JPS6012693B2 - Automatic focusing device in optical information reproducing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an automatic focusing device for an information recording lens in an apparatus for reproducing information on an information recording medium by means of a laser KOTO, and particularly relates to an automatic focusing device for an information detection lens on a recording medium of an information detection laser KOTO. Detects the focal position shift at , as a positional change along the detector of the spot due to the reflected laser beam reflected by the recording medium, and focuses the information lens on the recording medium accordingly. An object of the present invention is to provide an automatic focusing device that has a simple configuration and can accurately perform focusing operations by automatically performing the following steps.

Conventionally, there are roughly two types of devices for automatically focusing an information detection beam onto a recording medium in an optical information reproducing device.

■ In addition to the information detection beam, a focus detection beam is used,
The optical axis of this beam is caused to shift according to the vertical movement of the recording medium, the optical axis shift of this beam (change in the position of the beam spot) is detected, and the detected signal automatically determines the convergence point of the information detection beam. A device that matches the information on the disc.

0 ■ Using the information detection beam itself, the reflected beam from the information recording medium is passed through an optical element having a unidirectional lens action, such as a cylindrical lens, and the defocus is detected as a change in the shape of the reflected beam spot. Accordingly, the device adjusts the convergence point of the output beam to the disk information surface.

In the device (ii), the defocus is detected as a change in the position of the beam spot, so although it has the advantage of accurate detection, it has the following drawbacks.

Kawa: The optical system is complicated because it requires two optical systems.

(ii) Providing two light sources increases the cost of the device.

(iii) In order to obtain two beams from one light source, a high-power laser light source is required.

Considering the tracking correction and time axis error correction of ○, the focus detection beam needs to pass through a location unrelated to these correction elements, making the optical system extremely complicated.

In addition, in the above device (2), since a dedicated beam is not used for detecting focal position deviation, there are no inconveniences associated with using a beam for detecting focal position deviation, but
Since the photodetector is affected by the distribution shape of the reflected laser beam or the unbalance of the light distribution intensity, it has the disadvantage that correct automatic focusing cannot always be achieved.

The present invention provides an automatic focusing device that eliminates the drawbacks of the conventional devices and provides only the advantages thereof, and embodiments thereof will be described below with reference to the drawings.

FIG. 1 is a diagram showing an optical system of a first embodiment of an automatic focusing device in an optical information reproducing apparatus according to the present invention, and FIG. 2 is a diagram showing its control system.

Information detection laser light 2 emitted from a laser light source (semiconductor laser or He-Ne laser) 1 passes through a convex lens 3 and is magnified, passes through a semi-transparent mirror (light splitting element) 4 and is guided to an information detection lens 5. He uses the lens 5 to record the video disc 6.
is converged on the information surface. The reflected laser beam 7 that has read the information on the information surface is reflected by the semi-transparent mirror 4 and guided to a two-split photodetector 8 having two detection elements 8a and 8b arranged closely together. When the information surface of the video disc 6 is at the normal position A, it becomes the conjugate point A of the reflective laser beam 7.

Reference numeral 9 denotes a lens which is an important part of the present invention, and serves to convert changes in the conjugate point on the optical axis into optical axis displacements of the reflected laser beam, as will be described later.

This lens 9 is a normal convex lens, and is installed parallel to the optical axis 7a at a position where the lens axis 9a is deviated by a distance x from the optical axis 7a of the laser beam east 7 reflected from the semi-transparent mirror 4. . The reflected laser light beam 7 that has passed through the conjugate point A passes through the convex lens 9 for converting the optical axis 3, and its optical axis is shifted to form a light beam with the optical axis set to 10a, which is located at approximately the center of the photodetector 8. A
2 as a circular spot 11a (see FIG. 2).

In this section, displacement at position A2 when the video disc 6 rotating at high speed is accompanied by four-sided wobbling will be explained.

Due to rotational surface runout, the information surface of the video disc 6 is at position B.
, the conjugate point of the reflected laser light east from the displaced information surface is conjugate point A on the optical axis 7a, and position B shifted from the optical axis 7a.
, becomes.

