DE10257640A1 - Device for recording the color impression of a surface - Google Patents

Abstract

A device for detecting the color impression of a surface (8) contains an illumination device (2) for illuminating the surface (8) with a plurality of light sources (2a-d) for generating light of different spectral composition, and a control device (24) for temporally Successive switching on of the light sources, a light receiver (22a, b) for measuring the intensity (I¶a¶, I¶b¶) of the light reflected from the surface (8), and an evaluation device (26) for determining a color impression Characteristic from the measured intensities (I¶a¶, I¶b¶). This eliminates the need for spectral decomposition of the transmitted or received light.

Description

Device for recording the color impression 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 A1 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.

At the out US 4,464,054 A known device, 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 the latter in such a way that the light emerging from the fibers intersects this central axis at the same point. In the center of this annular arrangement and at a distance 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 intersection of the light emerging from the fibers, is fed to a commercially available evaluation device that determines a standardized color value from the measurement signals provided by the photodetectors.

The well-known facilities spectral decomposition of a broadband light signal as well as the resulting evaluation can prove to be very complex shape. The measurement signal can namely by the spectral sensitivity of the detector as well as by the Intensity profile of the Light source, the filter used within the beam path and / or other optical components in undesirable Way to be influenced. Therefore, in the known facilities in particular, a complex spectral calibration is required.

The object of the invention is now to provide a device for measuring the color impression of a surface, which, with sufficient accuracy and simple structure, provides reliable color characterization allows a surface.

The above object is achieved according to the invention solved with a device with the features of claim 1. According to these Features include a lighting device for Illuminate the surface with a first light source for generating light with a first spectral Composition, as well as at least a second light source for Generating light with a second spectral composition, the first and second spectral composition being different from one another are. For switching on the light sources sequentially in time a control device is provided. The intensity of the of the surface each reflected light is measured with a light receiver and transmitted to an evaluation device, from the measured intensities determines a parameter reflecting the color impression.

By using a plurality of light sources that have different spectral light from each other Emit composition, not applicable the need for a spectral decomposition of the reflected from the surface or scattered light. This is the structure of the measuring device simplified.

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

In particular, as a beam guidance device an optical fiber arrangement, preferably one made of a single one Component, in particular a plastic injection molded part, existing light guide arrangement is provided. this makes possible a particularly compact design of the facility. It can also use light sources and light receiver spatial separately from the exit or entrance aperture assigned to them be arranged so that the actual sensor head largely be miniaturized and also on very large objects or on objects with a complex surface structure can be measured easily.

Are preferred as light sources spectrally narrow-band LEDs intended.

In a further preferred embodiment of the invention, at least two exit apertures are provided for illuminating the surface at different angles of incidence (= exit angle). As a result, surfaces whose color impression depends on the viewing angle can be seen be characterized.

Each exit aperture is preferably assigned an entrance aperture, in particular each entrance aperture a light receiver assigned. Moreover each entry aperture is preferably at an entry angle arranged, which is the same size like the exit angle of the respectively assigned exit aperture.

In a further embodiment of the The invention provides an evaluation device for determining the parameter one Computing device for forming a quotient from the measured intensities includes.

To further explain the invention, reference is made to the embodiments referred to the drawing. Preferred, but in no way limiting, exemplary embodiments are shown the establishment. The drawing can not clarify either be made to scale and certain features are only shown schematically. Show it:

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

2 an enlarged view in the area of the exit and entrance apertures,

3 an alternative embodiment of the invention.

According to 1 the device contains a lighting device 2 with a plurality, in the exemplary embodiment four, of light sources 2a-d that emit light of different spectral composition. The light sources 2a-d are optically connected to a beam guidance device 4 coupled that from the light sources 2a-d each generated light to two exit apertures 6a, b lead from which the light emerges at different exit angles and with which the surface 8th a sample 10 is illuminated at different angles of incidence α, β.

The beam guidance device 4 is formed by a light guide arrangement, each light source 2a-2d to a light guide 12 connected. With Y-couplers 14 is that from the light sources 2a-d transmitted light coupled into a common transmission path, with the help of a Y-switch arranged at the end of the common transmission path 16 there is a renewed separation on two transmission links leading to the exit apertures 6a respectively. 6b to lead. In the exemplary embodiment are the last Y coupler 14 as well as the connected separating Y-switch 16 summarized as an X-coupler in one component.

