JP2002200548A - Polishing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polishing method capable of polishing an optical part having a free-form surface and a molding die for molding the optical part with high accuracy and high efficiency. . SOLUTION: The working surface of a tool 1 used for polishing is formed into a curved surface having a shape larger than the radius of curvature of the working surface of the tool used in the previous step.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polishing method for processing an optical component having a free-form surface and a molding die for molding the optical component with high accuracy and high efficiency.

[0002]

2. Description of the Related Art Hard brittle materials such as SiC have a very low polishing rate. Therefore, when all of the processing from the base material to the desired aspherical surface is performed by using these as a work piece, Requires extremely long machining times. for that reason,
Conventionally, after performing processing to a shape close to a desired aspherical surface by grinding, a period of 100 μm and an amplitude of 100 to 200 nm P · V formed by transferring the shape of a grindstone at the time of grinding are formed.
The correction of minute undulations and the removal of the brittle mode processing surface formed by grinding are performed by mechanical or hand polishing to obtain an aspherical mirror surface having a shape error of 30 nmPV and a surface roughness of 5 nmRa or less. Was.

For example, an aspherical lens having a rotationally symmetric axis, or a free-form surface having no rotationally symmetric axis, such as a lens, a molding die or a mirror thereof, is a diamond bite or a mirror tool. Using a grinding wheel, the shape is finished by cutting or grinding using the maternal principle of the machine tool.

FIG. 7 shows an example of an apparatus for grinding a concave aspherical mirror made of ceramics. The grinding apparatus has a Z on which a main body 53 having a main shaft 52 which rotates while holding a workpiece 51 is mounted. An axis table 54 and an air spindle 5 for driving a grinding wheel provided on a tool table 55 at a position facing the workpiece 51.
XY table 58 with a grinding wheel 57 fixed to 6
Is arranged. Thus, the rotating grinding wheel 57 is brought into contact with the rotating workpiece 51 to perform predetermined grinding.

[0005] Thereafter, in the case of mechanical processing, polishing is performed using a polishing apparatus as shown in FIG. The polishing apparatus includes a Z-axis table 64 on which a main body 63 having a main shaft 62 that holds and rotates the workpiece 51 is mounted, and a driving table provided on a tool base 65 at a position facing the workpiece 51. X equipped with a polishing tool 67 fixed to an air spindle 66 of
A Y table 68 is provided. The polishing tool 67
Is formed of an elastic body. Workpiece 51 rotating
The polishing tool 67 which is rotating with respect to, makes a predetermined polishing process. Since the polishing tool 67 is formed of an elastic body, the surface of the workpiece 51 is finished by performing a polishing process following the surface of the workpiece 51 until a desired surface roughness is obtained.

FIGS. 9A to 9C illustrate the state of the processing surface 51a of the workpiece 51 in these cases. As shown in FIG. Due to the rotational runout of the tool 57, the set feed interval of the tool 57, the positioning error of the tool 57, the vibration of the machine, etc., undulations (continuous or discontinuous depressions) corresponding to the shape of the working surface of the tool 57 occur on the processing surface. are doing.

In the polishing step, as shown in FIG. 9 (b), the polisher or polishing cloth of the polishing tool 67 is made of an elastic material such as resin or cloth.
The abrasive grains 71 act along the undulation shape of the surface 51a to be processed, thereby performing highly efficient polishing. As a result, FIG.
As shown in the figure, a finished surface of the work surface 51a of the work body 51 is obtained.

[0008]

However, the above-described method is effective as a method of reducing the surface roughness component of the surface to be processed in a short time (improving the surface roughness), but removes undulations. Efficiency is low. Therefore, in order to increase the efficiency of removing waviness, it is necessary to go through a rough polishing step using abrasive grains having a relatively large particle size. However, when using abrasives with a large particle size, it is very difficult to improve only the surface properties (improve waviness and surface roughness) while maintaining the shape created in the previous process (cutting or grinding). . For this reason, in the polishing step, shape accuracy measurement is performed as needed, and a shape correction process for partially adjusting the shape based on the measurement result is required, and the time and labor required for the polishing process are extremely large.

In the case of manual polishing, the quality of the processing greatly depends on the polishing skill of the operator, and it is difficult to perform polishing for a long time continuously. In the case of the aperture, the aspherical surface processing is extremely difficult. Therefore, the diameter of the mirror surface is approximately φ1 in hand polishing.
It was limited to about 00 mm.

Attempts have also been made to perform such polishing using a hard and brittle material with a super-precision machining apparatus controlled by an NC, but the radius of curvature of the polisher is significantly smaller than the radius of curvature of the desired aspherical surface. Therefore, the polishing action area is extremely small, and the polishing rate is low, which is not suitable for actual processing.

The present invention has been made in view of the above circumstances, and is intended to polish a free-form surface-shaped optical component and a molding die for molding the optical component with high accuracy and high efficiency. It is an object of the present invention to provide a polishing method capable of performing polishing.

[0012]

According to the first aspect of the present invention, there is provided a polishing method for performing a polishing process on a workpiece formed into a predetermined shape by processing in a previous step by cutting or grinding. The polishing method is characterized in that the polishing is performed using a tool having a curved surface having a shape of a working surface larger than a radius of curvature of the working surface of the tool used in the previous step.

According to the second aspect of the present invention,
The polishing method is characterized in that the polishing is performed using the tool made of copper, tin, or an alloy thereof.

According to the third aspect of the present invention,
In a polishing method for performing polishing on a workpiece formed in a predetermined shape by processing in a previous step by cutting or grinding, the polishing is performed by a working surface in which abrasive grains are dispersed around an outer periphery of an elastic body. This is a polishing method characterized in that the polishing is performed using a tool in which is formed.

According to a fourth aspect of the present invention,
The polishing method is characterized in that the polishing is performed using a tool whose working surface is formed of a soft metal.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of a polishing apparatus and a polishing method according to the present invention will be described below with reference to the drawings.

In the first embodiment, a case will be described in which a ceramic mirror is polished as a workpiece. This ceramic mirror has a diameter of 120mm
And a rotationally symmetric concave aspherical mirror made of ceramics having an approximate radius of curvature of 210 mm.

First, the workpiece 3 is ground using the ultra-precision aspherical surface processing apparatus shown in FIG. Since the structure of the ultraprecision aspherical surface processing apparatus has been described in the section of the related art, the description thereof will be omitted.

In the ultra-precision aspherical surface processing apparatus, a diamond wheel (grindstone mesh size # 1200: abrasive grain size of about 12 μm) having a flat R shape (radius 100 mm, working surface cross-sectional radius 100 mm, wheel thickness 10 mm) is used. Grind the concave aspheric mirror. The workpiece 3 is mounted on the end face of the spindle of the ultra-precision aspherical surface processing apparatus, and rotated at a speed of 20 rpm. The grindstone is an air spindle 5 for driving the grindstone
2 and rotated at a speed of 6000 rpm, and moved along the locus of the aspherical section curve by the simultaneous control operation of the X-axis and the Z-axis of the ultra-precision aspherical surface processing apparatus to grind the surface of the mirror which is the workpiece 3. I do.

The amount of one cut is set to 1 μm or less. As a result of this grinding, the aspherical mirror has an aspherical surface shape accuracy of 0.3 μmP-V, a waviness component of 0.15 μmP-V, and a surface roughness of 0.02 μmR.
a.

Next, as shown in FIG. 1, in the ultra-precision aspherical surface processing apparatus shown in FIG. 7, instead of the grindstone used for the grinding, the same shape (flat R shape) as the grindstone is used. The polishing tool 1 is mounted on an air spindle 2 for driving a grindstone, whereby the workpiece 3 is polished. The dimensions of the polishing tool 1 are 150 mm in radius and 15 mm in cross-sectional radius of the working surface.
0 mm in shape, larger than the radius of curvature of the working surface of the grindstone used in the grinding in the previous step, and smaller than the radius of curvature of the aspherical mirror that is the workpiece 3, and in the thickness direction of the polishing tool 1. The radius of curvature is smaller than that of the aspherical mirror.

In this case, the workpiece 3 is rotated at a speed of 20 rpm as in the case of the grinding. Polishing tool 1 is 10
A locus that is rotated at a low speed of about 0 to 500 rpm, and along the cross-sectional curve of the aspherical mirror that has already been ground in the previous process by the simultaneous control operation of the X axis and the two axes of the ultraprecision aspherical surface processing device like a grindstone. Move with. Polishing tool 1
Hard materials such as copper, tin or their alloys are used, and the working surface is provided with diamond abrasive grains (average grain size 3μ).
m) is supplied intermittently. At this time, the working surface of the polishing tool 1 keeps a gap without making contact with the aspherical mirror surface. The size of the gap is equal to the average particle size of the supplied abrasive grains (3 μm).
m).

In this polishing step, the rotation deviation set feed interval of the grinding wheel, the positioning error of the simultaneous control operation of the X-axis and the two-axis of the ultra-precision aspherical processing device, the vibration of the machine, etc. generated during the grinding process. The convex portion of the undulation (continuous or discontinuous depression) according to the working surface shape of the grinding stone is selectively polished.

Next, the condition of the work surface of the work body 3 in these steps will be described with reference to FIGS. 2 (a) to 2 (c).

As shown in FIG. 2 (a), in the grinding using a tool 4 made of a grinding wheel having a radius of curvature r which is the distance from the rotation axis to the grinding action surface, the rotational runout of the tool 4 and the tool Due to the set feed interval of 4, the positioning error of the tool 4, the vibration of the machine, etc., undulations (continuous or discontinuous dents) corresponding to the working surface shape of the tool 4 occur on the processing surface 3a of the workpiece 3. ing. In this case, the entire surface 3a to be processed is processed to have an aspherical shape accuracy of 0.3 μmP-V (= grinding accuracy), a swell component of 0.05 μmP-V, and a surface roughness of 0.002 μmRa.

In the polishing step, as shown in FIG. 2B, the entire surface of the aspherical mirror which is the workpiece 3 is polished using diamond abrasive grains 6 having an average particle diameter of 1 μm.
The workpiece a is processed to have an overall aspherical shape accuracy of 0.3 μm PV (= grinding accuracy), a swell component of 0.05 μm PV, and a surface roughness of 0.002 μm Ra. The dimensions of the polishing tool 1 are
The grinding wheel used is larger than the radius of curvature of the working surface of the grindstone used in the grinding in the previous step and smaller than the radius of curvature of the aspherical mirror. Since the polisher or polishing cloth of the polishing tool 1 is made of an elastic material such as resin or woven fabric, the diamond abrasive grains 6 act along the undulating shape of the processing surface 3b of the processing object 3, Highly efficient polishing is performed. As a result, as shown in FIG.
As a result, a finished surface with high removal efficiency of the undulation component can be obtained.

The required value of the surface roughness is 0.005 μm.
In the case of Ra or more, the polishing step can be omitted.

The diameter of the diamond abrasive used for the polishing is selected according to the undulation accuracy of the grinding.

The same operation can be obtained even if the configuration of the ultraprecision aspherical surface processing apparatus used for the polishing process is other than the configuration described above.

Next, a second embodiment of the present invention will be described.

FIG. 3 (a) is a schematic plan view of a main part of the polishing apparatus of the present invention, and FIG. 3 (b) is a side view thereof.

A polishing table 11 and an actuator 13 are mounted on a moving table 11 which is movable in three directions of XYZ.
Is provided, and a polisher 15 is attached to a spindle 14 supported by a static pressure bearing (not shown). The actuator 13 operates according to the detection result of the polishing pressure sensor 12. The rotation of the polisher 15 includes a rotary encoder and a servomotor, and is controlled by an NC control unit (not shown).

On the other hand, a holding table 16 holding the workpiece 3 is provided on a bed 17 at a position facing the polisher 15. The holding table 16 is provided so as to be rotatable at a predetermined angle on the XZ plane about the processing point of the polisher 15. This rotating operation also includes a rotary encoder and a servomotor, and is controlled by the NC control unit.

With these configurations, in the polishing process of the present embodiment, the polishing process is automated by realizing the polishing process as steady as possible. Therefore, the angle (# 1) formed between the normal of the machined surface (# 13) at the center point of the oscillating and polishing action area of the polisher 15 and the rotation axis (# 14) of the polisher 15 is determined.
The control for keeping 5) constant is simultaneously performed by the NC control unit.

The movement of the polisher 15 and the workpiece 3 required at that time is the rotational movement of the workpiece 3 or the polishing polisher 15 (# 16), the translation of the polishing polisher 15 or the workpiece 3 in the X-axis direction. Movement (# 17) and translation movement of the polishing polisher 15 or the workpiece 3 in the Z-axis direction (# 18)
It is.

Further, the polishing pressure is detected by the polishing pressure sensor 12 and the actuator 13 is operated in accordance with the detection result.
Is operated to finely move the polisher 15 in the axial direction to maintain the polishing pressure constant. The rotation of the workpiece 3, the rotation of the polishing polisher 15, and the rotation of the polishing polisher 15 are provided with a rotary encoder and a servomotor, and the rotation speed and the indexing position are controlled by an NC control unit.

The translation of the polisher 15 (# 17,
The guide of # 18) includes a linear motor guide, an air slide or a hydrostatic bearing, or a similar bearing, which includes a linear scale and a servomotor, and whose movement speed and position can be controlled by the NC control unit. It can be carried out.

A piezo element is used for the polishing pressure sensor 12 for detecting the polishing pressure and the actuator 13.

FIG. 4 shows a case where a desired aspherical surface can be approximated by a spherical surface in the above-mentioned machining method. The same parts as those in FIG. 3 are denoted by the same reference numerals, and their description is omitted.

In this case, the polisher 15 required to maintain a constant angle (# 15) between the processing surface normal (# 13) at the center of the polishing action area and the spindle 14 which is the rotation axis of the polisher 15 is required. The workpiece 3 or the polishing polisher 1 with the motion of the workpiece 3 as the center of rotation of the approximate spherical surface.
5 (# 22) and the Z-axis translation (# 23) of the polishing polisher 15 or the workpiece 3 can be simplified to two. Therefore, the control is simplified, and the productivity of processing can be improved.

Next, the working surface of the polisher 15 and the condition of the surface of the workpiece 3 during the above-described processing will be described in more detail.

FIG. 5 is an explanatory view microscopically showing how the polisher 15 acts on the workpiece 3 via the abrasive grains 18, and FIG. 6 is an explanatory view macroscopically showing the same operation. It is.

As shown in FIG. 5, the working surface 15a of the polisher 15 is microscopically formed of abrasive grains 1 having a diameter of 1 to 10 μm.
By dispersing and embedding 8 to the body 19, the workpiece 3 is efficiently polished. In addition, the shape of the grindstone used during the grinding process in the previous process is transferred to the workpiece 3 at a period of 100 μm.
m, a high polishing pressure is locally applied to the convex region 3e having a small waviness having an amplitude of about 100 to 200 nm PV
Are selectively removed by polishing.

For this purpose, the body 19 of the polisher 15
For abrasive grains 18 having a particle size of φ1 to 10 μm, a soft material for easily embedding the abrasive grains, and a period of 100 μm
It is formed of a material having a hardness that does not easily follow minute undulations having an amplitude of about 100 to 200 nm PV.

As shown in FIG. 6, the working surface 15a of the polisher 15 macroscopically follows the aspherical surface after grinding in a range of several tens to several hundreds of mm in diameter to secure a polishing action area. And demonstrate a high polishing rate. In this case, as shown in FIG. 5, the working surface 15a further has a brittle mode processing surface formed in the convex region 3e of the minute undulation on the surface of the workpiece 3 by the polishing action via the abrasive grains 18. (# 7) is removed, and the brittle mode processed surface (# 9) formed in the concave region 3f of the minute undulation is removed after the convex region 3e of the minute undulation is removed.

As a material for forming the working surface 15a of the polisher 15 satisfying such conditions, for example, a foil or plating of a soft metal such as copper is used.

The body 19 of the polishing polisher 15 applies a polishing pressure (# 10) to the working surface 15a, and this can be made to conform to the aspherical surface after grinding in the range of several tens to several hundreds of mm in diameter. It is necessary to have such elasticity as possible. As a material of the body 19 satisfying such conditions, for example, rubber, urethane, an air pad, or the like can be used.

Further, as the shape and dimensions, for example, there is a spherical surface having a curvature equal to the maximum curvature of a desired aspherical surface. As a method of forming the working surface 15a on the surface of the body 19, foil bonding, plating, or the like can be used. In the case of using plating, after performing a base treatment by electroless plating, the thickness is 0.1 μm to 0.3 μm by electroplating.
A μm Cu film is formed.

The polishing process is basically performed by rotating the workpiece 3 around the axis (# 11) and rotating the polishing polisher 15 (# 12).

As described above, according to the present invention, Si
Polishing using a polishing polisher 15 for processing a desired aspherical surface into a mirror surface having a shape error of 30 nm PV or less and a surface roughness of about 5 nm Ha or less using a hard and brittle material represented by C or the like as the workpiece 3. In the processing method, using a processing surface formed in advance to a shape close to a desired aspherical surface by grinding as a work surface, a period of 100 μm, an amplitude of 100 to 200 nm P · V formed by transferring the shape of a grindstone during grinding. In addition to correcting the slight undulation, the processing surface in the brittle mode formed during the grinding process is removed, and a desired aspherical shape including a mirror surface in the ductile mode can be created.

In addition, these polishing processes can be performed automatically, and further, by widening the polishing action area,
A high polishing rate can be secured.

[0052]

According to the present invention, an optical component having a free-form surface and a molding die for molding the optical component can be polished with high precision and efficiency.

[Brief description of the drawings]

FIG. 1 is a schematic explanatory view of an ultraprecision aspherical surface processing apparatus according to a first embodiment of the present invention.

FIGS. 2A to 2C are explanatory views of the state of a processing surface of a processing object according to a processing step.

FIG. 3A is a schematic plan view of a main part of a polishing apparatus according to a second embodiment of the present invention, and FIG. 3B is a side view thereof.

FIG. 4 is a modified example of the second embodiment of the present invention.

FIG. 5 is an explanatory diagram microscopically showing how a polisher operates.

FIG. 6 is an explanatory diagram macroscopically showing how the polisher operates.

FIG. 7 is a schematic view of a conventional grinding apparatus.

FIG. 8 is a schematic view of a conventional polishing apparatus.

FIGS. 9A to 9C are explanatory views of the state of a processing surface of a processing object according to a processing step.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Polishing tool, 3 ... Workpiece, 3a, 3b, 3c ... Workpiece surface, 4 ... Tool, 6 ... Diamond abrasive grain, 13 ... Polisher, 18 ... Abrasive grain, 19 ... Body

Claims (4)

[Claims] 1. A polishing method for performing polishing on a workpiece formed into a predetermined shape by processing in a previous step, wherein the polishing is performed using a tool whose working surface has a shape used in the previous step. A polishing method characterized by using a tool having a curved surface having a shape larger than the radius of curvature of the working surface. 2. The polishing method according to claim 1, wherein the polishing is performed using the tool made of copper, tin, or an alloy thereof. 3. A polishing method for performing a polishing process on a workpiece formed in a predetermined shape by a process in a previous step by cutting or grinding, wherein the polishing process includes the step of forming abrasive grains on an outer periphery of an elastic body. A polishing method, characterized in that the polishing is performed using a tool having a dispersed working surface. 4. The polishing method according to claim 3, wherein the polishing is performed using a tool whose working surface is formed of a soft metal.