Fail safe photoelectric sheet sensing machine control circuit

Claim 1

A FAIL SAFE DETECTING DEVICE FOR USE IN DETECTING MISFED SHEETS OF PAPER IN AN AUTOMATIC XEROGRAPHIC MACHINE INCLUDING: A CONTROL MEANS ADAPTED TO PERMIT OPERATION OF THE MACHINE WHEN ENERGIZED AND TO SHUT DOWN THE MACHINE WHEN DEENERGIZED, A THRESHOLD SWITCHING MEANS CONNECTED IN SERIES WITH THE CONTROL MEANS TO CONTROL CURRENT FLOW THROUGH THE CONTROL MEANS, A LIMITED CURRENT POWER SUPPLY CONNECTED TO SAID THRESHOLD SWITCHING MEANS AND SAID CONTROL MEANS, A PHOTOCELL ELECTRICALLY COUPLED TO SAID THRESHOLD SWITCHING MEANS AND SAID POWER SUPPLY TO TRIGGER SAID THRESHOLD SWITCHING MEANS AND THEREBY ENERGIZE SAID CONTROL MEANS AT A PHOTOCELL RESPONSE OF A PREDETERMINED VALUE, DIODE MEANS COUPLED TO SAID PHOTOCELL AND SAID POWER SUPPLY TO SHORT SAID POWER SUPPLY IN RESPONSE TO A PHOTOCELL RESPONSE OF HIGHER THAN SAID PREDETERMINED VALUE, A LIGHT SOURCE POSITIONED IN THE AUTOMATIC XEROGRAPHIC MACHINE TO REFLECT A PREDETERMINED AMOUNT OF LIGHT INTO THE PHOTOCELL UNDER NORMAL OPERATIVE CONDITIONS AND TO REFLECT AN INCREASED AMOUNT OF LIGHT INTO THE PHOTOCELL WHEN A SHEET OF PAPER IS MISFED IN THE MACHINE THEREBY PRODUCING A PHOTOCELL RESPONSE OF HIGHER THAN THE ABOVE MENTIONED PREDETERMINED VALUE, THE PHOTOCELL HAVING A RESISTANCE WHEN EXPOSED TO LIGHT, UNDER NORMAL OPERATING CONDITIONS, CAPABLE OF ALLOWING SUFFICIENT CURRENT TO PASS TO TRIGGER THE THRESHOLD SWITCHING MEANS AND THUS ALLOW PASSAGE OF SUFFICIENT CURRENT TO ENERGIZE THE CONTROL MEANS AND, UPON AN INCREASE OF LIGHT ABOVE SAID PREDETERMINED AMOUNT, A RESISTANCE LOW ENOUGH TO DRAW ENOUGH CURRENT TO ACTUATE SAID DIODE MEANS SO AS TO SHORT SAID POWER SUPPLY AND PREVENT OPERATION OF THE CONTROL MEANS AND, UPON A DECREASE OF LIGHT, A RESISTANCE LARGE ENOUGH TO PREVENT PASSAGE OF SUFFICIENT CURRENT TO TRIGGER THE THRESHOLD SWITCHING MEANS.