JPS59160833A - Driving device for projection lens - Google Patents

Abstract

PURPOSE:To read accurate information through a lens having low performance by linking two kinds of elastic support members which are displaceable only in the direction of the lens optical axis and at right angles there to, and providing a coil which drives and controls a projection lens holder and a magnetic field generating means which faces the coil. CONSTITUTION:When the output of a detector 8 is applied to coils 103a-103c, forces generated in directions A and B operate on coils 103a and 103 on a lens holder 102 supported by the 1st elestic support member 107 by permanent magnets 104 and 104b which are at distance in a radial direction of the support body 103, so the projection lens 101 moves at right angles and along an information track T. Further, a force in a direction C operates on a coil 103c on an elevation member 108 supported by the 2nd elastic support member 109 by a magnet 104c to move the porjection lens 101 at right angles to the information track surface. Thus, the lens of simple constitution positions a light spot at one point on the information track accurately to perform focusing.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a projection lens driving device that is used in an apparatus 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. In a disk-shaped recording medium, the information tracks are generally arranged concentrically or in a spiral pattern. A device for optically reading such information includes an optical system that projects a light spot onto a recording medium, and detects the relative positional relationship between the information track J3 on the recording medium and the light spot. Position detecting 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, 1
It rotates around axis 2-2- with a rotational speed of 800 ppm. (l!! On the other hand, the luminous flux emitted from the laser light source 3 is
The light passes through the auxiliary lens 4, the reflecting mirror 5 J3, and the 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 the video disc or reflected by the video disc changes. Information recorded on the disk can be extracted as an electrical output signal from a 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 followed by moving at a constant speed relative to the lateral force in 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.

Roughly speaking, the spot of light focused on the recording medium must be accurately positioned at one point on the information track to be read. The conventional reading device J5 uses electrical means to compensate 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 prevent horizontal deviation of the information track due to shape errors of the information track and eccentricity of the video disc, the reflector 5 is rotated around an axis that overlaps with the plane of the paper to position the light spot. is controlled.

As is clear from the above, conventional reading devices produce light spoilers at a specific point on the information track to be read. The three-dimensional position system (■) of - is performed using individual means corresponding to each dimension. However, in this positioning method, the projection lens must simultaneously satisfy the following conditions.

(1) The projection lens needs to have enough performance to focus the laser beam onto a spora l- of a predetermined size without being affected by the inclination angle of the reflecting mirror.

(2) It is usually very difficult to suppress the eccentricity of a video disc to within 0.1 mn1. For this purpose, the projection lens must be aberration-free over a range of less than 0.1 mm 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 109 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 number of manufacturing strokes.

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

In particular, an object of the present invention is to propose a projection lens drive device 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.

A further object of the present invention is to provide a compact and lightweight projection lens driving device capable of moving a projection lens in the lens optical axis direction and in a direction perpendicular to the lens optical axis direction.

The feature of the present invention is that, in an optical information reading device whose drive is controlled by an electromagnetic drive means in the direction of the optical axis of the lens, a first elastic support member that is displaceable only in the direction perpendicular to the direction of the optical axis of the lens; A support means for two-dimensional direction displacement control which can be independently displaced in directions orthogonal to each other is constructed by connecting the second elastic support member which can be displaced only in the direction of the optical axis of the lens. One end is fixed to the projection lens, the other end is fixed to the base, and at the same time, a coil for driving and controlling the projection lens holder in a direction perpendicular to the lens optical axis is fixed, and a coil is fixed so as to face this =1 ile. This is due to the arrangement of the magnetic field generating means.

The invention will now be described in more detail with reference to embodiments shown in the drawings. In the following description, the same reference numerals as those used in the IC part of the conventional device described above indicate the same parts, and corresponding parts are indicated by dashed numbers.

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-dimensional directions, as will be described later.

If the light spot deviates in three dimensions with respect to the reading point on the center of the information track, the position of the light spot can be determined by detecting this deviation with a known deviation detector 8 connected to the photodetector 7. It detects in which direction the deviated, and this detected low amount 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 according to 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 1 rack from the expected position is 0.1, the deviation of the optical spot from the optical axis is 0.005III11.

This means that the projection lens only needs to be aberration-free within a range of 0.005 mm. In addition, when collimating a parallel beam of light, it becomes M-0, so the deviation from the optical axis becomes 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.

