JPH1086051A - Grinding method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To grind even a complicated-shaped surface to be ground of a work to a supersmooth surface with high precision of shape. SOLUTION: A work W is fixed on a work table in a state in which the periphery of the work W is surrounded by a dummy material 22. And, the grinding face of a grinding tool 11 of a small diameter is abutted to the surface to be ground of the work W, the work is made to sweep at a low speed and a predetermined stroke in the generator direction by a work linear moving mechanism 40 while a grinding liquid is supplied in a state in which a predetermined machining pressure is applied by a ornamental hairpin 10, and the grinding tool 11 of a small diameter is oscillated at a high speed and a predetermined stroke in the meridian direction by a grinding tool linear moving mechanism 30 to perform grinding.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical system having a complicated surface shape such as a spheroidal surface, an elliptic cylindrical surface, a toroidal surface having a relatively large radius of curvature difference between a sagittal line and a generatrix and a relatively short radius of curvature of a generatrix. The present invention relates to a method for polishing an optical element having a surface.

[0002]

2. Description of the Related Art Conventionally, optics having complicated surface shapes such as a spheroidal surface, an elliptic cylindrical surface, and a toroidal surface having a relatively large curvature radius difference between a sagittal line and a busbar and a relatively short radius of curvature of a busbar. As a method for polishing the element, a polishing method as described below is employed.

For example, when a cylindrical surface of a mirror for short-wavelength light made of a CVD-SiC material is created, the absolute value of the same size as that of the cylindrical surface is the same, and the sign of the curvature is opposite to that of the sign (the unevenness is reversed). Using a full-surface polishing tool having a polished surface, the polishing surface of the full-surface polishing tool is formed on a cylindrical surface (hereinafter, referred to as a “work surface”) of a short-wavelength light mirror made of a pre-processed CVD-SiC material. Abrasion liquid in which abrasive grains such as chromium oxide fine powder, silica fine powder, and diamond fine powder are dispersed in water is applied between the surface to be processed and the polishing surface of the polishing tool. Polishing is performed by relatively swinging with the interposition.

[0004]

However, according to the above-mentioned prior art, for example, when the surface to be processed is a toroidal surface, it is extremely limited that the shape of the surface matches the shape of the polishing surface of the entire surface polishing tool. Only when they are in the specified positional relationship. Therefore, if the swing stroke is increased, the polished surface of the entire surface polishing tool and the work surface partially interfere with each other, causing uneven contact of the polished surface of the entire surface polishing tool. If the continuation is continued, the polishing removal amount of the portion where the polished surface of the full-surface dish polishing tool is unevenly contacted is increased, and the shape accuracy of the processed surface is deteriorated. Conversely, if the swing stroke is reduced, the surface shape of the polished surface of the full-surface dish polishing tool is transferred to the surface to be machined, causing undulation.

In particular, in the case of a CVD-SiC material, if the polishing removal rate of the surface to be processed is increased, the generation of pits (microscopic mosaic steps) is reduced, but the surface roughness is increased. Conversely, when the polishing removal rate of the surface to be processed is reduced, the surface roughness does not deteriorate, but pits are generated.

The present invention has been made in view of the above-mentioned problems of the prior art, and has a spheroidal surface, an elliptic cylindrical surface, a relatively large difference in radius of curvature between a sagittal wire and a generatrix, and a radius of curvature of a generatrix. To realize a polishing method capable of polishing a workpiece surface with a high shape accuracy and an ultra-smooth surface even if the workpiece has a workpiece surface having a complicated surface shape such as a relatively short toroidal surface. It is intended for.

[0007]

In order to achieve the above object, a polishing method according to the present invention has a polished surface having an area smaller than the area of a processed surface of a workpiece, and the polished surface has Using a polishing tool supported via a viscoelastic material that can be greatly deformed by an uneven distribution load, the polishing surface is brought into contact with the surface to be processed under a predetermined processing pressure, and a polishing liquid is applied between the two. While supplying, the workpiece and the polishing tool are relatively rapidly swung in one of the generatrix direction and the sagittal direction on the surface to be machined, and at the same time, relatively slowly scanned in the other direction. It is characterized by the following.

