Linear bearing

The bearing is intended for incorporation in devices effecting linear motions along axles of round section. It comprises a monolithic prismatic cassette and ball chains, disposed inside continuous two-track grooves. These grooves are machined totally in the thickness of the cassette walls, and the non-working sectors of the ball chains are disposed close to the cassette edges and along said edges. The external surface of the cassette is enclosed by the internal surface of the sleeve which is of identical geometric shape. This design makes possible the increase of the number of ball chains disposed in one wall and, hence, of the load-carrying capacity of the bearing.

This invention relates to a linear bearing with ball chains, more 
particularly to a bearing for linear motion along axles of round section, 
which can find application in machinery, instrument engineering, robotics 
and other fields of industry. 
There are known bearings for linear motion along axles of round section 
with ball chains made-up of an external cylindrical sleeve and a 
monolithic polyhedral prismatic cassette. The cassette and the sleeve are 
provided with respectively formed recesses which form a continuous 
double-way conveying groove filled with balls which form a ball chain. The 
working sectors of the ball chain in bearings of such design are machined 
in the walls of the polyhedral prismatic cassette and, for this purpose, 
the groove in this sector has a depth corresponding to the ball size. The 
non-working sectors of the ball chain are in the area of the edges of the 
cassette and, therefore, the depth of the groove there is reduced and this 
reduction is compensated by V-shaped slots machined in the internal 
cylindrical wall of the sleeve opposite to the geometric position of the 
edges of the cassette. Thus, the one branch of the continuous double-way 
conveying groove is disposed totally in the cassette wall and the other 
branch--partially in the cassette wall and partially in the sleeve 
embracing it, where the V-shaped slots are machined. Thus, both branches 
of the groove are of different shape. 
Moreover, in the area where the ball chain passes from one to the other 
branch of the groove, i.e. from the working to the non-working sector and 
vice versa, there is machined a transition step, so that the balls can 
pass in the V-shaped slot of the sleeve where they perform their parasitic 
motion. 
It follows from the aforementioned that the ball chains in the working and 
the non-working sector are disposed in two different levels. 
A drawback of the described design lies in the reduced load carrying 
capacity and, hence, the reduced life of the bearing as a result of the 
irrational disposition of the grooves for the ball chains and, hence, of 
the balls themselves. 
Another design drawback of the described bearing lies in the necessity of 
machining transition steps in the double-way conveying groove where the 
balls pass from working to non-working state and vice versa. 
Moreover, the described design is not ensured against eventual overturning 
or slippage of the cassette with respect to the sleeve, and in case of 
such overturning or slippage the forces are taken up tptally by the balls 
which are in the V-shaped slots of the sleeve, which is a substantial 
drawback of the design. 
A drawback of the described bearing lies also in the variety of the used 
forms, this requiring diverse machining equipment and, particularly, the 
different geometric shape of both inscribed one into the other 
surfaces--the external of the cassette and the internal of the 
sleeve--result into an excess clearance which increases the overall size 
of the bearing. 
It is therefore a general object of this invention to avoid the 
aforementioned drawbacks and to develop a linear bearing with ball chains 
and, particularly, a bearing for linear motion along axles of round 
section which is featured by increased load-carrying capacity and life at 
equal overall sizes, which is ensured against overturning and slippage of 
the cassette and the sleeve one with respect to the other, and is featured 
by a simplified design and adaptability to manufacture. 
This object is achieved by a linear bearing and, more particularly, by a 
bearing for linear motion along axles of round section, which is made-up 
of an external cylindrical sleeve which embraces a monolithic polyhedral 
prismatic cassette, in which there are machined continuous two-track 
grooves containing balls which form ball chains, and the depth of the 
grooves in both branches is machined in such a way that the ball chains 
arranged in them lie in one and the same level and totally in the cassette 
wall. Within the range of the working sectors of the ball chain, the 
grooves are pierced with regard to establish a working contact between the 
balls and the axle. The non-working sectors of the ball chains are 
disposed close to the edges of the cassette and along said edges, and on 
both sides of each edge there is one non-working sector of the ball chain, 
so that their working sectors remain disposed close to the 
mid-perpendicular of the cassette wall. 
