Four track-type endless rectilinear motion guide unit

A four track-type endless rectilinear motion guide unit is provided wherein a slide unit is mounted on a track rail member with a plurality of parallel-arranged cylindrical rollers being intervened therebetween for endless circulation. The four endless circulation passages for rollers, viz., a pair of lower and upper passages on each of the opposing sidewalls of the track rail member are arranged such that, as seen in a cross section of the slide unit, their longitudinal axes cross each other at right angles, while the two endless circulation passages differ from each other in size providing a longer endless circulation passage having a larger cross section and a shorter endless circulation passage having a smaller cross section, which are arranged such that the longer circulation passage encompasses the shorter circulation passages within the loop, but the lengths of the load-carrying trackway surfaces of said two circulation passages are the same. Thus is provided a four track-type endless rectilinear motion guide unit wherein the construction of the slide unit is particularly made simple and compact, consisting of the least possible number of parts thus eliminating any assembly error, while the load capacities of the upper and lower trackways are made desirably adjusted, yet minimizing the longitudinal length, as a whole, of the endless circulation passage to be formed in the slide unit.

BACKGROUND OF THE INVENTION 
1. Field of The Invention 
The present invention relates to an endless rectilinear motion guide unit, 
wherein a pair of lower and upper load-carrying trackways having different 
widths are formed on each side of a track rail member, viz., four 
trackways in all on both sides thereof and, on the inner sidewall of a 
slide unit are also formed the corresponding number of lower and upper 
load-carrying trackways for mating in size and position with said four 
load-carrying trackways of the track rail member, so that the slide unit, 
upon having been assembled in straddling relation with said track rail 
member with a plurality of cylindrical rollers being arranged in parallel 
with one another between the mating trackways, can freely and 
rectilinearly move on said track rail member with the desired load 
capacity ratio between the lower and upper trackways. 
In more details, the present invention provides an endless rectilinear 
motion guide unit wherein in each of the opposing sides of the slide unit 
are provided two endless circulating passages having different sizes, 
viz., a longer passage having a larger cross section and a shorter passage 
having a smaller cross section, which are so arranged, as seen in a cross 
section thereof, that their longitudinal axes cross each other at right 
angles, while the longer circulation passage having a larger cross section 
encompasses, within the loop, the shorter circulation passages having a 
shorter cross section, but the lengths of the load-carrying trackway 
surfaces of said two circulation passages are the same. 
2. Prior Arts 
German Utility Model Application No. 1971845 and Japanese Patent 
Application Publication No. 24646-1987 each disclose and endless 
rectilinear motion guide unit having four trackways along and through 
which a plurality of parallel-arranged cylindrical rollers move. 
However, the prior units have the following inherent disadvantages: 
In case of the German Utility Model, for example, two endless circulation 
passages having different sizes are formed on each side of the slide unit, 
which are so arranged that a longer passage having a larger cross section 
encompasses within the loop, a shorter passage having a smaller cross 
section but due to the difference in length of the load-carrying trackway 
surfaces, load capacities of the two passages differ from each other as 
the result with the shorter one having a shorter effective life, so that 
the prior art unit can find only limited utility. 
In case of the Japanese patent application, two endless circulation 
passages are provided in each of the opposing sides of the slide unit, 
which are linked each other like a chain so that through the load-carrying 
trackways of the two passages are the same in length, the longitudinal 
length as a whole of the associated endless circulation passages becomes 
greater, inevitably resulting in an enlargement of the unit as a whole. 
Furthermore, each of the above-mentioned prior rectilinear motion guide 
units has limited utility due to the limited load capacity, particularly 
for use in the case where a greater load capacity is required in the 
downward direction. 
SUMMARY OF THE INVENTION 
The object of the present invention therefore is to provide a four 
track-type endless rectilinear motion guide unit wherein the 
above-mentioned disadvantages of the prior art units can be eliminated, 
while load capacities of the lower and upper load-carrying trackways are 
made desirably adjusted depending on the particular uses, yet minimizing 
the longitudinal length, as a whole, of the endless circulation passages 
to be formed in the slide unit. 
