JP2008020547A - Lens, lens molding metal mold, and manufacturing method of lens molding metal mold - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a bifocal lens which is manufactured by joining lens parts having different radiuses of curvature and which can reduce occurrence of ghost and to provide a manufacturing method of a metal mold for the lens. <P>SOLUTION: A plurality of lens effective parts 3a, 3b which have mutually different surface shapes and are optically effective are joined at surfaces containing an optical axis 6. A plurality of lens effective parts 3a, 3b are arranged so that respective vertexes 7a, 7b are located on the optical axis 6 by being mutually deviated in an optical axis 6 direction. A direction of deviation is a direction where difference of area fellows not superposed on each other of projection faces of respective lens effective parts 3a, 3b on a joined surface, decrease. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a lens used in a small imaging device, in particular, a lens having a different surface shape, a lens molding die, and a method of manufacturing the lens molding die.

  In recent years, some information terminal devices such as mobile phones have a camera. The camera of the information terminal device is used not only for applications where the distance to the subject for photographing landscapes and portraits is long, but also for applications where the distance to the subject is extremely short as a barcode reader. Many information terminal devices are small, and it is difficult to provide a lens according to the distance to the subject.

  In order to solve this problem, an information terminal device using a bifocal lens has been proposed (see, for example, Patent Document 1). FIG. 8 is a cross-sectional view showing the subjects 131 and 132 and the information terminal device 101. The imaging lens 102 is formed by disposing a far lens effective portion 103 and a near lens effective portion 104 in the vertical direction on the paper surface. The imaging element 105 receives light that has passed through the imaging lens 102. The subject 106 is farther from the information terminal device 101 than the subject 107. The light that has passed through the far lens effective unit 103 from the subject 106 forms an image by the image sensor 105. On the other hand, the light that has passed through the near-lens effective portion 104 from the subject 107 forms an image by the image sensor 105.

In this manner, the long-distance subject 106 and the short-distance subject 107 can be photographed by the single imaging lens 102.
JP 2002-123825 A

  Since the imaging lens 102 of the conventional information terminal device 101 has different curvature radii of the lenses of the far lens effective unit 103 and the near lens effective unit 104, there is a step on the joint surface between the far lens effective unit 103 and the near lens effective unit 104. Arise. FIG. 9 is a cross-sectional view of a plane parallel to the joint surface of the near lens effective portion 104 and the far lens effective portion 103 in the vicinity of the apex of the bifocal lens.

  In the far lens effective portion 103 having a large curvature radius and the near lens effective portion 104 having a small curvature radius, the vertices 113 and 114 are arranged at the same position on the optical axis 111, respectively. Accordingly, a step is generated in the far lens effective portion 103 and the near lens effective portion 104 at the joint surface between the far lens effective portion 103 and the near lens effective portion 104. The stepped surface 112 exposed by this step increases in area as it moves away from the vertices 113 and 114.

  When the light incident on the imaging lens 102 is reflected or refracted unnecessary by the step surface 112, it becomes a ghost and is received by the imaging element 105. Due to this ghost, there is a problem that the picked-up image quality deteriorates. When lenses having different curvature radii are joined to form a bifocal lens, a stepped surface that causes ghost is inevitably generated.

  The present invention has been made to solve the above-described conventional problems, and in a lens in which lens portions having different curvature radii are joined, a lens capable of reducing the occurrence of ghost, a lens molding die, and the lens thereof It aims at providing the manufacturing method of a shaping die.

  In the lens of the present invention, a plurality of optically effective lens portions having different surface shapes are joined on a surface including the optical axis. In order to solve the above-mentioned problem, the plurality of lens effective portions are arranged such that the respective apexes are located on the optical axis and are displaced from each other in the optical axis direction. The projected surfaces of the joined surfaces of the respective lens effective portions are oriented such that the difference between areas that do not overlap each other is reduced.

  In the lens molding die of the present invention, two inserts each having a recessed insert portion are disposed to face each other. In order to solve the above-mentioned problem, at least one of the inserts is composed of a first insert and a second insert, and the insert portions of the first insert and the second insert are different from each other in rotating curved concave portions. The first insert and the second insert are joined at the surface where the respective rotation axes coincide and the partial recess is cut, and the respective parts are cut. The vertices of the recesses are arranged so as to be shifted in such a direction that a difference between areas where the projection surfaces of the respective partial recesses on the joined surfaces do not overlap each other is reduced.

