The present invention relates to an objective lens actuator, for fitting a focus position of an objective lens upon an target track on a recording surface of an optical disc, with driving the objective lens into a focusing direction and a tracking direction, so as to conduct reproducing or recording of information, which is recorded on the recording surface of the optical disc, and also a disc apparatus applying the same therein.
With the disc apparatus for recording information onto a disc-like information recording medium, or for reproducing the information recording thereon, an improvement of data transfer rate is achieved by rotating the optical disc with high speed. In the disc apparatus is mounted an objective lens actuator for driving the objective lens into the focusing direction and the tracking direction, so as to record and reproduce the information, correctly, with following a track on the optical disc.
In general, such objective lens actuator is constructed with a magnetic circuit, including a yoke and a permanent magnet, a moving portion including an objective lens and a driving coil attached therewith, a stationary or fixed portion for holding this moving portion thereon, and supporting members for elastically supporting the moving portion, which is connected with the fixed portion. When current flows through a focusing coil, within the magnetic field produced by the magnetic circuit including the yoke and the permanent magnet, then an electro-magnetic force is generated, and thereby the moving portion is driven into the focusing direction. In the similar manner, when current flows through a tracking coil, within the magnetic field produced by the magnetic circuit including the yoke and the permanent magnet, then an electro-magnetic force is generated, and thereby the moving portion is driven into the tracking direction.
For such the objective lens actuator, the following three (3) characteristics are required, mainly. First of all, for achieving a high accuracy positioning control while suppressing deflections due to disturbances, such as, wobbling and/or eccentricity of the disc, etc., it is necessary to increase driving sensitivity to be high. Next, for increasing control band fitting to high-speed of rotation number of the optical disc, it is necessary to bring amplitude to be small, at high-order resonance frequency of an elastic deformation mode of the moving portion. And, for dealing with high density while suppressing an aberration, which will be a cause of signal deterioration, it is necessary to reduce the tilt of the objective lens.
Among of those, in particular, relating to the driving sensitivity, there is already known an objective lens actuator, wherein a magnet is constructed with a first wide-width magnetic pole located at a center along the tracking direction, and second magnetic poles on both sides thereof, putting the first magnetic pole between them, and two (2) sides of the tracking coils provided in plural numbers thereof, on an inner side and an outer side thereof, are attached, opposing to the first magnetic pole and the second magnetic pole, respectively, thereby winding one (1) piece of the focusing coil around a peripheral side surface of the moving portion, and also a boundary portion between the magnetic poles of the magnet is disposed outside than the both side edges of the yoke (an example shown in the following Patent Document 1). With this, in the focusing direction, it is possible to increase a number of magnetic fluxes crossing the focusing coil, and also in the tracking direction, it is possible to generate driving forces on both sides, i.e., an inner side and an outer side of each tracking coil; thereby achieving an improvement of the driving sensitivity.
[Patent Document 1] Japanese Patent Laying-Open No. 2005-38496 (2005) (Claim 1 and FIG. 2).
In relation to the high-order resonance of the objective lens actuator, there is a bending vibration of a lens holder. Within such the magnetic circuit, i.e., widening the width of the inside magnet while narrowing the width of the outside magnet, as is in the prior art mentioned above, since a main electro-magnetic force in the focusing direction is applied on a loop of vibration when the bending vibration is generated on the lens holder, there is a possibility of exciting the vibration, and thereby enlarging the amplitude thereof.
An object of the present invention is to provide an objective lens actuator, for suppressing the amplitude of vibration of the objective lens, in relation to the bending vibration of the lens holder, and further for suppressing a tilt of a lens, in relation to an operation tilt, as well as, to provide a disc apparatus for enabling high-density and high-speed in recording of information onto the disc.
The object mentioned above, according to the present invention, is accomplished by an objective lens actuator, comprising: a lens holder for attaching an objective lens thereon; a piece of focusing coil, being wound along side surface of said lens holder around said objective lens; and three magnets, being disposed opposing to two surfaces each having a normal line perpendicular to both a focusing direction and a tracking direction, among four side surfaces of said lens holder, wherein said three magnets are aligned, continuously, along the tracking direction, differing a polarity thereof from one another, and width of the magnets on both outsides is wider than width of the magnet inside.
