JPH11197902A - Manufacture of diffractive surface form - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily cut a desired and accurate diffractive surface form. SOLUTION: A nose angle ε between an end cutting edged 3 and a side cutting edge 4 in a nose at the front end of a diamond tool 1, is set to 85 deg, and the length of the side cutting edge 4 is set to 5 ×m. A surface to be worked of a die 11 and the tool 1 have such a positional relationship that an angle α1 defined between a slope I having a diffractive function for the surface to be worked, and having a rise-up angle of less than 30 deg., and the side cutting edge 4 for cutting the slope I is set to be in a range from 2 to 3 deg. In this arrangement, a rotary shaft of a processing machine attached thereto with the die 11, is rotated at 7,000 rpm, and the nose of the diamond tool 1 is translated at a travel speed of 1.3 mm/min from the center of the die to the outer periphery of the latter, and from a lower position of the slope I to a higher position thereof. Thus, a desired diffraction surface form can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a diffractive surface shape applied to an optical element or a mold used in an optical system, a tool used therefor, and a diffractive optical element formed by a mold. .

[0002]

2. Description of the Related Art Conventionally, a method of processing a diffractive surface shape while translating a diamond tool or the like in accordance with the shape of the diffractive surface has been to use a tool having a small chamfer at the tip and an acute angle at the tip. Is disclosed in the 1992 Japan Society for Precision Engineering Spring Conference Academic Lecture Proceedings: OMRON Corporation "Ultra-precision cutting of Fresnel lens molds".

[0003]

However, the following problems occur in this conventional example. (1) Diffraction surface shape cannot be processed accurately due to wear of diamond tool. (2) The bottom shape and grating height of the diffraction grating cannot be accurately machined due to chamfering of the tip of the diamond tool. (3) The roughness of the slope having the diffraction function is increased.

An object of the present invention is to solve the above-mentioned problems,
An object of the present invention is to provide a method of manufacturing a diffractive surface shape that can easily cut a desired accurate diffractive surface shape.

[0005]

According to the present invention, there is provided a method of manufacturing a diffractive surface shape according to the present invention, wherein a diffractive surface to be cut and a cutting tool are relatively rotated and translationally moved. In the method of manufacturing a shape, a slope having a diffraction function is cut by a transverse cutting edge at the tool tip,
The length of the horizontal cutting edge is shorter than the length of the slope, and the length direction of the horizontal cutting edge is attached to the slope to be cut so as to be 30 ° or less. The cutting is performed by relatively moving in the direction of 30 ° or less from the top toward a high place.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail with reference to the illustrated embodiment. FIG. 1 shows a tip shape of a diamond tool 1 used in the present embodiment, and FIGS.
3 shows the tip shapes of comparative tools A and B made of various kinds of diamonds. Nose 2 at the tip of diamond tool 1
The angle between the front cutting edge 3 and the horizontal cutting edge 4, ie, the nose angle ε is 85
°, and the length L of the transverse cutting edge 4 is 5 μm. Similarly, the nose angle ε of the tools A and B is 85 °,
In the tools A and B, the length of the transverse cutting edge 4 is large, and particularly in the tool B, the tip of the nose 2 has a curvature of R = 0.5 μm.

FIGS. 4 and 5 show three axes N of XYZ used for machining.
FIG. 4 shows a perspective view of a C-control processing machine. In the processing machine of FIG. 4, a mold 11 to be cut is mounted on a rotating shaft 12 and the tool 1 is mounted on an XYZ table 13. In the processing machine of FIG.
The tool 1 is mounted on a rotating shaft 12 and the mold 11 is mounted on an XYZ table 13. In the embodiment, the processing machine shown in FIG. 4 is used.

In the case of manufacturing a mold 11 for obtaining a plastic diffractive optical element having a diffraction surface shape having a large number of circular grooves, for example, a desired diffraction surface shape is a disk-shaped flat surface having 100 diffraction gratings. This is a book, and the lattice height h is 1 μm, the lattice spacing is di = 500 μm at the innermost periphery, do = 50 μm at the outermost periphery, and the lattice spacing is gradually reduced from the innermost periphery toward the outermost periphery. . For example, mold 11
Electroless nickel plating as a processing layer on the surface of
It is applied with a thickness of 0 μm, and a steel material for a plastic mold is used as a base material.

As shown in FIG. 6, the positional relationship between the work surface S of the die 11 and the tool 1 is determined by a slope I having a diffraction function of the work surface S and the transverse cutting edge 4 for working the slope I. The angle α1 is set to be 2 ° to 3 °.

Here, the rotating shaft 12 of the processing machine to which the mold 11 is attached is rotated at 7,000 revolutions per minute,
By controlling the Z table 13, the nose 2 of the diamond tool 1 moves from the center O of the mold 11 toward the outer periphery and the slope I from a low place to a high place as shown by an arrow in FIG. The translation is performed at a moving speed of 3 mm so that a desired diffraction surface shape is obtained. Also,
The processing depth of the electroless nickel plating by the diamond tool 1 at this time is, for example, about 5 μm.

