Optical characteristic measuring device

Abstract

The present invention comprises: a sample opening (22); a measurement opening (23); an illumination optical system for illuminating a to-be-measured position of a measurement object (100) via the sample opening; and a light-receiving optical system for condensing light to be measured reflected from the to-be-measured position to a measurement unit, wherein either the illumination optical system or the light-receiving optical system includes a colorimeter (2) that is an optical system of diffused light reception or diffused illumination using an integrating sphere (21). In addition to the sample opening (22) and the measurement opening (23), a third opening (26) is provided in the integrating sphere (21). An angle ω formed by a line G2 connecting the center of the third opening (26) and the center of the measurement object (100), and a regular reflection direction G1 of the measurement object (100) with respect to an optical axis G3 of another optical system which is not the optical system using the integrating sphere (21) satisfies 15°<ω.

Description

Optical property measuring device

[0001] The present invention relates to an optical characteristic measuring device that includes an integrating sphere and measures optical characteristics such as the color of an object to be measured.

[0002] When measuring color, for example, with an optical property measuring device, the spectral reflectance of some measurement objects can change with temperature, and differences in the measurement environment can result in measurement errors. When measuring such objects whose spectral reflectance changes with temperature, it is necessary to investigate in advance how the spectral reflectance changes with temperature, measure the temperature of the measurement object during measurement, and correct for the change in spectral reflectance due to temperature.

[0003] However, in production processes where the color of products is controlled by a colorimeter, measuring temperature in addition to color measurement is undesirable because it complicates the work process and increases the amount of work required. For this reason, there is a demand for a colorimeter that can measure temperature in addition to measuring color.

[0004] Patent Documents 1 and 2 disclose a technique in which a radiation thermometer is used to measure the surface temperature of an object to be measured together with the color of the object, and the measured value of the color of the object is corrected based on the measured temperature.

[0005] JP 2000-88651 A JP 2004-510154 A

[0006] In the method of Patent Document 1, a single measuring device is equipped with the functions of measuring both color and temperature, but the color measurement area and the temperature measurement area on the surface of the object to be measured do not coincide, and the measured temperature may differ from the temperature in the color measurement area.

[0007] Patent Document 2 describes an apparatus that can measure the color of a surface of a measurement object at multiple measurement angles and measure the temperature at the same position using a radiation thermometer. In the apparatus described in Patent Document 2, color measurement is performed by illuminating the object at a 45° angle relative to the axis of the measurement head and receiving reflected light from the object at multiple angles. In a measuring instrument with this geometric arrangement, the optical path of the measurement light is limited, so it is easy to position the radiation thermometer outside of that optical path.

[0008] On the other hand, in the case of a colorimeter that uses diffuse illumination (or diffuse light reception) with a general integrating sphere, the area around the object to be measured is large and is in the optical path of the illumination light, so when placing a radiation thermometer, it is not easy to position it so as to avoid the optical path of the illumination light.

[0009] In an optical property measuring device using an integrating sphere, an opening is provided in the integrating sphere and a radiation thermometer is placed in this opening. In order to suppress the influence of the radiation thermometer on color measurement, the position of the opening in the integrating sphere is important.

[0010] This is an issue that should be considered not only in radiation thermometers, but also in cases where a camera for observing the object to be measured is placed in an opening in an integrating sphere, for example.

[0011] An object of the present invention is to provide an optical characteristic measuring device in which an opening for arranging a radiation thermometer or for observing a measurement target is formed in an integrating sphere in a state in which the influence on the measurement of optical characteristics is suppressed.