Further, in case of the upper and lower endless circulation passages, where 
the upper one, for example, is used for circulating cylindrical rollers 
having a smaller diameter, while the lower one for those having a larger 
diameter, the endless rectilinear motion guide unit exhibits a marked load 
capacity against downwardly directed loads, so that the present invention 
provides a four track-type endless rectilinear motion guide unit capable 
of meeting various operating conditions required. 
Further object of the present invention is to provide a four track-type 
endless rectilinear motion guide unit wherein two endless circulation 
passages which cross at right angles in the slide unit have center points 
of the loops displaced by some distance from each other as seen in a cross 
section of the slide unit, thereby reducing the width of the smaller 
circulation passage in the slide unit, as the result, increasing the 
distance (l in FIG. 8) between the lower surface of the slide unit and the 
lower surface, viz., fitting surface of the track rail member assembled 
therewith. 
Further object of the present invention is to provide a four track-type 
endless rectilinear motion guide unit wherein the construction of the 
slide unit is particularly made simple and compact, consisting of the 
least possible number of parts, while eliminating any assembly error and 
thus obtaining high precision units. 
According to the endless rectilinear motion guide unit of the present 
invention, a pair of lower and upper load-carrying trackways having the 
same lengths but different widths are formed on each of the opposing inner 
sidewalls of a slide unit, more specifically of the opposing inner 
sidewalls of an inner recess having an inverted U-shaped cross section 
provided underside thereof, four trackways in all are formed on both the 
inner sidewalls with said pair of load-carrying trackways on the same side 
forming parts of two endless circulation passages having different cross 
sectional areas in each of the opposing sides of the slide unit, and, said 
two endless circulation passages, as seen in a cross section thereof, 
being so arranged that their longitudinal axes cross each other at right 
angles, while the lengths and widths of the two endless circulation 
passages differ from each other such that the longer circulation passage 
having a larger cross section encompasses, within the loop, the shorter 
circulation passages having a smaller cross section but the lengths of the 
load-carrying trackway surfaces of said two circulation passages are made 
the same.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to FIG. 1, a slide unit 2 having a generally an inverted U-shaped 
cross section straddles with its recess having an inverted U-shaped cross 
section 7 on an elongated rod-shaped track rail member 1 having a 
generally I-shaped cross section with a plurality of parallel-arranged 
cylindrical rollers being intervened betweeen said track rail member 1 and 
slide unit 2. 
Referring to FIG. 1, on each side of the track rail member 1 is formed a 
longitudinally extending groove 8 defining a pair of load-carrying 
trackway surfaces 9 at and along the laterally opposing edge portions 
thereof which are inclined in themselves at an angle of 45.degree. 
symmetrical to said groove 8. 
The slide unit 2, as shown in FIG. 2, consists of a casing 3 forming the 
upper part thereof and a pair of leg-shaped trackway members 4 depending 
from the opposing end portions of said casing 3 as shown in the 
perspective view of FIG. 6, thus defining thereunder a recess 7 having an 
inverted U-shaped cross section between said pair of trackway members 4 
with which the slide unit 2 straddles on the track rail member 1 as shown 
in FIG. 1. 
The slide unit 2, in more details, further consists of a pair of sidewall 
retainers 18 each adapted to be fitted onto the inner sidewall of the 
trackway member 4 (FIG. 2 and FIG. 7), bottom wall retainer 16 and side 
panel 6 both of which are adapted to be fitted onto the bottom and 
sidewalls, respectively, of each of the trackway member 4 (FIGS. 1, 3 and 
4) and return passage covers 15 to be fitted onto the opposing outer wall 
of the trackway member 4 so that the rollers enclosed in the respective 
endless circulation passages formed in the slide unit do not fall off 
therefrom with the aid of said bottom wall retainer 16 and sidewall 
retainer 18, even if the slide unit 3 is removed from the track rail 
member 1. 
Facing the rail-side trackway surfaces 9 are formed trackway surfaces 10 on 
the innerwall surface of the inner recess 7 of the slide unit 2, more 
specifically, of each of the trackway members 4 as shown in FIGS. 2 and 6, 
thereby to form load-carrying trackways for rollers between the rail side 
trackway surfaces 9 and slide unit side trackways surfaces 10. These 
load-carrying trackways each form part of the endless circulation passage 
formed in the slide unit 2 as shown in FIGS. 2, 3 and 4, which together 
with a pair of direction changing passages (11' or 12') connecting the 
opposing ends of the load-carrying trackway portion and a return passage 
connecting the ends of the direction changing passages, can form a 
complete endless circulation passage. 
