendicularly opposed surfaces of the recess 17 as discussed above leaving a small clearance as can be seen best in Figure 3 of the drawings. In fact, the relative sizes of the shaft 18 and the recess 17 in the support 16 which receives that shaft are such that the two line contacts between the cylindrically curved surface of the shaft 18 and the respective mutually perpendicular flat surfaces of the recess 17 are located just inwardly from the corresponding edges of the recess 17 in the support 16 so as to avoid said lines of contact actually coinciding with those edges. When a plurality of the supports 16 are provided, they may be in the form of pedestals which are short in the direction of the longitudinal axis of the shaft 18 but, as an alternative, and particularly where heavy loads are to be carried, the support 16 may be in the form of a continuous or substantially continuous rail.

Figures 3 to 5 of the drawings illustrate a single shaft support 16 in the second of the two forms that have just been mentioned, that is to say, in the form of a continuous or substantially continuous rail. The outer shell 1 of the linear ball bearing 19 (illustrated in Figures 3 to 5 of the drawings) is surrounded, throughout the angular extent of that shell around the longitudinal axis of the shaft 18, by a housing 25 whose top is integrally formed with a platform 26 to which the machine tool table 14 or other linearly displaceable article (not shown in Figures 4 and 5) can be firmly but releasably secured by bolts or the like.

Referring once again to Figures 1 and 2 of the drawings, and particularly to the former figure, that figure shows two lines 27 which extend substantially, although not necessarily exactly, radially with respect to the axis of linear displacement 4. When the linear ball bearing of Figures 1 and 2 of the drawings is to be of the second form that has been discussed at the beginning of this specification, the material of the parts 1, 2, 3 and 10 that lies between the two lines 27 as shown in Figure 1 of the drawings is omitted thus leaving a narrow substantially radially extending gap. Means, such as lugs, is secured to the external surface of the outer shell 1 in such a case and further means, such as bolts or the like, interconnects pairs of the lugs so that they can, when required, be drawn towards one another by tightening said bolts to narrow the gap between the lines 27 against the strong resilient opposition of the parts 1, 2, 3 and 10 of the bearing. Bearing play can thus be substantially eliminated and the use of adjustable bearings of this kind is particularly desirable when the bearings may have to cooperate with shafts of marginally different diameters. Although the invention has been described in its application to linear ball bearings that are of circular cylindrical formation, it is emphasised that this is not essential and that a linear ball bearing in accordance with the invention could have a cross-section which includes a series of flat and curved portions or which is comprised substantilly wholly by a series of flats. Thus, such linear ball bearings could cooperate readily with support surfaces of square or oblong crosssection or with support surfaces that are basically of square or oblong cross section but which also include curved portions.

WHAT I CLAIM IS: 1. A linear ball bearing of the kind set forth, wherein the paths which contain a plurality of said series of recirculatable bearing balls are substantially radial recirculation paths (as hereinbefore defined) and have their planes inclined to corresponding strictly radial planes which contain the axis of linear displacement of the bearing, and wherein those series of bearing balls which are at one side of a strictly radial datum plane that also contains said axis have the planes of their recirculation paths inclined to said corresponding strictly radial planes in one direction whereas those series of bearing balls which are at the opposite side of said datum plane have the planes of their recirculation paths inclined to the corresponding strictly radial planes in the opposite

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. corresponding internally screwthreaded bores in the shaft support 16. It is advantageous for the shaft 18 to be supported by the two perpendicularly opposed surfaces of the recess 17 since high lateral loading upon the shaft 18 can then be tolerated and the formation of the recess 17 itself is facilitated because the motions of standard machine tools can be used to the best effect when producing the two relatively perpendicular supporting surfaces of the recess 17. The use of at least one stud 21 and at least two perpendicularly opposed set screws 24 to connect the shaft 18 rigidly to the support 16 is also simple and convenient since the shaft 18 can be offered up to the support 16 in a direction that is parallel to the length of the or each stud 21, it being unnecessary to have access to the machine frame 15 or other fixed member from beneath. It will be appreciated that the arrangement which can be seen best in Figure 3 of the drawings constitutes, in effect, a "secret" fixing of the shaft 18 relative to the support 16. It is only necessary temporarily to loosen the or each pair of perpendicularly opposed set screws 24, after first moving the machine tool table 14 or other linearly displaceable article to an appropriate position, when it is desired to disconnect the shaft 18 from its support 16. The "missing" segment of the or each linear ball bearing 19 has a magnitude that is marginally in excess of 90" in order to permit the shaft 18 to bear against the two perpendicularly opposed surfaces of the recess 17 as discussed above leaving a small clearance as can be seen best in Figure 3 of the drawings. In fact, the relative sizes of the shaft 18 and the recess 17 in the support 16 which receives that shaft are such that the two line contacts between the cylindrically curved surface of the shaft 18 and the respective mutually perpendicular flat surfaces of the recess 17 are located just inwardly from the corresponding edges of the recess 17 in the support 16 so as to avoid said lines of contact actually coinciding with those edges. When a plurality of the supports 16 are provided, they may be in the form of pedestals which are short in the direction of the longitudinal axis of the shaft 18 but, as an alternative, and particularly where heavy loads are to be carried, the support 16 may be in the form of a continuous or substantially continuous rail. Figures 3 to 5 of the drawings illustrate a single shaft support 16 in the second of the two forms that have just been mentioned, that is to say, in the form of a continuous or substantially continuous rail. The outer shell

1 of the linear ball bearing 19 (illustrated in Figures 3 to 5 of the drawings) is surrounded, throughout the angular extent of that shell around the longitudinal axis of the shaft 18, by a housing 25 whose top is integrally formed with a platform 26 to which the machine tool table 14 or other linearly displaceable article (not shown in Figures 4 and 5) can be firmly but releasably secured by bolts or the like.

direction.

