WO2004053441A1

WO2004053441A1 - System for detecting the perceived colour of a surface

Info

Publication number: WO2004053441A1
Application number: PCT/EP2003/012464
Authority: WO
Inventors: Reinhold Schneeberger; Joachim Kaiser; Heinrich Meyer
Original assignee: Siemens Aktiengesellschaft
Priority date: 2002-12-10
Filing date: 2003-11-07
Publication date: 2004-06-24
Also published as: AU2003298108A1; DE10257640A1

Abstract

The invention relates to a system for detecting the perceived colour of a surface (8). Said system contains an illumination device (2) for illuminating the surface (8) using a plurality of light sources (2a-d) for producing light from different spectral compositions, a control device (24) for connecting the light sources in a temporally successive manner, a light receiver (22a,b) for measuring the intensity (Ia,Ib) of the light respectively reflected from the surface (8), and an evaluation device (26) for determining - on the basis of the measured intensities (Ia,Ib) - a characteristic which reproduces the perceived colour. In this way, a spectral decomposition of the emitted or received light is rendered superfluous.

Description

description

Device for recording the color impression of a surface

The invention relates to a device for detecting the color impression of a surface.

Such a device is for example from the

DE 38 31 287 AI known. The known device contains a light source which emits spectrally broadband light, which is guided to the surface of a sample with the aid of a light guide, and which is irradiated at an angle of 45 °. The light scattered at 0 ° perpendicular to the surface of the sample is coupled into a light guide and spatially separated with the aid of a grating. The spectral components separated from one another in this way are recorded by a detector array and the color value of the sample is determined by comparing the individual spectral components.

In the device known from US Pat. No. 4,464,054 A, the light generated by a light source is coupled into a fiber-optic cable, the fibers of which are arranged in a ring around a common central axis and obliquely to it in such a way that the light emerging from the fibers hits this central axis cuts in the same place. At the center of this ring-shaped

Arrangement and spaced from this point is a cylindrical light guide which is optically coupled to three photodetectors. Color filters, which have different transmission characteristics, are arranged between the photodetectors and the light guide. The intensity of the light determined in this way in different spectral ranges, which is scattered by a surface that is arranged at the point of intersection of the light emerging from the fibers, is fed to a commercially available evaluation device, which uses the measurement signals provided by the photodetectors to produce a standardized color value determined. The spectral decomposition of a broadband light signal used in the known devices and the evaluation resulting therefrom can be very complex. The measurement signal can be determined by the spectral sensitivity of the detector and by the intensity profile of the light source, the filters used within the beam path and / or other optical components in an undesirable manner. Therefore, in the known devices, a complex spectral calibration is required in particular.

The invention is based on the object of specifying a device for measuring the color impression of a surface which, with sufficient accuracy and simple structure, enables reliable color characterization of a surface.

The stated object is achieved according to the invention with a device with the features of claim 1. According to these features, the device comprises an illuminating device for illuminating the surface with a first light source for generating light with a first spectral composition, and at least a second Light source for generating light with a second spectral composition, the first and second spectral compositions being different from one another. A control device is provided for successively switching on the light sources. The intensity of the light reflected from the surface in each case is measured with a light receiver and transmitted to an evaluation device which determines a characteristic variable which reproduces the color impression from the measured intensities.

The use of a plurality of light sources which emit light of different spectral composition eliminates the need for spectral decomposition. placement of the light reflected or scattered by the surface. This simplifies the construction of the measuring device.

In an advantageous embodiment of the invention, a beam guiding device is provided for guiding the light generated by the light sources to at least one common exit aperture. This ensures that the surface is irradiated by all light sources at the same exit angle and under identical incidence conditions. This ensures high measurement accuracy and high reproducibility even on uneven surfaces.

In particular, a light guide arrangement, preferably a light guide arrangement consisting of a single component, in particular a plastic injection molded part, is provided as the beam guiding device. This enables a particularly compact design of the facility. In addition, light sources and light receivers can be arranged spatially separate from the exit or entrance aperture assigned to them, so that the actual sensor head can be largely miniaturized and can also be easily measured on very large objects or on objects with a complex surface structure.

