JP2008036719A - Manufacturing method of axially symmetric lens - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing an axially symmetric lens capable of inexpensively forming a lens shape with high accuracy on a surface without restraints due to a shape of a material to be ground. <P>SOLUTION: An axially symmetric lens shape to be manufactured with its central axis matching a rotary center of a grinding tool 10 is formed in advance at an end of the grinding tool 10 rotary driven. The grinding tool 10 is pressed to a ground material 17 during a rotation condition, and the lens shape formed at the end of the grinding tool 10 is formed on the surface of the ground material 17. Here, a Frensnel lens can be used as a lens. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

The present invention relates to a method for manufacturing an axisymmetric lens in which a rotating grinding tool is pressed against a work material to form a lens shape formed at an end of the grinding tool on the surface of the work material.

With the miniaturization and weight reduction of semiconductor products and digital devices, fine high-precision parts have become necessary. As a result, the demands for mold miniaturization, higher precision, and shorter delivery times are becoming even more stringent for mold makers that produce molds for manufacturing parts. Many optical systems are used in digital devices such as mobile phones. Lenses for condensing light and the like are used in the optical systems of these devices, and there is an increasing demand for these lenses to be further reduced in size, thickness, accuracy, and delivery time. Therefore, as one of the methods for achieving a reduction in size and thickness of a lens, it has been studied to use a Fresnel lens from a conventional spherical lens as a lens of a digital device. However, it is difficult to cope with a mold of a fine Fresnel lens by a mold manufacturing method in which a final finish is manually performed as in the prior art. Therefore, as shown in FIG. 4, a work material 100 that is a base material of a lens mold is attached to a tip surface 102 of a main spindle 101 of a lathe, and a tool 103 is used as a tool to be attached to an end of the work material 100. Processing of the Fresnel lens shape is performed. In addition, as a method of performing a concave groove processing on an end portion of a work material, a method of using a grindstone instead of a cutting tool has been proposed (see, for example, Patent Document 1). Furthermore, as a method for performing the groove processing on the end portion of the work material, a processing method using a grindstone end face has also been proposed (for example, see Patent Document 2).

JP 2000-237942 A JP-A-9-70752

However, in the method using the cutting tool 103 as the tool, as shown in FIG. 4, it is necessary to perform processing while simultaneously moving the tip of the cutting tool 103 in two axes, and the accuracy of the lens mold is greatly increased in the movement accuracy of the lathe. There is a problem that the use of an ultra-precision lathe is premised and the processing cost is high. In the invention described in Patent Document 1, since the Fresnel-shaped arc portion and the arc-shaped portion of the grindstone interfere with each other during processing, the size of the Fresnel shape that can be processed is limited, and a sharp edge is formed at the groove corner. Becomes very difficult. Moreover, since a lathe is used, there is also a problem that the shape of the work material is limited to a cylindrical shape. In the invention described in Patent Document 2, it is possible to form sharp edges at the groove corners, but there is a problem that Fresnel-shaped processing cannot be performed.

The present invention has been made in view of such circumstances, and provides an axisymmetric lens manufacturing method capable of forming a highly accurate lens shape on the surface at a low cost without being restricted by the shape of the work material. Objective.

An axially symmetric lens manufacturing method according to the first invention that meets the above object is an axially symmetric lens to be manufactured by aligning the center axis with the rotation center of the grinding tool at the end of the rotationally driven grinding tool. A shape is formed in advance and pressed against the work material in a state where the grinding tool is rotated, and the lens shape formed at the end of the grinding tool is formed on the surface of the work material.

In the method for manufacturing an axisymmetric lens according to the first invention, the lens may be a Fresnel lens. Further, a horizontal portion is provided around the lens forming surface of the grinding tool, and the work material is formed with the lens forming surface formed at the end of the grinding tool and the horizontal continuous with the lens forming surface. The part can be copied accurately.

An axially symmetric lens manufacturing method according to the second invention that meets the above-mentioned object is an axially symmetric Fresnel to be manufactured by aligning the center axis with the rotation center of the grinding tool at the end of the rotationally driven grinding tool. A first step of pre-forming all lens surfaces that are the basis of the lens;
A second step of pressing the grinding tool manufactured in the first step against the work material in a rotated state and forming the entire lens surface formed on the end of the grinding tool on the work material; ,
A third step of cutting the periphery of the grinding tool manufactured in the previous step to form a lens surface having a smaller diameter than the lens surface manufactured in the previous step at the end of the grinding tool;
A fourth step of grinding the grinding tool manufactured in the third step to a predetermined depth with respect to the lens surface of the work material manufactured in the previous step by aligning the axis.
The third step and the fourth step are performed one or more times.

