A method and apparatus for measuring diffuse reflectance of a material surface

Abstract

The application provides a material surface diffuse reflectivity measuring method and device, and belongs to the technical field of material reflectivity testing.The device comprises an integrating sphere, an integrating sphere inner wall coating backfill module, a measured material backfill module, a light trap and a luxmeter.The integrating sphere comprises a light inlet and another opening.Illumination light is incident from the light inlet of the integrating sphere.The light receiving areas of the integrating sphere inner wall coating backfill module, the measured material backfill module and the light trap are matched with the other opening.The luxmeter is arranged on the inner wall of the integrating sphere, and the position of the luxmeter is away from the positions of the light inlet and the other opening.The material surface diffuse reflectivity is measured by using the integrating sphere, the light trap and other tools through a direct measurement method, without the aid of a standard reflector plate which needs to be calibrated in advance for diffuse reflectivity.Meanwhile, parameters such as the diffuse reflectivity of the inner wall of the integrating sphere and the brightness value of the illumination light source do not need to be measured.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of material reflectivity testing, and particularly relates to a material surface diffuse reflectivity measurement method and device. BACKGROUND

[0002] Diffuse reflectivity can be used to characterize the properties of materials. In the fields of physical science, industrial and agricultural production, aerospace, aviation, military weapons and equipment, there is a demand for measuring the diffuse reflectivity of surface-coated materials such as paint, pigment, film, and other types of materials.

[0003] Generally, the method of measuring the diffuse reflectivity of the material surface by using an integrating sphere 1 needs to use a standard reflector as a reference, and the diffuse reflectivity of the standard reflector is calibrated in advance by other means, and then the diffuse reflectivity of the measured material is obtained by indirect measurement. For example, a diffuse reflectance spectrum measurement device based on an integrating sphere 1 is proposed by Li Chenxi et al. in Chinese patent publication CN108827918A, and a material mirror reflectivity and diffuse reflectivity simultaneous measurement method based on an integrating sphere 1 is proposed by Zhang Xiaolong et al. in Chinese patent publication CN104833656A. These methods also require controlling the incident light beam to be fully irradiated on the measured sample / standard reflector, which is difficult to operate, and the calibration value of the standard reflector will introduce measurement error. SUMMARY

[0004] To solve the above technical problems, the first aspect of the present application proposes a material surface diffuse reflectivity measurement device, which comprises an integrating sphere, an integrating sphere inner wall coating backfill module, a measured material backfill module, a light trap and an illuminometer.

[0005] The integrating sphere comprises a first area of light inlet, a third area of another opening, and an incident illumination light from the light inlet of the integrating sphere,

[0006] The light receiving areas of the integrating sphere inner wall coating backfill module, the measured material backfill module and the light trap are matched with the other opening;

[0007] The illuminometer is arranged on the inner wall of the integrating sphere, and the position of the illuminometer is away from the positions of the light inlet and the other opening.

[0008] As described in the first aspect of the present application, the coating on the inner wall of the integrating sphere inner wall coating backfill module is the same as the coating on the inner wall of the integrating sphere, and has the same diffuse reflectivity, and the inner wall circular arc surface of the integrating sphere inner wall coating backfill module and the inner wall of the integrating sphere form a unified spherical surface.

[0009] As described in the first aspect of the present application, the inner wall of the measured material backfill module is coated with a measured material, the diffuse reflectivity of which is unknown, and the inner wall circular arc surface of the measured material backfill module and the inner wall of the integrating sphere form a unified spherical surface.

[0010] The device according to the first aspect of the present application, the inner wall coating backfill module of the integrating sphere, the measured material backfill module and the light trap are used to be placed in the other opening in turn during the measurement of the diffuse reflectivity of the material surface; and the illuminance values when the inner wall coating backfill module of the integrating sphere, the measured material backfill module and the light trap are placed in the other opening respectively are read by using the luxmeter.

[0011] The second aspect of the present application provides a method for measuring the diffuse reflectivity of the material surface, which comprises the following steps:

[0012] Step 1, calculating the opening ratio and the backfill ratio according to the first area of the light inlet and the third area of the other opening;

[0013] Step 2, the incident light beam is incident to the inside of the integrating sphere through the light inlet of the first area, and the diffuse reflection is generated;

[0014] Step 3, placing the inner wall coating backfill module of the integrating sphere, the light trap and the measured material backfill module in the other opening in turn, and reading the light readings of the luxmeter when the inner wall coating backfill module of the integrating sphere, the light trap and the measured material backfill module are placed respectively;

[0015] Step 4, calculating the diffuse reflectivity of the measured material according to the opening ratio and the backfill ratio calculated in step 1, the known diffuse reflectivity of the inner wall coating of the integrating sphere and the three light readings of the luxmeter obtained in step 3.