In addition, the speed of the high-speed swing and the speed of the low-speed scan are set such that the movement amount of the low-speed scan per one cycle of the high-speed swing is equal to or less than the length of the polishing surface of the polishing tool in the low-speed scan direction. The speed of high-speed swing and the speed of low-speed scanning
The amount of movement by low-speed scanning per high-speed swing cycle is
1/4 of the length of the polishing surface of the polishing tool in the low-speed scanning direction
Set within the range of 3/4.

Further, the polished surface is formed with a pitch which can follow the surface shape of the surface to be processed.

When the workpiece is an optical element having an optical surface having a complicated surface shape, the high-speed swing stroke and the low-speed scanning stroke are controlled by setting the polishing surface of the polishing tool to a beam effective portion of the optical surface. It is good to set each to the length which goes completely outside from.

Further, the workpiece is fixed to the workpiece table with its periphery surrounded by a dummy material, or the dummy material is made of the same material as the workpiece.

In addition, the processing surface of the workpiece is a CVD-S
A polishing liquid made of an iC material and having polycrystalline diamond abrasive grains dispersed in water is used.

[0013]

A polishing tool is used which has a polished surface having a small area compared to the area of the surface to be processed of the workpiece, and which is supported via a viscoelastic material capable of largely deforming the polished surface due to an unevenly distributed load. Therefore, the polished surface easily follows the polished surface of the workpiece and does not contact unevenly. In addition, the contact time distribution of the polished surface to the processed surface does not become uneven.

[0014]

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

First, an example of a polishing apparatus used for carrying out the polishing method of the present invention will be described.

As shown in FIGS. 1 and 2, a guide rail 12 extending in the longitudinal direction is provided on a workpiece support portion 1a of the base 1, and the guide rail 12 is provided with a workpiece rail. A workpiece table 13 for linearly moving (reciprocating) while holding W is guided so as to be linearly movable. A workpiece linear movement mechanism 40 is provided near one end of the guide rail 12, and the workpiece linear movement mechanism 40 is a first eccentric wheel that is rotated by a first rotation drive mechanism (not shown). 18 and an eccentric shaft 19 loosely fitted in a radially extending groove 18 a formed in the first eccentric wheel 18.
And a link 20 having one end pivotally connected to the eccentric shaft 19, and the other end of the link 20 is pivotally connected to one end of the workpiece table 13 by a pin 21.

When the first rotary drive mechanism is started, the workpiece linear movement mechanism 40 rotates the eccentric shaft 19 together with the first eccentric wheel 18, and the workpiece table 13 via the link 20. Is reciprocated at a predetermined stroke along the guide rail 12, and the length of the stroke is determined by moving the eccentric shaft 19 along the groove 18a to set the fixed position of the first eccentric ring 18 in the radial direction. It can be changed easily by changing it.

A guide groove 7 extending in a direction substantially perpendicular to the direction of linear movement of the workpiece table 13 is formed on the upper surface of the protrusion 1c provided on the polishing tool side support 1b of the base 1.
a guide 7 having a guide groove 7a
, A slider 6 having a lever 8 protruding at one end is fitted so as to be linearly movable. A tip 1 for holding a small-diameter polishing tool 11 to be described later is provided at the tip of the lever 8.
0 is supported movably in the axial direction. On the other hand, a polishing tool linear moving mechanism 30 is disposed near the guide 7 on the side opposite to the lever, and the polishing tool linear moving mechanism 30
Second eccentric wheel 3 rotated by the rotary drive mechanism 2
And a link 5 having one end pivotally connected to an eccentric shaft 4 loosely fitted in a radially extending groove 3a formed in the second eccentric ring 3, and the other end of the link 5 being a slider 6 At the other end by a pin 9.

The working pressure is prepared by preparing a plurality of weights having different weights which can be detachably attached to the upper end of the kansashi 10 and selecting a weigh having a predetermined weight from these weights. It can be changed by attaching it to the upper end of 10. Also, a hydraulic cylinder (not shown) for applying a pressing force to the kansashi may be provided, and the pressing force by the hydraulic cylinder may be changed.

When the second rotary drive mechanism 2 is started, the polishing tool linear movement mechanism 30 rotates the eccentric shaft 4 together with the second eccentric wheel 3, and the lever 8 is integrated with the slider 6 via the link 5. Is linearly moved at a predetermined stroke in a direction substantially orthogonal to the linear movement (reciprocating movement) direction of the workpiece table 13, and the length of the stroke is
It can be easily changed by moving the eccentric shaft 4 along the groove 3a and changing the fixed position of the second eccentric ring 3 in the radial direction.