In the method for manufacturing an axially symmetric lens according to the first and second inventions, the cutting portion of the grinding tool is one or more of diamond, cubic boron nitride, silicon nitride, silicon carbide, and alumina. It is preferable that the abrasive grains are held by a conductive metal bond.

In the method for manufacturing an axially symmetric lens according to claim 1 and claims 2, 3, and 5 dependent thereon, the grinding tool rotated around the axis is pressed against the work material. Therefore, it is possible to efficiently and inexpensively process a lens shape with high accuracy by preventing the occurrence of a processing error that depends on the motion accuracy of the lens. In addition, since the workpiece is fixed by rotating only the grinding tool, the lens shape is processed at multiple locations at the end of the arbitrarily shaped workpiece, for example, the square workpiece. Can be applied. As a result, it is possible to efficiently and inexpensively manufacture a transfer mold master mold for manufacturing an axisymmetric lens.

In particular, in the method for manufacturing an axisymmetric lens according to claim 2, the lens shape of the Fresnel lens can be efficiently and inexpensively formed on the surface of the work material.

The method for manufacturing an axisymmetric lens according to claim 3 accurately copies the lens forming surface formed on the grinding tool and the surrounding horizontal portion on the surface of the work material without exchanging the grinding tool halfway. A sharp corner can be formed efficiently and inexpensively at the connecting portion between the lens forming surface and the horizontal portion. And when forming the lens shape of a Fresnel lens, a corner | angular part and a corner | angular part can be easily provided in the both sides of each groove | channel of the formed concentric annular groove.

In the method for manufacturing an axially symmetric lens according to claim 4 and claim 5 dependent thereon, since the grinding tool rotated around the axis is pressed against the work material, the machining accuracy of the machine tool is improved. It is possible to prevent the occurrence of a processing error that is influenced and to form a Fresnel lens surface with high shape accuracy efficiently and inexpensively. In addition, since the work is performed by rotating only the grinding tool in a state where the work material is fixed, the work material having an arbitrary shape, for example, the Fresnel lens shape is processed at a plurality of positions at the end of the square work material. Can be applied. Since the lens surfaces having small diameters are sequentially formed on all the lens surfaces while grinding the periphery of the grinding tool, concentric annular grooves having clear corners and corners on both sides can be sequentially formed. As a result, it is possible to efficiently and inexpensively manufacture a transfer mold master mold for manufacturing an axially symmetric Fresnel lens.

In particular, in the method for manufacturing an axisymmetric lens according to claim 5, since the abrasive grains are any one or more of diamond, cubic boron nitride, silicon nitride, silicon carbide, and alumina, the shape of the grindstone changes during grinding. Can be suppressed. In addition, since the abrasive grains are held by conductive metal bonds (iron-based or non-ferrous metal-based), electric discharge machining can be used to form the grindstone, and the grindstone can be processed into any shape with high precision and ease. can do.

Next, embodiments of the present invention will be described with reference to the accompanying drawings for understanding of the present invention.
Here, FIG. 1 is a perspective view showing a situation when a Fresnel lens shape is formed by applying the method for manufacturing an axisymmetric lens according to the first embodiment of the present invention, and FIG. 2 is a method for manufacturing a coaxial symmetric lens. FIGS. 3A to 3D are side cross-sectional views showing a state during processing of the Fresnel lens shape by applying the above, and FIGS. 3A to 3D show the Fresnel lens to which the method for manufacturing an axisymmetric lens according to the second embodiment of the present invention is applied A side sectional view showing a shape processing step, (E) is a side view of the obtained Fresnel lens shape.

As shown in FIGS. 1 and 2, a grinding tool 10 used in the method for manufacturing an axisymmetric lens according to the first embodiment of the present invention is connected to a rotational drive shaft of a processing machine (for example, a machining center) not shown. A cylindrical tool holding portion 11 and a front end of the tool holding portion 11. As the abrasive grains 12, for example, a grindstone portion (made of a grindstone) in which diamond having a particle diameter of 3 to 25 μm is held by a metal bond 13. Cutting part) 14. Here, the tool holding part 11 is formed of any one of iron (carbon steel material or stainless steel material), cemented carbide, and ceramics, for example.
Further, on the inner side of the end face of the grindstone portion 14, a Fresnel lens shape which is an example of an axially symmetric lens shape to be manufactured by aligning the central axis with the rotation center of the grinding tool 10 (the opposite surface is a flat surface). Is formed, and a horizontal portion 16 is provided around the lens forming surface 15. A plurality of slits (not shown) are formed in parallel with the rotation center axis of the grinding tool 10 in the circumferential direction of the grindstone portion 14. By providing the slit, the grinding liquid can easily reach the center of the end face of the grindstone portion 14, and grinding waste generated at the end face of the grindstone portion 14 can be placed on the grinding liquid and discharged to the outside.

