CN1806280A - Optical pick-up actuator and method for assembling an optical pick-up actuator - Google Patents

Abstract

The method of assembling a pick-up actuator includes assembling a lens holder assembly to a base unit creating a magnetic gap between complementary electro-magnetic components of the lens holder assembly and the base unit, disposing a quantity of a volatile magnetic fluid or a low viscosity oil-based magnetic fluid into the magnetic gap created between complementary electro-magnetic components of a lens holder assembly and a base unit, fixing resilient support members between the lens holder assembly and the base unit. The optical pick-up actuator includes a lens holder assembly, a base unit, resilient support members connecting the lens holder assembly and the base unit, an electro-magnetic drive system, and a volatile magnetic fluid or a low viscosity oil-based magnetic fluid.

Description

Optical disc reading head actuator and its assembly method

Background of the invention

1. Technical field

The present invention relates generally to optical pickup actuator apparatus and methods, and more particularly to optical pickup actuators and methods of assembling optical pickup actuators using a fluid centering mechanism.

2. Background technology

A traditional optical disc pickup actuator usually includes an optical lens that focuses the light spot of the light beam to the center of the signal track of the optical disc. The optical pickup actuator operates to allow the optical lens to perform focusing and tracking functions. The focusing function consists of moving the optical lens up and down so that the light spot of the optical lens beam is within the range of the depth of focus on the signal track of the optical disc. The tracking function consists of moving the optics left and right so that the spot of the optics beam follows the center of the signal track. Therefore, by moving the optical lens up/down and left/right, the optical pickup actuator can follow the center of the signal track of the optical disc.

To achieve this up/down and left/right movement, a conventional optical pickup unit uses an electric current flowing through a coil and a magnetic field between the magnets. Generally, the optical pickup actuator has a base unit and a lens holder elastically connected to the base unit. The lens holder includes an objective lens mounted thereon, at least one opening in the lens holder, a resilient support member connected at one end to opposite sides of the lens holder and at the other end to the base unit, a focusing lens attached to the lens holder and wound parallel to the plane of the lens holder coil, and a tracking coil perpendicular to the focusing coil. A pair of magnets and yokes are attached to the base unit in close proximity to the focusing and tracking coils to create a magnetic gap between the magnets and the lens mount. A yoke is used to prevent flux leakage from behind the magnet. Controlling the current flow through the focusing and tracking coils causes the light carriage to move up/down and left/right as required to properly focus the laser beam and track the disc.

As with most electronic components, the trend in optical pickup actuators is for optical pickup systems to become thinner and smaller. In order to achieve an improvement in the size of the optical disc pickup system, various structural variants have been proposed. For example, the optics and lens design schemes were redesigned to move the optics from the center of the lens mount to the protrusion and to move the focus and tracking coils and magnets from the periphery of the lens mount to the center of the lens mount. However, this configuration results in a separation of the fixed point of the elastic member from the protruding portion containing the optical lens. As a result, jerky movements are produced in high-speed mode. Because the optical lens is placed on the protruding portion of the lens holder away from the center of the lens holder, the optical lens is more prone to resonance and vibration.

While reducing the volume, it is also constantly required to improve the precision of the optical disc pickup actuator, so it is impossible to meet the allowable error requirements of the optical tilt of the aforementioned structure with the traditional assembly method. One solution is to provide an optical pick-up actuator that can perform radial tilting motions with focus and tracking motions. This function is realized by placing the focus/tilt magnetic circuit in the center part of the lens holder and the tracking magnetic circuit in the left and right parts of the lens holder. US Patent 6,744,722 (issued to Choi in 2004) is one example of such a device.

Other prior art devices have attempted to solve the vibration problem by using damping materials. US Patent 6,330,120 (Shibusaka et al., 2001) discloses an actuator for an objective lens that includes a resilient support member between a lens holder and a base member to resiliently support the lens holder relative to the base member. A pair of auxiliary damping members extend along the length direction of the elastic support member. There is a sheet of viscoelastic material between the two auxiliary damping members to interconnect the two.

US Patent 6,091,553 (Song et al., 2000) discloses a read head actuator. The read head actuator has a base member, a pair of magnetic yokes placed on the base member and spaced apart from each other by a predetermined distance, a pair of magnets respectively connected to the inside surface of the yoke, a lens holder suspended by two pairs of wire springs The objective lens mounted on the lens holder so that it moves toward the focusing and tracking directions in the space defined between the magnets, the lens holder placed on the lens holder for driving the lens holder toward the focusing and tracking direction by electromagnetic interaction with the magnets A drive coil, a pair of support plates disposed on two opposite sides of the wire spring adjacent to one of the magnets, a damping fluid applied between the pair of support plates and the two opposite sides of the magnet.

