GB703694A - A method and means for sorting - Google Patents

Abstract

703,694. Photo-electric sorters. NATIONAL COAL BOARD, WHELAN P. F., and EDMONDS, DE L. E. Oct. 15, 1951 [Oct. 18, 1950], No. 25410/50. Class 40 (3). [Also in Group XXIX] Articles are sorted by determining photoelectrically the relative specular and diffuse reflectivity of each object. As shown, lumps of coal, the bright ones of which are to be diverted into a compartment 15 pass one at a time down a shoot into a compartment 14. Each passes over a narrow slit 1A in the shoot and the underside of the slit is illuminated by a source 3. Two photo-cells 4, 5 are provided which receive light reflected from the coal. Cell 4 receives specularly reflected light with the assistance of a reflector 4A and cell 5 which is situated in a reflector 5A receives diffused light. The output of the cells are compared in an amplifier 6 the output of which may depend on the difference of the cell responses or response of one cell and a multiple of the other. This output operates on an electromagnetically controlled valve allowing a fluid pressure servo system (vide infra) to move a deflecting flap 12. A time delay device may be incorporated in the amplifier circuit to allow the coal to reach the flap. In the embodiment of Fig. 2 (not shown) two separate light beams alternately chopped by a rotating wheel, Fig. 5 (not shown) are used. The first projects light at right angles to the conveyer surface, the second at 45 degrees. A single photo-cell is employed, the axis of the reflector being at 45 degrees to the conveyer surface, so that this cell receives alternately diffusely and specularly reflected light from the first and second light sources respectively. The amplifier compares the two sets of pulses and operation of the valve is as for Fig. 1. In the embodiment of Fig. 3 a single source 3 directs light from the reflector 19 through a lens 21 on to the aperture in the conveyer. Specularly reflected light is teflected back through the centre of the lens to a cell 4 while diffusely reflected light is received through the outside of the lens by cell 5. Otherwise operation is as for Fig. 1. In the arrangement of Figs. 4 and 7 (not shown) the light source and the lens are arranged as in Fig. 3 but specularly reflected light in passing back through the centre of the lens is directed by a prism through an outer row of apertures in a rotating disc ; diffusely reflected light passes through an inner row. This cell 24 receives alternately specularly and diffusely reflected light. Operation is otherwise as in the embodiment described in connection with Fig. 2.