Hammer firing circuit for impact printers

Claim 1

IN AN IMPACT PRINTER OF THE TYPE WHEREIN MEANS INCLUDING ELECTROMAGNETICALLY ACTUATED HAMMERS ARE CYCLICALLY OPERATED TO CAUSE CHARACTERS TO BE SELECTIVELY IMPRINTED UPON A RECORDING MEDIUM, THE COMBINATION COMPRISING: A RESPECTIVE ELECTROMAGNETIC COIL EFFECTIVE WHEN ENERGIZED FOR CAUSING THE ACTUATION OF EACH HAMMER; A SILICON CONTROLLED RECTIFIER CORRESPONDING TO EACH COIL; A SOURCE OF SUPPLY POTENTIAL INCLUDING A PLURALITY OF TERMINALS; AN ELECTRONIC SWITCH MEANS INCLUDING A HIGH POWER TRANSISTOR CONNECTING A FIRST ONE OF THE TERMINALS OF THE SOURCE TO A COMMON JUNCTION AND FURTHER INCLUDING A FIRST DIODE CONNECTING A SECOND ONE OF THE TERMINALS TO THE COMMON JUNCTION; A PLURALITY OF PARALLEL COIL ENERGIZING CURRENT PATHSS CONNECTED BETWEEN THE COMMON JUNCTION AND SAID SECOND TERMINAL, EACH PATH INCLUDING A RESPECTIVE COIL AND RECTIFIER CONNECTED IN SERIES AND AN ADDITIONAL DIODE INTERPOSED BETWEEN THE COIL AND RECTIFIER; A HOLD-RESET CIRCUIT MEANS CONNECTED TO THE JUNCTIONS BETWEEN EACH RECTIFIER AND ADDITIONAL DIODE FOR COUPLING ALL OF THE RECTIFIERS TO ONE OR ANOTHER OF THE SUPPLY TERMINALS TO MAINTAIN AN ENERGIZED RECTIFIER IN ITS CONDUCTING CONDITION OR ALTERNATIVELY TO RESET AN ENERGIZED RECTIFIER TO ITS NONCONDUCTING CONDITION; AND CYCLICALLY OPERATED CONTROL MEANS EFFECTIVE DURING AN INITIAL PORTION OF EACH PRINT CYCLE TO ENERGIZE SELECTED ONES OF THE RECTIFIERS AND TO RENDER THE HOLD-RESET CIRCUIT MEANS EFFECTIVE TO MAINTAIN THE LATTER RECTIFIERS ENERGIZED, SAID CONTROL MEANS THEREAFTER EFFECTIVE TO ENERGIZE THE HIGH POWER TRANSISTOR FOR A PREDETERMINED TIME INTERVAL TO MOMENTARILY COMPLETE THOSE COIL ENERGIZING CURRENT PATHS WHICH INCLUDE AN ENERGIZED RECTIFIER, SAID FIRST DIODE LIMITING THE VOLTAGE SWING AT SAID COMMON JUNCTION PRODUCED BY THE ENERGIZED COILS WHEN THE POWER TRANSISTOR DE-ENERGIZES, SAID CONTROL MEANS THEREAFTER EFFECTIVE TO OPERATE THE HOLD-RESET CIRCUIT MEANS FOR RESETTING THE ENERGIZED RECTIFIERS.