JP2007297229A - Method for manufacturing optical device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress the decentering due to molding and the development of flash caused by the decentering by correctly positioning a lens material on the central axis of a molding surface. <P>SOLUTION: A lens material 5 has a convexity having a larger radius of curvature than that of the concavity of a lower die 2. The lens material 5 is abutted against the peripheral part of the concavity in the state where a gap is provided between the deepest part of the concavity and the top of the convexity of the lens material 5, and is arranged in a set of molding dies 10 aligned by the difference of curvature between the concavity and the convexity of the lens material 5. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for manufacturing an optical element used in an optical system of a laser optical device or an imaging device, and particularly relates to a technique for manufacturing an optical element by a precision press molding method.

  In recent years, an aspherical lens having a performance superior to that of a spherical lens has been adopted as an optical element used for an optical disk device, a digital video camera, and the like from the viewpoint of effective use of light and reduction of aberration. An aspherical lens is generally produced by a precision press molding method because it is not preferable from the viewpoint of ease of production and production cost when it is attempted to produce it by a conventional polishing method.

  In this precision press molding method, when the aspherical lens is made of a glass material with various optical constants and a wide range of material selection, it is deformed by applying temperature and pressure according to the thermal characteristics of the glass material. I try to let them.

  In Patent Document 1, when a glass material is put into an internal space formed by an upper die and a barrel die, a glass material having an outer diameter approximate to the inner diameter of the barrel mold is used. A technique for preventing the generation of burrs by placing a glass material substantially at the center of the mold forming surface is disclosed.

  However, in the technique described in Patent Document 1, since molding is performed using a planar glass material, the sealed space between the mold molding surface and the sealed space partitioned by the mold molding surface and the glass material is large. In press operation for degassing, there is a possibility that the untransferred part of the lens surface may not be avoided unless it is repeatedly pressed and released, and it is necessary to insert the glass material between the glass material and the barrel inner diameter Since a clear clearance is indispensable, there is a problem that there is no guarantee that the glass material is necessarily placed at the center of the molding surface.

  Further, Patent Document 2 discloses a temperature difference between a temperature of a mold member that forms a non-optically effective surface and a temperature of a mold member that forms an optically effective surface using a mold composed of an upper and lower mold and a body mold. And a technique for setting the temperature of the mold member forming the non-optically effective surface low is disclosed. That is, a countermeasure against burrs is made by suppressing the flow of the glass material by lowering the temperature in the vicinity of the clearance between the upper and lower molds and the trunk mold, which are the places where burrs are generated.

  However, in the technique described in Patent Document 2, the non-optical effective surface (lens outer peripheral portion) and the optical effective surface (range from the lens central portion to the vicinity of the lens outer peripheral portion) are extremely close to each other, and the adjacent molds It is not only difficult to provide a temperature difference in the member due to heat conduction, but thermal distortion increases depending on the magnitude of the temperature difference, which may induce cracks and cracks in the molded lens.

  Patent Document 3 discloses preparing a chamfered material (a material chamfered by machining or molding) as a molding preliminary body. That is, a chamfering process is performed in advance on a portion where burrs of the molded product are likely to occur, thereby controlling the amount of deformation of the material and taking measures against burrs.

  However, the technique described in Patent Document 3 has a problem that the molded product becomes expensive, for example, preliminary processing is necessary to obtain the molded product, and two molding operations are required.

  In order to solve these problems, for example, when the lens surface has a convex shape, a glass material having a surface shape with a radius of curvature smaller than the radius of curvature of the aspherical surface to be the molding surface is used, and the shape of the molding surface is It is conceivable to obtain a lens having a desired shape by precisely transferring the lens to a glass material.

  FIG. 3 is a cross-sectional view showing a configuration of a conventional lens mold set. As shown in FIG. 3, the lens mold set includes an upper mold 31, a lower mold 32 disposed opposite to the upper mold 31, and a cylindrical shape in which the upper mold 31 and the lower mold 32 are slidably inserted. A body mold 33 is provided.

