Automatic focusing system for reading information from a recordi

Dynamic information storage or retrieval – Control of storage or retrieval operation by a control... – Mechanism control by the control signal

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Details

G11B 700

Patent

active

046270418

DESCRIPTION:

BRIEF SUMMARY
FIELD OF ART

The present invention relates to an automatic focusing system in an equipment for reading out information from a recording medium having a flat reflection surface such as a video disk, whereby an objective lens system and the recording medium are prevented from striking against each other at the time of an initial focusing of an automatic focusing apparatus which functions to set the distance between the recording medium and an objective lens at an optimum value.


BACKGROUND ART

Heretofore, there has been proposed an automatic focusing system wherein a change in state of a reflected light is detected as a change in an electrical signal and an objective lens driving unit is controlled on the basis of such electrical signal.
However, it is necessary to prevent an objective lens system from being accelerated and striking against a recording medium at the time of an initial operation of an automatic focusing apparatus, and in this regard there has been known a method wherein the entire objective lens system is moved up to a focal position between an objective lens and the recording medium by using a precise screw feed mechanism or the like and thereafter the automatic focusing apparatus is switched ON, or a method wherein when the distance between an objective lens and a recording medium decreases, an objective lens system is braked at a suitable timing, as shown in Japanese Patent Publication No. 1683/1979.


DISCLOSURE OF THE INVENTION

It is the object of the present invention to provide an automatic focusing system wherein a separate control signal is provided in addition to a focus error signal at the time of an initial focusing of an automatic focus control apparatus whereby a focusing is effected without collision of an objective lens with a recording medium.


BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a functional circuit diagram showing the automatic focusing system of the present invention;
FIG. 2 consisting of (a)-(c) is a view showing the relationship between the shape of a reflected light condensed on a photo detector and a focus error voltage;
FIG. 3 is a view showing the relationship between a deviation from a focal position of a recording medium and an objective lens and a focus error voltage;
FIG. 4 is a view showing an objective lens system; and
FIG. 5 is a waveform diagram for explanation of operation.


BEST FORM FOR PRACTICING THE INVENTION

Referring to FIG. 1, there is shown the automatic focusing system of the present invention, in which the reference numeral 1 denotes a photo detector composed of four photo detectors D.sub.1, D.sub.2, D.sub.3 and D.sub.4 for receiving light reflected and modulated by a recording medium; numerals 2 and 3 denote current-voltage conversion amplifiers for the summed outputs of diode pair D.sub.1 and D.sub.2 and the diode pair D.sub.3 and D.sub.4, respectively; 4 a differential amplifier; 6 an amplifier circuit; and 7 a drive circuit which is composed of transistors Q.sub.1 and Q.sub.2 and which causes a current flow in a coil 8 integrally with an objective lens.
The numeral 12 denotes a triangular wave generation circuit for generating a triangular wave having a low frequency of 1 Hz or so; 13 a square wave generation circuit for generating a square wave of 50% duty ratio having a high frequency of 20 kHz or so to which an objective lens system does not respond; 14 a differentiation circuit consisting of a capacitor C and a resistor R; 15 an addition circuit; 16 a level detection circuit consisting of mean value detecting circuit and an amplifier operated by the AC component of the summed outputs of of the amplifiers 2 and 3 passing through capacitance 18; and 17 a relay switch.
The objective lens 10 and the coil 8 are disposed as shown in FIG. 4, in which when current flows in the coil 8 integral with the objective lens 10, the objective lens 10 is moved in a direction away from a recording medium 9 by virtue of an electromagnetic force acting between the coil 8 and a permanent magnet 11 and settles down in a focal position.
Operation w

REFERENCES:
patent: 3974327 (1976-08-01), Van Dijk
patent: 3976828 (1976-08-01), Janssen
patent: 4123652 (1978-10-01), Bouwhuis
patent: 4128847 (1978-12-01), Roullet et al.
patent: 4280215 (1981-07-01), Okano
patent: 4286147 (1981-08-01), Tsuboi et al.
patent: 4337532 (1982-06-01), Oprandi et al.
patent: 4357696 (1982-11-01), Bierhoff et al.
patent: 4418405 (1983-11-01), Barnette et al.

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