[0012] The above object is achieved by the following means: [1] An optical property measuring device comprising: an integrating sphere having a sample aperture and a measurement aperture, an illumination optical system that illuminates a position to be measured on a measurement object through the sample aperture, and a light-receiving optical system that focuses the light to be measured reflected from the position to be measured onto a measurement unit, wherein one of the illumination optical system and the light-receiving optical system is an optical system for diffuse illumination or diffuse light-receiving using the integrating sphere, and a third aperture is provided in the integrating sphere in addition to the sample aperture and the measurement aperture, and the angle ω formed by a line connecting the center of the third aperture and the center of the measurement object and the direction of specular reflection of the measurement object relative to the optical axis of the other optical system that is not the optical system using the integrating sphere satisfies formula (1). 15°<ω (1) [2] The optical property measuring device according to the preceding paragraph 1, wherein one of the illumination optical system and the light-receiving optical system is a diffuse illumination optical system using the integrating sphere or a diffuse light-receiving optical system, and the other is an illumination optical system that illuminates the object through the measurement aperture with light at an angle φ within ±5° relative to the normal to the object, or a light-receiving optical system that receives reflected light through the measurement aperture at an angle φ within ±5° relative to the normal to the object, where φ satisfies formula (2). 0°<φ<10° (2) [3] The optical property measuring device according to the preceding paragraph 1 or 2, wherein a radiation thermometer is disposed outside the third aperture. [4] The optical property measuring device according to the preceding paragraph 3, wherein the radiation thermometer has a field of view of at least one measurement region within 15°. [5] The optical property measuring device according to the preceding paragraph 3, wherein the radiation thermometer measures the object at an angle of 45° or less from the normal to the object surface. [6] The optical property measuring device according to the preceding paragraph 3, wherein, when the diameter of the integrating sphere is R, the distance L from the center of the object to be measured to the radiation thermometer satisfies formula (3): 0.7 < L / R < 1.5 (3) [7] The optical property measuring device according to the preceding paragraph 1 or 2, wherein, when the internal area of ​​the integrating sphere when considered as a perfect sphere is S, the area A of the third opening satisfies formula (4): A / S < 0.01 (4) [8] The optical property measuring device according to the preceding paragraph 1 or 2, wherein the third opening is an observation opening for observing the position to be measured. [9] The optical property measuring device according to the preceding paragraph 8, wherein a camera is disposed outside the observation opening.

[0013] In the optical property measuring device according to the present invention, either the illumination optical system or the light-receiving optical system is an optical system using an integrating sphere for diffuse illumination or diffuse light-receiving. This optical property measuring device is capable of performing measurements under conditions similar to those of ordinary indoor lighting, thereby obtaining measurements highly correlated with visual observation when measuring the color, etc., of various measurement objects. The integrating sphere has a sample aperture and a measurement aperture. In addition to the sample aperture and the measurement aperture, the integrating sphere is provided with a third aperture, for example, for arranging a radiation thermometer or for observing the measurement object. The angle ω between the line connecting the center of this third aperture and the center of the measurement object and the direction of specular reflection of the measurement object relative to the optical axis of the light-receiving optical system or the illumination optical system satisfies equation (1), 15°<ω. Surfaces with various reflective properties are expected as measurement objects. Generally, smooth surfaces have the strongest reflection in the specular reflection direction, and as the surface condition becomes rougher, the distribution of reflection intensity spreads around the specular reflection direction. Therefore, the luminance of the inner wall of the integrating sphere near the position (specular reflection position) where light along the optical axis of the optical system not using an integrating sphere is specularly reflected by the object to be measured and reaches the integrating sphere has a large effect on the measurement value, while the luminance of a position far from the specular reflection position has a small effect on the measurement value. In other words, by satisfying formula (1), the third aperture can be sufficiently separated from the position of specularly reflected light from the object to be measured (specular reflection position), and the effect of the third aperture on the measurement can be kept small.

[0014] FIG. 1 is a diagram showing a schematic configuration of an optical property measuring device according to a first embodiment of the present invention. FIG. 3A is a perspective view of the optical property measuring device shown in a see-through state of the integrating sphere. FIG. 3A is a diagram showing the positional relationship between the radiation thermometer, the integrating sphere, and the measurement object in the optical property measuring device of FIGS. 1 and 2, as seen from a cross section passing through the center of the integrating sphere. FIG. 3B is a cross section perpendicular to the cross section. FIG. 4A is a diagram showing a cross section including the direction of the light-receiving optical system and the specular reflection direction in the optical property measuring device of FIGS. 1 and 2, and FIG. 4B is a cross section perpendicular to the cross section. FIG. 4A is a perspective view of an optical property measuring device according to a second embodiment of the present invention, shown in a see-through state of the integrating sphere. FIG. 7A to 7C are perspective views showing how light collected by the light-receiving optical system changes depending on the reflection characteristics of the measurement object. Graphs illustrating the reflection angle characteristics of the measurement object for 0° incident light. FIG. 10A shows the illuminance distribution on a cubic diagram of an integrating sphere obtained by ray tracing from the spectrometer side for a measurement target having a reflection angle characteristic for 0° incident light, as shown in FIG. 8. FIG. 10A is a diagram of the illuminance distribution of FIG. 9 plotted with the angle from the center of the measurement target as the vertical and horizontal axes. FIG. 10B is a graph showing the radiant intensity for each angle along a horizontal line passing through the position of the specular reflection direction of the measurement target in the image of FIG. 10A. FIG. 10C is a graph showing the radiant intensity for each angle along a vertical line passing through the position of the specular reflection direction of the measurement target in the image of FIG. 10A. FIG. 10D is a diagram showing the relationship between the degree of shading and radiant intensity in FIG. 10A. FIG. 11A is a diagram plotted with the angle from the center of the measurement target as the vertical and horizontal axes. FIG. 11B is a graph showing the radiant intensity for each angle along a horizontal line passing through the center of the circular region S2 corresponding to the temperature measurement aperture in the image of FIG. 11A. FIG. 11C is a graph showing the radiant intensity for each angle along a vertical line passing through the center of the circular region S2 in the image of FIG. 11A. FIG. 11D is a diagram showing the relationship between the degree of shading in FIG. 11A and the radiation intensity.

