Double shaft encoder using phase meter to indicate relative rotation

Claim 1

AN ELECTROMECHANICAL TRANSDUCER COMPRISING FIRST AND SECOND ROTOR ELEMENTS, EACH OF SAID ROTOR ELEMENTS HAVING A PLURALITY OF ALTERNATELY LIGHT TRANSMISSIVE AND NON-TRANSMISSIVE SECTORS DISPOSED CIRCUMFERENTIALLY THEREON; A STATIONARY ELEMENT IN CLOSE JUXTAPOSITION TO SAID FIRST ROTOR ELEMENT; AN INPUT ELEMENT IN CLOSE JUXTAPOSITION TO SAID SECOND ROTOR ELEMENT, SAID INPUT ELEMENT BEING RELATIVELY ROTATABLE WITH RESPECT TO SAID STATIONARY ELEMENT; DRIVE MEANS FOR ROTATING SAID FIRST AND SECOND ROTOR ELEMENTS AT SUBSTANTIALLY CONSTANT ANGULAR VELOCITY WITH RESPECT TO SAID STATIONARY ELEMENT; A FIRST LIGHT SOURCE FIXED TO SAID STATIONARY ELEMENT ON ONE SIDE OF SAID FIRST ROTOR ELEMENT AND PROJECTING LIGHT ONTO SAID FIRST ROTOR ELEMENT; A FIRST LIGHT SENSOR MOUNTED ON SAID STATIONARY ELEMENT ON THE OPPOSITE SIDE OF SAID FIRST ROTOR ELEMENT AND IN A POSITION TO RECEIVE LIGHT FROM SAID FIRST LIGHT SOURCE WHICH IS TRANSMITTED THROUGH SAID FIRST ROTOR ELEMENT; MEANS FIXED TO SAID STATIONARY ELEMENT IN THE REGION OF SAID FIRST LIGHT SOURCE AND SAID FIRST LIGHT SENSOR FOR MODULATING LIGHT FROM SAID FIRST LIGHT SOURCE SUCH THAT THE AMOUNT OF LIGHT RECEIVED BY SAID FIRST SENSOR VARIES IN ACCORDANCE WITH THE ANGULAR POSITION OF SAID FIRST ROTOR ELEMENT; A SECOND LIGHT SOURCE FIXED TO SAID INPUT ELEMENT ON ONE SIDE OF SAID SECOND ROTOR ELEMENT AND PROJECTING LIGHT ONTO SAID SECOND ROTOR ELEMENT, A SECOND LIGHT SENSOR MOUNTED ON SAID INPUT ELEMENT ON THE OPPOSITE SIDE OF SAID SECOND ROTOR ELEMENT FROM SAID SECOND LIGHT SOURCE IN THE POSITION TO RECEIVE LIGHT FROM SAID SECOND LIGHT SOURCE TRANSMITTED THROUGH SAID SECOND ROTOR ELEMENT; SECOND MODULATING MEANS MOUNTED ON SAID INPUT ELEMENT IN THE REGION OF SAID SECOND LIGHT SENSOR FOR MODULATING THE LIGHT FROM SAID SECOND LIGHT SOURCE SUCH THAT THE AMOUNT OF LIGHT RECEIVED BY SAID SECOND SENSOR VARIES IN ACCORDANCE WITH THE ANGULAR POSITION OF SAID ROTOR ELEMENT; SAID FIRST AND SAID SECOND SENSORS PROVIDING ELECTRICAL OUTPUT SIGNALS WHICH VARY IN ACCORDANCE WITH THE AMOUNT OF LIGHT RECEIVED AND PHASE SENSOR MEANS FOR DETERMINING THE AVERAGE PHASE RELATIONSHIP BETWEEN SAID OUTPUT FROM SAID FIRST LIGHT SENSOR AND SAID SECOND LIGHT SENSOR FOR EACH COMPLETE REVOLUTION OF SAID ROTOR ELEMENTS AND PROVIDING AN OUTPUT INDICATION OF THE AMOUNT OF ROTATION OF SAID INPUT ELEMENT WITH RESPECT TO SAID STATIONARY ELEMENT.