  Further, in the manufacturing method of the lens forming mold of the present invention, each of the plurality of inserts is formed with insert portions having different concave curved surfaces, and the inserts are divided along a plane including the rotational symmetry axis of the insert portions. When the divided inserts are joined to the divided inserts that are different from each other on the dividing surface, the apex of the insert portion is oriented so that the difference in the area where the divided surfaces of the respective inserts are exposed on the bonding surface decreases. Is shifted on the rotational symmetry axis, the insert is disposed, and the insert is joined.

  According to the present invention, by minimizing the area of the stepped surface of the lens effective portion, it is possible to reduce the occurrence of ghost in a lens in which lens effective portions having different curvature radii are cemented, a lens forming mold, and A method for manufacturing the lens molding die can be provided.

  The lens of the present invention may be configured such that the apex of each effective lens portion is arranged at a position where the difference in area between the effective surfaces of each lens where the projection planes do not overlap each other is zero. it can. With this configuration, it is possible to suppress the occurrence of ghosts.

  Further, the surface shape of the lens effective portion may be an aspherical shape.

  Also, one surface of the lens effective portion may have a different surface shape, and the other surface may have the same surface shape.

  In addition, the lens effective portions having different surface shapes can have different focal points. With this configuration, a multifocal lens with reduced image quality degradation can be obtained.

  Further, in the lens molding die, the vertexes of the respective partial concave portions are arranged at positions where the difference in area where the projection surfaces onto the joined surfaces do not overlap each other is zero. It can also be configured.

  Further, in the method for manufacturing a lens molding die, the insert can be arranged by shifting the apex of the insert portion so that the difference in the area where each insert is exposed on the joint surface becomes zero. .

  Moreover, it can also shape | mold with the metal mold | die manufactured with the manufacturing method of the said lens shaping die.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(Embodiment 1)
FIG. 1 is a plan view of the lens according to Embodiment 1 of the present invention when viewed from the subject side, and shows a case of a biconvex lens.

  A lens 1 shown in FIG. 1 is formed by joining a near lens portion 2 a and a far lens portion 2 b having two different semicircular surface shapes at a discontinuous portion 5 including an optical axis 6. The near lens portion 2a and the far lens portion 2b are a near lens effective portion 3a and a far lens effective portion 3b formed in a semicircular shape centered on the optical axis 6, respectively, and a lens barrel (not shown) on the outer side. ) Is formed with an edge 4 for controlling or fixing the position of the lens 1.

  FIG. 2 is a cross-sectional view showing a side configuration of the lens 1. In FIG. 2, a subject is placed on the left side of the lens 1 in the direction of the optical axis 6, and a semiconductor imaging element (not shown) that receives light imaged by the lens 1 is arranged on the right side. The curvature radius R1 of the near lens effective portion 3a on the subject side (hereinafter referred to as the first surface) of the lens 1 is smaller than the curvature radius R2 of the far lens effective portion 3b.

  The vertex 7a is a point where the optical axis 6 and the surface of the near lens effective part 3a intersect, and the vertex 7b is a point where the optical axis 6 and the surface of the far lens effective part 3b intersect. In the case of a lens having a convex surface such as the near lens effective portion 3a and the far lens effective portion 3b, the points closest to the subject side on the line of the optical axis 6 are the apexes 7a and 7b, and in the case of a lens having a concave surface. The points farthest from the subject side on the line of the optical axis 6 are the vertices 7a and 7b. In the meniscus-shaped lens, on the convex surface, points closest to the subject side on the line of the optical axis 6 are vertices 7a and 7b, and on the concave surface, points farthest from the subject side are vertices 7a and 7b.

  On the back surface of the first surface of the lens 1 (hereinafter referred to as the second surface), a convex back surface lens portion 2c having a curvature radius R3 is formed. The back lens portion 2c is formed as a rotationally symmetric aspherical shape with the optical axis 6 as the center. The aspherical surface is used to reduce spherical aberration, and the lens 1 in the present embodiment is formed in a shape that is obtained by a 10th-order coefficient as a known aspherical coefficient. Examples of the material of the lens 1 include cycloolefin polymer (COP). More specifically, the lens 1 is formed by injection molding using ZEONEX (trademark of Nippon Zeon). Needless to say, the lens 1 can be formed by reheating using optical glass.

