JPS59160838A - Information detection head - Google Patents

Abstract

PURPOSE:To make accurate read of information through a lens with low performance by providing two coils fixed to a projection lens barrel and magnets which are at right angles to one another. CONSTITUTION:When the output of a detector 8 is applied to coils 103a-103c, forces generated in the 1st and the 2nd directions A and B by permanent magnets 104a and 104b operate on the coils 103a and 103b on the lens barrel 102 supported by the eleastic support member 107 to move the projection lens 101 at right angles to and along an information track T. A force generated in the 3rd direction C by a magnet 104c operates on the coil 103c on an elevation member 108 supported by the elastic support member 109 to move the projection lens 101 at right angles to the information track surface. Thus, the projection lens of a simple constitution positions a light spot at one point on the information track and performs focusing.

Description

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

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

FIG. 1 shows an example of a known information reading device (see above). In the figure, reference numeral 1 indicates a video disk as an information recording medium, which rotates around an axis 2-2' at a rotational speed of, for example, 1800 rpm. 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 disc. According to the information recorded on the video disc, the intensity of the light transmitted through this video disc or reflected by this video disc changes, so the intensity of the light is detected by the light detection H7, and the information is recorded on the video disc. The detected information can be extracted as an electrical output signal of the photodetector.

In order to read recorded information, in known reading devices, a disc system (video disc 1) is connected to a light beam system (laser light source 3, auxiliary lens 4, reflector 5, and projection lens 6) on an information track. The information track is roughly tracked by moving at a constant speed relative to the reading direction (see arrow A in FIG. 1).

In such a case, the projection lens 6 is used to read the information correctly.
Therefore, the light from the laser light source 3 must be focused correctly onto the recording medium. To perform this focus adjustment,
Conventional reading devices use known focusing mechanisms.

Furthermore, the spot of light focused on the recording medium must be accurately positioned at one point on the information track to be read. Compensation is performed by means of a difference in the direction of the information track of the light spot that occurs when the rotation of the video disk is accompanied by speed fluctuations. In addition to this,
To deal with horizontal deflection of the information track due to shape errors of the information track or eccentricity of the video disc, the position of the light spot is controlled by rotating the reflecting mirror 5 around an axis perpendicular to the plane of the paper. .

As is clear from the above, in conventional reading devices, the three-dimensional position control of the light spot with respect to a specific point on the information track to be read is performed by individual means corresponding to each dimension. . However, in this positioning method, the projection lens must simultaneously satisfy the following conditions.

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

(2) It is very difficult to suppress the eccentricity of a video disc to within 0.1 tm. For this purpose, the projection lens must be aberration-free over a range of at least o, imm in the spot plane.

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

(4) In order to keep the spot focused on the disk surface, it is necessary to control the vertical position of the projection lens. Therefore, the weight of the projection lens must be 10 g or less.

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

The present invention seeks to eliminate the drawbacks of the prior art devices mentioned above.

SUMMARY OF THE INVENTION An object of the present invention is to propose an information detection head for an information reading device that is capable of reading information in the same way as conventional devices even with a lens of lower performance. In particular, it is an object of the present invention to provide an information detection head capable of optically correcting rotational unevenness of a disk even if the rotational unevenness occurs.

Akira Mizumoto, an optical system that projects a light spot onto a recording medium on which information is recorded in the form of a track, and a position detection system that detects the relative positional relationship between the information track on the recording medium and the light spot. The magnetic moving means includes a coil fixed to the projection lens and driving the projection lens in a transverse direction perpendicular to the tracks of the recording medium, and a coil driven in the same direction as the tracks. An information detection head is provided, characterized in that it is constituted by a coil and magnets arranged opposite each of the coils and at substantially right angles to each other.

The invention will be explained in more detail with reference to embodiments shown in the drawings. In the following description, the same reference numerals as those used for the conventional device described above indicate the same parts, and corresponding parts are indicated by numbers with a dash added.

