GB2075135A - Bearings - Google Patents

Abstract

A linear ball bearing of the kind which comprises a plurality of tangential or substantially tangential series of recirculatable bearing balls (5) is so constructed and arranged that the bearing balls (5) in those series which are at one side of a strictly radial datum plane (X-X) that contains the axis of linear displacement (3) of the bearing will all recirculate in one direction when the bearing is in use whilst the balls (5) in those series which are at the opposite side of said plane (X-X) will all recirculate in a second and opposite direction when the bearing is in use. An inner sleeve (2) of the bearing which wholly or partly defines the recirculation paths for said series of bearing balls (5) is formed at both of its axial ends with screwthreaded portions for purposes of mounting and/or axial adjustment of the bearing. The screwthreaded portions at the ends of the inner sleeve (2) will co-operate either with screwthreaded locking rings or with screwthreaded auxiliary fastening flanges, the latter being employable directly to secure the bearing in, for example, a machine frame with the aid of screws entered through holes in the flange. In modified embodiments sectors 13-13, 20-20A, or 20-20 may be omitted. <IMAGE>

Description

SPECIFICATION Linear ball bearings 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 tangentially or substantially tangentially disposed with respect to an imaginary circular cylindrical figure whose longitudinal axis coincides with the axis of linear displacement of the bearing.

Linear ball bearings of this kind are sometimes referred to as tangential ball bushings. A tangential or substantially tangential recirculation path is defined as being one in which the "loaded" and "unloaded or return" portions of the path are wholly or principally at the same side of a boundary surface between parts of the bearing concerned and there is a distinction between such tangential or substantially tangential recirculation paths and a radial or substantially radial recirculation path 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. The present invention does not relate to linear ball bearings which comprise radial or substantially radial ball recirculation paths.

The invention does, however, also relate 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 slotlike 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 around 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 (for example, 60 or 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 of the kind set forth and to facilitate the mounting of such bearings in, for example, machine frames in such a way as to allow axial adjustments of the bearings to be made and, preferably, without removing the possibility of marginal adjustments in diameter that are possible in linear ball bearings of the second form which is discussed above.

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 tangential recirculation paths (as hereinbefore defined), and wherein those series of bearing balls which are at one side of a strictly radial datum plane that contains the axis of linear displacement of the bearing are arranged so that the balls therein will all recirculate in one direction when the bearing is in use whilst those series of bearing balls which are at the opposite side of the same datum plane are arranged so that the balls therein will all recirculate in a second and opposite direction when the bearing is in use, and wherein an inner sleeve of said bearing which wholly or partly defines the recirculation paths for said series of bearing balls is formed at both of its axial ends with screwthreaded portions for purposes of mounting and/or axial adjustment of the bearing.

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 1 is an axial end view of a linear ball bearing in accordance with the invention provided with an auxiliary fastening flange, Figure 2 is a section taken on the line ll-ll in Fig. 1, Figure 3 is a section taken on the line Ill-Ill in Fig. 2, Figure 4 is a cross-section through a mounting for a shaft along which is axially displaceable a linear ball bearing in accordance with the invention, Figure 5 is a side elevation corresponding to Fig. 4, and Figure 6 is a plan view corresponding to Figs. 4 and 5.

Referring to the accompanying drawings, and particularly to Figs. 1 to 3 inclusive thereof, the linear ball bearing which is iilustrated 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, Fig. 3 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 shell 1 to the concave internal surface of which is secured an inner sleeve 2 that is disposed concentrically (with respect to an axis of linear displacement 3 of the bearing) inside the cylindrical shell 1.The inner sleeve 2 of the linear ball bearing has formed therein twelve pairs of principally axially extending grooves 4 and it will be seen from Fig. 3 of the drawings that one groove 4 of each pair is also partially defined by a recess in the concave inner surface of the surrounding shell 1. Each pair of grooves 4 receives a corresponding series of a large number of bearing balls 5 and it will be seen from Fig. 3, in particular, of the drawings that, for each series of bearing balls 5, one of the corresponding pair of grooves 4 defines a "loaded" ball channel whereas the companion groove 4 (i.e. the one which is defined partly by one of the recesses in the inner surface of the shell 1) affords an "unloaded" or "return" ball channel.

