Photoelectric shaft angle encoder and optical system therefor

Claim 1

A PHOTOELECTRIC SHAFT POSITION ENCODER COMPRISING A HOUSING, A SHAFT ROTATABLY MOUNTED ON THE HOUSING, A CODE DISC HAVING A PLURALITY OF CIRCULAR TRACKS COAXIALLY DISPOSED ABOUT THE SHAFT, EACH OF SAID TRACKS HAVING A PLURALITY OF SECTORS WITH DIFFERENT RATIOS OF TRANSMITTED LIGHT TO INCIDENT LIGHT, A LIGHT SOURCE MOUNTED ON THE HOUSING ON ONE SIDE OF THE CODE DISC, SAID LIGHT SOUCE PRODUCING TWO LINES OF LIGHT IN THE PLANE OF THE CODE DISC AND DISPOSED ON A COMMON AXIS INTERSECTING THE AXIS OF THE SHAFT, A FIRST GROUP AND A SECOND GROUP OF PHOTOCELLS MOUNTED ON THE HOUSING ON THE SIDE OF THE CODE DISC OPPOSITE THE LIGHT SOURCE CONFRONTING THE CODE DISC, THE FIRST GROUP AND SECOND GROUP OF PHOTOCELLS BEING ON OPPOSITE SIDES OF THE SHAFT AND DISPOSED ON A COMMON PLANE WITH THE AXIS AND THE TWO LINES OF LIGHT FROM THE SOURCE, EVERY OTHER TRACK OF THE CODE DISC CONFRONTING A PHOTOCELL OF THE FIRST GROUP AND EVERY TRACK BETWEEN SAID TRACKS OF THE CODE DISC CONFRONTING A PHOTOCELL OF THE SECOND GROUP.