Title of Invention	"AN OPTICAL PICKUP ACTUATOR AND ITS DAMPING DEVICE"
Abstract	Disclosed is a damping device of an optical pickup actuator in which a damping fluid for removing a resonance of, the actuator is put into a magnetic air gap formed between a magnet of a magnetic circuit unit of the optical pickup actuator and a lens holder facing the magnet to attach each other. The damping fluid includes ferrofluids having sub-micron sized particles in a carrier liquid.

Full Text

OPTICAL PICKUP ACTUATOR AND ITS DAMPING DEVICE BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a damping device of-an. 5 optical pickup actuator which is mounted at a compact disk player, etc. and detects recorded signals of a disk, and particularly to a damping device of an optical pickup actuator which reduces noticeably a resonance and is easily mounted 2. Description of the Related Art 10 Conventionally, an optical pickup actuator is widely used in a variety of devices including CD players, laser disk players, CD-ROM drives, DVD-ROM drives, etc. Referring to FIGs. 1 and 2, the structure of an optical pickup actuator assembly is roughly explained. At the surface 15 of a main body 15 which is integrally molded, a pair of yokes 6 and 6' are fixed facing each other. At the other surface of the main body 15, a printed circuit board (PCB) 11 is mounted. At the yokes 6 and 6', protrusions 6a and 6b a molded, a pair of yokes 6 and 6f are fixed facing each other. At the yokes 20 6 and 6', protrusions 6a, 6b and 6b' are formed respectively. Moreover, at both sides on the surface of a lens holder 2 which is an integral bobbin/carrier assembly, through holes 12a and 12b are formed. Between the through holes 12a and 12b, an objective lens 1 is inserted and fixed. Moreover, a 25 focusing coil 3 binds along the lateral surface of the lens holder 2. A tracking coil 4 binds both ends of the lens holder 2 perpendicularly to the focusing coil 3. In the actuator having the above-described structure, the protrusions 6b and 6b' are inserted in the through holes 12a 30 and 12b respectively. At the protrusions 6a and 6a' facing the tracking coil 4, magnets 5 and 5' are fixed. Moreover, the actuator is elastically fixed to a wire holder 8 by four wires 7 each of one end is fixed to a PCB 13 and maintains a predetermined magnetic air gap with magnets 5 and 5'. 2 When the disk is arrived, the lens holder 2 minutely moved in the focusing or tracking direction. At this time, the object lens 1 transmits laser beam and the actuator reads the signals stored in the disk. 5 In the optical pickup actuator, when the actuator is subjected to a physical impact from the outside or carries out the focusing or tracking operation, the actuator can rise a mechanical resonance, which can be stabilized in certain seconds or minutes. 10 Accordingly, the wire 7 is used as a damping device, order to reduce the movement of the lens holder 2 in vertical and horizontal directions, which is fixed to the wirejnolder 8 at the one end thereof. Conventionally, referring to FIG. 2, to obtain a damping 15 effect on a mechanical resonance of the wire 7, a damper bond 10 made of silicon lubber of gel state is entered inside of the wire holder 8 and the wire 7 is moved in the vertical and horizontal directions through the damper bond 10. However, even in the case of using the damper bond 10, 20 there is a problem in that the damper bond 10 cannot reduce the resonance magnitude generated due to the physical impact from the outside or its focusing and tracking operation. As shown in FIG. 4 A, the actuator has an undesired vibration characteristic because of the generation of the 25 mechanical resonance having the resonance magnitude Qo at a resonance frequency f0/ as shown in FIG. 4B, there is a disadvantage in that the actuator has an increase of the setting time thereof. As the vibration characteristic is worse and the setting 30 time is increased, the mechanical resonance can cause errors in reading information from the disk, particularly in high speed CD-ROM and DVD-ROM drives. Moreover, in the case of increasing the amount of the damper bond 10 to reduce the resonance magnitude Qo, the 35 sensitivity is rather declined. In the case of using the damper bond, it is difficult to put the damper bond 10 into wire holder 8. In addition, since 2A It requires a process of irradiating the ultraviolet and a separate inlet 9 for introducing the damper bond into the wire holder 8 is formed at the wire holder 8, the process becomes complicated. SUMMARY OF THE INVENTION Therefore, it is an object of the present invention to provide a damping device of an optical pickup actuator, wherein a damping fluid for minimizing a resonance of the actuator is put into a gap formed between a magnet of a magnetic circuit unit of said optical pickup actuator and a lens holder facing said magnet, said damping fluid being ferro fluids having sub-micron sized particles in a carrier liquid. Preferably, the magnetic particles include FesO4. Moreover,the ferro fluid has a predetermined viscosity. According to further another aspect of the present invention, there is provided an optical pickup actuator comprising a lens holder which is mounted on a body to be movable, and on which a tracking coil and a focusing coil are wound to be perpendicular to each other, for supporting an objective lens; magnets which are fixed on said body to be respectively opposite to said focusing