For comparison, the comparison tools A and B are formed in the same manner by using a slope I having a diffraction function of the surface S to be machined of the mold 11 and a side of the tools A and B for machining the slope I. An angle α1 formed by the cutting blade 4 was set so as to be 2 ° to 3 °, and processing was performed similarly.

The state of the diffraction surface processed by the diamond tool 1 and the diamond tools A and B having two different shapes for comparison are as follows.

Pitch Tool used Tool 1 Tool A Tool B No Measurement item 1 Slope roughness (PV: nm) 10 40 40 (Innermost circumference) Groove bottom shape (second pitch) 89.8 ° Multi-step groove Round bottom Grid height Height h (μm) 1.0 1.1 0.9 33 Slope roughness (PV: nm) 10 40 40 Groove bottom shape 89.7 ° Multi-step groove Round bottom Grid height h (μm) 1.0 1.2 0.9 66 Slope roughness (PV: nm) 10 60 60 Groove bottom shape 89.5 ° Multi-step groove Round bottom Lattice height h (μm) 1.0 1.2 0.9 100 Slope roughness (PV: nm) ) 10 80 80 (outermost) Groove bottom shape 88.8 ° Multi-step groove Round bottom Grid height h (μm) 1.0 1.1 0.9

As described above, in the processing method using the diamond tool 1, a desired shape can be formed over the entire surface of the diffraction grating.

On the other hand, in the machining with the comparative tools A and B, the machining surface becomes rough.
It is considered that the chips generated by the processing are involved in the gap having an angle of 2 ° to 3 ° between the horizontal cutting edge 4 and the slope I created. In the present embodiment, it is considered that the length L of the horizontal cutting edge 4 of the tool 1 causing the chip entrainment is as short as 5 μm and the probability of entrainment of the chip is reduced, so that the roughness of the slope I is good. Can be

Further, as for the shape of the groove bottom, in the comparative tool A, chips are wrapped around the tip, and as shown in FIG. 7, the seat portion of the slope I has a multi-stage shape, and in the comparative tool B, the curvature of the tip is directly transferred. As shown in FIG. 8, the bearing surface of the slope I has a round bottom shape. The grid height h also has an error of 0.1 to 0.2 μm from the desired value due to the disorder of the groove bottom shape in the comparative tools A and B.

Next, a case of manufacturing a diffractive optical element using an acrylic plate will be described. The desired diffraction surface shape is 100 diffraction gratings on a circular plane, the grating heights h are all 5 μm, the grating interval is di = 500 μm at the innermost periphery, and do = 50 μm at the outermost periphery. Is a shape that gradually decreases from the innermost circumference to the outermost circumference.

FIG. 9 shows the shape of the tip of the diamond tool 1 '. The length L of the transverse cutting edge 4 is 5 μm. FIG. 10 is a comparative tool C having a small chamfer at the tip of the nose 2 used for comparison. And the nose angle ε is 82 °. As in the first embodiment, an XYZ three-axis NC control processing machine shown in FIG. 4 was used for this processing.

An acrylic plate 14 to be processed is mounted on the rotating shaft 12 of the processing machine, and the diamond tool 1 'is mounted on the XYZ table 13. At this time, the positional relationship between the processing surface S of the acrylic plate 14 and the tool 1 ′ is such that the processing surface S has a diffractive surface I as shown in FIG.
Is set so that the angle α2 formed by the transverse cutting edge 4 of the diamond tool 1 'for machining is 0.5 ° to 5.6 °.

The rotary shaft 12 is rotated at 8000 revolutions per minute, and the XYZ table 13 is controlled by a program so that the diamond tool 1 'moves from the center O of the acrylic plate 14 toward the outer peripheral direction as shown by a straight arrow in FIG. From low to high on slope I, 1.2 minutes per minute
The translation is performed so that a desired diffraction surface shape is obtained at a moving speed of mm. In addition, as a comparative example of the processing method, processing was performed in which the translation direction of the diamond tool 1 ′ and the comparative tool C was the center O from the outer peripheral surface.

On the other hand, a comparative tool C was prepared in the same manner as in FIG.
As shown in FIG. 2, a slope I having a diffraction function of the surface S to be processed.
And the angle .alpha.2 formed by the transverse cutting edge 4 of the comparative tool C for machining the slope I was set so as to be 0.5 DEG to 5.6 DEG.

The processing depth of the acrylic plate 14 by the tool in this experiment was a minimum of about 5 μm and a maximum of about 25 μm.

The state of the diffractive surface created by the diamond tool 1 'and the comparative tool C by the processing method in which the translation direction is changed is as follows.

