JPS59113531A - Reproducing device of optical disc - Google Patents

Abstract

PURPOSE:To control a focus error, tracking error and skew error by quadrisecting the photodetecting part of a photodetector, and using the total quantity of light thereof, and the quantity of light in the vertical region, lateral region and region in a diagonal line direction thereof. CONSTITUTION:The incident luminous flux to a prism 5 changes to a divergent or convergent luminous flux according to the direction of the deviation of the surface of a disc D from the state of a focusing position and a focus error is detected by the difference (SI+SII)-(SIII+SIV) in the sum of the outputs projected in photodetecting regions I -IV (a' is a radial direction). A dark part is formed in the part of a dotted line or an alternate long and short dash line in accordance with the change in the luminous flux in the rise and fall stage of a reproduced information signal SI+SII+SIII+SIV with respect to the return luminous flux projected as shown by diagonal lines. Therefore the tracking error is detected by (SI+SIII)-(SII+SIV), and a tracking error control signal is obtd. by sampling and holding (SI+SIII)-(SII+SIV) at the rise or fall of the reproduced information signal. The tracking error is detected by (SI+SIV)-(SII+ SIII). A DC component is extracted by an LPF from said signal and the control signal is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention converges a light beam from a laser light source into a spot on the signal surface of a disk using an objective lens, and converges the return light beam due to reflection from the signal surface of the disk into a spot shape. The present invention relates to an optical disk retrieval device equipped with an optical pickup consisting of a reading optical system that causes an objective lens to enter a column and enter a light receiving section of a photodetector, and more specifically, to a control technique for a cystectomy optical system.

Background Art and Problems In this type of device, focus control is performed so that the light beam emitted from the laser light source and converged by the objective lens is focused on the signal surface of the disk, and the converged light beam is always focused on the signal surface of the disk. Tracking control is performed so that the information is positioned on a track formed by the information bit string.

However, in the past, focus control and tracking control were generally performed as shown in FIG.

That is, the arrow A indicates the objective lens (OLo) that converges the light beam from the laser light source in the reading optical system in the optical pickup (po) into a spot on the signal surface of the disk (Do). The direction of the optical axis (oAO) perpendicular to the signal surface of the disk (Do) as shown by arrow B.

As shown, it was provided so as to be movable in the radial direction a of the direct firing disc (D6) in the direction of the optical axis (OAo).

And arrow A by the objective lens (OLo) + driving means. Focus control by driving in the direction of arrow B. Tracking control was performed by driving in the direction.

However, in this case, as mentioned above, the objective lens (
OL. ) is arrow A. Direction and arrow B. Since control is performed by translationally driving in the
As shown in the figure, there is a skew Δθ on the signal surface of the disk (D.). , the luminous flux is on the disk (Do
), and due to the occurrence of coma aberration, the predetermined 0TF (0ptical
There was a problem in that it was not possible to obtain er function. Furthermore, when the disc (, Do) is a video disc, there is also the problem that crosstalk increases.

Purpose of the Invention The present invention was invented in view of the above-mentioned circumstances, and its purpose is to have a simple structure while allowing the light beam to be perpendicularly incident on the signal surface of the disk to obtain the required amount of light. It is an object of the present invention to provide an optical pickup and reproducing device that can obtain OTF characteristics and suppress an increase in crosstalk.

SUMMARY OF THE INVENTION In the optical pickup reproducing apparatus of the present invention, the optical pickup is positioned at the focal point of the objective lens in a plane perpendicular to the signal surface of the disk and in the radial direction of the disk. is provided to be swingable so as to draw an arcuate locus, and a first driving means for driving the optical pickup to swing is provided, and
A first drive means that detects a change in the returning light flux incident on the light receiving section of the photodetector and supplies this detection output to the first driving means to always position the light flux converged on the signal surface of the disk on the track. a detection control means, the optical pickup is movable in the radial direction of the disk, and a second drive means for driving the optical pickup to move; The light-receiving section of the disc is configured to form a pair of light-receiving areas that are arranged so as to be divided into two in the radial direction of the projected disk, and the return light beam incident on each of these receiving areas is The present invention is characterized in that a second detection control means is provided which detects a change in the output as a difference between the respective outputs, and supplies this detected output to the second drive means to make the difference between the outputs a constant value. .

As a result, although the configuration is simple, the light beam incident on the signal surface of the disk is always kept perpendicular to the signal surfaces of the disk, despite the inclination of the signal surface ζ of the disk due to bending, etc. The occurrence of coma aberration due to the inclination of the signal plane is prevented, and the desired OTF characteristics can be obtained.

Embodiment Next, an embodiment of the optical disc reproducing apparatus according to the present invention will be described with reference to the drawings.

FIG. 6 is an overall schematic diagram, and FIG. 4 is a partial vertical cross-sectional view taken along the optical axis of the reading optical system in FIG. 3 along IV-IVi.

