JP2511271B2 - Curvature radius measuring device and measuring method - Google Patents

Description

TECHNICAL FIELD The present invention relates to an apparatus and method for measuring the radius of curvature of a lens surface.

2. Description of the Related Art As a device for measuring the radius of curvature of a lens surface, FIGS.
The configuration shown in the figure has been proposed.

First, in the former measuring device shown in FIG. 8, a laser light source 1, a magnifying optical system 2, a reflecting flat plate 3 for reflecting a part of a light flux, a converging optical system 4, an optical bench 5, a stage 6, a camera 7, and a monitor. Eight. An object to be measured 9 is placed on the stage 6.

If the apex of the measured spherical surface 10 is placed at the convergence point P1 of the convergent light flux,
The reflected light beam from the DUT 9 and the light beam reflected by the reflecting flat plate 3 interfere with each other to form an interference pattern. This interference pattern can be observed by the monitor 8 via the camera 7. The position in the optical axis direction of the DUT 9 at this time is read by a length measuring machine (not shown).

Next, the DUT 9 is moved in the optical axis direction (in the case where 9 is a concave surface as shown in the drawing, the direction in which the DUT 9 is moved away from the converging optical system is a convex surface in the case of 9), and is indicated by a broken line. Thus, the center of curvature of the DUT 9 is located on the extension line of the light flux convergence point P1.

At this time, the light flux entering the measured spherical surface 10 is reflected in the direction exactly opposite to the entering direction, and returns to the optical path as it is. Therefore, the interference pattern is observed on the monitor 8 as before. At this time, the position of the DUT 9 in the optical axis direction is read. Then, the moving distance M of the DUT 9
Is found, and this is the radius of curvature of the measured spherical surface 10.

On the other hand, in the latter measuring device of FIG. 9, the converging optical system 4 of the measuring device of FIG. 9 is omitted. This is SPIE vol.1
92 Interferometry (1979) pp 75-84.

A light flux is emitted as a parallel light flux from the magnifying optical system 2, the light flux is reflected by the measured spherical surface 10, and the light flux is converged. When the light flux converging point P2 comes on the reflecting flat plate 3, an interference pattern occurs.

Next, as shown by the chain lines in FIG. 10 and FIG. 9, the DUT 9 is brought closer to the reflection plane plate 3, and the parallel light flux reflected by the measured spherical surface 10 becomes convergent light and is reflected on the reflection plane. The light flux is converged so that the light flux converging point P3 comes to the measured spherical surface 10. Since the interference pattern is generated at this time as well, the position can be determined.

From the moving distance M of the DUT 9, the radius of curvature r = 4 × M
The radius of curvature is calculated by.

The problem to be solved by the invention is that the former device cannot be stabilized if the radius of curvature is longer than the movable distance of the stage 6, that is, the measurement range of the radius of curvature is the length of the optical bench 5. Will be limited by.

Further, in the latter device, the parallel light beam from the magnifying optical system 2 is emitted to the measured spherical surface 10 side and the turning of the light flux is utilized, so that a radius of curvature longer than that of the optical bench 5 can be measured. However, the surface shape of the measured spherical surface 10 is limited to a concave surface, and the radius of curvature of the convex measured object cannot be measured. Also, in the measurement of the concave surface, as shown in FIG. 10, the light flux of five reflections is used, and there is a drawback that the visibility of the interference pattern is low.

OBJECT OF THE INVENTION It is an object of the present invention to provide a radius-of-curvature measuring device and a measuring method which can eliminate the above-mentioned drawbacks and can measure with high accuracy even if the concave and convex surfaces have a long radius of curvature.

SUMMARY OF THE INVENTION The radius-of-curvature measuring device of the present invention has the scope of claim 1 as its gist. Further, the curvature radius measuring method of the present invention has the scope of claim 5 as its gist.

Means for Solving the Problems Reference is made to FIG. 1 and FIG.

In the apparatus of the first invention of this application, a light source (a laser light source 21 in the embodiment) is designed to expand a light flux by a magnifying optical section 22 and then converge it by a converging optical section 24. An object 29 to be measured is placed on a stage 26, and the stage 26 is supported by an optical support (optical bench 25 in the embodiment) so as to be movable in the optical axis direction.

The moving amount of the stage 26 is read by the reading means (in the example, the measuring machine
Read according to 30). The storage means 31 has a distance L (back focus distance) from a lens surface (lens rear surface 24a in the embodiment) on the light exit side of the converging optics 24 to the light convergence point P3.
Is stored.

The calculation unit 32 calculates the moving distance S of the measured spherical surface 29a of the measured object.
And using the distance L Then, the radius of curvature r of the measured spherical surface 29a is calculated.

