JPS6333089B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a color measurement method and apparatus for inspecting the color of the surface of an object, and more specifically, to detecting defects in the average color of an object to be inspected such as decorative plywood. The present invention relates to a color measurement method and apparatus using an improved optical system of a Hunter type color difference meter.

Currently, two types of color measurement devices are provided: spectrophotometers and photoelectric colorimeters (color difference meters). A spectrophotometer is based on spectrophotometry, which measures the spectral reflectance of a colored object and determines tristimulus values from the reflectance at each wavelength to determine the color of the object. Therefore, since it is necessary to continuously change the wavelength in the visible wavelength range and find the reflectance of the object for each wavelength, the typical measurement time is approximately one minute. Although spectrophotometers have a very high degree of reliability in measuring the color of objects, they have problems in terms of measurement time. It is not possible to use it online during the process. The latter photoelectric colorimeter (color difference meter)
When measuring the reflected light from the surface of an object using a combination of the spectral characteristics of the light source, filter, and receiver, the same value can be obtained as when determining the tristimulus values by measuring the spectral reflectance with a spectrophotometer. This condition is called the Luther Condition and corresponds to the human color sense, and the light of each wavelength reflected from an object is passed through a filter and then sent to a receiver. The light is received all at once and measured as the total stimulus value for the entire wavelength range. Since this is nothing more than measuring each wavelength and then integrating it, the tristimulus values can be read directly, and there is no problem in terms of measurement time for online use. The most common photoelectric colorimeter is the Hunter type colorimeter. This method uses a light receiving element to measure the amount of reflected light from an object that has passed through three filters λ, λ, and λ that satisfy the router condition, and then calculates the color difference and correspondence from each measured amount (stimulus value) X, Y, and Z. It is easy to read the three numbers L, aLbL.
L represents lightness, and aL and bL represent chromaticity coordinates. This is the difference between these three values L, aL, and bL (difference between the standard stain and the material). Since the color difference ΔE can be easily calculated from ΔL, ΔaL, and ΔbL using the formula ΔE = √ () ² + () ² + () ² , it is especially useful among photoelectric colorimeters for detecting color difference defects such as decorative plywood. Are suitable. However, the conventional color difference meters that have been provided have a light source and receiver built into one, and have a small light receiving area (maximum diameter of about 30 mm), which makes it possible to measure the color of objects with patterns such as decorative plywood. Not suitable for measurement. In other words, when humans judge the difference in color of a patterned object like decorative plywood, they do not make a judgment by looking at the color of each part of the pattern, but by averaging a wide range of colors to determine the overall color. We judge it by looking at it as a color. Therefore, if the light-receiving area is small (this also applies to other photoelectric colorimeters and spectrophotometers), the colorimetric values will vary greatly depending on the measurement area, making it very difficult to judge color differences. It is difficult to Furthermore, there was no specification for this color difference meter that could be used online due to limitations in the optical system of the light receiver and the arrangement of the light receiving element.

The present invention has been made in view of the above points,
The main purpose of this is to project the image of the object to be inspected onto a screen and measure the color of the image that appears on this screen, thereby achieving a wide light receiving area and making it possible to produce decorative plywood, decorative sheets, and tile laminates. It is an object of the present invention to provide a color measurement method and device that can measure the color of an object with a pattern, such as a patterned object, and can vary the light receiving area so that the light receiving area is suitable for the object to be inspected, and other purposes. By connecting the screen and the light-receiving element with an optical fiber, the light-receiving element is completely separated from the light source, making it more suitable for online use, and the temperature characteristics of the light-receiving element reduce the accuracy of measurement values. Another object of the present invention is to provide a colorimeter that can measure only the necessary portions, such as the background color of a wood grain pattern, by masking the screen. is to provide.

