Phase-sensitive servo control system

Claim 1

A PHASE-SENSITIVE SERVO CONTROL SYSTEM COMPRISING MEANS FOR GENERATING TWO RECURRING PULSE STREAMS WHICH RELATIVE SHIFT IN PHASE ACCORDING TO THE DESIRED VALUE OF A CONTROLLABLE QUANTITY, MEANS FOR CONVERTING ONE OF SAID STREAMS INTO A CLIPPED SQUARE WAVEFORM, A THIRD HARMONIC REJECTION FILTER CONNECTED TO RECEIVE SAID SQUARE WAVEFORM, A BAND PASS FILTER CONNECTED TO RECEIVE THE OUTPUT OF SAID REJECTION FILTER AND HAVING ITS PASS BAND CENTERED SUBSTANTIALLY AT THE NOMINAL FREQUENCY OF SAID ONE STREAM, THE OUTPUT OF SAID BAND PASS FILTER BEING A SINUSOIDAL EXCITATION SIGNAL HAVING A FIXED PHASE RELATION TO SAID ONE STREAM, A SYNCHRONOUS INDUCTION DEVICE HAVING A ROTOR AND MEANS FOR MOVING THE ROTOR THROUGH AN ANGLE $ CORRESPONDING TO THE ACTUAL VALUE OF SAID CONTROLLABLE QUANTITY, MEANS CONNECTING SAID SINUSOIDAL EXCITATION SIGNAL TO SAID INDUCTION DEVICE TO CREATE A PULSATING MAGNETIC FIELD THEREIN; SAID INDUCTION DEVICE INCLUDING MEANS FOR PRODUCING TWO ALTERNATING VOLTAGES RESPECTIVELY PROPORTIONAL IN AMPLITUDE TO, AND AGREEABLE IN PHASE POLARITY WITH THE SIGNS OF, SIN $ AND COS $; MEANS INCLUDING A SERIES-RESONANT L-C CIRCUIT FOR CONVERTING ONE OF SAID TWO VOLTAGES INTO A FIRST AUXILIARY VOLTAGE PROPORTIONAL IN AMPLITUDE TO, BUT SHIFTED 90* IN PHASE FROM, SUCH ONE VOLTAGE; MEANS INCLUDING A NON-RELATIVE VOLTAGE DIVIDER FOR CONVERTING THE OTHER OF SAID TWO VOLTAGES INTO A SECOND AUXILIARY VOLTAGE PROPORTIONAL IN AMPLITUDE TO, AND IN PHASE WITH, SUCH OTHER VOLTAGE; MEANS FOR VERTICALLY ADDING SAID FIRST AND SECOND AUXILIARY VOLTAGES TO DERIVE AN OUTPUT VOLTAGE OF SUBSTANTIALLY CONSTANT AMPLITUDE AND SHIFTED IN PHASE BY AN ANGLE $; PHSE DISCRIMINATOR MEANS FOR CREATING A CONTROL SIGNAL CORRESPONDING TO THE PHASE MISMATCH OF THE OTHER OF SAID PULSE STREAMS RELATIVE TO SAID OUTPUT VOLTAGE; AND MEANS RESPONSIVE TO SAID CONTROL SIGNAL FOR CORRESPONDINGLY CHANGING SAID CONTROLLABLE QUANTITY.