JP2009116959A - Objective lens driving device and disk device using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an objective lens driving device wherein drive sensitivity and a high order resonance frequency are high by improving rigidity while lightening a lens holder. <P>SOLUTION: This invention relates to the objective lens driving device which drives an objective lens converging light from a light source on a recording plane of an optical disk being a recording medium of information in the focusing direction and in the tracking direction, wherein an optical element of a quadrangle is attached to a side of the power source for the objective lens of the lens holder holding the objective lens in a state in which an optical axis direction of the optical element is almost parallel with the focusing direction and all four sides of the optical element are not made parallel to the tracking direction. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an objective lens driving device used in an optical disc apparatus for reproducing information recorded on a recording surface of an optical disc or recording information.

  In an optical disc apparatus that records information on a disc-shaped information recording medium or reproduces recorded information, the data transfer speed is improved by rotating the disc at a high speed. An optical disk apparatus is equipped with an objective lens driving apparatus that drives an objective lens in a focusing direction and a tracking direction in order to accurately record or reproduce information following a track on the optical disk.

  A general objective lens driving device includes a magnetic circuit composed of a yoke and a permanent magnet, a movable part to which an objective lens and optical elements such as a diffraction grating and a wave plate are attached, a fixed part for holding the movable part, and a fixed part. In contrast, the support member is configured to elastically support the movable portion. A focusing coil and a tracking coil are attached to the movable part. When an electric current is passed through the focusing coil, the movable part is driven in the focusing direction by an electromagnetic force generated by the action of magnetic flux from a permanent magnet attached to the yoke. Similarly, when a current is passed through the tracking coil, the movable part is driven in the tracking direction by an electromagnetic force generated by the action of magnetic flux from a permanent magnet attached to the yoke.

  Characteristics required for the objective lens driving device include good vibration characteristics and high driving sensitivity. The vibration characteristic is an index expressed as the frequency response of the objective lens with respect to the input to the focusing coil or tracking coil. Since the objective lens driving device is an elastic body composed of a plurality of parts, high-order resonance becomes a problem in a high frequency region. Since the higher-order resonance of the objective lens driving device is an elastic deformation mode of the lens holder, it is necessary to reduce the weight of the movable part and improve the rigidity of the lens holder in order to obtain good vibration characteristics.

  The driving sensitivity is an index representing the displacement of the objective lens and the magnitude of acceleration with respect to the input voltage or input current to the focusing coil or tracking coil. In order to increase the drive sensitivity so as to reliably follow the disk runout and eccentricity within the range of power allowed for the coil, it is necessary to reduce the weight of the movable part.

  On the other hand, in this lens holder, it is necessary to secure a space for mounting an optical element such as an objective lens, a diffraction grating, or a wave plate, or to make a wall thin or notch for weight reduction. Since these reduce the rigidity of the lens holder, it is necessary to appropriately design the position where the thickness is reduced and the notch is provided and the size of the notch.

  In order to solve the problem of the rigidity of the lens holder, an objective lens driving device in which an objective lens and an optical element are respectively arranged at both ends of the lens holder in the focusing direction is known (example shown in Patent Document 1 below). According to this, the optical element acts as a counterweight of the objective lens, and the center of gravity of the movable part and the driving point can be matched, so that the lens holder can be thinned and the rigidity of the lens holder is increased by the optical element. It is said that the higher order resonance frequency can be increased.

JP-A-5-342605 (Claims 1 and 2)

  A general lens holder needs to be as small as possible to reduce the weight in order to improve the high-order resonance frequency and drive sensitivity. The lower limit of the length of the tracking direction and the focusing direction of the lens holder is determined from the performance aspects such as the length and arrangement of the coils necessary for generating sufficient driving force, but the length in the jitter direction is determined from the light source. Can be reduced as long as the light beam is not blocked and does not interfere with the mirror that raises the light beam. For this reason, the side wall on the light incident side is made closer to the other side wall than the outer diameter of the lens to reduce the size, thereby reducing the weight.

  As a result, the objective lens is attached to be shifted to one side with respect to the center line in the jitter direction of the lens holder, and a part of the side wall of the lens holder has a curvature along the outer shape of the objective lens. In order to avoid interference with the apex of the optical element when a rectangular optical element is attached to such a lens holder in the same manner as in the prior art, its side is parallel to the tracking direction. Since notches are required at two locations on the side wall of the holder, the width of the notch becomes large, and the rigidity of the lens holder may be reduced.

  An object of the present invention is to provide an objective lens driving device that improves the rigidity while reducing the weight of the lens holder, and has high driving sensitivity and high-order resonance frequency wave number.

