Patent GB-943274-A (GB)
Title: Improvements in or relating to check weighing apparatus
Inventor: MACDONALD ALEXANDER TORRANCE
IPC: B07C5/32
Filed: 1960-11-04
Abstract: 943,274. Weighing apparatus; voltage measurement. SPERRY GYROSCOPE CO. Ltd. Sept. 8, 1961 [Nov. 4,1960], No. 37952/60. Headings G1N, G1U and G1W. A check weigher comprises a signal generator actuated by a weighing head and means under the control of the output of the signal generator for slowly moving the indicating member from a datum position towards a position in which it gives an indication representative of the weight of the article, the sense in which the indicating member is moved with respect to the datum position being determined according as the weight of the article is greater or smaller than the weight represented by the position of the indicator during the weighting of the article. The articles to be check weighed are placed on a platform 1 which sinks against the resistance of a float cylinder 3. The consequent engagement of contacts 6 and 7 completes an electric circuit which operates as described in Specification 633,075 to accept articles in the expected range of weight. The movement of the platform 1 is detected by an electrical pick-off device 13 which emits a signal that varies in strength according to the position to which the platform 1 sinks under the weight of the article. The signal is fed to a device 22 which combines it with another signal fed from a second pick-off device 25. This pick-off device, energized from terminals 57, 58, is actuated by rotation of a shaft 54 and correspondingly controls the signal, transmitted through conductors 55, 56, to the combining device 22. The combined signal passes through an amplifier 26, phase-sensitive detector 27 and gating device 59 and is applied as a D.C. signal to a coil 28 which is rotated between the poles 29 of a magnet. The movement of the coil 28 operates the pick-off device 25 through a coupling comprising two radial arms 50, 53 with a connecting pin 51. The signal from the phase-sensitive detector 27 applied to the coil 28 represents the difference between the electric signals from the pick-off device 13 and the pick-off device 25 and is indicative of the amount and sense of any difference between the weight of the article and that of previous articles. The pickoff device 25 is moved in a sense which adjusts its output signal so that any difference which exists between it and the signal from the pick-off device 13 is minimised. A pen arm 39 is attached to the coil 28 near its upper bearing and is arranged to mark a chart 40 which is moved under it by a take-up reel 46 driven from a motor 44. No spring or other control is applied to the pen arm 39 and thus the friction between the pen 41 and the chart 40 maintains the pen in any position to which it is moved. The gating device 59 causes the signal to be applied to the coil 28 intermittently, the gating signal being derived from a gate pulse generator 60 which is synchronized with the movement of the weighing platform 1 by a synchronizing signal from a switch 65 coupled to the support 2 of the weighing platform 1, whereby the device 59 opens for a short time when the support 2 is at or near the lower part of its movement. Due to the timing of the operations of the check weigher and gating device the amplitude of the D.C. signal applied to the coil 28 indicates the sense of the difference which exists between the signals from the device 13 and 25 and the position taken up by the pen 41 indicates the average weight of the article weighed. A wavy line will be traced on the chart which will wander about the position that it would assume if all the articles weighed the same and if the pen traces a wavy line that deviates from that position it will show the variation in the average weight of the articles.