JPH01267844A - Detrack detector - Google Patents

Abstract

PURPOSE:To detect a detrack with high accuracy by using a sub light spot away from a main light spot by a prescribed distance and detecting the detrack. CONSTITUTION:A sub light spot SS is formed away from a main light spot S for reading recorded information by a 1/4 track pitch Tp/4 in the radius direction of an optical disk 1 and detrack signal SDE whose phase is shifted by 90 deg. from a tracking error signal STE is obtained. The detrack is detected with 0[V] which is the center voltage of the detrack signal SDE as a reference. When an off-track quantity goes to the 1/4 track pitch Tp/4 even when the reflectance of the optical disk 1 changes, the detrack can be surely detected. Thus, a detrack detector whose detection accuracy is particularly high can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to a detrack detection device, and is applied to, for example, a detrack detection device such as an optical disc device, a compact disc player, etc. that is capable of writing and erasing information on an optical disc. It is suitable for this purpose.

B. Summary of the Invention According to the present invention, in a detrack detection device, detrack can be detected with high accuracy by detecting detrack using a sub-light spot.

C. Prior Art Conventionally, in optical disk devices capable of writing and erasing information on optical disks, it is possible to switch between erasing and reading recorded information by changing the amount of light beam obtained from a laser light source. is being done.

Therefore, in this type of optical disk device, when erasing recorded information, the off-track amount is detected based on the tracking error signal obtained from the pre-group, and when the off-track amount exceeds a predetermined value (hereinafter referred to as detrack). ) By reducing the light intensity of the light beam, recorded information on adjacent recording tracks is prevented from being accidentally erased.

That is, as shown in FIG. 8, in the optical disc l, after forming a pregroup 2 at a depth of 178 wavelengths with respect to the wavelength of the light beam in the circumferential direction C of the optical recording medium, the adjacent pregroup 2, pits 3 are formed discretely at a depth of 1/4 wavelength relative to the wavelength of the light beam, thereby forming recording tracks on which optical information is recorded at a predetermined track pitch T.

On the other hand, in an optical disc device, the optical disc 1
A light beam is irradiated onto the optical disc 10 to form a light spot S, and the reflected light is focused on the light receiving surface of a two-split optical detector formed by dividing the light receiving surface into two in the radial direction of the optical disk 10.

In this way, as shown in FIG. 9, in the difference signal of the two-split optical detector,
The signal level changes sinusoidally at the track pitch T1 period, and thus the tracking error signal sty can be obtained.

Therefore, the tracking error signal STE and the reference levels ■L and ■. By obtaining a comparison output, it is possible to detect that the amount of off-track has changed beyond a predetermined value, and by switching the light intensity of the light beam based on the comparison output, erroneous erasure of recorded information can be prevented. can do.

D Problems to be Solved by the Invention However, in practice, in order to prevent recorded information from being erased by mistake, the off-track amount must be approximately 1/4 track pitch 1/4 T.
, it is sufficient to reduce the light intensity of the light beam within the above range.

By reducing the light intensity of the light beam within this range, it is possible to not only prevent erroneous erasing, but also to prevent the erasing operation of recorded information from being stopped more than necessary, thereby ensuring that the desired recorded information can be erased reliably and in a short time. can be erased.

In this case, since the signal level of the tracking error signal Stt varies sinusoidally with a cycle of one track pitch T according to the off-track amount, the signal level of the tracking error signal S□ is the maximum on the positive side and the negative side. It is detected whether or not a predetermined signal level has been exceeded near the value.

However, in the tracking error signal S□ whose signal level changes sinusoidally, the change in signal level with respect to the off-track amount is relatively small near the maximum values on the positive and negative sides, so the off-track amount must be set sufficiently. There is a problem in that it becomes difficult to detect with high accuracy, and it is therefore impossible to obtain detrack detection accuracy.

Therefore, in order to reliably prevent erroneous erasing, it is necessary to set the reference level for detecting detracking to a low value, which means that the erasing operation is stopped more than necessary, and the overall time required for erasing is reduced. There is a long problem.

