JPS6061925A - Optical information recording and reproducing device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] (Technical field) The present invention relates to an optical information recording/reproducing device.

(Prior art) An optical pickup optical system focuses a light spot onto the track of an optical disc having spiral or concentric tracks, and optical information is recorded on the trunk or recorded on the track. Optical information recording and reproducing methods for reproducing optical information are known.

In such a recording and reproducing system, in order to accurately record and reproduce optical information, it is necessary for the light spot to be correctly focused on the track. , alignment control is performed to align the focused position of the light spot with the track so that the focused position of the light spot coincides with the track.

This control is called tracking control. On the other hand, the control for focusing the light spot on the track is called focusing control.

By the way, if the optical disc's disc and disc surfaces are tilted or warped, there is a problem that tracking control will not work properly.

As a conventional technique dealing with this problem, Japanese Patent Laid-Open No. 58-5
There is a technique disclosed in Japanese Patent No. 3030.

In this technology, a recorded information signal (hereinafter referred to as RF signal), that is, a signal obtained from optical information recorded on an optical disk, is detected by a bandpass filter, and then envelope detection is performed.
Detect that peak. If the optical disc is tilted or the disc surface is warped, the RF multiplied signal will not reach a predetermined level.

Therefore, by adding a correction voltage that gradually increases in a stepwise manner to the servo system, R
By detecting that the F-fold signal has reached a predetermined level and holding the corrected voltage value at that time, tracking control is optimized.

The problems with this method are as follows.

First, since the RF multiplied signal is used for correction, it cannot be used at all if there is no RP multiplied signal, that is, when optical information is to be recorded on an unrecorded disc. Second, the correction voltage is not necessarily a positive voltage, and correction using a negative voltage may be necessary. However, it is not possible to determine whether the correction voltage is positive or negative based only on the RF multiplied signal level.

(Purpose) Therefore, the present invention always provides a method for recording and reproducing optical information.
The purpose of the present invention is to provide a novel optical information recording/reproducing device that can easily and reliably perform tracking control.

(composition) The present invention will be explained below.

In the optical information recording/reproducing apparatus of the present invention, prior to recording or reproducing optical information, a desired track is searched by scanning a light spot by an optical pickup optical system across the track. This track search is always performed.

For example, track search is performed even when optical information is recorded or reproduced from the outermost track.

Therefore, in such a case, the optical pickup optical system must be set so that the optical spot is located on the innermost track when the optical disc is set in the recording/reproducing device. Sequence control is performed so that recording or reproduction is performed after track exploration.

The reason why the track search is performed before recording and reproducing in this way is that the track search is used to correct the tracking control.

Now, the optical information recording/reproducing apparatus of the present invention has a DC offset voltage detection means, a holding means, an i-stage subtraction, and a servo system driving means.

The DC off-nut voltage JIL)J& means detects the DC offset voltage of the tracking control signal during scanning of the optical spot in order to search for a desired track. The DC offset voltage will be described later.

The holding means holds the value of the DC offset voltage at the time when the track search is completed.

The subtraction means subtracts the offset voltage value held by the holding means from the tracking control signal during recording or reproduction of optical information.

The servo system driving means drives the servo system using the output signal from the subtraction means to control the position of the optical spot.

Hereinafter, specific examples will be described with reference to the drawings.

FIG. 1 schematically shows only the main parts of an example of an optical pickup optical system used in the optical information recording/reproducing apparatus of the present invention. In the figure, numeral 1 is a semiconductor laser, numeral 2 is a coupling lens, numeral 3 is a polarizing beam splitter 1, numeral 4
5 is a quarter wavelength plate, 5 is an objective lens, 6 is an optical disk, 7 is a condenser lens, 8 is a light receiving element for trunk detection, and 9 is a light receiving element for focus detection.

The light beam emitted from the semiconductor laser 1 is made into a parallel light beam by a coupling lens 2, and is incident on the disk surface of an optical disk 6 via a polarization beam splinter 3, a quarter-wave plate 4, and an objective lens 5. At this time, the incident light flux is
Due to the action of the objective lens 5, a diameter of about 1.
Focus to a 6 μm light spot.

