JPH01296436A - Optical pick-up - Google Patents

Abstract

PURPOSE:To correctly load both preceding and following beams on a track by detecting the track error signals of both the preceding beam and following beam, loading a tracking servo with one error signal and loading a tangential servo with the other error signal. CONSTITUTION:When the track error signal is detected in a photodetecting element 31 by a preceding beam A for recording, the signal is outputted to a track servo circuit 32 and an actuator for objective lens drive is driven. Then, the signal is correctly positioned on the track and servo control is executed so that the track error signal can be 0. When there is no decentering in an optical disk 24, an SB for recording and reproducing is also positioned correctly on a track 41. When there is decentering, even in case that a spot SA for recording is correctly positioned on the track 41, track dislocation is generated in the spot SB. Since this dislocation is detected by a photo-detecting element 36, the error signal is outputted to a tangential servo circuit 40. Then, by loading the tangential servo to the objective lens actuator, the spot SB for recording and reproducing is also positioned correctly on the track 41.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an optical pickup in a multi-beam optical disc device.

Conventional technology Recently, the beam from a semiconductor laser is narrowed down to a minute spot by an objective lens and irradiated onto an optical disk to record information.
Optical disk devices that perform playback or erasing are attracting attention. This is because optical discs have advantages such as large capacity, low cost per bit, and the fact that the discs are removable and easy to handle.

However, it has the disadvantage that processing time is longer than that of hard disks such as magnetic disks. When recording on an optical disc, when there is a command, the micro/JS spot is first accessed and the desired address position is located before recording is performed, and after the recording is completed, the written information is played back to confirm it. This is to perform the action of That is, the recording mode of the optical disc is two operations: "Record #J 10R Confirmation Playback J".

In order to solve this disadvantage of processing time, a multi-beam type optical pickup has been proposed. That is, a plurality of laser beams are focused on the same track of an optical disk, and almost at the same time as recording is performed using the preceding beam, recorded information is reproduced for confirmation using the subsequent beam. According to this, since recording and confirmation reproduction proceed almost simultaneously, the time required for the recording mode can be shortened. Such a multi-beam optical pickup is known from, for example, Japanese Patent Publication No. 57-60697.

Here, FIG. 3 shows an example of a conventional multi-beam type optical pickup, for example, a two-beam type optical pickup.

First, there are two beams A with two light emitting points IA and IB,
A semiconductor laser 1 that emits B light is provided. These beams A and B are collimated by the collimating lens 2 and then enter the beam splitter 3, where they are sent to the optical disc 4.
deflected to the side.

At this time, the beam is focused into a minute spot by the objective lens 5, and the beam A is focused as a minute spot SA, and the beam B is focused as a minute spot SB. Here, a minute spot SA of beam A is shown by a broken line.
is the leading spot and is used for recording. In other words,
The recording beam A itself is modulated in accordance with recording information during recording. - On the other hand, the minute spot SB by the beam B shown by the solid line is a trailing spot formed on the same track as the minute spot SA, and is used for confirmation playback in the recording mode, and for normal playback in the playback mode. It will be done.

Next, the reflected light from the optical disk 4 passes through the objective lens 5 again, enters the beam splitter 3, is separated from the incident light, and is focused by the first focusing lens 6. Here, although the beams A and B are focused at different positions by the condenser lens 6, an aperture is arranged near the condensing point of the condenser lens 6, and after the reproduction (including confirmation reproduction) shown by the solid line. It is set so that only the row beam B passes through and the leading beam A for recording is blocked. First, the trailing beam B for reproduction that has passed through the aperture is condensed again by the second condensing lens 8 and directed toward a two-split light receiving element 9 for detecting a focus signal. At this time, the prism mirror 10 is projected to the optical axis.
The focus error signal is detected by the well-known knife method. Further, a portion of the light from the condenser lens 8 is reflected by a prism mirror 10 and directed toward a light receiving element 11 for detecting a track signal. Detection of this track signal is performed by the well-known push-pull method. The focus error signal and track error signal thus obtained are used for focus/track servo control of the optical pickup (objective lens 5). Note that the information signal is obtained from the light receiving element 11.

In such an optical pickup that simultaneously performs recording and confirmation/reproduction using two beams, servo control is performed by obtaining a servo signal for tracking/focusing from the following reproduction beam. This is because the reproduction beam side emits light with a constant power, so it is considered easier and more stable than obtaining a servo signal based on modulated light like the recording beam.

