JPS63168852A - Actuator of optical pick up - Google Patents

Abstract

PURPOSE:To make improvement in high dimensional accuracy, wear resistance, moisture resistance, etc., by forming a thin film consisting of a fluorine-contg. polymer on the sliding surface of a lens holder supporting shaft. CONSTITUTION:The thin film consisting of the fluorine-contg. polymer is formed on the sliding surface of the lens holder supporting shaft which is so supported that the shaft can move axially and rotate. The fluorine-contg. polymer is a polyfluoroalkyl polymer or fluoropolyether polymer, etc. The polyfluoroalkyl polymer refers to the polymer having a polyfluoroalkyl group as expressed by, for example, formula I. The fluoropolyether polymer has the unit expressed by formula II as a main constituting unit. In formula II, (x) is 1-4 integer. Since there is no possibility of rust generation on the supporting shaft, the supporting shaft withstands use even in high-temp. and high-humidity environment and has the excellent dimensional accuracy particularly in the sliding part between the supporting shaft and the holder.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an actuator for an optical pickup in an information recording/reproducing apparatus.

[Conventional technology]

Conventionally, optical information recording and reproducing devices include, for example, video disc players, digital audio players,
Optical disk files are known.

The optical pickups used to perform focus control and tracking control in these devices detect information by condensing a light beam that has passed through an objective lens onto the disk surface, so the optical pickup compensates for the focal shift caused by disk surface wobbling. It is necessary to form an image on the disk surface. Additionally, if there is a misalignment between the signal track (information bit string) on the disk and the optical axis of the objective lens (radial misalignment of the optical axis), accurate reading will not be possible. It is necessary to align the optical axis of the objective lens with the signal track. Compensation for such a focus shift is performed by focusing servo, and compensation for signal track shift is performed by tracking servo.

There are many types of structures for focusing drive systems and tracking drive systems, some of which are illustrated in FIGS. 1 and 2. This shows a drive system of an optical pickup in which a drive section is guided by a fixed support shaft 2 and moves in the focusing direction, and at the same time rotates around this support shaft 2 to perform tracking control. Here, the support shaft 2 is fixed to the base 1 together with the surrounding magnetic core 3, and the support shaft 2 is provided with a sleeve 5 made of metal (usually aluminum or its alloy) at the axial center of the lens holder main body 4. The lens holder body 4 is fitted with a rotatable state, and a drive coil 6 is provided on the outer peripheral surface of the lens holder main body 4, and an objective lens 8 is installed in the hole 7 of the lens holder at an eccentric position of the sleeve 5. It is being The drive coil 6 includes a focus coil wound around the axis of the sleeve 5,
It includes a tracking coil (not shown) which is wound in the optical axis direction of the objective lens 8 and placed at opposing positions with a plane containing the axis of the sleeve 5 as a plane of symmetry, and the current flows to the focus coil and the tracking coil. In such an actuator, the amount of axial movement and rotation of the lens holder body 4 is controlled according to the magnitude of the current, the weight of the lens holder body 4 is controlled in order to improve control responsiveness. It is preferable that the sleeve 5 be as light as possible, and that the gap between the inner diameter of the sleeve 5 and the support shaft 2 be as small as possible for the purpose of improving reading accuracy, and that the frictional resistance between the two be small and stable. For this reason, the lens holder body 4 is usually made of a material made of aluminum alloy or synthetic resin, and there is a gap between the inner diameter of the sleeve 5 (some of which is integrated with the lens holder body 4) and the outer diameter of the support shaft 2. Efforts have been made to improve accuracy and improve sliding characteristics by providing a lubricating coating such as a fluororesin composition on the sliding surfaces of both.

However, in the conventional method of forming a lubricating film such as a fluororesin composition on the inner diameter of the sleeve 5 and the surface of the support shaft 2, the lubricating film is made of polytetrafluoroethylene resin, tetrafluoroethylene hexafluoride propylene resin, etc. Because it is made by dispersing a fluorine-containing resin with high lubricity, such as resin or perfluoroalkoxy resin, in a binder resin such as polyimide resin, polyamideimide resin, or epoxy resin, which has excellent adhesion to the base material, it is possible to A resin-rich layer for binder is applied on the base material side (adhesive side), and a layer rich in binder resin is applied on the opposite side (sliding side).
To do this, a layer rich in fluorine-containing resin must be formed by taking advantage of differences in cohesive energy density, etc., and the thickness of the layer inevitably becomes thicker. It is difficult to obtain dimensional accuracy such as In addition, when forming on the inner diameter surface of the sleeve 5, a solution prepared by dissolving a fluororesin composition in an organic solvent has a considerably high viscosity even if diluted.

