Bearings – Linear bearing – Lubricating
Reexamination Certificate
1999-10-15
2001-12-11
Footland, Lenard A. (Department: 3682)
Bearings
Linear bearing
Lubricating
C384S045000
Reexamination Certificate
active
06328474
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a linear guide device, and particularly to a linear guide device that is suitably employed in, for example, a semiconductor producing apparatus in which usual grease or a lubricating oil cannot be used.
Conventionally, a linear guide device having the following configuration is known (for example, Japanese Patent Publication (Kokai) No. HEI5-248433). The linear guide device has a linear guide rail and a movable unit which is moved along the guide rail. The movable unit is configured by: a movable block in which leg portions are arranged in a lateral direction with respect to the moving direction, and which is disposed with straddling the guide rail; and plural rolling elements which, while circulating in rolling element circulation passages formed in the right and left leg portions of the movable block, roll between a rolling element raceway surface formed in the circulation passage, and other rolling element raceway surfaces respectively formed on both the sides of the guide rail.
In a linear guide device of such a type, usually, grease is used for lubrication between the rolling elements, and the guide rail and the movable block. The device is used in a state where the clearance between the guide rail and the movable unit and in a direction perpendicular to the moving direction is formed as a negative clearance, or a preload is applied between the movable block and the guide rail via the rolling elements.
When such a linear guide device is employed in an environment where high cleanness or oil free is required, such as in a semiconductor producing apparatus, usual grease or a lubricating oil cannot be used, and hence at least rolling element contact surfaces (raceway surfaces) of the guide rail and the movable block must be coated with a solid lubricating agent.
When a solid lubricating agent is used in a linear guide device, the life (dust evolution and torque life) of the device is more easily affected by a load as compared with the case where grease is used. As described above, a linear guide device of this type is used with being applied with a preload and forming a negative clearance. Therefore, the device is always in a state where a relatively large load is acting on the device, thereby producing a problem in that the device has a short life.
SUMMARY OF THE INVENTION
The invention has been conducted in order to solve the problems. It is an object of the invention to provide a linear guide device in which a solid lubricating agent can be used so that the device can be employed in an environment where high cleanness or oil free is required, and which has a long life.
In order to attain the object, the linear guide device of the invention is a linear guide device comprising a linear guide rail, the movable unit which is moved along the guide rail, the movable unit comprising: a movable block which has right and left leg portions in a lateral direction with respect to the moving direction, which is disposed with straddling the guide rail, and in which a rolling element circulation passage is formed in each of the right and left leg portions; and plural rolling elements which, while circulating in corresponding one of the rolling element circulation passages of the movable block, roll between a rolling element raceway surface formed in the circulation passage, and rolling element raceway surfaces respectively formed on both the sides of the guide rail, and characterized in that at least the rolling element raceway surfaces of the guide rail and the rolling element raceway surfaces of the rolling element circulation passages are coated with a solid lubricating agent, and a clearance between the guide rail and the movable unit and in a direction perpendicular to the moving direction (hereinafter, such a clearance is referred to merely as “clearance”) is 0 or positive.
In the invention, a fluororesin or molybdenum disulfide is preferably used as the solid lubricating agent.
The invention has been conducted based on results of various experiments on a linear guide device in which a solid lubricating agent is used. Unlike the case where usual grease or the like is used as a lubricating agent, the clearance is not formed as a negative clearance. When a solid lubricating agent is used, the clearance is set to be 0 or positive, whereby the life of the linear guide device can be largely prolonged.
According to results of experiments, when a solid lubricating agent is used for lubrication between the rolling elements, and the guide rail and the movable block, in the case where the clearance between the guide rail and the movable unit is positive or +6 &mgr;m, the life is prolonged two times as compared with the case of a negative clearance of −6 &mgr;m which is frequently employed in a linear guide device of this type wherein usual grease is used as a lubricating agent.
In the invention, the lower limit of the clearance is 0, and the upper limit is the maximum clearance which can satisfy requirements on the accuracy of positioning and that of rattling that are allowable in a linear guide device. A more preferable range of the clearance depends on the kind of the solid lubricating agent, the application thickness, the size of the rolling elements, and the like, and cannot be clearly specified at present. In the case where PFPE (perfluoropolyether), PTFE (polytetrafluoroethylene), or molybdenum disulfide is used in a coating thickness on the order of submicrons, excellent results are obtained when the clearance is in the range of 0 to about +10 &mgr;m.
REFERENCES:
patent: 3844628 (1974-10-01), McCloskey
patent: 5980111 (1999-11-01), Sasaki
patent: 8-240223 (1996-09-01), None
Fujiwara Arihiro
Tsuru Kazuo
Footland Lenard A.
Jacobson & Holman PLLC
Koyo Seiko Co. Ltd.
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