The light beam reflected by the disk surface 6 is reflected by the objective lens 5.1/4
The light passes through the wavelength plate 4 and the polarization beam splinter 3, is made into a convergent beam by the condenser lens 7, and part of it enters the light receiving element 8 and the other part enters the light receiving element 9.

First, focusing control will be briefly explained. The light receiving element 9 is arranged at a position P where the light focused by the condensing lens 7 would be focused if the focused light by the objective lens 5 was correctly focused on the disk surface. The light-receiving element 9 has a light-receiving section divided into two parts A and H, and each light-receiving section A and B can output signals A' and B', respectively. When the focused light beam by the objective lens 5 is correctly focused on the disk surface, the focused light by the condenser lens 7 is focused at point P, and the amounts of light received by the light receiving sections A and B are equal to each other. Therefore, at this time, outputs A and B are equal to each other, and A=B. However, objective lens 5
On the other hand, when the disk surface moves away and the focused light by the objective lens 5 is focused in front of the disk surface, the convergence point of the focused light by the condenser lens 7 shifts to the left in FIG. 1 from point P, and ξ As a result, the amount of light received by the light receiving part B increases relatively, and becomes A(B. Conversely, when the disk surface approaches the objective lens 5, the convergence point of the converged light by the condenser lens 7 becomes P The points and points also shift to the right in Figure 1.

As a result, the amount of light received by the light receiving section A increases relatively, and A>B.

Therefore, focusing control is performed by using A-B as the focusing control signal and driving the servo system to displace the objective lens 5 in the direction of its optical axis so that this focusing control signal becomes 0. be able to.

Note that A+B is used as the RF multiplied signal.

Next, tracking control will be explained.

FIG. 2 shows the cross-sectional shape of the optical disc 6 in an explanatory diagram. As the name suggests, the optical disc 6 has a disc shape, and one side of the optical disc 6, in the example shown in FIG.
A series of tracks...6i-1, 6i,
6i+1.6z+2. ... is formed in an uneven shape. As mentioned earlier, the track formation is spiral or concentric. The surface on which these tracks are formed is called the disk surface.

In the example shown in FIG. 1, the optical disk 6 is placed with the surface opposite to the disk surface, that is, the surface facing downward in FIG. 2, facing the objective lens 5.

Therefore, the light beam from the semiconductor laser 1 enters from the surface opposite to the disk surface, passes through the optical disk 6, and is focused on the disk surface. The depth of the tracks 6i, etc. on the disk surface is approximately 〒λ in terms of optical distance with respect to the wavelength λ of the laser beam emitted from the semiconductor laser 1, and the disk surface is virtually ineffective for focusing control. It is essentially flat.

Now, as shown in FIG. 3, the light receiving element 8 for track detection has a light receiving part divided into two parts C and D, and each light receiving part C,
Signals C' and D' can be output from D.

In FIG. 1, the dividing line that separates each of the light receiving sections C and D is in the vertical direction of the drawing, and in FIG. 1, the direction perpendicular to the track is the direction perpendicular to the drawing. In FIG. 3, reference numeral 3-1 indicates a light beam converged by the condenser lens 7, and a hatched portion with a broken line indicates a portion of the light beam incident on the light-receiving element 8.

Now, referring to FIG. 4, as shown in FIG. 4 (IT), when the focused light by the objective lens 5 is correctly focused on the track of the optical disk 6, the intensity of the light incident on the light receiving element 8 is are symmetrical with respect to the dividing line between light receiving sections C and D, outputs C' and D' are equal to each other, and C'=D'
becomes.

However, as shown in FIG. 4(I) or (m), when the focusing position of the focused light by the objective lens 5 deviates from the track, the difference between the track portion and other portions is /4.
Since there is an optical distance of λ, a phase difference of π occurs in the reflected light of the image area, and the light intensity IN on the light receiving element 8 is reduced due to the diffraction effect.
T becomes asymmetrical with respect to the dividing line, and the outputs c', D'
The relationship in magnitude is as follows: C'>D' (FIG. 4(r)) or c'<D' (FIG. 4(■)).

Therefore, in principle, tracking control can be performed by using C'-D' as a tracking control signal and driving the servo system so that this control signal becomes 0.

