Patent ID: 7112781

Claim:
An apparatus comprising: a code strip carrier having a plurality of code tracks thereon; an illumination system for illuminating said code tracks to generate a light signal from each code track, each code track comprising a plurality of dark and light stripes, said dark stripes generating a light signal having a lower intensity than the light signal generated by said light stripes; a plurality of read heads, each read head comprising a photodetector positioned to detect light from a corresponding one of said code tracks as that code track moves relative to said read head; a controller for generating an absolute position value related to the position of said code strip carrier relative to an origin position, wherein one of said code tracks comprises a first absolute position track that provides an indication of said absolute position value when said code strip carrier is at each of a plurality of predetermined absolute positions relative to said origin position; and a different one of said code tracks comprises an incremental position track for generating a digital value indicative of a displacement of said code strip carrier relative to the last predetermined absolute position, wherein said incremental position track comprises alternating dark and light stripes and wherein said read head corresponding to said incremental position track generates a first logic signal indicating the direction of travel of said code strip carrier relative to that read head and a second logic signal that changes state each time a boundary between a dark stripe and a light stripe passes under that read head, wherein said first logic signal is responsive to a change in said direction of travel independent of the position of said first absolute position track relative to said one of said read heads corresponding to said first absolute position track.