[0016] The method according to the second aspect of the present application, the inner wall coating of the integrating sphere is uniform, so that the diffuse reflectivity of the inner wall of the integrating sphere is consistent.

[0017] The method according to the second aspect of the present application, the inner wall coating backfill module of the integrating sphere is made by the opening cutting part when another opening is made on the wall of the integrating sphere.

[0018] The method according to the second aspect of the present application, the inner wall circular arc surface of the measured material backfill module is consistent with the inner wall of the integrating sphere.

[0019] The method according to the second aspect of the present application, the light inlet, the other opening and the luxmeter are arranged at different positions in the integrating sphere, so that the incident light cannot directly irradiate the light receiving surface of the other opening and the luxmeter.

[0020] The technical scheme of the present application uses the integrating sphere, the light trap and other tools to complete the measurement of the diffuse reflectivity of the material surface by using the direct measurement method, without the need for a standard reflector plate whose diffuse reflectivity needs to be calibrated in advance. At the same time, there is no need to measure the diffuse reflectivity of the inner wall of the integrating sphere and the brightness value of the illuminating light source and other parameters. It is convenient and fast, has high measurement accuracy and wide application range. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 Figure 1 is a schematic diagram of a material surface diffuse reflectance measuring device according to the present application, which places an inner wall coating backfill module of an integrating sphere;

[0022] Figure 2 Figure 2 is a schematic diagram of a material surface diffuse reflectance measuring device according to the present application, which places a light trap;

[0023] Figure 3 Figure 3 is a schematic diagram of a material surface diffuse reflectance measuring device according to the present application, which places a measured material backfill module.

[0024] In the figures, 1 is an integrating sphere, 2 is an entrance light port, 3 is a light beam projection area, 4 is an illuminometer, 5 is an inner wall coating backfill module of the integrating sphere, 6 is a light trap, and 7 is a measured material backfill module. DETAILED DESCRIPTION

[0025] The present application provides a material surface diffuse reflectance measuring method and device. The illuminating light is incident from the opening of the integrating sphere 1, and the inner wall coating backfill module 5, the light trap 6, and the measured material backfill module 7 are placed in the other opening of the integrating sphere 1 in sequence, and the corresponding readings of the illuminometer are read, and the measured material surface diffuse reflectance measuring result is calculated. Compared with the indirect measurement method with the aid of the standard diffuse reflectance plate, the present application has the advantages of convenience, speed, and small error introduction. And the influence of the diffuse reflectance of the inner wall of the measuring integrating sphere 1 and the brightness value of the illuminating light source on the final measurement result can be avoided.

[0026] The first aspect of the present application provides a material surface diffuse reflectance measuring device, which comprises an integrating sphere, an inner wall coating backfill module of the integrating sphere, a measured material backfill module, a light trap, and an illuminometer.

[0027] The integrating sphere comprises a first area of an entrance light port and a third area of another opening, and the illuminating light is incident from the entrance light port of the integrating sphere,

[0028] The light receiving areas of the inner wall coating backfill module of the integrating sphere, the measured material backfill module, and the light trap are matched with the other opening.

[0029] The illuminometer is arranged on the inner wall of the integrating sphere, and the position of the illuminometer is away from the positions of the entrance light port and the other opening.

[0030] As described in the first aspect of the present application, the coating on the inner wall of the inner wall coating backfill module of the integrating sphere is the same as the coating on the inner wall of the integrating sphere, has the same diffuse reflectance, and the inner wall circular arc surface of the inner wall coating backfill module of the integrating sphere constitutes a unified spherical surface with the inner wall of the integrating sphere.

[0031] The device according to the first aspect of the present application, the inner wall of the measured material backfill module is coated with the measured material, the diffuse reflectivity of the measured material is unknown, and the inner wall arc surface of the measured material backfill module and the inner wall of the integrating sphere form a unified spherical surface.

[0032] The device according to the first aspect of the present application, the inner wall coating backfill module of the integrating sphere, the measured material backfill module and the light trap are used to be placed in the other opening in sequence during the measurement of the diffuse reflectivity of the material surface; and the illumination values when the inner wall coating backfill module of the integrating sphere, the measured material backfill module and the light trap are placed in the other opening respectively are read by using the illuminometer.