That is, as shown in FIG.
1 and 212, and the difference between them is taken by the differential amplifier 22. This difference voltage is applied to the servo coil drive circuit 23 to drive the servo coil 24 of the servo system, and the objective lens 5 is The tracking control signal C'-D' is controlled to be zero by displacing it in a direction perpendicular to the axis, that is, a direction perpendicular to the track.

By the way, if the optical disc 6 is tilted with respect to the optical axis of the objective lens 5 due to poor setting or warping of the optical disc, and the optical axis is no longer orthogonal to the disc surface, the focused light will be distorted as shown in FIG. Even if the light intensity distribution INT on the light receiving element 8 is correctly focused on the track, the light intensity distribution INT on the light receiving element C
, D, and the tracking control signal C-D deviates from 0, and it is detected as if the light spot is deviated from the track, and tracking control is performed based on this. , the light spot is misaligned with respect to the track, and information cannot be recorded or reproduced correctly.

In the present invention, tracking control failure caused by tilting of the optical disk due to warping or the like is corrected as follows.

That is, prior to recording or reproducing optical information, a light spot is scanned across the track to search for a desired track.
Attention is paid to the tracking control signal during optical spot scanning, that is, the output voltage of the differential amplifier 22 in FIG.

This output voltage fluctuates sinusoidally as the optical spot scans, but if the optical disc 6 is not tilted,
As shown in FIG. 7, the fluctuations are symmetrical with respect to the OV line, but if the optical disc 6 is tilted, the fluctuations with respect to the OV line are not symmetrical, as shown in FIG. In such a case, if tracking control is performed using Ov as a reference, tracking control failure will occur as described above. As shown in FIG. 8, when the optical disc 6 is tilted, in order to perform proper tracking control, the MV
Control must be performed using the line as a reference. The difference between the 0■ line and the MV line is called an offset voltage Of. The MV line is
In reality, the offset voltage Of itself fluctuates as it fluctuates in accordance with changes in the slope, but the frequency of this fluctuation is sufficiently low compared to the fluctuation of the tracking control signal due to optical spot scanning. Therefore, this offset voltage is called a DC offset voltage.

Now, FIG. 9 shows a tracking control system in the optical information recording/reproducing apparatus of the present invention.

In the figure, symbols SWI and SW2 are switch circuits, and symbol 3
2 is a subtracter, 34 is an offset voltage detection circuit, 35 is an A-D converter, 36 is a latch circuit, 3
7 indicates a D-A converter, respectively.

Symbol E is a signal from a sequence control means (not shown), and the switch circuits SWI, SW2 and the launch circuit 36 are controlled by this signal E.

Tracking control will be described below in the case of recording and reproducing information.

When an address signal designating a trunk having information to be reproduced or a track in which information is to be recorded is sent to the sequence control means, the switch circuit Sw1 first uses the signal E to cause the differential amplifier 22 to detect an offset voltage. It is connected to the circuit 34, and the switch circuit sw2 is turned off.

Furthermore, the latch circuit 36 is placed in access mode.

Subsequently, the sequence control means drives the optical pickup optical system, and the optical spot produced by the optical system scans in a direction across the track. As a result, the aforementioned sinusoidal tracking control signal is generated at the output of the differential amplifier 22, and this signal is applied to the offset voltage detection circuit 34 as offset voltage detection means.

The offset voltage detection circuit 34 includes a maximum detection circuit 41, a minimum detection circuit 42, and an adder 43, as shown in FIG.
and resistors R1 and R2. Maximum/minimum detection circuit 4
1.42 is a well-known type composed of a comparator, a resistor, a capacitor, etc.

The sinusoidal tracking control signal FI applied via the switch circuit SWl is applied to the maximum detection circuit 41 and the minimum detection circuit 42, and the maximum voltage V1 and minimum voltage 2 detected in each detection circuit are added together. The output V]+V2 is added to the resistors R1 and R2. Resistors R1 and R2 have the same value and therefore provide a DC offset voltage to the output voltage between resistors R1 and R2.

This DC offset voltage is as shown in FIG.
It is converted into a digital value by the D converter 35, and the latch circuit 36
are applied sequentially.

When the search for the desired track is completed, the sequence control means again issues the signal E. This signal E causes the switch circuit SWI to connect the differential amplifier 22 to the subtracter 32, turn on the switch circuit SW2, and turn on the latch circuit 36.
Switch from access mode to recording or playback mode.

