Guide for the uniform bearing of a load in four directions and a reciprocating table including the same

A four-directional load bearing guide having an improved rigidity against a vertical, horizontal or momental load, and thereby maintaining an improved accuracy in position of a bearing body relative to a track during a reciprocating motion. Each of ball rolling surfaces on at least one of the track and the bearing body is defined by a groove having the shape of a Gothic arch in cross section, and consists of two curved surfaces joined together, and so positioned that a vertical or horizontal load bearing upon the guide may act upon one or the other of the curved surfaces substantially in the direction in which the load bears upon the guide.

FIELD OF THE INVENTION AND RELATED ART STATEMENT 
This invention relates to a guide for the uniform bearing of a load in four 
directions which is used, for example, on the sliding surface of a table 
saddle, or machining center in a machine tool, or on that part of a 
conveying apparatus which supports a heavy object and reciprocates, and to 
a reciprocating table including such a guide. 
A known guide for the uniform bearing of a load in four directions is 
disclosed in Japanese Patent Publication No. 38812/1982. It is generally 
shown at 40 in FIG. 11 of the accompanying drawings, and comprises a track 
42 having two ball rolling surfaces 44 formed in each of a pair of 
opposite sides thereof, a bearing body 46 having a concavity 50 for 
fitting the track 42, and formed on its inner surface with a total of four 
ball rolling surfaces 48 each facing one of the ball rolling surfaces 44 
of the track 42, and a multiplicity of balls 52 held between the ball 
rolling surfaces 44 of the track 42 and the corresponding ball rolling 
surfaces 48 of the bearing body 46. 
Each of the ball rolling surfaces 44 and 48 is defined by a groove having 
the shape of a single arc in cross section and has a radius of curvature 
which is substantially equal to the radius of the balls 52. The balls 52 
and the ball rolling surfaces 44 and 48 form load acting lines L each 
having an angle of 45.degree. to the horizontal. 
FIG. 12 shows another known guide for the uniform bearing of a load in four 
directions that is disclosed in Japanese Utility Model Publication No. 
24258/1988. The guide comprises a track 62 having ball rolling surfaces 
64, a bearing body 66 having ball rolling surfaces 68, and balls 72 held 
therebetween. Each ball rolling surface 64 of the track 62 is defined by a 
groove having the shape of a Gothic arch in cross section and consists of 
two curved surfaces 64a and 64b joined together. Likewise, each ball 
rolling surface 68 of the bearing body 66 is defined by a groove having 
the shape of a Gothic arch in cross section and consists of two curved 
surfaces 68a and 68b joined together. The balls 72 and the ball rolling 
surfaces 64 and 68 form load acting lines each having an angle of 
45.degree. to the horizontal, as in the device shown in FIG. 11. 
As the load acting lines lie at the angle of 45.degree. to the horizontal, 
however, the guide shown in FIG. 11 is too low in rigidity against a 
momental load to be suitable for uniaxial use, though it may be able to 
bear uniformly any load acting upon it vertically or horizontally. 
Moreover, it is likely that a load acting vertically or horizontally upon 
the guide may cause a change in the points of contact between the balls 
and the ball rolling surfaces, and thereby the displacement of the bearing 
body in the direction of the load and away from its accurate position 
relative to the track. 
The guide shown in FIG. 12 has likewise the drawback which is due to the 
load acting lines lying at the angle of 45.degree. to the horizontal. A 
load acting upon it vertically or horizontally is likely to cause the 
displacement of the bearing body away from its accurate position relative 
to the track. 
When a guide of the type under consideration is used, its track is fixed to 
a bed, and its bearing body to a table, and the guide is used to guide the 
reciprocating motion of the table in a straight line along the bed. No 
accurate reciprocating motion of the table has, however, been realized by 
any known guide, since the load acting upon it causes the displacement of 
the bearing body, as hereinabove stated. Therefore, a machine tool in 
which such a table is employed has been likely to make a significant 
dimensional error in machining a workpiece. 
OBJECTS AND SUMMARY OF THE INVENTION 
Under these circumstances, it is a first object of this invention to 
provide a four-directional uniform load guide which has a sufficiently 
improved rigidity against any momental load to be suitable for uniaxial 
use, and a drastically improved accuracy in the relative positions of a 
bearing body and a track in the direction of any load. 
