Safety system for automatically closing doors - has door reversal initiated by relay sensitive to closing speed dependent pulse rate

摘要

By means of a relay system, movement of a glass closing door is reversed when the closing speed is reduced by contact with an obstruction. Electrical pulses of frequency proportional to the door speed are produced by a micro-switch (13) actuated by a cam (15) on a wheel (12) which rotates as the door closes. The micro-switch is connected in a relay circuit, which includes a capacitor causing a relay closing delay. The relay thus only operates when the impulses in the solenoid circuit have a period greater than the relay delay, i.e. when the door closing speed is reduced past a predetermined value.