In FIG. 3 is shown the shorter endless circulation passage 11 having a 
smaller cross-sectional diameter as seen from the direction indicated by 
arrow lines A--A in FIG. 2, including opposing shorter direction changing 
passages 11' each consisting of a curved portion and adjoining straight 
portions thereby reducing the longitudinal length of the shorter endless 
circulation passage 11 as a whole, so that the shorter endless circulation 
passage 11 having a smaller cross section can be completely encompassed 
within the loop of the longer endless circulation passage having a greater 
cross section 12 including the longer direction changing passage 12' each 
consisting of a single semicircular arc portion, yet the longitudinally 
extending straight portions of both the endless circulation passages 11 
and 12 as well as the lower and upper load-carrying trackways can be made 
equal in length, each of which is formed by the mating rail-side trackway 
surface 9 and slide unit-side trackway surface 10 shown in FIG. 3 and FIG. 
4. Thus, a four track-type endless rectilinear motion guide unit can be 
provided with endless circulation passages each having not only different 
load capacity but also a shorter longitudinal length as a whole. 
FIG. 2 is a cross section of the right half of the present unit taken along 
line II--II on FIG. 1, and FIG. 6 is a perspective view of the trackway 
member 4, each illustrating the shape in details thereof. On both the 
longitudinally extending sides of the trackway member 4 are formed a 
plurality of right angle V-shaped grooves, wherein the inner sidewall of 
the trackway member 4 has an upper and lower right angle V-shaped grooves, 
each consisting of two flat surfaces adjoining at a right angle, one of 
which forms a slide unit-side trackway surface 10 arranges in facing 
relation with the related rail-side trackway surface 9, leaving the other 
surface as a guide surface 17 with which end surfaces of rollers are 
brought into contact while they are travelling therealong. It should be 
noted that one of the above-mentioned upper and lower right angle V-shaped 
grooves is made greater than the other in width so that it is adapted to 
receive cylindrical rollers having a larger diameter. 
On the outer sidewall of the trackway member 4, viz., the surface opposite 
to that facing the track rail member 1 (FIG. 2) are also formed an upper 
right angle V-shaped groove and a lower right angle V-shaped groove which 
in turn form the innerwall surfaces 14 of roller return passages. 
As shown in FIG. 7, the sidewall retainer 18 to be fitted onto the inner 
sidewall of the trackway member, has a generally trapezoidal cross section 
and is provided with longitudinally extending roller retaining ledges 19 
at and along the opposing bottom edges thereof, as well as a pair of 
relieved guide surfaces 17 extending in parallel with said roller 
retaining ledges 19, leaving a pair of longitudinally extending and 
laterally inclined surfaces 20 therebetween one for rollers having a 
larger diameter and the other for rollers having a smaller diameter so 
that the rollers travelling on and along the load-carrying trackway 
surfaces 10 can be effectively prevented from being subjected to skewing 
due to their end portions being kept in contact with and thus guided 
through by the laterally inclined surfaces 20 and relieved guide surfaces 
17 yet with reduced sliding resistance. 
Onto the inner sidewall surface of the trackway member 4, viz., the surface 
opposite to that facing the track rail member 1 is fitted a sidewall 
retainer 18 (FIG. 7) as mentioned above, while on the other sidewall 
surface is fitted a return passage cover 15 thereby to form closed return 
passages in the slide unit (FIGS. 1 and 2), thus these three members viz., 
sidewall retainer 18 (FIG. 7) the trackway member 4 (FIG. 6) and the 
return passage cover 15 (FIG. 1) are fastened together by means of a clamp 
bolt 23, thus forming a shorter and longer endless circulation passages in 
the slide unit 
In FIG. 3 is shown two endless circulation passages which are so arranged, 
as seen in a cross section of the slide unit, that their longitudinal axes 
cross each other at right angles, while as shown in FIG. 4, the 
longitudinal lengths of the two endless circulation passages differ from 
each other such that the longer circulation passage 12 encompasses the 
shorter circulation passage 11 within the loop as shown in FIGS. 3 and 4, 
but the lengths of the load-carrying trackway surfaces of said two 
circulation passages are the same, which is the very feature of the 
present invention. 
