JPH067107B2 - Defect detection device for information recording disc - Google Patents

Description

TECHNICAL FIELD The present invention relates to a defect detection device for an information recording disc in a disc player.

BACKGROUND ART For a player playing an information recording disc (hereinafter, simply referred to as a disc) such as a video disc or a digital audio disc, the information reading spot by the pickup should be properly focused on the recording surface of the disc, and However, a focus servo device and a tracking servo device that always control so as to accurately track the recording track on the recording surface are indispensable.

In a disc player equipped with these servo devices,
When there is a defect due to scratches on the recording surface of the disc to be played, when the information reading spot of the pickup tracks the recording track in the defect part, the error signal of the servo system is disturbed and a malfunction such as a track jump occurs. there is a possibility. Therefore, the servo is stabilized by detecting the defect of the disk and opening each servo loop or changing the equalizer characteristic in the loop at the time of the detection.

Conventionally, as a defect detection device, for example, a so-called three-beam system for generating a tracking error signal, which detects a defect on a disk based on a detection output level of one of a pair of detection beam spots for tracking, is known. There is. However, such a detection device has a drawback that it is easily affected by noise and an accurate detection operation cannot be performed.

SUMMARY OF THE INVENTION The present invention has been made in order to eliminate the above-mentioned drawbacks of the related art, and an object of the present invention is to provide a defect detection device capable of performing an accurate detection operation without being affected by noise.

The defect detecting device according to the present invention receives the reflected beam from the disc based on the pair of preceding and succeeding beam spots during the relative movement with respect to the disc, and generates the output according to the received light amount. In the disc player provided with the second photoelectric conversion means, the first
And the outputs of the second photoelectric conversion means are added, and the defect of the recording surface of the disc is detected based on the added output.

Example Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the present invention. In the figure, three beam spots obtained by converging a laser beam, that is, a pair of tracking information detection spots S ₂ preceding and succeeding each other when the information reading spot S ₁ and the disk of the spot S ₁ move relative to each other, The recording track T of the disc is irradiated from a pickup (not shown) in a positional relationship with S ₃ . Reflected beams from the disk due to these beam spots enter photoelectric conversion elements 1 to 3 incorporated in the pickup.

The photoelectric conversion element 1 is arranged so that each light receiving surface is divided into four by two straight lines orthogonal to each other, and is composed of four light receiving elements independent of each other, and the total output of these elements becomes a read RF signal. . On the other hand, the respective outputs of the photoelectric conversion elements 2 and 3 are supplied to the differential amplifier 4 including the resistors R _{1 to} R ₄ and the operational amplifier OP ₁ to detect the difference between the two outputs, and the difference output is the center line of the recording track T. Is a tracking error signal indicating the deviation amount of the information reading spot S ₁ in the radial direction of the disk.

In addition, each output of the photoelectric conversion elements 2 and 3 is a capacitor C ₁ ,
It is supplied via the C ₂ to the adder _{5 including} the resistors R _{5 to} R ₇ and the operational amplifier OP ₂ and added. This addition output becomes a comparison input of the comparator 7 after passing through a parallel connection circuit of the diode D and the resistor R ₈ and, for example, via the switch 6 that is closed during play. The input end of the switch 6 is grounded via the capacitor C ₃ . The comparator 7 produces an output when the comparison input level exceeds the reference level V. This comparison output is supplied to a tracking servo device or a focus servo device (neither is shown) as a detection signal indicating that there is a defect due to a scratch or the like on the recording surface of the disk, and for example, opens each servo loop, or It is used as a control signal to change the equalizer characteristic in the loop.

With such a configuration, the information reading spot S can be obtained during a normal performance.
_{When 1} passes through a defect portion having a size of, for example, about 500 to 1000 μm on the surface of the recording surface or the pit surface of the disc, the output ends of the photoelectric conversion elements 2 and 3 for the tracking servo are closed during the closing of the tracking servo. Figure 2 (a), obtained in a state which can be regarded as almost no time difference due to the much greater size of the defect relative to the distance between (b) to such output voltage indicated by the tracking information detecting spots S _2, S ₃ To be The dotted line shows the output voltage when there is no defect. These output voltages (a),
(B) is added by the adder 5 and the gain is increased to become an addition output (c). The added output (c) is compared with the reference level V by the comparator 7, and when it exceeds the reference level V, the comparison output (d) is generated. This comparison output (d) becomes a defect detection output and is supplied to the tracking servo device and the focus servo device. 2 is an operation waveform diagram of the circuit shown in FIG.
1 to (d) respectively show the waveforms of the signals (a) to (d) of the respective parts in FIG.

In this manner, by adding the respective outputs of the photoelectric conversion elements 2 and 3 and comparing the added output with the reference level V to perform the defect detection, for example, the output of the photoelectric conversion elements 2 or 3 has no noise. Even if this is the case, the noise becomes extremely small in level with respect to the added output, so that accurate detection operation can be performed without being affected by the noise. The defect detection time T can be arbitrarily set by selecting the diode D, the capacitor C _3, and the reference level V of the comparator 6.

Further, for example, the play signal is used as the control signal of the switch 6 to detect the defect only when the tracking servo loop is closed, so that the malfunction of the servo system due to the defect detection when the tracking servo loop is opened, the in-focus time, etc. It is possible to prevent malfunction of the circuit before the closing of the focus servo loop.

As described above, according to the defect detecting device of the present invention, the detection outputs based on the pair of preceding and succeeding beam spots are added during relative movement with respect to the disc, and the disc is output based on the added output. Since it is configured to detect defects on the recording surface of
Accurate detection operation can be performed without being affected by noise.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, and FIG. 2 is an operation waveform diagram of the circuit of FIG. Description of symbols of main parts 1-3 ... photoelectric conversion element 4 ... differential amplifier, 5 ... adder 7 ... comparator

Claims (1)

[Claims] 1. A first and a first that receive a reflected beam from the information recording disk based on a pair of preceding and following beam spots during relative movement with respect to the information recording disk and generate an output according to the amount of received light. A defect detecting device for an information recording disc in a disc player having two photoelectric conversion means, comprising an adder for adding the respective outputs of the first and second photoelectric conversion means,
A defect detecting device for detecting a defect on a recording surface of the information recording disk based on an addition output of the adder.