Frequency comparison devices included in step motor control circuitry

Claim 1

IN A CONTROL SYSTEM, MEANS FOR GENERATING AT LEAST ONE FIRST REPETITIVE ELECTRIC SIGNAL OF WHICH THE FREQUENCY REPRESENTS THE MAGNITUDE OF A FIRST QUANTITY ASSOCIATED WITH THE SYSTEM, MEANS FOR GENERATING AT LEAST ONE SECOND REPETITIVE ELECTRIC SIGNAL OF WHICH THE FREQUENCY REPRESENTS THE MAGNITUDE OF A SECOND QUANTITY ASSOCIATED WITH THE SYSTEM, FREQUENCY COMPARISON MEANS SUPPLIED WITH SAID FIRST AND SECOND REPETITIVE ELECTRIC SIGNALS AND ARRANGED IN RESPONSE TO GENERATE AN ERROR SIGNAL WHICH REPRESENTS THE DIFFERENCE BETWEEN THE MAGNITUDES OF SAID FIRST AND SECOND QUANTITIES, SAID ERROR SIGNAL COMPRISING A SET OF AT LEAST TWO FURTHER REPETITIVE ELECTRIC SIGNALS OF WHICH THE FREQUENCY IS A FUNCTION OF THE MAGNITUDE OF, AND OF WHICH THE MUTUAL RELATIVE PHASE-DISPLACEMENT REPRESENTS THE SENSE OF, THE DIFFERENCE BETWEEN THE FREQUENCIES OF SAID FIRST AND SECOND REPETITIVE ELECTRIC SIGNALS, AND AN ELECTRIC MOTOR OF THE SYNCHRONOUS TYPE ARRANGED TO BE DRIVEN BY SAID FURTHER REPETITIVE ELECTRIC SIGNALS, WHEREBY THE POSITION OF THE ROTOR OF SAID ELECTRIC MOTOR IS A FUNCTION OF THE INTEGRAL, WITH RESPECT TO TIME, OF THE DIFFERENCE BETWEEN THE MAGNITUDES OF SAID FIRST AND SECOND QUANTITIES.