A small-diameter polishing tool 11 which is a polishing tool having a polished surface whose area is smaller than the area of the surface to be processed of the workpiece.
As shown in FIG. 4, a tool shank 1 provided with a contact portion 11d on one side of which a tip portion of a kansashi 10 contacts.
1a and a foam 11b integrally provided on a side surface of the tool shank 11a opposite the abutting portion. A polished surface is formed by a pitch (asphalt) 11c attached to the surface of the foam 11b.

In the present invention, the foam 11b is preferably made of a viscoelastic material which can be largely deformed by an unevenly distributed load such as a polyvinyl alcohol foam or a polychloroprene foam.

As the pitch 11c, the penetration is 5
Those within the range of from 20 to 20 are preferred. When the penetration is smaller than 5, the shape of the polished surface formed by the pitch 11c does not follow the shape of the surface to be processed, so that only local contact can be made with the surface to be processed and polishing does not proceed. On the other hand, if the penetration is larger than 20, the shape of the polished surface is crushed by viscous flow, and the polished surface protrudes around the tool shank, which may make polishing impossible.

Further, cerium oxide,
A metal oxide abrasive such as zirconium oxide or a diamond abrasive is used. When using any of these abrasive grains, it is preferable to add a dispersant such as sodium hexametaphosphate in the range of 1 to 2% by weight based on the weight of the abrasive grains dispersed in the purified water.

In particular, it is preferable to use polycrystalline diamond abrasive grains for polishing a workpiece made of a CVD-SiC material.

Next, one embodiment of the polishing method of the present invention will be described.

On the workpiece table 13 of the polishing apparatus shown in FIG. 1 and FIG. 2, a workpiece W having a complex surface shape which has been pre-processed in advance, and a dummy material 22 around the workpiece W. It is fixed using a plurality of fixing tools 16 in the surrounding state. After that, the nozzle 1 is placed on the work surface of the work W.
5, the above-mentioned polishing liquid is supplied, and the polishing liquid flowing down to the container 14 is passed through a drain pipe 17 to an abrasive supply unit (not shown).
Return to.

After the above, the polishing surface formed by the pitch 11c (see FIG. 4) of the small-diameter polishing tool 11 is brought into contact with the processing surface of the workpiece W, and
The workpiece W is made to scan at a low speed integrally with the workpiece table 13 by a predetermined stroke by the workpiece linear movement mechanism 40 by contacting the leading end of the workpiece with the contact portion 11d to apply a predetermined processing pressure. And the lever 1 protruding from the tip of the slider 6 by the polishing tool linear moving mechanism 30,
The polishing is performed by swinging the small-diameter polishing tool 11 held at the leading end of the “0” at a predetermined stroke at a high speed.

Here, the relative relationship between the above-described low-speed scanning of the workpiece W and the stroke and speed of the high-speed swing of the small-diameter polishing tool will be described with reference to FIG.

As shown in FIG. 5, the small-diameter polishing tool 11
The workpiece W is swung at a high speed in the direction of the arrow B and the counter-arrow B, and the workpiece W is scanned at a low speed in the direction of the arrow A and the counter-arrow A.
In this case, the moving distance L of the small-diameter polishing tool 11 in one scan cycle of the high-speed swing of the small-diameter polishing tool 11 by the low-speed scanning is the length D of the small-diameter polishing tool 11 in the scanning direction (the low-speed scanning direction of the workpiece). Hereinafter, it is preferably set to be within the range of D / 4 to 3D / 4. By doing so, the small-diameter polishing tool 11 passes uniformly over the entire area of the surface to be processed.
The removal amount of the polishing over the entire area of the surface to be processed is constant, and the polishing can be performed with high precision.

The small-diameter polishing tool 11 and the workpiece W
When a high-speed swing and a low-speed scan are performed with a stroke that overhangs on the dummy material 22, the small-diameter polishing tool 11 having a large diameter compared to the distance from the beam effective portion to the end of the surface to be processed is used. Even if there is, the small-diameter polishing tool 11 can uniformly pass through the entire area of the beam effective portion, and the polishing removal amount of the entire area of the beam effective portion can be made constant.

[0032]

【Example】

(Example 1) The following workpiece, small-diameter polishing tool, and polishing liquid were prepared.

