JPH04341940A - Optical disk memory device - Google Patents

Abstract

PURPOSE:To make a device small and thin by constituting it of an aspherical mirror which bends light from a fixed optical system to a disk side, and in addition, can move finely to a focus side, and can move coarsely to the radial direction of a disk. CONSTITUTION:The light emitted from a semiconductor laser 12 is converted into parallel light by a collimator 13, and after passing through a beam splitter 14, it reaches a galvano-mirror 15, and the laser beam is converted by 90 degrees, and simultaneously, the change of the inclination of an optical axis necessitated for tracking is generated, and it reaches the aspherical mirror 18, and the 90 degree conversion of an optical path and the converging of the light are executed at a time. Since the recording surface 19 of the disk causes surface vibration in a vertical direction as accompanying the rotation of the disk, the mirror 18 is moved to the direction of an arrow mark in order to obtain a minimum spot diameter, and the best spot diameter is maintained. Then, reflected light from the disk 19 is converted in its optical path by the splitter 14, and reaches the beam splitter 20, and is divided to an error signal detecting system 21 and the detecting system 22 of a data signal. Thus, the weight of a movable part can be reduced.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk memory device. More specifically, the present invention relates to an improved configuration of a separation type head used in an optical disk memory device.

0002

2. Description of the Related Art FIG. 7 is a diagram schematically showing an optical disk memory device currently in use. The disk 1 is chucked by a spindle motor 2 and rotates at a constant speed. On the other hand, the optical head 3 that writes and reads data moves linearly in the radial direction of the disk and writes, erases, or reads data at a desired location by irradiating a laser spot onto the disk. . At this time, focusing and tracking of the laser spot on the disk is performed by two-dimensional driving of the objective lens 4.

Further, FIGS. 8 and 9 show the optical head 3 of FIG. 7 having a separate structure, in which only the tip of the head where the objective lens 4 is located is moved. That is, the optical path of the light emitted from the fixed optical section 5 is changed upward by the flip-up mirror 11 attached to the carriage 6, and then the light is focused onto the disk 1 by the objective lens 4. A moving coil 7 is attached to the carriage 6, and a portion of this coil is inserted into a gap in the magnetic circuit 8. Therefore, a force is applied to the coil in the horizontal direction according to Fleming's left-hand rule, and the carriage 6 is moved in the radial direction of the disk. The linear movement of the carriage 6 is restricted by a slide shaft 9 and a bearing 10. In this case, focusing is performed by vertically moving the objective lens 4, and tracking is performed by shaking a galvanometer mirror (not shown) on the fixed head 5 side, or by moving the aforementioned objective lens 4 in the horizontal direction, that is, by moving the objective lens 4 in the horizontal direction. This is achieved by driving the lens two-dimensionally.

0004

[Problems to be Solved by the Invention] Efforts have been made to reduce the weight of the movable parts to near zero and to increase the generated force in order to reduce the access speed in such heads for optical memory devices. Since the weight of the movable part cannot be completely reduced to zero, and there is also a limit to the size of the magnetic circuit, there is a limit to the reduction in head access speed. Incidentally, the value can be predicted to be about 20 ms. Also,
As computers become smaller, thinner, and portable, such external memory devices are required to be smaller, thinner, and lower in cost, and improvements in the structure of the head portion play an important role.

The present invention addresses these demands by 1) providing a means for reducing the weight of moving parts as much as possible, 2) providing a head configuration that can contribute to making the device smaller and thinner, and 3) The purpose is to reduce the number of parts in the head and reduce costs.

[0006]

[Means for Solving the Problems] The present invention provides a semiconductor laser and its collimating optical system, an error detection optical system that detects a focus error signal and a track error signal from disk reflected light, and a data signal detection optical system. , a fixed optical system having an optical deflection section consisting of a movable mirror that converts the direction of the collimated light from the semiconductor laser and finely controls the tracking direction; , an optical disk memory device characterized by having an optical head composed of various parts of an aspherical mirror that can move finely in the focus direction and finely and coarsely in the radial direction of the disk, further comprising: 1) an aspherical mirror; When viewed from the optical axis on the incident side, the reflecting surface is circular; and 2) the length of the effective diameter of the mirror element having an aspherical surface is made smaller than the beam diameter of the incident laser beam, and the mirror element is 3) The length of the effective diameter of the mirror element having an aspherical surface is made smaller than the beam diameter of the incident laser beam, and the mirror element is This optical disk memory device is characterized by being movable within the laser beam in a direction substantially perpendicular to the optical axis and in a direction parallel to the optical axis.

