Optics: measuring and testing – Inspection of flaws or impurities – Surface condition
Patent
1997-04-28
1999-02-02
Pham, Hoa Q.
Optics: measuring and testing
Inspection of flaws or impurities
Surface condition
3562434, 348128, G01N 2188
Patent
active
058672613
ABSTRACT:
A laser based inspection tool (LIT) for inspecting planar surfaces is described. In a preferred embodiment the LIT can simultaneously inspect both planar surfaces of disks for use in disk drives. The LIT uses a mechanical lifter which moves the disk through the laser scan lines (i.e. perpendicular to the scan lines) to allow the entire surface on each side of the disk to be scanned. The light reflected from the surface is routed to a detector which converts the intensity of the reflected beam into an analog signal. The analog signal is sampled and digitized to generate pixel data. A data acquisition system sequentially stores the pixel data in a buffer. The edges of the planar surface in the pixel data are determined for each scan line while data acquisition is in progress. A mask is applied to direct the defect detection only to meaningful areas of the disk while data acquisition is in progress. A median filter and derivative analysis can be applied to the pixel data to detect deviations indicating defects. An optional calibration mirror is taught which is positioned to reflect substantially all of the incident beam during a segment of the scan line as the reflected calibration beam which is converted to an analog signal, sampled and digitized similarly to the reflected beam from the surface being inspected. By comparing the intensity of the calibration beam to the reflected beam the reflectivity of the surface can be measured.
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Imaino Wayne Isami
Juliana, Jr. Anthony
Latta Milton Russell
Lee Charles H.
Leung Wai Cheung
International Business Machines - Corporation
Knight G. Marlin
Pham Hoa Q.
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