Japanese Patent 3,059,141 (issued to Shin Kyung-sik in 2000) discloses a read head actuator that uses a highly viscous magnetic fluid as the damping fluid between the base member and the lens holder.

Manufacturers of optical pickup actuators are also concerned with improving device performance. One factor that improves the performance of the read head actuator is the reduction of the magnetic gap between the focus and tracking coils and the magnet. However, current manufacturing techniques limit the size of the magnetic gap, that is, how narrow the magnetic gap can be made. This is due to the structure of the lens mount itself making it difficult to properly center the lens mount even with centering fixtures.

What is needed, therefore, is an assembly method that enables easy centering and hanging of a lens mount during manufacture. There is also a need for an assembly method that reduces the reject rate of the assembly process. There is also a need to use inexpensive assembly methods. In addition, it is also necessary to improve the assembly method of the shock absorption of the actuator of the optical disc pick-up.

Contents of the invention

The object of the present invention is to provide an optical pickup actuator and a method of manufacturing an optical pickup actuator which is cheap to implement. Another object of the present invention is to provide a method of manufacturing an optical disc pickup actuator, which positions and makes the optical lens holder and its electromagnetic drive system supplementary electromagnetic components and the supplementary electromagnetic components of the base unit during the assembly of the optical disc pickup actuator properly separated. Another object of the present invention is to provide a system to improve the vibration damping of the optical pickup actuator. It is yet another object of the present invention to provide improved heat transfer from the focus and tracking coils of the optical pickup actuator.

The present invention accomplishes these and other objects by providing a simple method and mechanism that positions and properly separates the electromagnetic drive system supplementary components of the optical lens mount from the base unit supplementary components of the electromagnetic drive system during assembly. The method comprises the steps of: adding a predetermined amount of magnetic fluid to the magnetic gap between complementary elements of the electromagnetic drive system of the optical disc pickup actuator. In one embodiment, if the electromagnetically complementary element of the lens mount is the focus and tracking coil, during assembly the magnetic fluid positions and properly separates the lens mount and focus/track coil in a magnetic gap relative to the magnet, which is Supplementary solenoid on base unit. The elastic support member connected to one end of the lens holder is then fixed to the base unit. Those skilled in the art should understand that the drive system of the optical pick-up actuator may have a magnet fixed to the lens mount and a focus/tracking coil fixed to the base unit.

The magnetic fluid can be a volatile magnetic fluid or a low viscosity oil-based magnetic fluid. Both types of magnetic fluids used in this application are colloids containing extremely fine magnetic particles with a diameter of about 10 nm, at least one surfactant modifying the surface of the magnetic particles, and a dispersion medium as main components. Ferrofluids are fluid but magnetic, and can be placed and held in place without a container.

In embodiments using a volatile magnetic fluid, the volatile magnetic fluid is only used during assembly. Once the lens mount and resilient support member are secured to the base unit or support structure of the pickup actuator, the volatile portion of the magnetic fluid is evaporated leaving a gap between the focus/tracking coils and the magnet/yoke of the pickup actuator. air gap. Magnetic particles are deposited on the surface of the magnet/yoke and focusing/tracking coils by evaporation of a volatile carrier liquid. Lubricating oil can optionally be added to the volatile magnetic fluid. In a preferred embodiment, the lubricating oil remains with the magnetic particles after evaporation of the volatile carrier fluid to form a thin layer of magnetic fluid on the surfaces of the magnets, yokes and coils.

An acceptable volatile magnetic fluid is one having a relatively volatile carrier base fluid containing a relatively small amount of lubricating oil. Typical volatile carrier fluids are volatile liquids that evaporate at room temperature or slightly warmer. For example, useful volatile liquids are water and aliphatic hydrocarbon solvents such as octane, heptane and hexane. The type and amount of lubricating oil is such that the magnetic particles and lubricating oil left behind after evaporation of the volatile carrier fluid can form an oil-based magnetic fluid film or layer along the magnets, yokes, and focusing/tracking coils. Light lubricating oils having a viscosity of 4 cST (centistokes) or less at 100°C are preferred. Oils of this type which can be used as light lubricating oils are, for example, hydrocarbons, esters, ethers, perfluorocarbons and silicones. Unlike oil-based liquid-carrier magnetic fluids, the magnetic fluids left in the present invention do not require high temperature performance. This is because the focus/tracking coil of the present invention is not exposed to magnetic fluid for a long period of time.

