JPS6350772B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an information detection head in a device for optically reading information recorded in a track shape on a recording medium.

[Conventional technology]

A typical example of a recording medium on which information is recorded in the form of a track 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 disk as an information recording medium, and the video disk rotates around 2-2' at a rotation 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 disk. According to the information recorded on the video disc,
Since the intensity of light transmitted through or reflected by this video disc changes, the information recorded on the video disc is detected by photodetector 7 by detecting the intensity of the light. It can be extracted as an electrical output signal of the device.

In order to read recorded information, in known reading devices, a disk system (video disk 1) is connected to an information track with respect to a light beam system (laser light source 3, auxiliary lens 4, reflector 5, and projection lens 6). Lateral direction to the reading direction (arrow A in Figure 1)
(see ) at a constant speed to roughly follow the information track.

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

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 light spot in the information track direction, which occurs when the rotation of the video disk is accompanied by speed fluctuations. In addition, the reflector 5 is used to prevent horizontal deflection of the information track due to shape errors of the information track and eccentricity of the video disk.
The position of the light spot is controlled by rotating it around an axis perpendicular to the plane of the paper.

As is clear from the above, in conventional reading devices, three-dimensional positional control of a light spot with respect to a specific point on an information track to be read is performed using individual means corresponding to each dimension. It's on.

[Problem that the invention seeks to solve]

However, in such a control means, 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 inclination angle of the reflecting mirror.

(2) It is usually very difficult to keep the eccentricity of the disk within 0.1mm. 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 the weight of the movable body including this lens increases, resulting in a decrease in response characteristics to error signals. Furthermore, it is difficult to reduce manufacturing costs.

SUMMARY OF THE INVENTION An object of the present invention is to provide an information detection head for an information reading device that is small, lightweight, and has improved response characteristics, eliminating the drawbacks of the conventional devices described above.

[Means and actions for solving problems]

The present invention scans, reads, and reproduces information recorded in a track shape on a recording medium using a light spot focused by a projection lens, and the relative position of the information track and the light spot on the recording medium is In an optical information reading device that detects and controls a projection lens independently of each other in two directions, one in the lateral direction across the information track and the other in two directions perpendicular to the plane of the information track, the projection lens and the projection lens are connected to a recording medium. A movable body is constructed by integrally fixing a coil for electromagnetically driving the lens in the two directions independently from each other to a projection lens support, and the projection lens is constructed from one aspherical lens. The information detection head is characterized in that it includes means for applying a restoring force to the movable body.

To track the information track, without rotating the reflector, a movable body with the projection lens and its driving coil fixed integrally can be moved in two directions: horizontally across the information track and in two directions perpendicular to the plane of the information track. Since the incident light on the projection lens is kept parallel to the optical axis and aberration correction is easy, the desired performance can be achieved by constructing the projection lens with a single aspherical surface. As a result, the movable body including the projection lens becomes smaller and lighter, and response characteristics to a focus error signal or a tracking error signal are improved.

(Example) The present invention will be described with reference to an example shown in the drawings. In the following description, the same reference numerals used in 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 invention is used in place of the projection lens 6 in the reading device of FIG.
As will be described later, it includes a projection lens supported movably in at least two dimensions.

When the light spot deviates from the reading point on the center of the information track, this deviation is detected by a known deviation detector 8 connected to the photodetector 7, and it is possible to determine in which direction the light spot position is deviated. The deviation 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 is 1/20 and the deviation of the reading point on the information track from the planned position is 0.1 mm, 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 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 for only 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. In addition, special public service
Publication No. 18781 describes an aspherical single lens for use in a projection lens, etc., with a numerical aperture of 0.46 to 0.75.
Eight specific design examples of large-diameter aplanat lenses are shown, and Japanese Patent Application Laid-Open No. 156945/1983 also describes a design in which a large-diameter lens with a numerical aperture of 0.45 to 0.6 is composed of an aspheric single lens. An example is shown, and it is also described that this lens is used as a projection lens for an information reading device as shown in FIG. In this way, by using an aspherical lens, a lens design having the above-mentioned desired performance can be realized with a single lens.

The above-mentioned publication discloses that an aspherical single lens is applied to the projection lens of the information detection head, but there is no mention of the means for supporting and driving this projection lens, at least in the direction perpendicular to the information tract. There is no suggestion as to driving the projection lens.

