JP7185241B1 - Reflected light distribution measuring device and method - Google Patents

Abstract

A reflected light distribution measuring apparatus and method capable of measuring BRDF and the like with high accuracy even when a surface to be measured is curved is provided. SOLUTION: A reflected light distribution measuring device 11 includes a light projecting side optical system 20, a light receiving side optical system 30, and a measuring section 40. The projection-side optical system 20 generates convergent light 22 from a point image of a point light source 21 and irradiates the spherical surface 50 to be measured so that the convergent light 22 is condensed at a focal point 51 of the spherical surface 50 to be measured. In the light-receiving-side optical system 30, the parallel light 31 reflected by the spherical surface 50 to be measured is received by the light-receiving-side collimator lens 32, formed into an image, and returned to a point image. The measurement unit 40 measures the light intensity distribution of the formed point image. [Selection drawing] Fig. 1

Description

The present invention relates to a reflected light distribution measuring apparatus and method for measuring the light intensity distribution of reflected light returned from a surface to be measured.

An autocollimator for measuring the angle of a surface to be measured projects a collimated light and converts the light reflected by the surface to be measured into a point image with a collimator optical system, and measures the angle of the surface to be measured from the position of the point image. is. A flat object with strong specular reflection, generally a mirror, is used as the surface to be measured.

Also, the inventor of the present invention has disclosed a technique for measuring a BRDF (Bidirectional Reflectance Distribution Function), which is the angular distribution of reflected light from an object, using a collimator optical system (Patent Document 1).

This BRDF is one of the reflection models, also called the bidirectional reflectance distribution function, and is a function that expresses how much light is reflected in another direction when it is incident from one direction at a point on the reflective surface. is. In the field of computer graphics, BRDF information will become more and more important in order to improve the texture of the surface of an object.

Japanese Patent No. 5204723 "Point image specular reflection light distribution measuring method and measuring apparatus"

However, in the technique of measuring the BRDF of an object using a collimator optical system, there is a problem that although a highly accurate measurement result can be obtained for a flat surface, the measurement accuracy for a curved surface decreases. In particular, objects to be displayed by computer graphics (for example, industrial products, works of art, etc.) are often composed of curved surfaces, so there is a long-awaited technology that can measure BRDF even on curved surfaces with high accuracy.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a reflected light distribution measuring apparatus and method capable of measuring BRDF and the like with high precision even when the surface to be measured is curved.

As a result of repeated experiments and considerations, the inventors of the present invention found that the incident parallel light is reflected by the curved surface and spreads, and the reflected light does not become parallel light. I found it. The present invention is made based on this finding.

That is, the reflected light distribution measuring device according to the present invention is
a projection-side optical system that generates convergent light from a point image of a point light source and irradiates the spherical surface to be measured with the converged light so that the convergent light is condensed at the focal point of the spherical surface to be measured;
a light-receiving-side optical system that receives the collimated light reflected by the spherical surface to be measured by a light-receiving-side collimator lens, forms an image, and returns the collimated light to a point image;
a measurement unit that measures the light amount distribution of the formed point image;
It is a device with

And the reflected light distribution measuring method according to the present invention includes:
generating convergent light from a point image of a point light source by the projection-side optical system, and irradiating the spherical surface to be measured so that the convergent light is focused on the focal point of the spherical surface to be measured;
The collimator lens receives the parallel light reflected by the spherical surface to be measured by the light-receiving-side optical system, forms an image, and returns it to a point image;
measuring the light intensity distribution of the formed point image by a measurement unit;
The method.

According to the present invention, the surface to be measured is approximated from a curved surface to a spherical surface, and the spherical surface to be measured is irradiated with convergent light so as to converge on the focal point of the spherical surface to be measured. Therefore, the collimator lens can be used to restore the point image with high accuracy, and even when the surface to be measured is curved, the BRDF and the like can be measured with high accuracy.

