JPH10328995A - Curved surface grinding method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a curved surface grinding method that can grind even an axially asymmetric curved lens with two orthogonal faces formed in axially asymmetric noncircular curved faces, with high accuracy. SOLUTION: A rotatable grinding tool 6 provided with a spherical grinding wheel with the specified radius of curvature is used, and the center of the radius of curvature of the grinding wheel is positioned on the rotating center axis of the grinding tool 6. In the state of the rotating locus of the grinding wheel being made completely spherical with the above-mentioned specified radius of curvature, the grinding wheel 6 is moved relatively to the machined surface of an axially asymmetric curved lens 1 to grind the machined surface of the axially asymmetric curved lens 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a curved surface grinding method for grinding an optically functional surface of an optical element or an optically functional surface of a mold for molding an optical element into a curved surface, particularly an asymmetrical curved surface.

[0002]

2. Description of the Related Art Conventionally, as a method for processing an optically functional surface of an object to be processed such as an optical element or a molding die into an axially asymmetric curved surface, a method using an NC surface grinder using an R-shaped outer peripheral surface or an NC milling machine There is a method using a ball end mill tool (hereinafter, simply referred to as a tool) according to the method described above.

[0003] In both of the above methods, machining is performed by controlling the relative position between a workpiece and a grindstone (or tool). It is said that there is a limit in accuracy, and the following proposals have been made as techniques for responding to further higher accuracy.

As one example, Japanese Patent Application Laid-Open No. Hei 8-257886 is disclosed.
(Hereinafter referred to as “prior art 1”)
There is. According to the prior art 1, an X-axis table and a Y-axis table are arranged so as to be movable and controllable in directions of X-axis and Y-axis orthogonal to each other, and a rotary spindle is rotated in a direction of Z-axis orthogonal to X-axis and Y-axis. Place. Then, a grindstone is attached to the lower end of the rotary spindle, and the rotary spindle is mounted on the X-axis table so that the tangent line of the workpiece to be processed and the grindstone always contact at right angles.

On the other hand, on the Y-axis table, a rotatable rotary shaft is arranged, and a holder for holding the workpiece at a desired distance from the center of rotation of the rotary shaft is mounted and fixed. The work piece is machined into an arc shape by matching the tip of the work piece held by the holder with the processing point of the grindstone, rotating the rotating spindle and rotating the rotating shaft.

[0006] By simultaneous two-axis NC control of the X-axis table and the Y-axis table, the workpiece held by the holder together with the rotating shaft is drive-controlled in the Y-axis direction to raise the workpiece into an aspherical shape. It is to be processed with precision.

Another example is disclosed in Japanese Patent Application Laid-Open No. 7-2997.
There is a technique disclosed in Japanese Patent Publication No. 46 (hereinafter, referred to as Conventional Technique 2). This prior art 2 is an aspherical surface processing apparatus for processing a three-dimensional non-rotationally symmetric aspherical surface on a workpiece using a disk-shaped grindstone having a spherical outer peripheral surface. A work slide table that moves in the X-axis direction while holding the workpiece by a vacuum chuck provided on the front surface of the work support table, and a grindstone is horizontally moved in the Z-axis direction perpendicular to the work slide table. It has a whetstone slide table and a whetstone head mounted on the whetstone slide table and having a disk-shaped whetstone mounted on a shank part of the whetstone so as to be movable in a Y-axis direction (vertical direction) orthogonal to the X-axis and the Z-axis.

A truing device to which a truer is fixed is provided on a work slide table for holding the workpiece, and a strobe device and a microscope are installed facing each other in the Z-axis direction on the bed. By positioning the grindstone supported by the grindstone slide table, the image of each end of the grindstone is detected and the diameter of the grindstone is measured. And
A truing device having a truer fixed in parallel with a work support is fixed on a work slide table for holding a workpiece.

By the above-mentioned truing device, the outer peripheral surface of the grinding wheel is trued with high precision into a spherical shape having a uniform radius from the center of the grinding wheel. Next, the diameter of the grinding wheel is measured, and the shape data is recalculated using the obtained grinding wheel radius R as correction data. Based on the new shape data, the X
The axis, the Y-axis, and the Z-axis are controlled, and machining of an asymmetrical curved surface is performed with high accuracy.

