Optical disc drive apparatus, method for measuring tilt of an optical disc, and method for correcting tilt of an optical disc

Abstract

Tilt (θ(r, φ)) is measured in a measuring location (P(r, φ) optical disc (). A pivotable objective lens () is brought to a first focus measuring location such as to focus a light beam () in a first anchor point (P(r−Δr, φ))having the same angular coordinate φ as said measuring location (P(r, φ)) and having a small radial distance Δrfrom said measuring location. The objective lens is brought to a second focus measuring location such as to focus the light beam in a second anchor point (P(r+Δr, φ)) having the same angular coordinate φ as said measuring location and having a small radial distance Δrfrom said measuring location, wherein said first and second anchor pints are located on opposite sides of said measuring location. Tilt in said measuring location is calculated from the coordinates of said two focus measuring locations of said objective lens.