GB834584A - Improvements in or relating to apparatus for monitoring the passage of articles through a machine - Google Patents

Abstract

834,584. Conveyers. METAL BOX CO. Ltd. Aug. 9, 1957 [Sept. 11, 1956], No. 27793/56. Class 78 (1). Apparatus for monitoring the passage of articles through a machine comprises a pair of detecting devices positioned at points spaced longitudinally or laterally of the path of the articles, means for counting the signals from each detecting device, and means controlled by the counting means for actuating an alarm if the numbers of signals from the two detecting devices do not correspond in a pre-arranged manner. As shown, steel sheets issuing from a lacquering machine are conveyed past two detector coils spaced along the path of the sheets, the spacing being such that a predetermined number of sheets are disposed between the coils. Each coil 1 is connected across a tuned circuit 2 controlling the frequency of an oscillator 4, so that the passage of a sheet past coil 1 modifies the oscillator frequency. A transformer 5 having tuned primary and secondary windings has its primary in the anode circuit of valve 4 and its secondary coupled to the signal grid of a pentode valve 5. The anode of valve 4 is also coupled by a condenser to the suppressor grid of valve 5 to provide a phase discriminating circuit by which the passage of a sheet past coil 1 results in a D.C. voltage being applied via line 6 to a cathode follower stage 7 which supplies a positive pulse to a Schmitt trigger circuit 9. This results in switching of the current through anode 13 of the trigger circuit 9. In the circuit for the first coil 1 a signal is transmitted via line 10 to a valve 23 controlling the grids of a dekatron counter 12 so that the latter is stepped one step. In the circuit for the second coil 1 a signal is transmitted by the trigger circuit 9 through operation of a relay 14 in the circuit of anode 13 which closes contacts 15 in a voltage divider to supply a pulse via line 17 to a valve 24 controlling the grids of a second dekatron 18 so that it is stepped one step. When operation is to commence a re-setting switch 42 is closed to supply a negative voltage to cathodes 9 of the two dekatrons to set these to the number 9 position.. The cathodes of each dekatron are paired as shown, grids 8 and 9 being connected through a rectifier 22 to prevent grids 8 being influenced by operation of the re-setting switch 42. Lines from the paired cathodes of the dekatron 12 are taken to one input of each of a number of coincidence gates 25-29 and lines from the paired cathodes of the dekatron 18 are taken to the other input of each of these coincidence gates. The arrangement of these lines is such that so long as the dekatrons 12 and 18 are stepped together with dekatron 12 four steps ahead of dekatron 18 no coincidence gate receives a pulse on more than one of its two inputs. If the pulses get out of step a signal is transmitted by one of the coincidence gates to a corresponding one of a number of trigger valves 30-35 causing it to strike and thereby cause extinguishing of a further trigger valve 35, the latter operating a Schmitt trigger circuit 38 to switch the current in anode 39, so releasing a relay 40 which results in the operation of an alarm 41. In operation, as the first four sheets from the machine pass the first coil, dekatron 12 is stepped successively from number 9 to number 3. When the fifth sheet passes the first coil the first sheet will normally pass the second coil so that as dekatron 12 is stepped on to number 5 cathode, dekatron 18 is stepped on to number 0 cathode and no signal is transmitted by any of the coincidence gates. If dekatron 12 is switched to number 5 cathode before dekatron 18 is switched to number 0 cathode the alarm is actuated via gate 25, trigger valve 30, trigger valve 35 and trigger circuit 38. A switch is provided in the grid circuit of trigger valve 35 which when closed causes valve 35 to strike, so re-setting the alarm.