[0010]

However, in the above-mentioned prior art 1, the cross-sectional shapes orthogonal to each other of the axially asymmetric processing surfaces of the forming die obtained by the above-mentioned processing can be processed into an arbitrary curved surface. However, the other cross-sectional shape is determined by the distance from the rotation center of the rotation shaft. Therefore, the prior art 1 has a problem that only one axially asymmetric curved surface having one circular arc on the same surface and the other orthogonal non-circular surface can be used.

In the above prior art 2, since processing is performed using a disk-shaped grindstone, the outer peripheral surface of the shank portion holding the disk-shaped whetstone and the outer edge of the workpiece as the desired axially asymmetric curved surface of the workpiece becomes hemispherical. This makes it easier for the parts to come into contact with each other, and is particularly restricted by a deep and small concave shape.
If the diameter of the shank is reduced to avoid this,
The rigidity of the shank is lost, leading to a deterioration in processing accuracy on the processing surface of the workpiece. Therefore, the prior art 2 has a problem that it is difficult to machine a hemisphere having a deep axially asymmetric curved surface and a small diameter.

The present invention has been made in view of the above problems, and even if the surfaces in two directions perpendicular to each other are non-circular, axially asymmetrical curved surfaces, the grinding tool and the grinding tool can be used regardless of the curvature. It is an object of the present invention to provide a curved surface grinding method capable of performing highly accurate grinding of an axially asymmetric curved surface or the like without interference with a workpiece.

[0013]

In order to achieve the above object, a curved surface grinding method according to a first aspect of the present invention uses a rotatable grinding tool provided with a spherical grinding wheel having a predetermined radius of curvature, wherein With the center of curvature radius of the grinding tool positioned on the rotation center axis of the grinding tool and the rotation trajectory of the grinding wheel being a true sphere having the predetermined radius of curvature, the grinding tool is moved relative to the processing surface of the workpiece. By relatively moving the workpiece, the processing surface of the workpiece is ground.

The curved surface grinding method according to a second aspect of the present invention is the curved surface grinding method according to the first aspect of the present invention, wherein the rotation center axis of the grinding tool is not positioned within the processing surface of the workpiece. The grinding spindle holding the grinding tool is tilted at a certain angle.

Further, a curved surface grinding method according to a third aspect of the present invention is the curved surface grinding method according to the first or second aspect, wherein the grinding tool has a rotation center of the grinding tool based on a radius of curvature of the grinding wheel. 90 from the shaft toward the outer circumference
The one in which the range of not less than ° is a grindstone was used.

That is, in the curved surface grinding method according to the first invention, the center of the radius of curvature of the grinding wheel is located on the rotation center axis of the grinding tool, and the rotation trajectory of the grinding wheel is changed to a true sphere having the predetermined radius of curvature. In this state, the grinding tool is moved relative to the processing surface of the workpiece to grind the processing surface of the workpiece.

Further, in the curved surface grinding method according to the second invention, the grinding spindle holding the grinding tool is fixed at a predetermined angle so that the rotation center axis of the grinding tool is not located within the processing surface of the workpiece. Tilt.

Further, the curved surface grinding method according to a third aspect of the present invention is a method of rotating a grinding tool having a range of 90 ° or more from the rotation center axis of the grinding tool toward the outer periphery with respect to the center of the radius of curvature of the grinding wheel. Let it.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION

(First Embodiment of the Invention) FIG. 1 is a perspective view of an axially asymmetric curved lens according to a first embodiment of the present invention, FIG. 2 is a front view thereof, and FIG. , BB is shown in FIG. FIG. 5 is an explanatory view of a processing machine for grinding an axially asymmetric curved lens with a grinding tool, FIG. 6 is an enlarged view of the grinding tool, and FIG. 7 is an explanatory view of a state in which the grinding tool is rotated. . Further, FIG. 8 shows a state in which the grinding tool acts on the center of the optical axis of the axially asymmetric curved lens which is a sectional view taken along the line BB of FIG. FIG. 9 shows a state in which the grinding tool operates on the axis center. FIG. 10 shows the processing order of the axially asymmetric curved lens and the trajectory of the grindstone during the processing.

In this embodiment, the angle θ between the line connecting the outermost periphery of the axially asymmetric curved lens 1 (glass lens) and the center of curvature shown in FIG.
_The concave axially asymmetric curved lens 1 is processed with a grinding wheel 8 having diamond abrasive grains so that the sum of ₁ and θ ₂ is 90 ° or less.

