JPH02113444A - Optical head - Google Patents

Abstract

PURPOSE:To perform high-speed access and accurate AF and AT control by dividing an optical system into a fixed section having a focus AF function and mobile section having a tracking AT function and providing no AF function to the mobile section. CONSTITUTION:An optical system is divided into a mobile and fixing sections and the mobile section performs AT control by means of a swing arm composed of an object lens 57, coil 61, and rotating shaft 60 the center line of which is aligned with the optical axis. The fixed section is provided with a relay lens 53 and performs AF control by means of a focus AF controlling mechanism 54. When a light spot is deviated from an information surface 58, the light spot is modified to an image forming luminous flux by means of the set of the lenses 53 and 57 and the reflected light is condensed to a photodetector 64. Thus a closed-loop feedback system is formed. Since the mobile section has no AF function and is light in weight, high-speed access and accurate AT and AF control can be performed.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an optical pick-up optical system (hereinafter referred to as an optical head) that optically records and reproduces information on an information recording medium. This invention particularly relates to an optical head having high-speed access performance.

[Conventional technology]

In an optical information recording/reproducing device, an optical head is a radar
A laser beam from a light source is focused on the surface of an information recording medium using an imaging optical system such as an objective lens to create a light spot with a spot size of about 1 μm in diameter, which is used to write or reproduce information. Known as an important unit.

Recently, there has been a strong demand for smaller and thinner optical heads for reasons such as (1) making optical information recording and reproducing devices smaller and thinner, and (2) increasing the speed of accessing information. Development research is actively being carried out with this aim in mind.

As an optical head that achieves this purpose, JP-A-63-
No. 4434 is publicly known. This is shown in FIG. In the figure, a light beam from a semiconductor laser 1 is converted into a parallel light beam by a collimator lens 2, passes through a polarizing beam sinter 3 and a single wavelength plate 4, is converted into circularly polarized light, and is reflected f! 10, and is imaged by the objective lens 6 as a light spot on the information recording surface. The reflected light from the information recording surface of the optical disc 5 follows the opposite path, is converted by the one-wavelength plate 4 into linearly polarized light with a polarization direction 90 degrees different from the forward direction, and is reflected by the polarizing beam splitter 3.
The sensor lens 7 focuses the light onto the light receiving element 8 .

In this conventional example, the optical head part is divided into a fixed part and a movable part.
Since only the movable part 11 moves over the head transport device 12 during optical and rad seek operations during information search, the weight of the movable part can be reduced and high-speed access can be achieved. Furthermore, in this conventional example, Out is used to correctly control the light spot on the information recording surface.

Focus (AF) control, Auto Tracki
ng (AT) control is achieved by controlling the position of the collimator lens 2, the movable part 11 has A
There are no heavy items such as actuator for F or AT, making it even lighter.

[Problem to be solved by the invention]

However, in this conventional example, the collimator lens 2 performs AT and AF control, so the correct Fo
There is a problem in that the CUS error signal and the Tracking X error signal cannot be obtained. For example, in a situation where the light spot produced by the objective lens 6 is in front of the information recording surface, the collimator lens 2 may be shifted slightly from its normal position toward the light source, so that the light beam after passing through the collimator lens becomes a slightly divergent light beam. In this case, the light spot created by the objective lens 6 needs to be located far away from the focal point of the objective lens, but in this way, the light flux returning from the optical disk will also be a light flux that is different from the parallel light flux, and the light rays will be Looking along the direction of travel, the light distribution that enters the polarizing beam splitter 3 as a slightly convergent light beam, is reflected, and is created on the light receiving element 8 is the same as when it was converted into a parallel light beam by the collimator lens 2. will be different. Therefore, it is converted into a parallel beam by the collimator lens 2, and a light spot is created at the focal point of the objective lens 6. At this time, if the information recording surface coincides with the light spot position, a correct focus error signal is generated. If the optical head system is adjusted to obtain zero, in the case mentioned above, the light distribution on the light receiving element 8 will be different, so even if the information recording surface and the light spot are aligned, , it becomes impossible to obtain a signal with zero focus error. A.T.
The same thing can be said about control systems. However, the conventional device shown in FIG. 4 does not create a correct closed loop feedback system.