It is a second object of this invention to provide a reciprocating table 
which can perform an accurate reciprocating motion. 
The first object of this invention is attained by a four-directional 
uniform load guide which comprises a track having a plurality of ball 
rolling surfaces formed on its outer surface, a bearing body having a 
concavity for fitting the track, and formed on its inner surface with a 
plurality of ball rolling surfaces each facing one of the ball rolling 
surfaces on the track, and a multiplicity of balls held between the ball 
rolling surfaces on the track and the corresponding ball rolling surfaces 
on the bearing body, each of the ball rolling surfaces on at least one of 
the track and the bearing body being defined by a groove having the shape 
of a Gothic arch in cross section, and consisting of two curved surfaces 
joined together, those curved surfaces being so positioned that a vertical 
and a horizontal load bearing on the guide may act upon the curved 
surfaces, respectively, along lines extending in those directions which 
are substantially equal to the directions of the loads bearing on the 
guide, respectively. 
The second object of this invention is attained by a reciprocating table 
comprising a bed, a plurality of substantially parallel linear guides 
provided on the bed, and a table adapted to be guided by the linear guides 
for performing a reciprocating motion in a straight line along the bed, 
each of the linear guides comprising a track secured to the bed and having 
a plurality of ball rolling surfaces formed on its outer surface, a 
bearing body secured to the table, having a concavity for fitting the 
track, and formed on its inner surface with a plurality of ball rolling 
surfaces each facing one of the ball rolling surfaces on the track, and a 
multiplicity of balls held between the ball rolling surfaces on the track 
and the corresponding ball rolling surfaces on the bearing body, one of 
the linear guides being a four-directional load guide as hereinabove 
defined, and the rest thereof being a radial load guide for bearing only a 
vertical load. 
It is essential that each of the ball rolling surfaces on at least one of 
the track and the bearing body in the four-directional load guide of this 
invention be defined by a groove having the shape of a Gothic arch in 
cross section. The ball rolling surfaces on the track may be defined by 
grooves having the shape of a Gothic arch in cross section, while the ball 
rolling surfaces on the bearing body are defined by grooves having the 
shape of a single arc in cross section, or vice versa. Alternatively, all 
of the ball rolling surfaces on the track and the bearing body may be 
defined by grooves having the shape of a Gothic arch in cross section 
(hereinafter referred to simply as "Gothic arch grooves"). 
Each ball rolling surface defined by a Gothic arch groove consists of two 
curved surfaces joined together, and so arranged that a load may act 
substantially vertically or horizontally upon either of the curved 
surfaces. This arrangement enables each curved surface to bear a large 
vertical or horizontal load, since the directions of lines along which the 
vertical and horizontal loads bearing upon the guide act upon the curved 
surfaces are substantially equal to the directions of the loads bearing 
upon the guide. Thus, the guide of this invention can bear a large 
momental load, and is sufficiently rigid against any momental load to be 
suitable for uniaxial use. 
The arrangement of the curved surfaces as hereinabove described also makes 
it possible to prevent, or control to a minimum, any change in position 
that a load bearing upon the guide might otherwise cause to the points of 
contact between the balls and the curved surfaces, since the tangential 
lines passing through the points of their contact are substantially 
perpendicular to the direction of the load. This enables a drastically 
improved accuracy in the vertical or horizontal position of the bearing 
body relative to the track. 
The reciprocating table of this invention includes a four-directional load 
guide of this invention as one of the linear guides which guide the motion 
of the table in a straight line. Therefore, it is possible to prevent, or 
control to a minimum, any displacement of the table in the direction of a 
vertical or horizontal load bearing upon it, and thereby improve 
drastically the working accuracy of, for example, a machine tool in which 
the table is employed. 
The rest of the linear guides is a radial load guide, or guides. The radial 
load guide is a linear guide which bears only a vertical load, and hardly 
bears any horizontal load. Each of the ball rolling surfaces on its 
bearing body and track may be defined by a groove having the shape of a 
single arc in cross section (hereinafter referred to simply as "single arc 
groove"), and consist of a single curved surface, if the direction of a 
line along which a load acts upon the curved surface is equal to the 
direction of a vertical load bearing upon the guide. 
It is for the reason which will hereunder be set forth, that only one of 
the linear guides is a four-directional load guide, while the rest thereof 
is a radial load guide, or guides. 