Here, the moving distance S is the position CP1 when the measured spherical surface 29a of the measured object is at the light flux converging point P3 and the measured spherical surface 29a.
Is close to the converging optical system 24, and the convergent light beam is reflected by the measured spherical surface 29a before being converged and turned back, and the light beam converging point P4 is on the light exit side lens surface 24a of the converging optical member 24.
Is the distance traveled between.

In the method of the second invention of this application, the luminous flux from the light source 21 is converged by the converging optical system and the measured spherical surface 29 of the measured object 29 is measured.
lead to a.

Then, the measured object 29 is moved along the optical axis so that the measured spherical surface 29a comes to the light flux converging point P3 of the convergent luminous flux, and the measured spherical surface 29a is brought closer to the converging optical system 24 to converge the convergent luminous flux. Before converging, the light is converged and reflected on the measured spherical surface 29a so that the converging light beam converging point P4 comes to the lens surface (lens rearmost surface 24a) of the converging optical system 24 on the light beam exit side.

From the position CP1 of the measured spherical surface 29a when the measured spherical surface 29a reaches the luminous flux convergence point P3 of the convergent luminous flux, the luminous flux convergence point P4 of the converged luminous flux is the lens surface on the luminous flux exit side of the converging optical system 24.
The moving distance S of the measured spherical surface 29a to the position CP2 at the time of reaching 24a, and the light flux converging point P3 from the lens surface 24a on the light flux exit side.
Distance to To calculate the radius of curvature r.

The curvature r can be obtained by obtaining the moving distance S and the back focus distance L of the measured spherical surface 29a and substituting these values into the equation for obtaining the radius of curvature r.

Example 1 Referring to FIG.

The radius-of-curvature measuring apparatus according to the first embodiment includes a laser light source 21, a magnifying optical system 22, a reflecting flat plate 23, a converging optical system 24, an optical bench 25 as an optical support, a stage 26, a camera 27, a monitor (monitor TV). ) 28, a length measuring machine 30 as a means for reading the amount of movement of the stage 26, a storage means 31, and a computing section 32.

[Laser Light Source and Enlarging Optical System] The laser light source 21 generates a coherent light beam,
For example, "He-Ne laser or the like is used. Magnifying optical system 22
Has lenses 33 and 34 and a half mirror 35. The magnifying optical system 22 magnifies the laser beam.

[Reflective Flat Plate] The reflective flat plate 23 is provided between the lens 34 and the converging optical system 24. The reflection plane plate 23 reflects a part of the expanded light flux. The front side of the reflective flat plate 23 is a camera 27.
Has a conjugate relationship with the image pickup plane.

[Converging optical system] The converging optical system 24 converges the expanded light beam to measure the object to be measured.
Lead to 29.

[Optical Bench and Table] The optical bench 25 is elongated in the optical axis direction or the light beam direction. On this, a stage 26 is movable along the optical axis direction. The movement of the stage 26 is performed by, for example, a pulse motor and a feed screw (not shown).

 A corner cube 36 is attached to the stage 26.

[Monitor optics] Camera 27, lens 37 and monitor 28 are magnifying optics 22
Belongs to the side. The camera 27, the lens 37, and the monitor 28 constitute an optical system for visually observing conjugate positions CP1 and CP2 (see FIGS. 1 and 2) of the light flux converging points, which will be described later.

[Measuring Machine] The measuring machine 30 has a laser light source 38, an optical system including a corner cube 36, and a processing unit 39. As the length measuring machine 30, for example, a known two-frequency laser interference type length measuring machine can be used. When using this type of length measuring machine, the processing unit 39 causes the reference signal (f1−f2) and the Doppler signal (f1−f2) reflected by the corner cube 36 and another corner cube (not shown) to be synthesized. By comparing with ± Δf), the moving distance of the stage 26 corresponding to ± Δf is calculated.
Since this type of measuring machine is known, the structural description thereof will be omitted.

The moving distance S of the stage 26 obtained by the processing unit 39, that is, the moving distance S of the measured spherical surface 29a of the measured object 29 and the distance information L already stored in the storage unit 31 are input to the calculation unit 32. To be done. The distance L of the storage means 31 is also called a back focus distance (or a back focal distance) and can be calculated in advance as follows.

That is, as shown in FIG. 3, the back focus distance L is unique to the converging optical system 24, and is from the lens rear end surface (lens surface on the light beam exit side) 24a of the converging optical system 24 to the light beam converging point P3. To the distance.

The position when the reflection plane 40 is at the light flux converging point P3 (shown by a broken line) and the position when the light flux converging point P4 is placed on the lens rear surface 24a of the converging optical system after being folded by the reflection plane 40 (in actual battle The back focus distance can be calculated by L = 2 × l using the distance l of

[Calculation Unit] Returning to FIG. 1, the calculation unit 32 uses the back focus distance L and the movement distance S to determine the radius of curvature r based on the imaging relational expression which will be described later.