Generally, for a given optical pickup actuator design, the saturation magnetization of the lens holder and focus/tracking coil positioning mechanism should be as small as possible, so that a thick magnetic particle and lubricating oil residue layer will not form on the magnetic surface. Furthermore, the volume percent of lubricating oil used in the volatile magnetic fluid is inversely proportional to the saturation magnetization of the fluid remaining after evaporation of the volatile carrier fluid. This is because the lower the volume percentage of lubricating oil to the total amount of volatile magnetic fluid plus lubricating oil, the higher the concentration of magnetic particles relative to the volume of lubricating oil left after evaporation of the volatile carrier fluid. The initial saturation magnetization range of the volatile magnetic fluid and the amount of lubricating oil used are application dependent. In other words, it depends on the type of disc pickup actuator, the size of the magnetic gap and the size of the focus/tracking coil.

In embodiments using a low viscosity oil-based magnetic fluid, the magnetic fluid typically uses a low volatility, relatively high molecular weight, oil-based carrier fluid such as an ester-based oil. These oil-based magnetic fluids are used to maintain even spacing of the lens mount and focus/tracking coils within the magnetic gap during assembly and as a vibration dampening and/or cooling fluid during operation of the optical pickup actuator. The reason why the magnetic fluid is an oil-based magnetic fluid is to prevent the magnetic fluid from evaporating at room temperature or higher during assembly, after assembly, and during use of the optical pickup actuator. The basic requirement for the use of oil-based ferrofluid in optical disc pickup actuators is that the oil-based ferrofluid stays in and fills the space between the focus/tracking coil and the yoke and magnet, ie the radial gap. If the oil-based ferrofluid evaporates, the ferrofluid will condense and cause the disc pickup actuator to fail.

Oil-based liquid carrier ferrofluids require high temperature performance because the current flowing through the focus/tracking coils in the magnetic gap containing the ferrofluid is a source of heat generation. Although the low viscosity oil-based magnetic fluid of the present invention requires high temperature performance, it is preferred to use a magnetic fluid having a viscosity at 27°C of less than 1000 cP, more preferably 500 cP or less, most preferably 300 cP or less. Low-viscosity oil-based magnetic fluid is applied in the magnetic gap of a conventional optical disc pickup actuator, between the magnet and coil of the pickup actuator, between the yoke and the coil, or between the magnet and the magnet with the coil in between. between the yokes. Sufficient amount of low viscosity oil-based magnetic fluid is used to contact the coils, but not so much that the magnetic fluid is splashed around due to shock or vibration operation applied to the above-mentioned position of the optical pickup actuator. The optimum filling quantity of magnetic fluid depends on the design of the actuator of the read head.

The use of a low-viscosity oil-based magnetic fluid also provides additional vibration dampening for lens mount movement during focusing and tracking. Vibrations in the lens mount caused by focusing and tracking functions are attenuated by an oil-based magnetic fluid in the magnetic gap.

Heat dissipation is also a concern, with low viscosity oil-based ferrofluid removing heat from the coils more effectively than not using ferrofluid. This is because ferrofluids are six times more thermally conductive than air. Heat transfer from the coil to the magnet and/or yoke via the magnetic fluid is therefore more efficient than via air in the magnetic gap in conventional optical pickup actuators. The base unit that holds the magnet and yoke uses thermally conductive material to further improve heat dissipation. Yokes can also be designed as base units.

And, unlike the use of high-viscosity oil-based magnetic fluid in the prior art, since the present invention uses low-viscosity oil-based magnetic fluid, the sensitivity of the optical disc pickup actuator using low-viscosity oil-based magnetic fluid in the present invention is lower when used at low temperature. Not affected.