  The above object is an objective lens driving device for driving an objective lens for condensing light from a light source onto a recording surface of an optical disc as an information recording medium in a focusing direction and a tracking direction, and a lens for holding the objective lens A rectangular optical element on the light source side with respect to the objective lens of the holder, the optical axis direction of the optical element is substantially parallel to the focusing direction, and all four sides of the optical element are parallel to the tracking direction. It is achieved by installing so that it does not become.

  The above object is achieved by having a notch through which one apex of the optical element penetrates the side surface of the lens holder.

  Another object of the present invention is to provide an objective lens driving device for driving an objective lens for condensing light from a light source on a recording surface of an optical disc as an information recording medium in a focusing direction and a tracking direction, and holds the objective lens. A pentagonal optical element in which the length of one of the five sides between the objective lens of the lens holder and the light source is half or less than the length of the other four sides is an optical axis of the optical element. This is achieved by mounting so that the direction is substantially parallel to the focusing direction, only the shortest side of the optical element is substantially parallel to the tracking direction, and all other four sides are not parallel to the tracking direction. The

  According to the present invention, it is possible to minimize the width of notching the side wall of the lens holder while keeping the outer shape of the lens holder small. Thereby, since the rigidity of the lens holder can be improved while reducing the weight of the lens holder, it is possible to provide an objective lens driving device having high drive sensitivity and high-order resonance frequency wave number.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a perspective view of an objective lens driving apparatus provided with an embodiment of the present invention.
FIG. 2 is a side view of an objective lens driving apparatus according to an embodiment of the present invention.

  1 and 2, the x-axis direction is a jitter direction which is a tangential direction of an optical disk not shown, the y-axis direction is a tracking direction which is a radial direction of the optical disk, and the z-axis direction is an optical axis direction of the objective lens 731. Indicates a certain focusing direction. In addition, the direction in which the objective lens 731 approaches an optical disk not shown is defined as an upward direction and the direction in which the objective lens 731 moves away is defined as a downward direction.

  The objective lens driving device 73 includes a movable part to which the objective lens 731 and the optical element 739a are attached, a fixed part 733 that holds the movable part, a support member 734 that elastically supports the movable part with respect to the fixed part 733, and a yoke. 735 and a permanent magnet 736. One end of the wire-like support member 734 is fixed near the end surface of the fixing portion 733, and the other end is fixed to both ends of the lens holder 732 using solder or the like.

  The objective lens 731 is attached to the upper surface of the lens holder 732, and an optical element 739 a is attached to the lower side of the objective lens 731. The optical element 739a is, for example, a wave plate or a diffraction grating. A tracking coil 737 and a focusing coil 738 are attached to the lens holder 732 with the objective lens 731 therebetween.

  Here, the objective lens 731, the optical element 739a, the lens holder 732, the tracking coil 737, and the focusing coil 738 are movable parts. That is, this movable part moves with respect to the fixed part 733.

  As shown in FIG. 2, a mirror 75 is disposed on the movable portion of the objective lens driving device and below the movable portion. As shown in this figure, the side surface of the lens holder 732 is provided with a notch 732s for attaching the optical element 739a.

FIG. 3 is a cross-sectional view of the objective lens driving device 73 shown in FIG.
In FIG. 3, the lens holder 732 needs to be made as small as possible to reduce the weight in order to improve the high-order resonance frequency and the drive sensitivity. The dimensions of the lens holder 732 in the y direction and the z direction are determined from the performance aspects such as the length and arrangement of the coils 737 and 738 necessary for generating a sufficient driving force. On the other hand, the length in the x direction can be made small as long as it does not block the light beam from the semiconductor laser 71 (shown in FIG. 10) and does not interfere with the mirror 75 that raises the light beam. The weight can be reduced by moving closer to the other side wall than the outer diameter of the objective lens 731. That is, the size W of the lens holder 732 in the x direction is reduced to a range indicated by a symbol M in which one end is reduced to the aperture stop A and the other end is contracted to the outer shape of the mirror, thereby reducing the weight of the lens holder 732. With this weight reduction, both the high-order resonance frequency and the drive sensitivity of the objective lens driving device 73 can be increased.

4 is a cross-sectional view of the objective lens driving device 73 of FIG. 2 taken along the line C-C showing the first embodiment.
In FIG. 4, as described above, the objective lens 731 is brought closer to the lens holder 732 by bringing the side wall of the lens holder 732 on which the light beam is incident closer to the other side wall opposite to the side wall. On the other hand, it is mounted with a displacement in the positive direction of the x-axis. As a result, a part of the side wall of the lens holder 732 has a shape having a curvature along the objective lens 731.

  In this embodiment, a rectangular optical element 739a including the aperture stop A is tilted below the objective lens 731 of the lens holder 732 so that all four sides thereof are not parallel to the y direction. It is installed.

