JPH0743836B2 - Optical pickup actuator - Google Patents

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, as an optical information recording / reproducing apparatus, for example, a video disc player, a digital audio player,
Optical disk files are known.

The optical pick-ups for focus control and tracking control of these devices detect the information by focusing the light beam that has passed through the objective lens on the disk surface and detect the information. Must be imaged on the disk surface. Also, if there is a deviation between the signal track (information bit train) on the disk and the optical axis of the objective lens (optical axis radial deviation), correct reading cannot be performed, so the signal track deviation is compensated. It is necessary to match the optical axis of the objective lens with the signal track. The defocusing is compensated by a focusing servo, and the tracking of the signal track is compensated by a tracking servo.

There are many types of structures of the focusing drive system and the tracking drive system, and one of them is illustrated in FIGS. 1 and 2. This shows an optical pick-up drive system in which the drive unit is guided by a fixed support shaft 2 to move in the focusing direction and at the same time rotates about the support shaft 2 to perform tracking control. Here, the support shaft 2 is fixed to the base 1 together with the magnetic core 3 around the support shaft 2, and the support shaft 2 is provided with a sleeve 5 made of metal (usually aluminum or its alloy) at the shaft core of the lens holder body 4 for rotation. The lens holder body 4 is fitted in a freely movable state, a driving coil 6 is provided on the outer peripheral surface of the lens holder body 4, and an objective lens 8 is attached to a lens attachment hole 7 at an eccentric position of the sleeve 5. The drive coil 6 is wound in the axial direction of the foramen lens 8 and the focus coil wound around the axis of the sleeve 5, and is disposed at the opposite position with a plane including the axis of the sleeve 5 as a plane of symmetry. A tracking coil (not shown) is included, and the amount of axial movement and the amount of rotation of the lens holder body 4 are controlled according to the magnitude of the current flowing through the focusing coil and the tracking coil.

In such an actuator, the weight of the lens holder body 4 is as light as possible in order to improve the control response, and the gap between the inner diameter of the sleeve 5 and the support shaft 2 is set in order to improve the reading accuracy. It is preferable that it is as small as possible, and that the frictional resistance between them is small and stable. Therefore, the lens holder body 4 is usually formed of a material made of aluminum alloy or synthetic resin, and the clearance 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 is provided. It has been attempted to improve the accuracy and further improve the sliding characteristics by providing a lubricating coating such as a fluorine resin composition on the sliding surfaces of both.

However, in the conventional method of forming a lubricating coating such as a fluorine resin composition on the inner diameter of the sleeve 5 and the surface of the support shaft 2, the lubricating coating is formed of tetrafluoroethylene resin, tetrafluoroethylene hexafluoride. Propylene resin, fluorine-containing fluorocarbon resin such as perfluoroalkoxy resin is dispersed in a binder resin having excellent adhesion to a substrate such as polyimide resin, polyamideimide resin, and epoxy resin. A resin-rich layer for the binder on the base material side (adhesive side) of the coating, and the opposite side (sliding side)
In this case, a layer rich in fluorine-containing resin must be formed by utilizing the difference in cohesive energy density, etc., and the film thickness is inevitably increased. It is difficult to obtain dimensional accuracy such as degree. Further, when forming on the inner diameter surface of the sleeve 5, a solution prepared by dissolving the fluorine resin composition in an organic solvent has a considerably high viscosity even when diluted, so that it is usually applied to a small hole having an inner diameter of 2 to 3 mm. It is extremely difficult to do. Therefore, the variation in the mounting clearance on the sliding surface between the sleeve 5 and the support shaft 2 becomes large,
This leads to a disadvantage in the stability of control. Furthermore, the combination of the lens holder body 4 made of a synthetic resin base material and the support shaft 2 (usually stainless steel) not provided with a lubricious coating is very advantageous in terms of cost, but the sliding characteristics are not preferable, and comparison is made. Since abrasion may occur when operated for a long period of time, and malfunctioning phenomenon due to abrasion powder may occur. In recent years, lens holder body 4 and stainless steel made of synthetic resin containing a solid lubricant such as fluorine resin have been used. A combination with a support shaft 2 made of a metal such as steel or a ceramic such as SiC has also been considered. However, in such a method, when a solid lubricant having a very small elastic modulus such as fluorine resin is mixed, the elastic modulus of the lens holder body 4 is low, which causes the resonance problem described above, and also causes the driving coil 6 and Since the adhesive force to the objective lens 8 and the like is reduced, even if the sliding characteristics are improved, it cannot withstand long-term use, which is not preferable. In addition, when the material of the support shaft 2 is metal such as stainless steel, there is a problem that malfunction occurs due to corrosion and adhesion of foreign matter such as dust.

