JP2000084815A - Manufacture of aspherical optical element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To manufacture an aspherical optical element using a form grinding wheel, capable of minimizing a difference of peripheral velocities between a center portion and a periphery of a machined workpiece and ensuring high shape accuracy. SOLUTION: A workpiece 21 is machined into an aspherical shape by using a form grinding wheel 24 of a desired aspherical shape. The form grinding wheel 24 has a desired aspherical shape on a side surface inclining at a predetermined angle θ. The workpiece 21 is made to contact with the form grinding wheel 24 by inclining a rotation axis 202 of the form grinding wheel 24 at the angle θto the rotation axis 201 of the workpiece 21, and the workpiece 21 is machined.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an aspherical optical element, which performs aspherical processing of a lens or a mold using a grindstone.

[0002]

2. Description of the Related Art Generally, an aspherical surface used in the optical field has many axisymmetric aspherical shapes. Conventionally, to create such an axisymmetric aspherical shape, a processing method based on trajectory control of a numerically controlled processing machine, or a processing method of transferring a shape using a general grinding wheel having a desired aspherical shape is used. Have been.

[0003] As a processing method by the numerical control processing machine,
Three methods as shown in FIGS. 3A, 3B, and 3C are known.

One is a method shown in FIG. 3A, in which a tool 32 having an R-shaped cutting edge is rotated around an X-axis while rotating a workpiece 31 around a Y-axis. And the tool 32
The tool 32 is relatively moved in the X-axis direction and the Y-axis direction so that the cutting edge moves along a predetermined aspherical shape curve. Therefore, the processing can be performed by a processing machine of simultaneous X-axis and Y-axis control. However, in the method of FIG. 3A, the processing points 32a and 32b of the cutting edge of the tool 32 that come into contact with the workpiece 31 change depending on the processing position of the workpiece 31, so that the R shape of the cutting edge of the tool 32 is changed. If it is not perfect, there is a problem that an error occurs in the aspherical shape.

In the method shown in FIG. 3B, in order to compensate for the disadvantage of the simultaneous two-axis control shown in FIG. 3A, a θ axis is added, and the tool 32 is moved in the θ axis direction with respect to the workpiece 31. The tip 32c of the cutting edge of the tool 32 is always set to a processing point during the processing movement. This is a method that can be processed by using a processing machine of simultaneous three-axis control.

In the method shown in FIG. 3C, the tool 33 having a radius r is rotated about the Z axis while rotating the workpiece 31 about the Y axis. Then, this is a processing method in which the tool 33 is relatively moved in the X-axis direction and the Y-axis direction such that a portion where the tool 33 contacts the workpiece 31 moves along a predetermined aspheric cross-sectional shape. In this case, the processing accuracy of the workpiece 31 depends on the radius r of the tool 33 and the accuracy of the rotation axis.

On the other hand, FIG. 4 shows a method of creating an axisymmetric aspherical shape using a full-form grindstone. The rotating shaft 402 of the grinding wheel spindle unit 45 and the rotating shaft 401 of the work spindle unit 43
Are arranged in parallel. Form whetstone 44
Is attached to the grindstone spindle unit 45. The workpiece 41 is moved by the jig 42 to the work spindle 43.
Attached to. Then, the grindstone 44 and the workpiece 41 are rotated around the respective rotation axes 402 and 401, and in this state, the grindstone 44 and the workpiece 41 are pressed against the respective rotation axes 402 and 401. . As a result, the aspherical shape of the formed grindstone 44 is transferred to the workpiece 41.

[0008]

However, since the machining method based on the trajectory control using the numerically controlled machining machine as described above is a method of machining a grinding stone along an aspherical shape, the grinding stone is formed on the workpiece. The part to be processed by contacting the point is a point contact (per point). Therefore, there is a problem that it takes a long time to process and a portion where the grinding wheel comes into contact is limited, so that the grinding wheel is rapidly worn.

In addition, since the control error of the locus of two axes of X and Y or three axes including θ is directly reflected on the error of the shape of the workpiece, it is necessary to obtain a highly accurate shape. There is a problem that a processing machine having accurate motion performance and control performance is required.