Next, a case where a Fresnel lens shape is formed by applying the method for manufacturing an axisymmetric lens according to the first embodiment of the present invention will be described.
As a first stage, a lens forming surface 15 is formed on the end of the grinding tool 10 that is rotationally driven, in which an axially symmetric Fresnel lens shape that is to be manufactured by aligning the central axis with the rotational center of the grinding tool 10 is formed. To do. Here, the grinding tool 10 is manufactured by the following method. First, a mixture of diamond powder and iron powder having a particle size of 3 to 25 μm in a bottomed cylindrical mold (not shown) composed of one or more of boron nitride material, graphite material, and ceramic material. Fill with powder and press mold. And the obtained molded object is put in a heating furnace, and iron powders are sintered. Thereby, the original whetstone part by which the abrasive grain of diamond was hold | maintained with the iron-type metal bond which has electroconductivity is obtained. Then, an original grinding tool is produced by brazing, for example, the tip of an iron bar member that is the basis of the columnar tool holding unit 11 with the obtained raw grinding stone part.
In addition, although it is preferable to perform sintering of iron powder in a vacuum, it can also be performed by filling an inert gas (for example, argon gas) in a heating furnace.

Here, the ratio of the diamond powder in the mixed powder is 25 to 50% by volume. If the diamond powder is less than 25% by volume, the diamond content per unit volume of the grinding wheel portion 14 is too small, and the grinding efficiency is lowered. On the other hand, when the diamond powder exceeds 50% by volume, the ratio of the nickel-based brazing filler metal powder relatively decreases, so that the holding power of diamond in the grindstone portion 14 decreases, and the strength of the grindstone portion 14 decreases. The grindstone portion 14 is easily worn, and uniform grinding cannot be performed, resulting in a decrease in processing accuracy.

Next, the outer peripheral portion of the rod member of the original grinding tool is turned to form the tool holding portion 11 having a perfect cross section, and the grinding tool 10 is manufactured. Then, the grinding tool 10 is formed by electric discharge machining so that the center axis is aligned with the center of rotation of the tool holding portion 11 and the entire surface of the axially symmetric Fresnel lens to be manufactured inside the end surface of the original grinding portion is formed. The grindstone part 14 is completed by forming the horizontal part 16 around the surface 15 and the outside thereof.

As a second stage, the grinding tool 10 that has completed the grinding wheel portion 14 is connected to the rotational drive shaft of the processing machine via the tool holding portion 11. Then, the work material 17 is fixed on the work material fixing table 18 of the processing machine, pressed against the work material 17 in a state where the grinding tool 10 is rotated, and a lens formed at the end of the grinding tool 10 is formed. A Fresnel lens shape portion 19 and a horizontal grinding portion 20 are formed on the surface of the work material 17 by the surface 15 and the horizontal portion 16. When the grinding tool 10 reaches a cutting depth set in advance with respect to the work material 17, as shown in FIG. 2, the work material 17 has a lens formed at the end of the grinding tool 10. The forming surface 15 and the horizontal portion 16 continuous therearound are accurately copied, and a sharp corner portion 20a is formed at the connecting portion between the Fresnel lens shape portion 19 and the horizontal grinding portion 20, and is concentric in the Fresnel lens shape portion 19. Sharp corners 20b and corners 20c are formed on both sides of each groove of the annular groove.

Here, as the work material 17, a ceramic material, for example, any one of alumina, zirconia, quartz, silicon carbide, and silicon nitride is used. By using a ceramic material, a master mold for producing a transfer mold for manufacturing a Fresnel lens by casting molten metal can be obtained.