[0033] The second aspect of the present application provides a method for measuring the diffuse reflectivity of a material surface, the method comprising the following steps:

[0034] Step 1, calculating the opening ratio and the backfill ratio according to the first area of the light inlet and the third area of the other opening;

[0035] Step 2, the incident light beam is incident into the integrating sphere through the light inlet of the first area, and diffuse reflection is generated;

[0036] Step 3, placing the inner wall coating backfill module of the integrating sphere, the light trap and the measured material backfill module in the other opening in sequence, and reading the light readings of the illuminometer when the inner wall coating backfill module of the integrating sphere, the light trap and the measured material backfill module are placed respectively;

[0037] Step 4, calculating the diffuse reflectivity of the measured material according to the opening ratio and the backfill ratio calculated in step 1, the known diffuse reflectivity of the inner wall coating of the integrating sphere and the three light readings of the illuminometer obtained in step 3.

[0038] The method according to the second aspect of the present application, the inner wall coating of the integrating sphere is uniform, so that the diffuse reflectivity of the inner wall of the integrating sphere is consistent.

[0039] The method according to the second aspect of the present application, the inner wall coating backfill module of the integrating sphere is made by using the opening cutting part when another opening is made on the wall of the integrating sphere.

[0040] The method according to the second aspect of the present application, the inner wall arc surface of the measured material backfill module is consistent with the inner wall of the integrating sphere.

[0041] The method according to the second aspect of the present application, the light inlet, the other opening and the illuminometer are arranged at different positions in the integrating sphere, so that the incident light cannot directly irradiate the light receiving surface of the other opening and the illuminometer.

[0042] Embodiment

[0043] As Figure 1As shown, the integral sphere 1 has a center O and a radius R, and its inner wall is regarded as an ideal diffuse reflector with a diffuse reflectivity p S . Assume that an illumination beam with a light flux of f is incident into the integral sphere 1 from the light inlet 2 and is projected onto the beam projection area 3, where the area of the light inlet 2 is S1, the area of the beam projection area 3 is S2, and A is an arbitrary point in the area. After the beam is diffusely reflected (assuming the 0th time of diffuse reflection) in the area, part of the reflected light is directly projected onto the illuminometer corresponding to No. 4, and M is the measuring point of the illuminometer. Another part is projected onto other areas of the inner wall of the integral sphere 1, and N is an arbitrary point thereon. An opening with an area of S3 is arranged at another position on the wall of the integral sphere 1, and the opening cut-off part is made into an integral sphere inner wall coating backfill module 5. The coating on the inner wall of the integral sphere inner wall coating backfill module 5 has the same diffuse reflectivity p S as the coating on the inner wall of the integral sphere 1, and the inner wall circular arc surface and the inner wall of the integral sphere 1 form a unified spherical surface.

[0044] Let the surface area of the inner wall of the integral sphere 1 be S = 4pR 2 , the opening ratio be , and the backfill ratio be , where R, S1, and S3 are all measured in advance when the integral sphere 1 is made and are known. Further, the values of f S and f T are also known.

[0045] (1) First, the 0th illuminance value E0 generated by the incident beam after the 0th diffuse reflection in the beam projection area 3 to the point M is calculated.

[0046] Take a small facet dS A at the point A, and the light flux d f of the direct light from the light source to the facet. Then, the illuminance value E A at the point A is

[0047]

[0048] According to the traditional diffuse reflection calculation formula recommended by the International Lighting Association, the brightness value at the point A caused by the illuminance E A is

[0049]

[0050] Then, by applying the first and second laws of illuminance, the light flux of the diffuse reflection light source with a brightness of L A from the point A to the facet dS M at the point M is

[0051]

[0052] where i1 is the included angle between the lines AM and AO, i1' is the included angle between the lines MO and MA, and r AMThe distance between A and M. (Note: the incident light does not have to pass through O, i.e. the line AO does not have to be parallel to the incident light.)

