Focus capture for optical disc system

The optical drive system described comprises an optical assembly, a light source, an objective lens disposed in an objective lens subassembly, an actuator assembly which suspends the objective lens subassembly for relative motion thereof with respect to the actuator assembly, first and second servomotors for moving the objective lens subassembly in tracking and focusing directions, respectively, relative to the actuator assembly, a third servomotor for moving the actuator assembly in the tracking direction relative to a medium, first electronic means for controlling the first, second, and third servomotors, a motor with a hub assembly for moving the medium relative to the objective lens subassembly, a photo detector, second electronic means responsive to an output signal of the photo detector for decoding information carried in the light returning from the medium, third electronic means for enabling the light source to emit light at a first intensity level to encode information on the medium and at a second intensity level to read information encoded thereon, data receiving means for accepting data that is storable on the medium, data encoding means being responsive to the data receiving means for representing the data to be stored in a predetemined format, the data encoding means also for directing data to the third electronic means, a magnetic field generator for producing a magnetic field on a portion of the medium and for coacting with the third electronic means and the light source to write and erase information on the medium, a cartridge loading assembly, servo error detecting means coupled to the first electronic means, and a housing structure for positioning components of the optical drive system with respect to one another.The system claimed include means to monitor and use a Quad Sum signal associated with the return light for focus capture.