A preferred method of the present invention includes obtaining a volatile magnetic fluid and adding a predetermined amount of lubricating oil to the volatile magnetic fluid. A mixture of volatile magnetic fluid and lubricating oil is then added to the magnetic gap of the optical pickup actuator. Volatile magnetic fluid can be added using a dispenser or by immersing a solid needle or hollow tube (ie capillary) in the ferrofluid and bringing the solid needle, hollow tube or dispenser close to the magnetic gap. The wettability of the ferrofluid and the magnetic force field of the magnet, yoke and coil make the volatile magnetic fluid fill the magnetic gap of the optical disc pickup actuator. The lens holder of the optical pickup actuator is then positioned relative to the magnet and yoke such that the coils of the lens holder are spaced from the magnet and/or yoke to create a magnetic gap. A volatile magnetic fluid will be placed between the focus/tracking coil and the magnet/yoke so that the lens mount will be positioned such that the resulting magnetic gap is evenly divided between the coil and the magnet/yoke.

A resilient support member extending from the lens mount may then be secured in place. Once secured, the volatile magnetic fluid is evaporated leaving a thin film/layer of lubricating oil containing magnetic particles distributed about the surface of the magnet and yoke and focus/tracking coils within the magnetic gap. The mixture of residual lubricating oil and magnetic particles is itself a low viscosity oil-based magnetic fluid. It has the feature that due to the magnetic force field it can form a thin film or layer along the surface of the magnet and yoke, which is also sufficient to keep the magnetic particles suspended within the magnetic fluid film.

Description of drawings

Figure 1 is a simplified schematic top view of one of the optical pickup actuator configurations.

Fig. 2 is a simplified cross-sectional view along A-A of the optical disc pickup actuator shown in Fig. 1 with volatile magnetic fluid in the magnetic gap.

FIG. 3 is a simplified cross-sectional view of the assembled optical disc pickup actuator shown in FIG. 2 after the volatile magnetic fluid in the magnetic gap evaporates.

Fig. 4 is a simplified schematic top view of an optical disc pick-up actuator with another structure.

FIG. 5 is a simplified cross-sectional view along B-B of the optical disc pickup actuator shown in FIG. 4 after the volatile magnetic fluid in the magnetic gap evaporates.

Detailed ways

A preferred embodiment of the present invention is shown in Figures 1-5. It should be understood that the dimensions and spacing between the illustrated elements are exaggerated and not to scale in order to facilitate understanding of the structural relationship between the various elements of the present invention.

FIG. 1 is a simplified schematic top view of an embodiment 10 of an optical disc pick-up actuator. The optical disc pickup actuator 10 includes a lens holder assembly 20 , a base unit 10 (not shown), and an electromagnetic drive system 50 . The lens mount assembly 20 and base unit have a supplementary electromagnetic element 52 of an electromagnetic drive system 50 . In this embodiment, the complementary electromagnetic element of the base unit is the magnetic assembly 60 . The lens holder assembly 20 includes a lens holder 22, an optical lens 24 supported by the lens holder 22, and a supplementary electromagnetic element 52. The supplementary electromagnetic element 52 includes a tracking coil 26 placed outside the lens holder 22 and a focusing coil 28 wound around the lens holder 22 In order to make the focusing coil and the tracking coil 26 orthogonal. The magnetic assembly 60 includes two magnets 62 placed at the front and rear of the lens holder assembly, respectively, and a yoke 64 placed at the rear of the magnets 62 to prevent magnetic flux leakage from the rear of the magnets 62 . Note that the supplementary electromagnetic components, i.e. the focus coil 28, the tracking coil 26 and the magnetic assembly 60, can be arranged such that the magnetic assembly 60 is part of the lens mount assembly 20, the coils 26, 28 are the base unit or provide the optical pickup actuator 10 Some combinations of focus and tracking functions are required.

In Fig. 1, the optical disc pick-up actuator 10 places the tracking coil 26 and the focusing coil 28 in the magnetic field or the magnetic gap 80 formed by the magnet 62 and the yoke 64 and the Lorentz force according to Fleming's left-hand law Focusing movement and tracking movement are realized by moving the optical lens 24 up and down and left and right. The pickup actuator 10 also includes a resilient support member 70 and a printed circuit board (not shown) that is mechanically connected to the base unit's fixing elements ( not shown).

Tracking coil 26 , focus coil 28 , magnet 62 and yoke 64 have residue layers 95 on various surfaces formed by evaporation of the volatile base carrier fluid of the volatile magnetic fluid used when mounting the optical pickup actuator 10 . The residual layer 95 consists of a mass of magnetic particles in the volatile magnetic fluid left after evaporation.

