Linear guide

Details Linear guide Linear guide

2001-07-13

2003-02-18

Footland, Lenard A. (Department: 3682)

Bearings

Linear bearing

Recirculating

Reexamination Certificate

active

06520680

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a linear guide, particularly relates to a linear guide used in industrial machines etc. Further, the present invention also relates to a linear guide that is suitably used in a stepper etc. used in a semiconductor element fabrication process.
Conventionally, as a linear guide used in general, there is known one, for example, which includes a guide rail
1
extending in the axial direction thereof and a slider
2
assembled to the guide rail
1
so as to cross over the rail, as shown in FIG.
1
. In such a linear guide, rolling element rolling grooves
3
,
3
,
3
,
3
are formed along the axial direction thereof at both side surfaces
1
b
,
1
b
of the guide rail
1
.
As shown in
FIGS. 1 and 2
, the slider
2
is formed by a slider main body
2
A and end caps
2
B,
2
B attached to the both end portions of the main body along the axial direction thereof. The slider main body
2
A has rolling element rolling grooves
4
,
4
,
4
,
4
opposing to the rolling element rolling grooves
3
,
3
,
3
,
3
of the guide rail
1
at the inner side surfaces of both sleeve portions
6
,
6
, respectively, and rolling element return paths
11
,
11
,
11
,
11
penetrating the thick portions of the sleeve portions
6
,
6
in the axial direction thereof (see FIG.
2
). These opposed rolling element rolling grooves
3
,
3
,
3
,
3
and
4
,
4
,
4
,
4
form rolling element rolling paths
10
,
10
,
10
,
10
.
As clear from
FIG. 3
showing the plan view of the linear guide in which the slider
2
is partially cut-away, the end caps
2
B,
2
B have curved paths
12
each for communicating the rolling element rolling path
10
and the rolling element return path
11
disposed in parallel to each other. The rolling element rolling path
10
, the rolling element return path
11
and the curved paths
12
at the both ends thereof form a rolling element circulation path. Many rolling elements
5
formed by steel balls, for example, are filled within the rolling element circulation path.
The slider
2
assembled to the guide rail
1
moves smoothly along the guide rail
1
through the rolling operation of the rolling elements
5
within the rolling element rolling paths
10
, and the rolling elements
5
circulate endlessly while rolling within the rolling element circulation path of the slider
2
.
Side seals
7
for sealing the openings of gaps between the guide rail
1
and the slider are attached to the both end portions (the end surfaces of the respective gaps
2
B) of the slider
2
. A symbol
8
of
FIG. 1
depicts a grease nipple.
In such a conventional linear guide, the surface roughness of the rolling element rolling grooves
3
,
4
is set in a manner that the average roughness Ra along the center line thereof is more than 0.20 &mgr;m by the grinding finishing process etc.
However, the aforesaid conventional linear guide has a problem that abrasion (initial abrasion) due to the shake-down among the members occurs at the initial stage of the usage (upon running of several km), so that the sliding resistance likely reduces and powder of the members due to the abrasion is likely generated.
Further, when the aforesaid linear guide is used in the working machine, since the sliding resistance changes with the lapse of time as described above, there arises a problem that the accuracy of the processing performed by using the working machine is badly influenced.
Further, since the sliding resistance changes in accordance with the moving speed of the slider
2
, when the cutting speed changes in the processing (for example, arc cutting etc.) performed by the working machine, there also arises a problem that the resistance value varies and so the processing with high accuracy can not be realized.
In addition to this, conventionally, the stepper (micro projection exposure apparatus) used in the semiconductor element fabrication process employs high-energy light such as excimer laser etc. as a light source. The linear guide for the stepper is usually lubricated by fluoro grease. The fluoro grease is a mixture of a base oil composed of liquid fluorinated polymer oil and a thickening agent composed of solid fluorinated polymer. Although the liquid fluorinated polymer oil is not necessary limited, there may be used perfluoro-polyether (hereinafter referred to as “PFPE”), a telomer of trifluoro-ethylene, fluoro-siliconepolymer, or the like. As the solid fluorinated polymer, there may be used polytetrafluoro-ethylene (hereinafter referred to as “PTFE”), a copolymer of tetrafluoro-ethylene and hexafluoro-propene, a copolymer of tetrafluoro-ethylene and perfluoro-propylvinylether, a mixture of these polymers, or the like. This is because, it is not preferable to use the stepper in such a circumstance where dust is likely generated. Further, when light with a high energy is irradiated on general grease (lithium system or urea system), vapor is generated from the grease and adhered to a lens, so that the lens is required to be exchanged frequently.
As shown in
FIG. 4
, the linear guide is configured by a guide rail
1
, a slider
2
and rolling elements
3
. The guide rail
1
has rolling element rolling grooves
11
extending in parallel to each other along the longitudinal direction thereof at both side surfaces
1
b
thereof. The slider
2
is engaged with the guide rail
1
so as to cross over the rail in a manner that the both inside surfaces
2
a
of the slider
2
are disposed to oppose to the both side surfaces
1
b
of the guide rail
1
, respectively. Rolling element rolling grooves
12
are formed at the both inside surfaces
2
a
of the slider
2
so as to oppose to the rolling element rolling grooves
11
of the guide rail
1
, respectively. The linear guide is arranged in a manner that when the rolling elements
3
roll along rolling paths formed by the both rolling element rolling grooves
11
,
12
, the slider
2
slides along the guide rail
1
.
Although a general linear guide has two pairs of rolling paths, that is, four columns of rolling paths, a small-sized linear guide for a stepper etc. has a pair of rolling paths, that is, two columns of rolling paths as shown in this figure. In this case, when a preload is applied, since the rolling element contacts with the rolling path at four points, there,arises a problem that differential slip becomes large. Further, it is required to make the friction small so as to drive the linear guide under the electronic control Thus, since the exposed thread due to the preload is suppressed to about 1 &mgr;m, a setting preload may not be held due to a slight abrasion. If the setting preload is not held, the accuracy of the linear guide degrades.
When the rolling element rolling grooves of the linear guide are lubricated by the fluoro grease which is deteriorated in lubrication characteristics as compared with general grease, initial abrasion of the linear guide occurs in a relatively short time.
Further, in the case of using a linear motor as the driving apparatus in order to attain a high acceleration and deceleration, the changes of the friction force becomes larger and so oscillation may occur.
Thus, in the case of lubricating the rolling element rolling grooves of the linear guide (particularly, a small-sized linear guide) by the fluoro grease, since the setting preload is not likely held at the time of the initial abrasion, there arises a problem that the accuracy of the linear guide is apt to degrade in a short time.
SUMMARY OF THE INVENTION
Accordingly, an object of the invention is to solve the problems of the aforesaid conventional linear guide. It is an object of a first aspect of the present invention to provide a linear guide in which reduction of a sliding resistance and generation of powder due to the abrasion caused by the initial abrasion are not easily occurred.
In order to solve the aforesaid problems, the first aspect of the present invention is configured in the following manner. That is, in the linear guide which includes a guide rail having at its outer surfaces

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