GB984232A - Apparatus for separating a preferred material of generally solid form from other matter - Google Patents

Abstract

984, 232. Sorting solid objects. NATIONAL RESEARCH DEVELOPMENT CORPORATION. May 17, 1961 [May 21, 1960; March 23, 1961], Nos. 18029/60 and 10572/61. Heading G1A. Relates to means for separating unwanted objects such as stones and lumps of earth from wanted vegetable objects such as potatoes, turnips, carrots, bulbs or tomatoes, the unwanted objects being relatively opaque to ionising radiation, e.g. X-rays, and the wanted objects being relatively transparent to such radiation. According to the present invention the objects to be sorted are deposited in a random manner on a moving conveyer belt 50, Fig. 6, of width greater than the combined widths of a plurality of said objects and at the end of the conveyer the objects fall between a radiation source and a radiation detecting arrangement on to an inclined grid comprising a plurality, e.g. 30, of closely spaced parallel elements 53 each pivotally mounted at one end, means being provided for preventing rotation of a member when an object falls thereon provided the intensity of radiation received by the detecting arrangement along a path intersecting the path of the object falling on the member exceeds a predetermined value so that a radiation-transparent wanted object is deflected by the grid to an acceptance receptacle but when a radiation-opaque unwanted object passes between the source and the detecting arrangement the grid elements in the path of the object are released thereby allowing the unwanted object to fall through the grid into a reject receptacle. In one embodiment, Figs. 1-5, the radiation source produces a radiation beam of width equal to the width of the grid and the radiation detecting arrangement comprises a row of detectors, each detector controlling a corresponding grid element. In a modification, Figs. 6-11, a single elongated detector is provided which is scanned by a narrow beam of radiation. As indicated in Figs. 1, 2 the mixed objects fed by a conveyer 21, and falling into a shoot 22 pass between a radiation source in a housing 32 and a bank of radiation detectors 33 individually associated with inclined fingers or keys 24 biased by springs 27 against a stop member 26. Each key 24 has a projection 29 held by a latch member 28 when an associated magnet 30 is de-energized, but can be rocked by the weight of an object when the magnet 30 is energized to release the latch. The radiation source e.g. one providing X-rays is pulsed for example at twenty five times per second, and a multi-channel amplifier, receiving impulses at the same rate, is also connected to the members 33 of the bank of detectors. When the beam passes through a wanted object, the detector member 33 provides a pulse which balances the pulse to the summing amplifier, so that the associated magnet 30 remains unoperated and the wanted object passes down the inclined path to an acceptance receptacle. A stone, however, reduces the pulse from one or more of the detectors 33 allowing the corresponding magnets 30 to be energized thereby unlatching the associated members 24 to be rotated by the stone which passes downwardly for rejection. The summing amplifier is connected to a mono-stable vibrator to provide lengthened pulses to operate the appropriate magnet or magnets 30. Each detector 33 is provided with a luminophor, for example lead sulphide, in conjunction with a photo-electron multiplier. In a modification, Figs. 6, 7 the objects 55 are fed by a conveyer 50 topass in front of a scintillation member extending over the width of the keys 53 operated by associated electromagnets 86 to permit rejection of stones &c. and normally allowing the wanted objects to pass via a conveyer 54 to a delivery container. The scintillator 66 is scanned by a beam from a vertical X-ray tube in conjunction with six equallyspaced slits in a rotating cylinder, each slit traversing the length of the member 66. A disc 70 having thirty holes 74 associated with a lightsource 75 and a photo-cell 76 completes one revolution whilst the beam traverses the scintillator 66, and each hole generates a pulse producing in timers 77, 78 respectively a pulse of 120 and 150 micro secs (Á secs.) duration. The timers allow a pulse to pass through a gate 82 to a gate 83 for the interval between 120 and 150 Á secs., and allow a diode pump integrator 79 to be operated by pulses from the photo-multiplier associated with the scintillator 66. At the end of the 150 Á secs. interval the integrator 79 is returned to zero for the next count. Normally for a wanted object the integrated count at the end of 120 Ásecs. balances the pulse from the timer 77 so that no second pulse is passed to the "AND" gate 83. If, however, a stone is detected, the count from the scintillation counter at the end of 120 Á secs. does not balance the pulse from the timer 77 so that in conjunction with the pulse from the gate 82, a pulse passes through gate 83 and a modulator to a radio-frequency generator energizing a coil 71 coupled to a coil 72 opposite one of thirty resonant circuits equally spaced circumferentially with respect to the disc 70, and linked by a pulsed lengthening circuit to a solenoid 86 operating its finger 53 to the vertical position to allow the stone or other unwanted object to be rejected.