JP2005219186A - Machining method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a machining method which is suitable for machining a forming die for an optical element represented by, for example, a diffraction lens, and can form a highly accurate machined surface. <P>SOLUTION: Because the cutting operation is carried out while a first edge portion T1 is being brought into contact with an optical transfer surface of a rotating die M, and while a diamond tool T is being moved in the direction separating from an optical axis O, the central portion of the die M can be cut in the unworn state of the cutting edge. As a result, the required characteristics of an optical element formed by transferring the die M can be satisfied. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a processing method, and more particularly to a processing method suitable for processing a mold for molding an optical element.

Conventionally, for optical transfer surface processing of a molding die for a high-precision optical element such as an objective lens for an optical pickup device, the nose radius of the rake face is about 0.1 to 1.5 mm, and the apex angle is 40 to 40. When an R bite made of single crystal diamond of about 60 ° is used, and the optical transfer surface shape is constituted by a single surface expressed by, for example, a general aspheric equation, an ultraprecision machine is used. Thus, it is possible to obtain a highly accurate optical transfer surface only by cutting. On the other hand, when creating an optical transfer surface having a finer shape structure, an R bite having a finer nose radius is used as described in Patent Document 1.
JP 2003-62707 A

  By using the R bite having a fine nose radius described in Patent Document 1, a more precise optical transfer surface can be created. By the way, in the field of optical pickup devices in recent years, it is desired to record and / or reproduce information with higher density using a blue-violet laser or the like. Further, at least one of the optical functional surfaces is divided into a plurality of optical functional areas centered on the optical axis, and at least one of the plurality of optical functional areas is divided into a ring-shaped area centered on the optical axis. In addition, there is an attempt to provide a diffraction structure in which a predetermined number of discontinuous steps are provided in each annular zone and the annular zones provided with the discontinuous steps are continuously arranged. However, in order to form such a fine diffractive structure with a step in an optical element, it is necessary to cut the optical surface of the mold deeply in a ring shape with a width of 100 μm or less. However, in the above-described R cutting tool, the edge part interferes, and the annular zone shape cannot be cut with such a narrow width.

  The present invention has been made in view of such a problem. For example, the present invention is suitable for processing a mold for molding an optical element represented by a diffractive lens, and provides a processing method capable of forming a highly accurate processed surface. The purpose is to do.

The processing method according to claim 1, wherein the rake face of the cutting edge made of diamond includes a linear portion extending linearly with a length of at least 100 μm in a direction intersecting the rotation axis of the mold. Using a diamond tool formed with one edge and a linear second edge and a third edge that are longer than the first edge and connected to the end of the first edge , At least one optical functional surface is divided into a plurality of optical functional areas centered on the optical axis, and at least one of the plurality of optical functional areas is divided into ring-shaped areas centered on the optical axis, In addition, a predetermined number of discontinuous steps are provided in each annular zone, and a gold for molding an optical element having a diffractive structure in which the annular zones provided with the discontinuous steps are continuously arranged. A processing method for processing an optical transfer surface of a mold,
A step of rotating the mold, and a direction of moving the diamond tool away from the rotation axis and a direction parallel to the rotation axis while contacting the first edge with the optical transfer surface of the rotating mold (The order of movement may be reversed, the same applies hereinafter). The “first edge including a straight line portion” may constitute the first edge portion only from the straight line portion, or another straight line connected to one end portion or both ends of the straight line portion. It means that the first edge may be constituted by a part or an arc.

  The present invention will be described with reference to the drawings. FIG. 1 is a view (a) and a side view (b) of a diamond tool T as viewed from the rake face side suitable for use in the machining method according to the present invention. In FIG. 1 (a), the diamond tool T extends linearly in a direction perpendicular to the first edge T1 (100 μm or less) of the tip extending linearly and both ends of the first edge T1. The second edge portion T2 and the third edge portion T3 are formed to form a rectangular rake face T5. The second edge T2 is connected to a fourth edge T4 that extends away from the third edge T3. Here, the square shape refers to the end portion (position of the distance β from the tip) on the fourth edge portion T4 side of the shorter second edge portion T2 of the edge portions T2 and T3 extending in parallel with each other. By drawing a line T6 parallel to one edge T1, a region surrounded by the edges T1, T2, T3 and the line T6 is meant. In this specification, the term “edges are connected to each other” means that the edges are indirectly connected via other single or plural straight lines and / or arcs in addition to the case where the edges are directly connected to each other. Including cases.

