Patent ID: 8400643

Claim:
A position sensing device comprising: a light source arrangement configured to radiate source light along a source light path, the light source arrangement comprising at least a light generating portion; a moving aperture arrangement constrained to move along a measuring axis direction and located to receive the source light along a source light path, the moving aperture arrangement including an aperture configuration that inputs the source light and outputs measurement light to first and second detection tracks which are aligned along the measuring axis direction and are spaced apart transverse to the measuring axis direction, the measurement light moving along the measuring axis direction corresponding to a position of the aperture configuration along the measuring axis direction, the aperture configuration movable at least over a total measuring range MR along the measuring axis direction; and a multiple position sensitive detector (PSD) arrangement, wherein: the multiple PSD arrangement comprises: a first position sensitive detector comprising a photodetector having a sensitive axis aligned along the first detection track to receive measurement light from the aperture configuration; and a second position sensitive detector comprising a photodetector having a sensitive axis aligned along the second detection track to receive measurement light from the aperture configuration; the first position sensitive detector and the second position sensitive detector are arranged such that during operation, the first position sensitive detector outputs a first displacement signal over a first detector range that is less than the total measuring range MR, and the second position sensitive detector outputs a second displacement signal over a second detector range that is less than the total measuring range MR and different than the first detector range; and the first and second detector ranges share a common portion of the total measuring range MR.