Furthermore, in the tracking error signal S□, the amplitude value changes around 0 [V] depending on the amount of reflected light obtained from the optical disc, so near the maximum values on the positive and negative sides, There is a problem in that the change in signal level due to the reflectance of the optical disk is large, and the accuracy of detrack detection due to the change in reflectance deteriorates accordingly.

Therefore, in order to reliably prevent erroneous erasure even on optical discs with low reflectivity, the reference level for detecting detracking must be set to a low value. The erasing operation is controlled to stop more than necessary, and the time required for erasing becomes longer as a whole.

Specifically, when trying to detect an off-track amount of 1/4 track pitch 1/4 T on an optical disc with a small reflectance where the maximum value on the positive side and negative side varies by up to 40% depending on the optical disc, With an optical disk having a high reflectance, detracking is detected when the optical disc is off-tracked by just 1716 track pitches of 1/16 TP, and the erasing operation is controlled to be stopped more than necessary.

The present invention has been made in consideration of the above points, and aims to propose a detrack detection device that can detect detrack with high accuracy.

E Means for Solving the Problem In order to solve this problem, in the present invention, a predetermined distance T, /
While irradiating the secondary light spot Ss at a distance of 4,
The reflected light from the secondary optical spot sensor is focused on a photodetector I)ss whose light-receiving surface is divided into two in the radial direction of the optical disc L, and detracked based on the difference signal S between the output signals of the photodetector OSS. to be detected.

F action A secondary light spot S5 is irradiated at a predetermined distance T, /4 apart, and the reflected light is focused on a photodetector 055 whose light receiving surface is divided into two in the radial direction of the optical disc 1. I) By obtaining a difference signal SOW of the output signals of ss, it is possible to obtain a difference signal S whose signal level changes with respect to the off-track amount with a phase corresponding to the distance T1/4 of the separation. .

Therefore, by setting the separation distance TP/4 so that the phase becomes a desired phase, detracking can be detected with high accuracy.

G example An embodiment of the present invention will be described in detail below with reference to the drawings.

[G1] First Embodiment In FIG. 1, in which parts corresponding to those in FIG. 8 are denoted by the same reference numerals, a light beam is separated into 0th-order light and 1st-order light using a diffraction grating, and is then transferred onto the optical disk 1. By condensing the light, a zero-order light spot S is formed for reading and erasing recorded information, and at the same time, the light spot S is spaced by 1/4 track pitch T, /4 in the radial direction of the optical disc 1. A light spot S5 of the primary light is formed.

Further, as shown in FIG. 2, the reflected light of the 0th order light and the 1st order light obtained from the optical disc 1 is detected by a two-split optical detector D whose light receiving surface is divided into two in the radial direction of the optical disc 1.

The light is focused on the light receiving surface, and light spots R3 and R5S are formed on the light receiving surface, respectively.

In this way, as shown in FIG. 3, a difference signal is obtained via the differential amplifier circuit 10 for the two output signals of the two-split optical detector D that focuses the zero-order light spot R3. By doing this, it is possible to obtain a tracking error signal SA (FIG. 3(A)) whose signal level changes depending on the off-track amount of the optical spot S.

On the other hand, a two-split optical detector D collects the primary light (optical spoiler) Rss via the differential amplifier circuit 11. If the difference signal is obtained, the optical spot S of the first-order light is l
/4 track pitch T.

Since the signals are separated by /4, the detrack signal S is 90° out of phase with respect to the tracking error signal sty.
I,! (Fig. 3(B)) can be obtained.

In this way, the amplitude value changes around O(V) together with the tracking error signal STE, and the change in the signal level with respect to the off-track amount is such that, contrary to the tracking error signal srt, the off-track amount is 174 track pitches. It is possible to obtain a detrack signal S, which is large near T,/4 and small near just tracking.

Therefore, based on the detrack signal SDt, 1/4
By detecting detrack near track pitch 2/4, detrack can be detected in a range where the change in signal level with respect to the off-track amount is large, and tracking error signal S7. Detection accuracy can be improved compared to the case where detrack is detected based on .