1 is a configuration diagram showing a reflected light distribution measuring device of Embodiment 1. FIG. FIG. 2 is a partially enlarged view showing an enlarged part of FIG. 1; 7 is a graph showing an example of the relationship between the distance from the origin in the optical axis direction to the point light source and the distance (optical path length) from the projection-side collimator lens to the condensing point of the converging light. 4 is a conceptual diagram showing the measurement principle of a convex surface in Embodiment 1. FIG. 4 is a conceptual diagram showing the measurement principle of a concave surface in Embodiment 1. FIG. FIG. 10 is a configuration diagram showing a reflected light distribution measuring device according to Embodiment 2;

EMBODIMENT OF THE INVENTION Hereinafter, the form (henceforth "embodiment") for implementing this invention is demonstrated, referring an accompanying drawing.

<Embodiment 1>
FIG. 1 is a configuration diagram showing a reflected light distribution measuring apparatus according to Embodiment 1. FIG. FIG. 2 is a partially enlarged view showing an enlarged part of FIG. 1. FIG. The following description will be made with reference to FIGS. 1 and 2. FIG.

The reflected light distribution measuring device 11 of Embodiment 1 includes a light projecting side optical system 20 , a light receiving side optical system 30 and a measuring section 40 . The projection-side optical system 20 generates convergent light 22 from the point image of the point light source 21 and irradiates the spherical surface 50 to be measured so that the convergent light 22 converges (converges) on the focal point 51 of the spherical surface 50 to be measured. In the light-receiving-side optical system 30, the parallel light 31 reflected by the spherical surface 50 to be measured is received by the light-receiving-side collimator lens 32, formed into an image, and returned to a point image. The measurement unit 40 measures the light amount distribution of the formed point image. In FIG. 2, the convergent light 22 and the parallel light 31 are shown considerably enlarged from the spherical surface 50 to be measured.

The projection-side optical system 20 includes a projection-side collimator lens 23 and a projection-side support 24 that supports at least one of the projection-side collimator lens 23 and the point light source 21 so as to be movable in the optical axis direction x. . As a result, the projection-side optical system 20 realizes the function of freely changing the condensing point 27 where the converging light 22 converges in the optical axis direction x. FIG. 2 shows a state in which the condensing point 27 is aligned with the focal point 51 .

In addition, in this Embodiment 1, the light projection side support body 24 which supports only the point light source 21 movably in the optical axis direction x is illustrated. The projection-side optical system 20 may be configured using a concave mirror or the like instead of the projection-side collimator lens 23 . Alternatively, for example, a varifocal lens or an electro-optical lens may be used to electrically change the condensing point 27 where the converging light 22 converges in the optical axis direction x.

The projection-side optical system 20 includes a point light source 21 , a projection-side collimator lens 23 , and a projection-side support 24 , as well as an aperture plate 25 and a half mirror 26 . The point light source 21 is composed of a light source 21a such as a light emitting diode or a semiconductor laser, and a pinhole plate 21b provided on the emission side of the light source 21a. With this configuration, a point image is obtained from the point light source 21 . The projection-side support member 24 has, for example, a stage, a feed screw and a pulse motor (not shown), and the position of the point light source 21 on the stage can be freely changed in the optical axis direction x by the feed screw and pulse motor. The feed screw may be manually rotated instead of the pulse motor.

The light receiving side optical system 30 has a half mirror 26 in addition to the light receiving side collimator lens 32 . The half mirror 26 is a component shared by the light-projecting side optical system 20 and the light-receiving side optical system 30 .

The measurement unit 40 has a two-dimensional image sensor 41 such as a CCD sensor or a CMOS sensor. The light-receiving surface of the two-dimensional image sensor 41 is positioned at the focal point of the light-receiving side collimator lens 32 . The point image formed on the light-receiving surface of the two-dimensional image sensor 41 is converted into an electric signal as the amount of light (i.e., light amount distribution) for each photocell on the two-dimensional coordinates, and output to a computer or displayed enlarged on a display. be done. The computer has a function of calculating the variable angle luminous intensity and the deflection angle luminous intensity of the measured spherical surface 50 based on the input light quantity distribution, and controls the light projection side support 24 so that the half width of the light quantity distribution is minimized. Functions may be implemented by computer programs.