The effect of this embodiment will be described with reference to FIGS.
FIG. 5 is a cross-sectional view of the objective lens driving device 73 shown in FIG.
In FIG. 5, the symbol θ represents an angle formed by the y axis that is the tracking direction and a line segment that connects the center of the optical element 739 a and one vertex. Symbol L represents the width of the interference portion between the lens holder 732 and the optical element 739a when the angle formed by the y-axis that is the tracking direction and the line segment connecting the center of the optical element 739a and one vertex is θ. That is, it represents the width of the notch 732s of the lens holder 732 necessary for attaching the optical element 739a.

  FIG. 6 shows the calculation result of the relationship between θ and L when the optical element 739a is square and θ is changed from 90 degrees to 135 degrees. In the figure, θ is changed only from 90 degrees to 135 degrees. However, when θ is in the range of 45 degrees to 90 degrees, the graph is axisymmetric about the line θ = 90 degrees. In other ranges where θ is less than 45 degrees and exceeds 135 degrees, the graph is repeated in the range where θ is between 45 degrees and 135 degrees.

  When the objective lens 731 is attached to the lens holder 732 so as to be shifted in the positive direction of the x-axis as in this embodiment, the square optical element 739a including the aperture stop A is formed on the wall of the lens holder 732. Of these, only the side surface on which the objective lens 731 is biased interferes. When θ is in the range of symbol S in the figure, the lens holder 732 interferes with only one vertex of the optical element 739a, and the notch 732s provided in the lens holder 732 is provided only at one place. On the other hand, in the range of the symbol D, the lens holder 732 interferes at two vertices of the optical element 739a, and the notches 732s provided in the lens holder 732 need to be provided in two places. As a result, the width of the notch 732 s when θ is in the range of the symbol D is approximately twice the width of the notch 732 s when θ is in the range of the symbol S. That is, the width of the notch 732 s of the lens holder 732 is attached by tilting the optical element 732 a with respect to the y direction so that θ where the width of the notch 732 s does not change is in the range of about 90 ° ± 10 °. Can be minimized.

  Next, the improvement effect of the vibration characteristic by suppressing the width | variety of notch 732s is demonstrated. As an example, FIG. 9 shows a frequency response diagram of y-direction displacement in the objective lens 731 when a driving force is generated in the tracking coil 737.

  FIG. 9A is a phase curve, and FIG. 9B is an amplitude curve. The solid line and the broken line in the figure are for the cases where θ in FIG. 5 is 90 degrees and 135 degrees, respectively. The positional relationship between the lens holder 732 and the optical element 739a when θ is 90 degrees is as shown in FIG. 4 of this embodiment, and the lens holder 732 has one notch 732s for avoiding interference with the optical element 739a. Only places are provided. On the other hand, when θ is 135 degrees, two sides of the optical element 739a are parallel to the y direction, and the lens holder 732 is provided with two notches 732s for avoiding interference with the optical element 739a. Yes. At this time, the width of the notch 732 s when θ is 135 degrees is approximately twice that of the present embodiment when θ is 90 degrees. As indicated by the arrows in the figure, by reducing the width of the notch 732s, the higher-order resonance frequency can be moved to a higher range and the amplitude can also be reduced. Thereby, since the rigidity of the lens holder can be improved while reducing the weight of the lens holder, it is possible to provide an objective lens driving device having high drive sensitivity and high-order resonance frequency wave number.

FIG. 7 is a side view showing the movable portion of the objective lens driving apparatus according to the second embodiment. In order to attach the optical element 739a as in the first embodiment to the side surface of the lens holder 732 of this embodiment, FIG. There is no notch. FIG. 8 is an EE cross-sectional view of the objective lens driving device 73 of FIG.
In this second embodiment, instead of the rectangular optical element 739a used in the configuration of the first embodiment, the length of one of the five sides is less than half the length of the other four sides. A pentagonal optical element 739b is employed, and only the shortest side of the optical element 739b is mounted substantially parallel to the tracking direction, and the other four sides are not parallel to the tracking direction. Since the other configuration of the second embodiment is the same as that of the first embodiment, detailed proof is omitted. By adopting such a configuration, it is not necessary to provide a notch in the side wall of the lens holder 732, so that the effect of further improving the rigidity of the lens holder 732 can be obtained. Thereby, since the rigidity of the lens holder can be improved while reducing the weight of the lens holder, it is possible to provide an objective lens driving device with higher drive sensitivity and higher order wave number.

  Note that the pentagonal optical element 739b used in this example was created by cutting one vertex of the rectangular optical element 739a used in the first example, or created by molding. But either is fine.

