Patent ID: 7116619
Filing Date: 2006-10-03
Classification: G11B

Abstract:
1. In an optical disc drive apparatus, of a type comprising: rotating means defining a rotating axis for an optical disc; optical scanning means for scanning an optical disc with a light beam, said optical scanning means comprising a displaceable objective lens for focussing the light beam onto said optical disc, said objective lens being displaceable in axial direction and capable of being pivoted about an axis directed in tangential direction; a method for measuring tilt in a measuring location of the optical disc; the method comprising the steps of: by pivoting and axially displacing the objective lens, bringing said objective lens to a first focus measuring location such as to focus the light beam in a first anchor point having substantially the same angular coordinate φ as said measuring location and having a small radial distance Δr by displacing and pivoting the objective lens, bringing said objective lens to a second focus measuring location such as to focus the light beam in a second anchor point having substantially the same angular coordinate φ as said measuring location and having a small radial distance Δr said first and second anchor points being located on opposite sides of said measuring location; the method further comprising the step of calculating tilt in said measuring location from the coordinates of said two focus measuring locations of said objective lens.