First, the outer casing f in the optical pickup (g)
To explain the reading optical system housed and held in the illumination light, for example, a beam emitted from a laser beam such as a semiconductor laser is converted into a parallel beam by a collimator lens (2) and sent to a polarizing beam splitter. (3).

This light flux is reflected by the polarizing beam splinter (3) and
The light is focused into a spot by the objective lens (OL) via the /4 wavelength plate (4) so as to form a fine spot on the circular signal surface of the disk (toward).

Then, the return light beam reflected by the signal surface of the disk (to) and modulated by the information pit array that forms concentric or spiral tracks on the signal surface is picked up by the objective lens (OL) and follows the optical path. Follow in the opposite direction and return to 1/4
The light is incident on the flat beam splitter (3) via the wave plate (4). At this time, since the light beam passes through the quarter-wave plate (4) twice in a round trip, the polarization axis is rotated by 90 degrees compared to the original light beam from the laser light source (L). Therefore, the returned light beam is transmitted without being reflected toward the laser light source 4), and is incident on the critical angle setting prism (5) whose reflective surface (5a) is set near the critical angle. This critical angle setting prism (5) is arranged so that a parallel returning light beam is incident on the signal surface of the disk (G) when the signal surface is in focus and there is no glare. The return light beam reflected by this reflecting surface (5a) is incident on the light receiving section (PD) of the photodetector.

The objective lens (OL) is provided so as to be movable in the optical axis (OA) direction of the light beam incident on the signal surface of the disk (to) as shown by arrow A. It is designed to be driven in the direction of arrow A by a driving means. On the other hand, the feed base (7) is provided so as to be movable in the radial direction a of the disk (G) guided by the feed guide rod (6). A cylindrical pickup housing (8) is installed on the upper surface (7a) facing the disc (CD) by a well-known fixing means, with the opening (8a) located on the upper end side, that is, on the disc (CD) side. Fixed.

Inside this pickup housing (8), the optical pickup P) is arranged such that the focal point of the objective lens (OL) is in a plane perpendicular to the signal surface of the disk (G) and in the radial direction a of the disk (G). It is provided so as to draw a circular arc locus X. That is, in this embodiment, the bottom peripheral side wall of the pickup housing (8) and the optical pickup (Pi
As shown in FIG.
A pair of supports N (9a) (9b) are provided so that their axes are located on a straight line perpendicular to the radial direction a of the disk (D). Then, the supporting shaft (
By rotating around the axes 9a and 9b, it can swing to draw the arc trajectory X. Also, the outer casing of the optical pickup CP) (magnetic screws are provided on both sides of the disk in 11 in the radial direction a).
(10a) (10b) are provided, and electromagnetic coils (11a) (iib) are provided on the circumferential side wall of the pickup housing (8) facing each of these magnets (10aX10b). These magnets (10a) (10b) and electromagnetic coil (11a)
) (11b) constitutes a drive mechanism which is the first drive means in the present invention for driving the optical pickup field (11b) to oscillate.

The feed base (7) is driven in the radial direction a of the screw cylinder (of the disk via 141) by rotating the feed screw (12+) about its axis by the feed motor Q31. The pick-up assistant is
The disk O is driven in the radial direction a.

These feed screw tt3, feed motor 03), and threaded cylinder α4) constitute a drive mechanism N, which is a second drive means in the present invention that drives the optical pickup (P) to move.

Therefore, the light receiving part (PD) of the photodetector is detected in the radial direction a' of the projected disc (G), which is a direction that intersects one page with the tangential direction of the track on the signal surface of the projected disc [F]. On the other hand, it is formed of four light receiving areas 1 to 1v arranged and positioned as shown in FIG.

Next, how can changes based on the focus error, tracking error, and skew error be detected by the returned light flux incident on the photodetector (PD) of the photodetector, and how can the focus error signal and tracking error control signal be detected? It will now be explained how the detection output, which becomes the skew error control signal, is applied to the respective drive means and drive mechanism M (Nl) to control it.

(i) The light flux incident on the focus error critical angle setting prism (5) is
The optical axis (
With respect to the luminous flux on the right side and the luminous flux on the left side in the drawing of FIG. 4 with OA) as the boundary, the angle of incidence on the reflecting surface (5a) of the critical angle setting prism (5) has an inverse relationship with respect to the critical angle. As a result, the light intensity distribution of the returned light beam projected onto the four light-receiving areas 1 to 2 is divided into two in the direction perpendicular to the radial direction a' of the projected disk (projection track direction). A pair of light-receiving areas, that is, a light-receiving area 11■ and a light-receiving area m, +v
Thus, the direction of the signal surface of the disk (6) is reversed depending on the direction of deviation from the in-focus position state.