Further, as another conventional example, Japanese Patent Laid-Open No. 160035/1983 is known. FIG. 5 shows this second conventional example.

In this second conventional example as well, the optical head section is divided into a fixed optical system section 45 and a movable section, and the movable section has an objective lens 38.
．． It includes an AF control coil 39 and a bar prism 35 as a light beam transmission member, and aims to reduce the weight of the movable part and achieve high-speed access. However, in this second conventional example, the AF control coil of the objective lens is missing.
This is one of the reasons for the increase in weight as a movable part, and in addition, magnetic yokes 40a, 40b for AF control are installed on the chassis side.
There are permanent magnets 41m, 41b, etc., resulting in a complex configuration of the device.

〔the purpose〕

The present invention was made in view of the problems of the prior art as described above, and its purpose is to provide a collimator lens for AT and AF.
This solves the problem that a closed-loop feedper system is not configured by controlling the
The object of the present invention is to provide an optical head that is light in weight without having an F' function, thereby enabling faster access and more accurate AT and AF control.

[Means to solve the problem]

According to the present invention, the above object is an optical head having an optical system that forms a light beam emitted from a light source as a light spot on an information track surface of an information recording medium; The movable part is divided into a movable part that can be rotated in a direction transverse to the movable part, and one end of the movable part has a driving means for controlling the rotation, and the other end has a fixed objective lens. , a relay lens that is optically combined with the objective lens to constitute the optical system is provided in the fixed part, and the relay lens of the fixed part is driven in the optical axis direction of the light beam passing through the lens. This is achieved by an optical head characterized in that focusing is controlled and auto-tracking is controlled by controlling the rotation of the movable part.

〔Example〕

Hereinafter, embodiments of the present invention will be described specifically and in detail based on the drawings.

FIG. 1 is a schematic perspective view showing a first embodiment of the present invention.

In the figure, 50 is a semiconductor laser, and 51 is a collimator lens that converts diverging light emitted by the semiconductor laser into parallel light. 52 is a beam sinter, and 53 is a relay lens for AF control. 54 is an actuator for AF control. 55 and 56 are mirrors, and 57 is a fixed objective lens. 58 is an optical disk, which is rotated by a spindle motor 59.

The parallel light beam from the collimator lens 51 passes through the relay lens 5.
3 and an objective lens 57 to form a light spot on the information surface within the optical disc. The reflected light from the optical disk follows the opposite path, is reflected by the beam sinter 52, and is focused onto the photodetector 64 via the sensor lens 63. In this embodiment, the objective lens 57 is subjected to tracking control using a swing arm method, and a coil 61 for this purpose is provided at the other end on the opposite side to the side where the objective lens 57 is provided.

Further, the optical axis of the parallel light beam from the collimator lens 51 coincides with the arm rotation axis of the swing arm 65, and a bearing 6o is provided below the center of this rotation axis. In this embodiment, in order to make the movement of the swing arm as fast as possible, a bearing is provided below the center of rotation of the swing arm, and the members on the arm are arranged so that the weight is balanced on the left and right sides of this bearing.

2 is a side view showing the optical path of the optical head section of the embodiment shown in FIG. 1. FIG. The illustrated section A is a fixed optical system section, which is supported by the main body of the apparatus. In this embodiment, the objective lens system includes a relay lens 53, which is a concave lens, and an objective lens 5.
7, and the relay lens 53 is connected to the AF control mechanism 54.
The objective lens 57 is fixed to the swing arm 65 and has no AF control coil structure. Therefore, the parallel light beam from the collimator lens 51 is converted into a slightly divergent light beam by the relay lens 53, reflected by the mirrors 55 and 56, and condensed by the objective lens 57 to form a light beam on the information surface. . The reflected light from the information surface follows the opposite path,
After passing through the objective lens 57, along the direction of ray propagation, the light beam becomes slightly convergent, is reflected by the mirror 56, 55, is converted into a parallel light beam by the relay lens 53, and is reflected by the beam cylinder 52. , sensor lens 6
3, the light is focused on a shift detector 64.

