JPS6010423A - Detector for error of focus position - Google Patents

Abstract

PURPOSE:To prevent erroneous detection in the case where a face to be detected is approximated to a condenser lens, by arranging an aperture in the optical path of a reflected wave from the face to be detected. CONSTITUTION:In the in-focus state shown in a figure (a), outputs Va and Vb of two light receiving faces 19a and 19b of a photodetector 19 are equal to each other, and an error detection signal Ve is zero. If a face 15 to be detected is deflected to a position more distant than the focus position, the signal Ve is positive. If the face 15 to be detected is deflected to a position nearer than the focus position, the signal Ve is negative. If the face 15 to be detected approaches a condenser lens 14 furthermore, the beam diameter of reflected light 16 should be larger but is controlled by an aperture 18. In this case, the signal Ve has not the polarity inverted if the size of the aperture 18 is so determined that this beam diameter does not exceed the beam diameter for the in-focus state. Consequently, the state where the face 15 to be detected is approximated to the condenser lens is not detected erroneously as the state where the face to be detected is more distant from the condenser lens.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to an apparatus that irradiates a detection surface with an original beam and reads information on the photodetection surface. 10 for the focal position error detection setup for detecting.

[Technical background of the invention and its problems]

Information such as audio, video, and various data signals is recorded on a recording medium (optical disk) by changing its optical form, such as the presence or absence of bits, and is read by irradiating it with a light beam as a minute spot. In so-called optical information recording and reproducing devices, one of the conditions for accurately reading information on an optical disk is to adjust the focus position of the condenser lens so that the light beam is accurately focused on the optical surface. It is necessary to perform automatic focus position control (focusing sensor).

In such a 7-ocusing laser, it is necessary to detect the error in the focal position of the condensing lens with respect to the optical disk surface, and one of the known error detection methods is the one shown in Figure 1. . This guides the reflected light 1 from the optical disk surface to a photodetector 2 whose light-receiving surface is concentrically divided into two parts, and detects changes in the beam size (diameter) of the reflected light I due to changes in the focal position of the condensing lens. Each light receiving surface 2a
, 2b are processed by the subtracter 3 to obtain the error detection signal ve.

That is, in a so-called focused state in which the focal position of the condensing lens coincides with the optical disk surface, the reflected light 1 is equally incident on the two light-receiving surfaces 2a and 2b, as shown in FIG. 2(a). If we set Va=v1 and ve=0, when the optical disk surface deviates to a further distance, the reflected light incident on the photodetector 2 will be reflected as shown in FIG. Since the beam diameter of 1 increases, va<v, and V becomes positive. The relationship between the focal position error Δ2 and the error detection signal V@ at this time is shown by the solid line in area A in FIG.

On the other hand, as shown in Fig. 2(c), when the optical disk surface deviates inward from the focal position of the condensing lens, the beam diameter of the reflected light becomes smaller, so that V, ) V, , and ShiV
8 is negative and exhibits the characteristics shown by the solid line in area B in FIG. Therefore, focusing servo can be performed by moving the condensing lens on the optical axis so that it approaches the optical disk surface when V is positive, and away from it when V is negative.

It begins to spread again, ■8<v, and V. is reversed from negative to positive, resulting in the characteristics shown in region C in FIG. Therefore, the error detection signal (18) has the same polarity as when the optical disk surface moves away from the focal position, making it impossible to control the focal position.

Particularly in optical information recording and reproducing devices, disturbances such as vibrations often cause the device to deviate from the area C in Figure 3.
In that case, the servo will run out of control increasing the focal position error, and in the worst case, an accident will occur in which the optical head collides with the optical disk.

[Purpose of the invention]

An object of the present invention is to provide a focus error detection device that can prevent erroneous detection when a detection surface is close to a condenser lens.