On the other hand, in the shape transfer processing method using a form grinding wheel, when the outer diameter of the workpiece increases, the outer diameter of the form grinding wheel to be used also needs to be increased accordingly.
There is a problem that the device becomes large. Further, the peripheral speed of the grindstone is slow at the central portion of the workpiece and is high at the outer peripheral portion, so that the peripheral speed is largely different between the central portion and the outer peripheral portion. For this reason, there has been a problem that the wear of the grindstone is biased and the shape is apt to change, and a uniform processed surface is not formed between the central portion and the outer peripheral portion of the workpiece.

The present invention relates to a method of manufacturing an aspherical optical element using a formed grindstone, wherein the difference in the peripheral speed of the grindstone between the central portion and the outer peripheral portion of the workpiece is small, and high shape precision is obtained. It is intended to provide a manufacturing method.

[0012]

According to the present invention, there is provided a method for manufacturing an aspherical optical element as described below.

That is, a method of manufacturing an aspherical optical element having a step of processing a workpiece into the aspherical shape by using a forming grindstone having a desired aspherical shape. As the forming wheel, one having the desired aspherical shape on a side surface inclined by a predetermined angle is used, and the rotation axis of the forming wheel is inclined by the angle with respect to the rotation axis of the workpiece. A process in which the workpiece is brought into contact with the formed grindstone in an arranged position to perform processing.

[0014]

An embodiment of the present invention will be described with reference to the drawings.

In this embodiment, an optical element having an axisymmetric aspherical shape is manufactured by using a processing apparatus using a general-purpose grindstone as shown in FIG. In the processing apparatus of the present embodiment, as shown in FIG. 2, the rotation axis 201 of the work spindle unit 23 is inclined by a predetermined angle θ with respect to the rotation axis 202 of the grinding wheel spindle unit 25. The forming whetstone 24 has a rotating shaft 202.
And a rotating body shape with a skirt spread centered on the center, and a grindstone layer 203 is formed on the side surface. The form grindstone 24 is attached to a grindstone spindle unit 25, and the workpiece 21 is attached to a work spindle unit 23. In this configuration, since the rotating shaft 201 is inclined at an angle θ with respect to the rotating shaft 202, the workpiece 21 is inclined and abuts on the forming grindstone 24. At this time, the profile in the radial direction of the side surface of the formed grindstone 24 (shaft side profile) is a shape in which a desired aspherical shape is formed on a side surface inclined by an angle θ with respect to the upper surface of the grindstone 24.

When processing is performed by this apparatus, the forming grindstone 24 and the work 21 are pressed against each other while the forming grindstone 24 and the work 21 are rotated. As a result, the formed grindstone 24 linearly contacts the workpiece 21 in the radial direction,
The aspherical shape of the side surface of the formed grindstone 24 is transferred to the workpiece 21 to manufacture an axisymmetric aspherical optical element.

In the processing apparatus of the present embodiment, the rotating shaft 201 of the workpiece 21 is
02, the peripheral speed of the forming grindstone 24 at a position in contact with the center of the workpiece 21 and the workpiece 2
The difference between the peripheral speed of the formed grindstone 24 and the portion contacting the outer peripheral portion of the first grinding wheel is smaller than that of the conventional configuration shown in FIG. For this reason, the unevenness of the abrasion of the forming wheel 24 is small, and the shape change of the forming wheel 24 can be reduced. Therefore, the shape accuracy of the workpiece 21 can be improved, and
A uniform machined surface can be obtained at the center and the outer periphery of the workpiece 21.

FIG. 1 shows the overall configuration of the processing apparatus shown in FIG.
This will be further described with reference to FIG.

This aspheric polishing apparatus is roughly divided into a work spindle section 23, a work slide table section 12,
Whetstone spindle 25, whetstone slide table 14,
It comprises a slide drive control unit 15.

The work spindle section 23 is a spindle with a built-in motor, and is mounted on the work slide table section 12. The workpiece 21 is screwed to the work spindle 23 by a jig 22 (FIG. 2). The work slide table section 12 uses a linear guide 12a as a guide, and a DC servomotor 15a and a feed screw 15a.
Slide by b. Work slide table 12
Slide direction is the rotation axis 2 of the work spindle unit 23.
01 direction. The position of the work slide table section 12 can be confirmed from the encoder 15c incorporated in the DC servo motor 15a and the lead of the feed screw 15b.