[0007]

【Example】

(Embodiment 1) FIG. 1 is a schematic diagram showing the configuration of an optical disk memory device according to the present invention. The light emitted from the semiconductor laser 12 is converted into parallel light by a collimator 13, passes through a beam splitter 14, and reaches a galvanometer mirror 15. The galvanometer mirror 15 has a mirror surface that rotates with respect to the optical axis, converting the angle of the laser beam by 90 degrees and at the same time creating a change in the inclination of the optical axis necessary for tracking. The laser whose direction is changed by the galvanometer passes through the afocal lens 16 and reaches the aspherical mirror 18 . The aspherical mirror 18 converts the optical path of the laser beam by 90 degrees toward the disk recording surface 19, and at the same time narrows down the light. Here, the afocal lens 16 suppresses the tip of the light beam whose optical path has been changed by the galvano mirror 15 so that it does not swing significantly even for a head with a long optical path length, and only suppresses the tilting of the optical axis on the aspherical mirror 18. It has a large inducing effect. That is, the spot position of the light focused by the aspherical mirror 18 is changed while minimizing the kicking of the light,
Perform tracking operations. In addition, in an actual optical disk memory device, the recording surface 19 of the disk causes surface vibration in the vertical direction as the disk rotates, so in order to obtain the minimum spot diameter, this mirror must be moved in the focus direction from beginning to end (in the vertical direction in the figure). (in the direction of the arrow) to maintain the best spot diameter. Therefore, the present invention adopts a configuration in which this aspherical mirror is directly driven in a direction perpendicular to the disk surface. Note that the afocal lens system can be omitted according to design accuracy requirements.

Now, the returning light reflected by the disk 19 follows the original optical path as it came, reaches the first beam splitter 14, and is converted to the signal detection side. Another beam splitter 20 is used in the signal detection system.
Here, the light is further divided into a focus track error signal detection system 21 and a data signal detection system 22. There are various methods of detecting error signals. For example, methods for detecting focus error signals include the astigmatism method,
These include the knife edge method and the Foucault method. In addition, there are push-pull methods, three-beam methods, etc. for detecting error signals of tracks, but these methods are essentially unrelated to the present invention, so only the names will be listed here. Data is detected by installing an analyzer on the magneto-optical disk and converting the direction of rotation of the plane of polarization into the intensity of light. In addition, phase change disk,
Alternatively, since the intensity of light changes depending on the presence or absence of data in a ROM type disk, this change in light may be detected directly with a photodiode. Furthermore, in the above description, the focus track detection system and the data detection system are separated, but a configuration in which they are used in common is also possible.

In the present invention, an optical head is constructed from the above-mentioned elements, and in particular, in order to meet high-speed access of the head, the part before the afocal lens 16 is made into a fixed optical part,
It is preferable to form a separate head by fixing it to the chassis of the drive and using only the aspherical mirror 18 as the movable part. In this case, the movable part is configured as in the conventional example, that is, as shown in FIG. 8, it is configured as a linear motor that moves linearly in the radial direction of the disk, and the aspherical mirror 18 is placed on the carriage 6. Therefore, the tracking operation of the device is a two-stage servo system in which a linear motor handles coarse movements that require high speed, and a galvanometer mirror handles fine movements that require precision. The above embodiment was explained as a separate configuration, but
The present invention does not cause any problem even if the above-mentioned head is integrated.

(Embodiment 2) An embodiment of the present invention is shown in FIG. A three-dimensional representation is as shown in FIG. 3, and the characteristic is that the reflective surface is an aspherical surface. This also includes the case of a rotating body whose cross-sectional shape including the optical axis is an aspherical surface, and the case where the cross-sections in both the X and Y directions are different aspherical surfaces. Furthermore,
When looking at the mirror from the incident side, it is best to have a circular shape. This may be because the aperture on the light source side is circular, but when the light is focused, it kicks out excess light and makes the spot shape a beautiful circle. As shown by the dotted line in FIG. 2, if there is no disk substrate 24, the light will ideally be focused at a focal point 25 with no aberration. However, in an optical memory device, after passing through the optical disk 24 with a substrate thickness of 1.2 mm, the recording surface 19
Since the light must be focused at , the light is refracted as it travels through the substrate, as shown by the solid line, and the focus position 26 moves to the rear of the original focal point 25 . Furthermore, in the process of condensing light, unlike a 45-degree plane mirror, the light rays converging at the condensing positions on the left and right sides of the figure are considered to be asymmetrically incident on the substrate, so that aberrations will also occur in the condensed spot. Therefore, when designing an aspherical mirror, it is necessary to take into account the suppression of aberrations caused by the disk substrate.