In the example which is being described, there are twelve pairs of the grooves 4 and twelve separate series of the recirculatable bearing balls 5 and each such series recirculates, during the use of the bearing, through a path which comprises the corresponding "loaded" ball channel and the co-operating spaced but parallel "unloaded" or "return" ball channel. The opposite ends of each "loaded" ball channel and of the corresponding "unloaded" or "return" ball channel are interconnected by curved transfer channels 6 (Fig. 2) each of which subtends an angle of 180 at its own centre of curvature and each of which channels 6 has the curved centre line thereof contained in, or substantially contained in, a corresponding imaginary plane that is obliquely inclined to the axis of linear displacement 3.It will be noted that the grooves 4 in the inner sleeve 2 which define the "loaded" ball channels are of such shapes that the slot-like openings which face inwardly towards the axis 3, and through which the balls 5 will partially project to perform their function when the bearing is in use, have widths which are less than the diameters of the balls 5 themselves so that said balls 5 cannot become lost from those grooves 4 through these openings when the bearing is not in surrounding relationship with a shaft.

Fig. 3 of the drawings illustrates a vertical datum plane X-X which contains the axis of linear displacement 3 of the bearing and which is thus a strictly radial plane. Each series of bearing balls 5 (except for those balls 5 which are in the corresponding two transfer channels 6) are contained in a plane which is substantially tangential to the surface of an imaginary right circular cylindrical figure which the linear ball bearing under discussion surrounds. All of the bearing balls 5 are located radially inwardly of the internal surface of the shell 1 and that internal surface, despite the fact that it is recessed to assist in forming the "unloaded" or "return" ball channels, may be considered as affording the "boundary surface" which is referred to near the beginning of this specification.Six of the series of bearing balls 5 are at one side of the datum plane X-X whilst the other six series are arranged symmetrically at the opposite side of said datum plane. This symmetrical arrangement is such, as will immediately be evident from a study of Fig. 3 of the drawings, that those six series of bearing balls 5 which are at one side of the plane X-X will all recirculate in one direction when the bearing is in use whilst the six series of bearing balls 5 which are at the opposite side of the same datum plane X-X will all recirculate in a second and opposite direction when the bearing is in use.Further study of Fig. 3 of the drawings will show that the twelve series of bearing balls 5 are not uniformly spaced apart from one another around the axis 3, those six series of bearing balls 5 which are above a radial plane Y-Y (as seen in Fig. 3 of the drawings) that contains the axis 3 being closer to one another than are the remaining six series of bearing balls 5 which are below said plane Y-Y as seen in Fig. 3. This arrangement has been found to increase the load carrying capability of the bearing, particularly when, as will be described below, segments of the bearing are removed from below the plane Y-Y (as seen in Fig. 3) to furnish the bearing in either the second or the third of the three forms which are discussed towards the beginning of this specification.In particular, when a bearing of the third form is to be provided, a minimum number of the series of bearing balls 5 has to be sacrificed when the pairs or grooves 4 are arranged in the manner which is under discussion.

The outer convex surface of the inner sleeve 2 is formed, at both its opposite ends, with screwthreads 7 (Fig. 2) and the left-hand screwthread 7, as seen in Fig. 2 of the drawings, co-operates with a matching internal screwthread of a locking ring 8. The external surface of the locking ring 8 is a close fit just inside the surrounding mouth of the cylindrical shell 1. It is emphasised that locking rings equivalent to the locking ring 8 may be provided at both axial ends of the inner sleeve 2 and that this enabies said inner sleeve to be adjusted axially relative to the surrounding shell 1 by turning the internally screwthreaded locking rings 8 relative to the external screwthreads 7 at the opposite ends of the sleeve 2. In cases in which vibration might lead to disadvantageous creeping of the locking rings 8 relative to the screwthreads 7, this can be prevented at the time of installation merely by using a commercially available thread locking preparation or, if preferred, by providing at least one retaining grub screw (not shown).

The right-hand end of the linear ball bearing as seen in Fig. 2 of the drawings is provided with an auxiliary fastening flange 9 (Figs. 1 and 2) which flange may take the place of one of the locking rings 8. The inner concave surface of the flange 9 is screwthreaded for co-operation with the screwthread 7 at one end of the inner sleeve 2 and this, of course, enables said flange 9 to be adjusted axially relative to the shell 1 and sleeve 2 to at least a limited extent. That side of the flange 9 which faces towards the shell 1 is formed with a blind annular recess 10 into which is received the corresponding axial end of the shell 1. However, the radial width of the blind recess 10 and its position relative to the shell 1 are such that clearances 11 exist between the external and internal surfaces of the shell 1 and the corresponding internal and external surfaces of the recess 10.The reason for this is to allow for tightening of the shell 1 and the inner sleeve 2 around a shaft when the bearing is provided in the second form that has been mentioned at the beginning of this specification and that will be referred to again below. The magnitude of the clearances 11 will, of course, depend upon the overall size of the bearing concerned. Three shouldered holes 1 2 are formed through the thickness of the auxiliary fastening flange 9 at 120 intervals around the axis 3 and these three holes 1 2 greatly assist in mounting the whole bearing in, for example, a machine frame with the aid of three machine screws which are entered therethrough. Clearly, the number and/or position of the holes 1 2 could be varied for particular applications.

