Patent ID: 6058081
Filing Date: 2000-05-02
Classification: G11B,H02K

Abstract:
An optical drive system, comprising:an objective lens subassembly for directing light from a light source toward an information storage medium, an amount of said light being returned therefrom;an objective lens disposed in said objective lens subassembly;at least one quad detector for detecting light returned from the storage medium;processing circuitry connected to said at least one quad detector to produce a Quad Sum signal related to the light detected by the quad detector;a first servomotor for moving said objective lens subassembly to effect focus capture, said first servomotor moving said objective lens to a first position, then away from said first position toward said storage medium while the medium is being read and said processing circuitry searches for a maximum Quad Sum signal, said first servomotor also moving said lens back away from said storage medium;first electronic means for controlling said first servomotor; andservo error detecting means including said at least one quad detector, said servo error detecting means being coupled to said first electronic means and implemented for determining when total light returned from said information storage medium exceeds a predetermined measured value, for searching for a first zero crossing, for determining when said Quad Sum signal exceeds a predetermined amplitude, and for indicating to said first electronic means to direct close of focus when said Quad Sum signal exceeds said predetermined amplitude.