  FIG. 2 is a perspective view of the mold M after being processed using the diamond tool of FIG. 1, and FIG. 3 is a schematic enlarged sectional view of the optical transfer surface. The mold M processed by the processing method of the present invention has at least one optical function surface divided into a plurality of optical function areas centered on the optical axis, and at least one of the plurality of optical function areas is a light beam. It is divided into ring-shaped regions centered on the axis, and each ring zone has a predetermined number of discontinuous steps, and the ring zones with the discontinuous steps are continuously arranged. It is suitable for use in molding an optical element having a certain diffractive structure. Such a diffractive structure has a stepped cross section, and is complementary to the optical transfer surface of the mold M as shown in FIG. -Preferably, copper plating is applied). In FIG. 3, the diamond tool T is movable in the X-axis direction (also referred to as a direction away from the rotation axis) and the Z-axis direction (also referred to as a direction parallel to the rotation axis of the mold). In the present specification, the “cutting direction” refers to a direction parallel to the rotation axis and approaching the mold.

  An example of the processing method of the present invention is as follows. First, as shown in FIG. 3, the mold M is rotated around an optical axis (also referred to as a rotation axis) O, and the first edge T1 of the diamond tool T is While being pressed against the optical transfer surface (here, the upper surface) of the mold M, the optical axis O is moved from the optical axis O toward the outer peripheral side (in the X-axis direction), and at the reference position (dotted line position) with respect to the optical axis O. And move in a direction (Z-axis direction) further pressed against the mold M in parallel. Then, the diamond tool T cuts the optical transfer surface of the mold M to form a ring-shaped groove, but the bottom surface of the groove is cut by the first edge T1, and the side surface of the groove is the second edge. Cutting is performed by the portion T2 and the third edge T3. Further, when the diamond tool T is moved away from the optical axis O while maintaining the position in the Z-axis direction, the side surface (inner peripheral surface) far from the optical axis O of the groove is cut by the second edge T2. Then, when further moved in the cutting direction, a part of the bottom surface of the groove is cut by the first edge T1. By repeating this multiple times, a structure having a stepped cross section is formed. After cutting to a predetermined depth, the diamond tool T is moved away from the mold M, and when the first edge T1 returns to the surface of the optical transfer surface or the vicinity thereof, the diamond tool is moved to the next reference position. All grooves can be processed by moving T in a direction away from the optical axis O, cutting an adjacent groove, and repeating this.

  Here, it is considered that a structure having a stepped cross section is formed while moving the diamond tool T from the outer peripheral side. In this case, the peripheral portion of the mold M is processed by the diamond tool T that is not worn, and the central portion near the optical axis of the mold M is processed by the worn diamond tool T. Here, when an optical element molded using the mold M is considered, a region that generally requires good optical characteristics is the central portion of the optical element. However, if the central portion of the mold M is processed by the worn diamond tool T, sufficient accuracy of the central portion of the optical element to be transferred cannot be secured, and the required optical characteristics may not be obtained. There is.

  On the other hand, according to the processing method of the present invention, as shown in FIG. 3, the diamond tool T is moved along the optical axis O while the first edge T1 is brought into contact with the optical transfer surface of the rotating mold M. Since the cutting is performed while moving away from the center, the central portion of the mold M can be cut without being worn, and the required characteristics of the optical element transferred and formed by the mold M can be satisfied. It becomes possible.

