Patent ID: 8335143

Claim:
A method for inspecting an optical information storage medium, the method comprising the steps of: irradiating the optical information storage medium with a laser beam and rotating the storage medium by a constant linear velocity control technique by reference to the radial location at which the laser beam forms a spot on the storage medium; changing the rotational velocities according to the radial location on the storage medium between at least two linear velocities that include a first linear velocity Lv 1 and a second linear velocity Lv 2 , which is higher than the first linear velocity Lv 1 ; generating a focus error signal and/or a tracking error signal based on the light reflected from the storage medium; performing a focus control and/or a tracking control on the laser beam that irradiates the storage medium based on the focus error signal and/or the tracking error signal; and passing branched outputs of the focus error signal and/or the tracking error signal through predetermined types of frequency band-elimination filters for the focus and/or tracking error signal(s) to obtain residual errors of the focus and/or tracking error signal(s) and comparing the residual errors to predetermined reference values, wherein the frequency band-elimination filter for the focus error signal includes a low-pass filter LPF with a cutoff frequency LPF_FcL and a band-pass filter BPF with a lower cutoff frequency BPF_FcL and a higher cutoff frequency BPF_FcH, wherein the branched output of the focus error signal is supplied to the low-pass filter LPF and the band-pass filter BPF, wherein if the optical information storage medium is rotated at the first and second linear velocities and subjected to the focus control to make a comparison to the predetermined reference value, LPF_FcL, BPF_FcL and BPF_FcH are switched one after another according to the ratio of the second linear velocity to the first linear velocity, wherein the frequency band-elimination filter for the tracking error signal includes a low-pass filter LPF with a cutoff frequency LPF_TcL and a band-pass filter BPF with a lower cutoff frequency BPF_TcL and a higher cutoff frequency BPF_TcH, wherein the branched output of the tracking error signal is supplied to the low-pass filter LPF and the band-pass filter BPF, wherein LPF_TcL and BPF_TcL are constant irrespective of the first and second linear velocities, and wherein BPF_FcH is switched one after another according to the ratio of the second linear velocity to the first linear velocity.