If in a system including a plurality of parallel linear guides for guiding 
the reciprocating motion of a table relative to a bed, the guides are out 
of parallel, or if there is any difference in thermal expansibility 
between the table and the bed, it is likely that the horizontal 
displacement of bearing bodies relative to tracks may bring about a sharp 
increase in the rolling resistance of balls. If all of the linear guides 
are four-directional load guides of this invention, no smooth 
reciprocating motion can be expected from the table, since the guides of 
this invention are high in rigidity against any vertical or horizontal 
load. 
According to this invention, therefore, only the linear guide serving as a 
base for the position of the table is a four-directional load guide to 
ensure the accurate positioning of the table, and the remaining linear 
guide (or guides) is a radial load guide which can absorb any horizontal 
displacement of its bearing body relative to its track. The reciprocating 
table of this invention can, therefore, perform an accurate and smooth 
reciprocating motion.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Description will now be made in detail of the four-directional uniform load 
guide and reciprocating table of this invention with reference to the 
accompanying drawings. 
Reference is first made to FIG. 1 showing one form of four-directional 
uniform load guide embodying this invention. The guide 10 is essentially 
of the same construction with the known guide disclosed in Japanese Patent 
Publication No. 38812/1982 as hereinbefore described. Accordingly, it 
comprises a track 12, a bearing body 16, and a multiplicity of balls 22 
which enable the bearing body 16 to perform a smooth reciprocating motion 
along the track 12. 
The track 12 has two ball rolling surfaces 14 formed on each of a pair of 
opposite sides thereof. Each ball rolling surface 14 is defined by a 
Gothic arch groove, and consists of two curved surfaces 14a and 14b joined 
together, as shown in FIG. 2. Each of the curved surfaces 14a and 14b is 
arcuate in cross section, and has a radius of curvature which is slightly 
larger than the radius of the balls 22. 
The bearing body 16 has a concavity 20 which is open at its bottom, and 
which is generally complementary to the cross-sectional configuration of 
the track 12. The bearing body 16 has an inner surface defined by its 
concavity 20, and formed with a total of four ball rolling surfaces 18 
each facing one of the ball rolling surfaces 14 on the track 12. The ball 
rolling surfaces 18 are of the same shape with the ball rolling surfaces 
14. In other words, each ball rolling surface 18 is defined by a Gothic 
arch groove, and consists of two curved surfaces 18a and 18b joined 
together, as shown in FIG. 2. The bearing body 16 also has ball passages 
23 each allowing for the circulation of the balls 22 under no load from 
one end of one of the ball rolling surfaces 18 to the other end thereof. 
The track 12 has on each side thereof a projection 12a on which two of the 
ball rolling surfaces 14 are formed. On the other hand, the bearing body 
16 has on each of two opposite sides of its concavity 20 a recess 20a in 
which two of the ball rolling surfaces 18 are formed, and in which the 
projection 12a on one side of the track 12 is fitted. 
A modified form of the guide shown in FIG. 1 is shown in FIG. 3. It is 
obtained by reversing the arrangement of the projections and recesses 
shown in FIG. 1. A track 13 has a pair of recesses 13a formed on its 
opposite sides, respectively, and a bearing body 17 has a pair of 
projections 21a formed on the opposite sides, respectively, of its 
concavity 21, and each fitted in one of the recesses 13a of the track 13. 
Referring to FIG. 2 again, the curved surface 14a forming one half of each 
ball rolling surface 14 and the curved surface 18a forming one half of the 
corresponding ball rolling surface 18 face each other vertically of the 
guide 10, while the curved surface 14b forming the other half of the ball 
rolling surface 14 and the curved surface 18b forming the other half of 
the ball rolling surface 18 face each other horizontally of the guide 10. 
Accordingly, the balls are held between the curved surfaces 14a and 18a 
vertically of the guide 10, and between the curved surfaces 14b and 18b 
horizontally thereof. 
It, therefore, follows that, when a vertical load has been applied to the 
guide 10, the direction of a load acting line L passing through the curved 
surfaces 14a and 18a is equal to the direction of the load bearing upon 
the guide 10. Likewise, the direction of a load acting line L' which 
passes through the curved surfaces 14b and 18b when a horizontal load has 
been applied to the guide 10 is substantially equal to the direction of 
the load. The direction of each load acting line means the direction in 
which the load acts upon the curved surfaces. 