The object is also achieved by that the internal surface of the external 
cylindrical sleeve has a geometric shape identic to the geometric shape of 
the external surface of the monolithic polyhedral prismatic cassette and, 
as a result, the ball chains are covered by the plane areas of the 
identical walls of the internal polyhedral prismatic surface of the 
sleeve. 
The thus built-up linear bearing makes it possible to provide in each wall 
of the cassette, if necessary, more than one ball chain and, moreover, 
there is provided a possibility to bevel the sharp edges of the 
polyhedron, this ensuring a possibility for reducing the overall sizes of 
the bearing. 
The linear bearing according to the invention is featured by an increased 
load-carrying capacity, resulting from the possibility to incorporate in 
each wall of the polyhedral prismatic cassette more than one ball chain. 
On the other hand, the identity of the geometric shape of both inscribed 
one into the other surfaces--the external surface of the cassette and the 
internal surface of the sleeve--makes impossible any possibility of 
overturning or slippage between the sleeve and the cassette since it is 
hindered by the edges of the polyhedron. Moreover, the identity of both 
inscibed surfaces provides for a tight contact between them, thus also 
reducing the overall sizes of the bearing. 
The machining of both branches of the groovesfor the ball chains of one and 
the same depth and shape simplifies the technological process. Moreover, 
there is thus eliminated the necessity of a transition step in the area 
where the balls pass from working into non-working state because of the 
displacement of the ball chains totally in one and the same plane--the 
cassette wall. 
Besides the aforementioned advantages, the linear bearing according to the 
invention is featured by simple design and good adaptivity to manufacture, 
and its assembly and disassembly are convenient and easy. 
For a better understanding of the invention reference should be made to the 
accompanying drawings in which there is illustrated and described a 
preferred embodiment of the invention.

As seen in FIG. 1, the linear bearing consists of an external cylindrical 
sleeve 1 and a monolithic cassette 2 which is coaxially connected to the 
sleeve, i.e. when assembling the bearing, the cassette 2 is inserted 
inside the sleeve 1. 
The bearing is reinforced laterally by the limiting discs 3 and the locking 
rings 4. For limiting the bearing in service, there are provided grooves 5 
in both ends of the sleeve 1 in its external surface. 
The cassette 2 is shaped as a polyhedral prism. Hence, it is a monolithic, 
polyhedral prismatic cassette, which is illustrated in FIG. 1 as a 
monolithic hexahedral prismatic cassette, but it could also be a 
trihedral, quadrihedral, pentahedral etc. prismatic cassette. The optimum 
number of faces 7 of cassette 2 is of from 2 to 12 and it is chosen 
depending on the diameter of the round axle. Most suitable for axles with 
diameter smaller than 20 mm are trihedral to hexahedral cassettes, and for 
axles with diameter greater than 20 mm--pentahedral to 12-hedral 
cassettes. 
The cassette 2 is provided with a central hole 6 intended for the axle of 
round section (not shown in the figure). After insertion of an axle in the 
hole 6 there is obtained a complete bearing unit. Each wall 7 of the 
monolithic polyhedral prismatic cassette 2 contains at least one 
continuous two-track groove 8, machined lengthwise in the wall 7 of 
cassette 2. The continuous two-track groove 8 is machined in such a way, 
that its one linear sector 9 (FIG. 2 and FIG. 3) is disposed close to the 
edge 10 of cassette 2 along the same. The disposition of the second linear 
sector 12 of the two-track groove 8 depends on the total number of grooves 
8 in the wall 7. Hence, if each wall 7 of cassette 2 contains only one 
continuous two-track groove 8, the second linear sector 12 is disposed in 
the mid-perpendicular 13 of wall 7, as shown in FIG. 2. However, if the 
walls 7 of cassette 2 are provided with two grooves 8 each, the second 
linear sectors 12 are disposed close to the mid-perpendicular 13 of each 
wall 7 and symmetrically to both sides of the same, as shown in FIG. 3. 