Next, a case where a Fresnel lens shape is formed by applying the method for manufacturing an axisymmetric lens according to the second embodiment of the present invention will be described.
As shown in FIG. 3A, the axially symmetric lens manufacturing method according to the second embodiment of the present invention is arranged at the center of rotation of the grinding tool 21 at the end of the rotationally driven grinding tool 21. There is a first step of pre-forming a horizontal portion 23 around the entire lens surface 22 and the entire lens surface 22 as the basis of an axially symmetric Fresnel lens to be manufactured with the axes aligned. Here, the grinding tool 21 is manufactured by lathing the outer peripheral portion of the rod member of the original grinding tool to form the tool holding portion 11 having a perfect cross section, and the grinding tool 21 is held by electric discharge machining. By aligning the central axis with the rotation center of the part 11 and forming the entire lens surface 22 inside the end face of the original grinding part and the horizontal part 23 around the outside, a grinding part (cutting part made of a grindstone) 24 is formed. Finalize.

Further, in the method for manufacturing an axisymmetric lens according to the second embodiment of the present invention, the grinding tool 21 manufactured in the first step is pressed against the work material 17 in a rotated state, and the work material 17 As shown in FIG. 3B, the second step of forming the entire lens surface 22 and the horizontal grinding surface 26 on the surface of which the entire lens surface 22 and the horizontal portion 23 formed at the end of the grinding tool 21 are copied. A third step in which the periphery of the grinding portion 24 of the grinding tool 21 manufactured in the previous step is shaved by electric discharge machining to form a lens surface 27 having a diameter smaller than the diameter of all the lens surfaces 22 at the end of the grinding tool 21; And a fourth step of grinding the entire lens surface 25 manufactured in the second step to a predetermined depth by aligning the axis of the grinding tool 28 manufactured in the third step. Therefore, after completion of the fourth step, the lens surface 29 is formed by copying the lens surface 27 inside the entire lens surface 25, and the first annular portion 30 that is the remaining part of the entire lens surface 25 is formed outside thereof. .

Furthermore, in the method for manufacturing an axisymmetric lens according to the second embodiment of the present invention, the third step and the fourth step are performed one or more times (three times in the present embodiment). That is, as shown in FIG. 3C, the periphery of the grinding portion 24 of the grinding tool 28 manufactured in the previous process is shaved by electric discharge machining, and the end of the grinding tool 28 has a diameter smaller than the diameter of the lens surface 27. A grinding tool 32 on which the lens surface 31 is formed is manufactured, and the lens surface 29 manufactured in the previous process is ground to a predetermined depth by aligning the axis of the grinding tool 32. As a result, a lens surface 33 in which the lens surface 31 is copied is formed inside the lens surface 29, and a second annular portion 34 that is the remaining part of the lens surface 29 is formed outside the lens surface 33.

Further, as shown in FIG. 3D, the periphery of the grinding portion 24 of the grinding tool 32 manufactured in the previous step is shaved by electric discharge machining, and the end of the grinding tool 32 has a diameter smaller than the diameter of the lens surface 31. A grinding tool 36 on which the lens surface 35 is formed is manufactured, and the lens surface 33 manufactured in the previous process is ground to a predetermined depth by aligning the axis of the grinding tool 36. As a result, a lens surface 37 in which the lens surface 35 is copied is formed inside the lens surface 33, and a third annular portion 38 that is the remaining part of the lens surface 33 is formed outside thereof. As a result, as shown in FIG. 3 (E), a Fresnel lens shape portion 39 including first to third annular portions 30, 34, 38 and a lens surface 37 is formed on the surface side of the work material 17. The

As described above, the present invention has been described with reference to the embodiment. However, the present invention is not limited to the configuration described in the above-described embodiment, and the matters described in the scope of claims. Other embodiments and modifications conceivable within the scope are also included.
For example, in the first and second embodiments, a grinding tool having a cutting portion made of a grindstone in which diamond abrasive grains are held by an iron-based metal bond is used, but the diamond abrasive grains have conductivity. It is also possible to use a grinding tool having a cutting part held by a non-ferrous metal (for example, copper, copper-tin) metal bond. Further, instead of diamond, any one of cubic boron nitride, silicon nitride, silicon carbide, and alumina can be used as the abrasive grains. Further, diamond, cubic boron nitride, silicon nitride, silicon carbide, and alumina can be used. Any two or more of these can also be used for the abrasive grains.

