JPH06194262A - Method and apparatus for meauring radius of curvature of surface - Google Patents

Abstract

PURPOSE:To provide a method and apparatus for measuring a radius of a curvature of a surface to be measured by a simple structure without a driving mechanism. CONSTITUTION:A light from a light source 11 is converted into a parallel beam by a collimator 12 and is refracted by an electro-optical lens 13 to be emitted to a surface 14 to be measured. A voltage applied to the electro-optical lens is varied by a voltage-applying means 19 so that the inputted beam to the surface 14 to be measured is emitted to focus on a point (A). The beam reflected by the surface 14 overlaps with the inputted beam and goes in the reverse direction to take back to the light source 11. In this stage, when the intensity of the reflected beam becomes a peak level is realized from an output of a photodetector 17 so that a focal distance of the electro-optical lens 13 at that time is obtained. Next, the inputted beam is emitted to focus on a center of curvature (O) in the surface 14 so that a focal distance is obtained likewise. The difference of both of the focal distances is calculated to obtain a radius of curvature (r) of the surface 14 to be measured.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for measuring a radius of curvature of an optical element having a spherical shape such as a lens.

[0002]

2. Description of the Related Art Conventionally, the method shown in FIG. 4 has been used to measure the radius of curvature of a spherical surface of a lens or the like. That is, in the figure, the laser beam emitted from the light source 1 is made into a parallel beam by the collimator 2, is irradiated onto the surface 4 to be inspected through the objective lens 3, and the objective lens 3 is moved on the optical axis. The objective lens 3 shown in the drawing shows a state in which the beam converges on the point A on the surface 4 to be inspected, and the objective lens 3 ′ shows a state in which the beam advances so as to converge on the center of curvature O of the surface 4 to be inspected.

When the objective lens comes to the position shown in FIG.
The beam converged to the point A on the surface to be inspected 4 is reflected by the surface to be inspected, and the vertical and horizontal directions are inverted, and all the reflected beams overlap the incident beam and pass through the objective lens 3 in the opposite direction to become a parallel beam. Return. If the position of the objective lens 3 shifts to the front or back, the reflected beam from the surface 4 to be inspected is diffused and the amount of light returning to a parallel beam is reduced.

Therefore, a half mirror 5 is placed between the objective lens 3 and the collimator 2, the reflected beam is taken out, and an image is formed on the photodetector 7 by the converging lens 6, and the amount of light is measured. That is, if the objective lens 3 is moved back and forth on the optical axis, and the processing circuit 8 monitors it to find the position of the objective lens 3 at which the output of the photodetector 7 reaches its peak, the beam A
The position that converges to a point can be obtained.

The objective lens 3 is moved to the right in FIG.
When the position of is also brought, the incident beam advances so as to converge on the center of curvature O of the surface to be inspected 4, and the light incident on the surface to be inspected 4 is
All are incident on the surface 4 to be inspected vertically. Therefore, the reflected beam traverses the same optical path as the incident beam, passes through the objective lens 3, and becomes a parallel beam. That is, also in this case, all the beams reflected by the surface 4 to be inspected overlap the incident beam, so that the output of the photodetector 7 similarly reaches a peak.

As described above, when the positions of the objective lenses 3 and 3'are determined and the distance S between them is determined, the radius of curvature r of the surface to be inspected 4 can be determined from the relationship of S = r.

[0007]

However, according to the above-mentioned prior art, a drive mechanism for moving the objective lens 3 along the optical axis is required, and at the same time, the half mirror 5, the converging lens 6, and the photodetector 7 are required. Must also move to the 5 ', 6', 7'positions respectively. Moreover, since the drive accuracy directly affects the measurement accuracy of the radius of curvature, in order to measure the radius of curvature with high accuracy, the drive mechanism also needs to have high accuracy, which makes the device complicated and very expensive. Will end up.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a method and an apparatus for measuring the radius of curvature of a surface to be inspected with a simple structure having no driving mechanism.

[0009]

In order to achieve the above object, the method of the present invention comprises a voltage applied to an electro-optical lens by refracting a parallel beam from a light source with an electro-optical lens to irradiate the surface to be inspected. The intensity of the reflected beam which is reflected by the surface to be inspected and goes back to the light source while being reflected is determined by a photodetector, and the fact that the intensity reaches a peak is used to irradiate the surface to be inspected. Characterized by the focal length of the electro-optical lens when the beam converges on the surface to be inspected and when it converges on the center of curvature of the surface to be inspected, and the radius of curvature of the surface to be inspected is calculated from the difference between the focal lengths. I am trying.