[0015] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0016] First Embodiment FIG. 1 is a diagram showing a schematic configuration of an optical characteristic measuring apparatus 1 according to one embodiment of the present invention, and FIG. 2 is a perspective view of the optical characteristic measuring apparatus 1 seen through an integrating sphere.

[0017] As shown in FIGS. 1 and 2, this optical property measuring device 1 has a radiation thermometer 3 mounted on a d:8 geometry colorimeter 2, and can measure both the color and surface temperature of a measurement object 100.

[0018] The colorimeter 2 includes an integrating sphere 21, and a sample opening 22 is formed at the bottom of the integrating sphere 21. A measurement target 100 is placed in the sample opening 22 via a target mask 4. Note that the target mask 4 is omitted in FIG. 2 .

[0019] A measurement aperture 23 is formed above the integrating sphere 21 at an angle of 8° relative to the normal to the measurement target 100 placed in the sample aperture 22. A light-receiving optical system including a light-receiving lens 24 and a measurement unit including a spectroscope 25 are arranged on a line connecting the measurement target 100 and the measurement aperture 23. That is, the light-receiving optical system receives reflected light centered at φ=8° from the normal to the measurement target. The divergence angle of the received reflected light is within 5°. Note that the angle φ relative to the normal to the measurement target is not limited to 8°, and is preferably 0°<φ<10° (Equation (2)). The light-receiving optical system preferably receives reflected light within φ±5°.

[0020] A temperature measurement opening 26, which is a third opening, is formed in the integrating sphere 21 on the opposite side of the measurement opening 23 with respect to the normal to the measurement object 100, and the radiation thermometer 3 is disposed outside the temperature measurement opening 26. The position of the temperature measurement opening 26 will be described in detail later.

[0021] Furthermore, an illumination opening 27 is formed at the midpoint in the height direction of the integrating sphere 21 on the same side as the measurement opening 23 with respect to the normal to the measurement object 100, and an illumination light source 28 is arranged outside this illumination opening 27.

[0022] A first light-shielding plate 29 is formed inside integrating sphere 21 at a position between illumination opening 27 and sample opening 23 to prevent illumination light from light source 28 from directly entering measurement opening 23. Similarly, a second light-shielding plate 30 is formed inside integrating sphere 21 at a position between illumination opening 27 and sample opening 22 to prevent illumination light from light source 28 from directly irradiating measurement object 100 facing sample opening 22.

[0023] Light source 28 irradiates the inner surface of integrating sphere 21 through illumination aperture 27, and the diffused light diffused by the inner surface of integrating sphere 21 illuminates the measurement position of measurement object 100 facing sample aperture 22. Therefore, in this embodiment, light source 28, the inner surface of integrating sphere 21, etc. constitute an illumination optical system. A light-receiving optical system including light-receiving lens 24 receives the measurement light, which is the diffused light illuminating measurement object 100 and reflected from the measurement position of measurement object 100, through measurement aperture 23. Specifically, the measurement light, which is the reflected light from the measurement position of measurement object 100, is received by the light-receiving optical system and focused on spectroscope 25, which then disperses the light and measures the reflectance of the measurement object for each wavelength. The measurement results are displayed on a display panel (not shown) or the like of optical property measuring device 1.

[0024] Target mask 4 is attached to a hole opened in integrating sphere 21, and measurement target 100 is placed in contact with sample opening 22 corresponding to the hole opened in target mask 4 from the outside, and is used for measurement. Radiation thermometer 3 is placed outside temperature measurement opening 26, and measures the temperature of measurement target 100 from outside integrating sphere 21 through temperature measurement opening 26.

