Optical disk drive with multiple data layer disk and system for focusing

Abstract

An optical disk drive with a multiple data layer optical disk uses computed axial velocity values of the data layers to optimize the interlayer transition of the focused light beam. In the preferred embodiment, the axial velocities of the data layers are computed for a set of radial and angular positions on the data layer surfaces using one of several techniques. The data layer axial velocity values are computed from the measured current values to the voice coil motor focus actuator or from the output of the detector that generates the focus error signal (FES). A routine is run at disk drive startup, or at various times during disk drive operation, to measure the coil current or FES at different radial and angular positions and compute the axial velocity values. The computed axial velocity values are then mapped into memory storage according to addresses corresponding to their radial and angular positions. When it is desired to move the focused light beam from one data layer (the initial or take-off data layer) to another data layer (the final or target data layer) the computed axial velocity values are retrieved for the radial and angular positions nearest the take-off and target sectors on the respective data layers. These velocity values are then used to modify the acceleration profile of the focusing lens so that the focused light beam arrives at the desired position on the target data layer with a velocity close to the target data layer axial velocity.