Spectrally narrow-band LEDs are preferably provided as light sources.

In a further preferred embodiment of the invention, at least two exit apertures for illuminating the

Surface provided at different angles of incidence (= exit angle). In this way, surfaces whose color impression depends on the viewing angle can be more clearly characterized.

An entry aperture is preferably associated with each exit aperture, with each entry aperture in particular Light receiver is assigned. In addition, each entrance aperture is preferably arranged at an entrance angle which is the same size as the exit angle of the respectively associated exit aperture.

In a further embodiment of the invention, an evaluation device is provided which comprises a computing device for determining the parameter to form a quotient from the measured intensities.

To further explain the invention, reference is made to the exemplary embodiments of the drawing. Preferred, but in no way restrictive, exemplary embodiments of the device are shown. For the sake of clarity, the drawing cannot be drawn to scale and certain features are only shown schematically. Show it:

1 shows a device according to the invention in a schematic diagram,

FIG. 2 shows an enlarged illustration in the area of the exit and entrance apertures,

Figure 3 shows an alternative embodiment of the invention.

According to FIG. 1, the device contains an illumination device 2 with a plurality, in the exemplary embodiment four, of light sources 2a-d, which emit light of different spectral composition. The light sources 2a-d are optically coupled to a beam guiding device 4, which guide the light generated by the light sources 2a-d to two exit apertures 6a, b, from which the light emerges at different exit angles and with which the surface 8 of a sample 10 is illuminated at different angles of incidence α, β. The beam guiding device 4 is formed by a light guide arrangement, each light source 2 a - 2 d being connected to a light guide 12. With Y-couplers 14, the light transmitted by the light sources 2a-d is coupled into a common transmission path, with the aid of a Y-switch 16 arranged at the end of the common transmission path, a new separation on two transmission paths takes place, which leads to the exit apertures 6a or lead βb. In the exemplary embodiment, the last Y-coupler 14 and the separating Y-switch 16 connected to it are combined as one X-coupler in one component.

The exit apertures 6a, b are assigned at the same entrance angle α, β entrance apertures 18a, b, which are also constructed from an optical fiber arrangement

Beam guiding device 20 are connected to a light receiver 22a or b, with which the light reflected on the surface 8 is detected.

Spectrally narrow-band LEDs are provided as light sources 2a-d, the emission spectra of which are different and overlap as little as possible. Light sources 2a-d and light receivers 22a, b are preferably mounted on a circuit board 23, which in particular at the same time contains further electronic components for their control and for the measurement signal processing. A control device 24 is used to sequentially control the light sources 2a-d. In an evaluation device 26, a characteristic variable representing the color impression is determined from the intensities measured by the light receivers 22a, b in the associated time windows and thus each belonging to a spectral range corresponding to the emission spectrum of the respectively controlled light source.

The beam guiding devices 4 and 20 are preferably integrated in a component, in particular an injection molded part made of plastic, which is mounted directly on the circuit board 23. can be tiert, so that a compact and at the same time inexpensive construction is possible.

Alternatively, the beam guiding devices 4 and 20 can also be constructed from several individual parts, in particular again in the form of simple injection molded parts made of plastic. Coupling elements, for example in y- or x-shape, and simple light-transmitting elements can be considered as individual parts. The individual parts are put together. This can be done by gluing.

The light guidance within the injection molded parts is based, for example, on the difference in refractive index between the plastic as the light-guiding medium and the surrounding atmosphere, in particular the air. Both in the one-part and in the multi-part embodiment, the beam guiding devices 4 and 20 can be implemented in a very compact manner. The size is in particular only a few cm, for example between 2 and 6 cm. Furthermore, direct mounting on the board 23 is possible, as a result of which complex adjustment processes during production can be avoided.

In addition to using simple injection molded parts, the beam monitoring devices 4 and 20 can also be implemented using commercially available plastic or glass optical fibers.

