Abstract:
A method of manufacturing an optical component having an optical element and a holder attached to the optical element, comprising the steps of: inserting a blank for the optical element into a through hole of the holder wherein the through hole has a narrowed portion at which the blank is prevented from passing through the through hole; sucking at least the blank from an upper side thereof in a state where the blank is inserted into the through hole; transporting the holder and the blank simultaneously to a molding device; placing the blank on a molding surface of the molding device; and heating and pressurizing the blank in the molding device so that the blank is deformed to obtain a predetermined optical surface and is press-fitted to an inner face of the holder.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a method of manufacturing an optical component by die molding, and particularly to a production method in which an optical component is molded integrally with a holder.  
         [0003]     2. Related Art  
         [0004]     An optical component (or, optical element) such as a lens is often used while being housed in a holding member (holder) made of a metal or the like. The function of an optical component may be impaired by stain or scratch, and hence it is difficult to handle an optical component. When a holder is previously disposed, it is not required to handle an optical component with directly contacting the component, also in a step of incorporating the component into a machine or the like, so that occurrence of stain or scratch can be reduced.  
         [0005]     In an optical component having an optical element and a holder in which the optical element such as a lens is made of glass, a resin, or the like and fixed into the holder, the holder and the optical element may be separately produced and then fixed together by adhesion. Alternatively, such an optical component having a holder is sometimes produced by a method in which a blank for the optical element is pressurized and deformed in the holder, and an optical surface is formed simultaneously with press fixation to the holder (for example, JP-A-61-114822 and JP-A-3-265529).  
         [0006]      FIGS. 1A through 1D  show a conventional procedure in the production of an aspherical lens by such a molding method. Hereinafter, the identical components are denoted by the same reference numerals, and their description may be often omitted. As shown in  FIG. 1A , first, a lower die  12  is incorporated in a cylindrical barrel die  10  with upward directing a molding surface  15 . In the lower die, a step  13  is formed, and a lower portion  14  has a larger diameter. A cylindrical inner sleeve  18  which is an auxiliary member is placed on the step  13 . In this state, first, a lens holder  130  made of a metal is inserted from an upper portion of the barrel die  10 , and placed at a predetermined position of the inner sleeve  18 . As shown in  FIG. 1B , then, a lens blank  120  is inserted into a through hole of the lens holder  130 , and placed on the molding surface  15  of the lower die  12 .  
         [0007]     The lens blank  120  is made of a glass material, and processed into a spherical shape as shown in  FIG. 2A . The lens holder  130  has a cylindrical shape as shown in  FIG. 2B , and comprises a through hole having a circular section shape. The inner diameter B of the through hole must be larger than the diameter A of the lens blank  120 . The relationship between A and B must be designed so that the lens after shaping is in close contact with the lens holder, and an excess of the blank is not produced.  
         [0008]     In this state, as shown in  FIG. 1C , an upper die  116  is inserted and lowered into the upper portion of the barrel die  10  to press the lens blank  120  which is softened by heating to a predetermined temperature. As a result of the above procedure, as shown in  FIGS. 2A and 2B , a molded product  122  which is defined by the shapes of the lower and upper dies  12 ,  116  and the lens holder  130  is formed. The molded product  122  is fixed to the lens holder  130 , but is not fixed to the lower and upper dies  12 ,  116  which are previously subjected to a releasing process, and can be released from the dies.  
         [0009]     After the molding process is completed, as shown in  FIG. 1D , the upper die is removed away, and an aspherical lens  150  having a holder is taken out. A holder and a lens blank are newly prepared, and the same procedure is conducted, whereby an aspherical lens having a holder can be repeatedly produced. According to this apparatus, only the upper die is taken out, and the other members are not required to be reassembled. Therefore, the repeated production is enabled within a short time period.  
         [0010]     The lens holder is usually transported onto the inner sleeve while being mechanically grasped or sucked by vacuum suction. The lens holder  130  has the through hole  136 . In order to mechanically grasp the lens holder, therefore, means such as that a tweezers-like grasping tool  160  grasps an outer peripheral portion  132  as shown in  FIG. 3A , or that the tool outward pushes an inner peripheral portion  134  to hold the lens holder as shown in  FIG. 3B  is taken.  
         [0011]     When vacuum suction is employed, a method such as that in which suction is conducted while a suction port  180  is in contact with a side face  132  as shown as shown in  FIG. 3C , or that in which suction is conducted while the suction port is in contact with an end face  138  that is deviated from the center, and that has a small area is selected.  
         [0012]     In the conventional method, the two transportation works of placing the lens holder onto the inner sleeve, and then transporting the lens blank to the lower-die surface in the through hole of the lens holder are required. Therefore, there is a problem in that the working efficiency is poor.  
