JPS5811692B2 - The current state of affairs - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an information detection head in an apparatus for optically reading information recorded in tracks on three recording media.

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.

Information tracks are generally 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, 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 disc as an information recording medium, and the video disc is, for example, 1800 rp.
It rotates around 2-2' with a rotational speed of m.

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 a video disc.

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 light intensity is detected by the photodetector 7. The information recorded in the photodetector can be extracted as an electrical output signal of the photodetector.

In order to read recorded information, a known reading device uses a light beam system (a laser light source 3, an auxiliary lens 4,
The information tracking is performed by moving the disk system (video disk 1) at a constant speed relative to the reflector 5 and projection lens 6 in the lateral direction (see arrow A in FIG. 1) with respect to the reading direction of the information track. is being tracked by Tazatsuba.

In such a case, in order to read the information correctly, the light from the laser light source 3 must be correctly focused onto the recording medium by the projection lens 6.

To perform this focus adjustment, conventional reading devices use known focusing machines.

Furthermore, the spot of light focused on the recording medium must be precisely positioned at one point on the information track to be read.

In conventional reading devices, compensation is performed by electrical means for the deviation of the optical spot in the information track direction, which occurs when the rotation of the video disk is accompanied by speed fluctuations.

In addition, in order to deal with horizontal deviation of the information track due to shape errors of the information track and eccentricity of the video disc, the light spot can be adjusted by rotating the reflector 5 around an axis perpendicular to the plane of the paper. The position is controlled.

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 such a positioning method, the projection lens must simultaneously satisfy the conditions listed below. It is necessary to have sufficient performance to focus light onto a spot of size.

(2) It is usually very difficult to suppress the eccentricity of a video disc to within Q, ltnm.

For this purpose, the projection lens must be at least 0.1
It must be aberration-free over the ig range.

(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.

It is an object of the present invention to particularly propose an information detection head for an information reading device that allows information to be read in the same way as conventional devices even with a lens of lower performance.

The present invention includes 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 means that detects the relative positional relationship between the information track on the recording medium and the light spot. An information reading device comprising: a projection lens inserted into the optical system; a lens barrel for holding the projection lens; and an elastic member for supporting the lens barrel movably in three-dimensional directions with respect to the information track. a support, and a magnetic means for three-dimensionally moving the lens barrel with respect to the information track, the magnetic moving means comprising two sets of spiral coils fixed to the lens barrel and one set of spiral coils. a helical coil; and three sets of magnets for applying a magnetic field to each set of the coils; The lens barrel is oriented in the same direction as the information track, the second permanent magnet and spiral coil set is oriented laterally at right angles to the information track, and the third magnet and helical coil are oriented transversely at right angles to the information track. An information detection head is provided, characterized in that the coils are arranged so that the lens barrels can be moved in directions perpendicular to the plane of the information track.

The invention will be explained in more detail with reference to the 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 of FIG. 1, and includes a projection lens supported movably in three dimensions, 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). M of the eccentricity of the information track)
It will be doubled.

For example, the reduction magnification M is 1/20. If the deviation of the reading point on the information track from the planned position is 0.1 iz, the deviation of the light spot from the optical axis is 0.005 mm.

This means that the projection lens only needs to be aberration-free within a range of 0.005 m.

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 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. .

In addition, a projection lens that satisfies the above conditions has a numerical aperture of 0.
．． 4 can be realized by 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 10 I or less, but also the construction of the projection lens is simplified, making it easy 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, a projection lens 101 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 spiral coils 1 are wound on this support 103.
03a and 103b (see FIG. 4) are fixed with adhesive or the like.

Furthermore, each of these coils 103a103b is
Permanent magnets 104a are spaced apart in the radial direction of the support 103.
, 104b, and the lead wires 106a, 10
The configuration is such that the control current is supplied via 6b.

The permanent magnets are arranged such that one permanent magnet 104a is oriented in the horizontal 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 (see FIG. 5). ).

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 capable of moving the projection lens 101 substantially in parallel on the recording medium 1 in the directions A and B through the lens barrel 102. shall be supported.

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 plate springs 109. It is supported so as to be movable in a direction perpendicular to the information track surface, that is, in the direction C in FIG. 3.4.

The elevating member 108 includes a base 11 as shown in FIG.
A cylindrical body 111 protruding vertically toward 0 is fixed,
A coil 103C is wound around the cylindrical body 111 in a spiral manner to face the cylindrical body 111.
An annular permanent magnet 104c is fixed to the magnet 0.

This permanent magnet 104c has an annular groove on its end face facing the elevating member 10B, 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 the annular groove of the permanent magnet 104C, and the lead wire 106
The configuration is such that the control current is supplied via c.

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, a force in the incoming direction as shown in FIG.

Furthermore, when a control current is supplied to the coil 103b, a force in the B direction in FIG. 3 acts on this coil, so the projection lens 101 moves in the B direction, that is, in the same direction as the information track T.

Furthermore, when a control current is supplied to the coil 103c, a force in the direction C in FIG. 3 acts on this coil.
The projection lens 101 moves in the C direction, that is, in the direction perpendicular to the information track plane.

Therefore, by controlling the current supplied to each of the coils 103a to 103c, 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 string-like elastic linear body 107 and the leaf spring 109 used in the previous embodiment.

Therefore, this leaf spring 112 has one end connected to the lens barrel 102,
Further, the other ends are each fixed to a fixing member 113, and this fixing member 113 is fixed to the base 110.

The spiral leaf spring 112 can be displaced in its axial direction, that is, in the C direction, similar to known bamboo springs,
If it is not tightly wound, it can be displaced in a plane perpendicular to the axial direction, and therefore in the A and B 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.

Further, in the example shown in FIG. 8, the elastic support member is composed of a pair of elastic bodies 115 and 116 that are three-dimensionally bent.

Of course, the elastic support members 114 and 115, 116 shown in FIGS. 7 and 8 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, the projection lens is
By moving the light spot dimensionally, it is possible to accurately position and focus the light spot on a specific point on the information track to be read.4Moreover, as mentioned above, the lens Since a simple configuration in which aberrations are removed only for points is sufficient, the information detection head can be made lighter and manufactured at a lower cost.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram showing a conventionally known information reading device, Fig. 2 is a schematic diagram similar to Fig. 1 showing an example of an information reading device to which the present invention is applied, and Figs. 3 to 5 are each according to the present invention. A perspective view, a vertical sectional view, and a bottom view showing one embodiment of the information detection head, FIG. 6 is a perspective view showing another embodiment of the information detection head according to the present invention, and FIG. 7 shows the information detection head also according to the present invention. FIG. 8 is a side view showing a partial cross section of another embodiment of the invention.
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, 101...
Projection lens 102 --- Lens barrel, 103a, 103b,
103C... Coil, 104a, 104b, 1
04C...Magnet, 107,109,112,1
14,115116...Elastic support member.

Claims (1)

[Claims] 1. 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 that detects the relative positional relationship between the information track on the recording medium and the light spot. an information reading device comprising: a projection lens inserted into the optical system; a lens barrel for holding the projection lens; and the lens barrel is movable in three-dimensional directions with respect to the information track. an elastic support for supporting the lens barrel; and a magnetic means for moving the lens barrel three-dimensionally relative to the information track, the magnetic moving means being connected to two sets of spirals fixed to the lens barrel. a spiral coil, one set of helical coils, and three sets of magnets for applying a magnetic field to each set of the coils; a pair of permanent magnets and a spiral coil orient the lens barrel in the same direction as the information track; and a helical coil arranged to move the lens barrel in a direction perpendicular to the plane of the information track.