Patent ID: 7548499
Filing Date: 2009-06-16
Classification: G11B

Abstract:
1. An offset amount measuring method of measuring an offset amount, which is a shift amount in a radial direction between radial positions on first and second recording tracks, the radial positions being associated with each other by a pre-format address given in advance to the first and second recording tracks, in an information recording medium comprising at least: a disc-shaped first recording layer in which the first recording track is formed to record therein record information; and a disc-shaped second recording layer in which the second recording track is formed to record therein the record information in a direction equal to or opposite to that in the first recording track of the first recording layer, said offset amount measuring method comprising: a recording process for measurement (i) of recording information for measurement, into the first recording track, by a predetermined section or by a predetermined length, from one measurement reference position which is specified by the pre-format address, and (ii) of recording the information for measurement, into the second recording track, by the predetermined section or by the predetermined length, from or toward a measurement correspondence position, which is associated with the one measurement reference position by the pre-format address; a first detecting process of detecting a first border position which is a border of a first recorded area in which the information for measurement is recorded and a first unrecorded area in which the information for measurement is unrecorded in the first recording track, on the basis of a difference in reflectance between the first recorded area and the first unrecorded area, with a central axis of said information recording medium as a reference; a second detecting process of detecting a second border position which is a border of a second recorded area in which the information for measurement is recorded and a second unrecorded area in which the information for measurement is unrecorded in the second recording track, on the basis of a difference in reflectance between the second recorded area and the second unrecorded area, with the central axis as a reference; and a determining process of determining the offset amount, on the basis of the detected first and second border positions.