1 and 2 show the case where the spherical surface 50 to be measured is convex. The spherical surface 50 to be measured is an approximation of the curved surface of an actual object surface to a spherical surface. In FIG. 2, the distance from the spherical surface 50 to be measured to the focal point 51 is the focal length r, and the distance from the spherical surface 50 to be measured to the center 52 of the spherical surface 50 to be measured is the radius of curvature R. A focal point 51 is a focal point defined by geometrical optics, and a ray heading for the focal point 51 is reflected by the spherical surface 50 to be measured and becomes a ray parallel to the optical axis. The center 52 is the center of a sphere having the spherical surface 50 to be measured as part of its outer surface. A focal point 51 and a center 52 are located on the optical axis. In the field of geometrical optics, it is known that the radius of curvature R and the focal length r have a relationship of R=2r.

FIG. 3 shows an example of the relationship between the distance X from the origin x0 in the optical axis direction x to the point light source 21 and the distance (optical path length) Y from the collimator lens 23 on the projection side to the condensing point 27 of the converging light 22. It is a graph showing. An example of the operation of the reflected light distribution measuring device 11 will be described below with reference to FIG. 3 in addition to FIGS. Here, the origin x 0 is the focal position of the collimator lens 23 . The position of the point light source 21 is the pinhole position of the pinhole plate 21b. Therefore, the distance X from the origin x0 to the point light source 21 is the amount of movement of the point light source 21 . When the distance X is 0.0, the point light source 21 is the focal position of the collimator lens 23, and the focal position of the converging light 22 is infinite, which is parallel light.

First, the spherical surface 50 to be measured is installed at a fixed position facing the reflected light distribution measuring device 11 . When the reflected light distribution measuring device 11 is turned on, a point image is emitted from the point light source 21 . The point image is converted into convergent light 22 by the collimator lens 23 on the projection side, and the convergent light 22 is reflected by the half mirror 26 toward the spherical surface 50 to be measured. As shown in FIG. 2, if the converging point 27 of the converging light 22 coincides with the focal point 51 of the spherical surface 50 to be measured, the converging light 22 is reflected by the spherical surface 50 to be measured and becomes a parallel light, as explained in geometrical optics. Become 31. The parallel light 31 passes through the half mirror 26 and the light-receiving side collimator lens 32 and forms a point image on the light-receiving surface of the two-dimensional image sensor 41 . At this time, if the half-value width of the light amount distribution measured by the two-dimensional image sensor 41 is minimized, the condensing point 27 of the convergent light 22 is perfectly aligned with the focal point 51 of the spherical surface 50 to be measured.

If the converging point 27 of the converging light 22 does not coincide with the focal point 51 of the spherical surface 50 to be measured, the converging light 22 spreads even if it is reflected by the spherical surface 50 to be measured and does not become parallel light 31 . As a result, only a blurred image appears on the light receiving surface of the two-dimensional image sensor 41, and the half-value width of the light quantity distribution also increases. In this case, the point light source 21 is moved little by little in the optical axis direction x by the light projecting side support 24 until the half width of the light amount distribution is minimized.

In FIG. 3, the horizontal axis is the distance X from the origin x0 of the optical axis direction x to the point light source 21, the vertical axis is the distance (optical path length) Y from the projection side collimator lens 23 to the converging point 27 of the converging light 22, The solid line is the calculated value, and the ▲ is the measured value. Here, the direction in which the point light source 21 separates from the projection-side collimator lens 23 is defined as the positive direction of the optical axis direction x. As shown in FIG. 3, the more the point light source 21 is moved in the positive direction of the optical axis direction x (the greater the distance X is), the closer the condensing point 27 of the converging light 22 is to the projection-side collimator lens 23 (the distance Y becomes smaller).