coil and said tracking coil of said lens holder; and a damping fluid which is disposed between said magnets and said lens holder. _ "3 _ BRIEF DESCRIPTION OF THE DRAWINGS A more complete appreciation of the present invention, and many of the attendant advantages thereof, will become readily apparent as the same becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings in which like reference symbols indicate the same or similar components, wherein: FIG.l is a perspective view illustrating the structure of a conventional optical pickup actuator; FIG.2 is a sectional view illustrating a damping device of the optical pickup actuator shown in FIG.l; FIG.3 is a sectional view illustrating a damping device of an optical pickup actuator according to the present invention; -4- FIG. 4A is a view illustrating the characteristic of an actuator of a conventional damping device; FIG. 4B is a graph showing a process of stabilization of the actuator in which the damping device according to the 5 conventional art is used; FIGs. 5A and 5B are views illustrating the characteristic of an actuator according to a damping device of the present invention; FIGs. 6A and 6B are views illustrating the characteristic 10 of an actuator employing a damper bond to the damping device of the present invention; and FIG. 7 is a graph showing a process of stabilization of the actuator in which the damping device according to the present invention is used. 15 DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The objects, characteristics and advantages of the above-described invention will be more clearly understood through the preferable embodiments referring to the attached drawings. Referring to FIG. 3, in magnetic air gaps between each 20 magnet 5 and 5' and both ends of a lens holder 2 on which a focusing coil 3 and a tracking coil 4 are wound, a damping fluid, i.e., a ferro fluid 20 is applied. The ferro fluid 20j' is mainly applied to the magnets 5 and 5' . A bobbin (not! shown) on which tracking coil 4 is wound is divided into two 25 parts so that the ferro fluid 20 comes into substantially contact with the focusing coil 3 and a part of the lens holder/ 2 through the bobbin 2. Preferably, the ferro fluid 20 is further provided for inner surfaces of inner yoke protrusion 6b and 6b1 in thruhole 30 12a and 12b. Furthermore, the wires 7 are directly fixed to a wire holder 8 without the use of the damper bond which is applied to the conventional art. According to the above embodiment of the present 35 invention, it is understood that only when the magnets 5 and 5' are attached to the outer yoke protrusions 6a and 6a1, the 5 ferro fluid 20 is provided for the outer yoke protrusions 6a and 6a'. However, in the case that the lens holder 2 is disposed between the outer yoke protrusions 6a and 6a1 and the magnets 5 and 5' are attached to the inner yoke protrusions 5 6b and 6a', the ferro fluid 20 is provided to the inner yoke protrusions 6b and 6a'. It is important to apply damping material to the magnets respectively opposing to tracking coil. Accordingly, in the case that the optical pickup actuator- 10 do not have the yoke protrusions which the lens holder 2 is inserted between and the magnets 5 and 5' are attached'vto the protrusions projecting from a body 15 of the actuator, the damping material is applied to the magnets, thereby obtaining the desired damping effect. 15 on the other hand, the ferro fluid 20 is a colloids suspensions in which magnetic particles are very sufficiently scattered in the fluid. Even in the case that a large centrifugal force or magnetic force are applied to the ferro fluid 20, since the magnetic particles are not separated from 20 the fluid, it is possible to accurately control the position of the optical pickup actuator. As the magnetic particle, Fe3O4 can be used. The ferro fluid has a predetermined viscosity. With reference to the damping effect, the viscosity of the ferro fluid causes .the movable element, for example the 25 lens holder to be subjected to a mechanical resistance. According to the damping device of the present invention having the aforesaid structure, even though the lens holder is moved due to the impact from the outside or during the its operation in the focusing direction or the tracking direction 30 and then stops, the lens holder vibrates in vertical and horizontal directions. At this time, by the damping operation of the ferro fluid 20, it is possible to reduce the setting time and to improve the vibration characteristic of the actuator, resulting in reducing the access time of the 35 actuator. . With reference to a characteristic test of the optical pickup actuator to which the damping device according to the 6 present invention is applied, as shown in FIGs. 5A and 5B, there is an advantage in that the resonance magnitude Qo is reduced to such an ideal value, i.e. 0 (zero) that the resonance cannot be generated at the resonance frequency f0 5 which is generated during the operation of focusing or tracking. As shown in FIG. 7, furthermore, it can be understood that the setting time can be remarkably reduced. -4 ^^ ~~* ? / material for the optical pickup actuator it is possible to, 10 perform only the operation of filling the gap formed between the yokes and the magnet exposed outside with the ferro fluid without the operation of introducing the damper bond, the-process is not complicated. Since by using the ferro fluid, the heat