         [0013]     Each of the lens holder transporting methods shown in  FIGS. 3A through 3D  has a problem. In the method of  FIG. 3A , the grasping tool  160  is placed outside the lens holder  130 , and hence a room for allowing the grasping tool  160  to pass must be formed between the outer diameter of the lens holder  130  and the diameter of the inner periphery of the barrel die. The upper and lower dies and the like must be correspondingly produced in a larger size, and the cost of the production apparatus is increased. In the method of  FIG. 3B , the lens holder is unstably held, and therefore easily drops during transportation.  
         [0014]     In the case where the side face  132  of the lens holder  130  is sucked as shown in  FIG. 3C , the lens holder must be rotated by 90° in the barrel die, and inadequate placement of the lens holder  130  as shown in  FIG. 4  easily occurs. In the case of  FIG. 3D , the suction port  180  must be inserted in close proximity to the inner peripheral face of the barrel die. Therefore, it is necessary to provide a room for the insertion, and the holding becomes easily unstable. In this case also, consequently, the problem such as shown in  FIG. 4  readily occurs.  
       SUMMARY OF THE INVENTION  
       [0015]     The invention has been conducted in order to solve the problems. It is an object of the invention to provide a production method in which a blank for an optical element such as a lens blank, and a holder such as a lens holder can be taken simultaneously and stably into a molding die and installed correctly therein. It is another object of the invention to provide a production method in which a special space for taking a holder for an optical component into a molding die is not required, and hence the size of a production apparatus is prevented from being increased.  
         [0016]     The method of manufacturing an optical component having an optical element and a holder attached to the optical element which is provided by the invention is basically implemented in the following steps: inserting a blank for the optical element into a through hole of the holder wherein the through hole has a narrowed portion at which the blank is prevented from passing through the through hole; sucking at least the blank from an upper side thereof in a state where the blank is inserted into the through hole; transporting the holder and the blank simultaneously to a molding device; placing the blank on a molding surface of the molding device; and heating and pressurizing the blank in the molding device so that the blank is deformed to obtain a predetermined optical surface and is press-fitted to an inner face of the holder.  
         [0017]     According to the method, when only the blank is sucked to be lifted up, the blank is caught by the narrowed portion of the through hole of the holder, and therefore also the holder can be lifted up together. When the blank and the holder are sucked together, the blank does not slip off from the holder because the narrowed portion exists in the through hole of the holder.  
         [0018]     Therefore, the blank and the holder can be taken simultaneously and stably into the molding device, and correctly placed. The outer diameter of a suction port can be made smaller than that of the holder, and hence a special space for inserting the suction port into the molding device is not necessary. In the specification, the upward means a direction opposite to the direction in which the gravitational force acts.  
         [0019]     Preferably, the molding device is fixed, an auxiliary member having a through hole for fixing the holder to a predetermined position with respect to the molding surface is disposed on a molding die, and the transported holder is placed at a predetermined position on the auxiliary member.  
         [0020]     According to the configuration, the blank and the holder which are simultaneously transported can be correctly placed at the same time on the fixed molding device and the auxiliary member, respectively, and an optical component having a holder in which the optical component is correctly fixed to a predetermined position of the holder can be easily produced.  
         [0021]     The through hole of the holder has a circular section shape, a portion which protrudes toward a center of the through hole is disposed in a part of an inner peripheral face of the through hole, the section shape of the through hole in the portion is symmetric about the center, and a minimum value of a distance passing the center is smaller than a maximum value of an external shape of the blank.  
         [0022]     In the case where the section shape of the through hole is circular, when the above-mentioned relationships are established, the blank does not slip off from the holder. When the through hole is centrosymmetric, the end face of the holder can be easily held to an approximately horizontal state in the case where the blank is sucked and lifted, and the blank can be correctly placed in the molding device.  
         [0023]     Preferably, the blank is circular, cylindrical, or spheroidal. In the case where the blank has such a shape, when the optical element is axisymmetric as in a lens, a molded product which is in close contact with the holder is easily configured. Here, deformation which is in the order of a shape error caused by a usual molding process is not considered in the terms of shapes such as “circular.” 