Workpiece: length 300 mm, width 100 m
m, a soft X-ray mirror element made of a synthetic quartz glass material having a toroidal optical surface having a thickness of 30 mm, a radius of curvature of a generatrix of 12.5 m and a radius of curvature of a sagittal of 350 mm.

Small-diameter polishing tool: a diameter of 30 mm, a surface shape (irregularities) opposite to the surface shape of the optical surface to be processed on the surface of the polyvinyl alcohol-based foam at a pitch of asphalt (penetration of 20). (Reverse) with a polished surface formed.

Polishing liquid: 0.1% by weight of cerium oxide abrasive grains having an average particle diameter of 0.25 μm was added to 40 liters of purified water and stirred, and 0.8 g of sodium hexametaphosphate fine powder was added thereto. Stirred for 24 hours.

In a state where the workpiece is surrounded by a dummy material made of a synthetic quartz glass material, the workpiece is fixed on a workpiece table of the polishing apparatus shown in FIGS. The polishing liquid is supplied onto the optical surface, which is the surface to be processed, through the container, and is returned to the polishing liquid supply section through the drain pipe of the container.

Following the above, the small-diameter polishing tool is oscillated at a high speed of about 24.5 (cycles / minute) at a stroke of 144 mm obtained by adding 21 mm to both sides of the small-diameter effective part in the sagittal direction with a width of 72 mm. Then, the workpiece was scanned at a low speed of about 8 mm / sec at a stroke of 320 mm obtained by adding 20 mm to both sides of the effective beam length in the generatrix direction with a length of 280 mm.

Observation of the polished optical surface showed that the surface roughness was 0.20 nm r without losing the shape accuracy of the optical surface.
An ultra-smooth surface of about ms was obtained. In addition, no deterioration of the surface to be polished such as generation of pits, appearance of abrasive grain passage marks (latent scratches) in the pre-processing, and generation of fogging (polishing burn) was observed on the optical surface, and the surface was of high quality. .

Example 2 The following workpiece, small-diameter polishing tool, and polishing liquid were prepared.

Workpiece: 160 mm in length, shown in FIG.
With a width of 160 mm and a thickness of 23 mm, the sagittal section indicated by line AA is a straight line, and the generatrix section indicated by line BB is elliptical. The change in the radius of curvature of the generatrix at the generatrix position is shown in FIG. As shown, a large mirror element for soft X-rays made of a CVD-SiC material.

Small-diameter polishing tool: 25 mm in diameter, a surface shape of a foamed body made of polychloroprene and a surface shape opposite to the surface shape of the optical surface to be processed (the unevenness is reversed) by a pitch of asphalt (penetration 20). ) With a polished surface.

Polishing liquid: 0.05% by weight of polycrystalline diamond abrasive grains having an average particle diameter of 1 μm was added to 40 liters of purified water and stirred, and 0.8 g of fine powder of sodium hexametaphosphate was added thereto for 24 hours. Stirred.

After the workpiece is fixed on the workpiece table of the polishing apparatus shown in FIGS. 1 and 2 by a plurality of fixtures, the polishing liquid is applied via a nozzle onto the optical surface which is the workpiece. And returned to the polishing liquid supply unit through the drain line of the container.

Subsequently, the small-diameter polishing tool is initially swung in the sagittal direction at a speed of 22 (cycles / min) with a stroke of 130 mm obtained by adding 15 mm on each side to the width of the effective beam portion in the sagittal direction of 100 mm. At the same time as moving the workpiece, the width of the effective ray portion in the generatrix direction is 100
130 mm with 15 mm added to each side
Polishing is performed by scanning at a low speed of about 7 mm / sec in the generatrix direction with m as a stroke, and thereafter, polishing is performed under the same conditions except that the high-speed swing and the low-speed scanning of the small-diameter polishing tool and the workpiece are reversed. Thereafter, both were alternately repeated.

FIG. 8 shows a state in which polishing of the optical surface, which is the surface to be processed, proceeds in this embodiment.

FIG. 8A shows the optical surface of FIG.
-Time passage (0 hours, 26
FIG. 8B is a graph showing the respective surface shapes after 65 hours), and FIG.
It is a graph showing each surface shape after a lapse of time (0 hour, 26 hours, 65 hours) in a straight line section indicated by line A.

This graph is displayed as an error shape obtained by subtracting the design shape. The closer the chart is to a straight line, the closer the design shape is.