[Problems to be solved by the invention]

As described above, the actuator of the optical pickup in the prior art, in particular, the supporting shaft 2 constituting the actuator is excellent in all aspects such as lubrication characteristics, high dimensional accuracy, wear resistance, moisture (rust) resistance and stain resistance. However, there is a problem that the focusing servo and tracking servo lack reliability and durability such as instability, uncertainty or inoperability.

[Means for solving problems]

In order to solve the above problems, the present invention adopts means for forming a thin film made of a fluorine-containing polymer on a sliding surface of a lens holder supporting shaft of an optical pickup actuator. The details will be described below.

First, the fluorine-containing polymer of the present invention is a polyfluoroalkyl polymer or a fluoropolyether polymer. And the polyfluoroalkyl polymer, for example, _{CF 3 (CF 2) 7 -} , H (CH 2) 6, CF 2 Cl (CH 2) 11 -, A polymer having a polyfluoroalkyl group such as
The fluoropolyether polymer is a polymer having a unit represented by the general formula —C _x F _2x —O— (where x is an integer of 1 to 4) as a main structural unit, and preferably a polymer having an average molecular weight of 1000 to 50000. is there. In this way, the fluorine-containing polymer contains a functional group having a high affinity for metals, such as an epoxy group, an amino group, a carboxyl group, a hydroxyl group, a mercapto group, an isocyanate group, a sulfone group, and an ester group. However, the following can be specifically mentioned as an example. That is, C ₆ F ₁₃ COOH, C ₈ F ₁₇ C ₂ H ₄ OH, C ₈ F ₁₇ F ₂ H ₄ SH, C ₁₀ F ₂₁ CONHC ₂ H ₄ OH, C ₁₀ F ₂₁ SO ₃ H _{HOOC-CF 2 OC 2 F 4} O m CF 2 O n CF 2 COOH, _{CH 3 OOC-CF 2 OC 2} F 4 O m CF 2 O n CF 2 COOCH 3, HOCH 2 -CF 2 OC 2 F 4 O m CF 2 O n CF 2 -CH 2 OH, And so on.

Such a fluorine-containing polymer may be used alone, but especially when the material of the supporting shaft is a metal, considering that there are a large amount of hydroxyl groups, for example, those containing an epoxy group or an isocyanate group are preferable. . When using an epoxy group, it is advisable to add amines, acid anhydrides, etc. to react the same with the epoxy group. When the isocyanate group is used alone, an isocyanate trimerization catalyst such as a tin compound may be added.

Further, two or more fluorine-containing polymers may be used in combination,
In that case, the epoxy group-containing one is combined with the one having at least one kind of group such as amino group, carboxyl group, hydroxyl group and mercapto group, or the one containing carboxyl group and at least one of amino group and hydroxyl group. A combination containing a group containing different types of groups, or a combination containing an isocyanate group and a group containing at least one type of group such as a hydroxyl group, an amino group, a mercapto group and a carboxyl group. It is desirable that the groups are reacted with each other to make the polymer have a higher molecular weight so that a film having excellent abrasion resistance can be obtained.

Further, 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. As a suitable example of such a combination, a combination of adding ethylene glycol or diaminodiphenylmethane to the isocyanate group-containing fluorine-containing polymer, or a combination of adding an isocyanate compound to the hydroxyl group-containing fluorine-containing polymer, etc. Can be mentioned.

The fluorine-containing polymer described above has a considerable affinity for the surface of the material of the supporting shaft by itself, but depending on the type of the mating material, it does not always have sufficient adhesion strength. Since it is not always shown, in such a case, a thin film (called a primer) having an affinity between the coating and the mating material for both
Is preferred, and one example of such a primer is a graft polymer having polymethyl methacrylate as a branch component and a methyl methacrylate unit or a hydroxyethyl methacrylate unit as a trunk component.

