Retainer for use in a linear motion rolling contact guide unit

A retainer for use in a linear motion rolling contact guide unit including a rail, a slider and a plurality of rolling members interposed between the rail and the slider is provided. The retainer is generally comprised of an elongated rectangular plate having a predetermined thickness and width. The retainer plate is formed with a plurality of pockets for receiving therein rolling members so as to keep the rolling members in position. In accordance with the present invention, the pockets have a first size in the transverse direction slightly larger than the characteristic size, e.g., diameter in the case of balls, of rolling members and a second size in the longitudinal direction substantially larger than the first size so that the pockets are generally in the shape of a slot with either a circular pocket provided in a central portion of the plate or the second size being large enough to accommodate two balls with a separator therebetween. With this structure, the sliding resistance of the retainer and thus the linear motion guide unit is significantly reduced.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention generally relates to a linear motion rolling contact guide 
unit, and, in particular, to a retainer for use in a finite stroke type 
linear motion rolling contact guide unit for retaining its rolling members 
in position. 
2. Description of the Prior Art 
A linear motion rolling contact guide unit is well known in the art, and, 
it generally includes a rail extending straight over a desired length, a 
slider slidably mounted on the rail and a plurality of rolling members 
interposed between the rail and the slider. Such a linear motion rolling 
contact guide unit can be either of the infinite stroke type or of the 
finite stroke type. In the former case, an endless circulating path, in 
which the rolling members are provided, is provided between the rail and 
the slider so that theoretically an infinite relative motion can be 
provided between the rail and the slider as long as the rail extends. On 
the other hand, in the latter case, only a straight guide channel is 
provided between the rail and the slider in which the rolling members move 
rolling back and forth so that only a finite stroke can be provided for a 
relative movement between the rail and the slider. 
A finite stroke type linear motion rolling contact guide unit for which the 
present invention can be advantageously applied is illustrated in FIGS. 6 
and 7. As shown, the finite stroke type linear motion rolling contact 
guide unit includes a bed or rail 28 extending straight over a desired 
length and having a generally rectangular cross section, a table or slider 
29 slidably mounted on the rail 28, and a plurality of rolling members or 
balls 31 in the illustrated embodiment interposed between the rail 28 and 
the slider 29. 
The rail 28 is formed with a pair of inner guide grooves 35 located one at 
each side surface thereof and extending in parallel with the longitudinal 
axis of the rail 28. The slider 29 has a horizontal section extending 
horizontally over the rail 28 and a pair of vertical sections each 
depending from a corresponding side of the horizontal section and spaced 
apart from the associated side surface of the rail 28. An inner guide 
groove 34 is formed at an inner side surface of each of the vertical 
sections of the slider 29 in an opposed relationship with the associated 
inner guide groove 35 to thereby define a straight guide channel between 
the rail 28 and the slider 29. 
A plurality of balls 31 as rolling members are provided in each of the 
guide channels such that they are partly received in each of the 
oppositely arranged inner and outer guide grooves 35 and 34. Also provided 
in each of the guide channels is a retainer 30 for retaining the balls 31 
spaced apart from each other and in position. The retainer 30 includes an 
elongated plate formed with a plurality of pockets 32 spaced apart from 
each other at an equal interval each receiving therein one of the balls 31 
rotatably. The balls 31 may be maintained in position in the guide channel 
by the retainer 30 even if the slider 29 moves relative to the rail 28. 
However, since each of the pockets 32 is substantially identical in shape 
and size, and the pockets 32 are circular in shape and approximately equal 
to the diameter of the balls 31 with a slight gap therebetween so as to 
allow the ball 31 to rotate therein. 