In FIG. 5, the processing machine is an ultra-precision CNC processing machine, and an X-axis slide table 2 and a Y-axis slide table 3 slidable in three directions of X-axis, Y-axis and Z-axis.
And a Z-axis slide table 4, which can be operated by simultaneous control of three axes, and has a main shaft 5 rotatable on the Z-axis slide table 4.

The material of the axially asymmetric curved lens 1 is held at the tip of the main shaft 5. On the other hand, the grinding tool 6 is held by the grinding spindle 7 so that its rotation center axis 10b is coaxial with the rotation center axis 10a of a spindle (hereinafter, referred to as the grinding spindle 7) that rotates precisely. Also, the grinding spindle 7 is a Y-axis slide table 3
Is mounted so as to be rotatable in the θ direction (circumferential direction) on the Y-axis plane and tilted arbitrarily.

In FIG. 6, a predetermined radius of curvature R ₁ having diamond abrasive grains provided at the tip of the grinding tool 6 is shown.
The center of curvature radius 9 of the grinding wheel 8 is located on the rotation center axis 10 b of the grinding tool 6. In addition, the grinding wheel 8 is provided with a grinding tool 6 based on the radius of curvature 9 of the grinding wheel 8 as a reference.
It has a central axis of rotation more than 90 ° of the grinding wheel the effective portion 12 toward the 10b toward the outer circumference, is arranged to the rotation locus 11 of the grinding wheel 8 shown by dotted lines in FIG. 7 is a spherical surface of radius of curvature R ₁ ing.

The shank portion of the grinding tool 6 (the grinding wheel 8
Of the grinding wheel 8) is smaller than the rotation locus 11 of the grinding wheel 8. This eliminates interference between the processing surface of the axially asymmetric curved lens 1 and the shank 6a, and enables processing of a hemispherical curved surface.

The inclination angle θ of the grinding spindle 7 of this embodiment is set as follows. In FIG. 4, the inclination angle θ = the effective range of the grinding wheel (°) / 2− (θ ₁ −
θ ₂ ) / 2.

Therefore, when the angle θ ₁ = θ ₂ , the inclination angle θ = the effective range (°) / 2 of the grinding wheel.

Next, a method of grinding an axially asymmetric curved lens by the above-described processing machine will be described with reference to FIGS. First, the position where the rotation center 9 of the grinding wheel 8 of the grinding tool 6 coincides with the optical axis center 13 of the axially asymmetric curved lens 1 and where the grinding wheel 8 is in contact with the axially asymmetric curved lens 1 is defined by the X and Y of the NC coordinate values. to 0, and rewrites the value of the radius of curvature R ₁ (with respect to the rotation center 9 of the NC program grinding wheel 8, moving each table 2, 3 and 4). This gives X
The reference positions of the axis, Y axis, and Z axis are set.

Grinding is performed from the processing start line L101 shown in FIG. 10, but the contact point 8a of the grinding wheel 8 of the grinding tool 6 is moved to the processing line so that the contact point 8a of the grinding wheel 8 passes through the processing start line L101. 8a, the position data of each processing point of the locus of the rotation center 9 of the grinding wheel 8 (the intersection of the Y direction movement line YL shown in FIG. 8 and the X direction movement line XL shown in FIG. 9) is calculated. To create an NC program.

With the NC program created, N
The movement of the C processing machine in each of the X-axis, Y-axis, and Z-axis directions is NC-controlled to process one line. When the processing of this one line is completed, the Y axis is NC-controlled, and the next line L102
To perform the same processing.

By processing all the lines subdivided in the Y-axis direction from the processing start line L101 to the lines L102, L103,..., The axially asymmetric curved lens 1 can be formed.

According to the present embodiment, by forming a grinding wheel of a grinding tool into a spherical shape, an NC program can be easily created even with a complicated axially asymmetric curved lens.
Continuous grinding can be performed with a grinding wheel having a constant peripheral speed, and a highly accurate optical surface can be obtained with an axially asymmetric curved lens. In addition, since diamond abrasive grains are used for the grinding wheel, a good optical surface can be obtained only by grinding.