The upper mold 31 and the lower mold 32 are formed with aspherical concave portions that serve as molding surfaces. A glass material 39 is disposed in the lens mold set, and a lens having a desired shape is molded by pressing with the upper mold 31 and the lower mold 32.
JP-A-8-301624 Japanese Patent Laid-Open No. 10-152331 JP 2001-163628 A

  However, when the curvature radius of the surface of the glass material 39 is smaller than the curvature radius of the molding surface, the glass material 39 is in contact with the molding surface at only two points P1 and P2 during molding. It is extremely difficult to match the central axis of the molding surface with the central axis of the glass material 39, and not only the shape of the transfer surface is deteriorated, but the glass material 39 is deformed non-axisymmetrically and eccentrically. There was a risk that burrs would occur on the outer periphery of the lens.

  The present invention has been made in view of the above points, and an object of the present invention is to accurately position the lens material on the center axis of the molding surface, and to determine the eccentricity caused by molding and the burrs caused by the eccentricity. It is to suppress the occurrence of.

  That is, in the method of manufacturing an optical element according to the present invention, a lens material having a convex portion having a curvature radius larger than the curvature radius of the concave portion of the lower mold is placed between the deepest portion of the concave portion and the topmost portion of the convex portion of the lens material. In the state where a gap is provided in the concave portion, it is brought into contact with the peripheral portion of the concave portion, and is aligned by the difference in curvature between the concave portion and the convex portion of the lens material, and is arranged in the mold set, and the arranged lens material is near the softening temperature. And the heated lens material is pressed with an upper mold and a lower mold to mold an optical element.

  As described above, according to the present invention, the lens material is accurately positioned on the center axis of the molding surface by utilizing the automatic centering action (bell clamp action) based on the difference in curvature between the lens material and the molding surface. This is advantageous in suppressing the eccentricity caused by molding and the generation of burrs caused by the eccentricity. Thereby, high-quality lens supply and high-productivity lens molding can be realized.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The following description of the preferred embodiments is merely exemplary in nature and is in no way intended to limit the invention, its application, or its application.

  FIG. 1 is a partial cross-sectional view for explaining a manufacturing method using an optical element manufacturing apparatus according to an embodiment of the present invention. As shown in FIG. 1, the optical element manufacturing apparatus includes a mold set 10, an upper heating plate 7, and a lower heating plate 8.

  The mold set 10 includes an upper mold 1 in which an aspherical concave portion serving as a molding surface is formed on the lower surface of a cylindrical member, and an aspherical concave portion disposed opposite to the upper mold 1 and serving as a molding surface on the upper surface. A lower mold 2 in which the upper mold 1 and the lower mold 2 are slidably inserted, and is fitted to the inner mold 3 and is higher in the axial direction than the inner mold 3. And an outer shell mold 4 formed so as to be high.

  The outer cylinder die 4 functions as a stopper that abuts on the upper heating plate 7 and regulates the position at the time of press molding, and is formed based on the axial dimensional difference between the inner cylinder die 3 and the outer cylinder die 4. The thickness of the lens to be set is set.

  The upper heating plate 7 is disposed in contact with the upper portion of the upper mold 1 and has a heater 6 embedded therein so that the upper mold 1 can be heated to a predetermined temperature.

  The lower heating plate 8 is disposed in contact with the lower portions of the lower mold 2, the inner trunk mold 3, and the outer trunk mold 4, and a heater 6 is embedded therein. The entire mold set 10 is heated to a predetermined temperature. It can be heated.

  A press shaft (not shown) is connected to the upper part of the upper heating plate 7 so that the pressure required for lens molding can be performed with a predetermined pressing force F.

  In FIG. 1, the temperature detection and temperature control of the upper heating plate 7 and the lower heating plate 8, the mold set 10, the upper heating plate 7, and the chamber in which the entire lower heating plate 8 is disposed in an inert atmosphere are illustrated. Is omitted.

  In the mold set 10, a lens material 5 that is molded into a lens is disposed. Specifically, the lens material 5 is formed in a substantially spherical shape, and has a convex portion having a radius of curvature larger than the radius of curvature of the concave portion serving as the molding surface of the lower die 2, and the deepest portion of the concave portion of the lower die 2. In a state in which a sealed space S is provided between the convex portion of the lens material 5 and the top of the convex portion of the lens material 5, the lower mold 2 is disposed so as to abut on the peripheral portion (circumferential portion including the contact points P2 and P3) of the concave portion. ing. As a result, when the molding surface of the upper mold 1 is brought into contact with the lens material 5, the lens material 5 has contact points P1, P2, P3 (more precisely, a circumferential portion including the contact points P2, P3, and The lens material 5 can be stably held in the mold set 10 by being supported by the contact point P1).