  The near-lens effective part 3a and the far-lens effective part 3b have different focal lengths because the curvature radii are different from those of R1 and R2. Therefore, the lens 1 is a bifocal lens having two focal lengths, the focal length of the far lens effective portion 3b is 3.8 mm, and the focal length of the near lens effective portion 3a is 3.6 mm. The lens 1 is formed so that the exit pupil position and the F number have the same value.

  FIG. 3 is a cross-sectional view showing a configuration of a surface parallel to the discontinuous portion 5 of the near-lens effective portion 3a in the vicinity of the apex of the lens 1 according to the present embodiment. The apex 7a of the near lens effective portion 3a and the apex 7b of the far lens effective portion 3b are both arranged on the optical axis 6, but are shifted along the optical axis 6. That is, the apex 7a of the near lens effective portion 3a is formed to protrude from the far lens effective portion 3b to the subject side.

  In such a configuration, in the discontinuous portion 5 near the apex of the lens 1, the far lens effective portion 3b is not joined to the near lens effective portion 3a, and a step is generated. Due to this step, a step surface 8a where the near lens effective portion 3a is exposed is generated. Further, in the discontinuous portion 5 near the periphery of the lens 1, the near lens effective portion 3a is not joined to the far lens effective portion 3b, and a step is generated. Due to this step, a step surface 8b in which the far lens effective portion 3b is exposed is generated. However, the total area of the step surfaces 8a and 8b can be smaller than the area of the step surface 163 of the conventional lens shown in FIG.

Next, the relationship between the area of the difference between the areas of the step surfaces 8a and 8b and the degree of occurrence of ghost will be described. here,
Sa: Area of the step surface 8a Sb: Area of the step surface 8b S = Sa−Sb: Difference area of the step surface.

  FIG. 4 is a graph showing a result of an experiment on the relationship between the degree of occurrence of ghosts and the difference area S between the step surfaces. The horizontal axis represents the difference area S between the step surfaces, and the vertical axis represents the degree of ghost occurrence. The reduction of the area S corresponds to the reduction of the sum of the areas Sa and Sb of the step surfaces 8a and 8b. When the area S is 0, the sum of the step surfaces 8a and 8b is minimized.

  It is difficult to quantify the degree of ghosting. In the present embodiment, the degree of occurrence of ghost is measured as follows. The halogen light of the point light source was used, and the evaluation was performed with weighting so that the extent of the ghost can be determined as objectively as possible based on the ratio of the effective light angle to the range of incident light in which the ghost is generated.

  Each measurement point is connected with a smooth curve. According to this curve, a correlation is recognized between the area S and the degree of occurrence of ghosts. That is, in the vicinity where the area S becomes 0, the occurrence of ghost is minimized, and as the area S increases, the degree of occurrence of ghost increases.

  Even if the area S is 0, a ghost is slightly generated. This is also expected from the occurrence of ghosts in commonly used lenses. Further, the ghost is generated in principle in the bifocal lens having the discontinuous portion 5. The results shown in FIG. 4 suggest that there is an optimum range for the area S for minimizing the occurrence of ghosts.

  By using this relationship, it is possible to determine the amount of deviation of the discontinuous portion 5 in the direction of the optical axis 6 by determining the allowable degree of ghost generation, that is, the degradation of image quality. Further, regarding the degree of influence on the degree of occurrence of ghosts depending on the sign of the area S, that is, the difference in the slope of the graph in FIG. 4, the lens power due to the difference in focal length with respect to the areas Sa and Sb of the step surface. It is presumed that this occurs due to the difference in the light flux density and the difference in the light flux density at the center and the periphery. In the present embodiment, by setting the area S to be 0 or slightly positive, it is possible to suppress the occurrence of ghost even if the discontinuity 5 in the lens 1 varies.