[0025] As shown in Figure 2, the line connecting the center of the temperature measurement opening 26 and the center P1 of the measurement object 100 (sample opening 22) is designated as G2. This line G2 is the same as the measurement direction of the radiation thermometer 3 and is also the optical axis of the radiation thermometer 3. For this reason, in the following description, the measurement direction and optical axis of the radiation thermometer 3 will also be referred to as G2. Furthermore, the line connecting the center P1 of the measurement object 100 and the center of the measurement opening 23, in other words, the optical axis of the light-receiving optical system including the light-receiving lens 24, is designated as G3. Furthermore, the direction of specular reflection of the measurement object 100 relative to the optical axis G3 of the light-receiving optical system is designated as G1.

[0026] In this embodiment, the temperature measurement opening 26 needs to be formed at a position where the angle ω between the measurement direction G2 of the radiation thermometer 3 and the specular reflection direction G1 of the measurement object 100 satisfies 15°<ω (Equation (1)). The reason for this is as follows.

[0027] That is, the colorimeter 2 having an optical system for diffused illumination using the integrating sphere 21 can perform measurements under conditions similar to those of general indoor lighting, making it easier to obtain visual correlation when measuring the colors of various objects. When the angle ω between the measurement direction G2 of the radiation thermometer 3 and the specular reflection direction G1 of the measurement target 100 satisfies the above formula (1), the temperature measurement opening 26 can be sufficiently separated from the specular reflection position P2 of the integrating sphere 21. This minimizes the effect of the temperature measurement opening 26 on color measurement, and ultimately minimizes the effect on measurement even when the radiation thermometer 3 is placed at the temperature measurement opening 26. Preferably, 20°<ω, and even more preferably, 25°<ω.

[0028] 2, the arrow x displayed on the measurement target 100 indicates the direction of a plane including the optical axis G3 of the light-receiving optical system and the specular reflection direction G1. The arrow y indicates the direction of the normal to the center P1 of the measurement target 100 (the center of the sample opening 22). The arrow z indicates the direction perpendicular to the arrows x and y.

[0029] In this embodiment, the diameter R of the integrating sphere 21 is 150 mm, the distance L from the radiation thermometer 3 to the center P1 of the measurement object 100 is 150 mm, and the viewing angle of the radiation thermometer 3 is 6°. The diameter R of the integrating sphere 21 and the distance L from the radiation thermometer 3 to the center P1 of the measurement object 100 are preferably set to satisfy 0.7 < L / R < 1.5...Equation (3). Exceeding the lower limit of Equation (3) ensures a sufficient distance from the measurement object 100, allowing the radiation thermometer 3 to be positioned away from the optical system of the colorimeter 2. Furthermore, falling below the upper limit avoids problems such as the radiation thermometer 3 being too far from the measurement object 100, resulting in an increase in size of the optical property measuring device 1, or the measurement area of ​​the radiation thermometer 3 being so wide that it measures temperatures other than those of the measurement object 100. In this embodiment, as described above, R is 150 mm and L is 150 mm, so L / R = 1, thereby satisfying Equation (3). Preferably, 0.75<L / R<1.3, and more preferably, 0.80<L / R<1.1.

[0030] Furthermore, it is desirable that the viewing angle of the radiation thermometer 3 be within 15°. The radiation thermometer 3 measures the average temperature within the viewing angle. To position the radiation thermometer 3 without interfering with the illumination optical system and light-receiving optical system of the colorimeter 2, it must be positioned at a certain distance from the measurement target 100. However, if a radiation thermometer 3 with a wide viewing angle is placed farther away from the measurement target 100, the field of view on the measurement target surface will be too wide, resulting in the measurement of an average temperature that includes areas other than the desired measurement location. By using a radiation thermometer 3 with a narrow field of view, the field of view does not become too wide even when the radiation thermometer 3 is placed farther away from the measurement target 100, allowing for accurate measurement of the temperature of the measurement area for color measurement. If the radiation thermometer 3 has multiple pixels and can measure multiple measurement areas, it is sufficient that the viewing angle of at least one measurement area is within 15°.