If a downward load F has, for example, been applied to the guide 10 as 
shown in FIG. 1, the load F is transmitted from the curved surfaces 18a to 
the balls 22 without producing any component force, since the direction of 
the load acting line L passing through each curved surface 18a is 
substantially equal to the direction of the load. The load F is then 
transmitted from the balls 22 to the curved surfaces 14a without producing 
any component force. As the directions of all the load acting lines L 
passing through the curved surfaces 14a and 18a are substantially equal to 
the direction of the load, the guide 10 can bear a large downward load. 
Likewise, it can bear a large horizontal load f, since the directions of 
all the load acting lines L' passing through the curved surfaces 14b and 
18b are substantially equal to the direction of the load f. 
The load F does not cause any displacement in the points of contact between 
the balls 22 and the curved surfaces 14a and 18a, since the load acting 
lines L are substantially equal in direction to the load F, nor does the 
load f cause any displacement in the points of contact between the balls 
22 and the curved surfaces 14b and 18b, since the load acting lines L' are 
substantially equal in direction to the load f. Therefore, the guide 10 is 
high in rigidity against any vertical or horizontal load, and is an 
optimum guide as a base for the positioning of a reciprocating table. 
Attention is now directed to FIG. 4 showing another four-directional 
uniform load guide 9 embodying this invention. It includes a track 11 
which is identical in construction to the track 12 as hereinabove 
described with reference to FIG. 1. No further description of the track 11 
will, therefore, be made. It also includes a bearing body 15 which is 
substantially identical to the bearing body 16 shown in FIG. 1. The only 
difference therebetween is that each ball rolling surface 19 formed on the 
bearing body 15 is defined by a single arc groove and consists of a single 
curved surface. 
Each ball rolling surface 24 formed on the track 11 consists of two curved 
surfaces 24a and 24b, as shown in FIG. 5. The curved surface 24a faces 
upward or downward, while the curved surface 24b faces horizontally. Each 
ball rolling surface 19 on the bearing body 15 is so formed that a load 
acting line m passing therethrough may have an angle of about 45.degree. 
to the directions of a vertical and a horizontal load bearing upon the 
guide 9. The curved surfaces 24a and 24b and the ball rolling surfaces 19 
hold balls 22 rollably therebetween. 
The load acting lines 1 along which a downward load F acts upon the curved 
surfaces 24a are equal in direction to the load F, and likewise, the load 
acting lines l' along which a horizontal load f acts upon the curved 
surfaces 24b are substantially equal in direction to the load f. The guide 
9 can, therefore, bear both a large vertical and horizontal load. 
The vertical or horizontal load bearing upon the guide 9 is transmitted 
from the bearing body 15 to the balls 22 along the load acting lines m 
passing through the ball rolling surfaces 19, and thereby presses the 
balls 22 against the curved surfaces 24a and 24b forming the ball rolling 
surfaces 24 along the load acting lines l and l'. Therefore, no 
displacement occurs to the points of contact between the balls 22 and the 
curved surfaces 24a and 24b, but the guide 9 exhibits high rigidity 
against both the vertical and horizontal loads. 
It is, however, likely that, if the vertical or horizontal load F or f 
exceeds a certain level, it may cause displacement in the points of 
contact between the balls 22 and the ball rolling surfaces 19, since the 
direction of the load acting lines m does not coincide with that of the 
load. It can, therefore, be said that the guide 9 is lower in rigidity 
than the guide 10 shown in FIG. 1. 
Reference is now made to FIG. 6 showing a reciprocating table 1 embodying 
this invention. The table 1 comprises a bed 80, a table 82 and two 
parallel linear guides secured to the bed 80 by bolts 81 and used for 
guiding the reciprocating motion of the table 82 in a straight line along 
the bed 80. One of the linear guides is a four-directional uniform load 
guide 10 of the construction shown in FIG. 1 which provides a base for the 
positioning of the table 82, and the other is a radial load guide 30 which 
bears only a vertical load acting upon the table 82. 
The guide 10 has a high rigidity against any vertical or horizontal load 
and thereby maintains a high accuracy in position, as hereinbefore stated. 
Therefore, it enables the reciprocating table 1 to support even a large 
vertical or horizontal load acting upon the table 82 without undergoing 
any appreciable displacement in the direction of the load. 
