| 摘要 |
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 four light detectors comprises a first input line (102) for receiving as an input an analog "S" curve signal, a second input line (104) receiving as an input an analog A + B signal from two light detectors (A, B), and a third line (106) receiving as an input an analog C + D signal from a further two light detectors (C, D). First and second comparators (110, 112) are associated with the first input line, the first comparator determining that the "S" curve signal is less than a certain predetermined value and the second comparator determining that the "S" curve signal is greater than a predetermined value, these two comparators together producing a first logic output signal. The third comparator (118) is associated with the second input line producing an output logic signal which is indicative that the A + B signal is within a predetermined range and produces a second logic output signal. A fourth comparator (120) is associated with a third input line and determines that the C + D signal is within a predetermined range and produces a third logic output signal. Logic circuitry (168, 172, 176) comprises the first, second and third logic output signals and produces a fourth logic output signal indicative that the objective lens is within the focusing region of a linear region (228) of the "S" curve signal, the logic circuitry requiring that the "S" curve signal is within predetermined limits and requires that the C + D signal and the A + B signal are predetermined limits. Control circuitry responsive to this fourth logic output signal controls the focus control system to be on when in focusing range. |