Please refer to FIG. When the measured spherical surface 29a of the object to be measured 29 is at the light flux converging point P3 as shown in FIG. 1 (shown by a broken line), the convergent light flux is folded back at the measured spherical surface 29a and the light flux converging point P4 is converged. 24 shows the case of being on the lens rear surface 24a. That is, the object 29 shown by the solid line shows a state in which the object 29 shown by the broken line has moved the moving distance S toward the convergent optical system 24 side.

[Measurement Procedure] Referring to FIG. 1, the coherent light flux of the laser light source 21 is expanded by the magnifying optical system 22, and then part of it is reflected by the reflecting flat plate 23 to be guided to the camera 27. Reflective flat plate 23
The parallel light flux passing through is converged by the converging optical system 24.

First, as shown by the chain line in FIGS. 1 and 2 (a), the measured spherical surface 29a is brought to the light flux convergence point P3 of the convergent light flux. Whether or not the light flux is converged on the measured spherical surface 29a can be determined as follows. That is, the fact that the light beam is reflected when it converges in a point shape is called cat's eye and is reflected by the object with respect to the optical axis, and if the symmetry is ignored, it seems as if it were going backwards in the original optical path. .

This reflected light beam and the above-described reflected light beam on the reflecting flat plate 23 become similar light beams and cause interference. camera
The interference pattern can be seen on the monitor 28 via 27.

Therefore, it is possible to easily determine whether or not the light flux converges on the measured spherical surface 29a.

Next, as shown by the solid line in FIG. 2A, the moving distance S of the object 29 to be measured is brought closer to the convergent optical system 24. Then, the convergent light flux is reflected by the spherical surface 29a to be measured and reflected, and the light flux convergence point P4 is brought to be on the rearmost lens surface 24a of the converging optical system 24. At this time as well, since the interference pattern is obtained as in the previous case, the monitor 28 can easily determine whether or not the light flux is converged.

The distance S between the two positions is read by the length measuring machine 30 as described above, and the moving distance S and the back focus distance L are calculated from the paraxial image formation relational expression. Since there is a relation of Ask for.

Here, since the object to be measured is a concave surface, the moving distance S and the back focus distance L have a relationship of S> L / 2, and r takes a negative value.

On the other hand, FIG. 2B shows the case where the object to be measured is a convex surface.

In this case, the moving distance S and the back focus distance L are S
It differs from FIG. 2A in which the object to be measured 29 is concave in that it has a relationship of <L / 2, but within the range of S <L / 2 described above, it converges similarly to FIG. 2A. The light beam is reflected by the spherical surface 29a to be measured and is reflected, so that the light beam convergence point P'4 can be moved so as to be on the final lens surface 24a of the convergence optical system 24. Note that r at this time has a positive value.

When the radius of curvature is measured by this arrangement, whether the measured object is a concave surface or a convex surface, the convergent light flux is turned over by the measured spherical surface 29a, and the convergent point P4 is brought to the lens rearmost surface 24a of the converging optical system 24. The position of the measured spherical surface 29a is always within the back focus distance L of the converging optical system 24. Therefore, the object to be measured is not limited to the concave surface and the convex surface, the radius of curvature can be measured, and the movable range of the stage 26 by the optical bench 25 is at most the back focus distance L of the converging optical system 24.
The degree will be good.

Second Embodiment In the first embodiment, the positioning of the object to be measured is determined by the generation of the interference pattern, but in the second embodiment, this is not the case but another method.

In FIG. 4, the reflecting flat plate 23 of FIG. 1 is not provided, but instead of the camera 27 and the monitor 28, light receiving means 49, that is, a light receiver 50, a light shielding plate 51, and a lens 53 are provided. Since the other parts of the second embodiment are substantially the same as those of the first embodiment, the same reference numerals are given and the description thereof will be omitted.

The light blocking plate 51 has a pinhole 52. In particular, the pinhole 52 of the light receiving means 49 is located at a conjugate position with the light flux converging points P5 and P6 (FIG. 5) of the convergent light flux. Receiver behind pinhole 52
Put 50. When the convergent light flux is reflected pointwise at the light flux converging point P5, all the reflected light flux passes through the pinhole 52 and the output of the light receiver 50 increases. Therefore, the positioning can be determined.

Further, as shown in FIG. 5, all the light fluxes reflected at the light flux convergence point P6 pass through the pinhole 52 and the light receiver.
52 output increases. Therefore, the positioning can be determined at this time as well.

