GB929104A - Improvements relating to the sorting of translucent objects - Google Patents

Abstract

929,104. Photo-electric sorting apparatus. R. W. GUNSON (SEEDS) Ltd. April 13, 1962 [April 20, 1961], No. 14386/61. Addition to 885,286. Class 40 (3). Apparatus for sorting translucent objects which modify the polarization of polarized light passing through them, such as rice grains, comprises means illuminating the objects with polarized light, a light-sensitive device receiving light passing through the objects and a polarization analyser, a sorter controlled by the lightsensitive device, and means to reduce or eliminate variations in the output of the device due to variations in object size. In a first embodiment light from a lamp 30 is collimated and passed through polarizer 33. It proceeds through halfsilvered mirror or glass plate 36, across the zone through which rice grains fall one at a time, to crossed polarizer 37, lens 38 and photo-cell 35. The output of the cell will be substantially zero in the absence of a grain and when a grain is present, rotating the plane of polarization, will depend on the transmissivity of the grain. Thus white and red centred grains may be separated in accordance with the cell output by a comparator and air-blast device 51 deflecting one type of grain to bin 54 and allowing the other type to fall vertically to bin 55. With a system as so far described the size of the grains affects the photo-cell output and to reduce the effect of this light from lamp 50 is reflected from background plate 40 and mirror or plate 36 towards the cell. The position and nature of the plate 40 are chosen so that the background light bypassing polarizer 33 is of the same order of intensity as that passing through a grain to the photo-cell. Thus a grain interrupts about the same amount of background light as it passes polarized light and variations due to grain colour show as deviations from a substantially constant level. In a second embodiment (Fig. 2, not shown) the background path arrangement is not used and instead a separate infra-red source provides energy reflected by each grain (when in the light path) through the analyser and by reflection from a beam-splitter to a second photo-cell having a filter in front of it capable of transmitting only infra-red. The light-sensitive device (35) is chosen to be insensitive to infrared. The outputs of the two detectors are fed to a difference circuit whose output controls the air valve. In a third arrangement (Fig. 3). light from a source 70 is directed through a system substantially as in Fig. 1 to detector 35 except that beam-splitters 63 and 71 and filter 72 are interposed in front of the detector. Filter 72 passes only visible red light and the reflected beam from beam-splitter 71 is directed through filter 74, passing yellow light, to a further photo-cell 73. An amplifier 75 is connected to give an output representative of the ratio of red and yellow light. To compensate for grain size the infra-red energy from the lamp 70 as interrupted by the grain is reflected from splitter 63 through filter 64, passing infra-red only, to detector 65. The output of this detector which is dependent on grain size is used to modify the output of amplifier 75 and make it substantially independent of grain size before it is applied to control the sorting.