JPH08254413A - Curvature radius measuring method and device - Google Patents

Abstract

PURPOSE: To measure curvature radius from the whole face of a face to be tested by finding the curvature radius and the distance from some reference point found from interference fringe information in a partial region of the face to be tested, finding a distance from some reference point found from the interference fringe decided by the whole face of the face to be tested, and calculating the difference between both distances and the partial curvature radius. CONSTITUTION: A measuring system 100 is provided with a body to be tested having a face to be tested and a prototype having a base reference face which forms interference fringe with the face to be tested. R1 , R2 are set as curvature radii regulated by the whole face of the face to be tested and a partial range respectively, Z1 , Z2 are set as the heights from some reference points (vertex of a face to be tested) respectively, and (d) is set as the radius of the prototype. The prototype is mounted so as to form the interference fringe and a Newton ring is observed by a CCD camera 110. An arithmetic processing 120 calculates ΔZ=Z2 -Z1 =d<2> /(2R2 )-d<2> /(2R1 )≈-(1/2).(d/R2 )<2> .(ΔR) introduced from an approximation related to the Newton ring. The (d) is known and when R is found, R can be calculated. It is assumed to be ΔR=R1 -R2 .

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to means for measuring a radius of curvature of an optical element having a lens surface, an optical surface, etc. having a curvature.

[0002]

2. Description of the Related Art As a conventional technique for measuring the absolute value of the radius of curvature of an optical lens, for example, the so-called "autocollimation method" is generally generally used. This method is based on "JIS-B7155 / 8 test / 8.2.
(2) Focal length of objective mirror (method using short-range collimator) ”, the arrangement state of an optical system including a collimator lens and a concave mirror is adjusted to perform“ ball-center reflection ”. "State" and "vertex reflection state (cat's eye reflection state)" are created, and between these two states,
By measuring the amount of movement of the test surface, the absolute value of the radius of curvature of the test surface is measured.

Further, since the radius of curvature of the entire surface of the surface to be inspected possessed by the object to be inspected is large, the measurement of the radius of curvature to the surface to be inspected to which the above-mentioned autocollimation method cannot be applied is spatially limited. There has been proposed a folding measurement method applying the above-mentioned auto-collimation method as disclosed in Japanese Patent Laid-Open No. 64-28534.

In this return measurement, an optical system having a plane mirror and a surface to be inspected is used in the return measurement of the convergent light beam.
This is a method of obtaining a large radius of curvature (hereinafter, referred to as "long R") of the surface to be inspected from information on the difference between the position of the plane mirror and the surface to be inspected.

[0005]

However, in the case of measuring a large radius R by the conventional folding measurement as described above, in order to use the information of the entire surface of the test surface, the measurement by the normal autocollimation method is performed. A measurement effective diameter (diameter required for measurement) that is approximately twice that at the time is required.

On the contrary, when the large radius R is partially measured by an ordinary measurement system, for example, when the sphericity on the entire surface to be inspected is poor, the radius of curvature defined on the entire surface to be inspected However, there was a problem that it could not be obtained accurately.

Therefore, the present invention was created in view of the problems of the above-mentioned conventional techniques, and even if the effective measurement radius of curvature cannot be sufficiently secured,
It is an object of the present invention to provide a curvature radius measuring means capable of measuring a large radius R defined on the entire surface to be inspected.

[0008]

In order to solve the above problems and achieve the object of the present invention, the following means can be considered.

A method for measuring a radius of curvature defined on the entire surface of a test object (the entire surface of the test surface), which is defined by a partial area of the entire surface of the test surface. (Partial curvature radius) and distance information from a certain reference point obtained from the interference fringe information are obtained, and then the distance from the certain reference point obtained from the interference fringe information, which is defined on the entire surface to be inspected. Information and and subtract both distance information.

Further, it is a curvature radius measuring method for obtaining a curvature radius defined on the entire surface to be inspected by referring to a predetermined relational expression based on the partial curvature radius and the subtraction result.

[0011]

First, a partial area of the entire surface to be inspected is defined as a partial area.