However, such a structure has been found to be disadvantageous in some 
cases, in particular when used under a preloaded condition, because of an 
increased sliding resistance between the rail 28 and the slider 29. When 
preloaded, the internal gap between the balls 31 and each of the rail 28 
and the slider 29 is set to be negative in value as shown in FIGS. 6 and 
7, and a linear motion guide unit having such a preloaded condition can 
provide an enhanced accuracy and smooth operation. Several causes are 
possible in increasing the sliding resistance, such as a slight error in 
the degree of parallelism between the inner and outer guide grooves 35 and 
34, variations in the lubricating condition along each of the guide 
channels; however, no truly viable solution to keep the sliding resistance 
lower has been proposed prior to the present invention. It is the present 
inventor that has pinpointed the major reason for an increase of the 
sliding resistance as a result of an extensive study regarding the causes 
of an increase of the sliding resistance between the rail and the slider. 
That is, according to the study made by the present inventor, it has been 
found that an interaction between the rolling members, typically balls or 
rollers, and the retainer plays an important role in the increase of the 
sliding resistance between the rail and the slider. 
Therefore, there has been a need to provide an improved retainer which can 
allow to keep the interaction with the rolling members as small as 
possible to thereby keep the sliding resistance of a linear motion guide 
unit as low as possible at all times. In addition, after using a linear 
motion guide unit for some time, there may occur a case in which the 
distance between the center line or longitudinal axis of the rail 28 or 
slider 29 and the center line of the retainer 30 vary or fluctuate, which 
is disadvantageous because of a degradation of the accuracy in linear 
motion. Thus, there also has been a need to solve such a problem. 
SUMMARY OF THE INVENTION 
In accordance with the present invention, there is provided an improved 
retainer for use in a linear motion guide unit for retaining rolling 
members in position. In one embodiment, the retainer includes an elongated 
plate provided with a plurality of windows or pockets, at least some of 
which have a first size larger than the diameter of the rolling member in 
its transverse direction and a second size substantially larger than the 
first size in its longitudinal direction in parallel with the longitudinal 
axis of the elongated plate. Preferably, all of the pockets have a slot 
shape defined by the first and second sizes. In one modification, the 
second size increases gradually toward each end of the elongated plate. 
Preferably, the first size is slightly larger than the diameter of the 
rolling members. In another modification, the second size has a plurality 
of values. In a further modification, the second size is set to be large 
enough to receive two or more rolling members. In a still further 
embodiment, when the second size of the pocket is large enough to locate 
two or more rolling members in one pocket, the pocket is formed with at 
least one inwardly extending projection to separate any two adjacent 
rolling members. 
With provision of the present retainer in a linear motion guide unit, when 
the slider moves relative to and along the rail as shown in FIGS. 6 and 7, 
the rolling members also move relative to the rail and along the rail 
generally at a speed half of that of the slider. Thus, the retainer also 
moves at a speed same as the average speed of the centers of the rolling 
members relative to the rail. In this instances, the travelling speeds of 
individual rolling members may vary depending on various reasons, such as 
slight differences in size of rolling members, variations of planarity 
along the guide channel and variations of lubricating conditions along the 
guide channel. In such a situation, if the pockets of the retainer for 
receiving therein rolling members were identical in shape and size and 
approximately the same as that of the rolling members as in the prior art, 
the rolling members would immediately interact with the retainer, so that 
a significant sliding resistance could be present between the rolling 
members and the slider at all times. However, with the provision of the 
present retainer, a retainer is so structured that the number of the 
rolling members which may come into interaction with the retainer at the 
same time is reduced, and the sliding resistance can be maintained at a 
lower level at all times. 
It is therefore a primary object of the present invention to provide an 
improved linear motion rolling contact guide unit having a reduced sliding 
resistance. 
Another object of the present invention is to provide an improved retainer 
for use in a linear motion guide unit. 
A further object of the present invention is to provide an improved 
retainer for use in a linear motion rolling contact guide unit of the 
finite stroke type capable of keeping the sliding resistance of the guide 
unit at lower a level. 
Other objects, advantages and novel features of the present invention will 
become apparent from the following detailed description of the invention 
when considered in conjunction with the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring now to FIG. 1, there is schematically shown a part of a retainer 
2 constructed in accordance with one embodiment of the present invention. 
As shown, the retainer 2 is generally comprised of an elongated plate 
having a predetermined thickness and width such that it may be 
advantageously provided in a guide channel defined by a pair of associated 
inner and outer guide grooves as described with reference to FIGS. 6 and 7 
above. 