  Further, the lens material 5 is centered (bell clamp action) by the difference in curvature between the concave portion of the lower mold 2 and the convex portion of the lens material 5, and is accurately positioned on the central axis of the concave portion serving as a molding surface. Yes. As a result, the lens material 5 can be placed very accurately with respect to the center of the molding surface.

  Specifically, in the present embodiment, a case where the focal length of the molded lens is 2 mm and the NA is 0.85 is described. Further, the molding surface of the lower mold 2 has a shape with a large amount of aspherical surface in which the paraxial radius R is 1.748 mm and the portion R gradually increases from the center toward the outer circumference. On the other hand, the molding surface of the upper mold 1 is also aspherical, but is formed with a paraxial radius R that is sufficiently large with respect to the radius of curvature of the lens material 5.

  Here, when the convex portion of the lens material 5 is brought into contact with the peripheral edge portion of the concave portion of the lower mold 2, a sealed space S is formed between the deepest portion of the concave portion and the topmost portion of the convex portion of the lens material 5. Therefore, when the distance D on the central axis of the sealed space S is large, the untransferred portion may remain on the lens surface due to the gas confined in the sealed space S.

  Therefore, the present inventor prepared several types of lens materials having a spherical shape and different radii, and changed the distance dimension D from the deepest portion of the concave portion of the lower mold 2 to the topmost portion of the convex portion of the lens material 5. A molding experiment was conducted on the presence or absence of untransferred portions and the presence or absence of burrs, and the optimum value of the interval dimension D was considered. The experimental results are shown below along with more specific experimental conditions.

  The mold set 10 was made of a cemented carbide containing tungsten carbide as a main component. The aspherical concave portions that form the molding surfaces of the upper mold 1 and the lower mold 2 were finished to a mirror surface by grinding. A platinum-based noble metal film for preventing fusion with the lens material 5 was formed on the molding surface by sputtering after polishing.

  The lens material 5 is made of a borosilicate glass material (glass transition point: 501 ° C., yield point: 549 ° C.) having a relatively low softening point, and the outer diameter is changed in order to change the distance dimension D from the molding surface. Three types of polishing balls with different sizes were prepared.

  And as conditions for shape | molding a lens, the upper heating plate 7 and the lower heating plate 8 set temperature so that it may respectively be 530 degreeC / 600 degreeC, and as shown in FIG. After holding the lens material 5 between the molding surfaces for 3 minutes, a pressing force F of 700 N is applied by a press shaft (not shown), and the lens material 5 is held until the upper heating plate 7 comes into contact with the outer body mold 4. Pressed. While this pressed state was continued, the energization of the heater 6 of the upper heating plate 7 and the lower heating plate 8 was stopped and cooled to 500 ° C.

  Thereafter, the pressing force was released and the molded lens was taken out by cooling to room temperature. As a result, a lens molded with a constant thickness was obtained.

  Table 1 shows the experimental results obtained under the above-described experimental conditions. In particular, Table 1 is a table in which the presence / absence of untransferred portions and the occurrence of burrs on the molding surface of the lower mold 2 is examined. .

  As shown in Table 1, when the transmitted wavefront aberration of the lenses obtained in Experiments 1 to 3 was measured using a Fizeau interferometer, an aberration of 0.03λ or less was confirmed by the RMS of the total wavefront aberration. I was able to.

  In Experiments 1 to 3, the untransferred portion of the lens on the molding surface side of the lower mold 2 was not confirmed when the distance D formed between the lens material 5 and the molding surface was 151 μm or less. Thus, when the convex portion of the lens material 5 is brought into contact with the peripheral edge portion of the concave portion of the lower mold 2, the distance dimension D from the deepest portion of the concave portion to the topmost portion of the convex portion of the lens material 5 is 170 μm. The following is considered preferable.

  As a comprehensive evaluation, in Experiment 2 and Experiment 3, a result that there was no functional problem as a lens was obtained, and in Experiment 1, a part of the aberration was slightly bad, but the lens was sufficiently usable. Moreover, generation | occurrence | production of the burr | flash was not confirmed in all the experiments.

