Classifications

• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
  • G02B6/02—Optical fibres with cladding with or without a coating
  • G02B6/02033—Core or cladding made from organic material, e.g. polymeric material
  • G02B6/02038—Core or cladding made from organic material, e.g. polymeric material with core or cladding having graded refractive index
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B3/00—Simple or compound lenses
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29D—PRODUCING PARTICULAR ARTICLES FROM PLASTICS OR FROM SUBSTANCES IN A PLASTIC STATE
  • B29D11/00—Producing optical elements, e.g. lenses or prisms
  • B29D11/00663—Production of light guides
  • B29D11/00721—Production of light guides involving preforms for the manufacture of light guides
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B3/00—Simple or compound lenses
  • G02B3/0087—Simple or compound lenses with index gradient

Definitions

• the present invention relates to a graded index (type) that can be usefully used as various optical transmission lines such as an optical converging optical fiber, an optical converging rod lens, and an optical sensor.
• the present invention relates to an optical transmitter made of blast and a method of manufacturing the same, and more particularly to an optical transmitter capable of transmitting a high-quality image with high resolution and little chromatic aberration, and a method of manufacturing the same.
• the refractive index is continuously reduced from the center to the outer periphery in the cross section of the optical transmission body, and the distribution has a mountain-shaped inclination.
• the attached GI optical transmitter is used.
• Such GI-type optical transmission suspensions are disclosed in Japanese Patent Publication No. 47-816, Japanese Patent Publication No. 47-28059, EP Publication No. 2008-159, etc. .
• the GI type optical transmitter disclosed in Japanese Patent Publication No. 47-1816 was made of glass and was made by the ion exchange method. Therefore, it is difficult to produce products with the same shape and the same performance between different lots because of low productivity, especially rods of the same length with a certain total conjugate length. It is difficult to make the same lens with the same performance between different rods. As a result, the length of the GI type optical transmitter with the same performance is not uniform, and the handling is difficult. There was a drawback that it became difficult.
• the GI-type plastic optical transmitter disclosed in JP-B-47-28059 is a mixture of two or more transparent polymers having different refractive indices and different solubilities in a specific solvent.
• a rod-shaped or fiber-shaped shaped article is immersed in the above-mentioned solvent, and the mixing ratio of the above-mentioned polymer is changed from the surface to the center of the shaped article. It is made by doing.
• a plastic GI optical transmitter can be produced for the time being, but a mixture of two or more polymers having different refractive indices tends to cause a disorder in the refractive index distribution. It is difficult to make the refractive index distribution from the part toward the outer periphery follow the optimum distribution curve.
• the transparency of the optical transmitter is reduced, and light scattering is likely to occur.
• the characteristics of the GI type optical transmitter are not sufficient, and the application development thereof is not progressing.
• EP Publication No. 0 218 159 discloses that at least one kind of thermoplastic polymer (A) is compatible with the polymer (A) when polymerized, and the polymer (A)
• the monomer (B) is volatilized from the surface of the molded article obtained by molding a homogeneous mixture of the monomer (B), which is a polymer having a different refractive index from that of the polymer (B), into a rod shape. This gives a continuous concentration distribution of the monomer (B) from the surface of the molded article to the center thereof, and then polymerizes the unpolymerized monomer in the molded article.
• a method of making a GI type plastic optical transmission medium is shown.
• the refractive index distribution curve of a GI optical transmission medium should have a quadratic distribution curve expressed by the following equation (3), and such a curve is indicated by the curve indicated by A in Fig. 2. It is said that
• N N 0 (1-ar 2 ) (3)
• the refractive index distribution curve measured with a microscope is shown at B in Fig. 2 and is 0.5 r from the center in the radial direction. ⁇ 0.75 r. (In the same figure, the range from c to d, and e indicates the outer periphery).
• the refractive index distribution curve has a shape relatively close to the optimal curve shown by equation (3).
• the outer and inner refractive index distributions have shapes that deviate significantly from the optimal curve.
• the light of the light source (42) is adjusted by the lens (43), as shown in FIG. 4, to calculate the MTF values of the optical transmitter of the prior art and the optical transmitter of the present invention.