Problems to be Solved by the Invention However, since the servo signal is obtained from the confirmation reproduction beam B during recording, the confirmation reproduction beam B does not suffer from track deviation, but the recording beam A may suffer from track deviation.

This is because even if the reproduction beam B is located at the correct position on the track, the recording beam A side is not necessarily located at the correct position on the track. As a result, track deviation may occur in the pits recorded by such recording beam 8, making it impossible to perform highly reliable recording.

Furthermore, if an information recording medium is recorded with such track misalignment or focus misalignment and is determined to have been recorded correctly during confirmation playback, an error may occur if the information recording medium is played back using another drive where the playback beam misalignment is different from the misalignment of the drive that recorded the information. This makes the information recording medium less reliable.

Furthermore, eccentricity of the information recording medium also causes track deviation in the recording beam, reducing recording reliability. That is, track deviation may be caused by a difference in curvature between the inner and outer circumferences of the track, by disturbance of the track, or by eccentricity of the optical disc.

There is also a method to obtain a signal for focus/track servo control based on the leading beam A for recording instead of the trailing beam B for reproduction, but similarly, the trailing beam for confirmation reproduction has a focus shift or l・Rack misalignment occurs. Therefore, even if the tracking servo is applied to the recording beam and the recording medium is correctly tracked, the eccentricity of the recording medium may cause a tracking deviation on the confirmation reproduction beam side.

Means for Solving the Problem Tracking control is performed in which a detector is provided to detect the tracking error signal of each of the leading beam and the trailing beam, and tracking servo is applied based on the tracking error signal detected based on the leading beam or the trailing beam. In addition, a tangential control system is provided which applies a tangential servo based on a tracking error signal detected based on the other trailing beam or leading beam.

First, when a tracking error signal is detected due to a track deviation in the leading beam for recording, the leading beam is correctly positioned on the track by tracking servo control by the tracking control system. At this time, according to the relationship between the center of the optical disc and the track, if the optical disc is not eccentric, the trailing beam for confirmation reproduction will also be correctly positioned on the track. .

However, if the optical disk is eccentric, a tracking error signal will be generated for the trailing beam. When tracking servo is applied based on the tracking error signal of this trailing beam,
This time, a track deviation occurs on the leading beam side, but here, both beams are controlled correctly on the track by displacing in the tangential direction according to the eccentricity of the optical disk by the tangential control system. This is the same even if the beam relationship is reversed.

Embodiment An embodiment of the present invention will be explained based on FIGS. 1 and 2. The basic optical pickup configuration is similar to that shown in FIG.

First, a semiconductor laser 2 is used as a laser array having two light emitting points 21A and 21B and emitting two beams A and B.
1 is provided. These beams A and B are collimated by a collimating lens 22, enter a beam splitter 23, and are deflected toward an optical disk 24. At this time, the beam A is narrowed down to a minute spot by the objective lens 25, and the beam A is irradiated to the minute spot S.
The beam A is focused, and the beam B is focused as a minute spot SB. Here, as in the case of FIG. 3, the minute spot SA of the beam A shown by the broken line is the leading spot and is used for recording. That is, the recording beam A itself is modulated in accordance with recording information during recording. On the other hand, the minute spot SB shown by the solid line by the beam B is a trailing spot formed on the same track as the minute spot SA, and is used for confirmation playback in the recording mode and for normal playback in the playback mode. Next, the reflected light from the optical disk 24 passes through the objective lens 25 again, and then enters the beam splitter 23 where it is separated from the incident light and sent to the first condenser lens 25.
6, the light heads toward the focus/track detection optical system 27 side.

Here, the beams A and B are focused at different positions by the focusing lens 26. The recording beam A side is condensed by a condensing lens 26, and then condensed again by a second condensing lens 28 and directed toward a two-split light receiving element 29 for detecting a focus signal. At this time, the prism mirror 3 protruded to the optical axis
0 is inserted, and the focus error signal is detected by the well-known knife method. Also,
A portion of the light from the condenser lens 28 is reflected by a prism mirror 30 and is directed toward a light receiving element 31 as a detector for detecting a track signal. Detection of this track signal is performed by the well-known push-pull method. The focus error signal and track error signal thus obtained are used for focus/track servo control of the actuator of the optical pickup (objective lens 25). Here, a track servo circuit 32 as a tracking control system based on a light receiving element 31 is shown.