  Since this characteristic is considered to vary depending on the parameters of the lens 1, it is desirable to investigate the relationship between the area S and the degree of ghost generation and optimize the lens 1. In the present embodiment, an example using a convex lens is shown. However, it is obvious that the present invention can be similarly applied to a concave lens or a meniscus lens 1. Furthermore, it goes without saying that the lens can be applied to a multi-segment lens having more than two segments, or a glass glass material.

  In addition, although the example which formed the discontinuous part 5 in the 1st surface of the lens 1 was shown, even if it forms in the 2nd surface of the lens 1, or it forms on both surfaces, the bifocal in which ghost generation | occurrence | production was suppressed. A lens can be formed.

(Embodiment 2)
FIG. 5 is a cross-sectional view showing a cross-sectional configuration of a mold for molding a lens according to Embodiment 2 of the present invention. With this mold, the lens according to Embodiment 1 can be molded. The mold 11 includes a movable part 12 and a fixed part 13. The movable part 12 is for forming the objective side of the lens. FIG. 6 is a partially enlarged view of the mold 11. The movable part 12 is formed by joining a first movable part 12a and a second movable part 12b. The first movable portion 12a has an insert portion that forms the near lens portion 2a shown in FIG. The second movable portion 12b has an insert portion that forms the far lens portion 2b. Moreover, the rectangular recessed part 14 for forming the edge part 4 is formed in the 1st movable part 12a and the 2nd movable part 12b.

  The fixed part 13 has an insert part for forming the rear lens part 2c. Further, as shown in FIG. 5, the fixing portion 13 is formed with an insertion port 15 into which the constituent members of the lens 1 are poured.

  Next, a method for manufacturing the lens 1 shown in Embodiment 1 using the mold 11 will be described. First, the movable part 12 and the fixed part 13 are brought into contact with each other. Next, the lens material 1 is formed by pouring molten lens material from the insertion port 15, holding the pressure, and cooling. Finally, the movable unit 12 is moved to take out the lens. Since the lens 1 varies in accuracy due to the flow of resin during molding, shrinkage anisotropy, temperature distribution of the molding machine, particularly the platen surface, etc., conditions and the like need to be particularly strictly controlled.

  Next, the manufacturing method of the metal mold | die 11 is demonstrated. FIG. 7 is a flowchart showing the manufacturing process of the mold 11 according to the present embodiment. Two inserts having surface-shaped insert portions corresponding to the radii R1 and R2 are created (step S101).

  First, the block is processed separately, and insert portions having different surface shapes with radii R1 and R2 are formed on the two inserts. An insert part is a recessed part for injection-molding the lens formed in the insert. The insert portion is formed by roughly processing a super steel or tool steel, then plating the surface with a high hardness such as Ni, and further using a precision lathe.

  Since the insert portion is processed by a precision lathe, the insert portion is formed in a concave shape of a rotating curved surface. Next, one insert is divided by a plane including the rotation axis of the insert portion (step S102). The shape of the insert portion formed when the shape of the concave shape of the rotating curved surface is divided by a plane including the rotational symmetry axis is referred to as a partial concave shape.

  When the insert is divided, the diamond cutter cuts the plane including the rotational symmetry axis to form two pieces, but due to the tooth width of the diamond cutter, there is only one piece including the rotational symmetry axis. And only the piece including the rotational symmetry axis is used. The cut surface is finished by lapping or the like so that sufficient accuracy can be obtained.

  By this procedure, an insert portion for forming the near lens portion 2a or the far lens portion 2b can be formed on each of the two inserts (the first movable portion 12a and the second movable portion 12b). Next, the first movable part 12a (first insert) and the second movable part 12b (second insert) are brought into contact with each other and moved in the optical axis direction (step S103). Next, it is determined whether or not the area S of the difference between the areas where the divided surfaces of the inserts are exposed is 0 (within an allowable range) on the abutted surface (step S104). If the area S is not 0, the process returns to step S103. In step S104, if the area S is 0, the first movable portion 12a and the second movable portion 12b are fixed by welding or the like (step S105). At this time, the sum of the areas where the divided surfaces of the inserts are exposed is minimized. Thereby, the main part on the movable side is completed.

