Patent ID: 6424407
Filing Date: 2002-07-23
Classification: G01D,G01P,G01S,G06F

Abstract:
A method for determining the relative motion of a surface with respect to a measurement device comprising:illuminating the surface with incident illumination; detecting a first portion of said incident illumination reflected from the surface in a first direction to form a first detected signal, the time variation of said first signal being responsive to the relative motion in a first direction, said first direction having at least a component in the direction perpendicular to the surface; detecting a second portion of said incident illumination reflected from the surface in a second direction, different from the first direction, to form a second detected signal the time variation of said second signal being responsive to the relative motion in a second direction, different from the first direction, said second direction having a component in a direction parallel to the surface and in a direction perpendicular to the surface; and determining the amount of relative motion parallel to the surface free of effects of motion perpendicular to the surface from said first and second detected signals.