Further, the apparatus of the present invention comprises a light source for irradiating a parallel beam, and an electro-optical lens for refracting the parallel beam whose focal length changes according to a voltage to irradiate the surface to be inspected.
It is characterized by a voltage applying means for adjusting the voltage applied to the electro-optical lens and a light detecting means for detecting the amount of reflected light reflected by the surface to be inspected and returning to the light source.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a diagram showing an embodiment of the radius-of-curvature measuring apparatus of the present invention. In the figure, 11 is a light source, which is composed of a laser diode (LD) and emits a laser beam. A collimator 12 collimates the laser beam from the light source 11 into a parallel beam. Reference numeral 13 denotes an electro-optical lens, which is a lens whose focal length changes depending on the applied voltage. 14 is a surface to be inspected, which is a spherical surface. Reference numeral 15 is an optical splitter, which uses a half mirror. Reference numeral 16 is a converging lens, and 17 is a photodetector. Reference numeral 18 denotes a signal processing circuit that changes the voltage applied to the electro-optical lens 13 in cooperation with the voltage application circuit 19 so that the signal output from the photodetector 17 reaches a peak.

The solid line in FIG. 1 indicates that the beam transmitted through the electro-optical lens 13 is converged on the point A on the surface 14 to be inspected.
The imaginary line indicates the state of irradiation so as to converge on the center of curvature O of the surface to be inspected 14. In either case, the reflected beam overlaps the incident beam and becomes a parallel beam when transmitted through the electro-optical lens 13. The reflected beam reaches the light splitter 15 where it is at least partially reflected and split into photodetectors 1
It is incident on 7. When the beam emitted from the electro-optical lens 13 converges on a position other than point A or point O in the figure,
The reflected beam only partially overlaps the incident beam,
Spreads over a wider angle than the incident beam. Therefore, even if it passes through the electro-optical lens 13, it does not return to a parallel beam but diverges,
The amount of reflected beam detected by the photodetector is reduced.

Therefore, if the beam intensity is monitored by the photodetector 17, the state shown in FIG. 1 can be created, and the focus of the electro-optical lens 13 in the case where the applied voltage at that time converges to the points A and O. The distance is known, and the radius of curvature r of the surface to be inspected can be obtained from the difference between both focal lengths.

The embodiment of FIG. 2 differs from the embodiment of FIG. 1 in that the converging lens 16 converges the reflected beam and then the photodetector 17
The configuration in which the pinhole 20 is made incident on and the configuration in which the pinhole 20 is placed at the converging point are added. With such a configuration, when the reflected beams bent by the light splitter 15 are not parallel, light is eclipsed by the pinhole 20 and light is lost. As a result, the radius of curvature can be measured with higher accuracy than in the embodiment shown in FIG.

FIG. 3 is a diagram showing another embodiment of the present invention. Since there are many points in common with the embodiment of FIG. 1, the points of difference will be mainly described. Reference numeral 15 'is the same as the above-mentioned optical splitter 15, but here, since the first optical splitter 21 is provided, 15' is referred to as the second optical splitter, and both use a half mirror. is doing. The second light splitter 15 'bends a part of the reflected beam out of the optical path, whereas this first light splitter 21 bends a part of the incident beam or a collimated beam from the light source. Reference numerals 22 and 23 denote first and second photodetectors, which are CCDs in this embodiment. Reference numeral 24 is an image processing circuit.

The laser beam from the light source (LD) 11 is collimated by the collimator 12 and partly reflected by the first light splitter 21 to enter the first photodetector 22. The rest passes through the electro-optical lens 13 and illuminates the surface 14 to be inspected. The solid line shows the case where the beam converges on the point A on the surface 14 to be inspected, and the imaginary line shows the case where the beam advances so as to converge on the center of curvature O of the surface 14 to be inspected. The beam reflected by the surface 14 to be inspected returns to the optical path of the incident beam, and the electro-optical lens 1
3 from the opposite side, bent by the second light splitter 15,
It is incident on the second photodetector 23. The first and second photodetectors 22 and 23 are arranged at the same angle with respect to the incident beam.

If the beam emitted from the electro-optical lens 13 converges at the point A or the point O, the incident beam and the reflected beam between the collimator 12 and the electro-optical lens 13 overlap with each other. The diameter is the same. Therefore, from the first and second optical splitters 21 and 15 ',
The diameters of the beams incident on the second photodetectors 22 and 23 are also the same as long as the angles of the respective photodetectors with respect to the beam are the same. If the beam of the electro-optical lens does not converge to the points A or O shown in FIG. 3, the first and second photodetectors 2
The beam diameters of 2 and 23 are not equal. Therefore, if the image processing circuit 24 is monitoring the beam diameters of the first and second photodetectors 22 and 23 to be the same, the state of FIG. 3 can be created, and the difference in focal length in each case can be created. To test surface 1
A radius of curvature of 4 can be obtained.