  On the fixed side, if an insert having one type of insert portion is made, the mold is completed. These inserts are assembled into the base to complete the mold 11 (step S106). The base (not shown) of the mold 11 is made of tool steel, and a die set or the like (not shown) used for normal resin molding is provided at a required position. If the mold 11 is used, the step of the lens 1 in the first embodiment can be molded by the movable portion 12. In step S104, the position is determined so that the difference area S between the step surfaces becomes zero, but may be slightly positive.

  According to the procedure of the present embodiment, since a highly accurate mold can be basically processed by lathe processing, it is possible to shorten time, reduce costs, and ensure accuracy compared to milling. The material for the mold, the surface treatment, etc. can be selected as appropriate.

  The lens of the present invention is a lens in which the occurrence of ghost is suppressed, and can be used as a lens for a portable information terminal.

1 is a front view showing a configuration of a lens according to Embodiment 1 of the present invention. Side view showing the configuration of the lens Side view showing the configuration near the apex of the lens The graph which shows the relationship between the difference area S of the level | step difference surface of a lens, and the generation | occurrence | production degree of a ghost. Sectional drawing which shows the structure of the metal mold | die of the lens which concerns on Embodiment 2 of this invention. Enlarged view of the mold A flowchart showing a manufacturing process of a lens according to Embodiment 2 of the present invention. Sectional drawing which shows the positional relationship of the to-be-photographed object, imaging lens, and image pick-up element in the conventional information terminal device Side view showing the configuration near the apex of a bifocal lens

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Lens 2a Near lens part 2b Far lens part 2c Back lens part 3a Near lens effective part 3b Far lens effective part 4 Edge part 5 Discontinuous part 6 Optical axis 7a, 7b Vertex 8a, 8b Step surface 11 Mold 12 Movable part 12a 1st movable part 12b 2nd movable part 13 Fixed part 14 Recessed part 15 Insertion port

Claims (10)

In a lens in which a plurality of optically effective lens portions having different surface shapes are joined on a surface including the optical axis,
The plurality of lens effective portions are arranged such that each vertex is positioned on the optical axis and is shifted from each other in the optical axis direction.
The direction of the deviation is a direction in which a difference between areas where projection surfaces of the cemented surfaces of the respective lens effective portions do not overlap with each other decreases.   The lens according to claim 1, wherein the vertexes of the respective lens effective portions are arranged at positions where the difference in area between the projection effective surfaces of the respective lens effective portions does not overlap with each other is zero.   The lens according to claim 1, wherein a surface shape of the lens effective portion is an aspherical shape.   The lens according to any one of claims 1 to 3, wherein one surface of the lens effective portion has the different surface shape, and the other surface has the same surface shape.   The lens according to claim 1, wherein the lens effective portions having different surface shapes have different focal points. In a lens forming mold in which two inserts each having a recessed insert portion are disposed relative to each other,
At least one of the inserts includes a first insert and a second insert,
The insert portions of the first insert and the second insert are partial recesses that are different from each other, and a rotation curved surface recess is cut by a surface including a rotation axis,
The first insert and the second insert are joined at the surface where the respective rotation axes coincide and the partial recess is cut,
The apex of each of the partial recesses is arranged so as to be shifted in a direction in which the difference between the areas where the projection surfaces of the respective partial recesses onto the joined surface do not overlap each other is reduced. Mold.   The lens forming mold according to claim 6, wherein the vertexes of the respective partial recesses are arranged at positions where the difference in area where the projection surfaces onto the joined surfaces of the respective partial recesses do not overlap each other is zero. . A plurality of inserts are formed with different recessed portions of rotational curved surfaces,
Dividing the insert at a plane including the rotational symmetry axis of the insert portion;
When each of the divided inserts is joined to the divided inserts that are different from each other on the dividing surface, the difference in the area where the divided surfaces of the respective inserts are exposed on the bonding surface is reduced. The apex is shifted on the rotational symmetry axis, and the insert is arranged,
A method of manufacturing a lens molding die, wherein the insert is joined.   The method for manufacturing a lens molding die according to claim 8, wherein the inserts are arranged by shifting a vertex of the insert portion so that a difference in an area where each of the inserts is exposed on the joint surface is zero.   A lens molded by a mold manufactured by the method for manufacturing a lens molding mold according to claim 8 or 9.

Images