Abrading – Abrading process – Side face of disk
Reexamination Certificate
1999-05-12
2001-04-17
Eley, Timothy V. (Department: 3723)
Abrading
Abrading process
Side face of disk
C451S262000, C451S267000, C451S905000
Reexamination Certificate
active
06217423
ABSTRACT:
BACKGROUND OF THE INVENTION
(i) Technical Field of the Invention
The present invention relates to an apparatus and a method for the mirror surface grinding of a magnetic disc substrate for a hard disk.
(ii) Description of the Related Art
A hard disk for a computer is a magnetic disk prepared by applying a magnetic substance to the surface (one side or both sides) of a disk-like substrate (e.g., made of aluminum), and reads information by rotating it at a high speed (e.g., 10000 rpm or faster) and moving a head along the magnetic surface.
The degree of parallelism (precision of the thickness) and the surface coarseness of substrate for a hard disk (hereafter, magnetic disk substrate) requires high precision to record information in a high density. For example, small magnetic disk substrates of a diameter of 2.5 inches (ca. 64 mm) and a diameter of 3.5 inches (ca. 95 mm) have a maximum acceptable range (difference between maximum and minimum thickness), for example, of 3 &mgr;m and 7 &mgr;m, respectively.
Conventionally for processing magnetic disk substrates of such high precision, a flatbed lap has been mainly used. The flatbed lap is a lap for simultaneous lapping both sides and has, for example, gear teeth surrounding a part for fitting a workpiece; the fitting part rotates by itself meshing with the central and surrounding gears, pressure is applied by an upper cylinder, and a free abrasive is put between a lap tool (or lapping machine) and the workpiece is processed by relative movement of the lap and the workpiece.
The aforementioned conventional lapping machine (e.g., a flatbed lap) is characterized by possible high processing precision by using relatively simple facilities. On the contrary, there are following problems.
(1) The conventional lap, when applied to processing using a free abrasive, results in a very low processing rate ({fraction (1/10)} or lower grinding rate) and is time consuming for processing. Therefore, a facility of a large size is normally used for simultaneous processing of a plurality of magnetic disk substrates. Notwithstanding this, the processing time required for a disk is longer.
(2) A standard lap is previously processed in high precision to process a workpiece to fit to the lap. Therefore, maintaining the precision of the lap itself, which is lowered by abrasion, etc. requires repeated processing of the lap. Normally in this case, “lapping adjustment” of the upper and lower laps is carried out for lapping the respective laps. By this step, uneven surfaces become even. However, the right angle against the rotational shaft cannot be kept constant, which lowers the degree of parallelism of the workpiece after processing. This means that constant pressure lapping allows truing (lapping adjustment) on a lapping machine; however, it does not allow readjustment of the degree of parallelism of a jig for holding the workpiece to a grinding wheel even if the flatness of the grinding wheel (the lap) has been improved. Therefore, the degree of parallelism (precision of thickness) of both sides of the workpiece cannot be improved by the adjustment.
In addition, very recently, crashing of hard disks, particularly of motors has very frequently occurred. One of the causes of disk crashing is an unbalanced thickness of a magnetic disc substrate. There is a problem that the unbalanced thickness of a magnetic disc substrate causes a decentering force which lowers the life of the bearings of the motor, finally resulting in crash of the motor in a short time. Thus, in order to increase the reliability of the hard disk, increasing the degree of parallelism (precision of thickness) of the magnetic disc substrate is required more than with conventional substrates. However, the conventional lap aforementioned does not achieve this object due to the requirement of a longer processing time that is not practical.
SUMMARY OF THE INVENTION
The present invention has been created to solve such problems. The purpose of the present invention is to provide an apparatus and a method for mirror surface grinding of a magnetic disc substrate capable of largely improving the processing rate of the magnetic disc substrate in comparison with the conventional lapping machine and of improving the degree of parallelism (precision of thickness) of both sides of the substrate and the surface coarseness in comparison with the conventional apparatus and method. According to a first aspect of the present invention, there is provided an apparatus for the mirror surface grinding of a magnetic disc substrate which comprises a metal bond grinding wheel (
12
) rotating around a vertical shaft center Z
1
and having a horizontal working surface (
12
a
); a workpiece holding and rotating means (
14
) having a horizontal supporting surface (
14
a
) opposite to said working surface and rotating around a vertical shaft center Z
2
; a voltage applying means (
16
) having said metal bond grinding wheel as a positive electrode and an electrode (
16
a
) as a negative electrode installed oppositely to said working surface of the metal bond grinding wheel in an uncontacted state and applying a pulsed voltage between both the electrodes; and a grinding fluid feeding means (
18
) for feeding an electroconductive grinding fluid to the working surface of said metal bond grinding wheel, wherein said workpiece holding and rotating means (
14
) holds and rotates a disk-like magnetic disc substrate (
1
) or a disk-like truing grinding wheel (
2
) so as to closely contact its supporting surface, and is horizontally and vertically movably constituted, whereby (A) the working surface (
12
a
) of the metal bond grinding wheel is subjected to flat grinding on the machine, and while the metal bond grinding wheel is then subjected to electrolytic dressing, simultaneously, (B) the grinding of the supporting surface (
14
a
) of the workpiece holding and rotating means, and (C) the grinding of the magnetic disc substrate (
1
) attached to the workpiece holding and rotating means are carried out on the machine.
According to the second aspect of the present invention, there is provided a method for mirror surface grinding of a magnetic disc substrate which uses a metal bond grinding wheel (
12
) rotating around a vertical shaft center Z
1
and having a horizontal working surface (
12
a
), and a workpiece holding and rotating means (
14
) having a horizontal holding surface (
14
a
) opposite to said working surface and rotating around a vertical shaft center Z
2
, said method comprising
(A) horizontally moving a workpiece holding and rotating means to subject the working surface (
12
a
) of the metal bond grinding wheel to horizontal flat grinding on the machine by a truing grinding wheel attached thereto,
subsequently, applying a pulsed voltage between a metal bond grinding wheel as a positive electrode and an electrode (
16
a
) as a negative electrode installed oppositely to said working surface of the metal bond grinding wheel in an uncontacted state, and simultaneously feeding an electroconductive grinding fluid between them, and subjecting the metal bond grinding wheel to electrolytic dressing, and simultaneously,
alternatively carrying out, on the machine, (B) a supporting surface grinding step for grinding the supporting surface (
14
a
) of the workpiece holding and rotating means by using the metal bond grinding wheel, and (C) a workpiece grinding step for grinding a magnetic disc substrate (
1
) attached to the workpiece holding and rotating means by using the metal bond grinding wheel.
According to the apparatus and the method of the present invention, (A) the working surface (
12
a
) of the metal bond grinding wheel can be ground to make a horizontal flat surface on the machine by horizontally moving the workpiece holding and rotating means (
14
) to which a truing grinding wheel (
2
) is attached. Thus, even if the precision of flatness of the working surface has been lowered by abrasion, etc., truing can be operated on the machine to maintain the right angle with respect to the rotational axis. This means that,
Ishii Shinji
Itoh Nobuhide
Ohmori Hitoshi
Shimizu Susumu
Uchino Junichi
Berry Jr. Willie
Eley Timothy V.
Griffin & Szipl, P.C.
The Institute of Physical and Chemical Research
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