  In addition, the central portion of the mold M has a low peripheral speed, so that the cutting efficiency may be poor, and there is a problem that it takes a long time to cut and a clean cutting surface cannot be obtained using a worn diamond tool. . On the other hand, according to the processing method of the present invention, as shown in FIG. 3, the diamond tool T is moved along the optical axis O while the first edge T1 is brought into contact with the optical transfer surface of the rotating mold M. Since the cutting process is performed while moving away from the center, the cutting time can be reduced and a clean cutting surface can be obtained by cutting the central part of the mold M without being worn. .

  Furthermore, as shown in FIG. 3, the present invention has the following advantages when a stepped groove that gradually decreases toward the outer periphery is formed in the mold M. First, let us consider processing and forming such a step-shaped groove while moving the diamond tool T from the outer peripheral side. In such a case, an angle C1 at which the first edge T1 and the third edge T3 of the diamond tool T intersect with each other continues to cut the mold M during the processing, so that the amount of wear increases. FIG. 8 shows a photomicrograph of the tip of the diamond tool without wear, and FIG. 9 shows a photomicrograph of the tip of the worn diamond tool.

  As is clear from the above, when a diamond-shaped tool T having a worn corner C1 as shown in FIG. 9 is used to process and form a stepped structure consisting of a plurality of steps, as shown in FIG. The corners of the stepped portion are bent, and when the optical element is molded using the mold M, there is a possibility that the optical characteristics of the diffractive structure are deteriorated.

  In contrast, according to the processing direction of the present invention, as shown in FIG. 3, the diamond tool T is moved along the optical axis O while the first edge T1 is brought into contact with the optical transfer surface of the rotating mold M. Since the cutting is performed while moving away from the corner C2, the wear amount is large at the angle C2 at which the first edge T1 and the second edge T2 of the diamond tool T intersect. Wear is suppressed at the corner C1 at which the first edge T1 and the third edge T3 intersect, and therefore the corner of the step is sag when a stepped structure having a plurality of steps is formed. Therefore, the mold M that can mold an optical element having good optical characteristics can be processed.

  According to a second aspect of the present invention, there is provided the machining method according to the first aspect, wherein the diamond tool is moved in a cutting direction in which the optical transfer surface of the mold is cut and then moved away from the rotation axis. Is performed a plurality of times.

  According to a third aspect of the present invention, in the invention of the second aspect, the length of the first edge portion of the diamond tool is smaller than the minimum width of the step portion of the optical element in the direction perpendicular to the optical axis. It is characterized by that. Depending on the type of diffractive structure provided in the optical element, the optical axis orthogonal width of the step portion may be different. In this case, the length α (see FIG. 1A) of the first edge T1 of the diamond tool is set. If the width is smaller than the minimum width B (see FIG. 3), grooves corresponding to all the diffractive structures can be formed.

According to a fourth aspect of the present invention, there is provided a processing method including: a straight portion extending linearly with a length of at least 100 μm in a direction intersecting a rotation axis of a mold on a rake face of a cutting edge made of diamond. Using a diamond tool formed with one edge and a linear second edge and a third edge that are longer than the first edge and connected to the end of the first edge , At least one optical functional surface is divided into a plurality of optical functional areas centered on the optical axis, and at least one of the plurality of optical functional areas is divided into ring-shaped areas centered on the optical axis, In addition, a predetermined number of discontinuous steps are provided in each annular zone, and a gold for molding an optical element having a diffractive structure in which the annular zones provided with the discontinuous steps are continuously arranged. A processing method for processing an optical transfer surface of a mold,
The diamond tool is moved to a position intersecting the rotation axis while the first edge is in contact with the rotating optical transfer surface of the mold, and the step of rotating the mold, And moving the diamond tool in a direction away from the rotation axis and in a direction parallel to the rotation axis.