2. A bearing as claimed in claim 1, wherein the planes which contain said series of recirculatable bearing balls are asymmetrical with respect to a plane which contains the axis of linear displacement of the bearing and which is perpendicular to said datum plane.

3. A bearing as claimed in claim 1 or 2, wherein said bearing comprises a body shell composed of inner and outer shells that are bonded to one another, "unloaded" or return channels for the series of recirculatable bearing balls being formed in the inner surface of said outer shell.

4. A bearing as claimed in claim 3, wherein channels defining the "loaded" runs of the series of recirculatable bearing balls are formed internally of the concave surface of said inner shell.

5. A bearing as claimed in claim 4, wherein the channels which define the "loaded" runs of said series of bearing balls are afforded by a plurality of ribs which are bonded to the inner concave surface of said inner shell.

6. A bearing as claimed in claim 4 or 5 wherein the openings of said "loaded" channels of the series of recirculatable bearing balls are smaller in width than the diameters of said bearing balls.

7. A bearing as claimed in any one of claims 3 to 6, wherein the bonding medium is an epoxy resin adhesive.

8. A bearing as claimed in claim 5 or in either claim 6 or claim 7 when read as appendant to claim 5, wherein said outer shell and/or said inner shell and/or said ribs is/are formed from metal.

9. A bearing as claimed in claim 5 or in any one of claims 6 to 8 when read as appendant to claim 5, wherein said outer shell and/or said inner shell and/or said ribs is/are formed from a synthetic plastics material.

10. A bearing as claimed in claim 9, wherein the synthetic plastics material is a polyamide material.

11. A bearing as claimed in any preceding claim, wherein curved transfer channels by which the bearing balls in each series move successively between a "loaded" channel and an "unloaded" or return channel of the corresponding path are formed in end caps of the bearing.

12. A bearing as claimed in claim 11, wherein each end cap is formed partly from metal.

13. A bearing as claimed in claim 11 or 12 wherein each end cap is formed partly from a synthetic plastics material.

14. A bearing as claimed in claim 13, wherein the synthetic plastics material is a polyamide material.

15. A bearing as claimed in any one of claims 11 to 14 when read as appendant to claim 3, wherein said end caps are releasably secured to the outer shell of said body shell by bolts or screws that extend parallel or substantially parallel to the axis of linear displacement of the bearing.

16. A bearing as claimed in any preceding claim and being of circular or substantially circular cross-section.

17. A bearing as claimed in any one of claims 1 to 15 and being of substantially square or substantially oblong cross-section.

18. A bearing as claimed in any one of claims 1 to 16, wherein the bearing is formed with a gap of sufficient width to enable it to be tightened around a shaft, and wherein means is provided by which said gap can be closed, against the resilient opposition of parts of the bearing, to an adjustable extent.

19. A bearing as claimed in claim 18, wherein said means comprises lugs at the opposite sides of the gap and at least one bolt or the like arranged to enable said lugs to be drawn towards one another to an adjustable extent.

20. A bearing as claimed in any one of claims 1 to 17, wherein a segment of the bearing is omitted of sufficient angular extent to enable the bearing to move axially relative to a shaft without fouling a support of that shaft.

21. A bearing as claimed in claim 20, wherein the omitted segment subtends an angle which is marginally in excess of 90" at the axis of linear displacement of the bearing.

22. An assembly of a shaft mounting, a shaft and a linear ball bearing as claimed in claim 21, wherein the shaft mounting comprises at least one support formed with a recess which exhibits two supporting surfaces that are perpendicular to one another, said shaft being received in the recess so as to abut against both the supporting surfaces.

23. An assembly as claimed in claim 22 wherein the sizes of said shaft and said recess are such that the edges of the two supporting surfaces are disposed beyond the lines of contact of those two surfaces with the surface of the shaft.

24. An assembly as claimed in claim 22 or 23, wherein said shaft is maintained in contact with the supporting surfaces of the or each recess by at least one stud that is substantially radially secured to the shaft and that has a head which is spaced from the shaft and located in a cavity of said support, the stud head being releasably retained in said cavity by releasable members which abut against relatively inclined portions of the head.

25. An assembly as claimed in claim 24, wherein the relatively inclined portions of the stud head are portions of a frusto conically tapering surface of that head which surface has a cone angle of 90 , and wherein the releasable members are set screws disposed in corresponding relatively perpendicular screwthreaded bores of said shaft support.

26. An assembly as claimed in any one of claims 22 to 25 wherein the shaft mounting takes the form of a rail that is continuous or substantially continuous throughout the length of said shaft.

27. A linear ball bearing substantially as hereinbefore described with reference to Figures 1 and 2 of the accompanying drawings.

28. An assembly of a shaft mounting, a shaft and a linear ball bearing as claimed in any one of claims 20, 21 or 27, the shaft mounting being substantially as hereinbefore described with reference to Figures 1 to 5 of the accompanying drawings.