Patent GB-1491813-A (GB)
Title: Mechanism for controlling safety guard or protective cover respectively on printing machines
IPC: F16P3/08
Filed: 1975-06-26
Abstract: 1491813 Machinery safety devices ROLAND OFFSETMASCHINENFABRIK FABER & SCHLEICHER AG 26 June 1975 [26 June 1974] 27121/75 Heading F2J In a machinery safety device for an offset printing press the opening of any guard or cover 20, 30, 40 operates, i.e. opens a first switch contact 21 of a control switch 22 to switch off the press but simultaneously operates, i.e. closes a second switch contact 24 of the switch 22 to condition a machine override, i.e. starting key 23 into a state of readiness whereby authorised maintenance personnel may run the press at a crawl, i.e. slow speed in order to be able to make any necessary adjustments, &c., the override starting key 23 and switch 22 being arranged in a control box 25 hidden, during normal press running, from unauthorized personnel by the guard or cover 20, 30, 40. Fig. 2 shows the electrical circuit for one safety guard 20 only, e.g. on a two-colour printing press during the normal operation of which the guard 20 is closed. With the guard 20 closed a relay 11 is switched on via the contact 21 of switch 22 whereby the press driving motor 12 may be energized by means of keys 13, 14 and a relay 15. On opening of the guard 20 the relay 11 is switched off by the opening of the contact 21 of switch 22 to stop the motor 12 and simultaneously the override key 23 is brought to a state of readiness by closure of contact 24 of the switch 22 such that the motor 12 can be started by the key 23 and the relay 15. Figs. 1 and 3 show a four colour offset printing press and an electrical circuit for controlling three safety guards or covers 20, 30, 40, three control boxes 25, 35, 45 each housing the respective switches 22, 32, 42 and override starting keys 23, 33, 43 being arranged, as in the first embodiment of Fig. 2, adjacent to and hidden behind the guards 20, 30, 40 when in their closed position, as shown. In this arrangement the opening of any one of the guards 20, 30 or 40 operates, as in Fig. 2, to switch off the machine via first switch contact 21, 31 or 41 and as before, closes the second switch contact 24, 34 or 44 to condition the override key 23, 33, 43 into a state of readiness for starting the press for maintenance work. However if while one guard (e.g. 20) is already open and a further guard (e.g. 30) is also opened a relay 16 is switched by contacts 26, 36 whereby the motor 12 cannot be started by the override keys 23, 33 thus ensuring that when the press is being operated by an override key 23, 33 or 43 only one such key is usable by the opening of only one guard 20, 30, 40, the opening of any additional guard 20, 30, 40 rendering all the override keys 23, 33, 43 inoperative to prevent accidents. In similar manner, the additional opening of the guard 40 with guard 20 already open renders the override keys 23, 43 inoperative by closing the contacts 27, 46. In each arrangement the guard control switch 22, 32, 42 is prevented from further operation, once the guard 20, 30 is opened, by means on the guard 20, 30, 40, which means may be a cam (28) (Fig. 4, not shown), a spring-biased plunger rod (51) (Fig. 6, not shown), a plunger (61) which covers and uncovers a pair of spaced light beams (62, 63) (Fig. 7, not shown) when the guard is closed or opened, or, a pair of spaced microswitches (72, 73) operated by a plunger (61) on a guard (60) (Fig. 8, not shown).