  The present invention will be described with reference to the drawings. FIG. 5 is a schematic enlarged sectional view of the optical transfer surface of the mold. As described above, the cutting efficiency is poor at the center of the mold M because the peripheral speed is low. Therefore, in the processing method of the present invention, first, the diamond tool T is moved to the initial position indicated by the dotted line in FIG. 5 and then the mold M is rotated, so that the position intersects the rotation axis, that is, the optical axis O. Move to (see thick arrow). Thereby, the processing of the central portion of the mold M can be performed using the diamond tool T with little or no wear. Thereafter, similarly to the above-described invention, the diamond tool T moved to the reference position is moved in a direction (Z-axis direction) further pressed against the mold M in parallel with the optical axis O, and then in the Z-axis direction. While maintaining this position, the diamond tool T is moved away from the optical axis O, and further moved in the cutting direction. By repeating this multiple times, a structure having a stepped cross section is formed. After cutting to a predetermined depth, the diamond tool T is moved away from the mold M, and when the first edge T1 returns to the surface of the optical transfer surface or the vicinity thereof, the diamond tool is moved to the next reference position. By moving T in a direction away from the optical axis O, the adjacent groove is cut, and this can be repeated to process all the grooves (see thin arrows).

  According to a fifth aspect of the present invention, in the processing method according to the fourth aspect, the diamond tool is moved in a cutting direction in which the optical transfer surface of the mold is cut and then moved away from the rotation axis. Is performed a plurality of times.

  According to a sixth aspect of the present invention, in the invention according to the fifth aspect, the length of the first edge portion of the diamond tool is smaller than the minimum width in the direction perpendicular to the optical axis of the step portion of the optical element. It is characterized by that.

  A processing method according to a seventh aspect is characterized in that, in the invention according to any one of the first to sixth aspects, nickel / adjacent / copper plating is applied to the optical transfer surface of the mold. In particular, nickel / neighboring / copper plating is excellent in machinability, so that a long tool life can be secured. Incidentally, nickel / adjacent plating may be used on the optical transfer surface, and a similar effect can be obtained by coating copper, aluminum, metallic glass or the like.

  Here, as the “optical element”, for example, a lens, a prism, a diffraction grating optical element (diffraction lens, diffraction prism, diffraction plate, chromatic aberration correction element), an optical filter (spatial low-pass filter, wavelength band-pass filter, wavelength low-pass filter, wavelength High pass filters, etc.), polarizing filters (analyzer, optical rotator, polarization separating prism, etc.), and phase filters (phase plates, holograms, etc.), but are not limited thereto.

  ADVANTAGE OF THE INVENTION According to this invention, it is suitable for the process of the metal mold | die for optical elements represented by a diffraction lens, for example, and can provide the processing method which can form a highly accurate processed surface.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 6 is a perspective view of a two-axis ultraprecision machine 10 that is a preferred embodiment for carrying out the machining method according to the first to seventh aspects of the present invention, and FIG. 7 is a perspective view of a diamond tool. FIG. In the two-axis ultraprecision machine 10 shown in FIG. 7, an X-axis table 2 that is driven in the X-axis direction by a control device (not shown) is disposed on a pedestal 1. On the X-axis table 2, a diamond tool T is attached. A Z-axis table 4 driven in the Z-axis direction by a control device (not shown) is disposed on the base 1. On the Z-axis table 4, a main shaft (rotating shaft) 5 that is rotationally driven by a control device (not shown) is attached. The main shaft 5 can be attached with an optical element molding die (see FIG. 2) having a transfer optical surface to be processed. The diamond tool T has a diamond tip Tc attached to its tip, and its shape is the same as that shown in FIG.

According to the machining method according to the present embodiment, the spindle 5 and the X / Z axis tables 2 and 4 have extremely high rigidity, and an ultra-precision machining machine having an axis control resolution of 100 nm or less is used to work the spindle 5 with a workpiece. A die for forming an optical element is attached, rotated at a spindle rotation speed of 1000 min ⁻¹ , and the cutting point of the cutting edge is being processed by the diamond tool T under conditions of a cutting depth of 1 μm and a feed of 0.2 mm / min. The groove corresponding to the diffractive structure including the step-like annular zone as shown in FIG. 3 can be created on the optical transfer surface of the mold by cutting in the ductile mode so that it moves continuously. it can.