[Summary of the invention]

In this invention, by arranging an aperture that limits the beam size of the reflected light in the optical path of the reflected wave from the surface to be detected from the condenser lens to the photodetector, the surface to be detected is This is to prevent the beam size of the reflected light incident on the photodetector from expanding when the photodetector is close to the photodetector.

〔Effect of the invention〕

According to this invention, since there is no polarity reversal of the error signal when the surface to be detected is close to the condensing lens, this state is erroneously detected as a state in which the surface to be detected has moved away from the condensing lens. Things will go away.

Therefore, it is possible to prevent the focusing servo from running out of control and to perform stable focal position control.

[Embodiment of the Invention] FIG. 4 shows the structure of a hot spot position error detection device according to an embodiment of the present invention.

In the figure, 11 is a light source, for example a laser diode, and a light beam 12 emitted from this passes through a beam splitter 13, is guided to a condensing lens I4, and is irradiated onto a detection surface 15 as a minute spot. Ru. On the other hand, the light reflected by the detection surface 15 returns to the beam splitter 13 via the condensing lens 14, and after being reflected by the beam splitter 13, an elliptical aperture is formed on the light-transmitting plate 17. −
The light passes through the channel 18 and is guided to a photodetector 19. Photodetector 1
For example, 9 has two concentric light-receiving surfaces as shown in Figure 1.
It is divided.

Here, the photodetector 19 is arranged behind the focal point P of the reflected light 16 by the condenser lens 14 in a so-called focused state, in which the focal position of the condenser lens 14 coincides with the detection surface 15, and In this example, the anomaly 18 is the above-mentioned imaging point P.
The photodetector 19 is placed in a position substantially symmetrical to the photodetector 19 in front of the photodetector 19 (see FIG. 5(a)). Each light receiving surface 19 of the photodetector 19
The outputs va and v for each of a and 19b are processed by a subtracter 20 and become an error detection signal ■e.

In this configuration, in the focused state shown in FIG. 5(a), the reflected light 16 is transmitted to the photodetector 19. Two light-receiving surfaces 1
9a and 19b equally, Va=vbl v,,=
o and l Ruyo'511C light receiving surface 19 a.

19b is divided, when the detection surface 15 is deviated far from the focal point of the condenser lens 14, the reflected light 1 that enters the photodetector 19 as shown in FIG.
Beam diameter force of 6; to widen the force, va<v, and v8
is positive and indicates the characteristics of area A in FIG.

Furthermore, when the detection surface 15 is shifted inward from the focal position of the condensing lens 14, the reflected light 16 as shown in FIG.
Since the beam diameter of becomes smaller, va>vb and V
is negative, indicating the characteristics of region B in FIG. The process up to this point is the same as the conventional case (FIG. 2).

On the other hand, as the detection surface 15 approaches the condenser lens 14, the beam diameter of the anti-body f16 tends to widen as shown in FIG.

In this case, if the size of the annocuture 18 is determined so that the beam diameter of the reflected light 16 incident on the photodetector 19 does not exceed the beam diameter at the time of focusing shown in FIG. 5 (-), the focal position error ΔZ The relationship between the error detection signal V and the error detection signal V is as shown by the broken line in FIG. That is, v8 does not undergo polarity reversal in the C region as in the conventional case (solid line) and is kept at 0. Therefore, by performing focusing search using this error detection signal Ve, runaway in the C region can be prevented without impairing the control characteristics near the in-focus state, and stable control can be achieved.

The present invention is not limited to the above-mentioned embodiment. For example, the position of the annular 9-cha is from the condensing lens 14 to the photodetector 1.
It can be anywhere in the optical path of the reflected light up to 9, and by using an a-piece of a size corresponding to that position, the 6th
As shown in the figure, although the ΔZ -V characteristic changes slightly, it does not change near the in-focus state, and a characteristic with no polarity reversal in the C region is obtained.In addition, the shape of the light-receiving surface of the photodetector is It may be divided into strips as shown in FIG. 7. In this example, it is divided into three parts,
A subtracter 20 performs arithmetic processing on the output of the central portion 21b and the outputs of the side portions 21* and 21c. Further, when the light-receiving surface is divided into strips in this manner, the aperture may have an elongated shape parallel to the dividing line of the light-receiving surface, as shown in FIG.

