Optical device employing multiple slit patterns for zero reference in a shaft encoder

Claim 1

IN AN ENCODER HAVING A SHAFT AND A CODE DISC MOUNTED ON SAID SHAFT FOR ROTATION THEREWITH WITH RESPECT TO A FIXED MEMBER, APPARATUS FOR INDICATING WHEN SAID SHAFT AND DISC ARE IN A PREDETERMINED ANGULAR POSITION WITH RESPECT TO SAID FIXED MEMBER COMPRISING MEANS FOR GENERATING A SLIGHTLY CONVERGENT LIGHT BEAM, MEANS DEFINING A FIRST SLIT PATTERN IN THE PATH OF SAID LIGHT BEAM WHEREBY A PROJECTED IMAGE OF SAID FIRST SLIT PATTERN IS FORMED WHEN SAID FIRST SLIT PATTERN IS ILLUMINATED BY SAID BEAM, SAID MEANS FOR GENERATING A LIGHT BEAM AND SAID MEANS DEFINING A FIRST SLIT PATTERN REMAINING IN A STATIONARY POSITION WITH RESPECT TO SAID FIXED MEMBER, A PLURALITY OF REFLECTING SURFACES FOR TRANSMITTING SAID IMAGES IN ONE DIRECTION, A CONCAVE SPHERICAL REFLECTOR STATIONARY WITH RESPECT TO SAID FIXED MEMBER AND POSITIONED TO RECEIVE SAID IMAGE TRANSMITTED IN SAID ONE DIRECTION AND TO INVERT AND REFLECT SAID IMAGE IN THE OPPOSITE DIRECTION BACK TO SAID REFLECTING SURFACES, MEANS DEFINING A SECOND SLIT PATTERN CONFORMING TO SAID INVERTED IMAGE, SAID SECOND SLIT PATTERN BEING STATIONARY WITH RESPECT TO SAID FIXED MEMBER AND POSITIONED TO RECEIVE AND TRANSMIT SAID IMAGE WHEN SAID REFLECTING SURFACES AND SAID REFLECTOR ARE DISPOSED IN A PREDETERMINED ANGULAR ARRANGEMENT, AND LIGHT RESPONSIVE MEANS FOR GENERATING AN ELECTRICAL OUTPUT VARYING IN ACCORDANCE WITH THE QUANTITY OF LIGHT TRANSMITTED BY SAID SECOND SLIT PATTERN, AT LEAST ONE OF SAID REFLECTING SURFACES DISPOSED FOR ROTATION WITH SAID SHAFT WHEREBY AS SAID ONE REFLECTING SURFACE ROTATES SAID IMAGE WILL SWEEP ACROSS SAID SECOND SLIT PATTERN AND WILL COINCIDE FULLY WITH SAID SECOND PATTERN WHEN SAID ONE REFLECTING SURFACE IS DISPOSED IN ACCORDANCE WITH SAID PREDETERMINED ANGULAR ARRANGEMENT.