Normally, it is extremely difficult to construct a small hole with an inner diameter of about 2 to 3 mm. Therefore, the variation in the mounting clearance on the sliding surface with the sleeve 5 (!: support shaft 2) becomes large, resulting in a disadvantage to the stability of control. Although the combination with the support shaft 2 (usually made of stainless steel) without a lubricating coating is very advantageous from a cost standpoint, the sliding characteristics are favorable, and wear occurs after relatively long periods of operation, resulting in wear particles. In recent years, a lens holder body 4 made of synthetic resin mixed with a solid lubricant such as fluororesin and a metal such as stainless steel or ceramic such as SiC has been developed. A combination with the support shaft 2 has also been considered.However, even with this method, if a solid lubricant with a very low elastic modulus such as fluororesin is mixed, the elastic modulus of the lens holder body 4 will be low. is low, causing the above-mentioned resonance problem and at the same time reducing the adhesion force to the drive coil 6, objective lens 8, etc., so even if the sliding characteristics are improved, it cannot withstand long-term use, which is undesirable. When the material is a metal such as stainless steel, there is a problem of malfunction due to corrosion and adhesion of foreign substances such as dust.

[Problem that the invention seeks to solve]

In this way, the actuator of the optical pickup in the conventional technology, especially the support shaft 2 that makes up the actuator, has excellent lubricating properties, high dimensional accuracy, wear resistance, moisture resistance (rust prevention), and stain resistance. However, there were problems in that the focusing servo and tracking servo lacked reliability and durability, such as instability, uncertainty, or inoperability.

[Means for solving problems]

In order to solve the above problems, the present invention adopts a method of forming a thin film made of a fluorine-containing polymer on the sliding surface of the lens holder support shaft of the actuator of the optical pickup.

The details will be described below.

First, the fluorine-containing polymer of the present invention is a polyfluoroalkyl polymer or a fluoropolyether polymer. Polyfluoroalkyl polymers include, for example, CF3(CF2)7-1H(CF2)6, CF2C1(
CF2)l,-.

It is a polymer having a polyfluoroalkyl group such as
The fluoropolyether polymer has a unit represented by the general formula % (where X is an integer of 1 to 4) as a main structural unit, and preferably has an average molecular weight of 1000 to 5000. Such fluoropolymers contain functional groups with high affinity for metals, such as epoxy groups, amino groups, carboxyl groups, hydroxyl groups, mercapto groups, isocyanate groups, sulfone groups, and ester groups. Preferred examples include the following.

Namely.

C6F13COOH1C8F1□C2H, 40H5C8
F1□C2I-i4SH.

CF CHOCNH(CH2)6NGO10゜CIoF2□C0NHC2H40H1C1oF21So
3H.

HooC-CF20+C2F4O valve-CF2o←CF2
COOH.

m n CH300C-CF20+-C2F4o→=CFO well C
F2C■CH3゜m 2 n HOCH2-CF20+-C2F4oHCF20'+-
CF2-CH300Cmn and the like.

Although such a fluoropolymer may be used alone, it is preferable to use one containing, for example, an epoxy group or an incyanate group, especially when the material of the support shaft is metal, considering that there are a large amount of hydroxyl groups. When using an epoxy group, it is preferable to add amines, acid anhydrides, etc. to react the epoxy group. Further, when using an incyanate group alone, it is preferable to add an incyanate trimerization catalyst such as a tin compound.

In addition, two or more types of fluoropolymers may be used in combination,
In this case, a combination containing an epoxy group and one having at least one type of group such as an amine group, a carboxyl group, a hydroxyl group, or a mercapto group, or a combination of one containing a carboxyl group and one having at least one type of group such as an amino group or a hydroxyl group. 1
A film with excellent abrasion resistance can be obtained by combining polymers containing various types of groups, or by reacting hydroxyl groups, amine groups, and mercapto groups with those containing incyanate groups to increase the molecular weight of the polymer. It is desirable to take care to ensure that

In addition, for fluorine-containing polymers having these functional groups,
An organic compound having a functional group that causes a chemical reaction with each functional group may be added to increase the molecular weight. Suitable examples of such combinations include adding ethylene glycol or diaminodiphenylmethane to a fluoropolymer containing an incyanate group, or adding an incyanate compound or the like to a fluoropolymer containing a hydroxyl group. I can do it.

