Patent ID: 7615737

Claim:
An absolute encoder, comprising: a light source; an encoded code rod with an axis of rotation, wherein the rod has an outer surface encoded with code marks configured in a plurality of adjacent segments along the axis of rotation of the rod for determining angular rotation position, wherein a first one of the segments comprises a straight single diagonal code line offset from the axis of rotation by a first non-zero angle and a second one of the segments comprises a plurality of straight parallel diagonal code lines offset from the axis of rotation by a second non-zero angle less than the first non-zero angle; and a light detector configured to detect light reflected from or transmitted through the code marks; wherein the light detector is configured to detect a first axial position of a first point of intersection between the single diagonal code line of the first segment and a first line defined by a first portion of the light detector, and configured to detect a second axial position of a second point of intersection between one of the plurality of straight parallel diagonal code lines of the second segment and a second line defined by a second portion of the light detector, wherein the first and second points of intersection move along the length of the code rod as the rod rotates.