(Embodiment 3) FIG. 4 is a model diagram in which an aspherical mirror according to the present invention is used as a movable end portion of a separation type head. The aspherical mirror 18 is placed on the carriage 6 and can be moved horizontally at high speed by the force of a linear motor (not shown). In addition, an electromagnetic or piezoelectric drive source 27 is installed in the vertical direction, and the mirror portion is loosely coupled to the carriage 6 by an elastic body 28, so that the focus that occurs due to surface wobbling of the disk can be controlled. It moves up and down according to the signal and focuses correctly on the disk recording surface. At this time, the diameter of the incident light is preferably set larger than the pupil of the aspherical mirror. FIG. 5 is a diagram showing the reason. That is, when the pupil of the aspherical mirror 18 is made larger than the diameter of the incident light, when the reflection position of the laser beam changes due to focusing (dotted line and solid line), the angle of the light beam incident on the disk substrate changes as shown in the figure. , the aberration of the spot changes each time, and there are cases where it is not possible to narrow down the aperture sufficiently. Therefore, in order to suppress this, the above-mentioned method is used in which the conditions do not change even if the aspherical mirror moves with respect to the light beam, and the relationship of (effective diameter of mirror element) + (amount of movement) < (diameter of incident laser beam) holds. I understand that is the best. In addition, as can be seen from the previous explanation, the light reflected by the aspherical surface tries to focus asymmetrically when it enters the substrate, so tracking using the same galvano mirror as in the conventional example may cause even greater aberrations. be. Therefore, in the separation type head according to the present invention, it is ideal that all tracking control be performed using only the linear motor. However, if this is not possible, as an alternative to precise tracking control using a galvano mirror, it would be better to configure a two-dimensional actuator that precisely drives the aspherical mirror also in the horizontal direction, as shown in FIG. One example is illustrated as a voice coil motor type actuator shown in FIG. This method is also effective when the present invention is applied to an integrated head.

(Embodiment 4) A parabolic rotating body was selected as the aspherical surface, and the equation of the parabolic surface was defined as follows.

[0013]

[Math. 1] Z=. 5C (X2+Y2) The surface used as a mirror is an off-axis surface that is off the axis of rotation. At this time, the laser beam system is 4 mm, the laser wavelength is 780 nm, the disk substrate thickness is 1.2 mm, the material is polycarbonate, and the working distance from the mirror end point is 1. A good spot diameter was obtained under the conditions of 28 mm and curvature C=0.291.

[0014]

As described above, the present invention uses an aspherical mirror to perform the functions of turning the laser 90 degrees and narrowing down the laser, which were conventionally performed using a 45 degree flip-up mirror and an objective lens, as shown in FIG. This was made possible with a single element. Further, although a paraboloid was used as a specific example in the above embodiment, the definition of an aspheric surface is not limited to this, and many variations are possible. In devices using such aspherical mirrors, the thickness of the head can be reduced by several millimeters by the amount of the objective lens, which has a significant effect in making the device thinner and smaller, and the weight of the movable parts can be reduced to increase access speed and improve linearity. At the same time, it is possible to downsize the motor. Furthermore, since the number of parts is reduced, the cost of the device can also be reduced. As a result of the above, the present invention provides a small, thin, and low-cost optical memory drive that is particularly suitable for external memory for portable personal computers.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of an optical memory device according to the present invention.

FIG. 2 is a diagram explaining the principle of an embodiment according to the present invention.

FIG. 3 is a perspective view of an embodiment of the present invention.

FIG. 4 is an embodiment of a separate head movable part according to the present invention.

FIG. 5 is a diagram explaining the principle of another embodiment of the present invention.

FIG. 6 is another embodiment of a separate head movable part according to the present invention.

FIG. 7 is a model diagram of a conventional example using an integrated head.

FIG. 8 is a conventional diagram of a separation type head.

FIG. 9 is a cross-sectional view of the movable part of a conventional separation type head.

[Explanation of symbols]

1 Optical disk 2 Spindle motor 3 Optical head 4 Objective lens 5 Fixed optical system 6 Carriage 7 Linear motor coil 8 Linear motor magnetic circuit 9 Slide shaft 10 Bearing 11 Flip-up mirror 12 Semiconductor laser 13 Collimator lens 14 Beam splitter 15 Galvano mirror 16 Afocal Lens 17 Missing number 18 Aspheric mirror 19 Disk recording surface 20 Beam splitter 21 Focus/track error detection system 22
Data detection system 23 Aspherical surface 24 Optical disk substrate 25 Original focal point 26 Focus position 27 Electromagnetic or piezoelectric drive source 28 Elastic body

Claims (4)

[Claims] 1. A semiconductor laser and its collimating optical system, an error detection optical system that detects a focus error signal and a tracking error signal from disk reflected light, a data signal detection optical system, and further a collimator from the semiconductor laser. A fixed optical system has a light deflection section consisting of a movable mirror that converts the direction of the light and performs fine movement control in the tracking direction; An optical disk memory device characterized by having an optical head composed of various parts of an aspherical mirror that can be moved slightly in the radial direction of the disk. 2. The optical disk memory device according to claim 1, wherein the aspherical mirror has a circular reflecting surface when viewed from the incident side optical axis. 3. An actuator in which the length of the effective diameter of a mirror element having an aspherical surface is made smaller than the beam diameter of an incident laser beam, and the mirror element is movable within the laser beam in a direction substantially perpendicular to the optical axis. The optical disc memory device according to claim 1, further comprising: 4. The length of the effective diameter of the mirror element having an aspherical surface is made smaller than the beam diameter of the incident laser beam, and the mirror element is arranged in the laser beam in a direction substantially perpendicular to and parallel to the optical axis. The optical disc memory device according to claim 1, further comprising a movable actuator.