JPS63288430A - Optical track tracing device - Google Patents

Abstract

PURPOSE:To obtain an accurate track deviation detection signal by correcting the track deviation detection signal due to a first light receiving part for track deviation detection by the medium inclination detection signal due to a second light receiving part. CONSTITUTION:First light receiving parts 10a and 10b of a photodetector for track deviation detection are arranged for a totally diffracted luminous flux 17, and second light receiving parts 18a and 18b of a photodetector for medium inclination detection are arranged in the area to which the diffracted luminous flux 17 is not projected. That is, not only the totally diffracted luminous flux 17 is moved in parallel but also the distribution of light intensity of this luminous flux 17 is changed when the medium is inclined. Consequently, the differential output signal of light receiving parts 10a and 10b of the photodetector for track deviation detection is corrected with the differential output signal of light receiving parts 18a and 18b of the photodetector for medium inclination detection, and the latter differential output signal is controlled to a minimum. Thus, stable track deviation control is performed.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a method for appropriately positioning and controlling the relative relationship between the position of light from a light source and the position of a track on an information recording medium in an optical disk device. The present invention relates to an optical track tracking device.

[Conventional technology]

As a prior art, an outline of an optical track tracking device using a diffraction phenomenon disclosed in Japanese Patent Laid-Open No. 59-191143 will be explained with reference to FIGS. 3 to 13.

Figure 3 shows an optical disk device using a diffraction-type track deviation detection method, in which light emitted from a semiconductor laser (1) is converted into a parallel beam by a collimator lens (2), reflected by a half-mirror lens (3), and then reflected by an objective lens ( 4) A spot is imaged on a disk-shaped information recording medium (5) that rotates 4×1. A track (6) is provided on the information recording medium (5), and when the track (6) is irradiated with a light beam, a diffraction phenomenon occurs in the reflected light. That is, the reflected light is separated into an O-order diffracted beam (7), a +1st-order diffracted beam (8), and a -1st-order diffracted beam (9). According to
phase shifts in the opposite direction. These diffracted light beams reflected from the medium (5) are turned into parallel light beams again by the lens (4), and then pass through the half mirror (3) into two symmetrical beams with respect to the track direction (in the figure, perpendicular to the plane of the paper). Detectors (10a) and (10b) are reached.

FIG. 4 shows the shape and separation direction of the 0th-order diffracted light beam (force), the +1st-order diffracted light beam (8), and the -1st-order diffracted light beam (9), which are diffracted and separated by the track (6).

Figure 5 shows the O-order diffracted light flux (
This figure shows each diffracted light beam passing through the objective lens (4) from the direction of diffraction of the light beam (7).
In a), a portion of the ±1st-order diffracted light beams (8) and (9) is blocked. Center AA of the aperture pupil (4a) (O-order diffracted light flux and ±
6(a), (b), and (c) show cross sections of the light intensity distribution on a line segment passing through the center of the first-order diffracted light. 'l? in figure (a)? (12) is a cross section of the light intensity distribution when there is no track deviation, and since the emitted light beam is strong at the center like a semiconductor laser, the light intensity distribution is strong at the center. When a track shift occurs, the phases of the +1st-order and 11th-order diffracted lights (8) and (9) shift in the opposite direction to the phase of the 0th-order diffracted light (7), so in the case of figure (b), - The 1st-order and 0th-order diffracted light (9), the f-force interfere and strengthen each other, +
As a result of the first-order and zero-order diffracted lights (8) and (7) weakening each other, the cross section of the light intensity distribution becomes a real m(13'). Further, Figure (c) shows the case where track waviness occurs in the opposite direction to Figure (b), and the light intensity distribution cross section is as shown by the solid line (14). The break (12) in figures (b) and fc) indicates the solid line (12) in figure (a). Also, the opening m in Fig. 5
It is off the center of (4a) and parallel to AA, as shown by (12aL (13a), (14a)) in B.