Therefore, the focus error is four light-receiving areas l~■
Difference between the sums of the respective outputs divided into two in the direction orthogonal to the radial direction a' of the projected disk (G) CB, + SI
) −(SI+s, ).

That is, the outputs of the two light-receiving regions 1 and II are applied to the input terminal of the adder 115), and the outputs of the two light-receiving regions
A focus error control signal as a detection output is obtained by applying the respective outputs to the input terminals of the adders α6) and applying the outputs of the respective adders (+5) (161) to the input terminals of the subtractor aη.

This focus error control signal is transmitted to the objective lens (OL).
A driving means for driving the optical axis (OA) in the direction of the optical axis (OA), more specifically, a light flux that is given to an electromagnetic coil constituting the driving means and converged by an objective lens (OL) is
Focus control is performed so as to focus on the signal plane of , that is, so that the focus error control signal becomes zero.

(iii) Tracking error Depending on the deviation of the light beam converged on the signal surface of the disc (to), that is, the spot, from the best tracking state, that is, the direction of the deviation from the track, as shown in the diagonal in Fig. 5, With respect to the projected return light flux, when the reproduced information signal 8.+ 8[+ 8.+ , S, Dark areas begin to form.

Therefore, the tracking error is caused by the reproduced information signal sl
+SR+S■+Detected by the difference (S, +S) - (g), +S■) of the sum of the outputs of each of the diagonal positions of the four light-receiving areas ■~■ at the rising or falling edge of sly. Ru.

That is, two light receiving areas 1. The outputs of the two light-receiving areas (1) and (2) are supplied to the input terminal of the adder (1) and (2) to the input terminal of the adder (1).
8) Give the output of Q9) to the input terminal of the subtracter Cω.

Then, subtract W (2 (1) A tracking error control signal is obtained as a detection output by sampling and holding the output using a hold circuit (two signals).

This tracking error control signal is applied to the electromagnetic coils (11a) (1lb) in the drive mechanism that drives the optical pickup P) so that the focal point of the objective lens (OL) draws an arcuate trajectory X. Tracking control is performed so that the light beam given and converged on the signal surface of the disk is always positioned on the track, that is, so that the tracking error control signal becomes zero.

In addition, adder a9α6)Q8) (19) (21)
, the subtracter (2), the hold circuit (22), etc. constitute the first detection control means in the present invention.

(iii) Skew error As shown in Figure 6, if the signal plane of the optical axis is tilted by Δθ in the radial direction a (-radial skew angle) and the focal length of the objective lens (OL) is j, then the optical axis (OA)
5, the returned light beam changes by 1 lateral displacement by 2・Δθ・j, and as shown by the two-dot chain line in the figure, with respect to the projected return light beam as shown by the slant in FIG. Then, the projected disk (g) is laterally displaced in the radial direction a'.

The displacement distance ΔL is 2・Δθ・f become.

Then, the disk on which the four light receiving areas 1 to ■ are projected (
A pair of light-receiving areas, ie, light-receiving areas 1. IV(!
: Difference Sa between the respective outputs in the light receiving areas II and II
= (81+S■) (8Il+81) is the seventh
As is clear from the figure, the relationship is SaocΔLCx−Δθ. Therefore, the skew error, that is, the radial skew angle (inclination Δθ) is detected using the output difference Sa.

The vertical axis in FIG. 7 represents the output sum 5b of the four light-receiving areas 1 to 2 = S 2 + S 10 SI + S 2, that is, the ratio to the reproduced information signal is 8a/Sb.

That is, the outputs of the two light-receiving areas 1.1■ are given to the input end of the adder (koji), and the outputs of the two light-receiving regions 1.1-1 are given to the input end of the adder (2). Adder (
The output of 231t241 is given to the input terminal of subtracter Q5).

Then, the output of the subtracter 251 is passed through a low-pass filter circuit (c) composed of a capacitor C and a resistor R to extract the DC component, thereby controlling the skew error (rtll(N)
number is obtained.

This skew error control signal is transmitted to the optical pickup (P
) to the feed motor 03 in the drive mechanism N that drives the disk (to) in the radial direction a,
The optical pickup (P) is moved 11 so that the skew error control signal has a constant value of zero. In other words, since the light beam converged on the signal surface (of the disk due to tracking control using the ω term) is always positioned on the track, if the signal surface of the disk (to) is tilted in the radial direction a, then Then, as shown in FIG. 8, the optical pickup is tilted by the movement of the disk (b) of the optical pink-up e) in the radial direction a. Then, the optical axis (OA) of the reading optical system is made perpendicular to the signal surface of the disk (2) so that the light beam is incident perpendicularly to the signal surface of the disk (b), and the skew error control signal is kept constant at zero. Skew control is performed so that the value is the same.

Note that the adder (231f, 24, 8 subtracters (29) and the loaf 1° filter circuit t, '61, etc. constitute the second detection control means in the present invention.