Thus, according to the reader of FIG. 2, the deviation of the light spot from the optical axis is the reduction magnification of the projection lens, and is therefore much smaller than in the reader of FIG. Furthermore, the projection lens that satisfies the above-mentioned conditions can be realized as a spherical system composed of at most three lenses, even if the numerical aperture is 0.4.
It is theoretically possible to achieve this with a single lens by using an aspherical lens. For this reason, it is not only extremely easy to reduce the weight of the projection lens to 10 g or less, but also the construction of the projection lens is 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, a projection lens 101 is mounted on one end of a hollow cylindrical lens holder 102, and a disc-shaped support 103 is attached to this lens holder 102. A pair of spiral coils 10 are wound around this support 1031.
3a and 103b (see Figure 4) are fixed with adhesive or the like. Furthermore, these coils 103a, 103b
are respectively spaced apart in the radial direction of the support 103 and are made of permanent magnets. :1i It is arranged between the magnetic poles of 104a and 104b, and a control current is supplied through lead wires 106a and 106b.

The above-mentioned permanent magnets are arranged such that one permanent magnet 104a is arranged in the horizontal direction A perpendicular to the information track T, and the other permanent magnet 104b is arranged in the same direction as the information track T. (See figure).The entire lens holder is attached via a first elastic support member 107 to an elevating member 108 having a configuration described later.This first elastic support member 1
In this example, 07 is composed of a string-like elastic linear body, and supports the projection lens 101 via the lens holder 102 so as to be substantially movable in parallel in the directions A and B on the recording medium 1-H. It shall be.

In this embodiment, the elevating member 108 is further formed into a disk shape with an opening [1] in the center, and is attached to the base 110 by an elastic support member, for example, a plurality of leaf springs 109, and this second elastic support member 109 The elevating member 108 is supported so as to be movable in a direction perpendicular to the information track surface, that is, in the direction C shown in FIGS. A cylindrical body 111 protruding vertically toward 110 is fixed, and a coil 103c is wound helically around this cylindrical body 111.
3c is wound (opposed to the rolled cylindrical body 111,
An annular permanent magnet 104c is fixed to the base 110 of. 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 the annular groove of the permanent magnet 104C, the lead wire 10
The configuration is such that the control current is supplied via 6C.

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 in six directions in FIG. 3 act on this coil, so that the projection lens 101 moves in six directions, that is, in the lateral direction perpendicular to the information track T. In addition, the coil 103
When a control current is supplied to b, a force in the direction B in FIG. 3 acts on this coil, so the projection lens 101 moves in the direction 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 1-rack plane.

It becomes possible to move the spot three-dimensionally and to position it on 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 plate spring 112 is used in place of the elastic linear body 107 in the form of a hanging cord and the plate spring 109 used in the previous embodiment. Therefore, the leaf spring 112 is fixed at one end to the lens holder 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 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 a normal conical spring 114, one end of which is connected to the disc-shaped support 103 that is integral with the lens holder 102, and the other end is connected to the base 11.
Each is fixed at 0. In addition, in the example shown in FIG.
Consists of 6. Elastic support members 114, 115, and 116 shown in FIGS.
10 so as to be movable in three dimensions.

As explained above, according to the present invention, the projection lens is
By moving the light spot dimensionally, it becomes possible to accurately position and focus the light spot on a specific point on the information track to be read. However, as mentioned above, the lens can have a simple structure in which aberrations are removed only at one point on the optical axis, so the information detection head can be made lighter and manufactured at a lower cost. It becomes possible to do so.

Further, the present invention supports the projection lens with a two-dimensional displacement control support means in which the first and second elastic support members which are mutually displaceable in the right angle direction are connected, and the projection lens holder is connected to the lens optical axis. Since the coil for driving in the perpendicular direction is fixed, the projection lens driving device has the effect of being significantly smaller and lighter.

[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 the diagram showing an example of an information reading device to which the present invention is applied, and FIGS. 3 to 5 are diagrams each showing the present invention. FIG. 6 is a perspective view showing an embodiment of the information detection head according to the present invention, and FIG. 7 is a perspective view showing an embodiment of the information detection head according to the present invention. FIG. 8 is a partially sectional side view showing an embodiment of the detection head, and FIG. 8 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 holder, 103a, 103b, 103cm...-1 il, 104
a, 104b, 104c... magnet, 107.10
9, 112, 114, 115, 116... Elastic support member. Patent applicant Figure 1 Figure 2 Figure 6 Figure 4 Figure 5 Figure 6

Claims (1)

[Claims] An optical information reading device in which a projection lens is driven and controlled in the lens optical axis direction by an electromagnetic driving means, comprising: a first elastic support member that is displaceable only in a direction perpendicular to the lens optical axis direction; One end of the support means for two-dimensional displacement control, which is connected to the second elastic support member which can be displaced only in the lens optical axis direction, is fixed to the projection lens, and the (l!! end is fixed to the base). and J(, a coil for driving and controlling the projection lens in a direction perpendicular to the lens optical axis is fixed to the projection lens holder, and a magnetic field generating means is arranged so as to face the coil, so that the projection lens is A projection lens drive mount whose drive can be controlled in a direction perpendicular to the optical axis direction and in a two-dimensional direction along the lens optical axis direction.