JPS62128028A - Automatic offset adjusting system - Google Patents

Abstract

PURPOSE:To attain stable servo by cancelling an offset component which is generated in each error signal due to reflection of optical parts or the like on an optical disc. CONSTITUTION:The offset component of each detected error signal generated by stray light or the like in an optical device is not concerned with signal recording and reproducing and is proportional to the quantity of light emitted from a light source 1. A part of incident light 2 from the light source 1 is separated directly by a beam splitter 4 provided in the optical path and is detected by the second photodetector 13, and the output is synthesized with a focus error signal 10 and a tracking error signal 11 respectively. Thus, offset is cancelled and thus the system can cope with the influence of change of the reflection factor on the surface of the disc or the like.

Description

[Detailed Description of the Invention] [Summary] Since the offset due to stray light, etc. in an optical disk device is proportional to the amount of light emitted from the light source, a part of the incident light from the light source is directly separated by a beam splitter installed in the optical path. The offset is canceled by detecting it with a photodetector and combining its output with a focus error signal and a tracking error signal, respectively.

[Industrial application field]

The present invention relates to an optical disc device, and more particularly to a method for removing an offset component mixed into a focus error signal and a tracking error signal.

In an optical disc device, a signal is reproduced by focusing recorded information on an optical disc as a recording medium, so a laser beam is focused on the disc surface where recording pits exist, and the recording pits are tracked so that the reading light is constantly directed to the disc. It is necessary to accurately illuminate the pit rows on the surface and to receive the reflected light from the recording pits.

Since the light beam is always focused on the disk, there is a conventional astigmatism method as a method for detecting focusing deviation. Further, as a push-pull method, a push-pull method is known that utilizes diffraction from a guide groove cut in advance on an optical disk.

[Conventional technology]

FIG. 3 shows a configuration diagram of a conventional optical disc device.

In the figure, a diverging beam 2 emitted from a light source 1 enters a collimator lens 3, is converted into a parallel beam, passes through a beam splitter 4, and is passed through an objective lens 5 to a disk 6.
The light is focused on.

The focused laser beam is reflected by the disk 6, travels backwards, passes through the objective lens 5, becomes a parallel beam, is separated by the beam splitter 4, and passes through a beam shape conversion optical system consisting of a convex lens 7 and a cylindrical lens 8. The light passes through and is received by the first photodetector 9.

FIG. 4 shows a diagram of the output shape of the third photodetector.

The first photodetector 9 is arranged at the position of the circle of least confusion of the astigmatic light beam when the disk 6 is in the just focus position.

FIG. 4 (al indicates the time of just focus; the light beam cross section is circular and divided into photodetectors 9a, 9b, 9c,
It is equally divided into each of 9d.

Figure 4 (bl) and Figure 4 (C) respectively show the cross sections of the light flux when the disk 6 approaches and moves away from the objective lens 5 side from just focus. Because it has a rotated elliptical shape, (9
a+9c)-(9b+9d) signal to differential amplifier 1
A focus error signal 10 can be obtained by combining with 0a.

FIG. 5 is a diagram showing the principle of detection of a tracking error signal. FIG. 5 (al) is the cross section of the beam on the first detector 9 when the focused spot accurately follows the guide groove, and the difference between the divided detectors (9a+9b) (9c+9d) becomes zero.

Figure 5 (bl) and Figure 5 (C) are the cross sections of the light flux when the condensed spot is shifted to the left and right sides from the guide groove, respectively, and the left and right light quantity balance is shifted, (9a + 9b
)-(9c+9d) by the differential amplifier 11a, the tracking error signal 11 can be obtained.

cProblem 3 to be Solved by the Present Invention In the optical system as described above, an offset occurs in each error signal due to the influence of reflection from optical components, etc.

FIG. 6 shows an operational characteristic diagram of a conventional focus error signal. In the figure, the horizontal axis X shows the distance, and the vertical axis V shows the output voltage of the differential amplifier 10a. 10 is a focus error signal, -Vo is an offset due to stray light, and Xo corresponding to point A is a just focus position. In this figure, the focus servo is applied at a position A shifted from the original zero point 0 due to the offset -Vo. If the reflectance of the disk changes from this state and the focus error signal 10 becomes the focus error signal 12 shown by the broken line, the focus servo will be applied at the position Xo' corresponding to point B, and ΔX=Xo'' There is a drawback that an offset of -Xo is generated.The tracking error signal 11 whose operation characteristics are not shown also has a drawback that an offset is generated.

The present invention was created in view of the above-mentioned drawbacks of the conventional art, and it is an object of the present invention to provide an automatic offset adjustment method capable of eliminating the above-mentioned offset.

