JP2002321144A - Method for manufacturing aspherics - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for grinding an aspherical face which can be used for processing the high accurate aspherical face efficiently by solving the problem that the surface accuracy is low due to a pit or the like generated in an aspherical face grinding process, and the problem that the efficiency is bad due to the length of grinding time in a partial correction grinding process for an aspherical face grinding. SOLUTION: This method is made to provide a method for manufacturing highly accurate and highly efficient aspherics by means of having an aspherical face grinding process forming the form of a first aspherical face on an object to be worked by grinding, a pit removal grinding process for taking off a crack generated on the above first aspherical face due to the above aspherical face grinding process, an undulation removal process for taking off an undulation generated on the above first aspherical face due to the above aspherical face grinding process, and a partial correction grinding process forming the form of a second aspherical face on the above object to be worked by carrying out a correction grinding partially in the method for manufacturing the aspherics.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for manufacturing an optical element.

[0002]

2. Description of the Related Art High-precision precision optical components are used in optical instruments such as cameras and semiconductor exposure apparatuses. For these precision optical components, glass having high transmittance called optical glass is usually used, and the outer shape is a spherical shape having a constant radius.

A lens using an optical glass (referred to as an optical lens) includes a spherical grinding process, a sanding process, a rough polishing process,
It is manufactured through a finish polishing process. In these steps,
Since the outer shape of the optical lens is spherical, the smoothness of the surface can be improved. The higher the smoothness of the surface of the optical lens, the higher the optical performance. Therefore, the technology for improving the smoothness of the surface of an optical lens by spherical polishing has become very high.

On the other hand, it has been found that by making the outer shape of the optical lens aspherical, there are effects such as improvement of imaging performance and reduction of the thickness of the optical lens. for that reason,
In recent years, there has been an increasing demand for highly accurate aspherical processing of optical lenses. However, the conventional spherical polishing process is based on the premise that a predetermined radius is polished, so that an aspheric surface cannot be polished. Therefore, methods of aspherical surface processing and aspherical surface polishing are being studied.

The following method has been proposed as a method of processing an aspherical shape. Optical glass processed into a spherical shape (called an approximate spherical surface) close to the target aspherical shape,
A target aspherical shape is obtained by shaving using a rotary grindstone or the like. This is called aspherical grinding.

[0006] In aspherical grinding, an optical glass is ground by a rotating grindstone. Due to the shear stress generated when the surface of the optical glass is shaved, minute cracks are generated in the optical glass. This is called a pit. The presence of these pits lowers the surface accuracy and lowers the performance of the optical lens. In addition, in the aspherical surface grinding, in addition to the pits, marks (referred to as tool marks) cut by a tool such as a rotary grindstone and periodic minute unevenness (referred to as undulations) remain on the surface. This undulation also lowers the surface accuracy, so that the performance of the optical lens is reduced.
That is, there is a problem that it is difficult to process an optical lens with high surface accuracy only by aspherical surface grinding.

[0007] In addition, using a small tool (called a small tool) capable of coping with various shapes, partial polishing is performed.
A method for realizing an aspherical shape has also been proposed. This is called partial correction polishing. In the partially modified polishing, the area that can be polished per unit time is small because the tool is small. Also, the volume that can be removed by polishing per unit time is small. Therefore, when the area to be polished is large or the shape has a large amount to be removed by polishing, there is a problem that the polishing time is long and the efficiency is low.

In order to solve the above-mentioned problems, a process as shown in FIG. 2 has been proposed. This is a method of performing aspherical grinding on a workpiece having a spherical shape and then polishing with a small tool. It was conceived that this method would improve the surface accuracy.

[0009]

However, it has become necessary to remove pits in the aspherical grinding step in the partially modified polishing step. Since the volume to be removed to remove the pits is large, the problem of a long polishing time in the partially modified polishing step has not been solved, and the efficiency remains poor.

It is an object of the present invention to solve these problems and to provide an aspherical surface polishing method for efficiently processing a highly accurate aspherical surface.

[0011]

According to a first aspect of the present invention, there is provided a method of manufacturing an aspherical lens, wherein an aspherical grinding step of forming a first aspherical shape on a workpiece by grinding, and the aspherical surface grinding step. A pit removal polishing step for removing cracks generated on the first aspheric surface, and a undulation removal polishing step for removing undulations generated on the first aspheric surface by the aspheric surface grinding step, And a partially modified polishing step of forming a second aspherical shape on the workpiece by performing modified polishing.