         [0024]     According to the manufacturing method of the invention, a blank for an optical element such as a lens, and a holder such as a lens holder can be taken simultaneously and stably into a molding device and installed correctly therein. Therefore, the production efficiency of an optical component having a holder can be improved. Only the blank placed in the through hole of the holder is sucked, and taken as it is into the molding device. Therefore, a special space for inserting a suction tool into the molding device is not required, and the size of a molding device can be prevented from being increased. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0025]      FIGS. 1A through 1D  are views illustrating a conventional procedure in the production of a lens having a holder;  
         [0026]      FIGS. 2A and 2B  are views showing a conventional example of a lens blank and a lens holder;  
         [0027]      FIGS. 3A through 3D  are views showing conventional methods of transporting a lens holder;  
         [0028]      FIG. 4  is a view illustrating problems in a conventional production method;  
         [0029]      FIGS. 5A and 5B  are views showing an example of a lens blank and a lens holder in the invention;  
         [0030]      FIG. 6  is a view illustrating a method of transporting a lens holder and a lens blank in the invention;  
         [0031]      FIGS. 7A through 7C  are sectional views of a suction port of a sucking device;  
         [0032]      FIG. 8  is a view of a molding device according to the invention;  
         [0033]      FIG. 9  is a view showing a process of molding a lens in the invention;  
         [0034]      FIGS. 10A and 10B  are views showing other examples of the shape of the lens blank; and  
         [0035]      FIGS. 11A and 11B  are views showing other examples of the shape of the lens holder. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0036]     Hereinafter, a method of manufacturing an aspherical lens having a holder with using the production method of the invention will be specifically described.  
         [0037]     A molding device used in molding of the lens is basically similar to the conventional apparatus shown in  FIGS. 1A through 1D , and pressurizes a lens blank by two molding dies to deform it, thereby forming a lens as an optical element. Therefore, the molding surfaces of the molding dies are previously processed in accordance with the designed surface shape of an aspherical lens.  
         [0038]     In a state before a lens blank and a lens holder are inserted, as shown in  FIG. 1A , the lower die  12  (which constitutes a part of molding device) is inserted into the through hole of the cylindrical barrel die  10 , and disposed so that the molding surface  15  is directed in the upward direction. The lower die  12  is not moved during a molding process. The lower die  12  has a step  13  below the molding surface  15 . The sectional area of the lower portion  14  which is lower than the step  13  is larger than that of the upper portion having the molding surface  15 . The inner sleeve  18  which has a through hole, and which is an auxiliary member is placed on the step  13 . At this time, an upper portion of the lower die  12  is inserted into the through hole of the inner sleeve  18 .  
         [0039]     In this state, the lens blank (blank) and the lens holder (holder) are loaded into the molding dies with using method which is a characteristic of the invention.  
         [0040]     The lens blank  20  is made of a glass material, and previously processed into a spherical shape (having a diameter A) as shown in  FIG. 5A .  
         [0041]     The used lens holder  30  is made of a metal material and cylindrical as shown in  FIG. 5B , and has a through hole having a circular section shape. In order to allow the lens blank to be inserted only, the shape of the conventional example such as shown in  FIG. 2B  may be used. In order to employ the production method of the invention, the through hole of the lens holder  30  must be partly narrowed so that the lens blank cannot pass therethrough.  
         [0042]     In the example of  FIG. 5B , an inward protruding portion  33  is disposed so that the diameter of the through hole is reduced in one end portion, or a portion of the through hole is narrowed so as to be smaller than the other portion. When an article which is molded into a spherical shape of a diameter A as shown in  FIG. 5A  is used as the lens blank  20 , the diameter C of the narrowed portion in the through hole of the lens holder  30  is made smaller than the diameter A of the lens blank  20  (C&lt;A). Of course, the diameter B of the through hole in the portion into which the lens blank  20  is to be inserted must be larger than the diameter A of the lens blank.  
         [0043]     The lens blank  20  and the lens holder  30  are prepared while being placed on a pallet  70  as shown in  FIG. 6 . The pallet  70  has plural recesses or hole portions  72  in each of which a step is formed between a part for supporting the spherical lens blank  20  and that for supporting the lens holder  30 , so that plural lens blanks and lens holders can be held while being placed on the pallet. As shown in  FIG. 6 , the lens holder  30  is placed on the pallet while the narrowed side of the through hole is positioned in the upper side so as to cover the spherical lens blank  20 .  
         [0044]     By arranging plural pairs of the lens blanks  20  and the lends holders  30  on the pallet  70  in a state that each lens blank  20  is inserted in the through hole of the corresponding lens holder  30 . By such the preparation with the pallet  70 , continuous manufacturing of a large number of the optical components can be performed.  
         [0045]     In the initial stage of the molding step, the lens blank  20  and the lens holder  30  which are on the pallet are simultaneously transported into the molding device. The transportation is conducted by means of suction. As shown in  FIG. 7A , a suction port  80  of a sucking device has a flat end face  82  having a required perpendicularity. In the case where the suction port  80  having an outer diameter which is substantially equal to the outer diameter of the lens holder  30  as shown in  FIG. 7B  is used, the lens blank and lens holder are sucked together. Even when such suction is conducted, the lens blank  20  does not slip off from the lens holder  30  because the upper end of the through hole of the lens holder is narrowed.  
         [0046]     In the case where a suction port  84  having an outer diameter which is smaller than the diameter of the through hole of the lens holder is used, only the lens blank  20  is sucked. Even when only the lens blank  20  is sucked to be lifted, the lens holder  30  is caught by the lens blank  20  and does not drop, because the upper end of the through hole of the lens holder  30  is narrowed.  