A radius of curvature (partial radius of curvature) defined by the partial area and distance information from a certain reference point obtained from the interference fringe information are obtained. In order to generate the interference fringes,
It suffices to mount a prototype for generating interference fringes having a known curvature on the subject.

Next, the distance information from the certain reference point, which is obtained from the interference fringe information and is defined on the entire surface to be inspected, is obtained, and both distance information are subtracted.

Further, based on the partial radius of curvature and the subtraction result, a radius of curvature defined on the entire surface to be inspected is obtained by referring to a predetermined relational expression.

As a result, a relatively large radius of curvature for the surface to be tested can also be obtained with a relatively small measuring system.

[0016]

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

FIG. 3 shows a block diagram of an example of the apparatus according to the present invention.

This apparatus comprises a measuring system 100 and a CCD camera 1.
10, the arithmetic unit 120, and the monitor 130.

The measurement system 100 comprises, for example, an object having a surface to be inspected and a prototype having a reference surface for generating interference fringes between the entire surface to be inspected. The reference surface is calibrated for sphericity error. An illumination system may be provided in order to generate the interference fringes.

The CCD camera 110 is a means for acquiring interference fringe information. That is, in the measurement system 100,
It has a function of acquiring information on the generated interference fringes.

Next, the arithmetic unit 120 uses the interference fringe information to perform an arithmetic operation based on an arithmetic expression, and from the separately given radius of curvature defined by the partial area of the inspected surface, the entire inspected surface. Find the radius of curvature defined by.

In the later-described portion of the embodiment, the contents of the calculation and the principle of the calculation performed by the calculation device 120 will be described.

Further, the monitor 130 includes the arithmetic unit 120.
Is a means for displaying at least the result of the calculation performed by
For example, it is realized by a CRT, a liquid crystal display, or the like.

Now, FIG. 1 is a view showing a cross-sectional shape of an object to be inspected having a surface to be inspected having a ring-like rotationally symmetrical undulation.

Now, the effective φD2 portion located at the center is
It is assumed that the point O2 is a perfect sphere having a radius R2 and having a spherical center. Further, the optimum approximate spherical surface (shown by the alternate long and short dash line) for the entire surface φD1 is a spherical surface having a radius R1 with the point O1 as the spherical center.

The "optimal approximate spherical surface" is a virtual spherical surface, and is a spherical surface that minimizes the volume of the deviation shape between the surface to be inspected and the main spherical surface.

When the sphericity of the surface to be measured is measured on this surface by an interferometer (not shown), the amount of deviation of the shape of the surface to be measured from the optimum approximate spherical surface can be grasped. . That is, the deviation shape data when the optimum approximate spherical surface is replaced on the reference plane is measured as a three-dimensional undulation.

Incidentally, such a measurement is performed by the measurement system 100.
Is equipped with an optical measurement system for shape measurement, and based on the interference fringe data obtained by the CCD camera 110,
This can be performed by the arithmetic device 120 having a configuration capable of measuring the sphericity according to a processing program stored in advance.

However, the measurement data obtained by an ordinary interferometer is
Since it is only necessary to detect the error amount in the normal direction of the surface to be inspected, it is necessary to convert the error amount to the error amount in the center line direction of FIG. 1 in order to use the principle described later.

By the way, the absolute value of R1 shown in FIG. 1 cannot be obtained only by obtaining the three-dimensional undulations of the surface to be inspected.

However, here, paying attention to the center φD2 portion of the measurement data of the entire surface to be inspected, the deviation of R2 from R1 is Δ.
When R, it can be defined as "ΔR≡R2-R1".

Therefore, the radius of curvature R2 of the center φD2 portion is measured separately, and if ΔR is further known, the radius of curvature R1 of the entire surface φD1 can be obtained as “R1 = R2 + ΔR”.

It should be noted that h corresponding to the amount representing the position of the spherical center O2 shown in FIG. 1 can also be obtained from the entire surface data.

