Positional servo system

Claim 1

AN INDEX HEAD, COMPRISING A MOVABLE FIXTURE, A MAIN COUNTER ADAPTED TO BE SET AT A COUNT REPRESENTATIVE OF A MOVEMENT THROUGH WHICH THE FIXTURE IS TO BE MOVED IN A FIRST DIRECTION, MEANS FOR DRIVING THE FIXTURE WITH A FORCE AT ANY TIME PROPORTIONAL TO THE COUNT IN THE COUNTER AFTER THE COUNT HAS BEEN REDUCED BELOW A PREDETERMINED VALUE, A TRANSDUCER ASSOCIATED WITH THE FIXTURE AND CONNECTED TO THE MAIN COUNTER TO TRANSMIT TO IT PULSES WHICH ADD TO OR SUBTRACT FROM THE COUNT DEPENDING UPON THE DIRECTION OF MOVEMENT OF THE FIXTURE, THE TRANSDUCER PRODUCING A FIRST SET OF PULSES AND A SECOND SET OF PULSES EACH PULSE OF WHICH LAGS A CORRESPONDING PULSE OF THE FIRST SET BY 90 ELECTRICAL DEGREES WHEN THE FIXTURE MOVES IN THE FIRST DIRECTION, THE PULSES OF THE FIRST SET LAGGING THE PULSES OF THE SECOND SET BY 90 ELECTRICAL DEGREES WHEN THE FIXTURE MOVES IN A SECOND DIRECTION, MEANS CAUSING THE PULSES TO SUBTRACT FROM THE COUNT WHEN THE PULSES IN THE FIRST SET LEAD THE PULSES OF THE SECOND SET AND CAUSING THE PULSES TO ADD TO THE COUNT WHEN THE PULSES IN THE SECOND SET LEAD THE PULSES IN THE FIRST SET, THE LAST-NAMED MEANS CONSISTING OF A TIME DELAY FOR THE FIRST SERIES OF PULSES AND A TIME DELAY FOR THE SECOND SERIES, A FIRST AND LOGIC UNIT WHEN OPERATIVE CAUSING THE MAIN COUNTER TO SUBTRACT ARRIVING PULSES FROM THE COUNT, A SECOND AND LOGIC UNIT WHEN OPERATIVE CAUSING THE MAIN COUNTER TO ADD ARRIVING PULSES TO THE COUNT, EACH LOGIC UNIT BEING RENDERED OPERATIVE BY THE PRESENCE OF TWO PULSES AT THE SAME TIME ON ITS INPUT SIDE, AND MEANS ASSOCIATED WITH THE COUNTER FOR MAINTAINING THE ADD OR SUBTRACT CONDITION OF THE COUNTER UNTIL A REVERSAL OF DIRECTION OF THE FIXTURE TAKES PLACE.