The fluorine-containing polymers mentioned above show considerable affinity to the material surface of the support shaft by themselves, but depending on the type of mating material, they may not necessarily show sufficient adhesion strength. In such cases, a thin film (called a primer) that has an affinity for both the coating and the other material is used.
An example of such a primer is a graft polymer having polymethyl methacrylate as a branch component and a methyl methacrylate unit or a hydroxylethyl methacrylate unit as a main component.

Here, the method of applying the fluoropolymer is not particularly limited, and may be any method used in normal painting, but for example, dissolving it in a suitable solvent and applying it (including spraying, dipping, etc.) The solvent may then be evaporated, and it is also possible to increase the molecular weight of the film-forming components by heating after forming the thin film. The thickness of the film coated on the surface of the support shaft is preferably 5μm or less, preferably 2μm or less, so as not to impair the dimensional accuracy of the support shaft.
It is desirable that the thickness be less than μm. Note that the material of the support shaft is not limited to metal, and may be synthetic resin, ceramics, etc. without causing any problems.

〔Example〕

The raw materials mainly used in the following examples are listed below. In addition, in order to simplify the raw material family names and chemical structural formulas, the numbers ■ to ■ assigned to each raw material were used, and the blending ratios were expressed in parts by weight.

Fluoropolymer: ■ Epoxy group-containing polyfluoroalkyl polymer ■ Amino group-containing polyfluoroalkyl polymer ■ Hydroxyl group-containing polyfluoroalkyl polymer HOC2H4 (CF2) 7C2H4
oH ■ Perfluoropolyether polymer containing incyaneto group (average molecular weight approximately 2000) ■ Perfluoropolyether polymer containing hydroxyl group (average molecular weight approximately 2000) HOCH2-CF2o + C2F4O → CF2o wood CF
2-CH20H ■ Perfluoropolyether polymer containing carboxyl group (average molecular weight 1500) Other compounds: ■ Incyanate compound (average value of n 0.6) ■ Dibutyltin dilaurate Examples 1 to 9: Shown in Table 1 A coating solution was prepared by diluting the raw material to 3% by weight with the solvent shown in the table, and was applied to the sliding part of the support shaft. After coating, it was heated at 70° C. for 1 hour and then at 120° C. for 3 hours to form a film of about 1 μm. Here, the stainless steel that is the material of the support shaft is SUS 420 J2, and the ceramic coating is made by thermally spraying SiC-based ceramics on the surface of stainless steel or aluminum to a film thickness of 25 μm.
A film of m is formed.

The coated support shaft was assembled into an optical pickup actuator as shown in Figs. 1 and 2, and a rusting test was carried out.
We investigated the durability test and the sliding characteristics before and after the durability test.

The PPS composition shown in the column of sleeve material in Table 1 is polyphenylene sulfide [PPS] resin (manufactured by Philips Co., USA: Ryton P-4) 70% by weight and carbon fiber (manufactured by Toshi Co., Ltd., fiber length: 70% by weight). This is a composition obtained by melt blending 30% by weight of aluminum (6 mm), and the aluminum is A2017.

The specific methods for the rust development test, durability test, and sliding property test are as follows.

(1) Rust development test: After being left for 500 hours, the presence or absence of rust on the surface of the support shaft 20 was observed using an optical microscope (x20).

(2) Attach the optical pickup actuator under durability test to the test stand, and connect it to the applied voltage generator consisting of the drive device (manufactured by our company) and the signal generator (signal generator TR98202 manufactured by Atopan Test Co., Ltd.). , a voltage of 0.5V is applied to the drive coil 6 of the pickup actuator by the applied voltage generator.

Continuous operation was performed in an indoor atmosphere. The operating time until malfunction occurs is used as a measure of durability, and for those that operated well and withstood long-term operation exceeding 500 hours, operation was discontinued after 500 hours.