FIG. 5 shows a perspective view of a direction changing passage-forming 
spacer 13 that is a part used for the formation of the above-mentioned 
associated outside (longer) and inside (shorter) endless circulation 
passages 12 and 11 in such arrangement that their longitudinal axes cross 
each other at right angles as mentioned above. 
Namely, as seen in a cross section of the slide unit, the traffic 
controlling of the rollers travelling along and through the direction 
changing passages 11' and 12' of the respective shorter and longer endless 
circulation passages 11 and 12 can be effected by means of a pair of 
spacers arranged at the longitudinally opposing ends of the associated two 
endless circulation passages 11 and 12, which are embedded within the 
sidewall panels 6 of the slide unit 2. 
The direction changing passage-forming spacer has the shape of a low height 
cylinder diametrically cut in half thereby having a semicircularly curved 
periphery with a rectangular-shaped tunnel formed therein at the generally 
center portion thereof wherein a bridge member is snugly fitted at the 
lower part of said tunnel thus providing a curved periphery forming a 
longer direction changing innerwall surface 22 of the longer endless 
circulation passage 12 as well as a tunnel forming a shorter direction 
changing innerwall surface 21 of the shorter endless circulation passage 
11, respectively, with the longitudinal axes of the two direction changing 
surface 21 and 22 crossing perpendicular to each other. 
According to the present invention track endless rectilinear motion guide 
unit, it is preferred that the logner direction changing passage 12' for 
rollers having a larger diameter has a generally single arcuate shape, 
while the shorter direction changing passage 11' for rollers having a 
smaller diameter has a linear portion and arcuate portions connected to 
the opposite ends thereof but so long as a shorter endless circulation 
passage for rollers having a smaller diameter and a longer endless 
circulation passage for rollers having a larger diameter may be formed in 
such a particular arrangement as mentioned above, the shorter and longer 
direction changing passages employed therein may take any desired shapes. 
FIG. 8 is a cross section of a second embodiment of the present invention 
particularly illustrating a slide unit structure wherein casing, trackway 
member, and roller return passage cover have been integrally formed, so 
that the constructional parts for assembling a slide unit can be reduced 
in the number and the production error involved can be eliminated. 
In the second embodiment as shown in FIG. 8, the return passage of the 
longer endless circulation passage can be simply and precisely formed by 
firstly forming within the body of slide unit an elongated throughbore 
having a circular cross section and then cutting right angle V-shaped 
grooves on and along the inner surface thereof at the four symmetrical 
portions in the cross section to form four shallow corner grooves by which 
the end faces of rollers are smoothly guided. 
By forming the four tracks of endless circulation passages in such a 
special construction as mentioned above, the lengths of the respective 
load-carrying trackways of all the four endless circulation passages are 
made the same. 
Further, the lower and upper endless circulation passages to be formed in 
slide unit can be much shortened in length thereby enabling to obtain a 
compact size slide unit. 
Further, the direction changing passage is relatively simple in shape, thus 
it can be manufactured simply and at low costs on a mass production basis 
from synthetic resin according to conventional injection molding. 
Consequently, the present four track-type endless rectilinear motion guide 
unit can find a wide range utility. 
In the second embodiment of the present invention, as illustrated in FIG. 
8, the associated two endless circulation passages in each side of the 
slide unit, one for rollers having a larger diameter being longer in 
length than the other for rollers having a smaller diameter are so 
arranged that the center points A and B of the loops of the respective 
passages are displaced by some distance from each other as seen in a cross 
section of the slide unit thus enabling to shift the position of the 
longer endless circulation passage having a larger cross section upwardly 
in the slide unit, thereby increasing the distance as much as possible 
between the lower surface of the slide unit and the lower surface of the 
track rail member for facilitating the operation and application of the 
present invention motion guide unit for various purposes. 
Dependent on the purpose for which the present unit is used, the upper 
endless circulation passage in the slide unit may be used for rollers 
having a larger diameter with the lower one for rollers having a smaller 
diameter, so that in operation, the unit is used in an upside down 
fashion, viz., the track rail member 1 upside and the slide unit downside, 
yet with a greater load capacity being exhibited in the downward 
direction.