Patent GB-966559-A (GB)
Title: Electrical color separation
IPC: B07C5/342
Filed: 1961-03-30
Abstract: 966,559. Photo-electric apparatus for sorting objects according to colour. MANDREL INDUSTRIES Inc. March 30, 1961, No. 11859/61. Heading G1A. [Also in Divisions G4 and H3] Reflected light from an object 165, Fig. 1, is divided by a half-silvered mirror 250 and analysed to determine the intensity of the red and green components by means of photo-electric cells 11R and 11G provided with colour filters 251 and 252, the resulting voltages being applied to linear amplifiers 253R and 253G the outputs from which are combined in predetermined proportions in mixing potentiometers 263, 265, 269 to provide control signals which fire thyratron units 274, 275, 276 when the control signals exceed predetermined levels. The thyratrons operate solenoids 186, 138, and 188 forming part of a sorting mechanism (not described) whereby objects are sorted according to their colour as determined by the photo-electric measurements. The amplifiers each have two cathode-follower output stages 15R, 16R and 15G, 16G which are arranged to provide oppositelyvarying output voltages, i.e. one output ("light-trip") increases with the intensity of reflected light whilst the other ("dark-trip") decreases. Reversing switches 57R, 57R<1>, 57R<11> and 57G, 57G<1>, 57G<11> permit either output to be selected for application to the mixing potentiometers. The magnitude of the mixed voltages applied to the thyratrons may be adjusted by potentiometers 277, 278 and 279. A more detailed circuit for one mixing potentiometer 268 is illustrated in Fig. 3 where 16R and 16G comprise two amplifier output cathode-followers (the reversing switches 57 being omitted), 18 comprises the thyratron and 285 comprises a cathodefollower interposed between the tapping of potentiometer 265 and the grid of the thyratron. Other parts of the circuit are described below. The principle of operation of the invention is described with reference graphs based on that shown in Fig. 4 where the red light intensity (abscissa) is plotted against green light intensity (ordinate). 304 denotes the grey line with black in the bottom lefthand corner and white in the top right-hand corner. Each colour occupies a unique position in the graph and the invention is concerned with sorting colours falling within a predetermined area of the graph from those falling outside the area. In a first type of operation, the tapping of potentiometer 265 is set to an intermediate position so that the thyratron firing voltage is a linear function of both "red" and "green" signals. The colour graph Fig. 5 is then divided by an inclined line 305, the slope of which is determined by the position of the tapping of potentiometer 265 and the sign of the slope of which is reversible by appropriate selection of "light-" and "dark-trip" signals. Fig. 5 illustrates the operation where the reversing switches are set for green "light-trip" and red "dark-trip". In a second type of operation, Fig. 8, the tapping of potentiometer 265 is set to an intermediate position to produce division of the colour graph by an inclined line 311, but the maximum amplitude of the "red" signal is limited to a value 312. This terminates the dividing line in a horizontal portion 314. By limiting the "green" signal similarly, a vertical portion may be added as shown in Fig. 9. Figs. 10-12 (not shown) illustrate the effect of selecting various combinations of "light-" and "dark-trip" signals. The signal limitation is effected by diodes 293, 300, Fig. 3, which are connected to the grids of the cathode followers 16R, 16G and have their cathodes returned to adjustable limiting potentials derived from the cathodes of valves 296, 303 whose grid potentials are determined by potentiometers connected across the circuit D.C. supply. Linear or non-linear resistors, Fig. 3A (not shown), may be inserted in series with the limiting diodes so that a reduced voltage variation instead of a constant voltage is produced by the limiter action, the resulting operation then occurring as indicated by the straight and curved lines 316 and 317 in Figs. 13 and 14 respectively. In a third type of operation, the diode limiters at the grids of cathode follower 16R and 16G are dispensed with and replaced by a triode limiter 321, Fig. 15, connected to the grid of the cathodefollower 285 which is connected between the tapping of mixing potentiometer 265 and the grid of thyratron 18. The grid of the limiter is connected via a potentiometer 326 to a switch 327 by means of which a selected one of the red and green " light-" and "dark-trip" signals appearing on lines 254-257 at the outputs of amplifiers 253R, 253G, Fig. 1, may be applied to the grid If the "dark-trip" green signal is used, operation proceeds as in Fig. 8; operation as shown in Fig. 9 is produced by the use of a second limiting triode connected to receive the "dark-trip" red signal. If the "lighttrip" red signal is used, the operation proceeds as shown in Fig. 17 and by the use of a second limiter connected to the "light-trip" green signal, sorting may be restricted to a completely bounded area as in Fig. 18. A modification, Fig. 16 (not shown), utilizes a limiting circuit comprised of a triode followed by a triode D.C. amplifier. A fourth type of operation, Fig. 19, consisting of sorting a coloured area bounded by three lines 343, 344, 345 of different slope is obtained by the use of three mixing potentiometers set to produce the three different slopes and whose outputs are applied through cathode-followers to fire thyratrons connected to operate a common solenoid mechanism.