JPS61230632A - Detecting device for focus error signal - Google Patents

Abstract

PURPOSE:To attain detection of a focus error signal having no shift to the temperature variation by securing the coincidence between the relative shift direction due to the difference of heat expansion coefficients between a base and a photodetector and the boundary line direction of the photodetector. CONSTITUTION:A photodetector is attached to a distributing board 8 and this board 8 is fixed to a base 7 by screws 9a and 9b at hole parts 8a and 8b on the same straight line as a boundary line 5a of a photodetector. When the temperature of an optical pickup is changed, the position of the photodetector is shifted toward a straight line connecting screws 9a and 9b against the base 7 owing to the difference of heat expansion coefficients between the base 7 and the board 8. However the coincidence is secured between the direction of the line 5a and the shift direction of the photodetector. Thus the shift of a focus error signal can be eliminated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to an optical pickup used in an optical video contrast player, and more particularly to a focus error detection device therein, and particularly to a focus error detection device therein. The present invention relates to a focus error detection device equipped with a photodetector so that signals do not shift.

[Background of the invention]

Conventionally, many methods for detecting focus error signals of optical pickups have been disclosed, including Japanese Patent Laid-Open No. 12147/1983, but these methods use lenses.

Although sufficient consideration has been given to the configuration and arrangement of optical elements such as prisms and photodetectors, -C
No consideration was given to the method of fixing the photodetector to the chassis to prevent the focus error signal from shifting.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a focus error signal detection device in which a photodetector is fixed so that the focus error signal does not shift even if the temperature of the optical pickup changes.

[Summary of the invention]

In order to achieve the above object, the present invention uses a photodetector configured with a light-receiving area divided by one boundary line or a plurality of parallel boundary lines. The attached wiring board is attached to a base on which a laser light source or the like is attached so that the direction of the boundary line coincides with the direction of relative displacement caused by the difference in coefficient of thermal expansion between the two.

[Embodiments of the invention]

Embodiments of the present invention will be described in detail below with reference to the drawings. The principle of detecting a focus error signal will be explained with reference to FIGS. 8 to 10.

Fig. 8 is an explanatory diagram showing the optical system for detecting the focus error signal, Fig. 9 is an explanatory diagram showing the occurrence of focus error in the photodetector, and Fig. 10 is a waveform diagram showing the output waveform of the photodetector. It is.

Approximately half of the luminous flux of reflected light 1 from a disk (not shown) is blocked by a light blocking plate 2 . The remaining approximately half of the light beam is focused by the convex lens 3.

A photodetector 5 is arranged at the focal point 4 of the reflected light 1,
The photodetector 5 is composed of two light receiving areas 5b and 5c divided into two by a boundary line 5a. When the disk is positioned at the focal point of an objective lens (not shown), the reflected light focuses 4 on the boundary line 5a of the detector 5, as shown in FIG. 9(b).

When the disk moves away from the focal point of the objective lens, the reflected light 1 from the disk becomes a focused beam, the focal point 4 is located closer to the convex lens 6 than the detector 5, and the reflected light 1 becomes the 9th focused beam.
As shown in Figure (a), the light receiving area 5b is irradiated. On the other hand, when the disk approaches the focus position of the objective lens, the reflected light 1 becomes diverging light, and the reflected light 1 is irradiated onto the light receiving area 5c as shown in FIG. 9(e). Here, as shown in FIG. 8, a focus error signal 6 is obtained from the difference between the output signals of the light receiving areas 5b and 5c.

FIG. 10 is a graph of the focus error signal 6. The horizontal axis is the relative distance between the objective lens and the disk, and the vertical axis is the pressure of the focus error signal. Here, (a) to ( in Fig. 10)
c) correspond to (a) to (e) in FIG. 9, respectively.

3. In the above configuration, if the photodetector 5 moves in a direction perpendicular to its boundary line 5a, a focus error signal l will be distorted as shown by the dotted line in FIG. 10, making it difficult to correctly focus the laser beam on the disk. It becomes impossible to shine. On the other hand, when the photodetector 5 moves in a direction parallel to the boundary line 4, no shift occurs in the focus error signal 6 unless the reflected light on the photodetector 5 protrudes.

Next, a method for fixing the photodetector 5 to the base will be explained.

FIG. 1 is a perspective view showing a first embodiment of the present invention. The light shielding plate 2 and the convex lens 3 are fixed to a base 7 of an optical pickup. On the other hand, the photodetector 5 is attached to a wiring board 8, and the wiring board 8 is fitted with screws 9l through holes 8a and 8b provided on a straight line that is substantially the same as the boundary line 5a of the photodetector 5.

