Focusing initialisation control system

Claim 1

A focusing initialisation control system for an optical recording device having an objective lens disposed relatively near recording media and controlled by a focusing control system having a plurality of light detectors, said focusing initialisation system being characterised by: first signal receiving means (102) for receiving as an input an analog "S" curve signal; second signal receiving means (104) for receiving as an input an analog A + B signal from two light detectors (A, B); third signal receiving means (106) for receiving as an input an analog C + D signal from a further two light detectors (C, D); first and second comparator means (110, 112) associated with said first signal receiving means, said first comparator means determining that said input "S" curve signal is less than a certain predetermined value and said second comparator means determining that said "S" curve signal is greater than a predetermined value, said first and second comparator means being arranged to produce a first logic output signal; third comparator means (118) associated with said second signal receiving means for producing an output logic signal indicative that said A + B signal is within a predetermined range, said third comparator means being arranged to produce a second logic output signal; a fourth comparator means (120) associated with said third signal receiving means for determining that said C + D signal is within a predetermined range, said fourth comparator means being arranged to produce a third logic output signal; logic means (168, 172, 176) for combining said first, second and third logic output signals to produce a fourth logic output signal indicative that said objective lens is within the focusing region of a linear region (228) of said "S" curve signal, said logic means being such as to require said "S" curve signal to be within predetermined limits and to require said C + D signal and said A + B signal to be within predetermined limits; and control means responsive to said fourth logic output signal from said logic means for controlling said focus control system to be on when in focusing range.

Claim 6

A system as claimed in any preceding claim characterised by including second timing means (196) for allowing said objective lens to be outside focusing range for a predetermined time before deactivating said focusing control system.

Claim 7

A system as claimed in any preceding claim characterised in that said logic means comprises first NAND gate means (168) connected to receive as a first input said first logic output signal and as a second input said second logic output signal, second'NAND gate means (172) connected to receive as a first input said first logic output signal and as a second input said third logic output signal, and third NAND gate means (176) connected to receive as a first input the output of said first gate means and as a second input the output of the second gate means, said third gate means producing as an output said fourth logic signal.