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

摘要

An optical inspection apparatus operates at high speed at very high resolution for detecting defects in reflective disks in a production environment. These reflective disks are of the type commonly used as disk platters in hard disk drives. This apparatus uses a laser which provides a light beam directed to a polygon scanner, which provides a linear scan of the beam along a radius on both sides of the disk by using two mirrors to direct the light beam. The disk to be inspected is rotated such that its entire surface passes the scan path of the light beam. The light beam is reflected off the reflective disk, and returns to the scanning optics and the polygon scanner in a path coincident with the transmitted light beam. The reflected light beam is distinguished from the transmitted light beam by using a beam splitter to direct the reflected light beam to a parallel detector array, which detects changes in the nominal Gaussian distribution of the light beam that correspond to defects in the surface of the reflective 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 in the light 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.