On the other hand, the light receiving element 29 for the recording advance beam A.
Not only the detection optical system 27 for the trailing beam B for confirmation and reproduction, but also the detection optical system 37 for the light receiving element 35 for detecting a focus signal and the light receiving element 36 as a detector for detecting a track signal, respectively. , the condenser lens 26
It is provided on the reflection side of the prism mirror 33 facing near the condensing point. This detection optical system 37 is also the optical system 2.
Similarly to the side 7, it includes a condensing lens 38 and a Knifezi prism 39, a focus signal is detected by a light receiving element 35 using the Knifezi method, and a track signal is detected by a light receiving element 36 using a push-pull method. and,
The output of the light receiving element 35 for the track error signal is output to a tangential servo circuit 40 serving as a tangential control system, and is used for tangential servo control.

In the configuration shown in 2, basically, when a tracking error signal is detected by the light receiving element 31 based on the preceding beam A for recording, it is output to the track servo circuit 32, which drives the actuator for driving the objective lens, and correctly detects the tracking error signal. It is located on the track and is servo controlled so that the track error signal becomes O.

In such control, the positional relationship of the two spots SA and SB with respect to the track 41 on the optical disc 24 will be considered with reference to FIG. First, according to the above control, the preceding recording spot SA is positioned on track 1 by tracking servo. At this time, if there is no eccentricity in the optical disc 24, there is a recording spot SA and a confirmation playback spot S'B at positions equidistant from the disc center C, as shown in FIG. 2(a). Playback spot S
B is also correctly located on the track 41.

However, for example, as shown in FIG.
4 is eccentric to the right side than it should be and the center is C', even if the recording spot SA is correctly positioned on the track 41 due to the tracking servo, the confirmation playback spot SB will be located on the track 41. Track deviation occurs at the inner circumference side position. Such track deviation is detected by the light receiving element 36. Therefore, the tracking error signal (including the direction of deviation) detected by the light receiving element 36 is output to the tangential servo circuit 40, and the objective lens actuator is moved in the tangential direction (circumferential direction) opposite to the eccentric direction of the optical disk 24. ). That is, when eccentric to the right as shown in Fig. 2(b),
Since the tracking error signal of the confirmation reproduction spot SB becomes negative, the objective lens 25 is tangentially displaced to the right in response to this. As a result, the recording spot SA
and the confirmation playback spot SB are correctly located on the track 41, and a highly reliable recording/confirmation playback operation or playback operation is performed.

FIG. 2(C) shows a state in which the optical disc 24 is eccentric to the left side compared to the original case, and the center is at CII.
Even if the recording spot SA is correctly positioned on the track 41 by the tracking servo, the confirmation playback spot SB causes a track shift to a position on the outer circumferential side of the track. Such track deviation is detected by the light receiving element 36. Therefore, the tracking error signal detected by the light receiving element 36 is output to the tangential servo circuit 40, and the objective lens actuator is servoed in the tangential direction. That is, in the case of eccentricity to the left as shown in FIG. 2(C), the tracking error signal of the confirmation reproduction spot SB becomes positive, so the objective lens 25 is tangentially displaced to the left in response to this. let As a result, the recording spot SA and the confirmation playback spot SB are correctly positioned on the track 4]1-, and a highly reliable recording/confirmation playback operation or playback operation is performed.

Note that the track servo circuit 32 and the tangential servo circuit 40 may be replaced to perform tracking servo control on the trailing beam B and tangential servo control on the leading beam A.

Effects As described above, the present invention detects the tracking error signal for both the leading beam and the trailing beam, applies tracking servo to one beam by the tracking control system based on the tracking error signal, and performs tracking for the other beam. If an error signal is generated, the tangential servo is applied by the tangential control system, making it possible to perform tracking servo control that is not affected by the eccentricity of the optical disk, allowing both beams to be placed correctly on the track. Therefore, highly reliable recording operations and confirmation playback operations can be performed.

[Brief explanation of the drawing]

FIG. 1 is a front view of an optical system configuration showing an embodiment of the present invention;
FIG. 2 is a plan view showing a state of track deviation due to eccentricity, and FIG. 3 is a front view showing the configuration of a conventional optical system.

Claims (1)

[Claims] In an optical pickup of an optical disc device, multiple beams from a laser array are focused onto the same track on an optical disc by an objective lens, recording or erasing is performed using a leading beam, and confirmation and reproduction of information immediately after recording is performed using a trailing beam. a tracking control system that includes a detector for detecting a tracking error signal of each of the leading beam and the trailing beam, and applies tracking servo based on the tracking error signal detected based on the leading beam or the trailing beam; and a tangential control system that applies tangential servo based on a tracking error signal detected based on the trailing beam or the leading beam.