Optics: measuring and testing – By shade or color
Patent
1997-10-15
1999-08-03
Hantis, K P
Optics: measuring and testing
By shade or color
G01J 346
Patent
active
059332433
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to the field of papermaking and more specifically to a device for color measuring.
2. Description of the Related Art
EP 0 240 610 B1 shows a device for measuring humidity and density of a web-shaped material at which coherent electromagnetic radiation with different frequencies is directed to the material and the reflected and transmitted radiation is evaluated. Herewith the emitted and irradiated radiation is not sensed.
If the material under test as e.g. paper is not completely opaque, then color measuring raises some difficulties. Under laboratory conditions it is possible to fold the material under test repeatedly in order to achieve a complete opacity, whereas this is not possible with respect to moved single-layer webs on paper machines. To this respect it is therefor prior art to produce an artificial background. To this end colored tiles, the color of which is matched to the material under test to be measured, are brought behind the material under test. The disadvantage of this solution consists in that already with small distances between the material under test and the color tile an error arises in the color measuring. Moreover, the variety of papers which are produced on a machine is often very large, and, therefore, it is not always possible to back it by a color tile with the right color.
Departing from this prior art, it is therefor the object of the present invention to devise a color measuring device which, independent of the opacity and without the requirement of backing the material under test, allows an accurate color measurement.
BRIEF SUMMARY OF THE INVENTION
The solution of this object is achieved by an improvement to a device for the color measuring of materials under test, in particular paper webs. The device includes a light source arranged to generate light in a plurality of spectral ranges and means for splitting the light irradiated by the light source into a first and a second beam of light, the first beam directed onto the material under test. The device further includes a first measuring apparatus for receiving and generating signals representative of the intensity of the light reflected off of the material under test for each spectral range received, and a second measuring apparatus for receiving and generating signals representative of the intensity of the light of the second beam for each spectral range received and a color computer for receiving and processing the signals from the first and second measuring apparatus. The improvement comprises a third measuring apparatus arranged to receive light from the first beam that is transmitted through the material under test and to generate signals representative of the light received therethrough for each spectral range received, whereby the color computer receives and processes the signals from the third measuring apparatus by subtracting the signals received from the third measuring apparatus from the signals received from the second measuring apparatus, thereby forming a difference signal for each spectral range. The color reflectivity is determined by the color computer by dividing the difference signal for each spectral range from the signals received from the first measuring apparatus for the associated spectral range.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
With respect to the figures of the attached drawing in the following the underlying problem of the invention and its solution shall be further described with respect to an embodiment whereby:
FIG. 1 shows the spectral reflectivity of a material under test as a function of the wavelength of the light with the thickness of the layer as a parameter;
FIG. 2 shows the spectral reflectivity of a material under test as a function of the wavelength with the distance of its backing as a parameter;
FIG. 3 shows a device for color measuring according to the prior art; and
FIG. 4 shows the improved device for color measuring of the present invention.
DETAILED DESCR
REFERENCES:
patent: 4288160 (1981-09-01), Lodzinski
Hantis K P
Honeywell Inc.
Miologos Anthony
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