The latch circuit 36 is a latch means that latches the offset voltage value at the time of mode switching, that is, the offset voltage value at the completion of the track search. Therefore, the output of the latch circuit 36 will hold the offset voltage value until the next time the access mode is switched.

The output of the latch circuit 36 is converted into an analog signal by a DA converter 37 and applied to the subtracter 32 . On the other hand, the output of the differential amplifier 22 is applied to a subtracter 32, which is a subtracting means, via a switch circuit Sw1. Latch circuit 3
6 constitutes a holding means for the offset voltage together with the AD converter 35, the DA converter 37, and the sequence control means.

Subtractor 32 subtracts the offset voltage value from the output of differential amplifier 22. As a result, the tracking control signal is corrected, and the output of the subtracter 32 becomes a correct tracking control signal with positive and negative symmetry. Therefore, by controlling the servo coil drive circuit 23 using this corrected signal, proper tracking control can be performed regardless of the inclination of the optical disc 6.

As mentioned above, the offset voltage fluctuation caused by the tilt of the optical disk is extremely close to direct current compared to the frequency band of the tracking control signal. Therefore, the low frequency pass filter LPF shown in FIG.
The offset voltage may be detected by using it as an offset voltage detection means and detecting the average value of the tracking control signal.

(Effects) As described above, according to the present invention, a novel optical information recording/reproducing device can be provided.

Since this device detects the offset voltage using track exploration, it is possible to detect the offset voltage including the signal on both an unrecorded optical disc and an optical disc on which optical information is recorded. Since the tracking control signal is corrected using this offset voltage, it is possible to compensate for the inclination of the optical disc caused by poor optical disk settings, warping, etc., and the presence of offsets and drifts in the components of the tracking control signal detection circuit. Therefore, proper tracking control can be performed.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing an example of an optical pickup optical system used in carrying out the present invention, FIG. 2 is a diagram for explaining an optical disc, and FIGS. 3 to 5 are diagrams showing tracking control. FIG. 6 is a diagram for explaining the principle of the optical disc, FIG. 7 and FIG. 8 are diagrams for explaining the offset voltage, and FIG. 10 is a diagram showing a tracking control system used to implement the present invention, FIG. 10 is a diagram showing one example of offset voltage detection means, and FIG. 11 is a diagram showing another example of offset voltage detection means. . DESCRIPTION OF SYMBOLS 1... Semiconductor laser, 2... Coupling lens, 3... Polarizing beam splitter 14... 1/4 wavelength plate, 5... Objective lens, 6... Optical disk, 7... Condensing lens , 8... light receiving element for track detection, 9...
- Light receiving element for focus detection, 32... Subtractor, 34...
- Offset voltage detection circuit, 36... latch circuit.

Claims (1)

[Claims] 1. An optical pickup optical system focuses a light spot on the track of an optical disc having tracks formed in a spiral or concentric form, and records optical information on the track, or An optical information recording and reproducing device that scans a pot across the track to search for a desired track, and detects a DC offset voltage of a tracking control signal while scanning a light spot to search for the desired track. means for holding the value of the offset voltage at the time when the exploration is completed; and means for subtracting the held offset voltage value from the tracking control signal during recording or reproduction of optical information; 1. An optical information recording and reproducing apparatus comprising: servo system driving means for controlling the position of the optical spot using an output signal from the subtracting means. 2. In claim 1, the means for detecting the DC offset voltage includes means for detecting the maximum value of the tracking control signal, means for detecting the minimum value of the tracking control signal, and both of these means. A means for adding outputs and 1/2 of the output of this means for adding.
1. An optical information recording and reproducing device, characterized in that it has means for obtaining an output. 3. The optical information recording and reproducing device according to claim 1, characterized in that the means for detecting the DC offset voltage has a low frequency pass filter for detecting the average value of the tracking control signal. Device. 4. In claim 1, 2, or 3, the means for holding the value of the offset voltage includes means for converting the 2-7 cent voltage into a digital value, and a trunk search lamp light. sequence control means for generating a control signal indicating the end of spot scanning; means for launching the output of the digital value converting means according to the control signal; and converting the output of the latching means into an analog voltage value. 1. An optical information recording and reproducing device, characterized in that it has means for.