JPS62239333A - Tracking signal detecting method - Google Patents

Abstract

PURPOSE:To detect an accurate tracking signal with no effect of the recorded information by irradiating plural secondary beams on different tracking tracks for detection of the tracking signal. CONSTITUTION:The light beams delivered from a light source 1 are turned into parallel luminous fluxes by a collimator lens 2 and divided into three beams by a diffraction grating 3. These three beams are reflected by a beam splitter 4 and condensed on an optical card 6 by an objective lens 5 to form three beam spots S1-S3. The light beams reflected by the card 6 are transmitted again through the lens 5 and then through the splitter 4 and separated from the incident beams Then those reflected beams are reflected by a mirror 7 and condensed by a sensor lens 8 and a cylindrical lens 9 to be made incident on optical sensors 101-103 respectively. These sensors are arranged so as to receive the beams from those spots S1-S3.

Description

[Detailed Description of the Invention] [Technical Field] The present invention relates to a tracking signal detection method, and particularly to a method for detecting a tracking signal in an optical information recording/reproducing apparatus that records or reproduces information by irradiating a light beam onto an optical recording medium. The present invention relates to a method of detecting a tracking signal for accurately guiding to a predetermined position. In the present invention, the optical information recording/reproducing apparatus includes all apparatuses that only record information, apparatuses that only reproduce information, and apparatuses that perform both recording and reproduction.

(Prior art) In recent years, commercialization, research and development of optical information recording and reproducing devices, such as electronic file systems using compact discs and write-once discs, and optical disc systems using erasable magneto-optical materials and phase change materials, have been carried out. Recently, optical recording media in the form of cards (hereinafter referred to as optical cards) have become popular.
Optical card systems for recording and reproducing information on media are attracting particular attention. Optical cards are easy to carry due to their form, and have a larger information capacity than disks despite their area (
In the case of a disk type, information is not recorded in the center).

By the way, the above-mentioned optical recording medium records information in optically detectable recording pit rows (information tracks) by scanning the medium surface with a light beam that is modulated according to the recorded information and focused on a minute spot. is recorded. At this time, in order to accurately record information without causing problems such as crossing of information tracks, the irradiation position of the light beam must be controlled in a direction perpendicular to the scanning direction (auto tracking,
(hereinafter referred to as AT). A conventional tracking signal detection method for such an AT will be described below.

FIGS. 9(a) and 9(b) are enlarged views of the medium surface of a conventional optical recording medium. In the figure, reference numeral 13 indicates a tracking track formed in advance on the medium surface in the form of a groove or a band-like region having different reflectance. Here, three beam spots 15.16
．． 17 is irradiated so that the beam spot 16 covers half of the tracking track 13, and the beam spots 15 and 17 cover half of the tracking track 13, and scan in the direction of arrow B. and beam spots 15 and 17
A tracking signal is derived by subtracting the detection signals obtained by detecting the respective lights from the beam spot 16 as shown in FIG. Information was recorded in the tracking track 13 as shown in a), or information already recorded in the tracking track 13 was reproduced as shown in FIG. 9(b).

However, in the conventional method described above, since recording pits 14 (shaded areas) exist within the scanning trajectory of beam spots 15 and 17 for detecting tracking signals,
In some cases, the signal from the recording pits 14 is mixed into the tracking signal, making it impossible to perform stable AT. In particular, when recording information as shown in FIG. 9(a), since the recording pits 14 exist only on the beam spot 15 side, an imbalance occurs in the light detection signals from the beam spots 15 and 17. It was difficult to obtain accurate tracking signals.

[Summary of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a tracking signal detection method that solves the problems of the prior art described above and allows stable AT.

The above object of the present invention is to irradiate an optical recording medium with at least one main beam to an optical recording medium having tracking tracks arranged at regular intervals, and to record or reproduce information between the tracking tracks. At the same time, at least two sub-beams are irradiated so that part of these beam spots overlaps different tracking tracks,
This is achieved by comparing the signals obtained by detecting the lights from these sub-beam spots, respectively, to obtain a tracking signal for accurately guiding the main beam between the tracking tracks.

〔Example〕

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to the drawings, taking as an example the case where an optical card is used as an optical recording medium.

FIG. 1 is a schematic diagram showing an embodiment of soundproofing for recording and reproducing information using the tracking signal detection method of the present invention. Here, a light beam emitted from a light source 1 such as a semiconductor laser is made into a parallel beam by a collimator lens 2, and divided into three beams by a diffraction grating 3. The divided light beams are reflected by the beam splitter 4 and focused onto the optical card 6 by the objective lens 5 to form three beam spots s1. s2. Form s3. The light beam reflected by the optical card 6 passes through the objective lens 5 again and is separated from the incident beam by passing through the beam splitter 4. Then, this reflected beam is reflected by the mirror 7, condensed by the sensor lens 8° and the cylindrical lens 9 to the optical sensor to1. io2,103. These optical sensors 101, 102. to3 is beams bok)
It is arranged to receive light from Sl, S2, and s3.

