JPS59160830A - Focus controller - Google Patents

Abstract

PURPOSE:To prevent the adverse influence of a flaw or stain on a disk surface by obtaining a focus correcting signal based upon the deviation between outputs of two photodetection parts which are provided to detect independently return light branched to two systems and are opposite in polarity to each other. CONSTITUTION:Photodetectors 5 and 5 provided as the photodetection parts in order to detect independently the return light 2 branched to the optical path systems 3 and 4 are opposite in polarity to each other. An arithmetic part 7 inputs signals from the photodetection parts 5 and 6 and outputs their deviation as the focus correcting signal. The detectors 5 and 6 have photodetecting elements A1, B1, C1, and D1, and A2, B2, C2, and D2. Incident light beams to the elements A1 and A2, C1 and C2, etc., are equal in an in-focus state with regard to a light-quantity distribution depending upon pits, stains, etc., on the disk surface, but when an out-of-focus state is entered, the detectors 5 and 6 output (A1+C1)-(B1+D1) and (B2+D2)-(A2+C2) respectively and both of them are added together to obtain {(A1-A2)+(C1-C2)}-{(B1-B2)+ (D1-D2)}, cancel ing the disorder of the light quantity distribution. Thus, accurate focus control is performed.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a focus control device that is most suitable as a pickup for compact disc players, video disc players, and the like.

Conventionally, this focus control device for the source pickup has been
The configuration shown in the figure is as shown in the figure, from the laser light source 21, the source passes through a collimation/reflector 22, a polarizing beam slitter 23, two λ/4 plates, four metal sheets, and an object lens 25, and then to the bit 27 in the disk 26. The condensed and diffused light is again divided into υ components by the polarizing beam sinter 23 through the objective lens 25, the λ/4 plate 2, and the metal plate 4, and is guided to the focus error detection section 281F3. A 4-split type or 2-split type photodetector 29 (photoelectric conversion element) is provided in the focus error detection section 28.
The reflected light from 7 is designed to form an image on this photodetector 29, and the image formation state is that of the light source 21 and bit 2.
It varies greatly depending on the distance from 7.

The photodetector 29 outputs a correction signal according to its imaging state, and the correction signal is used to perform surge control so that the light from the p light source 21 is accurately focused on the bit 27. There are various types of the focus error detection section 28, but in the one shown in FIG.
Convex lens 30, cylindrical lens (cylindrical lens) 3
The reflected light that has passed through the photodetector 29 is imaged on a four-part photodetector 29, and the light receiving elements A, B O
The above surge control is performed by calculating the output from D as (A10)-(B+D). Further, in the one shown in FIG. 3, a knife 32 is arranged at the focal point of the convex lens, and the light diffused from the tip of the knife 32 is imaged on the middle part of the two-split photodetector 29, and the light receiving element EF The above servo operation is performed by calculating the output of E-F.

Incidentally, in FIG. 4, the image is formed through a critical angle prism 33.

In this way, the conventional apparatus is configured so that so-called focusing is automatically performed by detecting the light amount distribution of the small amount of returned light introduced through a single optical path. However, in the conventional single-optical-path type device described above, if there are scratches or dirt on the disk surface, the light intensity distribution of the return light reflected from the bit changes greatly, and this fluctuation becomes noise. Focus control circuit Δ? There was a risk of making the loop unstable.

The purpose of this invention is to eliminate the drawbacks of the conventional ones mentioned above,
To provide a focus control device that is not adversely affected by scratches or dirt on a disk surface.

Hereinafter, the configuration of the present invention will be explained as shown in FIGS. 5 to 7 which are examples thereof.
This will be explained based on the diagram.

In the figure, 1 is an optical splitter for branching the returned light 2 into two systems (3, 4), and in the illustrated example, a half mirror is shown, and in this case, the transmitted light at the half mirror 1 and It is assumed that the amount of reflected light is equal. Reference numerals 5 and 6 designate photodetectors as light receiving sections provided to independently detect the inverse beams 2 branched into the respective optical path systems 3 and 4, so that the polarities are opposite to each other. Reference numeral 7 denotes an arithmetic unit which receives signals from the respective light receiving units 5 and 6 and outputs the deviation thereof as a quiet point correction signal.

