Photoelectrically controlled radiation pressure torque balance

Claim 1

APPARATUS FOR MEASURING VERY SMALL FORCES, COMPRISING IN COMBINATION, (1) A SENSOR DEVICE ROTATABLE ABOUT A FIXED POSITION AXIS OF ROTATION AND INCLUDING, (A) A SENSOR SUPPORT ELEMENT THROUGH WHICH PASSES THE ROTATIONAL AXIS OF SAID SENSOR, (B) A TARGET ELEMENT FIXEDLY SECURED TO SAID SENSOR SUPPORT ELEMENT AND UPON WHICH THE FORCE TO BE MEASURED MAY BE DIRECTED, SAID TARGET ELEMENT EXTENDING LATERALLY OF SAID AXIS OF ROTATION SO THAT A FORCE EXERTED THEREON PRODUCES A TORQUE TENDING TO ROTATE SAID SENSOR IN A FIRST SENSE ABOUT SAID AXIS OF ROTATION, AND (C) A RADIATION RECEIVING SURFACE CARRIED BY SAID SENSOR SUPPORT ELEMENT, DISPOSED LATERALLY OF SAID AXIS OF ROTATION AND UPON WHICH SURFACE RADIATION IS SELECTIVELY DIRECTABLE TO PRODUCE A TORQUE TENDING TO ROTATE SAID SENSOR ABOUT SAID AXIS OF ROTATION IN A SECOND SENSE OPPOSITE TO SAID FIRST SENSE, (2) MEANS FOR FREELY SUSPENDING SAID SENSOR BY ITS SUPPORT ELEMENT FOR ROTATION ABOUT SAID FIXED POSITION AXIS, (3) CONTROL SIGNAL GENERATING MONITOR MEANS EFFECTIVE TO DETECT ANGULAR DEVIATIONS OF SAID SENSOR FROM A PREDETERMINED REFERENCE POSITION AND GENERATE CONTROL SIGNALS UNIQUELY CORRESPONDING TO SAID ANGULAR DEVIATION AND TO THE RATE OF CHANGE THEREOF, (4) RADIATION PROJECTING MEANS DISPOSED FOR PROJECTING RADIATION ONTO THE SAID RADIATION RECEIVING SURFACE OF SAID SENSOR, AND (5) CONTROL MEANS COUPLED TO SAID MONITOR MEANS AND TO SAID RADIATION PROJECTING MEANS AUTOMATICALLY EFFECTIVE RESPONSIVE TO THE CONTROL SIGNALS GENERATED BY SAID MONITOR MEANS TO CONTROL THE QUANTA OF RADIATION PROJECTED ONTO SAID SENSOR TO THEREBY PRODUCE A TORQUE ON SAID SENSOR EQUAL AND OPPOSITE TO THAT PRODUCED BY THE FORCE BEING MEASURED, WHEREBY, THE ROTATION OF SAID SENSOR IS STOPPED AT AN ANGULAR DEVIATION FROM ITS AFORESAID PREDETERMINED REFERENCE POSITION WHICH UNIQUELY CORRESPONDS TO THE MAGNITUDE OF THE FORCE BEING MEASURED.