[0031] In this embodiment, the optical axis G2 of the radiation thermometer 3 is directed toward the center P1 of the object to be measured 100, and the angle between the optical axis G2 of the radiation thermometer 3 and the normal to the object to be measured 100 is 30°. In this arrangement, the measurement area of ​​the radiation thermometer 3 on the measurement surface of the object to be measured 100 is an ellipse measuring approximately 15.7 × 18.2 mm. This is shown in Figures 3A and 3B. Figure 3A is a diagram showing the positional relationship between the radiation thermometer 3, integrating sphere 21, and object to be measured 100 as seen from a cross section passing through the center of the integrating sphere 21, and Figure 3B is a diagram of a cross section perpendicular to that cross section.

[0032] It is preferable to set the angle between the optical axis G2 of the radiation thermometer 3 and the normal to the measurement object 100 to within 45°. In other words, it is preferable for the radiation thermometer 3 to measure the measurement object 100 at an angle of 45° or less from the normal to the measurement object surface. If the radiation thermometer 3 measures from a direction tilted by more than 45° from the normal to the measurement object surface, the measured value may be affected by the temperature of a different location due to surface reflection of the measurement object 100. By measuring at an angle close to perpendicular to the measurement object, within 45°, surface reflection is reduced, allowing for accurate temperature measurement.

[0033] On the other hand, the colorimeter 2 has a measurement diameter of 25.4 mm, and the center of the measurement area of ​​the colorimeter 2 and the measurement center of the radiation thermometer 3 are both aligned with the center P of the measurement object 100, with their measurement areas overlapping. With this arrangement, the measurement area of ​​the radiation thermometer 3 is smaller than the measurement area of ​​the colorimeter 2, so the measurement value does not include the temperature of parts other than the measurement object 100.

[0034] The diameter of the temperature measurement opening 26 in the integrating sphere 21 is set to Φ16 mm. The reason for this size is to prevent the outer wall of the integrating sphere 21 from entering the field of view of the radiation thermometer 3 due to an installation error of the radiation thermometer 3. The inner area S of the integrating sphere 21 is 4π×75 ２ mm 2 The opening area A of the temperature measurement opening 26 is π×8 2 mm 2 Therefore, A / S ≒ 0.00284.

[0035] In this embodiment, it is preferable to set A / S to satisfy A / S<0.01...Equation (4). By reducing the area of ​​the temperature measurement opening 26 so as to satisfy Equation (4), it is possible to minimize the effect of the temperature measurement opening 26 on color measurement. It is preferable to set A / S<0.0075, and even more preferable to set A / S<0.005.

[0036] 4A and 4B show the relationship between the light-receiving optical system of the colorimeter 2 and the measurement angle of the radiation thermometer 3. As described above, the colorimeter 2 according to this embodiment is a colorimeter with d:8 geometry. Therefore, the light-receiving optical system receives the light to be measured from a direction at an angle of 8° with respect to the normal to the measurement surface of the measurement object 100. The specular reflection direction G1 is symmetric with respect to the optical axis G3 of the light-receiving optical system and the normal to the measurement surface.

[0037] 4A shows a cross section including the optical axis G3 of the light-receiving optical system and the specular reflection direction G1, and FIG. 4B shows a cross section perpendicular to the cross section. In each cross section, the specular reflection direction G1 and the measurement direction G2 of the radiation thermometer 3 form an angle of 30° and 8°, respectively. However, within a plane including the specular reflection direction G1 and the measurement direction G2 of the radiation thermometer 3, the angle ω between the specular reflection direction G1 and the measurement direction G2 of the radiation thermometer 3 is approximately 30.95°, which satisfies the above-mentioned formula (1) 15°<ω.

[0038] Second Embodiment FIG. 5 shows an optical characteristic measuring apparatus 1 according to a second embodiment, and is a perspective view of the optical characteristic measuring apparatus 1 with an integrating sphere 21 seen through.

[0039] The basic configuration of the optical characteristic measuring device 1 is the same as that of the first embodiment.

[0040] The diameter R of the integrating sphere is 150 mm, the distance L from the radiation thermometer 3 to the center P1 of the measurement object 100 is 130 mm, and the field of view angle of the radiation thermometer 3 is 12°. L / R ≈ 0.86, satisfying the above-mentioned formula (3). The optical axis G2 of the radiation thermometer 3 is directed toward the center P1 of the measurement object 100, and the angle between the optical axis G2 and the normal to the measurement object 100 is 33.23°. In this arrangement, the measurement area of ​​the radiation thermometer 3 on the surface of the measurement object is an ellipse measuring approximately 27.3 × 32.7 mm.