FIG. 6 shows the relationship between the moving position of the object to be measured and the output of the light receiver. Here, x1 is the position where the convergent light flux of FIG. 5 is turned around on the measured spherical surface 29a and the light flux converging point P6 is at the lens rear surface 24a of the converging optical system 24, and x2 is the light converging point of the measured spherical surface 29a. The position is on P5.

 By the way, the present invention is not limited to the above embodiments.

For example, referring to FIG. 7, unlike the case of the first embodiment, the converging optical system 124 and the reflecting flat plate 123 can be integrated into a plano-convex lens shape. Also, a shape other than a plano-convex lens can be adopted.

Further, a line sensor or an area sensor may be provided at the conjugate position of the light flux converging point to detect the position where the light flux diameter of the reflected light flux is minimum.

Alternatively, the light source may be an incoherent light source, and the conjugate base of the light flux convergence point may be visually observed with an eyepiece lens.

EFFECTS OF THE INVENTION As described above, according to the present invention, the radius of curvature of a measured surface of an object to be measured can be concave or convex, and a longer curvature can be obtained within the moving range of the stage of the optical support. The radius can be measured.

 Therefore, the measurement becomes easy.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a first embodiment of a radius-of-curvature measuring apparatus of the present invention, and FIG. 2 shows a state in which an object to be measured has moved a moving distance S in the first embodiment. That is, (a) is a concave surface and (b) is a convex surface, FIG. 3 is a diagram for explaining the principle of measuring the back focus distance, and FIG. 4 is a diagram for showing the configuration of the second embodiment. FIG. 5 is a diagram showing a state in which the object to be measured has moved by the moving distance S in Example 2, and FIG. 6 is Example 2
FIG. 7 is a diagram showing the output of the light receiver with respect to the position of the object to be measured, FIG. 7 is a diagram of another embodiment, and FIGS. 8 to 10 are diagrams showing a conventional example. 21 ... Laser light source 22 ... Enlargement optical system 23 ... Reflecting flat plate 24 ... Convergence optical system 24a ... Lens surface (lens surface on the exit side of the light beam) 25 ... Optical bench 26 ... Mounting stage 27 ... Camera 28 ... Monitor 29 ... Target Measured object 29a ... Measured spherical surface 30 ... Length measuring machine 31 ... Storage means 32 ... Computing unit

Claims (5)

(57) [Claims] 1. A light source, a magnifying optical system for magnifying the luminous flux of the light source, a converging optical system for converging the magnified luminous flux and guiding it to an object to be measured, and the object to be measured is movable in its optical axis direction. An optical support that is supported by the device, a reading unit that reads the amount of movement of the DUT, a storage unit that stores the distance L from the lens surface on the light beam exit side of the converging optical system to the light beam convergence point, and the measured surface of the DUT. The position at the point of convergence of the light flux and the measured spherical surface are reflected and reflected by the surface to be measured before the convergent light flux approaches the converging optical system and converges, and the light flux converging point is at the light exit side of the converging optical system. From the distance S between the position when the lens is on the lens surface, and the distance L According to the present invention, there is provided a calculation unit for calculating the curvature radius r of the surface to be measured, and the curvature radius measurement device. 2. The magnifying optical system has an optical system capable of observing a conjugate position of a light flux converging point, and the light flux converging point is on a surface to be measured or a lens surface on a light flux exit side of the converging optical system. The first aspect of the present invention has a configuration that can be visually determined.
A radius-of-curvature measuring device described in the paragraph. 3. The magnifying optical system has a light receiving means at a conjugate position of a light flux converging point, and photoelectrically detects that the light flux converging point is on a spherical surface to be measured or on a lens surface on the light flux exit side of the converging optical system. The radius-of-curvature measuring device according to claim 1, which has a configuration capable of being detected. 4. A coherent light source is provided as the light source,
A structure is provided in the middle of the magnifying optical system and the converging optical system to reflect a part of the light beam, and an interference pattern is obtained when the light beam converging point is on the sphere to be measured or on the lens surface on the light beam exit side of the converging optical system. The radius-of-curvature measuring device according to claim 1 or 2, wherein 5. A light beam from a light source is converged by a converging optical system to be guided to a surface to be measured of the object to be measured, the object to be measured is moved along an optical axis, and the surface to be measured converges the light beam of the converged light beam. Before the converging light beam is converged by bringing the measured surface closer to the converging optical system, the converging light beam is reflected by the surface to be measured and turned back so that the converging light beam converges at the light exit side of the converging optical system. When the surface to be measured reaches the convergence point of the converged light beam from the position of the surface to be measured, the convergence point of the converged light beam reaches the lens surface on the light exit side of the converging optical system. And the distance L from the lens surface on the light beam exit side to the light beam convergence point A method for measuring the radius of curvature by substituting into