An original grinding tool was produced in which diamond abrasive grains were held with iron-based metal bonds. A mixed powder of diamond powder and brazing filler metal powder was filled into a bottomed cylindrical formwork, and this formwork was placed in a heating furnace. When the brazing filler metal powder is melted by heating to a temperature about 50 ° C. higher than the melting point of the brazing filler metal powder, and the entire brazing filler metal powder is melted, a cylindrical shape corresponding to the formwork shape from above the formwork The steel rod member that is the base of the tool holding part is inserted into the mold, and the molten brazing material is cooled while pressing from above, so that the gap that is the base of the cutting part is formed at the tip of the bar member. It is also possible to produce an original grinding tool in which a non-existing original grindstone portion is formed. The melting of the brazing filler metal powder is preferably performed, for example, in a vacuum, but may be performed by filling the heating furnace with an inert gas (for example, argon gas). As the brazing material, for example, any one of nickel, copper, cobalt, iron, and silver can be used.

In the first embodiment, the width of the end surface of the cutting part is an area in which the lens forming surface forming the entire Fresnel lens shape and the horizontal part formed around the lens forming surface are collectively contained. It may be an area that can accommodate only a lens forming surface on which a part of the shape is formed and a horizontal portion formed outside the lens forming surface. In this case, since the grinding liquid can easily reach the center of the end surface of the cutting part, the number of slits formed in the circumferential direction of the cutting part can be reduced, or the formation of slits can be omitted.

It is a perspective view which shows the condition at the time of forming the Fresnel lens shape by applying the manufacturing method of the axisymmetric lens which concerns on the 1st Embodiment of this invention. It is a sectional side view which shows the state in process of processing of the Fresnel lens shape by applying the manufacturing method of a coaxial symmetrical lens. (A)-(D) are sectional side views which show the processing process of the Fresnel lens shape which applied the manufacturing method of the axially symmetric lens which concerns on the 2nd Embodiment of this invention, (E) is the obtained Fresnel lens shape. FIG. It is explanatory drawing of the processing method of the Fresnel lens shape which concerns on a prior art example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10: Grinding tool, 11: Tool holding part, 12: Abrasive grain, 13: Metal bond, 14: Whetstone part, 15: Lens formation surface, 16: Horizontal part, 17: Work material, 18: Work material fixed table 19: Fresnel lens shape part, 20: Horizontal grinding part, 20a, 20b: Corner part, 20c: Corner part, 21: Grinding tool, 22: All lens surface, 23: Horizontal part, 24: Grinding part, 25: All Lens surface, 26: Horizontal grinding surface, 27: Lens surface, 28: Grinding tool, 29: Lens surface, 30: First annular portion, 31: Lens surface, 32: Grinding tool, 33: Lens surface, 34: Second Annular part, 35: Lens surface, 36: Grinding tool, 37: Lens surface, 38: Third annular part, 39: Fresnel lens shape part

Claims (5)

An axially symmetric lens shape to be manufactured by aligning the center axis with the rotation center of the grinding tool is formed in advance at the end of the grinding tool to be rotated, and the grinding tool is rotated and rotated. A method of manufacturing an axially symmetric lens, wherein the lens shape is formed on the surface of the work material by pressing against a work material and forming the lens shape formed at the end of the grinding tool. 2. The method for manufacturing an axisymmetric lens according to claim 1, wherein the lens is a Fresnel lens. 3. The method of manufacturing an axisymmetric lens according to claim 1, wherein a horizontal portion is provided around the lens forming surface of the grinding tool, and the work material is provided with the grinding tool. A method of manufacturing an axisymmetric lens, wherein the lens forming surface formed at the end and the horizontal portion continuous around the surface are accurately copied. A first step of pre-forming all lens surfaces that form the basis of an axisymmetric Fresnel lens to be manufactured by aligning the central axis with the rotation center of the grinding tool at the end of the grinding tool that is rotationally driven;
A second step of pressing the grinding tool manufactured in the first step against the work material in a rotated state and forming the entire lens surface formed on the end of the grinding tool on the work material; ,
A third step of cutting the periphery of the grinding tool manufactured in the previous step to form a lens surface having a smaller diameter than the lens surface manufactured in the previous step at the end of the grinding tool;
A fourth step of grinding the grinding tool manufactured in the third step to a predetermined depth with respect to the lens surface of the work material manufactured in the previous step by aligning the axis.
The method of manufacturing an axially symmetric lens, wherein the third step and the fourth step are performed one or more times. 5. The method for manufacturing an axisymmetric lens according to claim 1, wherein the cutting portion of the grinding tool is any one of diamond, cubic boron nitride, silicon nitride, silicon carbide, and alumina. A method for manufacturing an axially symmetric lens, comprising: a grinding wheel using the above as abrasive grains, wherein the abrasive grains are held by a conductive metal bond.

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