Patent GB-717031-A (GB)
Title: Improvements in or relating to machine guards
IPC: F16P3/04
Filed: 1949-11-28
Abstract: 717,031. Machinery guards. A. P. V. CO., Ltd., and BROWN. W. J. Nov. 28, 1950 [Nov. 28, 1949], No. 30428/49. Class 80 (4) A guard for a metal folding or other machine is operated by power means and carries one or more detector components associated with electric switches so that should the guard encounter an obstruction-e.g. operator's handduring closing it is returned to its open position. but if its 'closure is unobstructed a clutch is automatically engaged to start the machine. As shown, a guard beam 20 extends across a crankshaft-operated folding blade 11 and is linked to two air cylinders 26 by which the guard is held raised. Two or more detector gates 21 extending along the beam 20 are removably attached to slides, Figs. 3 and 4 (not shown), thereon so that as the descending guard Closes the gates are moved relatively to the beam and each slide simultaneously operates a pair of switches. The switches, which are mounted on the beam, are normally open and each pair comprises a switch 36. Fig. 5 and a switch 37, all the switches 36 being connected in parallel while all the switches 37 are connected in series. Fig. 5 shows the basic switching circuit controlled by a pedal switch having contacts 48, 51 Normally the contact 48 is closed so that.a relay CV is energized from the supply 49-50 and holds closed an exhaust valve in each air cylinder 26 sc that the guard is held raised. On depression of the pedal switch the contact 48 is opened, thus deenergizing the relay CV which opens the exhaust valves so that the guard 20 descends. At the same time contact 51 is closed so that when the gates 21 engage the work and close the switches 36 a relay HO is energized through contacts 51, 52, 36 to close hold-on contact 53 and to change over contact 52. If all the gates 21 have engaged the work simultaneously the series-connected switches 37 are all closed so that the change-over contact 52 energizes a relay AC which operates an air-controlled clutch to start the machine. The relay AC also opens a normally-closed contact 54 so that the relay CV remains de-energized. If, however, one of the gates 21 meets an obstruction in its descent the respective switch or switches 36 will be closed, thereby operating relay HO, but not all the switches 37 will be closed so that the relay AC remains de-energizedi.e. the clutch is not engaged and contact 54 remains closed so that the relay CV is operated to raise the guard. A development of this basic circuit is shown in Fig. 6. the parts being in the guard-open position. A pair of bottom limit switches 60 on the frame are connected in series with the switches 37 so that the guard will be operative with only one gate 21, if so required. In addition to the clutch relay AC and hold-on relay HO, the circuit includes a back stroke relay BS controlled by three cam-operated switches TLS, GLS, BSS actuated by the machine, a clutchoperating sclenoid ACO controlled by the relay AC, a pair of change-over switches MS, AS, and two 'solenoids CVF and CVS replacing the relay CV of Fig. 5, the former solenoid initially permitting. on energization, rapid exhausting of air from the cylinders 26, while the solenoid CVS thereafter (when contact 72 is broken) ensures a throtted exhaust, i.e. a controlled descent of the guard. The contact 72 is operated by a finger 106 on a block, Fig. 9 (not shown), frictionally supported on a rod depending from the lever 23, the block having limited movement between upper and lower stops. The circuit has power supply lines 49, 50 and is controlled by a pedal switch having two normally-open contacts 51, 64. The pedal may be responsive to two pressures so that on light pressure contact 51 is closed to actuate the guard mechanism, an uninterrupted descent of the guard resulting. as in the Fig. 5 arrangement in the energization of relay AC. while a heavier pedal pressure is required to close contact 64 and thereby supply power to the clutch-operating solenoid ACO. A lamp 90 may be provided to indicate completion of the circuit to AC. The manual switch AS enables the machine to be changed from control by the guard to direct control by the pedal switch 64 the contact 66 rendering the guard inoperative. Change-over of the manual switch MS brings down the guard and renders the blade 11 inoperative. thus enabling the guard to be set at various tooling heights, and the bottom limit switches to be adjusted. The switches TLS, GLS and BSS are operated by a plunger connected to the blade 11. As soon as the blade commences its downward stroke the switch TLS closes. and at predetermined point in its descent the switch GLS is closed thereby energizing relay BS which breaks the circuit to relays HO. AC and CVS but maintains the solenoid ACG energized so that the guard is raised while the blade 11 completes its stroke. During the blade's return a back stroke switch BSS is closed to maintain relay BS energized as switch GLS is opened, this relay being de-energized when switch TLS is opened at the upper Made position so that the solenoid ACO is de-energized. A mercury switch 85 on the relay BS closes and re-opens to re-establish the holding circuit of relay HO so that the guard is held raised until the pedal is released and re-depressed. In a modified circuit each switch 36 has associated therewith an overriding switch which is operated should the switch 36 fail, the overriding switches being connected in parallel to operate a relay having a contact in the line between relay AC and the switches 37.