(3) Sliding property test A lens holder displacement measuring device consisting of a optical actuator test head (manufactured by Atopan Test Co., Ltd.: TQ88091) and an analyzing recorder (manufactured by Yokogawa Hokushin Electric Co., Ltd.: 3656) was used for 100 hours after the durability test. ,20
A test pickup actuator for 0 and 500 hours was installed, and a voltage of 0. IV.

Based on the difference between the response waveform and the response waveform (the closer the two waveforms are, the better the lubricity), it is classified as good (○ mark), fair (△ mark), and poor (
It was evaluated in three stages (x mark).

The results of each of the above tests in Examples 1 to 9 were as shown in Table 2.

Comparative Examples 1 and 2: The support shaft of Comparative Example 1 was made of stainless steel, and the support shaft of Comparative Example 2 was coated with a ceramic spray coating similar to that of Example 8. In both cases, the sleeve was integrated into the holder body. A pickup consisting of a melt-blended composition of 70% by weight of integrated polyphenylene sulfide (PPS) resin (manufactured by Philips, USA: Ryton?-4) and 30% by weight of carbon fiber (manufactured by Toshi Co., Ltd., fiber length 6 mm). An actuator was manufactured and various tests similar to those in Examples were conducted. The obtained results are also listed in Table 2.

Comparative Example 3: Epoxy group-containing organopolysiloxane (Shin-Etsu Daini
Manufactured by Omote Kagaku Kogyo Co., Ltd.: Epoxy modified silicone oil KF 1
A coating liquid was prepared by diluting a composition in which 0.6% dibutyltin dilaurate ■ was added to 02) to a concentration of 3% by weight with Freon 113, and applied to the sliding part of a stainless steel support shaft. After coating, dry at 70℃ for 1 hour,
It was heated at ℃ for 3 hours to form a film with a thickness of about 1 μm. A pickup actuator consisting of this support shaft and a holder made of the resin composition used in Comparative Examples 1 and 2 was produced, and various tests similar to those in the Examples were conducted. The obtained results are also listed in Table 2.

Comparative Example 4: A coating solution was prepared by diluting hydroxyl group-containing organopolysiloxane (Silicone Diol Apply it to the sliding part of the support shaft,
After coating, it was dried at 70°C for 1 hour and heated at 150°C for 3 hours to form a film about 1 μm thick. A pickup actuator consisting of this support shaft and a holder made of the same resin composition as in Comparative Example 3 was prepared, and various tests similar to those in the Example were conducted. The obtained results are also listed in Table 2.

As is clear from Table 2, all of Examples 1 to 9 sufficiently ensured a durability test of 500 hours, and among them, Example 4.
Samples 5.7.8 and 9 were also excellent in terms of sliding properties after 500 hours. Furthermore, both Examples 3 and 5 used a fluorine-containing polymer containing a hydroxyl group, but Example 5 using a fluoropolyether polymer was superior to Example 3 using a fluoroalkyl polymer. It was found that the material had excellent sliding properties. On the other hand, Comparative Examples 1 and 2 in which no lubricating coating was formed on the support shaft, and Comparative Examples 3 and 4 in which the lubricating coating was formed using a material other than the fluoropolymer of the present invention, All of them were satisfactory in terms of durability (especially after aging), and in Comparative Example 1, rust was observed on the support shaft.

〔effect〕

As mentioned above, the actuator of the optical pickup of the present invention can withstand use even in a high temperature and humid atmosphere because there is no fear of rust on the support shaft, which is the main component, and the lens holder material has particularly good sliding properties. Since this does not require , a material with a high elastic modulus and good adhesiveness can be selected as the lens holder material, making it possible to solve the problem of high-order resonance. It also prevents adhesion with lenses, coils, etc., and provides excellent sliding characteristics in focusing drive and tracking drive, and in particular, excellent dimensional accuracy of the sliding part between the support shaft and holder.
Focusing servo and tracking servo with good stability and reliability can be implemented, and durability is also very good. Therefore, it can be said that the significance of this invention is extremely large.

[Brief explanation of the drawing]

FIG. 1 is a plan view illustrating the structure of an actuator of an optical pickup, and FIG. 2 is a sectional view of FIG. 1.

Claims (1)

[Claims] An actuator for an optical pickup, characterized in that a thin film made of a fluorine-containing polymer is formed on the sliding surface of a lens holder support shaft that is supported so as to be movable and rotatable in the axial direction.