In the present embodiment, the horizontal processing line controlled by the X, Y, and Z axes in the processing order is controlled by the Y-axis control with respect to the axially asymmetric curved lens as the workpiece. Grinding is performed by moving from top to bottom, but it is also possible to perform grinding by moving from top to bottom, and furthermore, a vertical processing line controlled by X-axis, Y-axis, and Z-axis. Grinding can be performed by moving the lens in the lateral direction with respect to the axially asymmetric curved lens by X-axis control.

The material of the workpiece is not limited to glass as long as it can be ground, and an optical resin such as an acrylic resin may be used. Hardness, ceramics, etc. may be used.

Further, c-BN is used for the grinding wheel of the grinding tool.
By using (cubic boron nitride), even for workpieces made of iron-based material with good affinity for diamond,
Processing can be performed with high precision.

(Second Embodiment of the Invention) The second embodiment of the present invention
FIG. 11 is a perspective view of the axially asymmetric curved lens according to the embodiment, FIG. 12 is a front view thereof, FIG. 13 is a cross-sectional view taken along line CC, and FIG. 14 is a cross-sectional view taken along line DD. And FIG.
FIG. 1 shows a state in which a grinding tool acts on the center of the optical axis or on the outermost periphery 16 of the axially asymmetric curved lens, which is a DD sectional view of FIG.
It is shown in FIG. FIGS. 16 and 17 show the processing order of the axially asymmetric curved lens and the trajectory of the grindstone during the processing.

In the present embodiment, the angles θ ₃ and θ ₄ between the line connecting the outermost periphery of the axially asymmetric curved lens 14 and the center of curvature shown in FIG. The concave axisymmetric curved lens 14 having a hemispherical concave shape was machined by a grinding wheel 8 having diamond abrasive grains so as to be 90 °.

The configuration of the processing machine of this embodiment is the same as that used in the first embodiment, and the inclination angle θ of the grinding spindle 7 shown in FIG. 5 is set to a state close to horizontal (0 °). ,
Processing is performed by dividing the upper surface and the lower surface of the line CC shown in FIG. The inclination angle θ of the grinding spindle 7 is
The grinding wheel effective range is less than -90 ° at 1 ° or more.

The X-axis, Y-axis, and Z-axis reference positions for processing the axially asymmetric curved lens 14 are set in the same manner as in the first embodiment, and the grinding is performed on the optical axis center 15 of the asymmetric curved lens 14. An NC program is created in the same manner as in the first embodiment, with the upper CC line (line L201) as the machining start line. Then, as shown in FIG. 16, the processing start line L201 to line L202, line L203,.
By processing all the lines subdivided in the Y-axis direction, a half surface of the axially asymmetric curved lens 14 is formed.

Next, as shown in FIG. 17, the axially asymmetric curved lens 14 is inverted by 180 ° about the optical axis center 15, and the processing start line L201 and line L20
By processing all the lines subdivided in the Y-axis direction with the line L203, the other half surface is formed, and the axially asymmetric curved lens 14 is formed.

According to the present embodiment, by inclining the grinding spindle, grinding can be performed even on a hemisphere or a curved lens close to the hemisphere, and a highly accurate optical surface can be obtained.

(Third Embodiment of the Invention) The third embodiment of the present invention
FIG. 18 is a perspective view of the off-axis non-curved surface molding die in the embodiment, and FIG. 19 shows the positional relationship between the off-axis aspheric surface molding die and the optical axis. FIG. 20 shows the processing sequence of the off-axis non-curved surface forming die and the trajectory of the grindstone during the processing. And
FIG. 21 is a side view showing a state where the grinding tool on the forming surface of the off-axis non-curved surface forming die acts.

In this embodiment, the off-axis aspherical molding die 17 shown in FIG. 18 is processed in the same manner as in the first embodiment. The configuration of the processing machine of the present embodiment is the same as that used in the first embodiment, and since the molding surface 17a does not include the optical axis 18 as shown in FIG.
The inclination angle θ of the grinding spindle 7 shown in FIG. 7 is set to a state close to horizontal (0 °), and processing is performed in the same manner as in the first embodiment.

The program for processing the off-axis non-curved surface forming die 17 is obtained by grinding the aspherical data within the range of the forming surface 17a to the line L301 shown in FIG. 21 as in the first embodiment. Rewriting is performed so that the contact point 8a of the grinding wheel 8 of the tool 6 passes. Then, as shown in FIG.
Processing is performed on all lines subdivided in the Y-axis direction, such as 302, line L303,. Thus, the off-axis aspherical molding die 17 is formed.

