Electromagnetic position-indicating system

Claim 1

A POSITION-INDICATING SYSTEM COMPRISING; A FRAME, MAGNETIC MEANS MOUNTED ON SAID FRAME FOR DEVELOPING A STEADY, CLOSED-LOOP, MAGNETIC FIELD AND HAVING OPPOSED POLE PIECES, AN ARMATURE CORE SUPPORTED BY SAID FRAME BETWEEN SAID POLE PIECES AND IN SPACED RELATION THERETO, THE ADJACENT SURFACES OF SAID POLE PIECES AND ARMATURE CORE DEFINING AN ANNULAR SPACE GAP, A SCANNING MEMBER, TWO OPPOSED PAIRS OF OPPOSED FLEXURE PIVOT ASSEMBLIES MOUNTING SAID SCANNING MEMBER ON SAID FRAME FOR ROTATION OF SAID SCANNING MEMBER ON SAID FRAME ABOUT THE AXIS OF SAID ANNULAR SPACE GAP, A DRIVE COIL MOUNTED FOR MOVEMENT WITH SAID SCANNING MEMBER AND DISPOSED IN SAID SPACE GAP FOR ANGULAR DISPLACEMENT IN ACCORDANCE WITH THE CURRENT FLOWING THROUGH SAID DRIVE COIL, A LOW-FREQUENCY DRIVE SOURCE HAVING A FREQUENCY LOWER THAN THE ELECTRO-MECHANICAL RESONANT FREQUENCY OF SAID DRIVE COIL AND ELECTRICALLY CONNECTED THROUGH SAID FLEXURE PILOT ASSEMBLIES TO SAID DRIVE COIL, SAID SCANNING MEMBER HAVING A SCANNING OUTPUT ADAPTED TO BE NULL WHEN THE NOMINAL POSITION OF THE LINE OF SIGHT OF SAID SCANNING MEMBER IS DIRECTED TOWARDS A DISCONTINUITY OF A RADIANT ENERGY SOURCE, MEANS RESPONSIVE TO VARIATIONS OF THE SCANNING OUTPUT OF SAID SCANNING MEMBER FROM NULL TO IMPRESS A D.C. VOLTAGE THROUGH SAID FLEXIBLE PIVOT ASSEMBLIES ON SAID DRIVE COIL TO ANGULARLY DISPLACE SAID DRIVE COIL AND SCANNING MEMBER TO A POSITION WHEREIN SAID SCANNING OUTPUT RETURNS TO NULL, A FIELD COIL INDUCTIVELY COUPLED TO SAID DRIVE COIL, AND A HIGHFREQUENCY EXCITATION SOURCE HAVING A FREQUENCY HIGHER THAN THE ELECTRO-MECHANIAL RESONANT FREQUENCY OF SAID DRIVE COIL AND ELECTRICALLY CONNECTED TO ONE OF SAID COILS, THE OTHER OF SAID COILS HAVING AN OUTPUT TERMINAL.