• the light passing through the grating (45) having a lattice constant of 4 (Limpano mm) is applied to the GI-type optical transmitter (41), and the lattice image passing through the optical transmitter is applied to the CCD sensor (46).
• the maximum value i réelle X and the minimum value i of the measured light quantity were measured as shown in FIG. 5 and determined by the following equation (4).
• MTF (3 ⁇ 4) ⁇ (im, xi »ln) / (im.x + im in) ⁇ X 100 (4) has a refractive index distribution that almost exactly follows the optimal curve defined by the above equation (3) GI-type plastic optical transmitters have not been developed yet.
• the present inventors Prior to the present invention, the present inventors used a monochromatic light source such as an LED, and had a resolution high enough to be usefully used as an optical transmitter for a facsimile image sensor and chromatic aberration.
• a monochromatic light source such as an LED
• a refractive index distribution approximating the refractive index distribution curve to be obtained is provided, and a grid image of 4 line Pano mm is formed on the CCD line sensor through the light transmitting body and measured.
• the refractive index distribution in the radial direction of the GI optical transmission body achieved by the present invention is as shown in [[] of FIG. 1 and is a curve [I] that follows the optimal curve of equation (3).
• the number of parts that correspond to the number increases, and when image transmission is actually performed with this optical transmitter, its performance is higher than the image transmission characteristics of a conventionally developed optical transmitter made of plastic. Has been significantly improved.
• a method of making the outer peripheral area blacker has been studied, and although some effects have been obtained, the image transmission effect of the entire optical transmission body is reduced by blackening accordingly. There is a problem of doing so and it is not enough.
• the present inventors assumed the bending as shown in [I] in FIG. A GI-type plastic optical transmission medium with a refractive index distribution is made to remove the areas C to D (F) from the areas C to E shown in Fig. 1. As a result, the present inventors have found that a GI-type optical transmitter can be obtained in which the above-mentioned difficulties have been remarkably improved, and the present invention has been completed.
• the gist of the present invention is the radius r.
• the GI type plastic optical transmission body is characterized in that the refractive index distribution in the range of (1) has an approximate refractive index distribution to the refractive index distribution curve defined by the following equation (1).
• n (r) n 0 ⁇ l- (gV2) r 2 ⁇ (1)
• ⁇ is the refractive index of the central axis of the optical transmission member, and is an arbitrary value within the range of 1.5 ⁇ 0.1.
• ⁇ (r) is the optical transmission member.
• the refractive index at a position at a distance r from the center axis of the optical transmission member to the outer peripheral direction, g represents the refractive index distribution constant of the optical transmission body, and is a value of 0.3 to 0.7, and r is the light transmission coefficient. Indicates the distance from the center axis of the transmission body toward the outer periphery.
• the radius L At least 0.25 from the central axis to the outer peripheral surface of the GI-type plastic optical transmission body preform having a circular cross section within the range of 0.5 ⁇ 0.1 mm. L. ⁇ 0.7 L.
• the feature is to remove the outer periphery of the optical transmitter preform having a refractive index distribution whose refractive index distribution approximates the refractive index distribution curve defined by the following equation (2). The method of manufacturing the GI-type plastic optical transmission body described above.
• n (L) No ⁇ l- (g 2/2) L 2 ⁇ (2)
• N. is a refractive index of the central axis portion of the optical transmission medium, and is an arbitrary value within a range of 1.5 ⁇ 0.1.
• the GI-type plastic optical transmission body of the present invention has at least 0.25r from the central axis toward the outer peripheral surface. ⁇ 0.8 r. , Preferably 0 ⁇ 25 ⁇ . ⁇ 0 ⁇ 85 ⁇ . Since the refractive index distribution in the range of has a refractive index distribution approximating the optimal curve of the refractive index distribution defined by the above equation (1), a grid image of 4 line pairs mm is transmitted through the optical transmission body to the CCD line. The maximum light intensity value i « ⁇ ⁇ and the minimum light intensity value i ⁇ measured by imaging on the sensor are measured, and the characteristic that the MTF calculated by the above equation (4) is 60% or more is provided. This and force 5 can and Do Ri, compared to the GI optical transmission article have been conventionally developed can and this performing quality image transmission, becomes excellent light transmission member, especially no image Bo Ke peripheral portion.