The retainer plate 2 illustrated in FIG. 1 is formed with a plurality of 
windows or pockets 3 spaced apart from one another as arranged along a 
longitudinal axis thereof. Preferably, these pockets 3 are provided at a 
predetermined interval, though the present invention should not be limited 
only to such a regularly spaced arrangement. Each of the pockets 3 has a 
first size B in the transverse or widthwise direction of the elongated 
retainer plate 2 and a second size L in the longitudinal direction, i.e., 
normal to the transverse direction, of the elongated retainer plate 2. A 
ball 3 having a diameter D as a rolling member is rotatably provided in 
the associated pocket 3. In the present embodiment, the first size B of 
the pocket 3 is set larger, preferably slightly larger, than the diameter 
D of the ball 3 and the second size L of the pocket 3 is set substantially 
larger than the first size B. As a result, generally speaking, the pocket 
3 has a shape of a slot or an oval shape. It is to be noted that according 
to the principle of the present invention, it is not necessary for all of 
the pockets 3 have such a slot-shaped pocket 3, but it is sufficient that 
at least some of these pockets 3 of the elongated retainer plate 2 have 
such a slot shape. 
With the provision of such slot-shaped pockets 3, the number of balls 3 
which come into sliding contact with the ends of the associated pockets 3 
during a relative motion between the rail and the slider can be reduced so 
that the sliding resistance between the balls 3 and the retainer 2 and for 
that matter between the rail and the slider can be maintained at a low 
level at all times. In addition, since there is less chance for the balls 
1 coming into contact with the ends of the associated pockets 3 during 
operation, the wear is reduced and the possibility of shift in position of 
the retainer 2 in a guide channel and thus relative to the rail and the 
slider is reduced. Therefore, it is possible to maintain the sliding 
performance at a constant for an extended period of time. 
Now, turning to a retainer 4 constructed in accordance with another 
embodiment of the present invention shown in FIG. 2, the retainer 4 is 
basically comprised of an elongated plate having a predetermined thickness 
and width and it is also formed with a plurality of windows or pockets 5, 
5A, 5B, 5C, . . . etc. spaced apart from each other as arranged along the 
longitudinal axis of the plate 4. In the present embodiment, the center 
pocket 5, which is located at the middle of the elongated plate 4, is 
substantially circular in shape and thus its first size B is substantially 
the same as its second size and larger, preferably slightly larger, than 
the diameter E of the ball 1 received therein. Those pockets 5A, 5B, 5C, . 
. . etc. which are located progressively further away from the center 
pocket 5 and thus toward the ends of the retainer plate 4 have second 
sizes M, N, P, . . . etc. which increase progressively as separated 
further away from the center pocket 5. All of the pockets 5, 5A, 5B, 5C, . 
. . etc. may have the same first size B, which is larger, preferably 
slightly larger, than the diameter E of the balls 1, or the first size B 
may also vary in a desired manner as separated further away from the 
center pocket 5, if desired. 
With the structure of the present embodiment also, the number of balls 1 
which may come into contact with the ends of the associated pockets can be 
decreased so that the sliding resistance between the balls 1 as rolling 
members and the retainer 4 and, therefore, between the rail and the slider 
can be significantly reduced and maintained at a low level at all times. 
As a modification of this embodiment, two or more pockets 5 having a 
substantially circular shape may be provided at the central portion of the 
elongated retainer plate 4, if desired. 
Now, referring to FIG. 3, there is also provided a retainer 6 constructed 
in accordance with a further embodiment of the present invention, and the 
present retainer 6 is also generally comprised of an elongated plate 
formed with a plurality of windows or pockets 7A, 7B, 7C, 7D, 7E . . . 
etc. each of which receives therein a ball 1 as a rolling member. In this 
embodiment, the pockets 7A, 7B, 7C, 7D, 7E, . . . etc. have substantially 
the same first size B, but they may have differing second sizes in a 
random fashion. That is, each of the pockets 7 may have a different second 
size, or, alternatively, some of the pockets 7 may have a first value of 
second size and some of the pockets 7 may have a second value of second 
size in a staggered or random fashion. In this case, the second size may 
have a value substantially equal to the value of the first size or a value 
larger than or significantly larger than the value of the first size. 