Now, with the apparatus of FIG. 3, ΔR
The principle for obtaining the above will be described in detail with reference to FIG.

It should be noted that, in FIG. 4, the φD2 portion is a concave surface for convenience of description and is not essential.

Now, let us consider by replacing the measured spherical wave of the interferometer with the standard reference surface of the prototype. This is equivalent to preparing in advance a prototype having an infinite number of arbitrary radii of curvature.

As described above, since the interferometer measurement data is deviation data from the standard reference plane, it will be considered to obtain ΔR using this property.

Now, as shown in FIG. 4, d, Z1 (height from a certain reference point), Z2 (height from a certain reference point), Δ
Take Z. Further, R1 is a radius of curvature which is to be determined and which is defined on the entire surface to be inspected, and R2 is a radius of curvature of a partial region which is separately measured. The reference point may be arbitrarily selected, but in FIG. 4, the vertex of the surface to be inspected is adopted.

By the way, when a prototype having a certain radius of curvature is attached and interference fringes are generated, a so-called Newton ring is observed by the CCD camera 110.

[0040] Then, from the approximate expression for Newton's rings, "Z1 ≒ d ² / (2R1)", "Z2 ≒ d ² / (2R
2) ”.

[0041] Thus, by the arithmetic unit processes the interference fringe data, ^{"ΔZ = Z2-Z1 = d 2} / (2
^{R2) -d 2 / (2R1)} ≒ - (1/2) · (d / R2) 2
・ (ΔR) ”, ΔZ is obtained. Here, d is a predetermined value, and R2 has already been obtained. Therefore, the unknown number R1, that is, the radius of curvature defined by the entire surface to be inspected, which is to be obtained, is obtained by calculation processing. Although ΔZ here is not exactly the same value as ΔR, it can be said that if it is understood as a uniquely corresponding value, ΔR is obtained.

As described above, the radius of curvature defined on the entire surface to be inspected can be obtained.

However, since FIG. 4 is illustrated on the assumption that the measurement is performed by the standard, the test surface and the reference reference surface of the standard are in contact with each other at the apex of the test surface, but in the case of the interferometric measurement, As shown in FIG. 1, it is necessary to correct the portion (“R2-h” in FIG. 1) corresponding to the prototype, which is included in the optimum approximate spherical surface corresponding to the test surface in FIG. Become.

Further, using the value of the power correction value of a commercially available interferometer, φ
Change amount of power correction value when interferometric measurement is performed only on D2 part
It is also possible to easily calculate ΔR from “P”. That is, the amount of error in the direction normal to the surface to be inspected may be taken as “Δz”.

The first embodiment makes it possible to measure long R by using the above measurement principle.

For example, according to the method described in the prior art, it is possible to limit the measurement effectiveness to φD2 and obtain the radius of curvature R2 of the partial area of the surface to be inspected.

Next, the sphericity of the entire surface to be inspected may be measured by a normal interferometer measurement or the like. Further, for a large-diameter surface to be inspected, for example, Japanese Patent Application Laid-Open No. 5-4002
A measuring device as disclosed in Japanese Patent No. 4 may be used. Then, from the obtained sphericity data of the entire surface to be inspected, the curvature radius difference ΔR between the entire surface to be inspected and the effective φD2 at the time of measuring the long radius R is calculated by the above-mentioned method.
R1 can be calculated by the calculation “−R”.

Next, a second embodiment according to the present invention will be described with reference to FIG.

The present embodiment is a method of measuring the polishing depth when a workpiece having a spherical shape is partially polished for polishing a predetermined portion.

FIG. 2A shows the entire spherical surface (φD before polishing).
1) is a cross-sectional view of a workpiece obtained by measuring, for example, an interferometer, in which an optimum approximate spherical surface is developed on a plane and illustrated.

FIG. 2B is a sectional view of a shape obtained by partially polishing the central portion of φD2 and measuring the entire surface of the polished spherical surface by, for example, an interferometer.