  The present invention has been described above with reference to the embodiments. However, the present invention should not be construed as being limited to the above-described embodiments, and can be modified or improved as appropriate. For example, the processing method of the present invention can be used in addition to processing a molding die for optical elements. Further, in the diamond tool used in the processing method of the present invention, the shape of the rake face may not be a square shape, but may be a tapered shape with a narrower base side than the first edge.

It is the figure (a) seen from the rake face side of the front-end | tip of the diamond tool T suitable for using for the processing method concerning this invention, and its side view (b). It is a perspective view of the metal mold | die M after processing using the diamond tool of FIG. 2 is a schematic enlarged cross-sectional view of an optical transfer surface of a mold M. FIG. 3 is a schematic enlarged cross-sectional view showing a relationship between a cutting edge shape of a diamond tool T and a step shape of a mold M. FIG. 2 is a schematic enlarged cross-sectional view of an optical transfer surface of a mold M. FIG. 1 is a perspective view of a biaxial ultraprecision machine 10 that is a preferred embodiment for executing a machining method according to the present invention. It is a perspective view of a diamond tool. It is a microscope picture which shows the front-end | tip of a diamond tool without abrasion. It is a microscope picture which shows the front-end | tip of the worn diamond tool.

Explanation of symbols

M Mold T Diamond tool 10 Ultra-precision machine

Claims (7)

A first edge portion including a straight portion extending linearly at a length of at least 100 μm in a direction intersecting the rotation axis of the mold on the rake face of the cutting edge made of diamond; Using a diamond tool that is longer than the edge and has a linear second edge and a third edge connected to the end of the first edge, at least one of the optical functional surfaces is an optical axis Is divided into a plurality of optical function areas, at least one of the plurality of optical function areas is divided into ring-shaped areas centering on the optical axis, and a predetermined number of discontinuities in each ring zone Processing method for processing an optical transfer surface of a mold for forming an optical element having a diffractive structure in which a step is provided and a ring zone provided with the discontinuous step is continuously arranged Because
Rotating the mold;
Moving the diamond tool in a direction away from the rotation axis and in a direction parallel to the rotation axis while bringing the first edge into contact with the optical transfer surface of the rotating mold. A processing method characterized by   The processing method according to claim 1, wherein the step of moving the diamond tool in a cutting direction for cutting an optical transfer surface of the mold and then moving in a direction away from the rotation shaft is performed a plurality of times.   The length of the 1st edge part of the said diamond tool is smaller than the minimum width | variety of the optical axis orthogonal direction of the said step part of the said optical element, The processing method of Claim 2 characterized by the above-mentioned. A first edge portion including a straight portion extending linearly at a length of at least 100 μm in a direction intersecting the rotation axis of the mold on the rake face of the cutting edge made of diamond; Using a diamond tool that is longer than the edge and has a linear second edge and a third edge connected to the end of the first edge, at least one of the optical functional surfaces is an optical axis Is divided into a plurality of optical function areas, at least one of the plurality of optical function areas is divided into ring-shaped areas centering on the optical axis, and a predetermined number of discontinuities in each ring zone Processing method for processing an optical transfer surface of a mold for forming an optical element having a diffractive structure in which a step is provided and a ring zone provided with the discontinuous step is continuously arranged Because
Rotating the mold;
The diamond tool is moved to a position intersecting the rotation axis while the first edge is brought into contact with the optical transfer surface of the rotating mold, and then the diamond tool is moved away from the rotation axis. Moving in a direction parallel to the direction and the rotation axis.   5. The processing method according to claim 4, wherein the step of moving the diamond tool in a cutting direction for cutting the optical transfer surface of the mold and then moving in a direction away from the rotation shaft is performed a plurality of times.   The length of the 1st edge part of the said diamond tool is smaller than the minimum width | variety of the optical axis orthogonal direction of the said step part of the said optical element, The processing method of Claim 5 characterized by the above-mentioned. The processing method according to claim 1, wherein the optical transfer surface of the mold is subjected to nickel / adjacent / copper plating.