The present invention relates to switches, and more particularly to deadman's switches.
It is known in the art of deadman's switches to provide a movable actuating element with a spring for urging the actuating element from a working position in which the switch is closed into a rest position in which a switch is open. On the other hand, such a switch is provided with an actuating member engageable with the actuating element and movable so as to displace the latter against the biasing force of the spring from the rest into the working position. Usually the member is also provided with a spring which is operative to counteract the force applied to the member when the latter moves into engagement with the actuating element.
Therefore, it is to be understood that in such a switch the actuating member is subject to considerable forces, on the one hand, a force applied to move the latter into engagement with the actuating element and, on the other hand, the counteracting forces of the springs. This is especially true if a control distance of the switch is comparatively small, which is the case with deadman's switches.
When a user operates such a deadman's switch for a relatively long time period, a situation may take place where the user slightly decreases the applied force not purposely but inadvertantly, if, for example, the user is tired and exhausted. If this is the case, even the slightest release of the actuating member will most likely lead to premature opening the switch, with subsequent undesirable results, for example premature stopping of a moving vehicle if such a deadman's switch is installed in the system of operation of the vehicle.