In Embodiment 1, the origin x0 of the optical axis direction x is set as the focal position of the projection-side collimator lens 23 . Therefore, when the pinhole plate 21b of the point light source 21 is positioned at the origin x0, the point image of the point light source 21 becomes parallel light, not convergent light, by the collimator lens 23 on the projection side. At this time, BRDF and the like can be measured for a plane (the radius of curvature R of the spherical surface 50 to be measured is infinite). When the point light source 21 is gradually moved from the origin x0 in the positive direction of the optical axis direction x (when the distance X is gradually increased), the condensing point 27 of the convergent light 22 moves slightly from infinity toward the collimator lens 23 on the projection side. It approaches gradually (the distance Y becomes smaller little by little). In other words, when the point light source 21 is gradually moved from the origin x0 in the positive direction of the optical axis x, the radius of curvature R of the spherical surface 50 to be measured gradually decreases from infinity. Of course, on the contrary, by gradually decreasing the distance X, the distance Y may be gradually increased.

The light projecting side support 24 also operates as a distance measuring section that measures the distance (focal length r) from the focal point 51 of the spherical surface 50 to be measured to the spherical surface 50 to be measured. When the spherical surface 50 to be measured is installed at a fixed position, the distance Y0 from the collimator lens 23 on the projection side to the spherical surface 50 to be measured is known. At this time, if the distance X is measured when the light projecting side support member 24 is operated, the distance Y corresponding to the distance X can be obtained from FIG. Since the distance Y is the distance from the projection-side collimator lens 23 to the condensing point 27 (that is, the focal point 51) of the converging light 22, r=Y-Y0. Therefore, the radius of curvature R is obtained from the relationship R=2r. Distance X can be measured, for example, by outputting it as an electrical signal or by reading a scale. If the radius of curvature R is not measured, the distance Y0 is not necessary, so the spherical surface 50 to be measured may be placed at an arbitrary position instead of the fixed position.

4A and 4B are conceptual diagrams showing the principle of measuring a convex surface according to the first embodiment. FIG. 5 is a conceptual diagram showing the measurement principle of a concave surface according to the first embodiment. 4 and 5 will be added to FIGS. 1 and 2 for explanation.

FIG. 4 shows the case where the spherical surface 50 to be measured is convex. The focal point 51 and the center 52 of the spherical surface 50 to be measured are located on the optical axis "inside" the object to be measured. FIG. 4 shows a state in which the focal point 51 is aligned with the condensing point 27 . FIG. 5 shows the case where the spherical surface 60 to be measured is concave. A focus 61 and a center 62 of the spherical surface 60 to be measured are located on the optical axis "outside" the object to be measured. A center 62 is the center of a sphere whose inner surface is the spherical surface 60 to be measured. FIG. 5 shows a state in which the focal point 61 is aligned with the condensing point 27 . The convex surface and the concave surface are the same in that the spherical surfaces 50 and 60 to be measured are irradiated with the convergent light 22 so as to converge on the focal points 51 and 61 of the spherical surfaces 50 and 60 to be measured, respectively. Therefore, the convergent light 22 becomes parallel light 31 regardless of which of the spherical surfaces 50 and 60 to be measured reflects. Therefore, even when the spherical surface 60 to be measured is concave, BRDF and the like can be measured in the same way as when the spherical surface 50 to be measured is convex.

As can be seen from FIG. 4, when the convergent light 22 is reflected by the spherical surface 50 (convex surface) to be measured before condensing at the focal point 51 and becomes parallel light 31, the light flux is inverted vertically and horizontally on the plane perpendicular to the optical axis. do not do. However, as can be seen from FIG. 5, when the convergent light 22 is condensed at the focal point 61 and then reflected by the spherical surface 60 (concave surface) to be measured to become the parallel light 31, the light beam is directed to the focal point 61 on the plane perpendicular to the optical axis. is flipped vertically and horizontally. This difference can be used to determine whether the spherical surface to be measured is convex or concave. For example, a point image (chart image) may be made asymmetric with respect to a straight line perpendicular to the optical axis.

Next, the effect of the reflected light distribution measuring device 11 will be described.

