Symmetrically saturated position servo control with dual amplitude optical offset scanning

Claim 1

ELECTRO-OPTICAL SENSING APPARATUS FOR DETERMINING THE POSITION OF REGISTRATION INDICIA RELATIVE THERETO AND FOR POSITIONING MATERIAL BEARING SAID INDICIA, COMPRISING ONE OR MORE ELECTRO-OPTICAL SENSING HEADS, EACH CYCLICALLY SCANNING AN AREA PARTICULARLY LOCATED WITH RESPECT TO SAID HEAD, EACH OF SAID SENSING HEADS HAVING OUTPUT SIGNALS REPRESENTATIVE OF THE POSITION OF A SINGLE REGISTRATION INDICIA WITHIN SAID SCANNED AREA, A SYMMETRICALLY SATURATING SERVO AMPLIFIER MEANS CONNECTED TO EACH OF SAID SENSING HEADS FOR CONVERTING THE OUTPUT SIGNALS THEREOF TO REVERSIBLE PHASE SERVO CONTROL SIGNALS HAVING AMPLITUDE CHARACTERISTICS PROPORTIONALLY RELATED TO THE POSITION OF SAID REGISTRATION INDICIA, REVERSIBLE SERVO MEANS CONNECTED TO EACH SYMMETRICALLY SATURATING SERVO AMPLIFIER MEANS AND PROPORTIONALLY RESPONSIVE TO SAID REVERSIBLE PHASE SERVO CONTROL SIGNALS FOR POSITIONING SAID REGISTRATION INDICIA RELATIVE TO SAID SENSING HEADS, AND A POSITION ANALYZING CIRCUIT CONNECTED TO EACH OF SAID SYMMETRICALLY SATURATING SERVO AMPLIFIER MEANS AND ADAPTED TO ANALYZE SAID REVERSIBLE PHASE SERVO CONTROL SIGNALS AT THE OUTPUT THEREOF SIMULTANEOUSLY WITH SAID INDICIA POSITIONING BY SAID SERVO MEANS AND TO INITIATE AN AUXILIARY CONTROL SIGNAL WHEN SAID SERVO CONTROL SIGNAL OUTPUT OF SAID SYMMETRICALLY SATURATING SERVO AMPLIFIER MEANS HAS CHARACTERISTICS WHICH REVEAL THAT SERVO POSITIONING OF SAID REGISTRATION INDICIA HAS BEEN SATISFACTORILY COMPLETED.