The present invention provides a method for securing and positioning lens mount assembly 22 relative to magnetic assembly 60 to create magnetic gap 80 during assembly. Embodiments of the methods of the present invention include the use of volatile magnetic fluids. Volatile magnetic fluids generally contain a volatile carrier or base fluid, a mass of magnetic particles, and a dispersant for dispersing the mass of magnetic particles in the volatile carrier liquid. Some useful carrier liquids are water and aliphatic hydrocarbons such as hexane, heptane and octane. Any conventional magnetic fluid with a volatile liquid as a carrier fluid can be used, and the formulation of such volatile magnetic fluids is well known to those of ordinary skill in the art. Although aromatic hydrocarbons and other polar solvents can be used as the base carrier fluid, it is assumed that the use of these types of fluids can affect the integrity of the adhesive (if any) used by the optical pickup actuator.

The number of magnetic particles per unit volume of magnetic fluid is represented by the saturation magnetization of the magnetic fluid, and it is measured in Gauss (mT). Fluids with low saturation magnetization will leave a thinner residual layer of magnetic particles than magnetic fluids with higher saturation magnetization. However, which ferrofluid is used will depend on which manufacturing process is used. Using a magnetic fluid with a low saturation magnetization allows for filling the magnetic gap with fluid to position the lens mount assembly 22 .

Using a magnetic fluid with a higher saturation magnetization should consider not completely filling the magnetic gap so that the magnetic gap has an air passage and provides a stronger magnetic centering adjustment force. Preferably, the saturation magnetization range used by the present invention is kept suitably low so that relatively thick residual layers of magnetic particles do not form on the focus and tracking coils 26, 28 and/or magnet 62 and/or yoke 64. It should be understood that the appropriate saturation magnetization for a given volatile magnetic fluid mixture will depend on many factors, including the type of carrier fluid used as the base volatile fluid in the volatile magnetic fluid, the size of the optical pickup actuator, Dimensions of radial clearance, etc.

To reduce the chance of any magnetic particles remaining as residue upon removal from the coils 26, 28, magnet 62 or yoke 64, lubricating oil may optionally be added to the volatile magnetic fluid. The type and amount of lubricating oil is such that when the volatile carrier fluid evaporates, the magnetic particles and lubricating oil left behind will form an oil-based magnetic fluid film or layer along the surfaces of the magnets, yokes, and focusing/tracking coils. Lubricating oils that can be used in the present invention are hydrocarbons, esters, ethers, fluorocarbons and silicones. Preferred oils are hydrocarbon oils including petroleum and synthetic hydrocarbons. Of these hydrocarbons, aromatics are more reactive than aliphatics with other materials used in optical pickup actuators. Alkanes, naphthenes and polyalphaolefins are more suitable. Polyalphaolefins are the most suitable choice due to their low pour point, low viscosity, low volatility and inert properties. In addition, polyalphaolefins used for shock absorption and heat conduction in traditional magnetic fluids have a viscosity of 6cSt or higher at 100°C, and it is better to use polyalphaolefins with lower molecular weight (below 6cSt) in the present invention, preferably is 4cSt or lower. This is because high molecular weight polyalphaolefin additionally requires a large amount of dispersant on the magnetic particles to disperse the magnetic particles within the higher molecular weight polyalphaolefin. Higher molecular weight polyalphaolefins are not preferred because a large amount of additional dispersant will produce a large amount of residual particles which leave a thicker residual layer after evaporation of the volatile carrier fluid.

The residual magnetic fluid layer left after evaporation of the volatile carrier fluid in the present invention should be as thin as possible. Therefore, the amount of lubricating oil in the solvent-based magnetic fluid should not exceed fifty percent (50 vol. %) of the total volume percent of the initial solvent-based magnetic fluid plus lubricating oil. The smaller the volume percentage of lubricating oil, the thinner the residual layer.

In another embodiment of the invention, a low viscosity oil-based magnetic fluid replaces the volatile magnetic fluid. In this case, the low viscosity oil-based ferrofluid remains in the optical pickup actuator 10 throughout its lifetime. Like the volatile magnetic particles, a low viscosity oil-based magnetic fluid is used to position the lens mount assembly 20 relative to the magnets and yokes 62 , 64 . There are additional advantages to using low-viscosity oil-based magnetic fluids, including, for example, shock absorption and heat dissipation from focusing and tracking movements of the lens holder or vibrations caused by external shocks. Using a low viscosity oil-based ferrofluid to remove heat from the coil is more efficient than not using a ferrofluid. This is because ferrofluids are six times more thermally conductive than air. Therefore, heat transfer from the coil to the magnet and/or yoke via the magnetic fluid is more efficient than heat transfer via the air in the magnetic gap of conventional optical pickup actuators. The use of thermally conductive materials for the base unit that holds the magnets and yokes further improves heat dissipation. Preferred low viscosity oils are ester oils.

