GB698579A - Dual-switch control means for starting machines - Google Patents

Abstract

698,579. Machinery safety devices. HERBERT, Ltd., A. Aug. 17, 1951, No. 19410/51. Class 80 (iv). A safety device for machines such as diecasting machines or presses in which two separate starting switches are provided for simultaneous operation by the two hands of an operator comprises a time delay switch in the circuit of the starting relay which is opened to prevent starting of the machine should there be a delay beyond a predetermined period between the operation of the twostarting switches. The onergising coil A of a starting contactor for the machine is arranged between the supply mains 11, 12 together with the coils of relays C, D, E and F. The relays C and D are controlled by the starting switches 16 and B respectively and actuate switches C1, D1 in series in the circuit of coil A. The relay E which is normally energised controls a switch E1, which is normally closed, also in the circuit of coil A. The relay F is a time delay relay which actuates a switch F1 in the circuit of relay E and is controlled by switches B1, 18, E2, D2, C2. A1 is a holding switch for coil A, 13 is an overload switch and 14 is a stop switch. When both switches 16 and B are actuated together to start the machine, the relays C and D are energised to close switches C1 and D1 and the circuit of coil A is completed, E1 being already closed so that the starting contactor is operated to start the machine. Relay F is not energised since switch B1 is opened, being,operated with B, and switch C2 is also opened whilst D2 is closed so that this relay does not effect the starting operation. If switch 16 is closed first relay C only is operated to close switch C1 D1 remaining open. Switch B1 remains closed under these conditions so that relay F is energised and after a predetermined interval of time opens switch F1 in the circuit of relay E. Relay E is then de-energised and allows switch E1 in the circuit of coil A to open and switch E2 in the circuit of relay F to close. Thus subsequent operation of switch B will operate relay D to close switch D1 but as E1 remains open no circuit to coil A is completed. The switch Bl will be opened on closing switch B but the energising circuit of relay F is maintained through switch E2. To de-energise relay F and operate El to close a resetting switch 18 must be opened and this switch is arranged at a remote point. If switch B is operated first, relay D closes switch D1 but C1 remains open. Switch D2 is also closed to energise relay F which again acts after a time interval to open switch E1. Thus in both cases unless the other switch is operated within the time interval before relay F is effective the circuit of the coil A of the starter contactor cannot be completed until the resetting switch 18 is operated. This prevents one switch being wedged open and the machine controlled by one switch and one hand of the operator only. Specification 648,181 is referred to.