The light beam that has passed through the conjugate point B passes through the convex lens 9, and its optical axis is shifted to become light beam 10b (different from the optical axis 10a), and is converged as a circular spot 11b at position &. . Also, if the disk information surface is reversely displaced to position C, the conjugate point of the reflected laser light east from the displaced information surface is conjugate point A on the optical axis 7a, which is shifted to the opposite side from the above conjugate point B. The position becomes C.

The light beam that has passed through the conjugate point C passes through the convex lens 9, and its optical axis is shifted to 10c (different from the optical axes 10a and 10c), and a circular spot 11 is formed at position C2.
It is converged as c. That is, the conjugate point is displaced on the reflection optical axis according to the surface wobbling of the video disc 6, and the reflection optical axis is shifted by the convex lens 9 according to the position of the conjugate point, so that a circular spot is formed on the photodetector 8. Change position without changing.

The two-split photodetector 8 detects a circular spot 11 at position A2.
They are positioned so that the output current values from both sensing elements 8a and 8b are equal when light a is received.

When the position of the circular spot 11a is displaced as described above due to the surface runout of the video disc 6, both detection elements 8a and 8b
A difference occurs in the output current values of the two, and the differential amplifier 12 outputs a control current according to the difference. After this control current is amplified by the drive amplifier 13, it is supplied to the mooring lens driving section 14, which displaces the morotori lens 5 in the lens axis direction and automatically focuses it on the upper side of the information surface of the video disc 6. . Further, the output currents from the pair of photodetecting elements 8a and 8b are amplified by a sum amplifier 15, and the sum thereof is used as an emotion reading signal. Next, a second embodiment of the present invention will be described with reference to FIG. 3. In FIG. 3, components that are substantially the same as those shown in FIG. do.

In this embodiment, a convex lens 16 is provided at a position in front of the conjugate point in the east path of the light reflected by the semi-transparent mirror 44, with its lens axis aligned with the optical axis 7a. This convex lens 16
has the role of reducing the amount of displacement of the conjugate point in response to surface runout of the video disc. The reflected laser beam from the information surface (position A) of the video disc is reflected by the semi-transparent mirror 4 and then converged through the convex lens 16, and the conjugate point is at the position indicated by A'.

Further, when the information plane is displaced to positions B and C in FIG. 1, the conjugate points are the positions indicated by B' and O, respectively. That is, by providing the convex lens 16, the amount of change in the position of the conjugate point with respect to disk surface runout is reduced. In this case, when a lens with f: 7.15 is used as the reading lens 5, the disc 6 moves 50 wm above and below the reference position in Z.
If it changes, the conjugate point is 8.8 ribs from the reference position,
and 11.1 rib displacement.

When a lens with f=15 is used as the convex lens 16,
The displacement values of the conjugate points are reduced to 1.2 Yanagi and 0.98 Yanagi, respectively. In addition, the optical axis of the light from the conjugate point is converted through the optical axis conversion convex lens 9 in the same way as in the previous case, and it is converged on the two-split photodetector 8, and a circular beam spot is formed according to the change in the conjugate point. The positions on the photodetector 8 change to A2, B'2, and 〇2. child)
If the f value of the reading lens 5 is 7.15 and the distance L from the point light source P to the main surface of the reading lens is 100 degrees, then the distance from the Kendori lens 5 to the information surface of the video disc 6 is L2.
There are about 10 ribs.

Using f=15 lenses as convex lenses 16 and 9,
When the deviation distance from the reflective optical axis of lens 9 is x3 skin,
Assuming that the information reflecting surface of the video disc is displaced up and down by 50 mm, the circular beam spot will be divided into two photodetectors 8
At the top, it moves about one willow left and right. That is, the amount of displacement of the circular beam spot is about 2M sound of the disc surface runout, and the disc surface runout can be detected with sufficiently high sensitivity. In the above embodiment, by newly adding the convex lens 16, the length of the optical path can be shortened, and the rate of change in the spot diameter when the circular beam spot is displaced on the photodetector 8 can be reduced.

Next, a third embodiment of the device of the present invention will be described with reference to FIG.