  Thus, it can be seen that a smaller sealed space S is advantageous for lens molding. There are several molding methods for reducing the sealed space S. One of the methods is to reduce the sealed space S by reducing the weight. FIG. 2 is a cross-sectional view showing the configuration of an optical element molded to be smaller than the weight required for the optical element.

  In the example shown in FIG. 2, lens surfaces 22 and 23 are formed on which the molding surface of the upper mold 1 and the molding surface of the lower mold 2 are accurately transferred. Even in this case, if the optically effective surface is transferred to the optical element, aberration based on the optical design can be obtained. In addition, the dashed-dotted line described in FIG. 2 represents that the desired effective optical path is ensured.

  In the present embodiment, the description has been made by taking a condensing lens having a convex lens shape as an example. However, even if the lens shape is a concave lens or a meniscus lens, the radius of curvature between the molding surface and the lens material 5 is the same as that of the present invention. By using the lens material 5 having the same relationship, that is, a concave portion having a radius of curvature smaller than the radius of curvature of the aspherical convex portion serving as a molding surface, an automatically aligning action (bell clamp action) is obtained. Of course, it is preferable because it can suppress the occurrence of eccentricity and burrs during molding.

  In addition, it is important to minimize the sealed space S according to the size of the lens, the radius of curvature of the molding surface, and the like. By using a lens material optimized to reduce the distance dimension D, the same effect can be obtained. An effect can be obtained. In this way, even if a lens material having a sealed space S is used, a plurality of press operations are not required, and lens formation without an untransferred portion can be performed by a single press operation.

  As described above, the present invention has a practicality in that the lens material can be accurately positioned on the central axis of the molding surface to suppress the eccentricity caused by molding and the generation of burrs caused by the eccentricity. Since it is highly effective, it is extremely useful and has high industrial applicability.

It is a fragmentary sectional view for demonstrating the manufacturing method using the manufacturing apparatus of the optical element which concerns on embodiment of this invention. It is sectional drawing which shows an example of the optical element shape | molded with the manufacturing method of the optical element which concerns on this embodiment. It is a fragmentary sectional view which shows the structure of the conventional lens shaping | molding die group.

Explanation of symbols

1 Upper mold 2 Lower mold 3 Inner trunk mold 4 Outer trunk mold 5 Heater 7 Upper heating plate 8 Lower heating plate 9 Lens material 10 Mold set S Sealed space D Spacing

Claims (4)

An upper mold, a lower mold disposed opposite to the upper mold, and a cylindrical body mold in which the upper mold and the lower mold are slidably inserted. At least one is a method of manufacturing an optical element using a mold set in which an aspherical concave portion to be a molding surface is formed,
A lens material having a convex portion with a radius of curvature larger than the radius of curvature of the concave portion is provided on the peripheral portion of the concave portion with a gap provided between the deepest portion of the concave portion and the topmost portion of the convex portion of the lens material. A procedure of making contact and aligning the concave portion with the convex portion of the lens material and arranging it in the mold set; and
Heating the arranged lens material to near the softening temperature;
A method of manufacturing an optical element, comprising: a step of pressing the heated lens material with the upper mold and the lower mold to mold an optical element. In claim 1,
The distance from the deepest part of the concave part to the topmost part of the convex part of the lens material when the convex part of the lens material is brought into contact with the peripheral part of the concave part is 170 μm or less. Device manufacturing method. An upper mold, a lower mold disposed opposite to the upper mold, and a cylindrical body mold in which the upper mold and the lower mold are slidably inserted. At least one is a method of manufacturing an optical element using a molding die set in which an aspherical convex portion to be a molding surface is formed,
A lens material having a concave portion with a radius of curvature smaller than the radius of curvature of the convex portion, and a peripheral portion of the convex portion with a gap provided between the topmost portion of the convex portion and the deepest portion of the concave portion of the lens material And aligning with the difference in curvature between the convex portion and the concave portion of the lens material and placing in the mold set,
Heating the arranged lens material to near the softening temperature;
A method of manufacturing an optical element, comprising: a step of pressing the heated lens material with the upper mold and the lower mold to mold an optical element. In claim 3,
The distance from the topmost part of the convex part to the deepest part of the concave part of the lens material when the concave part of the lens material is brought into contact with the peripheral edge of the convex part is 170 μm or less. Device manufacturing method.

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