FIG. 10 is a perspective view of an optical head 7 to which the objective lens driving device 73 of the present invention is applied.
In FIG. 10, an optical head 7 is a device for recording or reproducing information on a disk, and is mainly composed of three elements: an objective lens driving device 73, an optical system, and a flexible printed circuit board 74. The optical system includes a semiconductor laser 71 that emits laser light, a lens and a mirror (not shown) that branches the light from the semiconductor laser and condenses the light on the disk, and a photodetector 72 that receives the reflected light from the disk. Etc. The flexible printed circuit board 74 electrically connects the objective lens driving device 73 and the optical system to the circuit board 9 by a plurality of wiring patterns. By mounting the objective lens driving device 73 of the present invention as in this embodiment, the optical head 7 can obtain good optical characteristics up to a high frequency region.

FIG. 11 is an exploded perspective view of the disk device 1 to which the objective lens driving device 73 of the present invention is applied.
In FIG. 11, a disk device 1 mainly includes a bottom case 10, a disk tray 4 for carrying a disk as an information recording medium into or out of the apparatus, and electronic components mounted in the disk apparatus. The circuit board 9 and the like on which semiconductor components for performing drive control and signal processing are mounted. A top case 2 and a front panel 3 are provided on an upper surface and a front surface of the bottom case 10, respectively, and cover the upper surface and the front surface of the bottom case 10.

  A unitized mechanism (hereinafter referred to as a unit mechanism) 6 is attached to the disk tray 4, and its lower surface is covered with an under cover 8. The unit mechanism 6 is equipped with a spindle motor 5 for rotating the disk, an optical head 7, and an optical head feed mechanism for moving the optical head 7 in the radial direction of the disk along a guide shaft (not shown). ing. Since the optical head 7 equipped with the objective lens driving device of the present invention is used, information can be recorded on the disk or information on the disk can be reproduced at high speed.

  As described above, according to the present invention, the width at which the side wall of the lens holder is cut out can be minimized while keeping the outer shape of the lens holder small. Thereby, since the rigidity of the lens holder can be improved while reducing the weight of the lens holder, it is possible to provide an objective lens driving device having high drive sensitivity and high-order resonance frequency wave number.

It is a perspective view of the objective lens drive device which shows one Example of this invention. It is a side view of the objective lens drive device of one example of the present invention. It is sectional drawing of the objective lens drive device which shows one Example of this invention. It is sectional drawing of the objective lens drive device which shows one Example of this invention. It is explanatory drawing of the definition of the attachment angle of an optical element, and the notch width at that time. It is a calculation result of the attachment angle of an optical element, and the notch width at that time. It is a side view of the objective lens drive device of one example of the present invention. It is sectional drawing of the objective lens drive device which shows one Example of this invention. It is a frequency response diagram of tracking direction displacement of an objective lens. It is a perspective view of an optical head to which the objective lens driving device of the present invention is applied. It is a disassembled perspective view of the disc apparatus to which the objective lens drive device of the present invention is applied.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Disc apparatus 2 Top case 3 Front panel 4 Disc tray 5 Spindle motor 6 Unit mechanism 7 Optical head 8 Under cover 9 Circuit board 10 Bottom case 71 Semiconductor laser 72 Photo detector 73 Objective lens drive device 74 Flexible printed circuit board 75 Mirror 731 Objective Lens 732 Lens holder 732s Lens holder side cutout 733 Fixing portion 734 Support member 735 Yoke 736 Permanent magnet 737 Tracking coil 738 Focusing coils 739a, 739b Optical element L Notch width θ Optical element mounting angle A Aperture stop M Mirror and aperture stop Dimension limit width W inside the lens holder due to the width S inside the lens holder S Range of the mounting angle of the optical element where the lens holder and the optical element can interfere with each other D The interference between the lens holder and the optical element is 2 Range of mounting angles of optical elements that can be placed G Amplitude of tracking direction displacement of objective lens P Phase of tracking direction displacement of objective lens f Frequency

Claims (5)

An objective lens driving device for driving an objective lens for condensing light from a light source on a recording surface of an optical disc as an information recording medium in a focusing direction and a tracking direction,
A rectangular optical element is attached to the light source side of the objective lens of the lens holder that holds the objective lens so that all four sides of the optical element are not parallel to the tracking direction. An objective lens driving device. The objective lens driving device according to claim 1,
The lens holder has a notch through which one apex of the optical element penetrates on a side surface thereof. An objective lens driving device for driving an objective lens for condensing light from a light source on a recording surface of an optical disc as an information recording medium in a focusing direction and a tracking direction,
A pentagonal optical element in which the length of one of the five sides between the objective lens of the lens holder that holds the objective lens and the light source is less than half the length of the other four sides, An objective lens driving device, wherein only the shortest side of the optical element is mounted so as to be substantially parallel to the tracking direction and all the other four sides are not parallel to the tracking direction.   An optical head using the objective lens driving device according to any one of claims 1 to 3.   5. A disk device using the optical head according to claim 4.

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