JPS59160835A - Driving device for projection lens - Google Patents

Abstract

PURPOSE:To read accurately information through a lens with low performance by providing a flexible support member which links a base with a projection lens and is displaceable in three dimensions and an electromagnetic driving means which drives and controls the projection lens at right angles to the optical axis. CONSTITUTION:When the output of a detector 8 is applied to coils 103a-103c, forces generated by permanent magnets 104a and 104b in directions A and B operates on coils 103a and 103b on a lens barrel 102 supported by an elastic support member 107, so the projection lens 101 moves at right angles to and along an information track T. A force generated by a magnet 104c in a direction C operates on the coil 103c on an elevation member 108 supported by an elastic support member 109 fitted to the base 110 to move the projection lens 101 at right angles to the information track surface. Thus, the projection lens of simple constitution is moved in three dimensions to position a light spot at one point on the information track accurately, performing focusing.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a 1q shadow lens driving device 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 one rack is a disc-shaped recording medium, a so-called video disc. On a disk-shaped recording medium, information 1 to rack are usually 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 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, 1
It rotates around axis 2-2' with a rotational speed of 800 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 a video disc. According to the information recorded on the video disc, the intensity of the light that passes through the video disc or is reflected by the video disc changes. Information recorded on the disc can be extracted as an electrical output signal of the photodetector.

In order to read recorded information, known reading devices use a light beam system (Ray light source 3, auxiliary lens 4,
The disk system (video disk 1) is moved at a constant speed relative to the reflecting mirror 5 and the projection lens 6 in the lateral direction to the reading direction of the information track (see arrow A in FIG. 1), and the information track is moved at a constant speed V. is closely followed.

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. 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 reflector 5 is rotated around an axis perpendicular to the plane of the paper to position the light spot. is controlled.

As is clear from the above, in conventional reading devices, the three-dimensional position control of the light spot with respect to the information to be read i~ one specific point on the screen is performed by individual means corresponding to each dimension. There is. 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 spot 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 inch. 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 1 μm or less, the number of frontages 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 market, and furthermore, it is difficult to reduce manufacturing costs.

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

It is an object of the present invention to propose a projection lens driving device for an information reading device that is capable of reading information in the same manner as the conventional device even with a lens of higher quality and lower power.

The invention will be explained in more detail with reference to the embodiments shown in the drawings. In the following explanation, the same reference numerals as those used for the conventional device described above indicate the same parts.
Corresponding parts are indicated by dashed symbols.

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 included in the reading device of 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, this shift is detected by a known shift detector 8 connected to the photodetector 7, thereby detecting the light spoiler 1. ~Detect in which direction the position has shifted and amplify this detection signal. 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 set to M, the deviation of the optical axis in a plane perpendicular to the optical axis of the light spot is equal to the movement age of one nons (
If the deviation occurs only laterally or in the direction with respect to the information track, it will be M times the eccentricity of the information track.

For example, if the reduction magnification M is 1/2o1, and the deviation of the reading point from the expected position on the information track is 0.1 mm, the deviation of the light spot from the optical axis is 0.005 ml. This means that the projection lens only needs to be aberration-free within a range of 0.005 mm. Furthermore, when collimating a parallel light beam, M=O, 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 therefore, compared to the case of the reading device of FIG. In addition, if the above-mentioned conditions are not met, the projection lens can be realized with a spherical system composed of at most three lenses, even if the numerical aperture is set to 0.4.
It is theoretically possible to achieve this with a single lens if an aspherical lens is used. 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 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 103a, 103b (see FIG. 4) are fixed onto this support 103 with an adhesive or the like.
The permanent magnets 15104a and 15104b are spaced apart from each other in the radial direction of the support 103, respectively, and are arranged between the magnetic poles of the permanent magnets 15104a and 104b, and a control current is supplied through the lead wires 106a and 106b. The permanent magnet 104a is in the horizontal direction Δ perpendicular to the information track T, and the permanent magnet 104b is in the same direction B as the information track T.
Place them facing each other (see Figure 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
The projection lens 101 is projected onto the recording medium 1 through the
It is assumed that the support is substantially movable in parallel in the Jj and B directions.

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 through an elastic support portion (A, for example, a plurality of leaf springs 109). Reference numeral 109 denotes a lifting member 108. The lifting member 108 is supported so as to be movable in a direction perpendicular to the rack surface, that is, in the direction C in Fig. 3.4. A cylindrical body 111 protruding perpendicularly to the cylindrical body 111 is fixed, and a coil 103C is spirally wound around this cylindrical body 111. An annular permanent magnet 104C is fixed to the base 110. The permanent magnet 104C has an annular groove on its end face facing the unloading 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, and is configured to be supplied with a control current via the lead wire 106G.

The output of the detector 8 shown in FIG.
When 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,
Since a force acts on this coil in the direction to the left in FIG. 3, the projection lens 101 moves in the direction to the left, 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, the same direction as the information track T.

Roughly speaking, when a control current is supplied to the coil 103C, a force in the direction of C in Fig. 3 acts on this coil, so
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 is possible to move it dimensionally and to move it to a specific point on the information track 1 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 109 used in the previous embodiment. Therefore, this leaf spring 112 has one end attached to the lens barrel 1.
02 and the other end to the fixing member 113,
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, 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 mentioned above, the information detection head according to the embodiment of FIG. 6 operates in the same manner as those 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, the elastic support member is supported by a pair of elastic bodies 115 and 116 that are bent three-dimensionally. Elastic support member 114 shown in FIGS. 7 and 8
J3J: 115 and 116 connect the lens barrel 102 to the base 110
Of course, it is supported movably in three-dimensional directions.

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. Moreover, as mentioned above, the lens can be of a simple configuration in which aberration is removed only for one point on the optical axis, so the information detection head can be made lighter and manufactured at a lower cost. becomes.

[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 respectively information detection according to the present invention. Fig. 6 is a perspective view showing another embodiment of the information detection head according to the present invention, and Fig. 7 is the same (information detection head according to the present invention). FIG. 8 is a side view partially showing another embodiment of the 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・ffl cylinder, 103a, 103b, ”+03
c・ml il, 104a, 104b, 104a
...Magnet, 107, 109, 112, 114°11'
5,116...Elastic support part 2 material. Patent applicant Figure 1 Figure 2 Figure 3

Claims (1)

[Claims] A projection lens drive control device configured to drive and control a projection lens in the optical axis direction, which includes a flexible support member movable in three dimensions that connects a base and the projection lens, and a flexible support member that connects the projection lens at right angles to the optical axis. 1. A projection lens driving device characterized by comprising an electromagnetic driving means for driving a lens in a direction 1b11.