It is fixed to the base 7 by 9b.

Here, the material of the base 7 is general steel aluminum or an alloy mainly made of aluminum, while the material of the wiring board 8 is mainly made of phenol resin or epoxy resin. The thermal expansion coefficient of the wiring board 8 is generally several times larger than that of the base 7.4.

As a result, when the temperature of the optical pickup changes, the base 7
Due to the difference in thermal expansion coefficient between the base 7# and the wiring board 8, the position of the photodetector 5 in opposition to the base 7# is shifted in the direction of the straight line connecting the screws 9a9b. However, in the configuration shown in FIG. Since the direction of the boundary line 5a of the detector 5 and the direction of shift of the photodetector match, no shift occurs in the focus error signal 6.

FIGS. 2 and 3 show a second embodiment of the present invention. The configurations of optical components such as a light shielding plate and a convex lens shown in FIG. 1 are omitted because they are not related to the essence of the present invention. The photodetector 10 is divided into four parts by boundary lines 10a and 10b perpendicular to each other.
three light receiving areas 10c, 10d, 10e,
10f, the sum of 10c and 10d and 1
A focus error signal 6 is obtained from the difference between the sum of 08 and 1Of. In this case, the boundary line related to the detection of the focus error signal is 1
0a, and the wiring 1i28 to which the photodetector 10 is attached may be fixed to the base using the holes 8a and 8b that are substantially on the same straight line as the boundary line 10a.

4 and 5 show a sixth embodiment of the present invention. Photodetector 11ij: Consists of light-receiving areas 11c, 11d, and lie divided by boundaries 11a and 11b, and obtains a focus error signal 6 from the difference between the sum of 11c and 11e and 11d. In this case, the photodetector 11
The wiring board 8 to which the wiring board 8 is attached may be fixed to the base using holes 8a and 8b on straight lines that are substantially parallel to the boundaries 11a and 11b and passing approximately midway between them.

6 and 7 show a fourth embodiment of the present invention. The photodetector 12 is divided by boundary lines 12a and 12'b.

The light receiving areas 12c, 12d, 12e
, 12f, and the focus error signal 6 is determined from the difference between the sum of 12c and 12f and the sum of 12d and 12e.
I am getting . In this case, the wiring board 8 on which the photodetector 12 is attached is approximately parallel to the boundary lines 12a, 12b, and 12a, 1
It may be fixed to the base using holes 8a and 8b on a straight line passing approximately in the middle of 2b.

In the above configuration, the photodetector is attached to the wiring board and the wiring board is fixed to the base, but the photodetector 7 and the wiring board are integrated and the photodetector is fixed to the base. You can. Further, in this embodiment, the wiring board is fixed to the base with screws, but the fixing method is not limited to screws, and known methods such as adhesives may be used.

〔Effect of the invention〕

As explained above, in the past, no consideration was given to the method of fixing the photodetector, but according to the present invention, the photodetector is fixed to the chassis on a straight line that is approximately the same as the boundary line of the photodetector. By doing so, the focus error signal will not shift even if the temperature changes.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing a first embodiment of the present invention, FIG. 2 is an explanatory diagram showing another photodetector to which the present invention is applied, and FIG. 5 is a summary of the second embodiment of the present invention. FIG. 4 is an explanatory diagram showing still another example of the photodetector. FIG. 5 is an explanatory diagram showing the main part of the third embodiment of the present invention. FIG. 6 is an explanatory diagram showing the main part of the third embodiment of the present invention. FIG. 7 is an explanatory diagram showing the main part of the fourth embodiment of the present invention. FIG. 8 is an explanatory diagram showing an optical system for detecting a focus error signal. The figure is an explanatory diagram showing the occurrence of focus error in the photodetector, and FIG. 10 is a waveform diagram showing the output waveform of the photodetector. Explanation of symbols 5, 10.11.12...Photodetector 7...Chassis 8...Wiring board

Claims (1)

[Claims] 1) A base equipped with an optical system that focuses laser light onto a disk and receives reflected light from the disk is divided by one boundary line or multiple approximately parallel boundary lines. A photodetector consisting of a plurality of light-receiving areas is attached, and the reflected light received through the optical system is guided to the light-receiving area, and a focus error signal of the laser beam with respect to the disk is determined from the output of the photodetector at that time. In the focus error signal detection device, the photodetector is mounted on a base such that the direction of relative displacement caused by the difference in coefficient of thermal expansion between the base and the photodetector coincides with the direction of the boundary line. A focus error signal detection device, characterized in that it is attached to.