JPS6459685A - Disk for measuring jitter - Google Patents

Abstract

PURPOSE:To measure a jitter conveniently and accurately by writing plural mark signals of a constant width able to be identified as the difference in a reflection factor concentricly in the interval in the peripheral part of a disk. CONSTITUTION:A mark 2 of a constant width W is written in a prescribed interval on the one side surface of a reference disk 1 while it is positioned at the peripheral part of a disk 1. Here, the shape of the mark 2, which is made concentric toward the center, is made into the square, and the reflection factor is made different from the reflection factor of a substrate 1 which is exposed. The disk 1 like this is used as a disk for measuring a jitter, fitted to a spindle motor to be measured not shown in the figure, rotated, the reflecting light from the mark 2 is detected by the photodetector not shown in the figure and the width of the mark 2 is measured. The relation of the mark width and the eccentricity of the disk 1 becomes a circular arc-shaped detecting point locus and it can be clearly classified from the continuous circle when the eccentricity is not present.