Patent ID: 7057163

Claim:
An optical position sensing device for sensing a two-dimensional displacement, comprising: a first photosensor comprising at least four photodetectors arranged parallel to a first axis, the at least four photodetectors forming a first pair and a second pair of photodetectors; a second photosensor comprising at least four photodetectors arranged parallel to a second axis, the at least four photodetectors forming a third pair and a fourth pair of photodetectors, wherein the first and the second axes are at an angle with respect to each other; and an encoding means which interferes with a path of light incident on the photosensors such that a pattern consisting of light and shadow is cast onto the photosensors, wherein the encoding means and the photosensors are able to move with respect to each other, resulting in modulation of light received by the photosensors, and are arranged in an arrangement such that when the encoding means moves relatively in a direction parallel to the first axis, the modulation of light received by the second photosensor is larger than the modulation of light received by the first photosensor; and when the encoding means moves relatively in a direction parallel to the second axis, the modulation of light received by the first photosensor is larger than the modulation of light received by the second photosensor; and wherein the encoding means and the photodetector pairs are arranged such that the total amount of light received by each pair of photodetectors is substantially unchanged, and when the light received by one photodetector of one photodetector pair increases due to the movement of the encoding means, the light received by the other photodetector of the same photodetector pair decreases in a complementary manner.