JPH0230096B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an information detection head in a device for engineering reading of information recorded in track form on a recording medium.

A typical example of a recording medium on which information is recorded in the form of a track is a disk-shaped recording medium, a so-called video disk. Information tracks are generally arranged concentrically or in a spiral on a disc-shaped recording medium. A device for reading such information in an engineering manner includes an optical system that projects a light spot onto a recording medium, and a position detection system that detects the relative positional relationship between the information track on the recording medium and the light spot. and means are known.

FIG. 1 shows an example of the above-mentioned known information reading device. In the figure, reference numeral 1 indicates a video disk as an information recording medium, and the video disk is rotated at a rotation speed of, for example, 1800 rpm through an axis 2.
Rotate around 2'. On the other hand, the light beam emitted from the laser light source 3 passes through an auxiliary lens 4, a reflecting mirror 5, and a projection lens 6, and is focused onto the video disk. Since the intensity of the light transmitted through or reflected by the video disc changes according to the information recorded on the video disc, the intensity of the light is detected by the photodetector 7. Accordingly, the information recorded on the video disc can be extracted as an electrical output signal of the photodetector. In such a case, in order to read the information correctly, the spot of light focused on the recording medium by the projection lens 6 must be correctly positioned on the information track to be read.

In order to perform the above-mentioned positioning, in the known reading device, the disk system (video disk 1) is connected to the light beam system (laser light source 3, auxiliary lens 4, reflector 5, and projection lens 6) for reading information tracks. Lateral direction to the direction (arrow A in Figure 1)
(see ) at a constant speed to roughly follow the information track. In addition to this, the deviation of the information track due to the shape error of the information track and the eccentricity of the video disk is
The position of the light spot is controlled by rotating the reflecting mirror 5 around an axis perpendicular to the plane of the paper. However, in this positioning method, the projection lens must simultaneously satisfy the following conditions.

(1) The projection lens must have enough performance to focus the laser beam onto a spot of a predetermined size without being affected by the tilt angle of the reflecting mirror.

(2) It is usually very difficult to keep the eccentricity of a video disk within 0.1 mm. For this purpose, the projection lens must be aberration-free over a range of at least 0.1 mm in the spot plane.

(3) Since the width of the information track on the disk surface is less than 1 μm, the numerical aperture of the projection lens is approximately 0.4.
It must be of a certain degree.

(4) It is necessary to control the vertical position of the projection lens in order to keep the spot focused on the disk surface. Therefore, the weight of the projection lens is 10g.
Must be less than or equal to

A lens with such high-grade performance inevitably requires a large number of constituent lenses. For this,
It is difficult to reduce the weight and furthermore it is difficult to reduce the manufacturing cost.

FIG. 2 conceptually shows an improved version of the known optical information reading device, in which 1 is a disk as a recording medium, which rotates around an axis 2-2'. The beam emitted from the laser light source 3 passes through an auxiliary lens 4, a reflector 5 and a detection head 6'.
The light is then focused onto the disk 1. Depending on the information recorded on the disk, the intensity of the light that passes through or reflects on the disk changes, so by detecting the change in the amount of light with the photodetector 7, the information recorded on the disk can be electrically converted. It can be extracted as a physical output signal. The projection lens is magnetically supported so as to be movable in a direction perpendicular to the information track.

If the light spot deviates from the center of the information track in a direction perpendicular to the information track, the intensity of the light transmitted through the disk 1 will be unbalanced on the left and right sides of the center of the information track. By detecting this unbalance with a known two-quadrant detector 8 connected to the photodetector 7, it is detected whether the light spot position has shifted to the left or right, and this detection signal is amplified. The output of this two-quadrant detector 8 is connected to an information detection head 6' to form a control system for controlling the position of the projection lens according to the detected deviation of the light spot position. In this control system, if the reduction magnification of the projection lens is M, the deviation of the light spot from the optical axis is M times the amount of movement of the lens, and therefore the amount of eccentricity of the information track.

For example, if the reduction magnification is 1/20 and the amount of eccentricity of the track is
If it is 0.1mm, the deviation of the optical spot from the optical axis is
It becomes 0.005mm. This means that the projection lens only needs to be aberration-free within a range of 0.005 mm.
Furthermore, when collimating a parallel beam of light, M=0, so the deviation from the optical axis is completely zero. In other words,
In this case, it is sufficient that the projection lens has no aberration only at one point on the optical axis.

In this way, according to the reading device shown in FIG. 2, the deviation of the light spot from the optical axis is reduced by the reduction magnification of the projection lens, and therefore, compared to the case of the reading device shown in FIG. becomes smaller. Also,
A projection lens that satisfies the above conditions has a numerical aperture of
Even if it is 0.4, it can be realized with a spherical system composed of at most three lenses. Furthermore, if an aspherical lens is used, it is theoretically possible to realize this with a single lens. For this reason, it is not only extremely easy to reduce the weight of the projection lens to 10g or less, but also the projection lens has a simple configuration, making it easy to assemble, and therefore reducing manufacturing costs. It is.

