High speed optical inspection apparatus for a transparent disk using gaussian distribution analysis and method therefor

US6294793A · kind A · utility

Assignee

• Brown & Sharpe Surface Inspection Systems, Inc. · US

Inventors

• Andrei Brunfeld · Bat Yam, IL
• Joseph Shamir · Huntsville, US
• Gregory Toker · Jerusalem, IL
• Liviu Singher · Haifa, IL
• Ilan Laver · Kfar Sava, IL
• Ely Pekel · Kfar Sava, IL

Key dates

• Filing date: Dec 3, 1992
• Grant date: Sep 25, 2001
• Expiry date: Dec 3, 2012

Classification

• Technology area (CPC G): Physics
• CPC primary: G01N21/8806
• WIPO field: Measurement
• WIPO sector: Instruments

Abstract

An optical inspection apparatus operates at high speed at very high resolution for detecting defects in transparent disks in a production environment. These transparent disks are of the type commonly used as disk platters in hard disk drives. This apparatus uses a laser beam directed to a polygon scanner, which provides a linear scan of the beam along a radius of the disk. The disk to be inspected is rotated such that its entire surface passes the scan path of the laser beam. The laser beam, after passing through the unit to be inspected, is directed to a parallel detector array, which detects changes in the nominal Gaussian distribution of the laser beam that correspond to defects in the surface of the transparent disk above a programmable threshold level. This parallel detection method allows the inspection apparatus to identify defects much smaller than the diffraction limits of the optics used, and will accurately identify changes of the laser beam caused by defects in the disk. An automatic disk handler loads untested disks into the apparatus and unloads and sorts tested disks according to the results of the inspection.