• the optical transmitter of the present invention has a radius r.
• Has a circular cross-section in the range of 0.45 ⁇ 0.1 mm, so that at least r 0.25r. ⁇ 0.8 r. Within this range, the refractive index distribution can be made the optimum distribution.
• Radius r. Is in the above range For larger values, 0.25 r. ⁇ 0.8 r. It is difficult to satisfy Equation (1) in the range of.
• Radius r. Is in the above range For larger values, 0.25 r. ⁇ 0.8 r. It is difficult to satisfy Equation (1) in the range of.
• the refractive index n of the central axis portion If it is outside the above specified range, it will be difficult to increase the MTF to 60% or more. If the refractive index distribution constant g is larger than the above specified range, the conjugation length becomes too short and it becomes difficult to set a distance for operation. Conversely, if it is too small, the conjugate length will be long, and it will be difficult to reduce the size of a facsimile medium-scanner or the like incorporating an optical transmitter.
• the GI optical transmitter of the present invention will be further described together with the method of manufacturing the GI optical transmitter of the present invention.
• the optical transmitter according to the present invention produces an optical transmitter preform having a specific performance, and then removes the outer periphery of the preform by, for example, physically peeling off the outer periphery. It is obtained by
• the pli off O over arm is depends refractive index after curing each other, the viscosity at uncured state is prepared 3 or more uncured liquid substance is 1 0 3 to 1 0 8 Boi's, the non The cured liquid material is supplied to a multilayer composite spun nozzle, for example, so that the refractive index decreases gradually from the center to the outer peripheral surface, and is concentrically laminated. Trandoff Eye When the refractive index after curing of each layer and the thickness of the layer are made into a strand fin, the center position of each layer is the center from the strand fiber.
• the equation (2) should be made to match, and then this strand fiber An uncured strand fiber is applied while inter-diffusion treatment of the material between adjacent layers is performed or after inter-diffusion treatment so that the refractive index distribution between the layers becomes a continuous refractive index distribution. Can be obtained by hardening.
• Viscosity Yes displacement of the uncured liquid material used in the present invention also have 1 0 3 ⁇ 1 0 ⁇ and is not to like this in the range of Boi's.
• the viscosity tends to the formation of 1 0 3 Ri by Boi's small and Itosetsu Re filamentous product frequently during shaping becomes difficult. If the viscosity is greater than 10 ⁇ - voids, the shaping operability will be poor, making it difficult to arrange each layer concentrically, and shaping with large unevenness in thickness. It becomes easy to become things.
• the uncured liquid substance used in the present invention is a substance that can be cured, that is, polymerizable and cross-linkable, and may be a radically polymerizable vinyl monomer or the same.
• a composition comprising a monomer and a polymer soluble in the monomer can be used.
• the above-mentioned uncured liquid is used.
• Substance is on It is preferably composed of a vinyl monomer as described above, and a polymer and a force soluble in the butyl monomer.
• polymers having the same refractive index for each layer in order to adjust the viscosity, since a blast optical transmitter having a continuous refractive index distribution from the center toward the surface can be easily obtained.
• polymer methyl acrylate is excellent in transparency and has a high refractive index of itself, so that it is suitable as a polymer used in producing the GI type optical transmission body of the present invention. It is.
• the strand fiber formed from the uncured material it is preferable to add a heat curing catalyst and a photo-curing catalyst to the uncured material. No. That is, the thermosetting catalyst and Then, the strand fiber containing the photocuring catalyst is heated or heat-treated, or irradiated with light, preferably ultraviolet light, from the surroundings.
• thermosetting catalyst an ordinary peroxyside catalyst is used.
• Benzofuenone benzoin alkyl ether, 4'-isoprobiyl-1 2 -hydroxyl 2 -methyl-ropiophenone, light-curing catalysts as light curing catalysts Phenyl ketone, benzyl methyl ketone, 2,2-diethoxyacetophenone, chlorothioxanthone, thioxanthonone compound, benzophenone compound, benzophenone compound, 4-dimethylamino Ethyl benzoate, 41-dimethylaminoisoamyl benzoate, N-methyljetanolamine, triethylamine, and the like.