[0053] Because i1 = i1', r AM = 2Rcosi1, formula 3 can be derived

[0054]

[0055] Substituting formula 1, the light flux of the small face element dS A The 0th diffuse reflection light reaches the small face element dS M The generated illumination value dE0 is

[0056]

[0057] Integrating the area S2 of the entire light beam projection area 3, the 0th illumination value generated by the 0th diffuse reflection of the incident light beam reaching the point M is

[0058]

[0059] From formula 6, it can be seen that the 0th illumination value reaching the point M is independent of r AM or i1, and further, for any point on the inner wall of the integrating sphere 1, the 0th illumination value generated by the 0th diffuse reflection of the incident light beam at the point is E0.

[0060] (2) Next, the cumulative illumination value of the incident light beam reaching the measurement point M after multiple diffuse reflections on the inner wall of the integrating sphere 1 is calculated as Figure 1 shown, i.e. when the integrating sphere inner wall coating backfill module 5 is placed at the opening.

[0061] After the 0th diffuse reflection of the incident light beam irradiating the light beam projection area 3, it is projected onto all other areas of the inner wall of the integrating sphere 1, and the illumination value reaching each point is E0. Let N be an arbitrary point on the inner wall of the integrating sphere 1, the 0th diffuse reflection light beam reaches N and is diffused, and then reaches M again to generate an illumination value E1.

[0062] The brightness generated by the 0th diffuse reflection light irradiating N is

[0063]

[0064] The light flux of the small face element dS N once diffused at N reaches the small face element dS M at M is

[0065]

[0066] The corresponding illumination at M is

[0067]

[0068] The first-order illuminance of the incident beam diffusely reflected from the inner wall of the integrating sphere 1 to point M is:

[0069]

[0070] As can be seen from Formula 10, the illuminance value at point M and r NM If i2 is irrelevant, then it can be concluded that for any point on the inner wall of the integrating sphere 1, the first illuminance value produced at that point after the 0th diffuse reflection beam undergoes the 1st diffuse reflection is E1.

[0071] Similarly, the illuminance value of the nth diffuse reflection beam reaching point M can be derived.

[0072] E n =[ρ S (1-f S +f T )] n E0, n = 2, 3, 4... (11)

[0073] Summing the geometric series, we can obtain the expression for the cumulative illuminance value produced at point M after multiple reflections of the incident beam through the inner wall of integrating sphere 1, when the coating backfill module is placed on the inner wall of the integrating sphere.

[0074]

[0075] In fact, E m1 The value can be read directly from the illuminance meter.

[0076] (3) Figure 2 As shown, the coating backfill module 5 on the inner wall of the integrating sphere is removed, and a light trap 6 (serial number 6) is installed at the opening. The reflectivity of the light beam after entering the light trap 6 is 0. Referring to Formula 10, the first-order illuminance of the incident beam diffusely reflected from the inner wall of the integrating sphere 1 to point M in this case is:

[0077]

[0078] Referring to Formulas 11 and 12, the expression for the cumulative illuminance value generated at point M after multiple reflections of the incident beam through the inner wall of the integrating sphere 1 when the light trap 6 is placed is further obtained as follows:

[0079]

[0080] Similarly, E m2 The value can be read directly from the illuminance meter.

[0081] (4) Figure 3Remove the light trap 6 and install the test material backfill module 7 at the opening. Its inner wall is coated with the test material, and its shape is the same as the inner wall coating backfill module 5 of the integrating sphere, with the same area S3, where L is any point on it. Assume the diffuse reflectance of light incident on the test material is ρ. T The following derivation shows the first-order illuminance of the incident beam at point M after diffuse reflection from the inner wall of integrating sphere 1 and the backfill module of the measured material.

[0082] The brightness produced when the 0th diffuse reflection light shines on point L is:

[0083]

[0084] Small surface element dS at point L L A single diffuse reflection reaches the small surface element dS at point M. M The luminous flux is

[0085]

[0086] The corresponding illuminance produced at point M is

[0087]

[0088] The first-order illuminance of the incident beam diffusely reflected from the entire backfill module of the tested material to point M is:

[0089]

[0090] Combining Equation 13, the first-order illuminance of the incident beam after diffuse reflection from the inner wall of integrating sphere 1 and the backfill module of the measured material to point M is:

[0091] E1”=E1'+E 1T '=ρ S (1-f S E0+ρ T f T E0=[ρ S (1-f S )+ρ T f T E0 (19)

[0092] It can be seen that the first-order illuminance value is also independent of the location of the 0th diffuse reflection point and point M. Therefore, it can be concluded that when the backfill module of the tested material is placed, for any point on the inner wall of integrating sphere 1, the first-order illuminance value generated at that point after the 0th diffuse reflection beam undergoes the 1st diffuse reflection is always E1.