From the innermost circumference to the outermost circumference direction From the innermost circumference to the outermost circumference Pitch Tool 1 'Tool C Tool 1' Tool C No Measurement item 1 Slope roughness (PV: nm) 15 60 100 100 (Innermost circumference ) Groove bottom shape 89.4 ° Multi-stage shape 89.4 ° chamfered shape Grid height h (μm) 5.0 5.1 1.0 4.9 33 Slope roughness (PV: nm) 15 70 90 80 Groove Bottom shape 88.9 ° Multi-stage shape 88.9 ° chamfered shape Grid height h (μm) 5.0 5.2 1.0 4.9 66 Slope roughness (PV: nm) 15 80 80 70 Groove bottom shape 87.6 ° Multi-stage shape 87.6 ° chamfered shape Grid height h (μm) 5.0 5.1 1.0 4.9 100 Slope roughness (PV: nm) 15 100 80 60 (outermost circumference) Groove Bottom shape 84.3 ° Multi-stage shape 84.3 ° chamfered shape Grid height h (μm) 5.0 5.1 1.0 4.9

In processing with the tool 1 ', the acrylic plate 14
The desired shape can be formed over the entire surface of the substrate. on the other hand,
In the machining with the comparative tool C, the slope I became rough,
It is considered that this is because chips generated in the gap between the horizontal cutting edge 4 and the slope I created are wound in the same manner as in the first embodiment.
In the tool 1 ', it is considered that the length L of the horizontal cutting edge 4 was as short as 5 [mu] m, and the probability of winding chips was reduced, so that the slope roughness was good.

The groove bottom shape of the comparative tool C is a multi-stage shape in which chips are wound. The tool height C for comparison is also
From the desired value due to the disorder of the groove bottom shape at
An error of 0.2 μm occurred.

In the machining in which the translation direction of the tool is reversed, the roughness of the slope I of both the tool 1 'and the comparison tool C is large. It is considered that this is because the tool tip is easily deteriorated due to the margin of the cutting and the like, and the normal processing is not performed, and the inclined surface I is in a state of being raised. Further, in the groove bottom shape of the comparative tool C, since the tip chamfering shape of the tool C was transferred, the lattice height h was insufficient by about 0.1 μm.

Further, as a result of performing injection molding of an optical acrylic resin using the electroless nickel-plated mold 11 obtained in the previous embodiment, the shape of the diffractive optical element of the mold 11 has a transfer error of ± 2. %, And a diffractive optical element having a good shape was obtained.

Further, in a processing method similar to that of the previous embodiment, a metal mold on which a titanium nitride and a diamond-like carbon film are further formed by processing a deposited film mainly containing nickel and phosphorus on a cemented carbide is formed. As a result, the shape of the diffractive optical element of the mold 11 could be transferred within a transfer error of ± 4%, and a diffractive optical element having a good shape was obtained.

[0030]

As described above, according to the method for manufacturing a diffractive surface shape according to the present invention, the shape of the processing tool is selected, and the positional relationship between the processing surface and the processing tool and the moving direction of the processing tool are properly adjusted. By doing so, it is possible to obtain a diffraction grating surface having a desired shape and a good surface condition.

[Brief description of the drawings]

FIG. 1 is a sectional view of a tip shape of a diamond tool according to an embodiment.

FIG. 2 is a sectional view of a tip shape of a diamond tool for comparison.

FIG. 3 is a sectional view of a tip shape of a diamond tool for comparison.

FIG. 4 is a perspective view of a three-axis NC control processing machine.

FIG. 5 is a perspective view of a three-axis NC control processing machine.

FIG. 6 is an explanatory diagram of a processing state of a diffraction grating.

FIG. 7 is an explanatory view of a cutting state by a comparative diamond tool.

FIG. 8 is an explanatory diagram of a cutting state by a comparative diamond tool.

FIG. 9 is a sectional view of a tip shape of a diamond tool according to another embodiment.

FIG. 10 is a sectional view of a tip shape of a diamond tool for comparison.

FIG. 11 is an explanatory diagram of a processing state of a diffraction grating.

FIG. 12 shows a setting state of a diamond tool for comparison.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1, 1 'Diamond tool 2 Nose 3 Front cutting edge 4 Horizontal cutting edge 11 Die 12 Rotation axis 13 XYZ table 14 Acrylic plate A, B Comparison tool

Claims (8)

[Claims] 1. A method of manufacturing a diffractive surface shape while relatively rotating and translating a diffractive surface to be cut and a cutting tool, wherein a slope having a diffractive function is cut by a transverse cutting edge at the tip of the tool. The length of the horizontal cutting edge is shorter than the length of the slope, and the length direction of the horizontal cutting edge is attached to the slope to be cut so as to be 30 ° or less, and the tool is mounted on the lower surface of the slope. A method of producing a diffractive surface shape by relatively moving in a direction of 30 ° or less from a place to a high place for cutting. 2. The method according to claim 1, wherein the length of the transverse cutting edge of the cutting tool is greater than 2 μm. 3. The method according to claim 2, wherein the cutting tool is a diamond tool. 4. The method for manufacturing a diffractive surface according to claim 1, wherein the diffractive surface is a plastic surface of a lens member. 5. A tool used in the manufacturing method according to claim 1. 6. A plastic lens member having a diffraction surface shape manufactured by the manufacturing method according to claim 1. 7. A mold member having a diffraction surface shape manufactured by the manufacturing method according to claim 1. 8. A lens member having a diffraction surface shape formed by the mold according to claim 7.