GB1312111A - Web break detector - Google Patents

Abstract

1312111 Web break detectors HOE-CRABTREE Ltd 13 Jan 1971 [23 Jan 1970] 3506/70 Heading B8R A web break detector apparatus, associated with a printing machine which is supplied with a selective number of contiguous webs, is provided with a number of sensing members which are associated with a device, the device being arranged to provide a signal in response to the members sensing the absence of webs in the sensing zones and to be prevented from operation whilst the members make an initial sensing operation following start up of the machine but to be rendered inoperative to stop the machine when all the members sense the absence of webs when the machine is running at full output speed. Each web is associated a sensing member 21 in the form of a nozzle producing a fluidic signal at a sensor 22 coupled to the input of a fluidic NOR-gate 23 and a fluidie flip-flop 24 to set the latter to its switched-off state, the NOR-gate being operative to actuate an OR-gate 26, associated with an electric relay 27 in the circuit of a web severer and machine stopping, only when all three inputs are of zero fluidic value. To prevent operation of the NOR-gate 23 during starting up of the machine and until the machine has attained its full output speed and to prevent stopping of the machine due to sensing of the absence of web in a sensing zone in which the web has been omitted (not required for printing) all sensing zones are provided with fluidic valves 25 which during start up are supplied with fluidic signals. The signals are applied to the NOR-gate 23 to provide a positive signal and to the input of the flip-flop 24 to switch the latter on such that positive signals can be applied to the gate 23 and to the flip-flop 24, which is therefore mentioned in its switched-off position, by the sensor 22 when a web is present across the sensing member 21. The NOR-gate is inhibited due to the presence of web at the sensing zone and due to two positive signals being supplied to the gate 23. If a web is absent at the sensing zone the gate is still inhibited during the start up period since during this period the valve is supplied with the positive signals which are also applied directly to the gate. In the case of continued intended absence of the web at a selected sensing zone the machine is not tripped when at full speed in that the last positive signal from the valve 25 has switched on the flip-flop 24 which prevents the gate 23 from actuating gate 26. However when a web breaks when the machine is at full speed the signal from the sensor 22 is interrupted and since the flip-flop 24 has been switched-off by the preceding signals from the sensor 22, the three inputs at the NOR- gate are coincident i.e. negative and the gate 26 is actuated to stop the machine and operate the severer through the electric relay 27. A similar function is performed by an electric circuit associated with a pivotable finger driven by an electric motor (Figs. 1 and 2).