(1) According to the reflected light distribution measuring apparatus 11, the surface to be measured is approximated from a curved surface to a spherical surface, and the spherical surface to be measured 50 is irradiated with the convergent light 22 so as to converge on the focal point 51 of the spherical surface to be measured 50. Since the reflected light from the spherical surface 50 to be measured becomes parallel light 31, it can be returned to a point image with high accuracy by the collimator lens 32 on the light receiving side. BRDF etc. can be measured with accuracy.

(2) If the projection-side optical system 20 has a function of freely changing the condensing point 27 where the converging light 22 converges in the optical axis direction x, the converging light 22 can also be focused on the focal point 51 located in a wide range. Since the light can be condensed, the BRDF and the like can be measured with high accuracy even for the spherical surface 50 to be measured having a wide range of focal lengths r.

(3) When the projection-side optical system 20 has a projection-side support 24 that supports at least one of the projection-side collimator lens 23 and the point light source 21 so as to be movable in the optical axis direction x, the projection-side collimator lens Since the point light source 21 can be placed at the focal position of 23, the BRDF and the like can be measured with high precision on various surfaces to be measured, from flat surfaces to curved surfaces (convex and concave surfaces). It can also be used as an autocollimator capable of measuring the angles of various surfaces to be measured, from flat surfaces to curved surfaces (convex and concave surfaces).

(4) If a rangefinder is provided to measure the distance (focal length r) from the focal point 51 of the spherical surface 50 to be measured to the spherical surface 50 to be measured, the radius of curvature R can be obtained by doubling the focal length r. Therefore, the radius of curvature R can be measured at the same time as the BRDF and the like. Moreover, the measurement of the radius of curvature R can be simplified because it is sufficient to measure half the distance compared to the case of measuring the radius of curvature R itself.

(5) If the operation of the reflected light distribution measuring apparatus 11 is regarded as a method invention, it becomes a reflected light distribution measuring method including the following steps.
A step of generating a convergent light 22 from a point image of a point light source 21 by the projection-side optical system 20 and irradiating the spherical surface 50 to be measured so that the convergent light 22 is condensed at a focal point 51 of the spherical surface 50 to be measured.
A process in which the parallel light 31 reflected by the spherical surface 50 to be measured is received by the light-receiving-side collimator lens 32 by the light-receiving-side optical system 30 and is imaged to return to a point image.
A step of measuring the light amount distribution of the imaged point image by the measurement unit 40 .
This reflected light distribution measuring method also has the same functions and effects as the reflected light distribution measuring device 11 .

<Embodiment 2>
FIG. 6 is a configuration diagram showing the reflected light distribution measuring device of the second embodiment. A description will be given below with reference to FIGS. 2 and 6. FIG. In the second embodiment, the same reference numerals are assigned to the same components as in the first embodiment, and redundant explanations are omitted.

The reflected light distribution measuring apparatus 12 of Embodiment 2 includes a measurement side support 70 that supports a measurement target spherical surface 50 so as to be movable in the optical axis direction x instead of the light projection side support 24 (FIG. 1). It is different from the first embodiment in this respect. Like the light projection side support 24 (FIG. 1), the measurement side support 70 has, for example, a stage (not shown), a feed screw, a pulse motor, and the like. can be freely changed in the optical axis direction x by a feed screw and a pulse motor. In the projection-side optical system 80 in Embodiment 2, the point light source 21 is fixed so as not to move. That is, the position of the converging point 27 of the converging light 22 is fixed. The projection-side optical system 80, like the projection-side support 24 (FIG. 1), serves as a distance measuring unit that measures the distance (focal length r) from the focal point 51 of the spherical surface 50 to be measured to the spherical surface 50 to be measured. , may work. The positive direction of the optical axis direction x is the direction in which the spherical surface 50 to be measured approaches the light projecting side optical system 80 .