         [0047]     In both the cases, the lens blank  20  and the lens holder  30  can be simultaneously moved to a predetermined position inside the barrel die  10  as shown in  FIG. 6 . When the suction is cancelled at this position, or when a process of back blow is conducted in some cases, the lens blank  20  and the lens holder  30  are separated from the end face of the suction port  80 . As a result of the above, the lens blank  20  and the lens holder  30  are set simultaneously and accurately to predetermined positions on the molding surface of the lower die  12  and the inner sleeve  18 , respectively.  
         [0048]     Thereafter, an upper die (second molding die)  16  is inserted and lowered into the barrel die  10  with downward directing the molding surface as shown in  FIG. 8 . The lens blank  20  is heated to a temperature at which the blank is softened, and pressurized between the upper and lower molding dies  16 ,  12 . When the volume of the lens blank  20  is previously set to a predetermined value, the lens blank  20  is deformed by the pressurization, with the result that a molding product  22  is obtained which is in close contact with the inner peripheral face of the lens holder  30 , and which is molded into the surface shape of an aspherical lens defined by the molding surfaces of the molding dies as shown in  FIG. 9 .  
         [0049]      FIG. 9  shows molding of a plano-convex lens in which the molding surface of the lower die  12  is aspheric and that of the upper die  16  is flat. However, this is only a example. Alternatively, the lower die may have a flat face, and the upper die may have an aspheric face, or the both faces of the lens may be convex.  
         [0050]     After the molding product  22  is formed and press-fitted to the lens holder  30 , the molding product  22  is sucked and removed from the barrel die  10 . Such a sucking transportation is conducted in a similar manner to the transportation of the lens blank  20  and the lens holder  30  into the barrel die  10  as shown in  FIGS. 6 and 7 . Since the molding product  22  has been integrated with the lens holder  30 , even when only the molding product  22  is sucked to be lifted, the lens holder  30  is secured to the molding product  22  and does not drop.  
         [0051]     The above-described embodiment can attain the following effects. 
    (1) The vacuum condition which enables the suction operation is obtained by closing the through hole of the lens holder with the lens blank. At the same time as the lens blank, the lens holder can be sucked in the direction toward the through hole. Therefore, the lens blank and the lens holder can be simultaneously transported.     (2) Since the outer diameter of the end face of the suction port can be made equal to or smaller than that of the lens holder, a space into which the lens holder can be inserted is sufficient for enabling transportation and insertion.     (3) In the suction process, positioning and fixation are enabled by butting the end face of the suction port against that of the lens holder. Therefore, high accuracy can be achieved in the position and inclination in the case where the lens holder is set in the molding dies.    
 
         [0055]     The production method can be applied also to an optical component having a holder, other than an aspherical lens and a spherical lens. Examples of such an optical component are a Fresnel lens having a minute concave and convex structure, a diffractive optical element such as a diffraction grating, and a prism.  
         [0056]     The shape of the blank is not restricted to a spherical shape, and may be a cylindrical shape or a disk-like shape shown in  FIG. 10A , a spheroidal shape shown in  FIG. 10B , or the like. In this case, the diameter of the cylinder or the disk is considered to be equivalent to the diameter A of the sphere shown in  FIG. 5A , and the diameter C of the through hole in the narrowed portion of the holder shown in  FIG. 5B  is requested to satisfy the relationship of C&lt;A. In the case of a spheroid, the maximum width is considered as A, and then the same is applicable.  
         [0057]     The section shape of the through hole of the holder is not always necessary to be circular, depending on the shape of the optical element to be held. In order to conduct the pressure molding, however, it is preferable that the section shape is centrosymmetrical.  
         [0058]     The narrowed portion of the through hole is not always necessary to have a similar shape as the section of the other portion of the through hole as in the case of the holder  30  shown in  FIG. 5B . The through hole is requested to have a structure in which the blank cannot linearly pass through the through hole in at least one direction.  
         [0059]     For example, as in the case of a holder  230  shown in  FIG. 11A , plural convex portions  233  protruding toward the center may be disposed on the inner peripheral face of through hole so as to be symmetrical about the center of the through hole. The minimum value of the distance between the tip ends of the convex portions, i.e., the distance passing the center is indicated as D. When the relationship of D&lt;A is satisfied, the blank cannot pass through the through hole. Alternatively, as in the case of a holder  330  shown in  FIG. 11B , an opening  333  may have a square section shape. Also in the alternative, when the minimum value of the distance of the square opening passing the center of the through hole is indicated as E, E is requested to satisfy the relationship of E&lt;A.  
         [0060]     Other shapes may be employed as means for narrowing the through hole. In order to prevent the blank from being inclined or positionally displaced, a shape which is symmetric about the center of the through hole is preferably employed.