Here, the method of applying the fluorine-containing polymer is not particularly limited as long as it is a method used for ordinary coating, for example, it is dissolved in a suitable solvent and applied (including spraying, dipping, etc.). After that, the solvent may be evaporated, and it is possible to increase the molecular weight of the film-forming component by heating after forming the thin film. It is desirable that the thickness of the film covering the surface of the support shaft is 5 μm or less, preferably 2 μm or less so as not to impair the dimensional accuracy of the support shaft. The material of the support shaft is not limited to metal, and synthetic resin, ceramics, etc. will not cause any problems.

〔Example〕

The raw materials mainly used in the following Examples are collectively shown as follows. In addition, in order to simplify the raw material names and chemical structural formulas, the numbers # to each raw material are used, and the mixing ratio of these is shown in parts by weight.

Fluorine-containing polymer: Epoxy group-containing polyfluoroalkyl polymer Amino group-containing polyfluoroalkyl polymer Polyfluoroalkyl polymer containing hydroxyl groups HOC ₂ H ₄ (CF ₂ ) ₇ C ₂ H ₄ OH Perfluoropolyether polymer containing isocyanate groups (average molecular weight: 2000) Hydroxyl group-containing Po fluoropolyether polymer (average molecular weight of about _{2000) HOCH 2 -CF 2 OC 2} F 4 O m CF 2 O n CF 2 -CH 2 OH carboxyl group-containing perfluoropolyether polymer (average molecular weight 1500) Other compounds: Isocyanate compound (n average value 0.6) Dibutyltin dilaurate Examples 1 to 9: The raw materials shown in Table 1 were diluted with the solvent in the table to 3% by weight to prepare a coating liquid, which was applied to the sliding portion of the supporting shaft. After coating, the coating was heated at 70 ° C. for 1 hour and then at 120 ° C. for 3 hours to form a coating of about 1 μm. Here, the stainless steel as the material of the supporting shaft is SUS 420 J2, or the ceramic coating is the surface of stainless steel or aluminum formed by thermal spraying of SiC ceramics to form a film having a thickness of about 25 μm.

The coated support shaft is shown in FIGS. 1 and 2. It was incorporated into such an optical pickup actuator, and the rusting test, the durability test, and the sliding characteristics before and after the durability test were investigated. In addition, PP shown in the column of sleeve material in Table 1
The S composition is obtained by melt blending 70% by weight of polyphenylene sulphide [PPS] resin (manufactured by US Phillips Co., Ltd .: Ryton P-4) and 30% by weight of carbon fiber (Toray, fiber length 6 mm). And the aluminum is A2
It is 017.

The specific methods of the rusting test, durability test and sliding property test are as follows.

(1) Rust test: The lens holder body 4 was left in the constant humidity chamber of 40 ° C. and 95% relative humidity for 500 hours with the lens holder body 4 inserted into the support shaft 2 to prevent rust on the surface of the support shaft 2. Optical microscope (× 2)
Observed in 0).

(2) Durability test Attach the optical pick-up actuator to be tested to the test stand, and connect the drive unit (made by our company) and the load voltage generator consisting of the signal generator (Signal generator TR98202 made by Advantest). Then, a voltage of 0.5 is applied to the drive coil 6 of the pickup actuator by the load voltage generator.
A load voltage of V and a frequency of 20 Hz (sine wave) was applied, the lens holder body 4 was driven with an amplitude of ± 1.5 mm, and continuous operation was performed in an indoor atmosphere. Although it is a guideline for durability, it has a running time until it malfunctions.
For those that can withstand a long-time operation exceeding 0 hours, the operation was discontinued after 500 hours.

(3) Sliding property test: A lens holder displacement measuring device consisting of an optical actuator test head (Advantest: TQ88091) and an analyzing recorder (Yokogawa Hokushin Electric: 3656) was used. A 500-hour sample pickup actuator was attached, and a voltage of 0.1 V and a frequency of 0.1 were obtained by using a load voltage generator consisting of a drive unit (manufactured by our company) and a signal generator (FG-350 manufactured by Iwasaki Tsushinki Co., Ltd.). A triangular triangular wave loading voltage is applied to the driving coil 6 and the difference between the loading voltage wave system and the response waveform of the lens holder body 4 is large or small (the closer the two waveforms are to each other, the better the lubricity). (○
The evaluation was made in three grades: marked), acceptable (marked) and defective (marked x).

