GB2030721A - Colorimeter - Google Patents

Abstract

In a portable colorimeter for the measurement of surface colour to determine the characteristics of any given colour according to the CIE system and the SINOID system, the colour to be measured is optically contrasted with a colour obtained by additive mixing from standard etalons with standard black and standard white until a colour identical with the colour to be measured is produced. The phenomenon that the components of different primary or secondary light standards can be intermixed by using a surface that reflects all light diffusely is employed. The surface to be measured and the measuring surface, which latter is symmetrically variable with respect to the proportions of colour components but which is of constant overall size are illuminated by a common light source. The resulting colour, which can be varied by varying the relative areas of the standard components is mixed by being reflected from the measuring face to the observer by means of a diffusely reflecting mirror. <IMAGE>

Description

SPECIFICATION Colorimeter The invention relates to a simple, portable colorimeter of small dimensions suitable for the direct measurement of the colour of bodies in various positions and having various surfaces with the aid of which apparatus the characteristics according to the international colour scale system (CIE), and the colour tone, the saturation and hue as defined by the SINOID system, can be determined and the given colour can be visually presented by means of a group of numbers.

The invention accordingly concerns a colorimeter, the essence of which is that the colour to be measured by the colorimeter is optically matched with a colour mixed with standard colour etalons by the additive mixing method producing a colour which is identical with the colour to be measured.

In hitherto known visual colorimeters additive colour mixing is carried out with the aid of a so called Ulbricht-Sphere, Maxwell's disks or with filters made of opaque glass. Although these devices are suitable for the continuous measurement of all colours, they all have excessively large dimensions and are difficult to handle. Moreover, due to the necessary change of the colour standards or etalons for each group of colour tones, the handling of these devices is very time-consuming. If on the other hand this kind of device, but with reduced dimensions, is used, the field of application and the range of measurable colours is limited.

With the instrument according to the invention, and in contrast to known visual colorimeters, additive colour mixing is based on the physical phenomenon that the additive colour mixing of the light of different primary and secondary light sources can be carried out with the aid of a common surface that reflects diffusely the light of all light sources.

In the sense of the basic design principle of the instrument according to the invention which is different from known colorimeters the 48 colours functioning as secondary light sources for the additive colour mixing, as well as the white and black standard etalons are arranged on three, cylindrical surfaces which lie on a common geometrical axis but which are separately movable.

Turning rings for operating the movement of the cylindrical barrels and the ratio of the faces of each two adjacent colours serving as components for the colour mixing as well as the white and black standards, can be set on the measuring faces functioning as secondary light sources.

Within the spirit of the invention, in this instrument the surface to be measured and the measuring face, which is symmetrically variable but the total size of which corresponds to that of the face to be measured, and which is composed of two colours, the white and black etalons, are illuminated by a common light source. The resulting colour reflected from the measuring face can be changed by the light obtained from colour mixing effected by a diffuse reflecting mirror.

The comparison of colour is related to the illumination produced by one single light source built into the instrument, thus ensuring a perfect conformity of all optical paths. During the measurement process, the faces to be measured and the measuring face are reflecting surfaces under identical conditions. The optical paths are chosen in such a way that opaque (matt) surfaces and surfaces of high luminous density can be measured equally.

The invention is described, purely by way of example, by reference to a preferred embodiment illustrated in the accompanying drawings, wherein: Figure 1 is a schematic broken-away section of the instrument according to the invention, and Figure 2 illustrates the relative disposition of the colour standards or etalons and wedge elements embodied in the instrument.

As shown in the drawing, the apparatus has a cylindrical shape, where the diameter of the cylinder is 228 mm and the height is 120 mm. The cylinder is formed by three turnable rings 2, 3 and 4 guided by a sliding bearing 1. Since the turnable rings 2, 3 and 4 run on a rigid, stationary ring system 6 held together by outer spacers 5, the movement of the individual turnable rings 2, 3 and 4 takes place independently from one another. The diameter of the ring system 6 amounts to 266 mm; the system is bounded by a cover plate 7 and a base plate 8.

The colour standard etalon series 10 containing 48 periodically uniform, colour rings of different colour tones in close contact with each other is arranged on the internal surface of the central ring 3. The etalons are mounted on a spring-hard brass plate 9 with a thickness of 0.3 mm and snap interchangeably on the ring 3. The accuracy of positioning is ensured by a 0.4 mm deep notch machined into the central rotary ring 3. The colour standard etalon series 10 snapping into the ring 3 does not form a closed colour circle, so that in order to obtain continuity in colour mixing, the first colour at the end of the series of the colour standard etalons containing 48 colours and the last colour at the beginning of the series are repeated; thus the central turnable ring 3 contains 50 colour etalons within the colour standard etalon series 10.

