JPS5984351A - optical information reproducing device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to optical information reproduction in which information is read out in a non-contact manner using optical means from an information recording carrier on which information is recorded on concentric solid or spiral information tracks. It is related to the device.

The structure of the conventional example and its problems The recording density of an information recording carrier (hereinafter simply referred to as a disk) in which information is recorded on concentric solid or spiral information trunks (hereinafter simply referred to as a track) is Tracking control is indispensable for information reproducing devices that read information at high speeds and in a non-contact manner. Known examples of such discs include optical video discs, digital audio discs, and other data files.

When producing one such disc, read the information +t'1. Tracking control is generally performed in which a relative positional error between a light spot and a track is optically detected to obtain a tracking error signal, and the positional error is erased according to this tracking error signal. It will be done. However, if there is a defect in the disk and a large amount of noise is mixed into the tracking error signal, tracking control is disturbed and the tracking error signal is likely to jump to a nearby track. Particularly in the case of optical digital audio discs where the track linear velocity is slow, the transit time for defective areas is long, and this tendency is remarkable.

In order to improve this kind of drawback, some kind of processing such as a method of detecting a defect on the disk and maintaining the value of the tracking error signal immediately before the time of tracking the defective part is applied to the 1-racking control. This method has traditionally been used.

FIG. 1 is a block diagram showing a conventional example of tracking control means using the method described in "2", in which 1 is a disk, 1a is an information recording surface, 1b is a transparent protective layer, 2 is an optical head, 3 is an amplifier, 4 is a defect detection means, 5 is an error detection rotation, 6 is a processing means, 7 is a drive circuit, 8 is an actuator, and 9 is a waveform shaper.

The operation of the tracking four-mark means of the information reproducing apparatus constructed as above will now be described. The optical head 2 focuses a light spot on the information recording surface 1a of the disk 1 through the transparent protective layer 1b, reads the information and outputs a read signal, and also collects the information according to the rotation of the disk 1 and external vibrations. A tracking error detection signal is output that changes depending on the relative positional error between the track being generated and the 1-light distribution spot, that is, the tracking error. This I
・The method of obtaining the racking error detection signal is not particularly limited. For example, by dividing the information signal detector into two and comparing the levels of the respective detection signals, the imbalance in the brightness distribution of the reflected light from the disk can be detected. Alternatively, a method may be used in which two sub-spots for detecting tracking errors are formed by being shifted in opposite directions one by one without being offset. The error detection circuits receive the tracking error detection signal, extract a tracking error component, perform processing such as differential compensation or debt compensation as necessary, and output a tracking error signal. Normally, this 1-racking error signal passes through the processing means 6 and is input directly to the drive circuit 7 to drive the actuator 8 and control the position of the light spot.

On the other hand, the defect detection means 4 outputs a defect detection signal when the edge spacing of the one-digit digital signal obtained by shaping the output signal of the amplifier 3 by the waveform shaper 9 exceeds a predetermined value. do.

In general, signals recorded on a disk are modulated so that the maximum inversion interval is less than a predetermined length.1.When the edge interval of the reproduced signal exceeds a predetermined length, the reproduced signal is It is possible to detect gaps in the reading area of the disc, rather than serious problems. Specifically, the defect detecting means 4 is constituted by a stable multi-vibration brake whose time constant is longer than a predetermined length indicated by - and which is capable of detecting peaks.

However, if there are scratches or cracks on the surface of the transparent protective layer 1b, the order of the light beam focused on the information recording 1ffi 1a L is large, so that the read signal output from the optical node 2 is The level is only gradually decreasing. For this reason, the detection of the defect is delayed, and during this time, the tracking control signal is affected by external noise (111) (which has the disadvantage that the tracking control is easily disturbed by humans).

OBJECTS OF THE INVENTION The objects of the present invention are (1) to provide an optical information reproducing device capable of eliminating the above-mentioned conventional drawbacks and capable of EiJ stable tracking control against scratches and dirt on the surface of a transparent protective layer of a disk; That's true.

