Safety switch system for industrial machines

Claim 1

A safety switch system for passing electrical power from a power source to an industrial machine, including, in combination: (a) first and second touch plate switches physically positioned adjacent to the industrial machine to be energized thereby at a spacing from each other sufficient that both switches cannot be operated simultaneously with one hand of an operator but require both hands of the operator, each of said touch plate switches including an oscillating tuned circuit and amplifier; a touch plate connected to said oscillating tuned circuit, said oscillating tuned circuit being responsive to touching of the plate by an operator's hand to result in a signal change from said oscillating tuned circuit, said amplifier generating a trigger signal in response to said signal change, the frequency of the oscillating tuned circuit in said first touch plate switch being different from the frequency of said oscillating tuned circuit in the second touch plate switch; and a silicon controlled rectifier having its control terminal connected to receive said trigger signal; (b) first and second relay switches connected in series with each other between said power source and machine; (c) first and second relay coils respectively connected in circuit with the silicon control rectifiers of the first and second touch plate switches so as to be energized in response to firing of the silicon control rectifiers respectively whereby power cannot be passed to said industrial machine from said power source unless both said relay switches are closed and whereby operation of either one of said touch plate switches does not require any physical movement of the associated touch plate itself so that the risk of an operator developing carpal tunnel syndrome is substantially eliminated; and (d) third and fourth relay switches connected to said first and second relay coils, respectively, to open and close simultaneously with the opening and closing of said first and second relay switches, respectively; (e) an anti-cheat timer connected to said third and fourth relay switches to measure the time interval between the closing of said third and fourth relay switches; and (f) a fifth relay switch connected in series with said first and second relay switches, said fifth relay switch also connected to said anti-cheat timer such that if the time interval between the closing of said third and fourth relay switches exceeds a predetermined amount said fifth relay switch is opened thereby opening the circuit to said industrial machine.