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

Comparative Examples 1 and 2: Stainless steel was used for the supporting shaft of Comparative Example 1, and the same ceramic spray coating as in Example 8 was used for the supporting shaft of Comparative Example 2. Both sleeves were integrated with the holder body. Polyphenylene sulphide (PPS) resin (70% by weight of Ryton P-4 made by US Phillips Co., Ltd.) and 30% by weight of carbon fiber (Toray, fiber length 6 mm) are melt-blended. A pick-up actuator was produced and various tests similar to those of the example were conducted. The obtained results are also shown in Table 2.

Comparative Example 3: Epoxy group-containing organopolysiloxane (Shin-Etsu Chemical Industry: Epoxy modified silicone oil KF 10
A composition prepared by adding 0.6% of dibutyltin dilaurate to 2) was diluted with Freon 113 to a concentration of 3% by weight to prepare a coating liquid, which was applied to the sliding portion of a stainless steel support shaft. After coating, it was dried at 70 ° C. for 1 hour and heated at 150 ° C. for 3 hours to form a coating film having a thickness of about 1 μm. This support shaft and Comparative Example 1
A pick-up actuator consisting of the holder made of the resin composition used in Examples 1 and 2 was prepared and various tests similar to those in Examples were conducted. The obtained results are also shown in Table 2.

Comparative Example 4: Hydroxyl group-containing organopolysiloxane (Shin-Etsu Chemical Co., Ltd .: Silicone diol X-22-160C) was diluted with Freon 113 to a concentration of 3% by weight to prepare a coating solution, which was made of stainless steel. After applying to the sliding part of the support shaft,
It was dried at 70 ° C. for 1 hour and heated at 150 ° C. for 3 hours to form a film having a thickness of about 1 μm. A pick-up actuator consisting of this support shaft and the same holder made of the same resin composition as in Comparative Example 3 was prepared, and various tests similar to those of the example were conducted. The obtained results are also shown in Table 2.

As is clear from Table 2, in each of Examples 1 to 9, the endurance test was sufficiently secured for 500 hours.
5, 7, 8 and 9 were also excellent in sliding properties after 500 hours. Further, both Examples 3 and 5 use a fluorine-containing polymer containing a hydroxyl group, but Example 5 using a fluoropolyether polymer is more preferable than Example 3 using a fluoroalkyl polymer. It was discovered that it has excellent sliding properties. On the other hand, Comparative Examples 1 and 2 in which the lubricating film was not formed on the supporting shaft, and Comparative Examples 3 and 4 which were other than the fluorine-containing polymer in the present invention even when the lubricating film was further formed. None of them had satisfactory durability (particularly after aging), and in Comparative Example 1, rust was also found on the support shaft.

(Effect) As described above, the actuator of the optical pickup of the present invention has no fear of rusting of the supporting shaft, which is a main component thereof, and therefore can be used even in a hot and humid atmosphere, and is particularly suitable for lens holder materials. Since the slidability is not required, a material having a high elastic modulus and good adhesiveness can be selected as the lens holder material, and as a result, the problem of higher order resonance can be solved. It also provides excellent sliding characteristics in focusing drive and tracking drive without impairing the adhesiveness between the lens and the coil, etc. , The focusing servo and tracking servo with good reliability can be implemented and the durability is very good. Therefore, it can be said that the significance of the present invention is extremely great.

[Brief description of drawings]

FIG. 1 is a plan view for illustrating the structure of an optical pickup actuator, and FIG. 2 is a sectional view of FIG. 1 ... Base, 2 ... Support axis, 3 ... Magnetic core, 4 ...
Lens holder body, 5 ... Sleeve, 6 ... Driving coil, 7 ... Lens mounting hole, 8 ... Objective lens

Claims (1)

[Claims] 1. An actuator for an optical pickup, wherein a thin film made of a fluorine-containing polymer is formed on a sliding surface of a lens holder supporting shaft which is supported so as to be movable and rotatable in an axial direction. .