Patent GB-1373975-A (GB)
Title: Automatic grader
IPC: B07C5/342
Filed: 1972-02-29
Abstract: 1373975 Photo-electric sorting apparatus AMF Inc 29 Feb 1972 [20 May 1971] 9235/72 Heading G1A Tobacco leaves are examined sequentially as they pass over a coloured background by photoelectric apparatus producing first and second signals representing the intensities of reflected light of two different colours, the signals being used to provide respective logic signals representing the brightness and the colour tone of leaves relative to the background, these signals being supplied to a further logic circuit in which characteristics of leaves to be rejected can be programmed. Leaves T pass over background plate S, Fig. 1 which may be charged to provide the reference colour required, and reflected light is passed via lens A3 aperture plate A4, range filter OF and lens AS to red filter RF. Red light is detected at detecter RD and orange light reflected from the surface of filter RF by detector OD. For the brightness evaluation, preferably the outputs of the detectors are summed in an adding circuit forming part of circuit 34. However, if a single detector is used, a circuit as in Fig. 4 may be used. The photo-tube or photo-diode OD output is compared with a voltage representing the background brightness value, which is stored in capacitors C1, C2, to develop a signal detected by voltage follower field effect transistor and amplified by operational amplifier, which is applied to level sensing transistor circuit. A higher level of brightness of a leaf as compared with the background causes a signal at 38B1 and a lower level, a signal at 38B2. When a leaf is not present and the background is being sensed, a zero level is obtained at 126. During periods when leaves are being viewed, FET gate 108 is closed to prevent false data being stored in capacitors Cl, C2. In an alternative circuit, a photo-responsive field effect transistor is substituted for OD and ODNA. The colour tone evaluation is of the degree of greenness of a leaf in comparison with the background and is determined by subtracting the orange and red detector outputs in circuit 36 and applying the difference signal to detector circuit 40 which provides a higher or lower indication similar to that of the brightness detector. The resultant signal on four lines is in binary code and represents five conditions: light and not green; light and green; dark and not green; dark and green; and background only (leaf absent). The codes corresponding to leaves having conditions that make them unacceptable, are selected by colour selector 46Q2 as to produce an output from colour logic decoder 46Q1 which will cause the required rejection. The rejection signal is delayed in shift register 48Q1 and energizes solenoid pulse generator and driver 48Q2, Q3, to operate air jet reject mechanism 18. The circuit of Fig. 3 also shows the feedback loop whereby the background reference signal is applied to the colour detectors, including a control link 46M to alter the sensitivity to green. A clock pulse  generator C9 is used to synchronize operation of the circuit with the frequency of the A. C. supply to the lamps. The circuit includes a facility for detecting if leaves become lodged on the background plate. In an alternative mode of operation, acceptable leaves are operated on by the air jet and unacceptable ones follow the normal trajectory from the belt 12.