According to the present embodiment, even in an off-axis aspherical mold, grinding can be performed without using a special jig, and a highly accurate optical surface can be obtained. In the present embodiment, the off-axis aspherical mold is ground, but the off-axis aspheric mirror, lens, and the like can be ground.

[0045]

According to the curved surface grinding method of the present invention according to the first aspect, there is an effect that a curved surface such as an axially asymmetric curved surface or an off-axis aspherical surface can be machined regardless of the degree of curvature. Further, since the grinding wheel is a true sphere, there is an advantage that correction at the time of creating a program is easy.

According to the curved surface grinding method of the present invention according to the second aspect, in addition to the effect of the first aspect, there is an effect that the entire curved surface can be favorably machined. According to the curved surface grinding method of the present invention according to the third aspect, in addition to the effect of the first or second aspect, there is an effect that the processing can be performed with high accuracy even in the case of a hemispherical shape.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an axially asymmetric curved lens according to a first embodiment of the present invention.

FIG. 2 is a front view showing an axially asymmetric curved lens according to the first embodiment.

FIG. 3 is a sectional view taken along line AA of FIG. 2;

FIG. 4 is a sectional view taken along line BB of FIG. 2;

FIG. 5 is a side view showing the processing machine according to the first embodiment.

FIG. 6 is a front view showing the grinding tool according to the first embodiment.

FIG. 7 is a plan view showing the grinding tool according to the first embodiment.

FIG. 8 is a side view of a state in which a grinding tool acts on the center of the optical axis of the axially asymmetric curved lens.

FIG. 9 is a plan view showing a state where a grinding tool acts on the center of the optical axis of the axially asymmetric curved lens.

FIG. 10 is an explanatory diagram showing a locus of a grinding wheel and a processing order during processing.

FIG. 11 is a perspective view showing an axially asymmetric curved lens according to a second embodiment.

FIG. 12 is a front view showing an axially asymmetric curved lens according to a second embodiment.

FIG. 13 is a sectional view taken along the line CC in FIG. 12;

FIG. 14 is a sectional view taken along the line DD in FIG. 12;

FIG. 15 is a side view showing a processing state in the second embodiment.

FIG. 16 is a front view showing a trajectory of a grinding wheel at the time of processing one surface in the second embodiment.

FIG. 17 is a front view showing a trajectory of a grinding wheel during processing of the other surface in the second embodiment.

FIG. 18 is a perspective view showing an off-axis non-curved surface forming die according to a third embodiment.

FIG. 19 is a plan view showing the positional relationship between the off-axis non-curved surface forming die and the optical axis in the third embodiment.

FIG. 20 is an explanatory diagram showing a trajectory and a processing order of a grinding wheel during grinding according to the third embodiment.

FIG. 21 is a side view showing an operation state of a grinding tool on a forming surface of an off-axis non-curved surface forming die according to a third embodiment.

[Explanation of symbols]

 Reference Signs List 1 axis asymmetric curved lens 2 X axis slide table 3 Y axis slide table 4 Z axis slide table 5 spindle 6 grinding tool 7 grinding spindle 8 grinding wheel 14 axis asymmetric curved lens 17 off axis aspherical mold

Claims (3)

[Claims] A rotatable grinding tool provided with a spherical grinding wheel having a predetermined radius of curvature, wherein the center of the radius of curvature of the grinding wheel is located on the rotation center axis of the grinding tool, and the rotation locus of the grinding wheel is adjusted Curved surface grinding characterized by moving a grinding tool relative to a processing surface of a workpiece in a state of a true sphere having a predetermined radius of curvature and grinding the processing surface of the workpiece. Processing method. 2. The grinding spindle according to claim 1, wherein the grinding spindle holding the grinding tool is inclined at a predetermined angle so that the rotation center axis of the grinding tool is not located within the processing surface of the workpiece. Curved surface grinding method. 3. The grinding wheel of the grinding tool according to claim 1, wherein the grinding wheel has an effective portion in a range of 90 ° or more from a rotation center axis of the grinding tool toward an outer peripheral direction with respect to a center of a radius of curvature of the grinding wheel. Item 3. A curved surface grinding method according to Item 2.