• Light sources used for photopolymerization include carbon arc lamps, high-pressure mercury lamps, ultra-high-pressure mercury lamps, low-pressure mercury lamps, chemical lamps, and xenon lamps that emit light with a wavelength of 150 to 600 nm. , Laser light and the like.
• the radius of the rod of the optical transmission medium must be in the range of 0.5 ⁇ 0 ⁇ lmm, and if the radius is larger than this range, the radius of the bridge becomes larger. 0.25 L of home rod. ⁇ 0.70 L. It is difficult to obtain a refractive index distribution that is close to the highest expression represented by the expression (2) within the range described above, and the preform for manufacturing a high-resolution GI optical transmission body, which is the object of the present invention, is obtained. It becomes difficult to make a game.
• the composition of each uncured substance (monomer polymer ratio, refractive index, etc.)
• the refractive index of the preform rod can be set to 0.2 by appropriately combining the output ratio, the discharge nozzle temperature, the temperature at the time of mutual diffusion, time, light or heat curing (polymerization) conditions, and the like. 5 L. ⁇ 0.70 L. It can be approximated to the quadratic equation of equation (2) within the range of.
• the method of removing the outer periphery of the optical transmitter preform is as follows: (1) The outer periphery of the optical transmitter preform is swollen with a solvent and a predetermined size is obtained in that state. (2) a method of cutting the outer periphery of the optical transmission body preform with a cutting tool, (3) a method of cutting the swollen portion through a hole having a hole diameter of (3) Examples of the method include immersing the reform in an alkaline solution or the like, and dissolving and removing the outer peripheral portion.
• the method of swelling the optical transmission medium of (1) with a solvent is to put the plastic optical transmission medium in a solvent capable of dissolving the plastic. After immersion and swelling within a predetermined range, the swelled part is cut through a circular hole with a predetermined diameter, and the type of solvent used, immersion time in the solvent, swelling Depending on the temperature and the size of the circular hole, the cutting width can be adjusted.
• Solvents for dissolving the plastic for optical transmission medium such as black mouth form, methylene chloride, carbon tetrachloride, methyl ethyl ketone, acetate, and ethyl acetate. Can be mentioned.
• the method of shaving the outer periphery of the optical transmission body foam with the cutter of (2) can be performed, for example, by a method as shown in the perspective view of the cutter in FIG. it can.
• (10) is This is an optical transmission body form
• (11) is a GI type optical transmission body having high resolution characteristics of the present invention.
• the number of cutting teeth (22) may be one, but it is preferable to use them in combination.
• a plurality of cutting teeth are attached to the rotating body (21) and the driving source (24) is used. By rotating, the outer circumference of the optical transmission medium preform that passes through the hole at the center of rotation is efficiently cut and without causing unnecessary damage to the briform. it can.
• (12) is a cutting oil spraying device for preventing the preform from being cut poorly due to heat generated when cutting the optical transmission medium (10).
• (30) is a new blower for pulling out the GI-type optical transmission line of the present invention, and the cutting speed of the preform is the same as the rotation speed of the rotating tooth (22). This can be done by adjusting the take-off speed of the blower (30).
• Fig. 1 is a diagram showing the refractive index distribution of the optical transmission body of the present invention
• Fig. 2 is a diagram showing the refractive index distribution of an optical transmission body developed conventionally
• Fig. 3 is a lattice image observed with the optical transmission body.
• (A) is a grid image observed using an optical transmission body whose refractive index distribution approximates the quadratic curve defined by equation (3)
• (b) c) is a lattice image observed using an optical transmitter whose refractive index distribution is farther from the ideal refractive index distribution.
• Fig. 4 shows the maximum (i « ⁇ ⁇ ) and minimum (i min) values of transmitted light using a CCD sensor when observing a lattice image with an optical transmitter.
• FIG. 5 shows a device for measuring Fig. 6 shows the measurement results of the maximum light quantity and the minimum light quantity, and Fig. 6 shows the outer peripheral cutting device of the optical transmitter preform used to create the optical transmitter of the present invention.
• FIG. 7 is a diagram showing a refractive index distribution of the optical transmitter of the present invention.
• the width of each layer of the composite spinning nozzle used was such that the refractive index of the cured product of a plurality of types of uncured liquid material decreased gradually from the center, and the center position of each layer is the distance from the center axis to the strand fiber on the horizontal axis.