With this configuration, it is possible to provide a method of manufacturing an aspherical lens with high accuracy and high efficiency. According to a second aspect of the present invention, in the method for manufacturing an aspherical lens according to the first aspect, the pit removal polishing step is performed before the undulation removal polishing step.

With this configuration, it is possible to provide a method for manufacturing an aspherical lens with high accuracy and high efficiency. According to a third aspect of the present invention, in the method for manufacturing an aspherical lens according to the first aspect, the first aspherical shape is substantially the same as the second aspherical shape.

With this configuration, it is possible to provide a highly accurate and efficient method for manufacturing an aspherical lens. According to a fourth aspect of the present invention, in the method for manufacturing an aspherical lens according to the first aspect, the first aspherical shape is a shape obtained by adding a substantially uniform thickness to the second aspherical shape. Features.

With this configuration, it is possible to provide a method for manufacturing an aspheric lens with high accuracy and high efficiency. According to a fifth aspect of the present invention, in the method for manufacturing an aspherical lens according to the first aspect, the pit removal polishing step is a polishing step using a soft elastic body as a polisher.

With this configuration, it is possible to provide a method for manufacturing an aspheric lens with high accuracy and high efficiency. According to a sixth aspect of the present invention, in the method for manufacturing an aspheric lens according to the fifth aspect, the soft elastic body is a urethane foam sponge.

With this configuration, it is possible to provide a method for manufacturing an aspheric lens with high accuracy and high efficiency. The invention according to claim 7 is a method of manufacturing an aspherical lens, wherein: a spherical machining step of forming a spherical shape on a workpiece; and an aspherical grinding step of forming a first aspherical shape on the workpiece by grinding. A pit removal polishing step for removing a crack generated on the first aspheric surface by the aspheric surface grinding step; and a undulation for removing a undulation generated on the first aspheric surface by the aspheric surface grinding step. A polishing step, and a partially modified polishing step of forming a second aspherical shape on the workpiece by performing partially modified polishing, wherein the pit removal polishing step is performed more than the undulation removal step. Is also performed before.

With this configuration, it is possible to provide a method for manufacturing an aspherical lens with high accuracy and high efficiency. According to an eighth aspect of the present invention, in the method for manufacturing an aspherical lens according to the seventh aspect, the spherical processing step is a spherical polishing step.

With this configuration, it is possible to provide a method for manufacturing an aspheric lens with high accuracy and high efficiency.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION

[0021]

Embodiment 1 FIG. 1 is a conceptual diagram showing a procedure for carrying out the present invention. First, the optical glass is processed into a shape approximating the first aspherical shape (referred to as an approximate spherical surface) (S01). The first aspherical shape is substantially the same as the second aspherical shape which is the final outer shape of the aspherical optical lens. However, the processing accuracy of the surface accuracy and the outer shape of the first aspherical shape at the end of the aspherical surface grinding process may be larger than the target surface accuracy and the processing error of the second aspherical shape.

Next, aspherical grinding is performed using a high-precision precision grinding device (S02). As a grinding tool, a diamond / resin bond whetstone is used. The optical glass, which is a workpiece, is rotated, and the optical glass is scanned while rotating the grindstone along the first aspherical shape to cut out the first aspherical outer shape.

Further, pits generated by the aspherical grinding step are removed by pit removal polishing (S03). In the pit removal polishing, a polishing tool using foamed polyurethane is used as a polisher. This polishing tool is attached to a three-dimensional polishing apparatus, and the first aspheric optical glass ground in the aspheric cutting step is polished. Soft elastic material such as foamed polyurethane fits well into aspherical shapes,
Uniform polishing can be performed even on surface irregularities. Thereby, pits generated in the aspherical surface grinding step can be removed.

After pit removal polishing, undulation removal polishing is performed (S04). The undulation polishing uses a polishing tool using a viscoelastic body (pitch) as a polisher. This polishing tool is attached to a three-dimensional polishing apparatus, and the optical glass after pit removal polishing is polished. Thereby, undulation and tool marks generated in the aspherical grinding step can be removed.

Thereafter, shape measurement is performed (S05). Based on the measurement result, a partial correction polishing step is performed using a small tool (S06). The portion to be polished is calculated from the measurement result. Based on the calculated value, an NC program is performed to control the polishing of the small tool. In this partial correction polishing, the surface accuracy is also improved by selectively polishing a portion having a low surface accuracy.

After completion of the partially modified polishing step, shape measurement is performed. As a result, if the shape error with respect to the second aspherical shape is within the target standard, the processing is completed (S07).
If the shape error is outside the target specification, the partial correction polishing is performed again, and the operations of S05 → S06 are repeated until the shape error falls within the target specification.