The structure of this embodiment also allows to keep the sliding resistance 
of a linear motion guide unit at a low level. 
Referring to FIG. 4, there is schematically shown a part of a retainer 8 
constructed in accordance with a still further embodiment of the present 
invention. The retainer 8 is similarly comprised of an elongated plate 
which is formed with a plurality of windows or pockets 9 spaced apart from 
each other and arranged along the longitudinal axis of the plate. In this 
embodiment, each of the pockets 9 has a first size which is larger, 
preferably slightly larger, than the diameter of the ball 1 and a second 
size Z which is substantially larger than the first size and enough to 
receive two balls 1. That is, the value of the second size Z is preferably 
set larger, preferably slightly larger, than a sum of the diameters D of 
the two balls 1 provided in the pocket 9. 
This embodiment also allows to keep the sliding resistance at a low level 
at all times since the number of balls 1 which may come into contact with 
the ends of the associated pockets 9 is decreased. In addition, since each 
of the pockets 9 receives therein two balls 1, its load bearing capacity 
is increased so that it is suitable for use in heavy duty environments. As 
a modification of this embodiment, the slot-shaped pockets 9 may have 
different values for the second size, if desired, as described above. As a 
further modification, each of the pocket 9 may also be so defined to 
receive therein three or more balls 1 and some of the pockets 9 may 
receive different number of balls 1. 
FIG. 5 illustrates a modification of the embodiment shown in FIG. 4. That 
is, the present retainer 10 also have an elongated pocket 11 which can 
receive therein two or more balls 1. However, in the FIG. 5 embodiment, 
the retainer plate 10 is provided with a separator 12 which projects into 
the pocket 11 from its periphery so as to keep the two adjacent balls 1 
separated away from each other and prevent them from coming into sliding 
contact. Thus, the value of the second size of each of the pockets 11 
should be set at a value which is larger than a sum of the diameters of 
the balls 1 received in the associated pocket 11. 
With the structure of the FIG. 5 embodiment, even the balls 1 in the same 
pockets can be prevented from interacting each other during operation, the 
sliding resistance can be decreased even more as compared with the FIG. 4 
embodiment just described above. 
As described above, in accordance with the present invention, since the 
number of rolling members which come into contact with the ends of 
associated pockets is decreased, the sliding resistance of the retainer 
and thus of a linear motion guide unit can be significantly decreased and 
maintained at a low level at all times. Since the interaction between the 
retainer and the associated rolling members is reduced, the retainer can 
be properly maintained in position in its associated guide unit at all 
times, which also contributes to keep the sliding resistance of a linear 
motion guide unit at a low level. Since the present retainer can be 
maintained properly in position in its associated guide channel, it is 
prevented from slipping away from the guide channel. 
Besides, in accordance with the present invention, even if there are 
errors, such as asperity or twist, in the planarity of the inner and/or 
outer guide grooves due, for example, to manufacturing tolerances or the 
like, such errors can be advantageously absorbed by the gap between the 
retainer pockets and the associated rolling members. Even if the rolling 
members are in a preloaded condition, since there is a predetermined gap 
between the rolling members and the retainer pockets and thus the number 
of the rolling members that may strongly interact with the retainer is 
reduced, the sliding resistance of the retainer and thus its associated 
linear motion guide unit can be maintained at a low level. 
While the above provides a full and complete disclosure of the preferred 
embodiments of the present invention, various modifications, alternate 
constructions and equivalents may be employed without departing from the 
true spirit and scope of the invention. For example, although use has been 
made of balls as rolling members in the above-described embodiment, use 
may also be made of rollers as rolling members. In the case where balls 
are used as the rolling members, its characteristic size is a diameter of 
the balls, whereas, in the case where use is made of rollers as the 
rolling members, the characteristic size can be either their height or 
their diameter. Therefore, the above description and illustration should 
not be construed as limiting the scope of the invention, which is defined 
by the appended claims.