And, the object mentioned above is accomplished by the objective lens actuator, as described in the above, wherein among said three magnets, the width of the magnets on both outsides is 1.3 to 4.3 times wider than the width of the magnet inside.
Also, according to the present invention, the object mentioned above is accomplished by an objective lens actuator, comprising: a lens holder for attaching an objective lens thereon; a piece of focusing coil, being wound along side surface of said lens holder around said objective lens; and one magnet, being disposed opposing to two surfaces each having a normal line perpendicular to both a focusing direction and a tracking direction, among four side surfaces of said lens holder, wherein said magnet is magnetized into three poles along the tracking direction, and among said three poles, width of the poles on both outsides is wider than width of the pole inside.
And, the object mentioned above, is accomplished by the objective lens actuator, as described in the above, wherein among said three poles, the width of the poles on both outsides is 1.3 to 4.3 times wider than the width of the pole inside.
According to the present invention mentioned above, it is possible to provide the objective lens actuator for suppressing the amplitude of vibration of the objective lens, in relation to the bending vibration of the lens holder, and further for suppressing the tilt of the lens, in relation to the operation tilt, as well as, to provide the disc apparatus for enabling the high-density and the high-speed in recording of information onto the disc.
Those and other objects, features and advantages of the present invention will become more readily apparent from the following detailed description when taken in conjunction with the accompanying drawings wherein:
Hereinafter, embodiments according to the present invention will be fully explained by referring to the attached drawings.
In this
An end of the wire-like supporting member 734 is fixed in the vicinity of an end surface of the fixed portion 733, while the other end thereof is fixed to projecting portions, which are provided on both ends of the lens holder 732 with using a solder, etc. The objective lens 731 is attached on an upper surface of the lens holder 732. Also, upon two (2) side surfaces of the lens holder 732 in the x-axis direction, putting the objective lens 731 between them, there are attached or adhered tracking coils not shown in the figure, and further a focusing coil 738 is wound along a side surface of the lens holder 732. Herein, the objective lens 731, the lens holder 732 and the focusing coil 738 build up the moving portion. Thus, this moving portion is moved with respect to the fixed portion 733.
In such the objective lens actuator, the lens holder 732 has a box-like shape of a rectangular parallelepiped, being opened on the lower surface thereof. The bending vibration of such the lens holder 732 is in a vibration mode of elastically deforming the lens holder as is shown by broken lines in
For a guideline mentioned above, the feature of the present embodiment lies in that, as is shown in
An effect is shown in
The an upper limit value “Alim.” is a value, which is caused due to a necessity of suppressing the amplitude in the high-order resonance frequencies to be equal or lower than the amplitude at 10 kHz, for the purpose of increasing the control band. As is shown in the graph, it is possible to reduce the increasing amount “A” of amplitude of the objective lens 731 due to the bending vibration when the ratio between “Lp” and “Lc” is larger than one (1), comparing to that when the ratio between “Lp” and “Lc” is smaller than one (1). Further, in case when the ratio between “Lp” and “Lc” is around two (2), it is possible to bring the point of action of the main electro-magnetic force “F” acting upon the focusing coil 738 to coincide with the position of the node of the bending vibration; therefore, it is possible to lower the increasing amount “A” of amplitude of the objective lens 731 due to the bending vibration, down to nearly zero (0). Herein, the region where the increasing amount “A” of amplitude does not exceed the upper limit value “Alim.” lies between 1.3 to 4.3 of the ratio between Lp” and “Lc”.
Next, explanation will be made on other one effect of the present invention, i.e., reducing the operation tilt.