It is generally true that, if there is any difference in thermal 
expansibility between a reciprocating table and a stationary bed, or if 
two linear guides for guiding the table are not satisfactorily parallel to 
each other, the bearing bodies in the linear guides which are fixed to the 
table are horizontally displaced from the tracks fixed to the bed, 
resulting in a sharp increase of resistance to the motion of the table by 
the guides. No smooth reciprocating motion can, therefore, be expected 
from the table. 
The radial load guide 30, however, hardly bears any horizontal load, but 
absorbs any horizontal displacement of the bearing body 31 from the track 
32. The combination of the radial load guide 30 with the four-directional 
load guide 10 enables the reciprocating table 1 to perform a smooth 
reciprocating motion without having any substantial resistance to its 
motion. The positional accuracy of the table 82 is maintained by the guide 
10. 
Attention is now drawn to FIG. 7 showing in detail one form of radial load 
guide. The radial load guide 2 is substantially identical in construction 
to the four-directional load guide 10 shown in FIG. 1. Each ball rolling 
surface 25 on a track 3 is defined by a Gothic arch groove and consists of 
two curved surfaces 25a and 25b joined together, and each ball rolling 
surface 26 on a bearing body 4 is also defined by a Gothic arch groove and 
consists of two curved surfaces 26a and 26b, as shown in FIG. 8. The 
arrangement of the curved surfaces 25a, 25b, 26a and 26b is identical to 
that of the curved surfaces 14a, 14b, 18a and 18b on the guide 10 which is 
shown in FIG. 2. 
The radial load guide 2 differs from the guide 10 in that the curved 
surfaces 25b and 26b facing each other have therebetween a distance which 
is greater than that between the other curved surfaces 25a and 26a facing 
each other. Therefore, the balls 22 which are held between the ball 
rolling surfaces 25 on the track 3 and the ball rolling surfaces 26 on the 
bearing body 4 contact the curved surfaces 25a and 26a, but do not contact 
the curved surfaces 25b and 26b. This relationship is achieved, as the 
horizontally spaced apart curved surfaces 26a on the bearing body 4 have 
therebetween a distance P.sub.1 which is greater than the distance P.sub.2 
between the horizontally spaced apart curved surfaces 25a on the track 3. 
If the distance P.sub.1 were equal to P.sub.2, the balls 22 would contact 
all of the curved surfaces 25a, 25b, 26a and 26b, and the guide 2 would be 
identical to the guide 10 shown in FIG. 1. 
The direction of the load acting line L passing through each pair of curved 
surfaces 25a and 26a contacting the balls 22 is equal to the direction in 
which a vertical load acts upon the guide 2. The guide 2 can, therefore, 
bear a large vertical load without having any appreciable change in 
height, since no displacement occurs to the points of contact between the 
balls 22 and the curved surfaces 25a and 26a. 
When a horizontal load has been applied to the guide 2, the clearances 
between the balls 22 and the curved surfaces 25b and 26b permit some 
horizontal displacement of the bearing body 4 from the track 3. This 
displacement does not impede the smooth action of the guide 2. 
FIG. 9 shows another form of radial load guide. The radial load guide 5 
comprises a track 6 having a total of four ball rolling surfaces 27, a 
bearing body 7 having a total of four ball rolling surfaces 28 each facing 
one of the ball rolling surfaces 27 on the track 6, and a plurality of 
balls 22 held rollably between the ball rolling surfaces 27 and 28, as the 
guide 2 shown in FIG. 7 does. 
Each of the ball rolling surfaces 27 and 28 is, however, defined by a 
single arc groove and consists of a single curved surface, as shown in 
FIG. 10. The direction of the load acting line L passing through each pair 
of ball rolling surfaces 27 and 28 is equal to the direction in which a 
vertical load acts upon the guide 5. The guide 5 can, therefore, bear a 
large vertical load without having any appreciable change in height. 
The guide 5 does not have any ball rolling surface that restricts the 
horizontal movement of the balls 22. A horizontal load acting upon the 
guide 5, therefore, causes a shift in the points of contact between the 
balls 22 and the ball rolling surfaces 27 and 28, and thereby the 
horizontal displacement of the bearing body 7 from the track 6. This 
displacement does not impede the smooth motion of the guide 5.