Servo nulled autocollimator having a pair of rotatable wedges

Claim 1

IN A POLARIZED LIGHT AUTOCOLLIMATING SYSTEM FOR MONITORING ROTATIONS OF A REFLECTING SURFACE ABOUT TWO ORTHOGONAL AXES WHICH SYSTEM INCLUDES MEANS FOR PRODUCING AT LEAST ONE BEAM OF POLARIZED LIGHT, THE PLANE OF POLARIZATION OF WHICH ROTATES, MEANS FOR COLLIMATING SAID BEAM AND THE BEAM BEING AIMABLE AT THE REFLECTING SURFACE AND BEING REFLECTED BACK THEREFROM IN A BEAM STRIKING THE SAID MEANS FOR PRODUCING COLLIMATION, THE IMPROVEMENT WHICH COMPRISES (A) POLARIZING ANALYZING MEANS HAVING POLARIZATIONS TOTALING FOUR AND COMPRISING PAIRS OF POLARIZING MEANS POLARIZED AT RIGHT ANGLES TO EACH OTHER IN EACH PAIR AND 45* TO EACH OTHER BETWEEN PAIRS, (B) SAID MEANS FOR COLLIMATING SAID BEAM FURTHER CAUSING THE REFLECTED BEAM FROM THE REFLECTING SURFACE TO BE IMAGED ON THE ANALYZING MEANS, (C) RADIATION DETECTING MEANS TRANSFORMING RADIATION INTO FOUR ELECTRICAL SIGNALS IN PHASES AT 90* TO EACH OTHER, A PAIR OF THE SIGNALS, 180* TO EACH OTHER, BEING DERIVED FROM THE REFLECTED BEAM THROUGH ONE PAIR OF SAID POLARIZING ANALYZING MEANS AND THE OTHER PAIR DERIVED FROM THE OTHER PAIR OF POLARIZING ANALYZING MEANS, (D) TWO TRANSPARENT WEDGES, THE RESPECTIVE TAPERS OF SAID WEDGES BEING INITIALLY SUBSTANTIALLY AT RIGHT ANGLES TO EACH OTHER AND POSITIONED TRANSVERSE TO THE COLLIMATED BEAM SO THAT THE BEAM, BEFORE AND AFTER REFLECTION FROM THE REFLECTING SURFACES, PASSES THERETHROUGH, (E) MEANS FOR ROTATING THE WEDGES INDEPENDENTLY THROUGH LIMITED ARC $1 AND $2 RESPECTIVELY, THE AXES OF ROTATION BEING PARALLEL TO THE COLLIMATED BEAM AND THE ARCS BEING LESS THAN ABOUT 30*, EACH MEANS BEING ACTUATED BY ONE OF SAID PAIRS OF SIGNALS FROM THE DETECTING MEANS, AND (F) ELECTRONIC RESOLVING MEANS CONNECTED TO MOVE THROUGH THE SAME ANGLES AS THE TWO WEDGES AND PROVIDED WITH INPUT A.C. VOLTAGES AND OUTPUT CIRCUITS, ONE GIVING A SIGNAL PROPORTIONAL TO SIN $0+COS $2-1 AND THE OTHER AN OUTPUT SIGNAL PROPORTIONAL TO SIN $02+COS $1-1, WHEREBY THE OUTPUTS FROM THE RESOLVING MEANS INDICATE THE AMOUNT OF ROTATION OF THE REFLECTING SURFACE ABOUT THE TWO AXES.