However, with the present embodiment, also the negative component “f” in the z-axis direction acts at the position opposing to the inside magnet 736c having narrow width, in addition to the positive components “F” in the z-axis direction acting at the respective positions opposing to the magnets 736p having wide width on both outsides of the focusing coil 738. For this reason, moment of rotation “Mf” due to the secondary negative electro-magnetic force “f” in the z-axis direction acting at an inside of the focusing coil 738 cancels unbalance “MF” of moment of rotation due to the main positive electro-magnetic forces “F” in the z-axis direction acting on both outsides of the focusing coil 738, and therefore there is hardly generated a moment for rotating the moving portion. In this manner, because of the feature of the present embodiment, it is possible to reduce the moment of rotation generating on the focusing coil 738, even when the objective lens moves, and therefore it is also possible to reduce the tilt of the objective lens 731 down to be small.
However, in the present embodiment, as is shown in
First of all, explanation will be made on the constituent elements of the unit mechanism 6. The spindle motor 5 is a motor for rotating a disc 3, on which a turntable 2 is provided for loading the disc 3 thereon, with lessening the wobbling and/or the eccentricity of the disc 3. The feed motor 4 is a motor for moving the optical head 7 to a desired position in the radius direction of the disc along a guide bar as a reference. The mechanical chassis holds the parts mentioned above thereon, and is attached on a main body of the disc apparatus 1 through an insulator, which is made of an elastic material. Next, explanation will be made on the controller circuit. An objective lens driver circuit 14 receives a focusing error signal and a tracking error signal responding to light-receiving signals from the optical detector 72, and controls current to be outputted into the focusing coil 738 and the tracking coil 737.
The feed motor driver circuit 10 conducts a feed control of the optical head 7 upon basis of the signals mentioned above, i.e., such a control that the optical head 7 is always located at an appropriate position. The spindle motor driver circuit 15 conducts a rotation control of the spindle motor. The laser driver circuit 74 receives the information as an irradiation pattern of laser beam, and controls a power of the laser beam, which the laser diode 71 irradiates. Because of using the optical head 7, mounting the objective lens actuator according to the present invention therein, this disc apparatus is able to conduct the recording of information onto a high-density disc or to reproduce the information of the disc 3, at high speed.
In relation to the high-order resonance of the objective lens actuator, since the main electro-magnetic force in the focusing direction is applied in the vicinity of the node of vibration even when the bending vibration is generated on the lens holder, then the vibration comes to be dormant. Accordingly, it is possible to reduce the amplitude of vibration of the objective lens.
Further, in relation to the operation tilt, even when the moving portion is moved, among those three (3) electro-magnetic forces, since the moment of rotation due to the secondary electro-magnetic force acting at the inside of the focusing coil cancels unbalance of the moment of rotation due to the main electro-magnetic forces acting on both outsides of the focusing coil, therefore the moment of rotation acting upon the focusing coil as a whole comes to be small. Accordingly, it is possible to provide the objective lens actuator having a small tilt of the objective lens.
With such present invention as was mentioned above, it is possible to provide the objective lens actuator for suppressing the amplitude at the position of the objective lens, in relation to the bending vibration of the lens holder, and further for suppressing the tilt of the objective lens, in relation to the operation tilt, and also within the disc apparatus applying the same therein, to achieve the high-density and the high-speed of the information recording onto the disc.
While we have shown and described several embodiments in accordance with our invention, it should be understood that disclosed embodiments are susceptible of changes and modifications without departing from the scope of the invention. Therefore, we do not intend to be bound by the details shown and described herein but intend to cover all such changes and modifications that fall within the ambit of the appended claims.
Number | Date | Country | Kind |
---|---|---|---|
2008-235852 | Sep 2008 | JP | national |
Number | Name | Date | Kind |
---|---|---|---|
20050013213 | Fujita | Jan 2005 | A1 |
20070147197 | Huang et al. | Jun 2007 | A1 |
20100067353 | Ochi | Mar 2010 | A1 |
Number | Date | Country |
---|---|---|
101676759 | Mar 2010 | CN |
11-191228 | Jul 1999 | JP |
2002-358675 | Dec 2002 | JP |
2005-038496 | Feb 2005 | JP |
2005-310237 | Nov 2005 | JP |
2006-004485 | Jan 2006 | JP |
2010-73225 | Apr 2010 | JP |
Number | Date | Country | |
---|---|---|---|
20100067353 A1 | Mar 2010 | US |