Patent ID: 6472658
Filing Date: 2002-10-29
Classification: G01D

Abstract:
A position measuring system, the system comprising:a light source for providing divergent illumination; a first grating structure illuminated by the divergent illumination; a second grating structure in the form of a phase grating arranged downstream of the first grating structure; a third grating structure arranged downstream of the second grating structure; at least one photodetector for detecting a first set of light beams which pass through the first, second and third grating structures and are modulated by the phase grating of the second grating structure; a support on which the second grating structure is disposed, the support is arranged displaceably in a measuring direction with relation to the first and third grating structures; a reference marker in the form of an amplitude structure disposed on the support and illuminated by a portion of the divergent illumination so that the reference marker generates a second set of light beams that are modulated; and at least one photodetector for detecting the second set of modulated light beams, wherein said at least one photodetector generates a signal representative of an absolute position of said reference marker.