The present invention will be described below based on the illustrated embodiment. In Fig. 1, 1 is a projector, 2 is a condenser,
3 is a light receiver, and the light emitter 1 has a halogen lamp as a light source 10 and a light emitter lens 1 as shown in FIG.
1, the object to be inspected 7 is irradiated. At this time,
The irradiation area is kept constant by enlarging and projecting the shape of the slit 12 onto the object 7 to be inspected, and therefore, by changing the shape and size of the slit 12, the shape and size of the irradiation area can be changed. . The condenser 2 includes a condenser lens 20 as shown in FIG.
The light projector 1 includes a semi-transparent screen 21 arranged at the position where the object to be inspected 7 is imaged by the condenser lens 20 and onto which an image of the object to be inspected 7 is projected.
The focal length of the condenser lens 20, the distance between the condenser lens 20 and the screen 21, and the distance between the condenser lens 20 and the object to be inspected 7 are set so that the irradiation area becomes substantially the light receiving area. The image projected on the screen 21 of the condenser 2, that is, the reflected light from the surface of the object to be inspected 7 within the irradiation area, is sent to the light receiver 3 through the optical fiber 4.
The receiver 3 is connected to an optical fiber 4 as shown in FIG.
A diffusion optical system 30 consisting of an integrating sphere that diffuses the reflected light sent through the tristimulus value filters xλ, λ, λ, and each stimulus value filter λ,
A light receiving element 3 consisting of a photomultiplier tube that performs photoelectric conversion and amplification upon receiving the diffused light that has passed through yλ, λ.
1, 31, and 31. Note that the tristimulus value filters λ, λ, and λ herein include correction and adjustment filters such as a spectral distribution adjustment filter of the light source 10 and a spectral sensitivity correction filter of the light receiving element 31. However, this does not apply in cases where a spectral distribution adjustment filter for a light source is placed on the projector 1 side.

In this way, the projector 1 and the condenser 2 are connected to the object to be inspected 7.
The object to be inspected 7 is irradiated with the projector 1 from directly above the object to be inspected. As mentioned above, since this irradiation area is substantially the light receiving area, the irradiation area is set to a range suitable for the object 7 to be inspected by moving the projector 1 up and down or by changing the size of the slit 12. Although the distance of the condenser 2 from the object 7 to be inspected must be changed depending on the irradiation area, the setting can be performed reliably by viewing the image projected on the screen 21. In other words, since the portion reflected on the screen 21 is the light-receiving area, the setting can be performed without causing any misalignment between the irradiation area and the light-receiving area. When using this device as a colorimeter, each angle of light emission and light reception is
The emitter 1 and condenser 2 are set as shown in Fig. 5 according to condition 1 (0°: 45° light emission/reception, or 45°: 0° light emission/reception) shown in JIS Z8722. If you do this, you can measure the correct color, but when using it as a color difference inspection machine that only measures relative colors rather than absolute colors, the most It is possible to set the light emitting/receiving angle to be easy to distinguish between the emitter 1 and the receiver 3.
In the present invention, in which the input end of the light condenser 2 is separated from the light condenser 2, the angle of light projection and reception can be set to any desired angle, as shown in FIG. A plurality of projectors 1 may be set at different angles. Once the light emitter 1 and the light collector 2 are installed in this way, the light receiver 3 connected to the light collector 2 by the optical fiber 4 is placed outside the path line in a place where it is less likely to be affected by the environment. It is best to place the receiver 3 in a thermostatic chamber, but in any case, the receiver 3 should be placed in a thermostatic chamber.
Since they can be completely separated by the optical fiber 4, the light receiving element 31 of the light receiver 3 will not be affected by the heat of the light source 10 of the projector 1.
Furthermore, since it can be installed at a distance from the condenser 2, which is the input end of the light receiver 3, the degree of freedom in setting for online use increases, making installation easier.

The object to be inspected 7 illuminated by the projector 1 emits reflected light with a spectral reflectance based on the color of its surface.
This reflected light is guided to the screen 21 by the condensing lens 20 of the condenser 2, and a reduced image of the light-receiving area of the object 7 to be inspected is projected onto the screen 21.
The reflected light that has passed through the screen 21 enters the diffusing optical system 30, which is an integrating sphere of the light receiver 3, through the optical fiber 4, where it is completely diffused, and then passes through each stimulus value filter λ, λ, λ. They enter the light receiving elements 31, 31, 31, respectively. These light receiving elements 31,
The light intensity measured at 31 and 31 is tristimulus value X, respectively.
These are numerical values corresponding to Y and Z, and from these stimulus values X, Y, and Z, the arithmetic unit 6 calculates the brightness L, chromaticity coordinate (chromaticity index) aL,
bL Hue H, saturation C, and color difference ΔE are calculated.