Furthermore, by doing this, even if the amplitude value changes depending on the amount of reflected light obtained from the optical disc, the change in signal level due to the reflectance of the optical disc will be smaller than near the maximum values on the positive and negative sides. Detracking can be detected in a small range, and deterioration in detracking detection accuracy due to changes in the reflectance can accordingly be effectively avoided.

Thus, for the main light spot S consisting of the 0th order light, 1
By detecting detrack using the secondary optical spora (Ss), it is possible to detect detrack with much higher accuracy than in the past.

That is, by applying the detrack signal SDt to the comparison circuit l2 whose reference level is 0 [V] and outputting the comparison signal to the light beam control circuit 13, the detrack signal S
, the detrack detection signal SC0M (FIG. 3(C)) whose signal level rises from the 0 level is obtained, and the detrack detection signal scoI
The light intensity of the light beam is switched based on 4.

Therefore, according to this embodiment, the detrack signal S has an amplitude value that changes around 0 [■]. By detecting detrack based on 0 [■], which is the center voltage of , even if the amplitude value of the detrack signal Sat changes,
When the off-track amount becomes 1/4 track pitch TP/4, the light intensity of the light beam can be reliably switched.

In the above configuration, a light spot S is formed at a distance of 174 1-rack pitch Tr/4 in the radial direction of the optical disc l with respect to a light spot S for reading recorded information, and the reflected light is transmitted to a two-split optical detector. The light is focused on the light receiving surface of the DS3.

The two-split optical detector D. The two output signals are input to the differential amplifier circuit 11, and thereby the amplitude value changes around 0 [V] together with the tracking error signal STE, and the change in signal level with respect to the off-track amount becomes the tracking error signal STE. Contrary to STt, the off-track amount is large near 174 track pitch T, /4, and the detrack signal S is small near just tracking. E is obtained.

The detrack signal 5ill! , the reference level is O[V
), and the comparison signal is output to the light beam control circuit 13, thereby switching the light intensity of the light beam.

According to the above configuration, the secondary optical spot S is formed at a distance of 174 track pitches T, /4 in the radial direction of the optical disc 1 from the main optical spot S for reading recorded information, thereby causing tracking error. 90″ for signal STE
By obtaining the phase-shifted detrack signal SDI and detecting detrack based on O (V), which is the center voltage of the detrack signal SDE, it is possible to detect a large change in the signal level with respect to the off-track amount. Detrack can be detected within a range of 174 track pitches Tp/
4, it is possible to reliably detect detrack, and thus a detrack detection device with significantly higher detection accuracy than the conventional one can be obtained.

[G2] Second Embodiment In FIG. 4, recording is performed by separating the light beam into 0th-order light, 1st-order light, and 11th-order light using a diffraction grating, and condensing the light beam onto the optical disk l. 0 for reading and erasing information
In addition to the light spot S of the secondary light and the light spot S of the primary light, a light spot SsI of the primary light is formed symmetrically with respect to the light spot S.

Furthermore, the reflected light of the light spot S31 is converted to the light spot S31.
By focusing the reflected light on a two-split optical detector in the same way as the reflected light of S. Obtain t2.

Furthermore, a detrack signal S, and a second detrack signal S. A composite detrack signal is obtained by obtaining the difference signal, and detrack is detected based on the composite detrack signal in the same manner as in the first embodiment.

On the other hand, a tracking error signal is generated by obtaining a sum signal for each of the two-split optical detectors for the first-order light and the -first-order light, and obtaining a difference signal between the sum signals.

Thus, in this embodiment, a tracking error signal is obtained from the main optical spot S consisting of the 0th-order light, the secondary optical spots S and S□ consisting of the 1st-order light and the -1st-order light, and the tracking error signal is Detracking is detected based on the two sub-light spots S and S□.

According to the configuration shown in FIG. 4, two auxiliary optical spots S and SS+ designed to obtain tracking error signals are used to generate detrack signals each having a phase shift of 90'' with respect to the tracking error signal STE. In this case, the same effect as in the first embodiment can be obtained.