When the optical surface after polishing was observed, pits were formed on the optical surface, traces of passing abrasive grains (latent scratches) in the pre-processing were exhibited,
No deterioration of the processed surface such as generation of fogging (polishing burnt) was observed.
An ultra-smooth surface with a surface roughness of about 0.20 nm rms was obtained.

[0049]

Since the present invention is configured as described above, the following effects can be obtained.

Since the non-uniform contact between the work surface of the work and the polishing surface of the polishing tool and the non-uniform contact time distribution of the polishing surface with the work surface are eliminated.
It is possible to obtain a uniform ultra-smooth surface without deterioration of the surface to be processed such that the surface shape of the surface to be processed does not collapse, generation of pits, appearance of abrasive grain passage marks, generation of fogging (polishing burn) and the like. it can.

As a result, there is no need to finely change the polishing conditions and the shape of the polishing tool as in the above-described conventional technique, and to proceed with the polishing while observing the polishing state of the surface to be processed. Since polishing can be performed, the processing efficiency is significantly improved.

[Brief description of the drawings]

FIG. 1 is a schematic front view showing an example of a polishing apparatus used for carrying out a polishing method of the present invention.

FIG. 2 is a schematic plan view of the polishing apparatus shown in FIG.

FIG. 3 is a schematic perspective view showing a workpiece and a dummy material.

FIG. 4 is an explanatory view of a small-diameter polishing tool and a kansashi used for carrying out the polishing method of the present invention.

FIG. 5 is an explanatory diagram showing a polishing locus of a small-diameter polishing tool in the polishing method of the present invention.

FIG. 6 is a schematic perspective view showing an example of a workpiece according to the present invention.

FIG. 7 is a graph showing a change in a radius of curvature of the workpiece shown in FIG.

FIG. 8 is a graph showing a progress of polishing of a surface to be polished of a workpiece in Example 2 of the polishing method of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Base 2 Rotation drive mechanism 3,18 Eccentric wheel 4,19 Eccentric shaft 5,20 Link 6 Slider 7 Guide 7a Guide groove 8 Lever 9,21 Pin 10 Kansashi 11 Small diameter polishing tool 12 Guide rail 13 Workpiece table 14 Container 15 Nozzle 16 Fixture 17 Drain line 22 Dummy material 30 Polishing tool linear movement mechanism 40 Workpiece linear movement mechanism

Claims (9)

[Claims] 1. A polishing tool having a polished surface having a small area compared to the area of a surface to be processed of a workpiece, and the polishing surface being supported via a viscoelastic material capable of being largely deformed by an unevenly distributed load. The polishing surface is brought into contact with the surface to be processed in a state where a predetermined processing pressure is applied, and a polishing liquid is supplied between the two while the workpiece and the polishing tool are brought into contact with the surface to be processed. A relatively high-speed swing in one of the generatrix direction and the sagittal direction and a relatively low-speed scan in the other direction. 2. The speed of the high-speed swing and the speed of the low-speed scanning,
The amount of movement by low-speed scanning per high-speed swing cycle is
2. The polishing method according to claim 1, wherein the length is set to be equal to or less than the length of the polishing surface of the polishing tool in the low-speed scanning direction. 3. The speed of the high-speed swing and the speed of the low-speed scanning,
The amount of movement by low-speed scanning per high-speed swing cycle is
1/4 of the length of the polishing surface of the polishing tool in the low-speed scanning direction
2. The polishing method according to claim 1, wherein the setting is made within a range of 3/4. 4. The polishing method according to claim 1, wherein the polishing surface is formed at a pitch that can follow the surface shape of the surface to be processed. 5. The polishing method according to claim 4, wherein the pitch is within the range of a penetration of 5 to 20. 6. A workpiece is an optical element having an optical surface having a complicated surface shape, wherein a high-speed swing stroke and a low-speed scanning stroke are such that the polishing surface of the polishing tool has a beam effective portion of the optical surface. The polishing method according to any one of claims 1 to 5, wherein the length is set so as to completely exit from the surface. 7. The polishing method according to claim 1, wherein the workpiece is fixed to the workpiece table in a state where the workpiece is surrounded by a dummy material. 8. The polishing method according to claim 7, wherein the dummy material is made of the same material as the workpiece. 9. The polishing liquid according to claim 6, wherein a surface to be processed of the workpiece is made of a CVD-SiC material, and a polishing liquid in which polycrystalline diamond abrasive grains are dispersed in water is used. Polishing method.