The exit apertures 6a, b are at the same entry angle a, ß entry apertures 18a, b assigned, via a beam guidance device also constructed from a light guide arrangement 20 to a light receiver 22a respectively. b are connected with that on the surface 8th reflected light is detected.

As light sources 2a-d spectrally narrow-band LEDs are provided, the emission spectra of which are different and overlap as little as possible. light sources 2a-d and light receiver 22a, b are preferred on a board 23 mounted, which in particular contains other electronic components for their control and for measurement signal processing. A control device 24 is used for sequential control of the light sources 2a-d , In an evaluation device 26 becomes a parameter that reflects the color impression from that of the light receivers 22a, b in each case measured in the associated time windows and thus in each case associated with a spectral range corresponding to the emission spectrum of the respectively controlled light source.

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

Alternatively, the beam guidance devices 4 and 20 but also be made up of several individual parts, in particular again in the form of simple injection molded plastic parts. 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. The beam guidance devices can be used both in the one-part and in the multi-part embodiment 4 and 20 realize very compact. The size is in particular only a few cm, for example between 2 and 6 cm. Furthermore, there is an immediate assembly on the board 23 possible, which means that complex adjustment processes during production can be avoided.

In addition to using simple injection molded parts, the beam monitoring devices can also be used 4 and 20 can also be realized using standard plastic or glass fiber optic cables.

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 ,

Because the intensity of the reflected light from any light source 2a-2d is measured at two angles, by forming a quotient I _a / I _b from with the light receivers 22a, b each with the same controlled light source 2a-d Spectral calibration is not required at the intensities I _a , I _b measured at the reflection or incident angles α, β. In particular, one can Comparison of the quotients I _a / I _b of measurements on the surfaces 8th two different samples (second sample is in 1 not shown) determine whether both surfaces 8th are the same color. No spectral calibration is required for the individual measurements here either.

By comparing the intensity quotients I _a / I _{b of} two surfaces 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, by using a single exit aperture for each exit angle α, β, the light from each light source 2a-d impinging on the same surface area and the light reflected there in each case being recorded 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.

According to the enlarged representation 2 is also more clearly recognizable that the exit apertures 6a, b relative to the surface 8th of the sample are arranged in such a way that the light emerging from them irradiates the same surface area. In other words: the exit apertures 6a, b respective center axes of the light emerging from them intersect at a point P on the surface 8th the sample correctly positioned on the device 10 lies so that one and the same place 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 embodiment according to 3 alternatively, every angle of incidence α, β is a light source arrangement 2a-d respectively. 2e-h assigned, which are constructed identically, so that for each spectral composition two light sources 2a, e - 2d, h available. In this case it is either necessary that the intensity of the spectrally related light sources 2a, e - 2d, h remains at least constant in terms of both their amount 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 using a reference receiver (not shown in the figure) to determine the intensity R _a ,... R _{h of} each light source 2a-h is measured and one of these measured values for the spectrally related light sources 2a, e - 2d, h formed quotient R _a / R _e , ... R _d / R _h for the correction with the light receivers 22a and b measured intensities are used. Alternatively, 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 it is also diffuse on the surface 8th reflected light, ie light emanating from the exit aperture 6a into the entrance aperture 18b or from the exit aperture 6b into the entrance aperture 18a occurs, can be used to assess the color impression.

Claims (8)

Device for recording the color impression of a surface ( 8th ), comprising a) an illumination device ( 2 ) to illuminate the surface ( 8th ) with a plurality of light sources ( 2a-d ) for generating light of different spectral composition, b) a control device ( 24 ) for switching on the light sources successively in time, c) a light receiver ( 22a, b ) for measuring the intensity (I _a , I _b ) of the surface ( 8th ) each reflected light, and d) an evaluation device ( 26 ) to determine a characteristic value representing the color impression from the measured intensities (I _a , I _b ). 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 ). Device according to claim 2, in which the beam guiding device ( 4 ) a light guide arrangement are provided. Device according to one of the preceding claims, in which the light sources ( 2a-d ) spectrally narrow-band LEDs are provided. Device according to one of the preceding claims, in which at least two exit apertures ( 6a, b ) to illuminate the surface ( 8th ) are provided at different angles of incidence (α, β). Device according to claim 5, in which each outlet apparatus ( 6a, b ) an entrance aperture ( 18a respectively. b ) assigned. Device according to claim 6, in which each entrance aperture ( 18a, b ) a light receiver ( 2a respectively. b ) assigned. 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 ).