FIG. 2 shows an example of an information reading device equipped with an information detection head according to the present invention.

In the present invention, the reflecting mirror 5 is not rotatable as in the reading device shown in FIG. 1, but is fixedly arranged.

The information detection head 6' according to the present invention is used in place of the projection lens 6 in the reading device shown in FIG. 1, and includes a projection lens supported movably in three-dimensional directions, as will be described later.

When the light spot shifts in three dimensions with respect to the reading point on the center of the information track, the spot position of the light can be determined by detecting this shift with a known shift detector 8 connected to the photodetector 7. The direction in which the signal has shifted is detected and this detection signal is amplified. The output of this displacement detector 8 is connected to the information detection head 6' according to the present invention to form a control system for controlling the position of the projection lens in accordance with the detected displacement of the light spot position. In this control system, if the reduction magnification of the projection lens is M, the deviation from the optical axis of the light spot in a plane perpendicular to the optical axis is the amount of movement of the lens (the deviation occurs only in the lateral direction with respect to the information track). In this case, it is M times the eccentricity of the information track.

For example, if the reduction magnification M is 1/20 and the deviation of the reading point on the information track from the planned position is 0.1, the deviation of the optical spot from the optical axis is 0.005 mrn'. 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 O. In other words, in this case, it is sufficient that the projection lens has no aberration for only one point on the optical axis.

In this way, according to the reading device of FIG. 2, the deviation of the light spot from the optical axis is reduced by the reduction magnification of the projection lens, and is therefore much smaller compared to the case of the reading device of FIG. . Further, the projection lens satisfying the above-mentioned conditions can be realized by a spherical system composed of at most three lenses even if the numerical aperture is 0.4. Roughly speaking, it is theoretically possible to achieve this with a single lens by using an aspherical lens. For this purpose, the Ni of the projection lens
Not only is it extremely easy to reduce l to 10 g or less, but the structure of the projection lens is also simplified, making it easier to assemble, and therefore, it is possible to reduce manufacturing costs.

3 to 5 show an embodiment of the information detection head according to the present invention.

In this embodiment, the projection lens 1o1 is attached to one end of a hollow cylindrical lens barrel 102, and a disk-shaped support 103 is attached to this lens barrel 102.

A pair of spirally wound films 1 on this support 103
03a, 103b (see Figure 4) are fixed with adhesive etc.Furthermore, these coils 1゜3a, 103b are fixed.
are arranged between the magnetic poles of permanent magnets 104a and 104b, spaced apart in the radial direction of support 103, and are supplied with a control current via lead wires 106a and 106b. The permanent magnets are arranged such that one permanent magnet 104a is oriented in a lateral direction A perpendicular to the information track T, and the other permanent magnet 104b is oriented in the same direction B as the information track T (Fig. 5). reference). Note that the entire lens barrel is attached via an elastic support member 107 to an elevating member 108 having a structure described later. In this example, the elastic support member 107 is composed of a string-like elastic linear body, and is
The projection lens 101 is projected onto the recording medium 1 through the
and B-direction so as to be substantially movable in parallel.

In this embodiment, the elevating member 108 is further formed into a disk shape with an opening in the center, and is attached to the base 110 by an elastic support member, for example, a plurality of leaf springs 109. It is supported so that it can be displaced in a direction perpendicular to the track surface, that is, in the direction C in FIG. 3.4. As shown in FIG. 4, the lifting member 108 includes a cylindrical body 1 that projects vertically toward the base 110.
11 is fixed, and a coil 10 is placed around this cylindrical body 111.
Wrap 3c in a spiral shape. An annular permanent magnet 104C is fixed to the base 110 so as to face the cylindrical body 111 around which the coil 103G is wound. This permanent magnet 104C has an annular groove on its end face facing the elevating member 108, and the annular groove has different polarities on its inner and outer peripheries. The coil 103c wound around the cylindrical body 111 is positioned within an annular groove of the permanent magnet 104C, and is configured to be supplied with a control current via a lead wire 106c.