From FIGS. 6 and 7, the 80th line passing through the aperture pupil (4a)
and FIG. 9 show the portion (15
) and the unchanged part (16) are shown. Therefore, by detecting the change in light intensity in the area (L5) in FIG. 5, a track deviation signal can be obtained. In this area (15), if the diameter of the detection light beam on the photodetector surface is φ and 1, then a circle with a diameter φ centered on the optical axis of the detection light beam is perpendicular to the track direction from the center. ′? overlaps two H’s with a diameter of −, centered on two points a certain distance apart in both directions. A
This is an area that does not include the area where the above three circles overlap.

The two-split photodetectors (10a) and (10b) in FIG. 3 are the above-mentioned JiL33J! splits the luminous flux into two photodetectors (10
A) and (lOb) are divided into equal areas, and each light intensity distribution change due to track deviation is detected. A track deviation signal can be obtained by inputting the signal into the track deviation signal and detecting the difference. The light spot is controlled to follow the center of the track by moving the light beam in a direction perpendicular to the track direction in accordance with this track deviation signal. As a tracking means for moving the light beam, for example, a means for moving the objective lens by supplying a track deviation signal to an actuator attached around the objective lens O, a light deflection means such as a galvanometer mirror, or a means for moving the entire optical head. There are well-known methods.

By the way, when the information recording medium (5) is tilted at an angle α as shown in FIG. Each diffracted light beam that can pass through the aperture ri (4a) of the lens (4) +73. The regions GA) and (9) are also translated in the lateral direction compared to FIG.゛[Problem to be Solved by the Invention 1] The conventional optical track tracking device as described above.

12 and 13 are AABB in FIG.
As in Figure 1, this shows the cross section of the light intensity distribution on the AA and BB lines of the GLT diagram, and the solid line indicates the portion that changes due to track misalignment when there is no disk tilt, which corresponds to Figures 8 and 9. In (15), the part that does not change is shown as a solid line (16)
Indicated by When the disc tilts, the dashed line (1
Translation is performed as shown in 5a) and (16a). As a result, the peak part of the light intensity distribution shifts, and in the track misalignment detection method using a two-split photodetector symmetrical in the track direction, a DC-like bias (tracking offset) occurs, making it difficult to detect track misalignment accurately. The problem was that it was not possible to do so.

This invention was made in order to solve the above-mentioned problems, and it is possible to detect the offset caused by the recording medium K and correct the track deviation due to the offset, thereby obtaining a more stable track deviation signal. The objective is to obtain an optical track tracking device that can.

[Means for solving problems]

The optical track tracking device according to the present invention includes, as a track positional deviation detecting means, a pair of first
a pair of second light receiving parts (for detecting the tilt of the medium) arranged symmetrically with respect to the track direction in an area where the diffracted light beam is not irradiated when the recording medium is not tilted. It is equipped with a photodetector having the following.

A photodetector for a second light-receiving section (for detecting the inclination of the medium) is attached to the photodetector (for detecting deviation), and the second light-receiving section detects the inclination of the medium. Correction is performed using the signal to obtain an accurate track deviation detection signal.

〔Example〕

FIG. 1 shows an embodiment of the present invention. In the figure, a pair of first light receiving sections (1
0a) and (10b) are arranged. Furthermore, when the recording medium (5) is arranged perpendicularly to the light source (1), a pair of photodetectors for detecting the inclination of the medium (5) are arranged symmetrically with respect to the track direction in an area that is not irradiated with the diffracted light beam (17). second light receiving sections (18a) and (18b) are arranged. The second light receiving portions (18a) and (18b) have a diffracted light beam (1
7) is placed as close as possible to the irradiation area.

The other configurations are the same as shown in FIG. 3, and their explanation will be omitted.

Next, the operation will be explained. The operating principle of the diffraction-type track deviation detection method is the same as that of the conventional system, so a description thereof will be omitted here.

In FIG. 1, if there is no track deviation, the differential output signals of the track deviation detection photodetectors (10a) and (10b) and the tilt detection photodetector (18) of the medium (5) are shown.
The differential output signals of aL (18b) are both zero.

Next, when a track shift occurs (assuming that the medium (5) is not tilted), the light intensity distribution of the total diffracted light beam (17) changes as shown in Figures 6 to 9. However,
A photodetector (10a”) that is irradiated with the total diffracted light beam (17)
), (10b)-(18a)*(18b), the differential output signals of the photodetectors (18a) and (18b) for detecting the inclination of the medium (5) are zero, and the position on the track Displacement detection photodetector (10a), (10b
) Track deviation can be detected using the differential output signals.

When the medium (5) is tilted, the total diffracted light flux (17) moves in parallel and the total diffracted light flux (
17) The light intensity distribution also changes as shown in FIGS. 12 and 13. Therefore, the differential output signal of the photodetector (tOa), (10b) for detecting track deviation is transmitted to the medium (5).
The differential output signal of the tilt detection photodetector (18aL (18b)) of the medium (5) is corrected, and the differential output signal of the tilt detection photodetector (18a), (18b) of the medium (5) is controlled to the minimum. By doing so, stable track deviation control can be performed.

〔Effect of the invention〕

As described above, according to the present invention, the track positional deviation detection means includes a pair of first light receiving parts arranged symmetrically with respect to the track direction with respect to the diffracted light beam from the recording medium, and a pair of first light receiving parts arranged symmetrically with respect to the track direction, and By including a photodetector having a pair of second light-receiving parts arranged symmetrically with respect to the track direction in an area where the diffracted light beam is not irradiated when there is no inclination, even if the recording medium shifts, its offset can be avoided. By correcting the amount using the output signal of the photodetector of the second light receiving section, it is possible to always perform stable and accurate positioning control regardless of the inclination of the recording medium.

[Brief explanation of drawings]

FIG. 1 is a front view of essential parts of an embodiment of the present invention, and FIG. 2 is a front view of essential parts for explaining the operation of the apparatus shown in FIG. 3 to 13 show a conventional optical track tracking device, FIG. 3 is an optical layout diagram, FIGS. 4 and 5 are schematic diagrams explaining the output of diffracted light, and FIGS. 6 to 13 show a conventional optical track tracking device. Figure 9 is a diagram illustrating changes in the light intensity distribution of diffracted light due to track deviation, Figures 10 and 11 are schematic diagrams illustrating the output of diffracted light when the recording medium is tilted, and Figure 12. and FIG. 13 are diagrams illustrating changes in the light intensity distribution of diffracted light when the recording medium is tilted. (11...Light source, (4)...Objective lens, (5)...Information recording medium, (6) --) Rack, (10a), (1
0b)・轡1st Q light receiving section, (17) --Total diffracted light flux, (
18a). (18b)...Second light receiving section. In each figure, the same reference numerals indicate the same or corresponding parts. Agent Teru Tseng 1. ;1st
Isa, 18k): 12 light receiving parts 2g:J Fig. 3 Fig. 4rA 85 Fig. 7 Fig. 8 Keyaki, Fig. 10 Fig. 12 Fig. 9 IC: 1 11 Fig. $113 Fig.

Claims (2)

[Claims] (1) A light source, an optical means for focusing the light emitted from the light source onto a track provided on an information recording medium, and a distance between the focusing position of the light and the position of the track using a diffracted light beam from the information recording medium. an optical track tracking device comprising: a detection means for detecting the displacement of the diffraction; and a displacement means for displacing the relative distance between the position of the light and the position of the track by the output of the detection means; a pair of first light receiving sections arranged symmetrically with respect to the track direction with respect to the light beam; and a pair of first light receiving sections arranged symmetrically with respect to the track direction in an area that is not irradiated with the diffracted light beam when the information recording medium is arranged perpendicularly to the light source. and at least one pair of second light-receiving sections, wherein a difference signal between the outputs of the first light-receiving section is corrected by a difference signal between the outputs of the second light-receiving section. Device. (2) The optical track tracking device according to claim 1, wherein the second light receiving section is arranged close to the irradiation area of the diffracted light beam.