Defect detecting method

Details Defect detecting method Defect detecting method

1990-04-18

1993-06-08

Chin, Tommy

Dynamic information storage or retrieval

With servo positioning of transducer assembly over track...

Optical servo system

369 4426, 369 4432, G11B 700

Patent

active

052185893

ABSTRACT:
In a method for detecting a defect in a prepit as a sampling object formed on a recording face of an information recording medium in an optical or magnetooptic disk drive unit, an optical or magnetooptic disk is used as the information recording medium and focusing and tracking controls are performed by using a sample servo system at recording and reproducing times of information. This method has the steps of disposing a device for checking a plurality of reproducing signals provided when a light spot moves onto the prepit in the detection of the defect therein and calculating an average value in voltage with respect to these reproducing signals; setting the average value as a reference voltage level of the reproducing signals and setting a constant window width with respect to the average value; calculating the difference in voltage between the reference level and a sampling value of each of the reproducing signals corresponding to the prepit every time when each of the reproducing signals is sampled; comparing the voltage difference every sampling with the window width; and judging that the prepit is defective when the voltage difference exceeds the window width.

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