The colour standard etalon series 10 can be set to within + 1 mm, and after setting, can be calibrated.

A wedge element 11 made of a spring-hard brass plate, 0.3 mm thick, is fastened to the inner face of the upper turnable ring 2. The wedge element 11 can be screwed to the upper turnable ring 2 via a shim plate, which also has a thickness of 0.3 mm. Thus the said wedge element 11 can move about the etalon series 10 without actually touching it.

If the upper turnabie ring 2 and the central turnable ring 3 are shifted relatively to one another, the wedge element 11 can cover each individual member of the colour standard series 10 in the range between 0% and 100%. The inner face of the wedge element 11 of the upper turnable ring 2 is painted white with titanium oxide and this white face serves as white etalon standard for the colour mixing. The wedge element 11 can be set with an accuracy of +1 mm and arrested after the completion of the setting. An overrun of the wedge element 11 is prevented by a back stop.

Another wedge element 12 made of a 0.3 mm thick spring-hard brass plate is fastened on the inner face of the lower turnable ring 4. The wedge element 12 can be screwed on the lower turnable ring 4 via a shim plate which also has a thickness of 0.3 mm. Thus the wedge plate 12 can be moved directly over the colour standard series 10 without actually contacting the talons. If the relative position of the lower turnable ring 4 and the central turnable ring 3 is changed, the wedge element 12 can continuously cover each individual member of the colour standard etalon series 10 within the range of 0% to 100%. The inner face of the wedge element 12 of the lower turnable ring 4 is painted black and this black surface serves as a black standard. The wedge element 12 can be set with an accuracy of +1 mm. and after calibration, it can be arrested.The overrun of the wedge element 12 is blocked by a back-stop.

An optical system 1 3 is arranged as a selfcontained unit is so disposed in the interior of the cylinder consisting of the turnable rings 2, 3 and 4 as well as of the stationary ring 6 that one of the planes of symmetry of the optical system 13 forms the plane of bisection of the cylinder.

The testing aperture 14 of the optical system 13 is inserted into an opening 1 5 of the base plate 8 of the instrument; a mixing aperture 1 6 is arranged at such a distance from the colour standard etalon series 10 that the wedge elements 11, 12 can move along and in front of the etalon series without actually touching the mixing aperture 1 6. The framework of the optical system 13 is formed by a tube system, the interior of which is painted black and which is provided with three openings. The optical system 13 can be set in a radial direction with an accuracy of +0.25 mm to enable measurement errors caused by inaccuracies in the manufacture of the instrument to be corrected.

The optical system consists of the testing branch 17 as well as of the mixing branch 18 the optical paths of which are identical.

The testing face 1 9 and the measuring face 20 are illuminated by a built-in incandescent lamp 21. The incandescent lamp 21 can be rotated together with its lampholder; its position in relation to the axis of rotation can be set and arrested in the required position.

Through setting of the position of the incandescent filament along both optical paths an illumination of equal brightness can be achieved.

After removal of the cover plate 7 the incandescent lamp 21 may be replaced simply without changing the position of the optical system 13.

The correspnding colour temperature is established with the aid of a built-in, readily interchangeable colour filter 22; the illumination is provided by a 10W haiogen lamp 21. The incandescent lamp 21 can be cooled by natural air circulation through air channels 23 completely separated from the branches 17, 1 8.

The light of the incandescent lamp 21 in the testing branch 1 7 reflected by the surface 19 to be measured and the light in the mixing branch 18 reflected by the measuring surface 20 are mixed by a diffusing mirror 24. Thereafter, the light is directed via prisms 25 into the observation branch 26 of the optical system 13. The image definition can be controlled by adjusting an -eyepiece 27.

The surface to be measured can be reduced to one-half or to one-quarter of its size by changing a locking plate 28; the width of the aperture of the locking plate 28 is constant. By changing the locking plate 28 colours with higher saturation than the ones included in the colour etalon series 10 cap also be measured. The colour etalon series are produced from pigments of high stability which do not discolour under the effect of light and from dyestuffs with binders of a synthetic resin base that scarcely changes with time. An early staining of the colour etalon series 10 is avoided by the totally enclosed system formed by the turnable rings 2, 3 and 4 as well as the stationary ring 6.