Structure of the Invention The optical information reproducing device of the present invention provides an information recording surface in which digital information with a limited maximum reversal interval is recorded on concentric or spiral information tracks on an information recording surface covered with a transparent protective layer. 1. On the information recording surface of the carrier, a light spot is focused through the transparent protective layer, the digital information is optically detected as a change in the amount of light, and this change in the amount of light is converted into an electrical signal, which is a read signal. an optical head that outputs
-1- A tracking control means for controlling the light distribution spot to follow the above-mentioned information I/rack; detection means for substantially attenuating the envelope signal to output a base α signal having a level between the level of the envelope signal and the DC level of the reproduced signal; a waveform shaping means for shaping the waveform of the distributed signal to - as a threshold value and outputting a detection digital signal; and a waveform shaping means for outputting a defect detection signal by detecting that the edge interval of the detection digital signal has exceeded a predetermined length. a defect detection means;
When the defect detection signal is output, T1 is processed so that the trunking control described in -1- is not easily disturbed by noise.
! The discharge time constant when the detection means performs envelope detection is: 1. The thickness of the transparent protective layer is Dl, its refractive index is n, and the numerical aperture of the focusing lens that focuses the light spot is NA, when the relative linear velocity of the information trunk to the optical spot is ■, I)/(vLT] page〒``〒
), so that tracking control is less likely to be disturbed even by scratches or dirt on the transparent protective layer.

Incidentally, optical information reproducing devices generally require tracking control to control the radial direction of the disc, and focus control to control the direction perpendicular to the track on the disc, but both of these have a wide range of functions. In this sense, it can be regarded as tracking control, and the tracking control referred to here includes both of these.

DESCRIPTION OF EMBODIMENTS Below, embodiments of the present invention will be described with reference to the drawings.

FIG. 3 shows a block diagram of a tracking control device in an embodiment of the present invention, in which 1 is a disk, 1a is an information recording surface, 1b is a transparent protective layer, 2 is an optical head, 3 is an amplifier, and 5 is an error Detection circuit; 6, processing means; 7, drive circuit; 8, actuator; 9, waveform shaper;
2 is a coefficient unit, 23 is a detection means, and 24 is a comparator.

The operation of the tracking control device q of this embodiment configured as described above will be described below.

The optical head 2 reads the information (V) from the disk 1 and outputs a read signal, and also optically detects a tracking error, which is a relative position error between the optical spot and the track, and changes the information according to this tracking error. Outputs tracking error detection signal. The error detection circuit 5 extracts from this tracking error detection signal a tracking error signal that changes approximately in proportion to the tracking error. ;■,!H During normal operation, this tracking error signal is processed by the processing means. 6][n] and input to the drive circuit 7.The drive circuit 7 amplifies the power of this wooden sword signal and drives the actuator 8, so as to cancel the tracking error described in 1-1-light distribution spot. 1. Error detection circuit 5. The drive circuit 7 and the actuator color constitute tracking control means.

- - If the surface of the transparent protective layer 1b of the disc 1 is scratched or dirty, an abnormality appears in the read signal. The scratches and dirt listed in 1-1 are detected as defects by the stable multi-by-break 10, and during this time, the processing means 6 performs processing such that the tracking control is less likely to be disturbed by noise mixed into the tracking error signal due to the defects listed in 1-1. Specifically, as this process, it is effective to maintain the value of the tracking error signal immediately n11 of the defect, to block high frequency components, etc.

Next, the detection means 23. The operation of defect detection by the comparator 24 and the retrigger monostable multi-by-break 10 will be described in more detail with reference to the signal waveform diagram in FIG. In FIG. 3, 30 is a reproduction signal output from the amplifier 3, 31 is an envelope signal obtained by detecting the envelope of the reproduction signal M 30 with an envelope detector 21 having a sufficiently long discharge time constant, and 32 is an envelope signal of this reproduction. The base θ signal 33 is obtained by attenuating the line signal 31 at a constant ratio by the coefficient unit 22, and the signal 33 is a detected digital signal obtained by comparing the regenerative signal 30' and the reference signal 32 with the comparator 24 and shaping the waveform. 2 is a waveform diagram. The level of the reference signal 32, which is the threshold of the comparator 24, is usually different from the threshold of the waveform shaper 9, and the waveform of the endogenous digital signal output from the liquid distribution shaper 9. In addition, in Fig. 3, the tJf raw signal 30
is assumed to change in the positive direction in the figure when the amount of light detected by the throat 2 increases. Figure 3 (usually iM
This shows the signal waveform at the time of raw data, and as shown in the figure, the detected digital signal 33 always has rising or falling edges corresponding to the inversion of recorded digital information. Therefore, these edge spacings are generally limited to less than or equal to the maximum reversal spacing limited by the variable RIM scheme. For example, in the case of MFM modulation, if the length corresponding to one pit is r, the maximum inversion interval is 2.
Therefore, the edge spacing of the two detection digital signals is also limited to approximately 2T.