[0018]

As described above, according to the present invention, the use of the electro-optical lens eliminates the need for a drive system such as that in the conventional device, and enables a simple structure.
At the same time, the radius of curvature of the surface to be inspected can be measured with high precision, and if a pinhole is used, even higher precision can be measured.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention and is a diagram showing a configuration of a radius-of-curvature measuring device for a surface to be tested.

FIG. 2 is a view showing a second embodiment of the present invention in which a pinhole is provided between a converging lens and a light detecting means.

FIG. 3 is a diagram showing a configuration of a third exemplary embodiment of the present invention.

FIG. 4 is a diagram showing a configuration of a conventional curvature radius measuring apparatus for a surface to be inspected.

[Explanation of symbols]

 11 Light Source 13 Electro-Optical Lens 14 Test Surface 15 Light Splitter 15 'First Light Splitter 16 Converging Lens 17 Photodetector 19 Voltage Applying Means 20 Pinhole 21 Second Light Splitter 22 First Photodetector 23 Second photodetector

Claims (8)

[Claims] 1. A parallel beam from a light source is refracted by an electro-optical lens to irradiate the surface to be inspected, and while the voltage applied to the electro-optical lens is changed, the incident beam reflected by the surface to be inspected goes backward to the light source. The intensity of the reflected beam that returns
By utilizing the fact that the intensity reaches a peak, the focal length of the electro-optical lens when the beam applied to the surface to be inspected converges on the surface to be inspected and when it converges to the center of curvature of the surface to be inspected A method for measuring a radius of curvature of a surface to be inspected, characterized by obtaining the radius of curvature of the surface to be inspected from the difference between both focal lengths. 2. When obtaining the intensity of the reflected beam by a photodetector, the reflected beam is converged by a converging lens and then incident on the photodetector, and a pinhole is provided at the converging position to cut ambient light. The method for measuring the radius of curvature of the surface to be inspected according to claim 1, wherein. 3. A reflected beam in which a parallel beam from a light source is refracted by an electro-optical lens to irradiate the surface to be inspected, is reflected on the surface to be inspected while changing the voltage applied to the electro-optical lens, and is incident in the opposite direction. The outer diameter of the beam and the outer diameter of the parallel incident beam are measured with a photodetector, and the fact that the outer diameters of both beams are the same is used, and the beam irradiated on the surface to be inspected The curvature of the surface to be inspected, which is characterized in that the focal length of the electro-optical lens is obtained at the time of convergence and at the time of convergence to the center of curvature of the surface to be inspected, and the radius of curvature of the surface to be inspected is obtained from the difference between both focal lengths. Radius measuring method. 4. A light source for irradiating a parallel beam, an electro-optical lens for changing a focal length according to a voltage to refract the parallel beam to irradiate a surface to be inspected, and a voltage applied to the electro-optical lens. And a light detection unit that detects the amount of reflected light that returns to the light source after being reflected by the surface to be inspected, and a radius-of-curvature measuring device for the surface to be inspected. 5. An optical splitter for branching at least a part of the reflected beam from the surface to be inspected is provided between the electro-optical lens and the light source, and the reflected beam emitted from the optical splitter is made incident. The curvature radius measuring apparatus for the surface to be inspected according to claim 4, further comprising a converging lens which is emitted to said light detecting means. 6. The converging lens is arranged so that the reflected beam emitted from the lens is converged in front of entering the light detecting means, and a pinhole is provided at the converging position. Item 5. The radius-of-curvature measuring device for the surface to be inspected according to item 5. 7. A light source for irradiating a parallel beam, an electro-optical lens for changing a focal length according to a voltage to refract the parallel beam and irradiate the surface to be inspected, and a voltage applied to the electro-optical lens are adjusted. Voltage applying means, a first photodetector for measuring the outer diameter of the parallel beam from the light source, and a second light for measuring the outer diameter of the reflected beam reflected by the surface to be inspected and returning to the light source. An apparatus for measuring a radius of curvature of a surface to be inspected, comprising: a detection unit. 8. A first light splitter that splits a part of a parallel beam from the light source between the electro-optical lens and the light source, and splits at least a part of a reflected beam from the surface to be inspected. 8. A radius of curvature measuring apparatus for a surface to be inspected according to claim 7, further comprising: a second light splitter, wherein the beams branched by the respective light splitters are made incident on the first and second light detecting means. .