Safety control circuit for hand operated machine - used continually monitored switches with working and holding contacts

摘要

A switch circuit which is used to control hand operated machines such as power presses, uses electronic elements that have fail safe characteristics. All signals ar transmitted by safety switches which employ working contacts in conjunction with holding contacts. The antivalence of the holding and working contacts is continually monitored and so is the duration of a antivalence disturbance. A starting signal for a machine cycle is only given when the hand operated contacts are closed within a required time interval, and the interlocking safety contacts are made. The starting signal is cancelled if the feed back signals from the machine have not arrived inside a required time interval.