The light receiving surface of the optical sensor 102 is 4 as shown in FIG.
The astigmatism introduced by the aforementioned cylindrical lens 9 is detected by subtracting the sum of the detection signals of the two diagonally arranged light-receiving surfaces. By the principle, we get the focusing signal.

In addition, when reproducing information, this optical sensor 102
Get more playback signal. Also, optical sensor -101゜103
The detection signal of is differentiated by the differential amplifier 11,
2 is output as a tracking signal ST. This tracking signal ST is fed back to the lens actuator 18 by a circuit not shown, and AT is performed by moving the objective lens 5 in a direction perpendicular to the optical axis.

The optical card 6 is reciprocated in the direction of arrow R by a drive mechanism (not shown), thereby causing the optical spot S1. s2. s3 scans the optical card 6. Further, the optical head 19 including the above-mentioned optical system etc. is configured to be able to move eight times in a direction perpendicular to arrow R, that is, in a direction perpendicular to the plane of the paper in FIG. 1, for track access.

FIG. 3 is a plan view of the optical card 6. optical card 6
The recording layer 20 is formed of a silver salt-based material, a dye-based material, a chalcogen-based material, or the like on a substrate made of plastic or the like.

The recording layer 20 has a tracking track 2 that can be optically detected in advance due to unevenness or a difference in reflectance.
1 are formed in plural parallel to each other. These tracking tracks 21 are arranged at equal intervals, and a recording area in which information is recorded is provided between each track.

FIG. 4 is an enlarged view of the recording surface of the optical card 6, illustrating the recording process using the apparatus shown in FIG. Between the tracking tracks 211, 212, 213 are recording areas 221, 2.
It has 22. Beam spot s1. The beam spot S3 is irradiated so as to partially cover the tracking tracks 211 and 212, respectively, and the beam spot S2 is irradiated onto the recording area 221. If the irradiation positions of the beam spots 31 to S3 are shifted in the direction perpendicular to the track, an imbalance will occur between the light amount of the reflected beam from the spot S1 and the light amount of the reflected beam from the spot S3. Therefore, as shown in FIG. 1, by detecting the light from these spots and subtracting the signals obtained, a tracking signal ST indicating the amount and direction of the shift can be obtained. Then, by performing AT based on this tracking number 13, the beam spot S2 is accurately guided to the recording area between the tracking tracks, and information can be recorded as shown by the recording bit 23. Furthermore, when recording information in the recording area 222, the beam spot s1. S2. It is sufficient to irradiate the tracking track 211, the recording area 222, and the tracking track 222 with s3, respectively. The light intensity distribution of the beam spots S, S3 on the optical card is usually a Gaussian distribution with a high concentration in the center, so if each of these beam spots is set so that half of it covers the tracking track, the light intensity changes due to track deviation. is large, allowing highly sensitive tracking signal detection.

In FIG. 4, the diameters of the beam spots S□, s2°S3 (the beam width in the direction perpendicular to the track if the beam spots are not circular) are D, , D, , r1, . ．． Then, it is desirable that the width W of the tracking tracks 211 to 2.13 satisfies W≦D (−D:+) (1). This is because if the beam spot diameter is larger than the tracking track width and the beam spot falls completely within the tracking track, there will be no change in light intensity due to movement of the beam spot in the direction perpendicular to the track. be. In addition, recording area 2 between tracking tracks
2. The width of 222 is preferably L≧D2+%D, 10%D3 (=D2+Dt). This is to prevent the recording bit 23 recorded at beam spot S2 from being detected at beam spot S3, and to obtain a stable tracking signal. However, here 01, D2. D3 was set to have a diameter of 1-1 at a portion having an intensity of 1/e 2 x 4 when the peak value of light intensity was 1.

Therefore, from equations (1) and (2), an optical recording medium suitable for applying the present invention has a recording area between tracking tracks whose width is at least twice the width W of the tracking track.
That is, it satisfies the relationship L>2W (3).

Although the case of recording information has been described in FIG. 4, the tracking signal can be detected in exactly the same way as during recording even when reproducing information already recorded in the recording area. For example, in FIG. 5, when reading the recording bit 23 of the recording area 221 with the beam spot S2, the beam spots S1 and S3 are placed on the tracking track 221, respectively.
1! and 212, and a tracking signal is obtained by comparing the amounts of reflected light from these S1 and S3. Furthermore, in Fig. 4, the beam spot is irradiated on the edge of the tracking track close to the recording or reproducing area, but for example, as shown in Fig. 6, the beam spot is irradiated on the edge of the tracking track on the side far from the recording or reproducing area. Even if S1°S3 is applied, it is possible to detect a tracking signal at all on the studs. Note that the same parts in Figure 6 as in Figure 4 are:! (The same reference numerals are given and detailed explanations are omitted.

