1. Field of the Invention
The present invention relates to an optical disc apparatus.
2. Description of Related Art
In a typical optical disc apparatus, upon start-up, adjustments are performed by following a procedure described below.
First, using a tracking error signal as an index, a rough adjustment of spherical aberration correction is performed, followed by automatic gain control of the tracking error signal, and tracking control is pulled in. Moreover, after that, using an RF signal as an index, a fine adjustment of spherical aberration correction is performed, and a focus control loop gain and a tracking control loop gain are adjusted, after which the start-up is completed. This completion of the start-up enables playback of an optical disc.
In the fine adjustment of spherical aberration correction carried out after tracking control has been turned on, however, a balance value of a tracking error signal varies with a change in the position of a movable lens for spherical aberration correction disposed in an optical system of an optical pickup, and due to the variation in the balance value, a tracking servo may become unlocked, rendering the adjustment in progress unable to be continued.
JP-A-2008-84417, JP-A-2004-241100, JP-A-2005-38472, the publication of Japanese Patent No. 4407623, and the publication of Japanese Patent No. 4556117 disclose arts related to spherical aberration correction. None of these, however, discloses or suggests a technique for preventing, when spherical aberration correction is performed, a tracking servo from becoming unlocked due to a variation in the balance value of a tracking error signal.