Electricity: measuring and testing – Magnetic – With means to create magnetic field to test material
Reexamination Certificate
1998-12-21
2001-08-14
Strecker, Gerard R. (Department: 2862)
Electricity: measuring and testing
Magnetic
With means to create magnetic field to test material
C324S210000, C324S232000, C324S262000, C033S533000
Reexamination Certificate
active
06275032
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a flatness measuring apparatus for measuring flatness of a surface of a plate-shaped object such as a magnetic disk to be used as storage medium for computers.
2. Related Art Statement
For example, magnetic disks to be used as storage medium for computers typically comprise a substrate made of aluminum alloy or glass and a magnetic film formed on the surface of the substrate.
For manufacturing high quality magnetic disks, the disks are required to show a certain level of surface flatness, so their substrates are normally checked for flatness of the surface in an after-fabrication process.
Electric micrometers are known as means for checking whether the object of examination such as a plate-shaped product shows a predetermined level of surface flatness. The electric micrometer is in fact a displacement sensor comprising a probe and a transducer for transducing any mechanical displacement of the probe into an electric signal such that, as the probe is driven to slidingly move on the surface of a plate-shaped object, any displacement of the probe on the surface is transferred to the core of the actuator transformer of the sensor and detected as electric signal representing the surface condition of the object.
However, with a method of measuring the surface flatness of an object by holding a contact probe in contact with the surface of the object, the contact probe may damage and leave one or more than one flaws on the surface. Such a flaw should be avoided by any means particularly when it comes to a magnetic disk that requires a mirror finish to say nothing of a highly smoothed surface. Additionally, for the purpose of measuring efficiency, the operation of observing the surfaces of products supplied on a mass production basis is preferably automated.
SUMMARY OF THE INVENTION
Thus, it is an object of the present invention to provide a flatness measuring apparatus adapted to measure the flatness of the surface of a plate-shaped object such as a disk in a non-contact fashion.
Another object of the present invention is to provide a flatness measuring apparatus adapted to automatically measure flatness of a surface of a plate-shaped object such as a disk.
According to the invention, the above objects and other objects are achieved by providing a flatness measuring apparatus for measuring the flatness of the surface of an object comprising a measuring table for removably holding thereon an object of measurement, a sensor head arranged along said measuring table with a predetermined gap between itself and the surface of said object of measurement held on said measuring table so as to be movable relative to said object of measurement, a plurality of eddy current undulation sensors arranged in said sensor head to generate an eddy current in said object of measurement and detect any undulation on the surface of said object of measurement, and a control section for drawing a flatness map for the surface of said object of measurement based on a signal representing the relative positions of said sensor head and said object of measurement and on signals from said respective eddy current undulation sensors so as to output a map data to an output section.
According to another aspect of the invention, there is provided a flatness measuring apparatus for measuring flatness of a surface of a disk comprising a measuring table for removably holding thereon a disk, said measuring table having a projection for being engagedly received in a central through hole of said disk, a sensor head arranged along said measuring table with a predetermine gap between itself and the surface of said disk held on said measuring table so as to be able to linearly reciprocate relative to said disk, a plurality of eddy current undulation sensors arranged in said sensor head to generate an eddy current in said disk and detect any undulation on the surface of said disk, and a control section for drawing a flatness map for the surface of said disk based on a signal from a position detector for detecting the position of said sensor head and on signals from the respective eddy current undulation sensors so as to output a map data to an output section. Preferably, a flatness measuring apparatus according to the invention further comprises an inverting means adapted to be able to horizontally reciprocate to a position right above said measuring table and invert said disk while holding said disk so as to automatically measure flatness of each of opposite sides of said disk.
Preferably said measuring table is adapted to be able to vertically reciprocate. Still preferably, said disk is a magnetic disk substrate.
Thus, according to the invention, since the flatness of the surface of an object of measurement is measured by means of eddy current undulation sensors of a non-contact type that are not brought into contact with the surface of the object of measurement for measuring the surface flatness, the object of measurement is protected against any damage and deformation during the measurement and the surface flatness can be precisely determined.
The above objects and other objects of the present invention as well as the novel features of the invention will become apparent by reading the following detailed description made by referring to the accompanying drawings.
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Hirokawa Makoto
Iwata Tetsuya
McCormick Paulding & Huber LLP
Strecker Gerard R.
System Seiko Co., Ltd.
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