[0041] On the other hand, the colorimeter 2 has a measurement diameter of 25.4 mm, and the center of the measurement area of ​​the colorimeter 2 and the measurement center of the radiation thermometer 3 are both aligned with the center P1 of the measurement object 100, with their measurement areas overlapping. In this arrangement, the measurement area of ​​the radiation thermometer 3 is larger than that of the colorimeter 2, but the measurement area of ​​the colorimeter 3 occupies the majority (approximately 72%) and has little effect on the measurement values ​​of other parts.

[0042] The diameter of the temperature measurement opening 26 in the integrating sphere 21 was Φ8 mm. The inner area S of the integrating sphere 21 was 4π×75 ２ mm 2 , the area A of the temperature measurement opening 26 is π×4 2 mm 2 Therefore, A / S ≈ 0.00071 < 0.01, which satisfies A / S < 0.01 in equation (4).

[0043] In a plane including the specular reflection direction G1 of the light receiving optical system and the measurement direction G2 of the radiation thermometer 3, the angle ω formed by the specular reflection direction G1 and the measurement direction G2 is approximately 37.59°, which satisfies 15°<ω in equation (1).

[0044] Third Embodiment FIG. 6 shows an optical characteristic measuring apparatus 1 according to a third embodiment, and is a perspective view of the optical characteristic measuring apparatus 1 with an integrating sphere 21 seen through.

[0045] The basic configuration is the same as that of the first embodiment.

[0046] The integrating sphere 21 has a diameter of 150 mm, and the distance L from the radiation thermometer 3 to the center of the object 100 is 160 mm. The radiation thermometer 3 is capable of measuring in-plane distribution by dividing the measurement area into a grid pattern, and the field of view per pixel is 2°. L / R is approximately 1.067, satisfying the aforementioned equation (3). The optical axis G2 of the radiation thermometer 3 is directed toward the center P1 of the sample opening 22, and the angle between the optical axis G2 and the normal to the object 100 is 17°. In this arrangement, the measurement area of ​​one pixel of the radiation thermometer 3 on the measurement surface of the object 100 is a rectangle measuring approximately 5.6 × 5.8 mm.

[0047] On the other hand, the colorimeter 2 has a measurement diameter of 8 mm, and the center of the measurement area of ​​the colorimeter 2 and the measurement center of the radiation thermometer 3 are both aligned with the center P1 of the measurement object 100, with their measurement areas overlapping. In this arrangement, the measurement area of ​​one pixel of the radiation thermometer 3 is smaller than the measurement area of ​​the colorimeter 2, so by selecting the pixel value of the measurement area that coincides with the measurement area of ​​the colorimeter system, it is possible to measure the temperature of only the color measurement area.

[0048] The size of the temperature measurement opening 26 in the integrating sphere 21 was Φ8 mm. The inner area S of the integrating sphere 21 was 4π×75 ２ mm 2 , the opening area A of the temperature measurement opening 26 is π×4 2 mm 2 Therefore, A / S ≈ 0.00071 < 0.01, which satisfies A / S < 0.01 in equation (4).

[0049] In the plane including the specular reflection direction G1 of the light receiving optical system and the measurement direction G2 of the radiation thermometer 3, the angle ω between the specular reflection direction G1 and the measurement direction G2 is approximately 18.74°, which satisfies 15°<ω in equation (1).

[0050] The values ​​of ω, φ, L / R, A / S, and the measurement angle of the radiation thermometer 3 in each of the above-described first to third embodiments are summarized in Table 1 below.

[0051]

[0052] As described above, the angle ω formed by the specular reflection direction G1 and the measurement direction G2 of the radiation thermometer 3 within a plane including the specular reflection direction G1 and the measurement direction G2 of the radiation thermometer 3 must satisfy the expression (1), 15°<ω. That is, by satisfying the expression (1), the temperature measurement opening 26 can be sufficiently separated from the specular reflection position P2, thereby minimizing the effect of the temperature measurement opening 26 on color measurement. This effect will be explained in more detail below.

[0053] The light collected by the light-receiving optical system including the light-receiving lens 24 onto the spectroscope 25 is light coming from a position reached by ray tracing from the spectroscope 25 back toward the light-receiving optical system (reverse propagation of light rays). In the case of a measurement object 100 that is smooth and does not diffusely reflect, such as a mirror, the collected light is light coming from the periphery of the integrating sphere wall at a position (specular reflection position) symmetrical to the optical axis of the light-receiving optical system with respect to the normal to the measurement object 100, as shown in FIG. 7A. On the other hand, in the case of a measurement object 100 that has a perfectly diffuse reflecting surface, as shown in FIG. 7B, the collected light is light from the entire integrating sphere 21. Furthermore, in the case of a measurement object 100 that has a diffusivity between a smooth surface that does not diffusely reflect and a perfectly diffuse reflecting surface, light is collected from a range corresponding to the diffusivity, centered on the specular reflection position, as shown in FIG. 7C.