[0093] Furthermore, referring to Formulas 11 and 12, the expression for the cumulative illuminance value generated at point M after multiple reflections of the incident beam through the inner wall of the integrating sphere 1 when the backfill module of the tested material is placed is:

[0094]

[0095] Similarly, the values of E m3 can be read directly by a luxmeter.

[0096] (5) Solving the equation group of formula 12, formula 14, formula 20, we get

[0097]

[0098] wherein, E m1 , E m2 , E m3 are read directly by a luxmeter, the opening ratio f S and the backfill ratio f T are obtained by measuring the opening area when the integrating sphere 1 is made.

[0099] Finally, it should be noted that the above embodiments are merely intended to illustrate the technical solutions of the embodiments of the present application and not to limit the same, and although the embodiments of the present application have been described in detail with reference to the above preferred embodiments, it should be understood by those skilled in the art that the technical solutions of the embodiments of the present application can be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for measuring the diffuse reflectance of a material surface, characterized in that, A material surface diffuse reflectance measuring device is used, the device comprising: an integrating sphere, an integrating sphere inner wall coating backfill module, a material under test backfill module, an optical trap, and an illuminometer; The integrating sphere includes a light inlet of a first area and another opening of a third area, through which illumination light is incident. The light-receiving areas of the integrating sphere inner wall coating backfill module, the tested material backfill module, and the light trap are all matched with another opening; The coating on the inner wall of the integrating sphere inner wall coating backfill module is the same as the coating on the inner wall of the integrating sphere, and has the same diffuse reflectance. The arc surface of the inner wall of the integrating sphere inner wall coating backfill module and the inner wall of the integrating sphere form a unified spherical surface. The inner wall of the test material backfill module is coated with the test material, the diffuse reflectance of which is unknown. The arc surface of the inner wall of the test material backfill module and the inner wall of the integrating sphere form a unified spherical surface. The reflectivity of light rays after entering the optical trap is 0; The illuminance meter is disposed on the inner wall of the integrating sphere, and the position of the illuminance meter is away from the position of the light inlet and the other opening; The integrating sphere inner wall coating backfill module, the test material backfill module, and the optical trap are placed sequentially at the other opening during the measurement of diffuse reflectance of the material surface; the illuminance values ​​are read using an illuminance meter when the integrating sphere inner wall coating backfill module, the test material backfill module, and the optical trap are placed at the other opening respectively. The method includes the following steps: Step 1: Calculate the opening ratio and backfill ratio based on the first area of ​​the light inlet and the third area of ​​the other opening. Step 2: The incident beam is incident into the interior of the integrating sphere through the light inlet of the first area, and diffuse reflection is generated; Step 3: Place the integrating sphere inner wall coating backfill module, the light trap, and the test material backfill module in sequence at the other opening, and read the illumination readings of the illuminance meter when placing the integrating sphere inner wall coating backfill module, the light trap, and the test material backfill module, respectively. The coating backfill module for the inner wall of the integrating sphere is made using the portion of the opening cut off when another opening is made on the wall of the integrating sphere. Step 4: Based on the opening ratio and backfill ratio calculated in Step 1, the known diffuse reflectance of the coating on the inner wall of the integrating sphere, and the three illumination readings of the illuminometer obtained in Step 3. , , Calculate the diffuse reflectance of the material : , When the integrating sphere inner wall coating backfill module is placed, the cumulative illuminance value generated at point M after the incident beam is reflected multiple times by the inner wall of the integrating sphere is... When placing the optical trap, the cumulative illuminance at point M after multiple reflections of the incident beam through the inner wall of the integrating sphere is [value missing]. When placing the backfill module for the material under test, the cumulative illuminance value generated at point M after multiple reflections of the incident beam through the inner wall of the integrating sphere is [value missing]. M is the measurement point where the illuminance meter is located; , , The aperture ratio is read directly from the illuminance meter. and backfill ratio It is obtained by measuring the opening area when making the integrating sphere.

2. The method as described in claim 1, characterized in that, The inner wall coating of the integrating sphere is uniform, resulting in a consistent diffuse reflectance of the inner wall of the integrating sphere.

3. The method as described in claim 1, characterized in that, The light inlet, the other opening, and the illuminance meter are positioned at different locations within the integrating sphere, so that the incident light cannot directly illuminate the other opening and the light-receiving surface of the illuminance meter.

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