In contrast, in the present invention, the projection lens is driven not only in the direction of the optical axis but also in a direction perpendicular to the optical axis. Therefore, if the lens support including the projection lens is not lightweight, the response to the control signal will not be quick. This results in a lack of sex. In the present invention, since the incident light to the projection lens is always incident at right angles to the projection lens, the aberration correction of the projection lens only needs to target the light beam parallel to the optical axis, and the conventional mirror Since there is no need to consider oblique light beams, unlike when tracking is performed by rotating the lens, lens design is extremely easy, and the numerical aperture is approximately 0.4
Aspheric singlet lenses with desired performance of some degree can be easily designed. For this reason, it is extremely easy to reduce the weight of the projection lens to 10g or less, and the movable body including the projection lens can be configured to be small and lightweight.
Response characteristics to error signals are improved.

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

In these embodiments, a projection lens 101 is attached to one end of a hollow cylindrical lens barrel 102, and a disk-shaped support 103 is integrally fixed to this lens barrel 102.

A pair of spirally wound coils 103a and 103b (see FIG. 4) are fixed onto this support 103 using an adhesive or the like. Furthermore, these coils 10
3a and 103b are spaced apart in the radial direction of the support body 103, and are connected to permanent magnets 104a and 104b.
The control current is provided between the magnetic poles of the magnetic head and the control current is supplied through the lead wire. The permanent magnets are arranged such that one permanent magnet 104a is oriented in the transverse direction A perpendicular to the information track, and the other permanent magnet 104b is oriented in the same direction B as the information track (see FIG. 3).

As shown in FIG. 4, a cylindrical body 111 protruding vertically toward the base 110 is integrally fixed, and a coil 103c is attached around the cylindrical body 111.
Wrap it in a helical shape and fix it. This projection lens
In order to elastically support the movable body to which the coil and support body are integrally fixed, one end of a conical spring 114 is fixed to the base 110, and the other end is fixed to the lens barrel 102 as a disc-shaped support body 103. Fixed to. A cylindrical body 111 around which the coil 103c is wound
An annular permanent magnet 104c is fixed to the base 110 so as to face the permanent magnet 104c. This permanent magnet 104c
has an annular groove on its end surface, 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 a lead wire.

When the output of the detector 8 shown in FIG. 2 is supplied as a control current to the coils 103a to 103c via lead wires, the projection lens 101 is displaced as follows.

First, when a control current is supplied to the coil 103a, a force in the direction A in FIG. 3 acts on this coil, so that the projection lens 101 moves in the direction A, that is, in the lateral direction perpendicular to the information track.

Furthermore, when a control current is supplied to the coil 103b, a force in the direction B 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. Furthermore,
When a control current is supplied to the coil 103c, a force in the C direction in FIG. 3 acts on this coil, so that 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 moved three-dimensionally to a specific point on the information track to be read. becomes.

The embodiment shown in FIG. 3 uses one spirally wound leaf spring 112 as an elastic support member for the movable body. This leaf spring 112 has one end connected to the lens barrel 1.
02 and the other end 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, like the known bamboo spring, and because it is not tightly wound, it can be displaced in a plane perpendicular to its axial direction, that is, in the C direction. It can be displaced in the A and B directions. Therefore,
Except for the structural differences in the elastic support member described above, the information sensing head according to the embodiment of FIG. 3 operates in the same manner as that shown in FIG.

FIG. 5 shows another example of the elastic support member of the information detection head of the present invention.

In this example, the elastic support member is composed of a pair of elastic bodies 115 and 116 bent three-dimensionally, one end of each is fixed to the base 110, and the other end is fixed to the lens barrel 110.
It is designed to be attached to a member integrally fixed to 02.

〔Effect of the invention〕

According to the present invention, it is possible to accurately position a light spot with respect to a recording medium by controlling a movable body integrally formed with a projection lens and its drive coil, and the projection lens is positioned at one point on the optical axis. By using an aspheric surface, the desired performance can be easily obtained with a single lens, and the information detection head can be made extremely small and lightweight. Since the information detection head has good response characteristics to control signals, it is possible to provide an information detection head at low 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. FIG. 101... Projection lens, 102... Lens barrel, 103...
Support, 103a, 103b, 103c... Coil, 104a, 104b, 104c... Magnet, 11
2,114,115,116...Elastic support member.

Claims (1)

[Claims] 1 Information recorded in a track shape on a recording medium is scanned and read and reproduced using a light spot focused by a projection lens, and the relative position of the information track and light spot on the recording medium is detected. In the optical information reading device, the projection lens is controlled independently of each other in two directions, one in the lateral direction across the information track and the other in the direction perpendicular to the plane of the information track.
A movable body is constructed by integrally fixing the projection lens and a coil for electromagnetically driving the projection lens in the two directions independently of each other with respect to the recording medium, and An information detection head characterized in that the lens is constituted by one aspherical lens and is provided with means for applying a restoring force to the movable body.