The work slide table section 12 is mounted on a tilt mechanism (not shown) for tilting the work slide table to an arbitrary angle. When the work slide table section 12 is tilted by this tilt mechanism, the rotation axis 201 of the work spindle section 23 can be tilted by an arbitrary angle θ with respect to the rotation axis 202 of the grindstone spindle section 25.

On the other hand, the grindstone spindle unit 25 is a spindle with a built-in motor, and is mounted on the grindstone slide table unit 14. A forming grindstone 24 having a one-sided contour shape inclined at an arbitrary angle with respect to a desired aspherical shape is screwed to a grindstone spindle portion 25. The whetstone slide table section 14 is slid by a stepping motor 15d and a feed screw 15e with the linear guide 14a serving as a guide. The operation of the stepping motor 15 d is controlled by the slide drive control unit 15. The sliding direction of the whetstone slide table unit 14 is the whetstone spindle unit 2
5 coincides with the rotation axis 202. The position of the grinding wheel slide table section 14 can be confirmed by the digital micrometer 15f.

As shown in FIG. 2, the profile of one side of the shaping wheel 24 has a desired aspherical shape formed on a side surface inclined by an angle θ with respect to the upper surface of the shaping wheel 24. . This angle θ is equal to the angle θ between the rotation axis 201 of the work spindle unit 23 and the rotation axis 202 of the grinding wheel spindle unit 25.

Next, a procedure for manufacturing an aspherical glass lens using the processing apparatus of the present embodiment will be described.

First, a workpiece 21 made of an aspherical glass lens material is attached to a jig 22 using beeswax, and the jig 22 is screwed to a work spindle 23 (FIG. 2). Similarly, the formed grindstone 24 having the above-described shape is screwed to the grindstone spindle 25.

Next, the grindstone slide table section 14 is slid to adjust the positions of the workpiece 21 and the formed grindstone 24 in the direction of the axis 202. When adjustment is completed,
While rotating the work spindle section 23 and the grindstone spindle section 25, the work slide table section 12 is moved at a low speed, and the form grindstone 24 is brought into contact with the work piece 21 to cut the form grindstone 24 into the work piece 21. Let it go. The cutting speed is set so as to be balanced with the speed at which the forming grindstone 24 processes the workpiece 21. When it is desired to increase the removal amount per time of the workpiece 21 (increase the processing speed),
The formed grindstone 24 having a large grindstone diameter of the grindstone layer 203 is used. Conversely, if it is desired to reduce the surface roughness of the workpiece 21 and reduce the error (shape accuracy) from the desired aspherical shape even if the amount of removal per time is somewhat sacrificed, a total grinding wheel with a small abrasive grain size is used. Use 24. In the case of using the formed grindstone 24 having a very small abrasive particle diameter, the cutting speed is very small, and the work slide table 12 is moved in consideration of the very low moving speed of the work slide table 12. It is effective to adopt a configuration in which a pressure actuator is used to move the work slide table section 12 separately from means for forcibly sending the work slide table. The processing speed can be improved by applying a constant pressure to the work slide table section 12 using this pressure actuator to press the workpiece 21 against the forming grindstone 24 and cut it.

Table 1 shows an example of processing conditions in the case of using a grinding wheel 24 having a relatively large abrasive grain size.

[0028]

[Table 1]

Under the conditions shown in Table 1, it is possible to perform processing with a processing accuracy of several hundred μm to several mm in terms of the center thickness of the workpiece 21 and a shape accuracy within several μm in a shorter time as compared with the prior art. Met.

Table 2 shows the processing conditions in the case where the forming wheel 24 having a small abrasive grain diameter is used to make a cut under a constant pressure.

[0031]

[Table 2]

Under the conditions of Table 2, a sufficient shape accuracy of several μm was obtained with a processing amount of several tens μm in terms of the center thickness of the workpiece 21.

