Signal Analysis of Scratch-Detection on Magnetic Disc by Using Light Reflection Approach

Abstract

In hard disk manufacturing, a process of quality inspection of magnetic disc is crucially focused on finding traces of scratch that occur on the surface by various sources such as production process, machinery, tribology or recording head. It may affect the efficiency of magnetic disc’s read/write ability. Many approaches have been proposed to detect the scratch by either destructive or non-destructive testing. In this study, it shows an analysis of signals from the detected scratches on the magnetic disc by reflection light method, using a CD pick-up head. It works by producing an incidental laser beam to the surface and then detecting it by a photodiode detector. The results showed that when the laser beam is incident onto the magnetic disc with/ without scratch, reflecting lights to the photodiode are different and the signal changes according to the intensity of the incidental/reflecting lights.