However, if the surface of the transparent protective layer 1b has defects such as scratches or cracks, the maximum amount of light detected by the optical head 2 will decrease. A depression occurs in the line.) in Fig. 3 shows the signal waveform at this time. As shown in the figure, based on the above (signal 3
The level of 2 is set to an appropriate value between the level of the color scheme signal 31 and the DC level of the reproduced signal 3o of 1, and the envelope detector 21 detects such a fast drop in the envelope. If the discharge time constant is made long enough to prevent sufficient response,
In such a defective part, the detection digital signal 33
edges are missing. For this reason, the edge interval of the detection digital signal 33 becomes extremely long, so that the interval between the edges of the detection digital signal 33 is a predetermined length, for example, MF.
In the case of M modulation, the above defect can be detected by detecting that the length is longer than 2T). In addition, in order to simplify the circuit configuration of the defect detection means, only either the rising edge or the falling edge is detected, and the edge interval is longer than twice the maximum reversal interval determined by the modulation method. Defects may be detected by As a specific means for detecting that the edge is near the edge or has become longer than a predetermined length, for example, as in this embodiment, a retriggerable retriggering method in which the time constant τ is set slightly longer than the predetermined length is possible. However, a monostable multi-bibreak 10 can be used. This retrigger monostable multi-by-break 1o is triggered by the edge of the detection digital signal 33 and outputs H' only for a period of time.
′, normally this image trigger is stable.The multi-by-break 10 is constantly triggered because the trigger is repeated at a period less than τ, and the output is ゛°.
Continue in the H-pa state. However, due to a defect in the disk, the edge of the detected dilter signal 33 is missing and the edge interval becomes less than τ, the output of the monostable multivibrator 10 is in a stable state.
become. That is, when the output of the trigger stable multivibrator 1o becomes 'L' in 1.11j, the failure can be regarded as a defect detection signal. Therefore, by processing the 1-ranking control so that it is less likely to be disturbed by noise, such as by holding a tracking error signal according to this defect detection signal, track jumps due to disk defects can be prevented. I can do something.

2. In FIG. 3, the reproduced signal 30 is obtained by amplifying the read signal including its DC component, and therefore the fluctuation of the envelope of the reproduced signal 30 is vertically asymmetric. If low frequency components are removed to a relatively high frequency using a high-pass filter, fluctuations in the envelope of the reproduced signal 30 become vertically symmetrical. In that case, the envelope detector 21 can detect the envelope on either side of the reproduced signal.The thickness of the transparent protective layer is Dl, and its refractive index is n1 of the optical head that focuses the light spot. The numerical aperture of the focusing lens is N
A.) When the linear velocity of the rank is ■, the time td at which the envelope of the reproduced signal drops due to dirt on the surface of the transparent protective layer is ta D/ (V (n/NA)
"1'j, so if the discharge time constant of the envelope detector 21 is made longer than about td, defects on the surface of the transparent protective layer J2 can be detected0. For example, D=
1.21Tun, V:=1.3m, n=
1.5. If NA=0.6, then td'; 0.33 m5.

On the other hand, tracking errors occurred due to external vibrations, etc.
In the case of JA, the level of the read signal component decreases as in the case where there is a defect in the disc.
When low frequency components are removed by a high-pass filter with a high cutoff frequency, the tracking error causes depressions both above and below in the envelope of the reproduced signal. Therefore, when the defect detection sensitivity is increased, changes in the reproduced signal due to tracking errors are more likely to be mistakenly detected as defects. However, as in the case of No. 31, the reproduced signal 3o contains even a DC component, or at least 10087. In the case where the above low frequency components are included, the change in the reproduced signal 3o due to a short time tracking error mainly appears as a depression in the lower envelope, and the upper envelope hardly changes. I don't receive it. This is because the tracking error detected by the optical head 2 only increases its minimum value: ji'i, and the dog value hardly changes. Therefore, if the level of the reference signal 320 is set between the level of the envelope signal 31 and the DC level of the reproduced signal 30, false detection due to such tracking error can be avoided. can.