After completion of the calibration of the etalon series 10 with the aid of a high precision calibrating instrument (spectrophotometer), reading scales 29, 30, 31,32 and 33 are formed and secured to the outer side of the turnable rings.

The scale won the scale 29 of the uppermost turnable ring 2 has uniform divisions and changes evenly between 0 and 1. The reading on scale w gives the quantity of the colour "white" in the mixing.

The following scales are located, from top to bottom, on the scales 30, 31, 32 of the central turnable ring 3; on the uppermost scale 30 the colour tone A, on the central scale 31 the colour saturation Te of the etalon and on the lower scale 32 the coefficient of the luminous density Ye (according to the CIE Colour System) of the colour of the etalon can be read.

On the scale 33 of the lower turnable ring c=1 -S, where s is the quantity of the colour "black" of the etalon in relation to the whole of the measuring face. The scale 33 varies linearly from 0 two 1.

From the readings taken from scales 29, 30, 31, 32, 33 the SlNOID-coordinates can be calculated by the following formulae: A=is given by direct reading T=(c--w)T, V=100d, where: Y=(c=w!Ye+wY,,+(1 (1-c)Y6and Y6=the Y,,=the brightness or hue of the standard- white Y,,6=the brightness or hue of the standardblack The ClE-Colour characteristics can be calculated from the formulae: pRa+0.980706w pSa+3.1 62955w pya+w Ye pSa+3.1 62955w where:: p=c-w S=1-c

R=f,(A) The values can be obtained from ya=2(A) J tables attached to the instrument.

s=xa+ya+zce=3(A) Y=(c-w)Ye+wYwe+ (1 -c)Yse Should the colour etalon series 10 become soiled, they have to be removed and replaced; the reading scales 29, 30, 31,32, 33 need only be changed if the new etalons do not conform with the previous ones.

The measuring of colour is carried out with the instrument according to the invention as follows: The colour 1 9 to be measured is placed under the aperture 1 5 of the instrument. The incandescent lamp 21 is switched on by a pushbuttom switch 34. Thereafter, on looking into the instrument through the eyepiece 27 the colour to be measured appears in the lower part 36 of the field of vision 35. The colour appearing in the upper part 37 of the field of vision 35 is modified by turning the turnable rings 2, 3 and 4 until it coincides with the colour appearing in the lower part. The colour modification begins by moving the centre turnable ring 3, whereby to adjust the colour tone.

Hereafter, the lower ring 4 or the upper ring 2 is turned in order to obtain the required colour saturation and brightness (hue). If the saturation and hue controls have "used up" all further possibility of approximation, the colour tone is repeatedly modified and set to a more accurate value resulting from the approximative saturation and hue; thereafter the coincidence of the hue and saturation is corrected again by the turnable rings 2, 4.

The procedure of correction is continued until a position is arrived at, where no difference between the parts 36,37 of the field vision 35 can be observed. If this position is arrived at, the corresponding values are read from the scales 29, 30, 31, 32 and 33 and from the readings the coordinates of the tested colour are determined.

Claims (7)

Claims

1. The colorimeter instrument for eiiminating the CIE and SINOID coordinates of coloured surfaces and for visually presenting colours defined by the coordinates, comprising a visual sensor coupled to the colour standard etalon series built into the instrument and the visual sensor being adapted for the comparison of the colour to be measured with a colour obtained by additive mixing from the said etaloti series by way of a diffusely reflecting surface.

2. A colorimeter according to claim 1 wherein the colour etalons built into the instrument are movable on a concentric ring system so as to enable the additive mixing all colours perceptible by the human eye within the limits of saturation resulting from the colour standards.

3. A colorimeter according to claim 1 or 2, wherein the white and black colour content are respectively adjusted by directly admixing the light providing the illumination and by reduction of the intensity of illumination.

4. A colorimeter according to any preceding claim, wherein a locking plate is insertable into a testing aperture of the instrument to enable colours with higher colour saturation than the colours contained in the etalons to be measured.

5. A colorimeter according to any preceding claim, wherein the etalon mounting is of a readily exchangeable kind so that soiled etalons can be replaced by new calibrated etalons and by changing the etalons the associated reading scales can also be changed.

6. A colorimeter according to any preceding claim, wherein the CIE and SlNOID-colour coordinates can be calculated from the readings taken from the scales of the instrument by means of simple formulae.

7. A colorimeter substantially as herein described with reference to and as shown in the accompanying drawing.