Patent GB-688894-A (GB)
Title: Apparatus for use in colour matching
IPC: G01J3/46
Filed: 1946-10-16
Abstract: 688,894. Calculating-apparatus. AMERICAN CYANAMID CO. Oct. 16, 1946 (Nov. 2, 1946], No. 30839/46. Class 106 (i). [Also in Group XXXVI] Apparatus for determining the integrated tristimulus values for a mixture of dyes comprises means, for each dye, for generating, for each of a selected number of wavelengths of light, a physical quantity corresponding with the product of the concentration of the dye and the particular value of an additive light-absorption function, means, for each selected wavelength, for summing these quantities to produce a quantity representing the reflectance of the mixture at the particular wavelength, means, for each selected wavelength, to produce three quantities corresponding with the products of reflectance and the tristimulus values, and means for summing these three sets of quantities to determine the integrated tristimulus values. As shown, the three tristimulus values of a colour to be matched are set on the apparatus which then computes the relative concentrations of three dyes, on a given substrate, necessary to produce a match. The concentrations of the dyes are represented by the vertical positions of three horizontal arms, e.g. 286, driven up and down scaled racks by motors, e.g. 288. Eleven chains secured to each arm are also each secured to a corresponding arm, e.g. 311, of one of eleven pivoted balances, e.g. 331, corresponding with eleven selected wavelengths. The position of the chain on each balance arm is set according to the corresponding value of the appropriate light-absorption function K so that the resultant moment on each balance represents the sum of the products of the concentrations and the values of the functions K. An arm, e.g. 351, carried by each balance controls a reversing switch 431 for a motor 371 which controls a balancing chain and also drives a cam 443 so as to position a further set of three chains 450 according to the reflectance of the mixture at that wavelength. These chains and those of the similar balances are also secured to three balances 428 at distances along the balance-arms 447 corresponding with the tristimulus coefficients for the corresponding wavelengths. The moment thus applied to each balance represents the corresponding integrated tristimulus value and is opposed by the moment of a counter-weight, e.g. 451, set on an arm 342 in accordance with the corresponding tristimulus value of the colour it is desired to match. The arm 342 controls a reversing switch 322 for the corresponding motor 288 to adjust the concentration of one of the dyes in a direction to produce a match. When the machine stops, the required concentrations of the dyes may be read from the scales on the racks of the arms, e.g. 286. In an alternative arrangement, given concentrations are hand-set and the final balances are achieved automatically by motors which also operate tristimulus indicators. Arrangements employing electrical analogues are also described (see Group XXXVI). The several steps of the calculation may be performed variously by mechanical or electrical means. Specification 432,306, [Group XX], is referred to.