JPH0540422Y2 - - Google Patents

Description

[Detailed description of the invention] <Industrial application field> The present invention relates to a colorimeter that measures the color of a sheet-like object such as paper online, and more specifically, a colorimeter that is not affected by the reflectance of the sheet-like object. Regarding colorimeter.

<Prior Art> Conventionally, a device shown in FIG. 4 has been proposed as an on-line measuring device for the color of paper. A is a detection unit, and inside the housing 1 there are a light source 3 that irradiates light at an angle of 45° to the surface of a sheet of paper 2, and a lens 4 that collects light reflected in the vertical direction of the paper 2. , a spectroscope 5 that separates reflected light into spectra, a linear array sensor 6 formed on the focal plane of the spectrometer, and a signal processing section 7 that processes detection signals from the linear array sensor 6. . The linear array sensor 6 is a diode array sensor in which, for example, 1024 photodiodes are arranged in the wavelength distribution direction of the spectrum.

With this configuration, color measurement is performed by outputting the spectral measurement values detected by the linear array sensor 6 as they are, or by calculating the color tristimulus values X, Y, and Z from the spectral measurement values in the signal processing section 7. This is output, or the L, a, and b values are calculated from the tristimulus values and output as quantitative color measurement values.

<Problems to be solved by the invention> In such a device, if the color of the paper 2 is moss green or dark blue, which has a very low reflectance, the measurement output becomes extremely small and measurement becomes impossible. Sometimes. In this case, increasing the amount of light irradiated onto the paper 2 makes it possible to measure objects with low reflectance, but in the case of objects with high reflectance, such as when the color of paper 2 is white, the linear array The sensor 6 becomes saturated and measurement cannot be performed.

Of course, if a sensor with a large dynamic range is used, measurements can be made regardless of the reflectance of an object, but such a sensor is very expensive and not easily available.

The technical problem to be solved by the present invention is to make it possible to accurately measure color without being affected by the reflectance of paper using a readily available and inexpensive linear array sensor.

<Means for Solving the Problems> The configuration of the present invention is such that the colorimeter monitors the magnitude of the zero-order light of the spectral spectrum detected by the linear array sensor, or reflectance detection means for detecting the reflectance of the object by monitoring the sum of detection outputs for each wavelength; and stepwise changing the amount of light irradiated from the light source to the object based on the signal from the reflectance detection means. and a light amount changing means for increasing the light amount when the reflectance of the object becomes small, and performing span correction on the detection output from the linear array sensor in accordance with this change in the light amount.

<Operation> The above technical means operates as follows. That is,
The zero-order light in the optical spectrum is a white light signal,
This corresponds to reflected light from the object, and when the reflectance of the object is small, the signal level of the zero-order light becomes small. Further, the sum of detection outputs of the primary light at predetermined wavelength intervals also corresponds to the reflectance from the object.

When these signal levels fall below a predetermined value, the amount of light irradiated from the light source to the object is increased in stages. As a result, a detection signal of a predetermined magnitude can be obtained, and even objects with small reflectance can be measured. At the same time, span correction is applied to the detection signal to prevent span errors from appearing in the output.

<Examples> Examples of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of an apparatus according to an embodiment of the present invention. In the figure,
Elements that are the same as those in FIG. 4 are given the same reference numerals, and explanations thereof will be omitted. Reference numeral 8 denotes a reflectance detection means for detecting the reflectance of the paper 2 based on the detection signal from the linear array sensor 6. One method for detecting the reflectance of the paper 2 is to monitor the zero-order light of the spectroscopic spectrum and detect the reflectance based on the magnitude of the zero-order light. FIG. 2 shows a spectrum detected by the linear array sensor 6. zero order light
SP ₀ is not used for color measurement; it uses primary light for measurement.
SP ₁ is used. The zero-order light SP ₀ is a white light signal and corresponds to the reflected light from the paper 2, and changes in the reflectance of the paper 2 can be detected from the level of this signal.

Another method for detecting the reflectance of the paper 2 based on the spectroscopic spectrum is to sample the detection outputs of multiple wavelengths λ ₁ , λ ₂ , λ ₃ at predetermined wavelength intervals of the primary light SP ₁ and calculate the sum of these outputs. There are ways to monitor it. This sum signal corresponds to the reflected light from the paper 2,
Based on this, changes in the reflectance of the paper 2 can be detected.

The reflectance detection means 8 compares the zero-order optical signal SP ₀ or the sum signal with a set voltage of an internally provided comparator, and generates, for example, three types of light intensity change signals according to the levels of these signals. Generates S ₁ to S ₃ .

Reference numeral 9 denotes a light amount changing means, which operates to increase the amount of light irradiated onto the paper 2 when the reflectance of the paper 2 is low. The specific method of changing the light amount differs depending on the type of light source. In the case of a DC lighting type light source, as _{shown in FIG .}
, and change the voltage applied to the light source 3 step by step.

When the light source 3 is a pulse lighting type xenon lamp, the number of times the lamp is lit is changed based on the light intensity change signals _S1 to _S3 , and the amount of light irradiated onto the paper 2 is changed in stages.

The light amount change signals S ₁ to _{S 3} from the reflectance detection means 8 are also given to the signal processing unit 7 at the same time, and when the light amount is changed, span correction is applied to the detection output from the linear array sensor 6 based on this signal. Therefore, span errors do not occur regardless of changes in light intensity.

<Effects of the Invention> According to the invention, color can be measured using a readily available and inexpensive linear array sensor, and color can be accurately measured without being affected by the reflectance of paper.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an apparatus according to an embodiment of the present invention, FIG. 2 is a spectral distribution diagram, and FIG. 3 is a block diagram showing a specific example of the light amount changing means in the apparatus according to an embodiment of the present invention.
FIG. 4 is a configuration diagram of a conventional device. A...detection unit, 2...sheet-like paper, 3...light source, 5...spectroscope, 6...linear array sensor,
7... Signal processing unit, 8... Reflectance detection means, 9...
...Light amount changing means, _S1 to _S3 ...Light amount changing signal.

Claims (1)

[Scope of utility model registration request] Light is irradiated from a light source onto a sheet-like object at a predetermined angle, the vertically reflected light from this object is separated into spectra by a spectrometer, the spectral spectrum is imaged on a linear array sensor, and based on this spectral measurement value, the signal processing section In a colorimeter that performs calculations and outputs quantitative color measurements,
reflectance detection that detects the reflectance of the object by monitoring the magnitude of the zero-order light of the spectroscopic spectrum detected by the linear array sensor, or by monitoring the sum of detection outputs at predetermined wavelength intervals in the linear array sensor; and a light amount changing means that changes stepwise the amount of light irradiated from the light source to the object based on the signal from the reflectance detection means, and when the reflectance of the object becomes small, the amount of light changes. The colorimeter is characterized in that the detection output from the linear array sensor is subjected to span correction in accordance with the change in the amount of light.