• the refractive index of each layer was plotted on the vertical axis, the one designed to follow the quadratic curve represented by the above equation (2) was used.
• the mixture was heated and mixed with C to obtain an unhardened liquid material for forming the first layer (center).
• a fiber optic with a radius (L.) of 0.5 mm is run at a speed of 50 cmZ at a speed of 50 cmZ so that it passes through the center of the illuminated section.
• the reform was taken off with a mini-proler.
• the refractive index distribution was 1.512 at the center (N.) and 1.470 at the periphery, and the refractive index distribution constant (g) was 0.52. 0.25 L from the center to the outer surface as shown in the figure. ⁇ 0.75 L.
• the end faces of the optical transmitter body were polished to a lens length of 7.2 mm, and the MTF measured using a 4-line Pano mm grid was 57%. Had a conjugate length of 15.4 mm.
• the image of the obtained lattice was a clear image with little distortion, but distortion was observed in the peripheral part.
• a plurality of the optical transmitters are assembled into an optical transmitter array having a lens length of 7.1 mm having a structure as shown in FIG.
• the MTF measured using a 4-line-pair Zmm mm grid of the body array was 49% and the conjugate length was 15.4 mm.
• the above-mentioned optical transmission medium was immersed for 45 seconds in a black-hole hologram in which the temperature was kept at 10, and passed through a small hole made in a 1-mm-thick silicone rubber sheet.
• the portion swollen with the mouth holm portion F in Fig. 1 was removed to obtain an optical transmitter with a radius (r) of 0.448 mm.
• the refractive index distribution of the optical transmission body is 1.512 at the central axis (n.) And 1.474 at the periphery, and the refractive index distribution constant ()
• the value of 0.52 is 0.24r from the central force toward the outer peripheral surface.
• ⁇ 0.82 r. Has a refractive index distribution that approximates the quadratic curve I that satisfies Eq. (1).
• Both ends of the optical transmission body were polished to a lens length of 7.2 mm, and the MTF measured using a 4-line pair / mm grating was 65%, with a conjugate length of 1.5 mm. It was 4 mm.
• the image of the obtained grating is the light before the surface is scraped. It was a clear image with very little distortion including the peripheral part as compared with the transmission body form. .
• a plurality of these optical transmitters are assembled into an optical transmitter array having a lens length of 7.2 mm having a structure as shown at 47 in FIG.
• the MTF measured using a grating with a line pair of Zmm was 56%, and its conjugate length was 15.4.
• An image scanner was assembled by combining an LED with a light source and a CCD as a light receiving element on this optical transmitter array. This image scanner had a high resolution and was able to transmit clear images.
• the mixture obtained by heating and kneading parts by weight at 65 was used as the liquid material for forming the second layer, and the liquid material for the second layer used in Example 1 was used for the third layer.
• the mixture was heated and kneaded in the above to form a liquid material for forming the fourth layer.
• a concentric four-layer composite nozzle is made from the above four types of liquid substances.
• an extruded strand fiber was used at the same time.
• the viscosity of the Shi pushed out liquid material of the first layer is 4. 5 X 1 0 4 Boi's
• liquid material of the second layer is 4.0 1 0 4 Boi's
• liquid material of the third layer is 2.0 X 1 0 "
• the liquid-like material of the fourth layer is 2. was 2 X 1 0 4 Boi's. temperature of the composite Roh nozzle met 6 0 e C.
• an optical transmission body foam having a hardening (L.) of 0.48 mm was obtained by curing in the same manner as in Example 1.
• the optical transmission medium obtained when the discharge ratio is (first layer): (second layer): (third layer): (fourth layer) is set to 2: 1: 1: 1.
• the refractive index distribution measured with an interface microscope is the central axis (N.
• the peripheral part is 1.479, and the refractive index distribution constant (g) is 0.53. From the center to the outer peripheral surface as shown in ⁇ in FIG. 0.2 L towards you. ⁇ 0.75 L. The refractive index distribution approximated to the quadratic curve IV shown by the equation (2) in the range of (2).