2 and 3 illustrate the method of the present invention in relation to the optical pickup actuator shown in FIG. 1 . It should be understood that the method can be used with most conventional optical pickup actuators. FIG. 2 is a cross-sectional view of the position of the coil/magnet/yoke in the read head actuator shown in FIG. 1 . In this particular example, a base unit (not shown) includes a magnetic assembly 60 comprised of a frame mount or yoke 64 and a magnet 62 . The yoke 64 is U-shaped and has a magnet 62 fixed to the inside of one of the legs of the yoke 64 . The other leg of the yoke 64 is located in the opening between the focusing coil 28 and the lens mount 22 .

A predetermined amount of volatile magnetic fluid 90 is added to magnetic gap 80 . Adding magnetic fluid 90 may be performed by using a dispenser, placing the dispenser near magnetic gap 80 , and delivering a predetermined amount of volatile magnetic fluid into magnetic gap 80 . Of note, a properly sized capillary can replace the needle shaft. Due to the magnetic force field established by the magnet 62 and the yoke 64, the volatile magnetic fluid 90 fixes and places the lens holder 22 in an evenly spaced and magnetically balanced position with respect to the magnet and the yoke 62, 64, so as to secure the elastic support The member 70 then properly positions the lens mount assembly 20 . The lens mount assembly 20 is secured in place to a base unit (not shown).

After the lens holder assembly 20 is fixed in place, the volatile magnetic fluid 90 evaporates from the optical pickup actuator 10, as shown in FIG. 3 . Although the volatile base carrier fluid evaporates, a residual layer 95 remains on the surface of the magnetic gap 80 . In a preferred embodiment, the residual layer 95 contains a large amount of magnetic particles dispersed in the lubricating oil due to the evaporation of the volatile magnetic fluid.

If the present invention selects a low viscosity oil-based magnetic fluid instead of a volatile magnetic fluid, the low viscosity oil-based magnetic fluid will remain within the magnetic gap 80 in a similar position as shown in FIG. 2 .

Figure 4 shows a simplified schematic top view of another optical pick-up actuator 100 in which a magnetic circuit is established to avoid the optical path of the light source. The optical disc pickup actuator 100 includes a lens holder assembly 120 and a magnetic assembly 160 . The lens holder assembly 120 includes a lens holder 122, an optical lens 124 supported by the lens holder 122 at the protruding portion 123, a focusing coil 128 wound on the inner part of the lens holder opening 125 of the lens holder 122, and the lens holder opening installed on the lens holder 122 The tracking coil 126 in 125 is orthogonal to the focusing coil 128 . Magnetic assembly 160 includes two magnets 162 positioned within lens mount opening 125 such that one magnet is positioned within the opening defined by focus coil 128 and the other magnet is positioned within an opening spaced from tracking coil 126 , further comprising a magnet positioned between each magnet. 162 behind each magnet 162 to prevent magnetic flux leakage from behind the yoke 164 .

In FIG. 4, the optical pickup actuator 100 performs focus motion and tracking by positioning the tracking coil 126 and focus coil 128 within a magnetic field or gap 180 formed with the magnet 162 and yoke 164 and moving the optical lens 124 up and down and side to side. sports. The disc pickup actuator 100 also includes a resilient support member 170 and a printed circuit board (not shown) mechanically connected to the base unit fixing elements (not shown) by having fixing points 172 on the left and right sides of the lens holder assembly 122 .

Tracking coil 126 , focus coil 128 , magnet 162 and yoke 164 have a residue layer 195 on each surface resulting from evaporation of the volatile base carrier fluid of the volatile magnetic fluid used in the assembly of the optical pickup actuator 100 .

FIG. 5 shows the method of the present invention related to the optical disc pick-up actuator shown in FIG. 4 . FIG. 5 is a cross-sectional view showing the position of the coil/magnet/yoke of the read head actuator in FIG. 4 . In this particular example, a base unit (not shown) contains a magnetic assembly 160 formed from a frame mount or yoke 164 and a magnet 162 . The yoke 164 is U-shaped and has a magnet 162 fixed to the inside of each leg of the yoke 164 .