If the light spot deviates from the information surface, the relay lens 53 is AF-driven in the vertical direction in FIG. is controlled so that it is formed. At this time, the reflected light from the information surface of the optical disk passes through a pair of objective lens 57 and relay lens 53, and is then reflected and split by Sihims glitter 52 into a parallel beam of light.
A correctly focused light distribution is formed on the photodetector 64. Therefore, in the present invention, a correct closed loop feedback system is constructed, which is different from the conventional example.

Furthermore, in this embodiment, in the AF sub-control of the relay lens 53, which is a concave lens, it is necessary to devise an actuator mechanism that will prevent the optical axis of the lens from shifting or tilting. Compared to the conventional imaging system using a single convex lens, it has more flexibility in design, such as eliminating chromatic aberration and improving angle of view characteristics, and has better optical performance. An optical head can be realized.

FIG. 3 is a schematic perspective view showing a second embodiment of the invention.

In this embodiment, the fixed optical system section is fixed on the support base B. The fixed optical system section in this embodiment is a modification of the embodiment disclosed in Japanese Unexamined Patent Publication No. 104232/1983, which is a known document. That is, the diverging light flux from the semiconductor radar is collimated into a horizontally flat parallel light flux, which is converted into a circular light flux by the diffraction action of the diffraction grating 67 through the mirror 66.55, and this diffracted light flux is passed through the objective lens 5.
7 to form a spot light on the optical information surface. Therefore, in this embodiment, the fixed optical system section B can be made very thin. In this example as well, the objective lens is A
It is composed of a combination of a relay lens in the F actisator 54 and a fixed objective lens 57 supported by an arm 65.
What can be sub-controlled by F is the relay lens in the AF actuator 54 in the fixed optical system. In this embodiment, the reason why the one-wavelength plate 68 is used is to rotate the polarization direction of the linearly polarized light from the semiconductor radar by 90'.
This is to increase the reflection at 6.55 and the diffraction efficiency (certain diffraction order light it/incident light f) at the diffraction grating, thereby increasing the light utilization efficiency.

In this embodiment as well, each member is arranged so that the optical axis coincides with the rotation center of the swing arm and the left and right sides of the arm are kept in balance.

〔Effect of the invention〕

As explained above, according to the present invention, since the objective lens fixed to the swing arm does not have an actuator structure, the movable part is significantly reduced, and high-speed access and more accurate AT and AF sub-control are possible. It is possible to provide an optical head.

[Brief explanation of the drawing]

FIG. 1 is a schematic perspective view showing a first embodiment of the present invention;
The figure is a side view showing the optical path of the optical head section of the embodiment shown in FIG.
FIG. 3 is a schematic perspective view showing a second embodiment of the present invention;
1 and 5 are schematic side sectional views showing a conventional example. 50: Semiconductor radar-53: Relay lens, 54:
AF control actuator, 57: Objective lens, 60
: Bearing, 61: Coil, 65: Swing arm.

Claims (1)

[Claims] (1) An optical head having an optical system that forms a light beam emitted from a light source as a light spot on an information track surface of an information recording medium; One end of the movable part has a driving means for rotation control, and the other end has a fixed objective lens, and the objective lens and the optical Relay lenses that are combined to form the optical system are provided in the fixed part, and autofocusing is controlled by driving the relay lenses of the fixed part in the optical axis direction of the light beam passing through the lenses, and the movable An optical head characterized in that automatic tracking is controlled by controlling the rotation of the optical head.