In Fig. 8 (,), two light-transmitting plates 22 a r 22 b
are arranged in parallel to form an aperture 23 consisting of a parallel gap, and in FIG. 8(b), an elongated aperture 25 is formed in one light-transmitting plate 24. The method of dividing the light-receiving surface shown in FIG. 7 is disclosed in Japanese Patent Application Laid-open No. 135326/1983, and by combining this method with the anno-cha as shown in FIG. 8, optical information can be divided. When the present invention is applied to a recording/reproducing device, even if the light beam moves in a direction perpendicular to the optical axis for tracking, by matching the moving direction with the direction of the dividing line of the light-receiving surface, the light beam can be Stable focal position error detection can be performed without being affected by beam movement.

Further, the aperture may be integrated with the photodetector as shown in FIG. In other words, a light shielding plate 35 having a hole 34 on a light receiving window 33 attached to an opening of a housing 32 housing a light receiving element 31 of a photodetector.
Paste or deposit by vapor deposition, etc. This eliminates the need to adjust the installation position of the aperture and simplifies the overall structure of the device.

In addition, the present invention can be modified as appropriate, such as the arrangement and configuration of various optical system elements shown in FIG. It can be applied to various optical devices.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the principle of the focal position error detection method, Figures 2 (,) to (d) are diagrams for explaining the focal position error detection operation in a conventional device, and Figure 3 is a diagram showing the conventional device and the present invention. A diagram showing a comparison of the focal position error detection characteristics of the apparatus, FIG. 4 is a configuration diagram of an embodiment of the present invention, and FIGS. 5(a) to (d) are diagrams for explaining the operation of the embodiment. , FIG. 6 is a diagram showing changes in focal position error detection characteristics when the installation position and size of the aperture are variously changed, FIG. 7 is a diagram showing other examples of the shape of the light-receiving surface of the photodetector, and FIG. Figures (a) and (b) are the seventh
FIG. 9 is a cross-sectional view of a main part of another embodiment of the present invention. DESCRIPTION OF SYMBOLS 11... Light source, 12... Light beam, 13... Beam splitter, 14... Condenser lens, 15... Detection surface, 16-... Reflected light, 17I22a, 22b. 24.35...Light shielding plate, 18.23, 25°34
...Aperture, 19...Photodetector, 20...Subtractor. Applicant's Representative Patent Attorney Takehiko Suzue Figure 1 Figure 3 Figure 4

Claims (5)

[Claims] (1) A light beam is irradiated onto the surface to be detected through a condensing lens, and the reflected light is transmitted through the condensing lens. The light reflected by the condensing lens is guided to a photodetector which is placed behind the imaging point and whose light-receiving surface is divided into a plurality of parts, and the output of each light-receiving surface of this photodetector is processed by arithmetic processing. A device for detecting an error in the focal position with respect to a detection surface, characterized in that an aperture that limits the beam size of the reflected light is arranged in the optical path of the reflected light from the condensing lens to the detector. Focus position 1δ error detection device. (2) The light receiving surface of the photodetector is divided into concentric circles, and the aperture is circular.
The focus position error detection device described in . (3) The light-receiving surface of the photodetector is divided into strips, and the aperture has an elongated shape parallel to the dividing line of the light-receiving surface.
The focus position error detection device described in . (4) According to any one of claims 1 to 3, the aperture is arranged at a position substantially symmetrical to the photodetector in front of the imaging point. Focus position error detection equipment. (5) The focus position error detection device according to any one of claims 1 to 3, wherein the aperture is formed in a light receiving window attached to the front surface of the light receiving surface of the photodetector. .