[0054] For example, in the case of a measurement target 100 having a reflection angle characteristic for 0° incident light as shown in Fig. 8, the illuminance distribution on the three-dimensional diagram of integrating sphere 21 obtained by ray tracing from the spectroscope 25 side is as shown in Fig. 9. In Fig. 8, the horizontal axis represents the reflection angle, and the vertical axis represents the normalized reflection intensity.

[0055] Due to the regressive nature of light rays, this illuminance distribution is equivalent to the distribution of light collected by the light-receiving optical system on the integrating sphere 21. In the illuminance distribution in Fig. 9, the illuminance is greatest at position P2 in the specular reflection direction of the object to be measured, and decreases with increasing distance from position P2 in the specular reflection direction.

[0056] Figure 10A is a diagram of the illuminance distribution in Figure 9, plotted with the angle from the center of the measurement target 100 on the vertical and horizontal axes. The shading in the diagram represents the magnitude of the radiant intensity, and the relationship between the degree of shading and the radiant intensity is shown in Figure 10D. P2 in Figure 10A is the position in the specular reflection direction of the measurement target 100, and the circular region centered at position P2 has the greatest radiant intensity. The circular region S1 shown in Figure 10A corresponds to the sample aperture 23.

[0057] Fig. 10B is a graph showing the radiation intensity for each angle along a horizontal line passing through position P2 in the specular reflection direction of measurement target 100 in the image of Fig. 10A. Fig. 10C is a graph showing the radiation intensity for each angle along a vertical line passing through position P2 in the specular reflection direction of measurement target 100 in the image of Fig. 10A. The distortion in the graph of Fig. 10B is due to the influence of measurement aperture 23.

[0058] 8, if the temperature measurement opening 26 is located near the position P2 in the specular reflection direction, the illumination light from that direction will escape. This reduces the amount of light received, resulting in an error compared to the measurement value under ideal illumination.

[0059] When measuring a measurement object 100 having the reflection angle characteristics shown in Figure 8 using the optical characteristic measuring device of embodiment 3, the illuminance distribution on the integrating sphere 21 of the light collected by the light receiving optical system will be as shown in Figures 11A to 11C.

[0060] Figure 11A is a diagram plotted with the angle from the center of the measurement target 100 on the vertical and horizontal axes. The shading in the diagram represents the magnitude of the radiation intensity, and the relationship between the degree of shading and the radiation intensity is shown in Figure 11D. P2 in Figure 11A is the position in the specular reflection direction of the measurement target 100, and the circular region centered at position P2 has the greatest radiation intensity. The circular region S1 shown in Figure 11A corresponds to the sample aperture 23, and the circular region S2 surrounded by a black line corresponds to the temperature measurement aperture 26.

[0061] Fig. 11B is a graph showing radiation intensity for each angle along a horizontal line passing through the center of the circular region S2 corresponding to the temperature measurement opening 26 in the image of Fig. 11A. Fig. 11C is a graph showing radiation intensity for each angle along a vertical line passing through the center of the circular region S2 corresponding to the temperature measurement opening 26 in the image of Fig. 11A. The small steps in the middle of the graphs of Fig. 11B and Fig. 11C are parts affected by the temperature measurement opening 26.

[0062] Simulation results showed that the measured value was 0.27% smaller than that in the case of ideal lighting (without the temperature measurement opening 26). The smaller the difference in the measured value from that in the case of ideal lighting for the measurement target 100 with such characteristics, the better, but if it is within 0.3%, it can be ignored.

[0063] On the other hand, when the temperature measurement opening 26 having the same opening size as in Example 3 is provided at a position of ω=14.4°, the measured value is 0.35% smaller, and the difference in the measured value is not negligible.

[0064] The difference in measurement value from this ideal illumination becomes larger as the temperature measurement aperture 26 approaches the specular reflection position P2, so the difference can be kept small by satisfying the condition ω>15°.

[0065] Other Embodiments In the above description, the third opening 26 is a temperature measurement opening in which a radiation thermometer is disposed. However, the third opening 26 may be a multipurpose opening that can be used for multiple purposes. For example, the third opening 26 may be an opening for observing a measurement target, and an optical property measurement device in which a camera is disposed outside the third opening 26 may be used.

