Transducer position control apparatus

Claim 1

IN A SYSTEM FOR READING A DOCUMENT HAVING TOWS OF INFORMATION RECORDED IN PARALLEL THEREON, THE COMBINATION COMPRISING: A ROTATING DRUM FOR TRANSPORTING SAID DOCUMENT; A READER MOVABLE PARALLEL TO THE AXIS OF SAID DRUM FOR SENSING INFORMATON ALONG A LINE GREATER IN EXTENT THAN THE HEIGHT OF A ROW AND FOR PRODUCING SIGNALS IN RESPONSE TO SENSED INFORMATION; MEANS FOR NORMALLY FEEDING SAID DOCUMENT TO SAID DRUM WITH THE ROWS OF INFORMATION SKEWED RELATIVE TO SAID AXIS SO THAT THE CENTERLINES OF SAID ROWS LIE ON A HELIX HAVING A PITCH APPROXIMATELY EQUAL TO THE DISTANC BETWEEN ADJACENT SAID CENTERLINES; FIRST MEANS FOR MOVING SAID READER IN A FIRST DIRECTION PARALLEL TO SAID AXIS TO FOLLOW SAID HELIX AS SAID DRUM ROTATES; MEANS RESPONSIVE TO ONES OF SAID SIGNALS REPRESENTING INFORMATION SENSED WITHIN FIRST AND SECOND OPPOSITE END REGIONS OF SAID SENSING LINE FOR PRODUCING FIRST AND SECOND CONTROL LEVELS, RESPECTIVELY; A FIRST SOURCE OF CLOCK PULSES; MEANS RESPONSIVE TO THE OUTPUT OF SAID FIRST SOURCE AND TO SAID FIRST AND SECOND CONTROL LEVELS FOR PRODUCING CONTROL PULSES FOR MOVING SAID READER IN SAID FIRST DIRECTION AND A SECOND, OPPOSITE DIRECTION, RESPECTIVELY, PARLLEL TO SAID AXIS; FIRST AND SECOND COUNTING MEANS RESPONSIVE TO SAID CONTROL PULSES AND TO SAID FIRST AND SECOND CONTROL LEVELS, RESPECTIVELY; MEANS FOR GENERATING A SPECIAL SIGNAL AFTER EACH ROW IS READ; MEANS RESPONSIVE TO SAID SPECIAL SIGNAL AND TO A DIFFERENCE IN THE OUTPUTS OF SAID FIRST AND SECOND COUNTING MEANS FOR PRODUCING ONE OF SAID FIRST AND SECND CONTROL LEVELS; MEANS FOR GENERATING AN "ERROR" SIGNAL WHEN IT IS DESIRED TO REREAD A ROW; A SECOND SOURCE OF CLOCK SIGNALS; AND MEANS RESPONSIVE TO SAID "ERROR" SIGNAL AND TO THE OUTPUT OF SAID SECOND SOURCE FOR PRODUCING A PREDETERMINED NUMBER OF SAID CONTROL PULSES FOR MOVING SAID READER IN SAID SECOND DIRECTION.