As described above, a predetermined amount of volatile magnetic fluid or low-viscosity oil-based magnetic fluid is added in the magnetic gap 180 . Due to the magnetic force field established by the magnet 162 and the yoke 164, the magnetic fluid 190 fixes and places the lens holder 122 in an evenly spaced and magnetically balanced position relative to the magnet and the yoke 162, 164, so that the elastic support member 170 is fastened The lens mount assembly 120 was previously properly positioned. The lens mount assembly 120 is fixed in place on a base unit (not shown).

It should be noted that the present invention can be used with read head actuators where the structural design of the actuator does not include a yoke, or where the magnetic assembly is assembled as part of the lens mount assembly and the focus and tracking coils are secured to the base unit or in a readhead actuator that provides combined focusing and tracking motion of the lens holder.

While preferred embodiments of the invention have been described herein, the foregoing description is illustrative only. Modifications of the invention disclosed herein will occur to persons skilled in the art, and all such modifications are considered to be within the scope of the invention.

Claims (31)

1. with the method for lens bracket assembled to the base unit of pick-up actuator, wherein said lens bracket assembly and described base unit comprise additional electromagnetic component separately, additional electromagnetic component forms electromagnetic driving system jointly to control focusing and the pursuit movement of described lens bracket assembly with respect to described base unit, described electromagnetic component comprises tracking coil, focusing coil and magnetic system perpendicular to described tracking coil, form magnetic gap when wherein assembling between the described electromagnetic component of the described electromagnetic component of described lens bracket assembly and described base unit, described method comprises:

Described lens bracket assembly of assembling and described base unit form described magnetic gap mutually;

In described magnetic gap, arrange the volatile that comprises the base carrier liquid of volatilizing of scheduled volume;

Spring support member is fixed between described lens bracket assembly and the described base unit; And

Evaporate described volatile base carrier fluid from described volatile.

2. method according to claim 1 further comprises the described volatile of preparation.

3. method according to claim 2, wherein said preparation steps further comprises obtains a large amount of magnetic particles, described a large amount of magnetic particles are suspended in the described volatile base carrier fluid, and the spreading agent that adds q.s in described volatile base carrier fluid is to be dispersed in described a large amount of magnetic particles in the described carrier fluid.

4. method according to claim 3, wherein said preparation steps further comprises the lubricating oil that adds scheduled volume.

5. method according to claim 3 further comprises from described carrier fluid and removes unnecessary spreading agent.

6. method according to claim 4, the described step of wherein adding described lubricating oil comprise adds a certain amount of lubricating oil, wherein saidly a certain amount ofly is less than or equals 50 percent of described volatile percent by volume.

7. method according to claim 4, the described step of wherein adding described lubricating oil further comprise adds a kind of in hydrocarbon, ester, ether, perfluocarbon or the silicone lubricating oil.

8. method according to claim 3, the described step of wherein adding described lubricating oil further comprise and are added on the lubricating oil that 100 ℃ of viscosity are lower than 6 centistokes.

9. with the method for lens bracket assembled to the base unit of pick-up actuator, wherein said lens bracket assembly and described base unit comprise additional electromagnetic component separately, additional electromagnetic component forms electromagnetic driving system jointly to control focusing and the pursuit movement of described lens bracket assembly with respect to described base unit, described electromagnetic component comprises tracking coil, focusing coil and magnetic system perpendicular to described tracking coil, form magnetic gap when wherein assembling between the described electromagnetic component of the described electromagnetic component of described lens bracket assembly and described base unit, described method comprises:

Described lens bracket assembly of assembling and described base unit form described magnetic gap mutually;

Arrange that in described magnetic gap the viscosity in the time of 27 ℃ of scheduled volume is lower than the low viscosity oil-based magnetic fluid of 1000cP; And

Spring support member is fixed between described lens bracket assembly and the base unit.

10. method according to claim 9, wherein said magnetic fluid viscosity in the time of 27 ℃ is lower than 500cP.

11. method according to claim 9, wherein said magnetic fluid viscosity in the time of 27 ℃ is lower than 300cP.

12. optical pick-up actuator comprises:

Base unit;

The lens bracket assembly; And

Described lens bracket assembly is connected to the spring support member of described base unit, each self-contained additional electromagnetic component of wherein said lens bracket assembly and described base unit, additional electromagnetic component forms electromagnetic driving system jointly to control focusing and the pursuit movement of described lens bracket assembly with respect to described base unit, described electromagnetic component comprises tracking coil, perpendicular to the focusing coil and the magnetic system of described tracking coil, wherein between the described electromagnetic component of the described electromagnetic component of described lens bracket assembly and described base unit, form magnetic gap; And

Be arranged in the lip-deep residual magnetosphere of one or more described electromagnetic driving systems in the described magnetic gap zone, described residual magnetosphere comprises a large amount of magnetic particles.