The output of the detector 8 shown in FIG.
If a control current is supplied to the coils 103a to 103C via 106C, the projection lens 101 is displaced as follows. First, when a control current is supplied to the coil 103a, forces act on this coil in the six directions shown in FIG. Also, coil 10
When a control current is supplied to coil 3b, a force in direction C in FIG. 3 acts on this coil, so that projection lens 101 moves in direction C, that is, in the same direction as information track T. Furthermore, when a control current is supplied to the coil 103C,
Since a force in the direction C in FIG. 3 acts on this coil, the projection lens 101 moves in the direction C, that is, in a direction perpendicular to the information track plane.

Therefore, by controlling the current supplied to each of the coils 103a to 1030, the light spot can be divided into three
It becomes possible to move it dimensionally and to move it to a specific point on the information track T to be read.

FIG. 6 shows another embodiment of the information detection head according to the present invention.

In this embodiment, only one spirally wound leaf spring 112 is used in place of the elastic linear body 107 in the form of a hanging string and the leaf spring 10'9 used in the previous embodiment. Therefore, the leaf spring 112 is fixed at one end to the lens barrel 102 and at the other end to the fixing member 113, which in turn is fixed to the base 110. The spiral leaf spring 112 can be displaced in its axial direction, that is, in the C direction, like the known bamboo spring, or in a plane perpendicular to the axial direction if it is not tightly wound. and thus can be displaced in the A and C directions. Therefore, except for the structural difference of the elastic support member described above, the information detection head according to the embodiment of FIG. 6 operates in the same manner as that shown in FIGS. 3 to 5.

7 and 8 show other examples of the elastic support member in the information detection head according to the present invention.

That is, in the example shown in FIG. 7, the elastic support member is constituted by an ordinary conical spring 114, one end of which is fixed to the disk-shaped support 103 integral with the lens barrel 102, and the other end fixed to the base 110. In the example shown in FIG. 8, a pair of elastic bodies ii5. Configure with iie. Elastic support member 11 shown in FIGS. 7 and 8
4, 115, and 116 support the lens barrel 102 so as to be movable in three dimensions with respect to the base 110.

As explained above, according to the present invention, it is possible to move the projection lens three-dimensionally to accurately position and focus the light spot on a specific point on the information track to be read. It becomes possible. Moreover, as mentioned above,
Since the lens may have a simple structure in which aberration is removed only for one point on the optical axis, the information detection head can be made lighter and manufactured at a lower cost.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram showing a conventionally known information reading device, Fig. 2 is a schematic diagram similar to the diagram showing an example of an information reading device to which the present invention is applied, and Figs. A perspective view, a vertical sectional view, and a bottom view showing one embodiment of the information detection head according to the invention, FIG. 6 is a perspective view showing another embodiment of the information detection head according to the invention, and FIG. 7 is a perspective view showing another embodiment of the information detection head according to the invention. FIG. 8 is a side view partially showing another embodiment of the situation detection head in cross section;
The figure is a route diagram showing an embodiment of the elastic support member of the information detection head according to the present invention. 6'... Information detection head, 1o1... Projection lens,
1102-1t1.103a, 103b, 103c
mm1 il, 104a, 104b, 104c...
Magnet, 107, 109, 112, 114° 115.11
6...Elastic support member. Patent applicant Figure 1 Figure 2 Figure 6 Figure 4 Figure 5 Figure 6

Claims (1)

[Claims] In an information reading device comprising a projection lens that projects a spot of light onto a recording medium on which information is recorded in the form of a track, and a means for magnetically moving the projection lens, the magnetic moving means moves the projection lens. A coil that is fixed and drives the projection lens in a lateral direction perpendicular to the tracks of the recording medium, a coil that drives the projection lens in the same direction as the tracks, and magnets that are opposed to each of the coils and arranged at substantially right angles to each other. An information detection head characterized by comprising: