JPH11246240A - Workpiece and its surface processing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a precision processing method optimum for executing shape correction of precision parts, such as aspherical face lenses and aspherical face molds, having intricate shape with high accuracy. SOLUTION: In the plasma CVM(chemical vaporization machining) method for executing processing of a workpiece surface by supplying a reaction gas to the peripheral of the workpiece, generating a plasma locally between the electrode 3 near the workpiece and the workpiece to form the radical of the reaction gas and reacting the workpiece and the radical, then removing the reaction product by volatilization; an SiO2 layer which is a reactive material giving rise to volatilization removing reaction is formed on the surface of the work piece and this reactive material layer 2 is subjected to plasma CVM processing, by which the shape correction of the workpiece not suitable for plasma CVM processing is executed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing an optical element such as an image forming apparatus, a camera or the like, an optical element of a precision machine product, a precision part, a precision molding die or the like using an electrophotographic technique. .

[0002]

2. Description of the Related Art Conventionally, the most general technique for manufacturing a lens is based on a polishing method. For example, JP
As described in JP-203744, a polishing plate is preliminarily processed into a shape having a reciprocal relationship with a lens shape to be processed, the polishing plate is pressed against a glass material, and abrasive grains are formed in a gap between the polishing plate and the glass material. It is a method of supplying and rubbing. In this method, since polishing is performed using very fine abrasive grains, the processing stress applied to the glass material during processing is small, and therefore, there is an advantage that distortion remaining in the workpiece is small. However, since the processing cannot be performed unless the final finished shape of the workpiece is a simple shape, the degree of freedom in selecting the processing shape is small.

On the other hand, as the performance of the optical system is required to be higher, it is important to improve the accuracy of the lens shape and to make the lens shape aspherical. It is difficult to process an aspherical surface by the above-described polishing method, and generally, an aspherical surface is formed by machining using NC control. According to the NC processing, a desired shape can be processed, but it is difficult to obtain a mirror surface that can withstand use as a lens.
By the way, if the ductile mode grinding is performed, it is possible to obtain a mirror ground surface even with a brittle material such as glass.

For example, according to an aspherical lens processing method described in Japanese Patent Application No. 2-53557, a workpiece is mounted on a table rotated by a motor, and a grindstone for processing these workpieces. Is attached to an air spindle and rotates at a rotation speed of about 10,000 rpm. Then, a pulse is detected from a rotary encoder directly connected to the rotation axis of the rotary table, and processing data is supplied to the piezo actuator based on the pulse, and the linear table is continuously moved back and forth. The air spindle is step-feeded every rotation of the rotary table, and changes its position to change the contact position between the grindstone and the workpiece. According to this method, any non-axisymmetric aspherical shape can be processed. Furthermore, in this method, the cutting depth of the grindstone with respect to the workpiece can be controlled on the order of submicron, so that brittle materials can be ground in ductile mode, and a mirror surface sufficient for use as a lens by grinding alone can be obtained. It is possible to obtain.

[0005] However, this method requires a long processing time for finishing the aspherical surface portion, and further causes variations in shape accuracy due to the processing. Therefore, when processing an optical element such as a lens by NC processing, in order to improve the surface roughness of the processed surface and further reduce the variation in shape accuracy,
Finishing is required.

In general, a polishing method is often used as a finishing method. In the case of finishing the aspheric surface by the polishing method, for example, the operation of rubbing diamond abrasive grains with a soft pad such as felt on the finished surface is repeated to adjust the state of the finished surface. When the main purpose is to adjust the shape accuracy, an arbitrary position on the finished surface may be locally polished using a small pad, but the processing time is slow.
Further, when polishing is performed using a large pad, the processing time is shortened, but the shape cannot be corrected as a matter of course.

Recently, a distortion-free processing method using a radical reaction has attracted attention as a processing method replacing polishing.
For example, the method described in Japanese Patent Application Laid-Open No. 1-125829 is particularly applicable to plasma CVM (Chemical Vaporization).
(Mori et al., Proceedings of the Japan Society for Precision Engineering Spring Meeting, p. 637 1992) uses plasma for radical generation. Plasma CVM generates plasma locally on the surface of a workpiece using a processing electrode under a high pressure, and supplies a reaction gas having a high electronegativity to generate radicals of the reaction gas. In this method, the radical is reacted with the surface of the workpiece, and the reaction product is volatilized to perform processing.

A high-precision processing method using a plasma CVM is described in, for example, JP-A-09-254268. That is, by comparing the actual shape and the design shape of the workpiece,
The convex portions in the actual shape are removed by plasma CVM processing. According to this method, shape correction on the order of submicrons can be performed in a processing time comparable to that of mechanical processing (Takino et al., Proc.
87 1997).

[0009]

As described above, the plasma C
Although VM is a very effective processing technique for finishing a high-precision surface, currently, the work material to which the plasma CVM can be applied is limited to several kinds of materials including quartz glass. Therefore, for example, when plasma CVM is used to correct the shape of a lens molding die, processing cannot be performed unless the material of the die is quartz glass.

An object of the present invention is to provide a shape creating method capable of processing a workpiece such as an optical element or a mold with higher precision.

[0011]

The processing method of the present invention for achieving the above object is as follows. That is, a quartz glass layer is provided on the surface of the workpiece, and the quartz glass portion is subjected to plasma CVM processing to create the shape of the workpiece. That is, Si
An O ₂ thin film is formed. The thickness of this SiO ₂ is formed to be larger than the working margin.

As a means for forming the SiO ₂ thin film, there is a method such as vacuum deposition or plasma CVD, or a method such as applying and firing a material such as polysilazane. Polysilazane is a polymer composed of Si, N, and H (or an organic group), has a property of being converted into silica (SiO ₂ ) by heating or the like, and is used for a semiconductor insulating film or the like. As described above, even when the material of the workpiece is not quartz glass, plasma CVM processing can be performed by forming the SiO ₂ thin film layer on the surface by the above-described method.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the accompanying drawings.

(Example 1) The surface of a stainless disk (SUS420) having a diameter of 50 mm and a thickness of 10 mm is machined by a surface grinder until the surface has an average surface roughness of 0.05 μm. Next, the surface is wrapped until the average surface roughness becomes 0.015 μm. In this state the particle size
A polisher made of felt coated with 0.25 μm diamond abrasive grains is rubbed against the sample surface with a pressing load of 10 g at 300 rpm and polished for 600 seconds over the entire sample surface. As a result, the average surface roughness of the sample surface was 0.012 μm.
On the other hand, the undulation of the surface was measured in a range of the central portion of the sample having a length of 40 mm. Next, a 0.5 μm thick SiO ₂ thin film 2 was formed on the surface of the sample 1 using plasma CVD (FIG. 1). When the surface roughness and the amount of undulation were measured, they were almost the same as those in the pretreatment.
Next, plasma CVM processing was performed as shown in FIG. In processing, the positions of the processing electrode 3 and the sample 1 ′ are controlled so as to selectively process the convex portion of the processing surface so that the processing surface after processing becomes flat, and the plasma state 4 is locally generated. Then, plasma CVM processing was performed. As a result, the average roughness of the machined surface was improved to 0.007 μm, and the waviness of the surface was improved to 0.08 μm P-P in the range of the sample central part length of 40 mm.

Next, this sample flat plate was assembled in a mold body, and a resin disk having a thickness of 3 mm was formed using an injection molding machine. Acrylic was used as the resin material. Mold temperature 110 ℃,
Molding was performed continuously at a maximum injection pressure of 600 kg / cm2 for 2000 shots. The surface accuracy of the molded product is almost the same as that of the mold surface, that is, the average surface roughness is 0.008 μm.
The range of 40 mm was 0.12 μm PP. Although the undulation of the molded article has increased slightly, this is due to the undulation component generated when the molded article is removed from the mold after molding because the molded article is a resin and the thickness of the molded article is thin. It is considered something.

(Example 2) A concave spherical lens having a radius of curvature of 50 mm is processed using glass (glass material BK7). First, a glass block is cut into a predetermined size, and a rough surface lens 6 having a concave surface with a radius of curvature of 50 mm is manufactured using a curve generator 5 (FIG. 3A). Next, a metal dish provided with diamond pellets having a radius of curvature of 50 mm is swung on a rough lens to perform so-called smoothing. Next, a mirror surface is obtained by polishing the lens surface using a polisher 7 (FIG. 3B). When the shape of the lens surface was measured, the average surface roughness was 0.007 μm, and the undulation amount was 0.31 μm P-P in the range of the central portion of the sample having a length of 30 mm. Therefore, plasma CVM processing was performed to reduce the undulation component of the lens. At present, when performing plasma CVM processing,
Since BK7 glass cannot be applied well, a pure SiO ₂ thin film 8 was formed on the surface of the produced glass lens. In the present embodiment, a method of applying a polysilazane, which is a polymer made of Si, N, and H (or an organic group), which is converted into silica (SiO ₂ ) by heating or the like, and baking it is used. Silazane is a compound having a Si—N bond, and polysilazane is based on SiH ₂ NH. Dissolve Tonen Polysilazane "Tonen Polysilazane" in xylene,
The prepared glass lens was immersed in the solution and pulled up to form a thin film. For polysilazane, a plasma CVD method requires an expensive and special apparatus, while a film can be formed by a simple method and a thick film can be easily formed.
Moreover, it is rich in adhesion.

After air drying, firing was performed in an electric furnace at 600 ° C. for 1 hour (FIG. 3C). Analysis of the thin film surface shows that almost 10
It was in a state of 0% pure quartz glass. The quartz glass thin film layer had an average thickness of 0.8 μm and an average surface roughness of 0.007.
μm. The amount of undulation on the glass lens surface was 0.45 μm P-P in the range of 30 mm in the central part of the sample. This is SiO
_It is considered that the film thickness unevenness generated when forming the _two thin films was added. When finishing the lens surface using plasma CVM processing, the amount of processing was controlled such that the amount of undulation of the surface was about 0.1 μm as in the case of Example 1 (FIG. 3D).

As a result, the average surface roughness was 0.005 μm, and the waviness was 0.08 μm P-P within the range of the central part length of 30 mm, and the surface shape was improved.

Embodiment 3 Using a glass (glass material BK7), a concave axisymmetric aspheric lens having a radius of curvature of about 50 mm is processed. The processing steps and the contents are almost the same as those in the second embodiment. However, the difference is that NC processing for producing a rough lens is performed. A series of steps were performed to produce an aspherical glass concave lens, and the shape was measured.As a result, the average surface roughness was 0.012 μm.
Surface undulation amount is 0.38μmP in the sample center length 30mm
-P. Therefore, plasma CVM processing was performed to improve the surface condition of the lens. Also in this example, a method of applying polysilazane and firing was used. Example 2
Is exactly the same as

The average thickness of this quartz glass thin film layer is 0.75 μm.
m, and the average surface roughness was 0.01 μm. The amount of undulation on the glass lens surface was 0.51 μm P-P in the range of 30 mm in the central part of the sample. As in the case of Example 2, the amount of processing was controlled so that the undulation amount of the surface was about 0.1 μm. As a result, the average surface roughness is
The 0.006μm undulation amount is 0 in the range of 30mm in the central part of the sample.
The surface shape was improved to 08μm P-P. Next, using this lens as a master, a convex axisymmetric aspheric lens was manufactured. The manufacturing process is shown in FIG. That is, a convex glass spherical lens 10 having a radius of curvature very close to the radius of curvature of the concave aspherical lens 9 serving as a master is used as a substrate lens, and the aspherical shape of the master lens is transferred to the surface thereof using a resin. As the resin, an ultraviolet curable resin 11 is used.
That is, an appropriate amount of ultraviolet curable resin is dropped on the surface of the substrate lens, and a master lens having an aspherical shape is pressed with an appropriate pressure from above to transfer the shape of the master lens to the substrate lens side, and then irradiated with ultraviolet light and cured. And release. The completed lens is an aspherical lens 12 having a so-called hybrid structure in which a resinous aspherical lens having an aspherical shape is integrated with a surface of a glass lens having a spherical shape. As described above, the method of the present invention is also effective for mold processing of a hybrid lens.

(Embodiment 4) Next, an example of correcting the shape of a thick large-diameter non-axisymmetric aspherical fθ glass lens will be described. FIG. 5 shows the shape of the thick thick large-diameter non-axisymmetric aspherical fθ glass lens 13 used in the experiment. Here, the large diameter represents the length in the width direction of the lens, and the A surface has a radius of curvature R1 in the main scanning direction, a radius of curvature r in the sub scanning direction different from R1, and r1, r2, r
Numeral 3 is a non-axisymmetric aspherical shape having different radii of curvature. The surface B has a flat or spherical shape. BK7 was used for the lens glass material. The surface A side of the glass material has a radius of curvature R1 in the main scanning direction and a radius of curvature r in the sub-scanning direction.
It has a so-called deformed toric shape that differs depending on the location of 1, r2, and r3, and the B surface is a planar shape.
Furthermore, both the A and B surfaces are mirror-finished, especially the surface roughness of the A surface is 0.015 μm in average surface roughness, and the waviness of the glass lens surface is 0.35 μm P-P with a length of 8 mm in the sub-scanning direction. Met. Then, in order to improve the surface state of the lens by plasma CVM processing, polysilazane was applied to the lens surface and baked to form a quartz glass thin film layer. The film production method is exactly the same as in Examples 2 and 3.

The average thickness of the quartz glass thin film layer is 0.5 μm.
m, and the average surface roughness was 0.012 μm. The amount of undulation on the glass lens surface was 0.45 μm P-P in the range of 30 mm in the central part of the sample. As in the case of Example 2, the amount of processing was controlled so that the undulation amount of the surface was about 0.1 μm. As a result, the average surface roughness was 0.009 μm, and the undulation amount was 0.15 μm P-P, and the surface shape was improved. Mount this lens on the optical system of the laser printer,
As a result of measuring the light-gathering characteristics, a uniform beam diameter of 60 μm was obtained over the entire scanning width. When printing was performed using a printer equipped with this lens, high quality printing performance was obtained compared to a lens manufactured using only the NC machining method.

[0023]

As described above, if the method according to the present invention is used, a plasma CV which is a very effective processing technique for shape creation is provided.
The application range of M processing can be greatly expanded, and processing of parts having complicated shapes and requiring high accuracy can be easily performed in a short time.

[Brief description of the drawings]

FIG. 1 is a cross-sectional structure (SiO ₂ / stainless steel material) of a workpiece in plasma CVM processing.

FIG. 2 is a schematic view showing a state of plasma CVM processing.

FIG. 3 is a schematic view showing a spherical lens manufacturing process using the present invention.

FIG. 4 is a schematic view showing a hybrid lens manufacturing process.

FIG. 5 is a perspective view of a thick large-diameter non-axisymmetric aspherical fθ glass lens.

[Explanation of symbols]

1: Sample (stainless steel disk), 1 ′: Sample (SiO ₂ / stainless steel disk) 2: Reactive substance layer (SiO ₂ thin film) 3: Plasma generating electrode 4: Plasma 5: Curve generator 6: Rough lens 7: Polisher 8: Reactive substance layer (converted from SiO ₂ thin film polysilazane) 9: Concave glass aspheric lens 10: Convex glass spherical lens 11: UV curable resin 12: Aspheric hybrid lens 13: Thick large diameter non-axisymmetric Aspheric surface fθ glass lens A surface is non-axisymmetric aspherical shape, B surface is flat or spherical shape, R1 is radius of curvature in main scanning direction, r1, r2, r3 is radius of curvature in sub scanning direction, T1,
T2 is the thickness.

Claims (10)

[Claims] 1. A method for forming a reactive material suitable for chemical processing on a surface of a workpiece, and forming the reactive material surface on a plasma CVM.
A surface processing method for a workpiece, wherein the surface is processed by a method. 2. The method according to claim 1, wherein an SiO ₂ layer is formed as a reactive substance. 3. The method according to claim _{2, wherein} the thickness of the SiO ₂ layer is 10 μm or less. 4. The method for processing the surface of a workpiece according to claim 2, wherein the SiO ₂ layer is formed by converting polysilazane applied to the surface of the workpiece. 5. A workpiece characterized in that a reactive material layer formed on the surface and adapted for chemical processing and a reactive material layer whose surface is precisely processed by a plasma CVM method are formed on the surface. 6. The workpiece according to claim 5, wherein the reactive material layer is a SiO ₂ layer converted from polysilazane. 7. The workpiece according to claim 6, wherein an optical element made of a glass material is selected as the workpiece, and a SiO ₂ layer is formed on the surface of the glass material. 8. The workpiece according to claim 6, wherein a mold for molding an optical element is selected as the workpiece. 9. The optical element molding die is made of metal, and a SiO ₂ layer is formed on the metal surface.
The workpiece as described. 10. An optical device comprising the optical element according to claim 7.