Figs. 4 to 6 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 1 5. The machine frame 15, which is shown only diagrammatically in Fig.

4 of the drawings, carries a shaft support 1 6 that is of basically square cross-section, one corner (in cross-section) of the square being formed with a recess 1 7 which receives a hardened shaft 1 8 of circular cross-section.

There will usually be at least two linear ball bearings for the axially slidable support of the machine tool table 1 4 but only one such linear bearing, which is generally indicated by the reference 19, is diagrammatically illustrated in Figs. 4 to 6 inclusive. The bearing 1 9 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.Fig. 3 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 1 9 that is diagrammatically illustrated in Figs. 4 to 6 inclusive. It is noted that the shaft 1 8 is retained in the recess 1 7 of the shaft support 1 6 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 1 8 and has a head 22 at its outermost end, the shape of the or each head 22 being illustrated in Fig. 4 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 1 8 is entered into a substantially cylindrical cavity 23 in the shaft support 16, the frusto-conically tapering surface of the head 22 being engaged by two perpendicularly opposed set screw 24 that are received in corresponding internally screwthreaded bores in the shaft support 16.It is advantageous for the shaft 1 8 to be supported by the two perpendicularly opposed surfaces of the recess 1 7 since high lateral loading upon the shaft 1 8 can then be tolerated and the formation of the recess 1 7 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 1 7. The use of at least one stud 21 and at least two perpendicularly opposed set screws 24 to connect the shaft 1 8 rigidly to the support 1 6 is also simple and convenient since the shaft 1 8 can be offered up to the support 1 6 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 1 5 or other fixed member from beneath. It will be appreciated that the arrangement which can be seen best in Fig. 4 of the drawings constitutes, in effect, a "secret" fixing of the shaft 1 8 relative to the support 1 6. 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 1 8 from its support 16.

The "missing" segment of the or each linear ball bearing 1 9 has a magnitude that is marginally in excess of 90 in order to permit the shaft 1 8 to bear against the two perpendicularly opposed surfaces of the recess 1 7 as discussed above leaving a small clearance as can be seen best in Fig. 4 of the drawings.In fact, the relative sizes of the shaft 1 8 and the recess 1 7 in the support 1 6 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 1 7 are located just inwardly from the corresponding edges of the recess 1 7 in the support 1 6 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 1 8 but, as an alternative, and particularly where heavy loads are to be carried, the support 1 6 may be in the form of a continous or substantially continuous rail.

Figs. 4 to 6 of the drawings illustrate a single shaft support 1 6 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 cylindrical shell 1 of the linear ball bearing 19 (illustrated in Figs. 4 to 6 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 Figs. 5 and 6) can be firmly but releasably secured by bolts or the like.Although the "missing" segment of the bearing in the third form thereof advantageously, for most purposes, subtends an angle of substantially 90 at the axis 3 as depicted by the radial lines 20 in Fig. 3 of the drawings, a "missing" segment which subtends an angle of only 60 at the axis 3 is sufficient for some purposes and said segment is shown in Fig. 3 of the drawings as lying between one of the radial lines 20 and a radial line 20A.It will be noted that, as seen in Fig. 3, both the 90 (missing" segment between the lines 20 or the 60 "missing" segment between one of the lines 20 and the line 20A lie beneath the radial plane Y-Y, said segments being so disposed that, in the case of the removal of the substantially 90 segment, only three of the series of bearing balls 5 will be omitted from the total of twelve whereas, in the case of the smaller "missing" segment of substantially 60 around the axis 3, only two of the series of bearing balls 5 are omitted from the total of twelve such series.

Referring once again to Fig. 3 of the drawings, that Figure shows two lines 1 3 which extend substantially, although not necessarily exactly, radially with respect to the axis of linear displacement 3. When the linear ball bearing of Figs. 1 to 3 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 and 2 that lies between the two lines 1 3 as shown in Fig. 3 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 cylindrical 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 1 3 against the strong resilient opposition of the parts 1 and 2 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.As discussed above, the clearances 11 between the walls of the blind annular recess 10 and the end of the shell 1 which they surround are sufficient to allow such adjustments to eliminate bearing play without interfering with the fastening of the bearing in a machine frame or the like by means of the flange 9 and the bolts which co-operate with the shouldered holes 12 therein.

