Patent ID: 8223346

Claim:
A system to determine position of an object moving in a principal direction substantially within a plane, and having lateral and transverse directions orthogonal to the principal direction and each other, the system comprising: a wedge capable of moving along said principal direction between a first and a second location, and comprising first and second surfaces spaced apart to form laterally opposite sides of at least a portion of said wedge, said opposite sides spaced apart a distance varying in a known manner along said principal direction; a first sensor spaced away from said first surface to detect a first distance reflecting a proximity therebetween in said lateral direction; a second sensor spaced away from said second surface to detect a second distance reflecting a proximity therebetween in said lateral direction; a processing element determining movement of said wedge in said principal direction by adding values, reflecting said first and second distances, to provide a correction cancelling the effect of a mechanical error in said lateral position of said wedge between said first and second sensors.