[G3] Third Embodiment FIG. 6 shows a sub light spot made of first-order light and -first-order light with respect to the optical spora S (see FIG. 4) of the 0th-order light for reading and erasing recorded information. S and SS+ are formed at a distance of 175 track pitches T, 15, in the radial direction of the optical disc 1, and detrack is detected based on the off-track amount of 115 track pitches T215.

In this way, as shown in FIG. 7, the primary light and -
The reflected light of the primary light is divided into two optical detectors 055 and DSS.
By condensing the light onto I and obtaining the difference signal through the differential amplifier circuits 20 and 21, the tracking error signal S7
．． (Fig. 7 (A)), respectively 72° (=360
A detrack signal SI whose phase is shifted by '15),
! , and 3.4 (Fig. 7(B)) can be obtained.

The comparison circuits 22 and 23 receive the detrack signal S IIEI
and S DI! 4 and receive the detrack signal S, respectively.
When the signal levels of 013 and SDE4 rise from O(V), comparison signals 5COH+ and 5caHt (FIG. 7 (C) and (D)) whose signal levels rise are output to the AND circuit 25 and the OR circuit 26.

Therefore, via the OR circuit 26, it is possible to obtain a detrack detection signal whose signal level rises when the off-track amount reaches 115 track pitch T215, and on the other hand, via the AND circuit 25, a de-track detection signal can be obtained when the off-track amount reaches 6/20) rack pitch. A detrack detection signal whose signal level rises at 6T, /20 can be obtained.

According to the configuration shown in FIG. 6, even when detracking is detected when the off-track amount is 174 track pitch T, other than /4, the same effect as in the second embodiment can be obtained.

[G4] Other Embodiments In the above-described embodiments, a case has been described in which the timing at which the signal level of the detrack signal rises from O(V) is detected and the light intensity of each light beam is switched. However, even if a desired darkness value is set in the vicinity of 0 [■] and the light intensity of the light beam is switched based on the threshold value, the detracking is detected based on the tracking error signal. detracking can be detected with significantly higher accuracy.

Furthermore, in the above-described embodiment, the case where detracking is detected when the off-track amount is 1/4 track pitch TP/4 and 115 track pitch TP15 is described, but the present invention is not limited to this, and the present invention is not limited to this. It can be widely applied in detecting detrack.

Furthermore, in the above-described embodiments, the present invention is applied to an optical disc device that is capable of writing and erasing information on an optical disc. It can be widely used in detrack detection devices such as iW and compact disc players.

H Effects of the Invention As described above, according to the present invention, by detecting detracking using a sub optical spot with respect to a main optical spot, detracking can be detected based on a tracking error signal. In comparison, the detrack detection device can detect detrack in a range where the change in signal level with respect to the off-track amount is large and in a range where the change in signal level due to the reflectance of the optical disk is small, and the detection accuracy is accordingly high. can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a route diagram showing a light spot on an optical disk according to the first embodiment of the present invention, FIG. 2 is a block diagram showing the detrack detection device thereof, and FIG. 3 is a signal waveform diagram for explaining its operation. , FIG. 4 is a route map showing a light spot on an optical disk according to the second embodiment, FIG. 5 is a signal waveform diagram for explaining its operation, and FIG. 6 is a detrack detection device according to the third embodiment. 7 is a signal waveform diagram to explain its operation, FIG. 8 is a route diagram showing a light spot on a conventional optical disk, and FIG. 9 is a signal waveform diagram to explain its operation.゜■...Optical disc, 2...Pregroup, 3...Bit, S, Ss, Ss+...
...Light spot.

Claims (1)

[Claims] A photodetector that irradiates a sub-light spot on an optical disc at a predetermined distance from a main light spot, and that divides the light-receiving surface into two in the radial direction of the optical disc to receive reflected light from the sub-light spot. What is claimed is: 1. A detrak detection device, characterized in that the detrak is detected based on a difference signal between the output signals of the photodetector.