In the block diagram of FIG. 3, the detection means 23 is composed of an envelope detector 21 and a coefficient multiplier 22, but a circuit having both of these functions may be used. Fourth
The figure is a circuit diagram showing an example of such a detection means. In the figure, transistor Q1 operates only when it is positively biased and has a rectifying effect, and the charging time constant of capacitor C (
By making RlC) smaller than the discharge time constant (R2O), envelope detection is performed, and by dividing the voltage into R2/(R1+R2), it also functions as a coefficient unit.The effect of the invention is clear from the above explanation. As such, the present invention provides an optical information reproducing device including an optical head that reads signals using a light spot focused on a disk and outputs a read signal, and also optically detects a tracking error and outputs a tracking error detection signal. , tracking control means for causing the optical spot to follow the trunk, and substantially attenuating an envelope signal obtained by envelope detection of a welfare signal obtained by amplifying the read signal as necessary; and a waveform shaping means that outputs a detected digital signal by shaping the reproduced signal using the reference signal as a threshold and outputting a detected digital signal. Defect detection means detects when the edge interval of the detection digital signal exceeds a predetermined length and outputs a defect detection signal; The detector is configured such that the discharge time constant when the detection means performs envelope detection is an appropriate length. This has the effect that tracking is less likely to be disturbed by dust or dirt.

Further, the reproduced signal includes a low frequency component of at least 100 Hz or more of the read signal, and the detection means performs envelope detection of the reproduced signal on a side corresponding to a maximum value of the light beam detected by the optical head. This provides the effect that the defect detection means is less likely to erroneously detect a tracking error caused by external vibration or the like as a disk defect.

[Brief explanation of the drawing]

The first building is a block diagram of a tracking control means in a conventional optical information reproducing device, FIG. 2 is a block diagram of a tracking control means in an embodiment of the present invention, and FIG.
), (B) , (C1 is a signal waveform diagram of each part in the embodiment of FIG. 2, and FIG. 4 is a circuit diagram showing a specific configuration example of a part of the embodiment of FIG. 2. 1... ... Disc, 1a ... Information recording surface, 1b ... Transparent protective layer, 2 ... Optical head, 6 ... Error detection circuit, 6. ...processing circuit, a...drive circuit, 8...actuator, 21...envelope detector, 22...
... Coefficient unit, 23 ... Detection means, 24 ...
... Comparator, 1o ... Retrigger monostable multivibrator. ζ゛C1 diagram/η 'N 20 ζ, ゛53 diagram

Claims (2)

[Claims] (1) The transparent protective layer is placed on the information recording surface of the information recording carrier in which digital information with a limited maximum reversal interval is recorded in concentric or spiral information tracks on the information recording surface covered with the transparent protective layer. an optical head that focuses a light spot through the optical head, optically detects the digital information as a change in the amount of light, converts this change in the amount of light into an electrical signal, and outputs a reading signal; tracking control means for controlling the tracking;
``The envelope signal obtained by envelope detection of the reproduced signal obtained by amplifying the read signal as required is substantially attenuated by r, and the level of the envelope signal is between the level of the envelope signal and the DC level of the reproduced signal. a detection means for outputting a reference signal having a level of , a waveform shaping means for shaping the reproduced signal using the reference signal as a threshold and outputting a detected digital signal, and an edge interval of the detected digital signal having a predetermined length a defect detection means for detecting that the above has occurred and outputting a defect detection signal; and processing for processing so that the tracking control is less likely to be disturbed by noise when the defect detection signal in 2 is output. and the discharge time constant when the detection means performs envelope detection is the thickness of the transparent protective layer D.
When its refractive index is n, the numerical aperture of the focusing lens that focuses the light spot is N, and the relative linear velocity of the information track to the light spot is ■, then D/(Vr surface 57). An optical information reproducing device characterized by a large size. (2) The reproduced signal is at least 10011 times larger than the read signal.
z or higher, and the detection means performs envelope detection of the internal signal on the side corresponding to the maximum value of the optical signal detected by the optical head. An optical information N71r production device according to claim 0).