Next, an example of the operation of the reflected light distribution measuring device 12 will be described. For example, the position (fixed) of the converging point 27 of the converging light 22 is defined as the origin x0, and the spherical surface 50 to be measured is set at the origin x0. In this case, when the reflected light distribution measuring device 12 is turned on, the condensing point 27 of the converging light 22 does not match the focal point 51 of the spherical surface 50 to be measured, so the reflected light from the spherical surface 50 to be measured does not become the parallel light 31. . Therefore, the spherical surface 50 to be measured is moved little by little in the optical axis direction x by the side support 70 to be measured until the half-value width of the light amount distribution measured by the two-dimensional image sensor 41 is minimized. That is, from the position where the spherical surface 50 to be measured coincides with the converging point 27 (fixed) of the converging light 22 to the position where the focal point 51 of the spherical surface 50 to be measured coincides with the converging point 27 (fixed) of the converging light 22, the The measurement spherical surface 50 is moved in the positive direction of the optical axis direction x. At this time, as shown in FIG. 5, if the spherical surface 60 to be measured is concave, the direction of movement is reversed. Since the moving distance corresponds to the focal length r, the radius of curvature R can also be obtained by doubling the focal length r. If the radius of curvature R is not measured, the moving distance (focal length r) of the spherical surface 50 to be measured does not need to be measured.

According to the reflected light distribution measuring device 12, it is not necessary to provide the projection-side optical system 80 with a function to freely change the condensing point 27 where the converging light 22 is condensed in the optical axis direction x. System 80 can be simplified. As a result, an existing autocollimator can be used for the reflected light distribution measurement device 12 with only minor modifications. Other actions and effects of the reflected light distribution measuring device 12 are the same as those of the reflected light distribution measuring device 11 (FIG. 1) of the first embodiment. The reflected light distribution measuring device 12 may be provided with both the measured side support 70 and the light projection side support 24 (FIG. 1).

<Others>
Although the present invention has been described with reference to the above embodiments, the present invention is not limited to the above embodiments. Various modifications that can be understood by those skilled in the art can be made to the configuration and details of the present invention, and such modified techniques are also included in the present invention.

11, 12 reflected light distribution measuring device 20, 80 projection side optical system 21 point light source
21a light source
21b pinhole plate 22 convergent light 23 collimator lens 24 light-projecting side support 25 aperture plate 26 half mirror 27 condensing point 30 light-receiving side optical system 31 parallel light 32 light-receiving side collimator lens 40 measuring section 41 two-dimensional image sensor 50, 60 spherical surface to be measured 51, 61 focal point 52, 62 center 70 side support to be measured x optical axis direction x0 origin r focal length R radius of curvature X, Y, Y0 distance

Claims (6)

a projection-side optical system that generates convergent light from a point image of a point light source and irradiates the spherical surface to be measured with the converged light so that the convergent light is condensed at the focal point of the spherical surface to be measured;
a light-receiving-side optical system that receives the collimated light reflected by the spherical surface to be measured by a light-receiving-side collimator lens, forms an image, and returns the collimated light to a point image;
a measurement unit that measures the light amount distribution of the formed point image;
Reflected light distribution measuring device with The light projecting side optical system has a function of freely changing the condensing point where the converging light is condensed in the optical axis direction,
The reflected light distribution measuring device according to claim 1. The projection-side optical system has a projection-side collimator lens, and a projection-side support that supports at least one of the projection-side collimator lens and the point light source movably in an optical axis direction.
The reflected light distribution measuring device according to claim 2. a support on the side to be measured that supports the spherical surface to be measured so as to be movable in the direction of the optical axis;
4. The reflected light distribution measuring device according to claim 1, further comprising a reflected light distribution measuring device. a distance measuring unit that measures the distance from the focal point of the spherical surface to be measured to the spherical surface to be measured,
5. The reflected light distribution measuring device according to claim 1, further comprising a reflected light distribution measuring device. generating convergent light from a point image of a point light source by the projection-side optical system, and irradiating the spherical surface to be measured so that the convergent light is focused on the focal point of the spherical surface to be measured;
The collimator lens receives the parallel light reflected by the spherical surface to be measured by the light-receiving-side optical system, forms an image, and returns it to a point image;
measuring the light intensity distribution of the formed point image by a measurement unit;
Reflected light distribution measurement method.

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