13. topworks according to claim 12, wherein said residual magnetosphere is the volatile base carrier fluid formation by the evaporating volatile magnetic fluid.

14. topworks according to claim 12, wherein said residual magnetosphere comprises the magnetic particle that is dispersed in a large number in the lubricating oil.

15. topworks according to claim 13, wherein said residual magnetosphere is the volatile base carrier fluid formation that comprises the volatile of scheduled volume lubricating oil by evaporation.

16. topworks according to claim 13, wherein said lubricating oil is lower than 6 centistokes 100 ℃ of viscosity.

17. topworks according to claim 13, wherein said lubricating oil is a kind of in hydrocarbon, ester, ether, perfluocarbon or the silicone oil.

18. topworks according to claim 13, the saturation magnetization of wherein said residual magnetic fluid layer is 1000 Gausses or lower.

19. topworks according to claim 12, wherein said magnetic system comprises magnet or magnet and yoke.

20. optical pick-up actuator comprises:

Base unit;

The lens bracket assembly; And

Described lens bracket assembly is connected to the spring support member of described base unit, each self-contained additional electromagnetic component of wherein said lens bracket assembly and described base unit, additional electromagnetic component forms electromagnetic driving system jointly to control focusing and the pursuit movement of described lens bracket assembly with respect to described base unit, described electromagnetic component comprises tracking coil, perpendicular to the focusing coil and the magnetic system of described tracking coil, wherein between the described electromagnetic component of the described electromagnetic component of described lens bracket assembly and described base unit, form magnetic gap; And

Be arranged in the low viscosity oil-based magnetic fluid in the described magnetic gap, wherein said magnetic fluid viscosity in the time of 27 ℃ is lower than 1000cP.

21. optical pick-up actuator according to claim 20, wherein said magnetic fluid viscosity in the time of 27 ℃ is lower than 500cP.

22. optical pick-up actuator according to claim 20, wherein said magnetic fluid viscosity in the time of 27 ℃ is lower than 300cP.

23. optical pick-up actuator comprises:

Base unit;

The lens bracket assembly; And

Described lens bracket assembly is connected to the spring support member of described base unit, each self-contained additional electromagnetic component of wherein said lens bracket assembly and described base unit, additional electromagnetic component forms electromagnetic driving system jointly to control focusing and the pursuit movement of described lens bracket assembly with respect to described base unit, described electromagnetic component comprises tracking coil, perpendicular to the focusing coil and the magnetic system of described tracking coil, wherein between the described electromagnetic component of the described electromagnetic component of described lens bracket assembly and described base unit, form magnetic gap; And

Be arranged in the volatile in the described magnetic gap, described volatile contains volatile carrier liquid temporarily.

24. topworks according to claim 23, wherein said volatile comprises the lubricating oil of scheduled volume.

25. topworks according to claim 23, wherein said volatile carrier liquid is one or more in water, aliphatic hydrocarbon, aromatic hydrocarbons and other polar solvents.

26. topworks according to claim 25, wherein said aliphatic hydrocarbon is chosen from the group that comprises hexane, heptane and octane.

27. according to right 24 described topworkies, the described volatile that wherein comprises described scheduled volume lubricating oil comprises that the spreading agent of volatile carrier liquid, a large amount of magnetic particle and q.s is to be dispersed in described a large amount of magnetic particles in the described volatile carrier liquid.

28. according to right 24 described topworkies, wherein said volatile has enough low saturation magnetization, so that after removing described volatile carrier liquid, on the surface in described magnetic gap, comprise the amount minimum of the residual magnetic fluid of described a large amount of magnetic particle and described lubricating oil.

29. according to right 24 described topworkies, wherein before adding described lubricating oil to described volatile, described lubricating oil is lower than 6 centistokes 100 ℃ of viscosity.

30. according to right 24 described topworkies, wherein said lubricating oil is a kind of in hydrocarbon, ester, ether, perfluocarbon or the silicone oil.

31. according to right 24 described topworkies, the concentration of wherein said lubricating oil is 50 or lower percent of described volatile percent by volume.

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