Since the shape of the entire surface of the spherical surface after polishing is shown with reference to the optimum approximate spherical surface with respect to the entire surface of the spherical surface before polishing, the optimum approximate spherical surface deviates from the flat surface in FIG. 2B. This power change amount is set to "ΔP1" as shown in FIG. Here, the “power amount” is the amount of change in curvature represented by Δz described above.

Now, for all spherical whole surface data, the central portion φD2 is masked in the arithmetic unit (the arithmetic processing is performed assuming that there is no data in the central portion φD2), and the data of the remaining portion other than the masked portion is obtained. On the other hand, if "power correction" is performed, exactly the same data as shown in FIG. 2C should be obtained. This is because the area that is not masked is not polished and therefore has exactly the same shape information.

Similarly, in the description of FIG. 2 (c), since the workpiece shape is illustrated with the optimum approximate spherical surface for the entire surface before polishing as a reference, the optimum approximate spherical surface is deviated from the flat. This power change amount is defined as “ΔP2”. As can be seen from the figure, the sign is opposite to "ΔP1".

As described above, the data before and after polishing has the same shape in the region where partial polishing is not performed,
For each data, when masked (ie
The power change that occurs when the φD2 part is masked)
It can be obtained as “ΔPZ = ΔP2” and “ΔPG = ΔP2-ΔP1”.

Therefore, referring to both of the above equations, the amount of change in power “ΔP1” before and after polishing is calculated as “ΔP1 = ΔPZ−
ΔPG ”is calculated. On the contrary, when power is reapplied to the entire surface data after polishing by this power variation amount (the unevenness amount of the work is corrected), the shape of the non-polishing area becomes exactly the same. Therefore, if the difference between the two (power before polishing and power after polishing) is calculated, the polishing removal shape, which is the three-dimensional absolute shape of the workpiece polished and removed by the partial polishing, can be obtained.

As described above, by using the radius-of-curvature measuring means according to the present invention, it is possible to measure the radius-of-curvature of a spherical surface having a large diameter, which is difficult to measure with the conventional method. Become. It is also possible to measure the difference in shape between two test objects having partially the same shape.

[0058]

According to the present invention, it is possible to provide an apparatus capable of measuring the radius of curvature of a spherical surface or the like having a large diameter, which is difficult to measure the radius of curvature by the usual method.

[Brief description of drawings]

FIG. 1 is a principle diagram of the present invention.

FIG. 2 is an example according to the present invention.

FIG. 3 is a configuration diagram of an example of an apparatus according to the present invention.

FIG. 4 is a principle view of the present invention.

[Explanation of symbols]

1 ... Inspected surface, 100 ... Measuring system, 110 ... CCD camera,
120 ... Arithmetic unit, 130 ... Monitor

Claims (2)

[Claims] 1. A method for measuring a radius of curvature defined on the entire surface of a test surface having a test object (the entire surface of the test surface), which is defined by a partial region of the entire surface of the test surface. The radius of curvature (partial radius of curvature) and the distance information from a certain reference point obtained from the interference fringe information are obtained, and then from the certain reference point obtained from the interference fringe information defined on the entire surface to be inspected. And subtracting both distance information, and further based on the partial curvature radius and the subtraction result,
A radius-of-curvature measuring method characterized in that a radius-of-curvature defined on the entire surface to be inspected is measured with reference to a predetermined relational expression. 2. An apparatus for measuring a radius of curvature defined on the entire surface of an object to be inspected (the entire surface of the object to be inspected), and imaging an interference fringe formed by the entire surface of the object to be inspected and a reference surface. And an arithmetic unit that calculates the radius of curvature defined on the entire surface to be inspected by using at least the interference fringe information, and the arithmetic unit is a partial region of the entire surface to be inspected. Defined in a partial area, the distance information from a certain reference point obtained from the interference fringe information, and the distance information from the certain reference point obtained from the interference fringe information, which is defined on the entire surface to be inspected, is obtained. Curvature radius measurement characterized by subtracting both distance information and measuring a radius of curvature defined on the entire surface to be inspected by referring to a predetermined relational expression based on the subtraction result and the partial radius of curvature apparatus.