Although a bearing in accordance with the invention will usually be formed wholly or principally from at least one metallic material, this is by no means essential and any one or more of the parts 1, 2, 8 and 9 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 grooves 4 are formed by machining in the case of a metallic construction or by moulding and a finishing step in the case of a polyamide or other synthetic plastics construction.

The grooves 4 are, it is noted, strictly radial with respect to the axis 3 and can thus be very easily formed by conventional machining or moulding techniques.

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 substantially wholly by a series of flats. Thus, such linear ball bearings could co-operate readily with support surfaces of square or oblong cross-section or with support surfaces that are basically of square or oblong cross-section but which also include curved portions.

Claims (21)

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 tangential recirculation paths (as herein before defined), and wherein those series of bearing balls which are at one side of a strictly radial datum plane that contains the axis of linear displacement of the bearing are arranged so that the balls therein will all recirculate in one direction when the bearing is in use whilst those series of bearing balls which are at the opposite side of the same datum plane are arranged so that the balls therein will all recirculate in a second and opposite direction when the bearing is in use, and wherein an inner sleeve of said bearing which wholly or partly defines the recirculation paths for said series of bearing balls is formed at both of its axial ends with screwthreaded portions for purposes of mounting and/or axial adjustment of the bearing.

2. A linear ball bearing as claimed in claim 1, wherein said plurality of series of bearing balls are arranged symmetrically at opposite sides of the strictly radial datum plane.

3. A linear ball bearing as claimed in claim 1 or 2, wherein said plurality of series of bearing balls are arranged asymmetrically at opposite sides of a strictly radial plane that contains the axis of linear displacement of the bearing and that is perpendicular to said datum plane.

4. A linear ball bearing as claimed in claim 3, wherein those series of bearing balls which are located at one side of the radial plane which is perpendicular to the datum plane are spaced apart from one another by greater distances than are those series of ball bearings which are disposed at the opposite side of said radial plane which is perpendicular to the datum plane.

5. A linear ball bearing as claimed in any preceding claim, wherein the bearing includes at least one locking ring having a screwthread which is arranged to co-operate adjustably with the screwthreaded portion at one end of said inner sleeve and also with the surrounding end of an outer shell of the bearing.

6. A linear ball bearing as claimed in any preceding claim, wherein the bearing includes at least one auxiliary fastening flange which flange is internally screwthreaded for adjustable co-operation with the screwthreaded portion at one end of said inner sleeve.

7. A linear ball bearing as claimed in claim 6, wherein one side of the auxiliary fastening flange is formed with a blind recess which receives the adjoining end of an outer shell, or of said outer shell, of the bearing, said end of the outer shell being received in said recess with clearance at both the radially inner and radially outer sides thereof.

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

9. A bearing as claimed in any one of claims 1 to 7 and being of substantially square or substantially oblong cross-section.

1 0. A bearing as claimed in any one of claims 1 to 8, 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 a'n adjustable extent.

11. A bearing as claimed in claim 10, 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.

1 2. A bearing as claimed in any one of claims 1 to 9, 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 supporting of that shaft.

1 3. A linear ball bearing as claimed in claim 12, wherein the omitted segment subtends an angle of substantially 60 at the axis of linear displacement of the bearing.

14. A bearing as claimed in claim 12, wherein the omitted segment subtends an angle which is marginally in excess of 90 at the axis of linear displacement of the bearing.

1 5. An assembly of a shaft mounting, a shaft and a linear ball bearing as claimed in claim 14, wherein the shaft mounting comprises at last 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.

16. An assembly as claimed in claim 15, 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.

1 7. An assembly as claimed in claim 1 5 or 16, 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.

18. An assembly as claimed in claim 17, 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.

1 9. An assembly as claimed in any one of claims 1 5 to 18, wherein the shaft mounting takes the form of a rail that is continuous or substantially continuous throughout the length of said shaft.

20. A linear ball bearing substantially as herein before described with reference to Figs.

1 to 3 of the accompanying drawings.

21. An assembly of a shaft mounting, a shaft and a linear ball bearing as claimed in any one of claims 12, 13, 14 or 20, the shaft mounting being substantially as hereinbefore described with reference to Figs. 1 to 6 of the accompanying drawings.