As described above, when an axisymmetric aspherical glass lens is manufactured by using the processing apparatus of the present embodiment, since the unevenness of the wear of the formed grindstone 24 is small, a glass lens with high shape accuracy is obtained. be able to. In addition, since the unevenness of the wear of the formed grindstone 24 is small, the effect of extending the life of the formed grindstone 24 can be obtained. Further, since the shape of the formed grindstone 24 is a shape in which the side surface is inclined, even if it is a formed grindstone for processing the workpiece 21 having the same outer diameter, the shape of the formed grindstone 24 is smaller than that of the conventional formed grindstone 44 of FIG. Can also be a compact grinding wheel 24 having a small outer diameter.

In the working method of the present embodiment,
The contact between the formed grinding wheel 24 and the workpiece 21 is shown in FIG.
Unlike conventional machining methods based on trajectory control such as (a), (b) and (c), the machining is performed not on a point but on a line, so that machining efficiency is good and grinding wheel wear is small. In addition, since the movement of the apparatus only requires cutting in one direction, there is an advantage that there is no need for simultaneous two- or three-axis control, and simple single-axis control is sufficient.

As described above, according to the present embodiment, an axisymmetric aspherical optical element can be easily and efficiently manufactured, and the shape accuracy can be improved even for a workpiece having a large outer diameter. Accuracy can be maintained and a uniform processing surface can be obtained over the entire surface.

In the above-described embodiment, the workpiece 2
Although the case of manufacturing a glass lens was described as 1,
The present invention is not limited to this, and the workpiece 21 made of metal or ceramics can be processed. Therefore,
It is also possible to manufacture a mold for molding an axisymmetric aspheric lens by this method. Further, the workpiece 21 can be adapted to either a convex surface or a concave surface.

[0037]

As described above, according to the present invention,
A method for manufacturing an aspherical optical element using a general-purpose grindstone,
It is possible to provide a manufacturing method in which the difference in the peripheral speed of the grindstone between the central portion and the outer peripheral portion of the workpiece is small, and high shape accuracy can be obtained.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing a configuration of a processing apparatus used in a method for manufacturing an aspherical optical element according to an embodiment of the present invention.

FIG. 2 is a sectional view showing a detailed configuration of the processing apparatus of FIG. 1;

FIGS. 3A, 3B, and 3C are explanatory views showing a method of manufacturing an aspherical optical element by trajectory control of a conventional numerically controlled processing machine.

FIG. 4 is a cross-sectional view showing processing of a workpiece using a conventional formed grindstone.

[Explanation of symbols]

12: Work slide table, 12a: Linear guide, 14: Grindstone slide table, 14
a: linear guide, 15: slide drive control unit, 15a: DC servo motor, 15b: feed screw, 15c: encoder, 15d: stepping motor, 15e: feed screw , 15f ...
・ Digital micrometer, 21 ・ ・ ・ Workpiece, 2
3 Work spindle part, 24 Form whetstone, 2
5: Grinding wheel spindle unit, 31: Workpiece, 32
... Tool, 32a, 32b ... Processing point, 32c ...
・ Tip, 33 ・ ・ ・ Tool, 41 ・ ・ ・ Workpiece, 42 ・
..Jig, 43 ... Work spindle part, 44 ...
Form grinding wheel, 45: grinding wheel spindle, 201: rotating shaft, 202: rotating shaft, 203: grinding wheel layer.

Claims (3)

[Claims] 1. A method of manufacturing an aspherical optical element having a step of processing a workpiece into the aspherical shape by using a forming wheel having a desired aspherical shape, wherein the step includes: As the forming wheel, one having the desired aspherical shape on a side surface inclined by a predetermined angle is used, and the rotation axis of the forming wheel is inclined by the angle with respect to the rotation axis of the workpiece. A method for manufacturing an aspherical optical element, wherein the workpiece is brought into contact with the shaped grindstone in a disposition to perform processing. 2. A method for manufacturing an aspherical optical element according to claim 1, wherein a table on which the workpiece is mounted is forcibly moved using a feed screw in order to bring the workpiece into contact with the formed grindstone. A method of manufacturing the aspherical optical element, wherein the workpiece is cut so as to cut the formed grindstone into the workpiece. 3. The method for manufacturing an aspherical optical element according to claim 1, wherein a table on which the workpiece is mounted is moved using a pressure actuator so that the workpiece is brought into contact with the formed grindstone. And forming the formed grindstone into the workpiece with a constant pressure.