Patent ID: 7141780

Claim:
A position determination device comprising: a light detector, a light source, and first and second relatively movable elements that together produce a change in light intensity at the light detector, wherein: the first element has a first pattern and the second element has a second pattern, one of said first and second elements is a measurement scale, the other of said first and second elements is relatively movable along the measurement scale, the corresponding first or second pattern on the measurement scale defines a positional reference point along the measurement scale, the first and second patterns and light from the light source interact when the first and second patterns coincide at said positional reference point to produce a signal that discriminates said positional reference point from other points along the measurement scale, and the first and second patterns have a correlating relationship, one of the first and second patterns is a reduced scale version of the other of the first and second patterns, and the light from the light source is uncollimated.