[0066] However, even in this case, the third aperture 26 must be formed at a position where the angle ω formed by the line G2 connecting the center of the third aperture 26 to the center P1 of the measurement object (sample aperture) 100 and the specular reflection direction G1 of the measurement object relative to the optical axis G3 of the light-receiving optical system satisfies 15°<ω. By satisfying this condition, the third aperture 26 can be sufficiently separated from the specular reflection position P2. Therefore, the influence of the third aperture 26 on color measurement can be minimized, and even if a camera is placed at the third aperture 26, the influence on the measurement can be suppressed. Again, it is preferable that the angle ω be 20°<ω, and even more preferable that the angle ω be 25°<ω.

[0067] The optical property measuring device 1 has been described in which the integrating sphere 21 has the function of diffusing illumination light from the light source 28 and irradiating it onto the measurement target 100, in other words, the integrating sphere 21 forms the illumination optical system. However, the light-receiving optical system and the illumination optical system may be reversed. That is, the present invention may also be applied to an optical property measuring device that directly irradiates the measurement target 100 with light and measures the diffused light that is received and diffused by the inner surface of the integrating sphere 21, in other words, an optical property measuring device in which the integrating sphere forms the light-receiving optical system. In short, any optical property measuring device may be used in which the integrating sphere 21 is used in at least one of the illumination optical system and the light-receiving optical system.

[0068] This application claims priority from Japanese Patent Application No. 2024-134373, filed on August 9, 2024, the disclosure of which is incorporated herein by reference in its entirety.

[0069] The present invention can be used in an optical characteristic measuring device that measures optical characteristics such as the color of an object to be measured.

[0070] REFERENCE SIGNS LIST 1 Optical property measuring device 2 Colorimeter 3 Radiation thermometer 4 Target mask 21 Integrating sphere 22 Sample aperture 23 Measurement aperture 24 Light receiving lens 25 Spectrometer 26 Temperature measurement aperture (third aperture) 27 Illumination aperture 28 Light source 29 First light shielding plate 30 Second light shielding plate 100 Measurement object

Claims

1. An optical property measuring device comprising: an integrating sphere having a sample aperture and a measurement aperture; an illumination optical system that illuminates a position to be measured on a measurement object through said sample aperture; and a light-receiving optical system that focuses the light to be measured reflected from said position to a measurement unit, wherein one of said illumination optical system or light-receiving optical system is an optical system for diffuse illumination using said integrating sphere or diffuse light-receiving, said integrating sphere is provided with a third aperture in addition to said sample aperture and said measurement aperture, and the angle ω formed by the line connecting the center of said third aperture and the center of the measurement object and the direction of specular reflection of the measurement object relative to the optical axis of the other optical system that is not an optical system using said integrating sphere satisfies formula (1): 15°<ω (1) 2. The optical characteristic measuring device according to claim 1, wherein one of the illumination optical system and the light receiving optical system is a diffuse illumination or diffuse light receiving optical system using the integrating sphere, and the other is an illumination optical system that illuminates the object through the measurement aperture with light at an angle φ within ±5° relative to the normal to the object, or a light receiving optical system that receives reflected light through the measurement aperture at an angle φ within ±5° relative to the normal to the object, where φ satisfies formula (2): 0°<φ<10° ... (2) 3. An optical characteristic measuring device according to claim 1 or 2, wherein a radiation thermometer is disposed outside the third opening.

4. The optical characteristic measuring device according to claim 3, wherein the radiation thermometer has at least one measurement area with a viewing angle of 15° or less.

5. The optical characteristic measuring device according to claim 3, wherein the radiation thermometer measures the object at an angle of 45° or less from the normal to the surface of the object.

6. The optical characteristic measuring device according to claim 3, wherein when the diameter of the integrating sphere is R, the distance L from the center of the measurement object to the radiation thermometer satisfies the following formula (3): 0.7<L / R<1.5 (3) 7. The optical characteristic measuring device according to claim 1 or 2, wherein the area A of the third opening satisfies formula [4], where S is the internal area of ​​the integrating sphere when considered as a perfect sphere: A / S<0.01 (4).

8. An optical characteristic measuring device according to claim 1 or 2, wherein the third opening is an observation opening for observing the position to be measured.

9. The optical characteristic measuring device according to claim 8, wherein a camera is disposed outside the observation opening.

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