Here, a technique in which a projection lens is driven by a coil and a permanent magnet instead of rotationally driving a reflecting mirror is described in JP-A-48-101103. In this prior art, a coil is fixed to the projection lens via a relatively long rod-like member, and a single permanent magnet is placed opposite the coil. However, in such a configuration, the projection lens can be used with high precision.
It has the disadvantage that it cannot be driven with high efficiency. On the other hand, a technology to drive a coil by arranging two permanent magnets was published in 1973.
-Explained in Publication No. 89505. However, in this technology, tracking is performed by a combination of a projection lens and a rotationally driven mirror, which are unrelated to the tracking drive, as explained above with reference to FIG. It is for rotating around the center. Such a mirror-driven type has disadvantages such as requiring a high-grade lens for the above-mentioned purpose, and also requires a mirror with a rotation axis in addition to the projection lens, resulting in a large number of parts. be.

The object of the present invention is to provide an information detection head that eliminates the above-mentioned drawbacks.

The information detection head in the information reading device of the present invention irradiates a recording medium on which information is recorded in a track shape with convergent light from a lens and reads the information by moving the lens parallel to the surface of the recording medium and across the information track. In an information detection head of an information reading device configured to be driven in one direction, at least one coil having a substantially flat surface at a portion where a magnetic flux directed in one direction intersects with a part of the conductor array; and the lens. and a lens holder to which the coil is integrally fixed; and a connecting member that provides a restoring force to the lens holder when the lens holder moves and is connected between the lens holder and the base. and a first permanent magnet and a second permanent magnet that are fixed to the base and are arranged to cause the magnetic flux to intersect with the conductive wire array and are spaced apart from each other in a linear direction substantially parallel to the surface of the recording medium. and a permanent magnet, and the lens holder is arranged so as to be drivable between the first permanent magnet and the second permanent magnet.

FIG. 3 is a reference diagram for explaining the operating principle of driving the projection lens.

A projection lens 101 is attached to one end of a lens holder 102, and a spirally wound coil 103 is attached to the other end of this lens holder 102.
This coil 103 is arranged between the magnetic poles of one permanent magnet 104 and is configured to be able to supply current through a lead wire 106. Note that the entire lens holder is attached to a base 108 via an elastic support member 107. The elastic support member 107 supports the projection lens 101 via the lens holder 102 so as to be able to move in parallel in a direction A perpendicular to the information track T on the recording medium 1.

If the output of the two-quadrant detector 8 shown in FIG. 2 is supplied to the coil 103 via the lead wire 106,
Since a force in the direction A in FIG. 3 acts on this coil, the projection lens 101 moves in the direction A, that is, in the direction perpendicular to the information track T. Therefore, by controlling the current flowing through the coil 103, it is possible to move the light spot onto the information track T.

However, in the configuration shown in Figure 3 above, the number of permanent magnets is 1.
Since only one movable body is arranged, the driving force of the movable body is small, and as a result, the responsiveness of the tracking drive is not good.

FIG. 4 shows an embodiment of the information detection head according to the present invention.

In FIG. 4, an equivalent permanent magnet 105 is provided at a position opposite to the permanent magnet 104, and these permanent magnets 104 and 105 are arranged so that their polarities are opposite to each other. In such a case, it goes without saying that the electromagnetic force for moving the projection lens 101 in the direction A is twice that in the example of FIG. 3.

Here, the coil 103 can be fixed to the lens holder with an adhesive.

In the embodiment of the present invention described above, the relative positional relationship between the information track and the light spot is detected using transmitted light, but even when reflected light is used, the idea of the present invention must be completely changed. Needless to say, it can be applied without any need. In addition, in the embodiment, a recording medium having a spiral information track such as a video disk was described, but a recording medium in which information is recorded in a spiral shape on a cylinder,
The present invention can be applied to any type of recording medium on which information is recorded in the form of tracks.

As described above, in the present invention, the first permanent magnet (for example, the permanent magnet 104 as shown in FIG. 4) and the second permanent magnet (for example, the permanent magnet as shown in FIG. 4) are arranged in a straight line substantially parallel to the recording medium surface. 105) are arranged apart from each other, and a lens holder in which at least the lens and the coil are integrally fixed is arranged between the first permanent magnet and the second permanent magnet, so that the lens can be driven. The force becomes large, and the responsiveness of the lens drive becomes extremely good.

In addition, since the lens holder is placed between the first permanent magnet and the second permanent magnet, the drive of the lens holder is well-balanced, and as a result, the tracking drive is highly accurate and efficient. Become.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing a conventionally known information reading device;
Figure 2 is a schematic diagram similar to Figure 1 showing an example of an information reading device to which the present invention is applied, Figure 3 is a reference diagram for explaining the operating principle of lens drive, and Figure 4 is information detection according to the present invention. 1 is a schematic diagram illustrating one embodiment of a head. 6'... Information detection head, 101... Projection lens, 102... Lens holder, 103... Coil, 104, 105... Permanent magnet, 107... Elastic support member.

Claims (1)

[Scope of Claims] 1. When reading the information by irradiating convergent light from a lens onto a recording medium on which information is recorded in the form of a track, the lens is driven in a direction parallel to the surface of the recording medium and across the information track. In the information detection head of the information reading device, at least one coil has a substantially flat surface at a portion where a magnetic flux directed in one direction intersects a part of the conductor array, and the lens and the coil A lens holder that is integrally fixed, a connecting member that provides a restoring force to the lens holder when the lens holder moves and is connected between the lens holder and the base, and the conductive wire arrangement. a first permanent magnet and a second permanent magnet that are fixed to the base and are arranged spaced apart in a linear direction substantially parallel to the surface of the recording medium; An information detection head for an information reading device, characterized in that the lens holder is movably disposed between the first permanent magnet and the second permanent magnet.