generated from" 15 a lens holder is transmitted to the yokes and then radiaLeu. to the outside, it can prevent the lens holder aridV tft'e objective lens from being melted due to the rise of heat in the focusing coil and the tracking coil. In addition, the vibrational characteristic is noticeably 20 improved by removing the minor vibration of the wire which supports the lens holder and a centering effect is realized by the characteristic of the ferro fluid itself. In another embodiment, the conventional damper bond can be applied to the damping device of the present invention, as 25 shown in FIGs. 6A and 6B. Here, when the ferro fluid is used for the actuator to which the damper bond is applied, the resonance magnitude Qo is greatly reduced at the resonance frequency f0 and the damping effect which is noticeably improved can be obtained. 30 While there have been illustrated and described what are considered to be preferred embodiments of the present invention, it will be understood by those skilled in the art that various changes and modifications may be made and equivalents may be substituted for elements thereof without 35 departing from the true scope of the present invention. 7 We Claim : 1. A damping device of an optical pickup actuator, wherein a damping fluid for minimizing a resonance of the actuator is put into a gap formed between a magnet of a magnetic circuit unit of said optical pickup actuator and a lens holder facing said magnet, said damping fluid being ferro fluids having sub-micron sized particles in a carrier liquid. 2. The damping device as claimed in claim 1, wherein said magnetic particles comprise FesO4. 3. The damping device as claimed in claim 1, wherein said ferro fluid has a predetermined viscosity. 4 . An optical pickup actuator comprising : a lens holder which is mounted on a body to be movable, and on which a tracking coil and a focusing coil are wound to be perpendicular to each other, for supporting an objective lens; magnets which are fixed on said body to be respectively opposite to said focusing coil and said tracking coil of said lens holder; and a damping fluid which is disposed between said magnets and said lens holder. -8- 5. The optical pickup actuator as claimed in claim 4, wherein said damping fluid comprises ferro fluids. 6. The optical pickup actuator as claimed in claim 5, wherein sub-micron sized particles are scattered in said ferro fluid. 7. The optical pickup actuator as claimed in claim 5, wherein said magnetic particles comprise FesOi. 8. The optical pickup actuator as claimed in claim 5, wherein said ferro fluid has a predetermined viscosity. 9. The optical actuator as claimed in claim 4, wherein said lens holder is fixed by wires to said body. 10. An optical pickup actuator comprising : yoke which is formed integrally on a body; pairs of first and second yokes which are projected from a surface of said yoke to be spaced apart from each other; a lends holder which is disposed between the outer second yokes opposite to each other to be movable and on which a focusing coil and a tracking coil are wound to be perpendicular to each other, for supporting an objective lens; ¦9- magnets which are attached to the inner first yokes opposite to each other to face said lens holder; wires which fix said lens holder to a wire holder resiliently and apply an electric signal to said focusing coil and said tracking coil; and a damping fluid which is applied to said magnets in a gap between said magnets and said lens holder opposite to said magnets. 11. An optical pickup actuator comprising : yoke which is formed integrally on a body; pairs of first and second yokes which are projected from a surface of said yoke to be spaced apart from each other; a lens holder which is disposed between the inner first yokes opposite to each other to be movable and on which a focusing coil and a tracking coil are wound to be perpendicular to each other, for supporting an objective lens; magnets which are attached to the outer second yokes opposite to each other to face said lens holder; wires which fix said lens holder to a wire holder resiliently and apply an electric signal to said focusing coil and said tracking coil; and a damping fluid which is applied to said magnets in a gap between said magnets and said lens holder opposite to said magnets. -10- 12. A damping device of an optical pickup actuator, substantially as herein described, particularly with reference to the accompanying drawings. 13. An optical pickup actuator, substantially as herein described, particularly with reference to the accompanying drawings. Disclosed is a damping device of an optical pickup actuator in which a damping fluid for removing a resonance of, the actuator is put into a magnetic air gap formed between a magnet of a magnetic circuit unit of the optical pickup actuator and a lens holder facing the magnet to attach each other. The damping fluid includes ferrofluids having sub-micron sized particles in a carrier liquid.

Documents:

00793-cal-1998 abstract.pdf

00793-cal-1998 claims.pdf

00793-cal-1998 correspondence.pdf

00793-cal-1998 description (complete).pdf

00793-cal-1998 drawings.pdf

00793-cal-1998 form-1.pdf

00793-cal-1998 form-18.pdf

00793-cal-1998 form-2.pdf

00793-cal-1998 form-3.pdf

00793-cal-1998 form-5.pdf

00793-cal-1998 g.p.a.pdf

00793-cal-1998 letters patent.pdf

00793-cal-1998 priority document others.pdf

00793-cal-1998 priority document.pdf