[Means for solving problems]

As shown in FIG. 1, the automatic offset adjustment method of the present invention allows incident light 2 from a light source 1 to pass through, and the transmitted light is reflected by a recording medium 6, and the reflected light that travels backward is totally reflected and is a beam splitter 4 that separates the light beam from the beam splitter 4; and a first beam splitter 4 that detects the total reflected light from the beam
In an optical disc apparatus, a focus error signal 10 and a tracking error signal 11 are generated by the output of the first photodetector 9, and a part of the incident light 2 is reflected and separated. A second photodetector 13 that constitutes the light separation means 4 and detects the part of the reflected separated light is provided, and the output of the second photodetector 13Q) is used as the focus error signal 10 and the tracking error signal 11. The present invention is characterized in that it is provided with synthesis circuits 14 and 15 for synthesizing the images, respectively.

[Effect]

The offset of each detection error signal caused by stray light, etc. in an optical disk device is a component that is not involved in recording or reproducing signals, and is proportional to the amount of light emitted from the light source 1. a11
Directly separates a part of the incident light 2 from the second photodetector 1
3 and synthesizes its output with a focus error signal 10 and a tracking error signal 11, respectively, to cancel the offset and deal with the effects of changes in reflectance on the surface of the disk, etc.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings.

Note that, in order to make the explanation of the configuration and operation easier to understand, the same parts are given the same reference numerals throughout all the figures, and repeated explanation thereof will be omitted.

FIG. 1 shows a schematic diagram of the automatic offset adjustment method of the present invention. In the figure, reference numeral 13 denotes a second photodetector, in which the diverging light beam 2 emitted from the light source 1 enters the collimator lens 3, is converted into a parallel light beam, and when transmitted through the beam splitter 4, the transmitted light is The reflectance of the collimator lens 3 is set so that a part of the light is reflected to the side opposite to the convex lens 7.

The difference from Fig. 3 is that the beam splitter 4 and the light source 1
A photodetector 13 shown in FIG. 2 is added for receiving a light beam after reflecting and separating a part of the transmitted light from the second photodetector 13, and the output of the second photodetector 13 and the output of the first photodetector 9. A synthesis circuit 14 that synthesizes the focus error signal 10 obtained from the
The only difference is that a synthesis circuit 15 for synthesizing the output of the second photodetector 13 and the tracking error signal 11 is added.

Since the output of the second photodetector 13 directly separates the light incident on the beam splitter 4 of the light source 1, the amount of received light is proportional to the amount of light emitted from the light source 1. Therefore, the sixth
The offset amount -Vo (luminous flux component not involved in signal recording and reproduction) explained in the figure can be canceled by being combined by the combining circuits 14 and 15, and the change in the focus error signal 10 or the change in the tracking error signal 11 can be canceled. It is possible to prevent the occurrence of offcents due to Reference numerals 16 and 17 indicate a focus error signal and a tracking error signal, respectively, from which offset components have been removed by synthesis.

FIG. 2 shows an operational characteristic diagram of the focus error signal of the present invention. In the figure, a focus error signal 16 and a focus error signal 18 indicated by a broken line indicate changes in the focus error signal due to the reflectance of the disk and the like. In this case, since there is no offset, the just focus point Xo does not move.

[Effects of the present invention]

According to the present invention, it is possible to cancel the offset generated in each error signal due to reflection from optical components on the optical disc, so that stable servo can be realized.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram of the automatic offset HJm adjustment method of the present invention, Fig. 2 is a diagram of the operating characteristics of the focus error signal of the present invention, Fig. 3 is a block diagram of a conventional optical disc device, and Fig. 4 is a schematic diagram of the automatic offset HJm adjustment method of the present invention.
FIG. 5 is a diagram of the detection principle of a conventional tracking error signal, and FIG. 6 is a diagram of the operating characteristics of a conventional focus error signal. In the figure, 1 is a light source, 2 is incident light, 4 is a beam splitter, 6 is a recording medium, 9 is a first photodetector, 10 is a focus error signal, 11 is a tracking error signal, 1
3 represents a second photodetector, and 14 and 15 represent combining circuits, respectively. Figure 1 Futomei-h-7J Z 1 Nira-C No. 1 Motion 4 Shimoimoimo Rigo A Figure 2

Claims (1)

[Claims] A beam that transmits incident light (2) from a light source (1), and that transmitted light is reflected by a recording medium (6) and the reflected light that travels backward is totally reflected and separated from the transmission direction. It is composed of a splitter (4) and a first photodetector (9) that detects the totally reflected light from the beam splitter (4), and is focused by the output of the first photodetector (9). Error signal (
10) and a tracking error signal (11) in an optical disc device that generates a tracking error signal (11), comprising a light separating means (4) that reflects and separates a part of the incident light (2), and detects the part of the reflected separated light. A second photodetector (13) is provided, and the output of the second photodetector (13) is used as the focus error signal (10).
and a tracking error signal (11), respectively.