The tracking signal detection method of the present invention is characterized in that it is resistant to tilting of the optical recording medium surface. This will be explained below.

FIG. 7(a) shows a part of the optical system of the device shown in FIG.
Identical members are given common symbols. Here, if the optical recording medium surface 61 is perpendicular to the optical axis, the chief ray of the luminous flux passes along the optical axis and is guided to the sensor 10, as shown by the solid line. However, when the medium surface 6 is tilted by .theta. and becomes in the vertical state 6', the chief ray of the reflected light beam is deviated from the optical axis and guided to the sensor as shown by the broken line. The light receiving surface of the sensor 10 is a lens system (objective lens 5, sensor lens 8, cylindrical lens 9
), the light flux moves by Δd on the sensor surface if it is not placed at a position F conjugate with the recording medium surface.

As a result, in the so-called push-pull method, in which a photosensor with divided light-receiving surfaces 241 and 242 is arranged on the lens pupil plane as shown in FIG. The movement Δd of the light flux is directly detected as an asymmetry in the distribution of the detection light, and an offset occurs in the tracking signal, making it impossible to perform accurate AT.

In contrast, in the method of the present invention, it is possible to arrange the optical sensor at a position conjugate to the medium surface, and even if the optical sensor is located away from the conjugate position, 1. Figure 7 (b
), move the optical sensors 101 and 103! lI amount Δd
(If it is made so thick that it does not affect the media, no offset will occur and an accurate tracking signal can be detected even if the medium surface is tilted.)

As described above, since the method of the present invention is less affected by the inclination of the medium surface, it is particularly effective for portable optical cards among optical recording media.

Another embodiment of the invention is shown in FIG.

In the embodiment described above, the autofocusing signal was detected using the astigmatism characteristic of the beam spot S2. However, it is conceivable that the presence or absence of recorded bits also influences the autofocusing signal at the beam spot S2, as shown in FIG. 9. In this case, Fig. 8 (
As shown in b) and (c), a beam angle molecule III element that utilizes the backside reflection of a wedge and the birefringence of a crystal such as a Wollaston prism is installed between the diffraction grating 3 and the beam splitter 4 in Fig. 1. and beam spot S1~
S3. At the same time, the beam spot S4°s5. s6 is formed on the optical card 6. At this time, a spot S5 is placed in the non-recording area between the signal track 25 where recording bits are formed and the tracking track 21, and by detecting a focusing signal from this beam spot s5, the Ig? of the recording bit is determined. Stable auto four + IS that does not receive J/”/Nol Meshita;
The present invention is not limited to the embodiments described above, and can be applied to various applications.For example, as an optical recording medium, it can be applied to optical disks as well as optical cards. In optical discs, tracking tracks are formed concentrically or spirally. When formed in a spiral shape, the starting points and ending points of adjacent tracking tracks are connected, and there appears to be only one tracking track, but such a case is also included in the present invention.

(Effects of the Invention) As explained above, the present invention irradiates a plurality of sub-beams for detecting tracking signals to different tracking and tracks, so accurate tracking signals that are not affected by recorded information can be obtained. It became possible to detect.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing an example of an optical information recording/reproducing apparatus to which the method of the present invention is applied, FIG. 2 is a diagram showing the light receiving surface of the optical sensor shown in FIG. 1, and FIG. The plan view of the card, FIG. 4, FIG. 5, and FIG. 6 are respectively an enlarged view of the recording surface of the optical card, and FIG. 7(a), which explains the present invention in detail.
(b). (C) is a diagram illustrating the influence on the tracking signal due to the inclination of the medium surface, and FIG. 8(a). 9(b) and 9(c) are diagrams for explaining other embodiments of the present invention, respectively, and FIGS. 9(a) and 9(b) are diagrams for explaining a conventional tracking signal detection method, respectively. s! , s2.53---beam spot, 211.2
12,213---one tracking track, 221.222---one recording area, 23---one recording pit.

Claims (1)

[Claims] (1) At least one main beam is irradiated onto an optical recording medium having tracking tracks arranged at regular intervals, and information is recorded or reproduced between the tracking tracks, and at the same time at least two sub beams are irradiated. By irradiating some of these beam spots so that they overlap different tracking tracks, and comparing the signals obtained by detecting the light from these sub beam spots, the main beam can be accurately aligned between the tracking tracks. A tracking signal detection method for an optical information recording/reproducing device for obtaining a tracking signal for guiding.