Both linear sectors 9 and 12 are connected in their ends by circular 
sectors 14 and are divided apart by means of the insular part 15, which 
forms the internal wall 16 of the two-track groove 8, the external wall 17 
of which is formed by the thickness of wall 7 of cassette 2. The height of 
the insular part 15 is the same as that of the wall 7. 
Each continuous two-track groove 8 is filled with balls 18 (FIG. 1), which 
are arranged tightly one to another in the groove forming thus a ball 
chain 19. The size of the balls and, hence, of the groove depends on the 
standard size of the bearing, which for its part depends on the diameter 
of the round axle with which the bearing forms one unit. In principle, the 
linear bearing can be produced for axles with diameters of from 5 to 150 
mm. 
The continuous two-track groove 8 can be regarded as composed of two 
branches: one branch 25 for idle motion and the second branch 26 for 
working motion of the ball chain 19. At that, the basis of branch 25 of 
the groove for idle motionis compact, while that for branch 26 of the 
groove for working motion is a through hole 20. 
It becomes thus clear, that the branch 25 of the groove for working motion 
effects the functions of a working sector of the ball chain 19 thanks to 
the fact, that through the through hole 20 there is ensured the necessary 
contact between the ball chain 19 and the round axle. 
Thus, it should be understood that the working sectors 21 (FIG. 1) of the 
ball chain 19 is the position taken up by the balls 18 in the through hole 
20 at a given moment of time. Its non-working sector 22, respectively, 
will be determined by the position taken up by the balls 18 in the 
remaining portion of groove 8, i.e. the portion outside the through hole 
20 in given moment of time. 
It should be noted, that the working sector 21, as well as the non-working 
sector 22 of the ball chain 19 are in one and the same level, and that the 
necessary difference in the distance of these sectors from the round axle 
is achieved as a result of transposing the ball chain and of the 
continuous two-track groove 8, respectively, close to the cassette edge. 
Thus, each edge of the monolithic polyhedral prismatic cassette 2 is 
enclosed from both sides by the non-working sectors of the ball chains. 
In a preferred embodiment of the cassette 2 (FIG. 4) its edges 10 are 
beveled, thus forming plane sectors 11.This provides a possibility for 
reducing the overall size of the cassette and, hence, of the overall sizes 
of the bearing. 
Moreover, according to the invention, the internal surface 23 of the 
cylindrical sleeve 1 is identical to that of the external surface 24 of 
the cassette 2. Thus, there is ensured a tight inscribing of both surfaces 
23 and 24 one into the other and a covering of the non-working sectors of 
the ball chain by a plane sector, such as the opposite wall of the 
internal prismatic surface 23 of sleeve 1. The described inscription of 
surfaces 23 and 24 makes impossible any overturning or slippage of both 
basic parts of the bearing--the sleeve 1 and the cassette 2--one with 
respect to the other. 
There are also possible design variants of the linear bearing in which the 
integrity of the cylindrical shape is violated. More particularly, the 
bearing can be made-up as a "split 2" one by cutting the cassette 2 and 
the sleeve 1 through one of the walls 7 in a portion unoccupied by a 
groove 8. 
Another design variant of the linear bearing is the "open" linear bearing 
intended for mounting onto long axles which requires the use of supporting 
consoles (not shown in the drawings). In this design variant, the 
cylindrical sleeve 1 and the monolithic polyhedral prismatic cassette 2 
are connected in such a way, that one metal portion of them, in which one 
ball chain 19 has been incorporated, it taken out. It is possible to use 
for this type of bearings all types of polyhedral cassettes, with the 
exception of the trihedral and quadrihedral prismatic cassettes. 
The assembly of the aforedescribed linear bearing, according to the 
invention, is effected as follows: 
The continuous two-track grooves 8 are filled with balls. Then, the 
cassette with the balls arranged in it, which form ball chains, is 
introduced into the cylindrical sleeve 1, the internal surface of which 
has been previously shaped as a prism, identical to that of the cassette. 
Then, there are placed in both ends of the cassette in succession the 
limiting discs 3 and the locking rings 4. Thus, the bearing is ready for 
mounting on the round axle. When the bearing is mounted on the axle, the 
latter comes in contact with the working sector 21 of the ball chain 19, 
which is limited by the through hole 20, and the axle slips along the 
balls 18.