Patent GB-1460527-A (GB)
Title: Automatic grader for sorting objects according to brightness and colour tones
IPC: B07C5/342
Filed: 1974-04-10
Abstract: 1460527 Photo-electric sorting AMF Inc 10 April 1974 [15 May 1973] 15838/74 Heading G1A In a system for sorting articles such as tobacco leaves according to their brightness and colour tones, the articles are illuminated with polychromatic light as they pass over a background of known colour, and the light reflected from the articles is measured in three spectral bands; these measurements are combined to give the brightness of the articles and also the amount of two different colour tones, the results being compared with pre-selected values and the articles being rejected if they fall outside a given deviation from the preselected values. One of the three spectral bands is chosen such that the reflectivity of the articles in that band is uniform from one article to the next, so that by measuring in that band an estimate of the article size is made and the signals in the other two bands can be normalized.  Fig. 1 shows tobacco leaves T projected over a background plate S by a conveyer 12. A set of lamps L illuminated the leaves, and reflected light is collected by telescope A2 and directed to detectors RD, FD, ID. These detectors comprise photodiodes or transistors each having a filter to select a spectral band. For tobacco the filters are centred on 540nm. (green), 670nm. (red) and 900nm. (infrared). The signals from the detectors are combined according to given equations, the infrared signal being used basically to determine leaf size and the red and green signals to determine its colour. If a leaf is unsatisfactory the electronic circuitry 14 activates an air blaster 18 to deflect the leaf into a bin BR, while satisfactory leaves pass to bin BA. The apparatus operates on a cyclic basis synchronized with the mains supply. Each detector signal is integrated in each cycle for a length of time determined by switches on a control panel. By setting these switches, an operator can thus set values into the apparatus and the leaves are compared with these values. If, after manipulation by the circuitry, the combined integrated values fall outside a given range, the leaf is rejected. The control panel is shown in Fig. 2 and is divided into six zones of brightness and colour. By setting control switches ZBD, ZBG, ZBR, ZDG, ZDR the shapes of the zones can be changed, and switches TS1-TS6 determine whether leaves falling in a given zone are kept or rejected. Thus to accept only bright green leaves, ZBG and ZDG would be set to define the amount and range of greenness falling in the bright green zone, and TS1 would be set to "keep", all other TS switches being set to "reject." The background plate S of Fig. 1 serves as a reference calibration. The colour of this plate is measured and stored in each cycle to compensate for drift in the system. The use of a coloured plate also allows allowance to be made for leaves which do not fill the whole field of views of the detector, since the amount of light reflected from the plate is known. A blower is provided to keep the plate clear of debris, and if a leaf etc. becomes stuck on the plate, a lamp on the control panel indicates this. Details of the mathematical operations effected on the signals are given, as are details of the analogue and logic circuitry involved and of the manner in which the control panel switches are pre-set for  desired results. An embodiment is described which is basically four of the above systems which are controlled by a common programmer; the four systems operate simultaneously, their outputs being computed in serial form through a common logic arrangement. The four systems have their controls all on a common panel, and operate in series on a batch of leaves to sort them into desired categories.