There may be various forms of the optical path systems 3, 4 and the light receiving sections 5, 6, but in the embodiment shown in FIG. A four-segment type photodetector is used as the photodetectors 5 and 6, each having a light receiving element A1 . B1. C1, Dl
・A2. It has B2+ Ct+ Dt e. When the focus is right, the incident light on A1 and A, , cl, 02, etc. will be the same due to the light intensity distribution due to pits and dirt on the disk surface, but if the focus is shifted (focus error), the incident light will be the same from the photodetector 5. is (A100t) (
B1 + Dt), but from the photodetector 6 (B2 +
B2 ) - (A4 + 02) is output, and when both are added, (A! + 01) ('lh + Dt
) +(B2+D2)(4+0t)=((AIA2)
+(OIOx) ) ((BIBz)+(Dt D
z) ), and the disturbance in the light amount distribution is canceled out.

2. shown in FIGS. 6 and 7, respectively. In the third embodiment, two-split type photodetectors 5 and 6 are used, and the optical path system 3°4 includes a convex lens 8 and a knife lens 10 for the former, and a critical angle prism 11 for the latter.
is used. The photodetector 5 includes a light receiving element A.
3°B, but the photodetector 6 has a light receiving element A4.
B.

are provided, and when the focus is correct, the output is the same, but when the focus is off, the outputs of each photodetector are A3-B3 and B4-A4, and when they are added, ( As −A4 )(Bs B4
), and the disturbance in the light amount distribution is canceled out.

Incidentally, in the first and second embodiments, if the convex lens is placed in front of the half mirror 2, the two convex lenses 8 become unnecessary. Also, the photodetector is not necessarily divided into two parts or four parts.
It is not limited to the divided type, and may be divided into many parts. moreover,
Of course, the scope rhythm method or the like can be used to detect focus errors.

In addition, when using a half mirror, if its transmission speed and reflectance are unequal, the gain balance of the signals obtained from the two photodetectors can be calculated by 77III to equivalently make them both equal. can do.

Furthermore, the entire optical system such as a convex lens in one optical path may be omitted and a metal photodetector divided into four or two parts may be used.

According to the focus control device according to the present invention, an optical splitter for branching the return source into two systems and an optical splitter for independently detecting the branched return nu are provided, and the polarities are opposite to each other. It is equipped with two light-receiving sections and a calculation section that detects the output from each light-receiving section and outputs the deviation as an all-focus correction signal, so it can be used in digital disc players, etc. Even if there are scratches or dirt on the disk surface, or foreign objects or scratches between the objective lens and the disk, the negative optical effects caused by these can be offset, allowing accurate focus control. . Therefore, there is no need to particularly increase the optical detection sensitivity, and the assembly precision can be low, making design and manufacture easy. Furthermore, it has excellent features such as no deterioration in accuracy due to temperature changes.

[Brief explanation of the drawing]

1 to 4 are side views showing a conventional focus control device;
FIGS. 5 to 7 are side views showing embodiments of the focus control device according to our invention. 1: Half mirror 15, which is an optical splitter; 6: Light receiving section;
7: Arithmetic unit patent applicant Trio Co., Ltd. Figure 4 Figure 5 Figure 6

Claims (1)

[Claims] The photoelectric conversion is performed by introducing the returned p light from a reflector such as a disk plate into a photoelectric conversion element having a light-receiving surface divided into a plurality of parts, and changing when the distance between the reflector and the light source becomes an off-focal distance. In a focus control device that detects all defocus by detecting the distribution of light amount to the element,
An optical splitter for splitting light into two systems, two light receiving sections provided to independently detect the branched returned light and having mutually opposite polarities, and the respective light receiving sections. and a calculation section configured to detect all outputs from the output and output the deviation as a focus correction signal.