Overall, a very small structure is achieved, so that the device can also be designed as a portable measuring device. This favors a measurement even on a very large sample 10.

Since the intensity of the reflected light of each light source 2a-2d is measured at two angles, by forming a quotient I _a / Ib from the light receivers 22a, b controlled by the light receivers 22a, b under the reflection or irradiation angles , ß measured intensities I _a , Ib omitted spectral calibration. In particular, a comparison of the quotients Ia / Ib of measurements on the surfaces 8 of two different samples (second sample is not shown in FIG. 1) can determine whether the two surfaces 8 are of the same color. No spectral calibration is required for the individual measurements here either.

By comparing the intensity quotients I _a / Ib of two surfaces respectively determined in different spectral ranges, it can be determined whether the two surfaces are of the same color without having to carry out a spectral calibration of the individual measurements. In addition, since the use of a single exit aperture for each exit angle, ß the light from each light source 2a-d strikes the same surface area and the light reflected there is received via a single entrance aperture, there are identical geometric conditions for each spectral composition, so that the color impression cannot be falsified by differences between different surface areas.

In the enlarged representation according to FIG. 2, it can also be seen more clearly that the exit apertures 6a, b are arranged relative to the surface 8 of the sample in such a way that the light emerging from them irradiates the same surface area. In other words: the center axes of the light emerging from them each belonging to the exit apertures 6a, b intersect at a point P which lies on the surface 8 of the sample 10 correctly positioned on the device, so that one and the same point of the sample 10 is irradiated at different angles. In this case too, falsification is largely suppressed by linking measurement results from different surface areas. In the exemplary embodiment according to FIG. 3, a light source arrangement 2a-d or 2e-h is alternatively assigned to each beam angle α, β, which are constructed identically, so that two light sources 2a, e - 2d, h are available for each spectral composition. In this case, it is either necessary that the intensity of the spectrally associated light sources 2a, e - 2d, h remains at least constant both with regard to their magnitude and their spectral composition, or reference measurements must be carried out regularly before the actual measurements. Such a reference measurement could be carried out by measuring the intensity R _a ,... R _{h of} each light source 2a-h with the aid of a reference receiver (not shown in the figure) and one of these measured values for the respective spectrally associated light sources 2a, e - 2d, h formed quotient

R _a / R _e , ... d / R _{h is used} to correct the intensities measured with the light receivers 22a and b. As an alternative to this, it is also possible to carry out a reference measurement with a specular sample before the actual measurement.

The advantage of such an arrangement is that light which is diffusely reflected on the surface 8, ie. H. Light that enters the entrance aperture 18b from the exit aperture 6a or enters the entrance aperture 18a from the exit aperture 6b can be used to evaluate the color impression.

Claims

claims

1. A device for detecting the color impression of a surface (8), comprising a) an illumination device (2) for illuminating the surface (8) with a plurality of light sources (2a-d) for generating light of different spectral composition, b) one Control device (24) for switching on the light sources successively, c) a light receiver (22a, b) for measuring the intensity (Ia _/ Ib) of the light reflected from the surface (8), and d) an evaluation device (26) to determine a characteristic variable representing the color impression from the measured intensities (I _a , I _b ).

2. Device according to claim 1, with a beam guiding device (4) for guiding the light generated by the light sources (2a-d) to at least one common exit aperture (6a, b).

3. Device according to claim 2, in which a light guide arrangement is provided as the beam guiding device (4).

4. Device according to one of the preceding claims, in which spectrally narrow-band LEDs are provided as light sources (2a-d).

5. Device according to one of the preceding claims, in which at least two exit apertures (6a, b) for illuminating the surface (8) are provided at different angles of incidence (α, β).

6. Device according to claim 5, in which each exit apparatus (6a, b) is assigned an entrance aperture (18a or b).

7. Device according to claim 6, in which each entrance aperture (18a, b) is assigned a light receiver (2a or b).

8. Device according to one of the preceding claims, the evaluation device (26) for determining the parameter comprises a computing circuit for forming a quotient from the measured intensities (I _a , I _b ).