Patent ID: 7480222

Claim:
Method for recognizing type (CD; DVD) of an optical disc, wherein: a light beam ( 32 ) is generated, directed towards the optical disc ( 2 ), and caused to reflect from the optical disc ( 2 ), wherein the light beam passes an optical lens ( 34 ); said optical lens ( 34 ) is caused to move axially with respect to said optical disc ( 2 ); the reflected light beam ( 32 d ) is received by an optical detector ( 35 ); an output signal (S R ) from said optical detector ( 35 ) is analyzed to detect when (P 1 ; t S ) a focus point of said light beam ( 32 ) substantially coincides with a surface of the optical disc ( 2 ) and to detect when (P 2 ; t L ) said focus point of said light beam ( 32 ) substantially coincides with an information layer of the optical disc ( 2 ); wherein a thickness time Δt is calculated in accordance with the formula: Δ t=t L −t S t S being the time of coincidence with said disc surface; t L being the time of coincidence with said information layer; wherein the measured thickness time Δt is compared with a reference value (Δt REF ), and wherein it is decided that the optical disc is of a first type (CD) if the measured thickness time Δt is larger than said reference value (Δt REF ), and that the optical disc is of a second type (DVD) if the measured thickness time Δt is smaller than said reference value (Δt REF ); wherein said reference value (Δt REF ) is calculated from an experience-based average value (Δt AV (CD) ) of the thickness time Δt of CD discs, or from an experience-based average value (Δt AV (DVD)) of the thickness time Δt of DVD discs, or from both.