L=100Y aL=175(1.02X-Y)/√ bL=70(Y-0.847Z)/√ H=aL/bL C=√() ² +() ² ΔE =√() ² +() ² +() ² Then, from these values, evaluate each part and the whole, evaluate at two types of irradiation angle, and evaluate at two types of irradiation light wavelength, and check the difference between the color of the object to be inspected and the standard color. It determines the difference in color. 8 in the figure is a standard plate for calibration, which is placed in the pass line and calibrated every time the object to be inspected 7 passes.
To perform color measurement with high accuracy.

As the standard plate 8 for calibration, a white material such as white ceramics, which is white and shows little change over time, is used.
Since calibration is performed using this standard plate 8, in terms of relative color measurement, the spectral characteristics of other members do not need to be very biased.
Even if these changes occur over time, it is possible to ultimately obtain measurement results that are stable over time.
As for the screen 21, it is preferable that the screen 21 has a diffusivity sufficient to allow an image to be reflected and at the same time has a flat absorption wavelength, and may be made of a white glass surface made of frosted glass, a translucent acrylic plate, or the like.

The object to be inspected 7 is a decorative plywood sheet with a wood grain pattern, and the color is not an average color obtained by additive color mixing of the ground color part and the pattern part of the object to be inspected 7.
When you want to measure only the ground color, as shown in FIG.
The screen 21 may be masked with a masking material 5 corresponding to the pattern 7, such as black tape.
It is also possible to measure only a part of the colors within the light receiving area very easily.

In the present invention as described above, the reflected light from the object to be inspected is not directly guided to the light-receiving element, but is projected onto a screen and then guided to the light-receiving element, so it is independent of the light-receiving angle of the light-receiving element. To,
By changing the magnification of the image projected onto the screen, the light-receiving area can be set as large as desired, and conversely, the light-receiving area can be arbitrarily set to suit the object to be inspected.
In order to measure the diffused light of the image projected on the screen, it is possible to average a wide range of colors and determine the overall color, making it easier to distinguish between different colors of patterned objects. Furthermore, the light-receiving element measures the overall average color at once, making it possible to identify colors in real time. In addition, the combined invention includes a condenser consisting of a screen and a condenser lens that projects an image onto the screen, and a diffusion optical system that diffuses light on the screen surface of the condenser. It is capable of real-time color measurement without the need for complex processing, and can be provided at low cost.
Furthermore, since the projector, the condenser with a screen, and the light receiver can be individually arranged, there are fewer restrictions on online use, and online automatic 100% inspection is now possible.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of an embodiment of the present invention, FIG. 2 is a sectional view of the same emitter, FIG. 3 is a sectional view of the concentrator, and FIG. 4 is a sectional view of the light receiver. Figure 5 is a partial front view of the same as above, Figure 6 is a front view of the same as above, Figure 7 is a front view of the same as above.
Figures a and b are explanatory diagrams showing masking. 1
is a light projector, 2 is a condenser, 3 is a light receiver, 4 is an optical fiber, 5 is a masking material, 10 is a light source, 20 is a condensing lens, 21 is a screen, 30 is a diffusing optical system, 31 is a light receiving element, λ , λ, λ indicate stimulus value filters.

Claims (1)

[Claims] 1. Irradiating the object surface with light from a light source, projecting the reflected light from the object surface using a condensing lens onto a screen placed at the imaging position of the condensing lens, and projecting the light onto the screen. A colorimetry method characterized in that each diffused light of the image is measured by a light receiving element through a tristimulus value filter. 2. A light projector equipped with a light source for irradiating the surface of an object, a condenser consisting of a screen and a condensing lens that projects an image onto the screen placed at an imaging position;
It is equipped with a diffusion optical system that diffuses the light on the screen surface of the condenser, a tristimulus value filter, and a light receiving element corresponding to each stimulus value filter, and the light is received by the diffusion optical system, the tristimulus value filter, and the light receiving element. A color measurement device characterized by comprising a container. 3. The color measuring device according to claim 2, characterized in that the condenser and the light receiver are connected by an optical fiber. 4. The color measuring device according to claim 2 or 3, characterized in that a masking material can be freely disposed on the screen surface of the condenser.