In these steps, it is important to perform the pit removal polishing step before the undulation removal polishing step. FIG. 3A is a diagram showing the state of the surface of the optical glass as the workpiece at the end of the aspherical grinding step. As shown in this figure, at the end of the aspherical grinding step, the workpiece has undulations and tool marks, and pits have occurred on the surface layer.

FIG. 3B is a view showing a state in which a pit removal polishing step is performed after the aspherical surface grinding step. When the pit removal polishing step is performed, pit portions on the surface are removed, and undulations and unevenness of tool marks become visible on the surface. FIG.
FIG. 3C is a view showing a state in which the undulation polishing step has been performed after FIG. In this way, the projections of the unevenness are polished, and a surface with less unevenness can be processed.

FIG. 3D is a view showing a state in which a undulation polishing step has been performed after the aspherical grinding step. In the undulation polishing step, the convex portions are selectively removed. As a result, pits remain in the concave portions as shown in FIG. FIG.
FIG. 3E is a diagram showing a state in which a pit removal polishing step has been performed after FIG. Pits on the surface are removed, and tool marks and undulations appear on the surface.

As described above, if the beat polishing step is performed before the pit polishing step, residual pits, tool marks and undulations remain on the surface of the workpiece. These irregularities reduce the surface accuracy. Therefore, in order to increase the surface accuracy, the pit removal polishing step needs to be performed before the undulation removal polishing step.

The first aspherical shape may be different from the second aspherical shape. For example, in the pit removal polishing step, the surface is uniformly removed from the first aspherical shape. Therefore, the thickness removed in the pit removal polishing step may be added to the second aspherical shape. The amount to be added is calculated based on a measured value in a pit removal polishing step performed in advance.

When the polishing is performed by this method, the removal amount in the partial correction polishing step is reduced as compared with the above-mentioned method, and the efficiency of manufacturing the aspherical lens is improved.

[0033]

According to the present invention, in a method of manufacturing an aspherical lens, an aspherical surface grinding step of forming a first aspherical surface shape on a workpiece by grinding, and the first aspherical surface grinding step by the aspherical surface grinding step. A pit removal polishing step for removing a crack generated on the aspheric surface, a undulation removal polishing step for removing the undulation generated on the first aspheric surface by the aspheric surface grinding step, and partially correcting polishing. By performing a partially modified polishing step of forming a second aspherical shape on the workpiece by performing the method, a highly accurate and highly efficient method of manufacturing an aspherical lens can be provided.

[Brief description of the drawings]

FIG. 1 is a schematic view of an aspherical surface polishing method according to the present invention.

FIG. 2 is a schematic view of a conventional polishing method.

FIG. 3 is a diagram illustrating a sequence of steps in the aspherical surface polishing method according to the present invention.

Claims (8)

[Claims] 1. A method for manufacturing an aspherical lens, comprising: an aspherical grinding step of forming a first aspherical shape on a workpiece by grinding; and a crack generated in the first aspherical surface by the aspherical grinding step. A pit removal polishing step for removing undulations; a undulation removal polishing step for removing undulations generated on the first aspherical surface by the aspherical surface grinding step; A partially modified polishing step of forming a second aspherical shape on an object. 2. The method of manufacturing an aspheric lens according to claim 1, wherein the pit removal polishing step is performed before the undulation removal polishing step. 3. The method of manufacturing an aspheric lens according to claim 1, wherein said first aspherical shape is substantially the same as said second aspherical shape. Production method. 4. The method for manufacturing an aspheric lens according to claim 1, wherein said first aspherical shape is a shape obtained by adding a substantially uniform thickness to said second aspherical shape. Method of manufacturing an aspherical lens. 5. The method for manufacturing an aspheric lens according to claim 1, wherein the pit removal polishing step is a polishing step using a soft elastic body as a polisher. 6. The method for manufacturing an aspheric lens according to claim 5, wherein said soft elastic body is a urethane foam sponge. 7. A method for manufacturing an aspherical lens, comprising: a spherical machining step of forming a spherical shape on a workpiece; an aspherical grinding step of forming a first aspherical shape on the workpiece by grinding; A pit removal polishing step for removing a crack generated on the first aspheric surface by the aspheric surface grinding step; and a undulation removal polishing for removing the undulation generated on the first aspheric surface by the aspheric surface grinding step. And a partially modified polishing step of forming a second aspherical shape on the workpiece by partially performing modified polishing, wherein the pit removal polishing step is performed before the undulation removal polishing step. A method of manufacturing an aspherical lens. 8. The method of manufacturing an aspheric lens according to claim 7, wherein the spherical processing step is a spherical polishing step.