In this embodiment, a concave lens is used as the optical axis conversion lens, and components that are substantially the same as those shown in the first diagram in the figure are given the same reference numerals, and their explanations will be omitted. 17
is a concave lens for optical axis conversion, and its lens axis 17a is deviated by a distance x from the optical axis 7a of the reflected laser light east 7 from the semi-transparent mirror 4, parallel to the optical axis 7a, and in front of the conjugate point. It is installed on the side.

When the concave lens 17 is not provided, when the information recording surface of the video disc 6 changes to positions A, B, and C,
Accordingly, the conjugate point of the reflected light east shifts to A, B, C, and so on.

In this case, when the concave lens 17 is provided, the optical axis of the reflected light from the semi-transparent mirror 4 is deflected by the concave lens 17, and each conjugate point A'', B'', C'', is displaced along the two-split photodetector 8. That is, the circular beam spot moves on the light-receiving surface of the photodetector 8 according to the surface deflection of the video disc 6. A signal current corresponding to the surface wobbling of the video disk 6 is output, and the electric circuit system shown in FIG. 2 displaces the lens 5 to focus it on the information surface.

This embodiment is configured with a shorter optical path than the first embodiment.

In each of the above embodiments, the lenses 9 and 17 are provided with their axes parallel to the reflective optical axis 7a, but the axis is not limited to this, and the lens axes may be parallel to the reflective optical axis 7a as necessary.
It can also be installed at an appropriate inclination with respect to a.

As described above, according to the automatic focusing device in the optical information reproducing apparatus according to the present invention, the reflected laser beam from the information recording medium of the information detection laser beam is aligned with the center of the lens from the optical axis of the reflected laser beam. The focal position shift on the information recording medium is converted into an optical axis shift through a convex or concave lens provided in a deflected manner, this optical axis shift is detected by a photodetector, and the information reading lens is activated according to the output signal from this. Since the focus is moved to align with the recording medium, surface wobbling of the recording medium can be converted into a change in the position of the beam spot on the photodetector without using a dedicated beam for focus detection. Therefore, it has excellent features such as being able to simplify the configuration, be manufactured at low cost, and perform automatic focusing with high accuracy.

0 Brief Description of the Drawings FIG. 1 is a diagram showing an optical system of a first embodiment of an automatic focusing device in an optical information reproducing device according to the present invention, and FIG. 2 is a diagram that cooperates with the device shown in FIG. 1. 3 and 4 are diagrams showing the optical systems of second and third embodiments of the automatic focusing device according to the present invention, respectively.

1... Laser light source, 2... Laser light east for information detection, 3... Convex lens, 4...
Semi-transparent mirror, 5...Information discussion lens, 6...
...Video disc, 7...Reflection laser light east, 7a
...Optical axis, 8...Two-split photodetector, 8
a, 8b...detection element, 9...convex lens for optical axis conversion, 9a...lens axis line, 10a,
10b, loc...deflection optical axis, 11a, 11b, 1
1c...Circular spot, 12...Differential amplifier,
13...Drive amplifier, 14...Reading lens drive unit, 16...Convex lens, 17...Concave lens for optical axis conversion, 17a...Lens axis line, A,,B ,C
,,A',,B'',,〇,,A'',,B'',,〇',
...Conjugate point, A2, &, C2, A'2, B'2, 〇2・
...Convergence point.

Figure 1 Figure 2 Figure 3 Figure 4

Claims (1)

[Claims] 1. In a device that reproduces an information recording medium by irradiating an information detection laser beam from a laser light source onto the information recording medium through an information reading lens, the reflected laser beam from the information recording medium of the information detection laser beam is transmitted through the lens. The reflected laser beam passes through a convex or concave lens whose center is deviated from the optical axis center of the reflected laser beam, converts the focal position deviation on the information recording medium into an optical axis deviation of the reflected laser beam, and The optical axis shift of the reflected laser beam is detected by a photodetector, and the information reading lens is moved in the lens axis direction according to the output from the photodetector, so that the focal point of the information reading lens is focused on the information recording medium. 1. An automatic focusing device in an optical information reproducing device, characterized in that the automatic focusing device is configured to automatically focus on the object.