Abrading – Abrading process – Glass or stone abrading
Reexamination Certificate
1999-11-30
2001-08-28
Hail, III, Joseph J. (Department: 3723)
Abrading
Abrading process
Glass or stone abrading
C451S063000, C451S270000, C451S271000, C451S287000, C451S291000
Reexamination Certificate
active
06280296
ABSTRACT:
This application is based on Japanese Patent Application No. 10-342847, the content of which is incorporated hereinto by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to surface polishing method and apparatus using a polishing plate or wheel which has a polishing face for polishing, lapping or grinding a surface of the workpiece in a plane.
2. Discussion of the Related Art
A surface polishing method and an apparatus for practicing the method are known for polishing, lapping or grinding a surface of the workpiece in a plane, such that the workpiece is held in sliding contact with a polishing face of a rotating polishing or lapping plate or wheel while the workpiece is rotated about its axis parallel to the axis of rotation of the polishing plate. The polishing face has a polishing surface, which has abrasive grains fixed or bonded thereto or on which loose or free abrasive grains are present. In this type of surface polishing method and apparatus, there is a general tendency that the polishing distance over which the abrasive grains are moved relative to the workpiece surface is different at different radial positions of the workpiece, in particular, at the peripheral and central portions (radially outer and inner portions) of the workpiece. This difference of the polishing distances at the different local radial positions of the workpiece surface increases with an increase in the size of the workpiece surface to be polished, lapped or ground, and is relatively large when the diameter of the circular workpiece surface or the length of a side of the rectangular workpiece surface is several tens of centimeters or more. The difference of the polishing distances causes a difference in the local polishing efficiency of the workpiece surface, which tends to cause the central portion of the polished workpiece surface to be raised or upwardly convexed, resulting in deteriorated flatness of the polished workpiece surface.
There is proposed another type of surface polishing method and apparatus wherein a plurality of workpieces are held on the work holding surface of a work holder plate adapted to be rotated about its axis, such that the workpieces are arranged around the axis of rotation of the work holder plate. In this type of surface polishing method and apparatus, the axis of rotation of the work holder plate does not lie within the workpiece surface to be polished, so that the problem of the central raised or convexed portion of the polished workpiece surface can be solved. However, the workpiece surface is subjected to a greater amount of stock removal by the abrasive grains at a local circumferential portion thereof which is relatively distant from the axis of rotation of the work holder plate, whereby the polished surface of each workpiece is inclined, resulting in deteriorated geometrical and dimensional accuracies of the polished surface. Further, this type of surface polishing method and apparatus requires the work holder plate which is as sufficiently large as about two or more times the diameter or size of the workpiece, whereby the required size of the polishing plate and that of the surface polishing apparatus are inevitably increased, leading to an increased cost of manufacture of the apparatus and an accordingly increased cost of polishing operation.
SUMMARY OF THE INVENTION
It is therefore a first object of this invention to provide a surface polishing method which permits even a large-sized workpiece to be polished with a high degree of flatness, with a relatively small-sized apparatus.
A second object of the invention is to provide a relatively small-sized surface polishing apparatus suitable for practicing the method of the invention.
The first object may be achieved according to a first aspect of this invention, which provides a method of polishing a surface of a workpiece in a plane such that the workpiece is held in sliding contact with a polishing face of a rotating polishing plate, the method comprising the steps of: rotating the workpiece about an autorotation axis thereof which is parallel to an axis of rotation of the polishing plate and which lies within the surface of the workpiece; and revolving the autorotation axis of the workpiece about a revolving axis which is parallel to the axis of rotation of the polishing plate and which lies within a circumscribed circle of the surface of the workpiece.
In the surface polishing method of the present invention, the workpiece held in sliding contact with the polishing face of the polishing plate is rotated about its autorotation axis parallel to the axis of rotation of the polishing plate, while at the same time the autorotation axis of the workpiece is revolved about the revolving axis which is parallel to the axis of rotation of the polishing plate and which lies within the circumscribed circle of the workpiece surface. As a result of the revolution of the autorotation axis of the workpiece as well as the autorotation of the workpiece about the autorotation axis, the tendency of formation of a central raised or upwardly convexed portion of the polished surface of the workpiece or inclination of the polished workpiece surface can be minimized to thereby improve the flatness and the geometric and dimensional accuracies of the polished workpiece surface, even when the workpiece is relatively large-sized. Further, since the revolving axis about which the autorotation axis of the workpiece is revolved is located within the circumscribed circle of the workpiece surface, the present method does not require a work holder plate which is as large as two or more time the size (diameter) of the workpiece, making it possible to reduce the sizes of the polishing plate and the surface polishing apparatus used, thereby permitting a significant reduction in the cost of a surface polishing operation and the cost of manufacture of the surface polishing apparatus.
In one preferred form of the present method, the rotation of the polishing plate about the axis of rotation, the autorotation of the workpiece about the autorotation axis and the revolution of the autorotation axis of the workpiece about the revolving axis take place in the same direction. In this arrangement, the difference in the polishing speed of the workpiece at a relatively radially inner portion and a relatively radially outer portion of the polishing face of the polishing plate is reduced, resulting in an improvement in the flatness of the polished surface of the workpiece.
In another preferred form of the method, the workpiece is rotated about the autorotation axis with a rotating period T
A
while the autorotation axis is revolved about the revolving axis with a revolving period T
B
, so as to satisfy 0.1≦T
B
/T
A
<1, or 1<T
B
/T
A
≦10, namely, 0.1≦T
B
/T
A
≦10, and T
A
/T
B
≠1, more preferably, so as to satisfy 0.8≦T
B
/T
A
<1, or 1<T
B
/T
A
≦1.25, namely, 0.8≦T
B
/T
A
≦1.25, and T
A
/T
B
≠1. In this case, the rotating period T
A
and the revolving period T
B
are made different from each other so as to assure a sufficiently high degree of flatness of the polished workpiece surface.
In a further preferred form of the method, a radius of an orbit of the autorotation axis of the workpiece about the revolving axis is not smaller than 5% of a radius of an inscribed circle of the workpiece, and more preferably, the radius of the orbit of the autorotation axis is not smaller than the radius and is not larger than a radius of the circumscribed circle of the workpiece. This arrangement contributes a further improvement in the flatness of the polished workpiece surface.
In a still further preferred form of the method, the polishing face of the polishing plate consists of an annular surface, and the revolving axis of the autorotation axis of the workpiece lies between an inside diameter and an outside diameter of the annular surface of the polishing face. More preferably, the inside diameter of the annular surface of the polishing face is larger than a diameter of an orbit of the
Sato Makoto
Tomikawa Noriyuki
Yamaguchi Yukio
Hail III Joseph J.
McDonald Shantese
Noritake Co. Ltd.
Oliff & Berridg,e PLC
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