• the MTF measured using a 4-line-pair Z mm grid was 5.7% at a lens length of 7.1 mm and a conjugate length of 14.9 mm.
• the MTF was 53%.
• Both ends of the optical transmission body were polished to a lens length of 7.1 mm, and the MTF measured using a 4-lane Zmm grating was 71%, with a conjugate length of 14.9. mm.
• the obtained image of the grating was a clear image with very little distortion including the peripheral part, compared to the optical transmission medium before shaving the surface.
• a plurality of these optical transmitters are assembled into an optical transmitter array having a lens length of 7.1 mm and having a structure as shown in FIG. 4 at 47, and the optical transmitter array is assembled into four line pairs.
• the MTF measured using a lattice of Zmm was 63% at a conjugate length of 14.9.
• An image scanner was assembled by combining an LED with a light source and a CCD as a light receiving element on this optical transmitter array. This image scanner has a high resolution and was able to transmit clear images.
• Example 1 Each of the liquid materials for forming the first to fourth layers used in Example 2 and the solution material for forming the fifth layer were used for forming the third layer in Example 1. These liquid materials for each layer are supplied to five layers of concentric composite nozzles, extruded at the same time, made into a strand fiber, cured, and cured to form an optical transmitter preform. I got it.
• the refractive index distribution of the briform (L .: 0.48 mm) measured by an interferometer interference microscope was 1.514 at the central axis (N.) and around the periphery.
• the refractive index distribution constant (g) is 0.57, and 0.15 L from the center toward the outer peripheral surface. ⁇ 0.79 L. In the range, the refractive index distribution approximated the optimum curve shown by the equation (2).
• the MTF measured using a 4-line pair Z mm lattice was 5.9% with a lens length of 8.0 mm and a conjugate length of 15.9 mm. Furthermore, the MTF of the optical transmitter array prepared in the same manner as in Example 1 using this optical transmitter preform was 57% (measured with a grid of 4 line pairs / mm). Was.
• the optical transmitter preform was removed from the outer peripheral surface using a water-resistant sandpaper (No. 200), and the optical transmitter having a radius (r.) Of 0.44 mm was used. I got The refractive index distribution of this optical transmission body is 1.514 at the central axis ( n .) And si.4722 at the peripheral portion, and the refractive index distribution constant (g) is 0.57. 0.13 L from center to outer circumference. ⁇ 0.89 L. The refractive index distribution approximated to the optimal curve represented by the equation (1) in the range of (1).
• the MTF measured in the same manner as in Example 1 had a lens length of 8.0 mm and a conjugate length of 15.9. It was 75% in mm.
• the MTF of the optical transmitter array prepared using this optical transmitter in the same manner as in Example 1 was 71% (measured on a 4-line-pair mm grid). Image scanners are not always used, and always transmit high-resolution images. I was able to do it.
• the GI-type plastic optical transmission body of the present invention has at least 0.25 mm from the center thereof. ⁇ 0 '8 0 ⁇ . Since the refractive index distribution in the range of is very similar to the distribution curve shown in equation (1), it is possible to perform high-quality image transmission with no image blur at the periphery and particularly high resolution. It is extremely useful as an optical transmitter for copiers, facsimiles, and LED printers that require a high speed.

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• Physics & Mathematics (AREA)
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• Engineering & Computer Science (AREA)
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• Manufacturing & Machinery (AREA)
• Ophthalmology & Optometry (AREA)
• Mechanical Engineering (AREA)
• Light Guides In General And Applications Therefor (AREA)
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• 1992
  • 1992-02-26 EP EP92906216A patent/EP0527239B1/en not_active Expired - Lifetime
  • 1992-02-26 JP JP50606592A patent/JP3301760B2/ja not_active Expired - Lifetime
  • 1992-02-26 WO PCT/JP1992/000210 patent/WO1992015901A1/ja active IP Right Grant
  • 1992-02-26 US US07/949,479 patent/US5287222A/en not_active Expired - Fee Related
  • 1992-02-26 DE DE69213866T patent/DE69213866T2/de not_active Expired - Fee Related
  • 1992-02-26 KR KR1019920702704A patent/KR100260568B1/ko not_active Expired - Fee Related
  • 1992-03-12 TW TW081101883A patent/TW255016B/zh active

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