Patent ID: 7078677

Claim:
An optical encoder disk comprising: a disk; a first region on said disk, wherein said first region increases continuously in size in a radial direction from a minimum at a first angular position to a maximum that is 360 degrees from said first angular position, said first region defined by a circular first boundary and a second boundary that is continuous from said minimum to said maximum; a second region on said disk adjacent to and encompassing said first region, wherein one of said first and second regions allows a greater amount of light to be transmitted therethrough than the other of said first and second regions; a circular-shaped third region encompassed by said first region, wherein one of said first and third regions allows a greater amount of light to be transmitted therethrough than the other of said first and third regions; and a ring-shaped fourth region encompassing said second region, wherein one of said second and fourth regions allows a greater amount of light to be transmitted therethrough than the other of said second and fourth regions; wherein light transmitted through said first and second regions produces a first electrical output, light transmitted through said first and third regions produces a second electrical output, and light transmitted through said second and fourth regions produces a third electrical output, wherein said second and third outputs are reference outputs used to adjust said first output, and wherein said first, second and third outputs are used to determine an angular position of said disk.