In this embodiment, the so-called DPD method was used to detect the tracking error, but it is also possible to use a six-spot method by modifying the light receiving section (PD) of the photodetector.

Similarly, a knife etching method, a concentric circle method, or the like may be used instead of the so-called critical angle method to detect focus errors.

Furthermore, the optical pickup (P) is connected to the objective lens (OL).
A linear motor, a lead screw, a feed belt, or the like may be used to constitute the drive 4a structure that is driven to swing the focus so that it traces an arcuate locus X. Also,
The same applies to the configuration of the drive mechanism N that drives the optical pickup CP) in the radial direction a of the disk (Dl).

Effect of the invention The present invention has the following advantages.

■The optical pickup is swingably installed so that the focal point of the objective lens is perpendicular to the signal surface of the disk and draws an arcuate locus in a plane that is in the radial direction of the disk.
By tilting the optical pickup, that is, the entire reading optical system, the light beam converged on the signal surface of the disk is always positioned on the track. Therefore, since the light beam is always positioned on the track as described above, the difference in output between the light receiving areas of the light receiving area of the photodetector divided into two in the radial direction of the projected disk. By detecting the inclination of the signal surface of the disk in the radial direction,
By applying this detection output as a control signal to the drive means, so-called feeding mechanism, that moves the optical pickup in the radial direction of the disk, the optical pickup tilts as it moves in the radial direction of the disk, and is incident on the signal surface of the disk. The light beam of the reading optical system and the signal surface of the disk become perpendicular.

In other words, even if the signal surface of the disk is tilted in the radial direction due to bending or the like, the optical axis of the reading optical system is always kept perpendicular to the signal surface of the disk by detecting the tilt. The occurrence of coma aberration due to the inclination of the signal surface of the disk is prevented, and the required OTF characteristics can be obtained. Further, in a video disc, increase in crosstalk can be suppressed.

(2) Furthermore, if we are using an optical pickup that can be oscillated to draw an arcuate trajectory as described above for tracking, then the optical pickup must be driven to move in the radial direction of the disk. It is only necessary to give the above-mentioned detection output of the inclination in the radial direction of the signal surface of the disk as a control signal to the driving means, so-called feeding mechanism, and φ1 can be achieved with an extremely simple configuration.

[Brief explanation of the drawing]

1 and 2 are schematic diagrams for explaining a conventional device, and FIGS. 3 to 8 are diagrams for explaining an embodiment of an optical disc reproducing device according to the present invention,
Fig. 6 is an overall schematic diagram, Fig. 4 is a partial longitudinal sectional view of the reading optical system along the optical axis of the reading optical system in Fig. 6, and Fig. 5 is a block circuit diagram, showing the optical axis showing the lateral displacement. FIG. 7 is a diagram showing the experimental results of the relationship between the radial skew angle and the output, and FIG. 8 is a schematic diagram for explaining the skew error control state. In addition, in the symbols used in the drawings, (15) α
6) 08X11,,,. 0. direction, vessel (211 (
23) (2) ρ0) (251...... Subtractor (22
)......Song...Hold circuit (26j River/Song...Low pass filter circuit (mouth...)
...Song... Disc (L)...
Curved laser light source (Foundation) N...Curved rotation mechanism (OL)...Curved objective lens (IP)...
・・・・・・・・・・・・Optical pickup (P, D
, )...... Light receiving part 1, n, I, of the four-way detector
IV... Light receiving area. Agent: Masaru Doatsu〃 Miya Bao Yoshio Figure 1 ■ Figure 2

Claims (1)

[Claims] A reading method in which the light beam from the laser light source is focused into a spot on the signal surface of the disk by an objective lens, and the return light beam reflected from the signal surface of the disk is incident on the light receiving section of the photodetector via the objective lens. In an optical disc reproducing apparatus equipped with an optical pickup consisting of an optical system, the focal point of the objective lens is arranged in a circular arc trajectory in a plane perpendicular to the signal surface of the disc and in a radial direction of the disc. The optical pickup is provided so as to be swingable so as to draw the optical pickup, and is provided with a first driving means for driving the optical pickup to swing, and detects a change in the returning light flux incident on the light receiving section of the photodetector. A first detection control means is provided which supplies this detection output to the first drive means and always positions the light beam converged on the signal surface of the disk on the track, and also moves the optical pickup to the radius of the disk. A second driving means is provided to be movable in the direction and to drive the optical pickup to move the optical pickup, and the light receiving part of the photodetector is divided into two in the radial direction of the projected disk. A pair of light-receiving areas are formed, and a change in the return light flux incident on each of these light-receiving areas is detected as a difference between the outputs of the husband and wife, and this detection output is An optical disk reproducing device characterized in that a second detection control means is provided for making the difference between the outputs of the second drive means ζ and the output thereof constant.