GB1335541A - Colour measuring devices - Google Patents

Abstract

1335541 Photo-electric colorimeters PAINT RESEARCH ASSOCIATION 6 Jan 1971 [19 Jan 1970] 2520/70 Heading G1A [Also in Divisions G2 and G3] In a device for measuring the colour of a surface 14 illuminated by a lamp 36 (e.g. via a fibre optic light guide 34), reflected light is collected by a sensing head 12 and conducted by a plurality of light guides 16-21 to a detector head 22, at least one light guide having associated therewith a filter chosen so that the detector output is representative of one of the three primary tristimulus values X, Y, Z defined by the Commission Internationale de l'Eclairage. By dispensing with the filter(s), and illuminating the surface with light from a monochromator, the device may be used as a spectrophotometer. The sensor head comprises a hemispherical shell through the top of which the input light guide protrudes with a plurality of output fibre optic guides arrayed symmetrically about the input Figs.3-5 (not shown). The detector head comprises two mutually rotatable cylinders 23, 24. The outer cylinder contains ports 23a receiving the output light guides. The inner cylinder contains two rows of apertures 24a each containing filters 26. These filters are arranged in four sets, two sets to each row. A different filter set is positioned by either rotating or axially moving the inner cylinder. A diffusing screen 33 is placed between the guide ends and a photo-multiplier 32. To measure the colour of a surface the sensing head is placed adjacent the surface and, with a particular filter set in position, the photomultiplier output indicated on a digital voltmeter and a counter 52 indicates one tristimulus value. The other values are measured with other filter sets. The colorimeter is calibrated by illuminating the detector head directly by the lamp 36, which is supplied from a stabilized source, via a light guide 40. A movable slit 42 is provided adjacent the lamp for this purpose. There may be additional subtractive filters 25, 46, 48. Automatic process control in paint manufacture is described Fig.7 (not shown). Variable capacity pumps (74-77) controlled by a central control unit (84) supply differently tinted bases to a mixer (78). On its way from the mixer to a storage vessel a portion of the paint is diverted to a constant level device Fig.6 (not shown) and its colour detected by the colorimeter. The colorimeter output is supplied via a computer (83) to the control unit, which adjusts the speeds of appropriate pumps to maintain the paint colour constant. The colorimeter may be used to monitor the colour anodizing of aluminium and in other processes such as paper manufacture, ceramics, textile dyeing and heat treatments such as hardening or annealing.