Patent ID: 9651877
Date: 2017-05-16
CPC Classifications: G01D,G02B,G03F

Claim:
1. A position measurement system configured to determine a position of a first object relative to a second object, comprising: an encoder head mounted on the first object and configured to emit a measurement beam, a grating mounted on the second object and configured to diffract the measurement beam, wherein the grating comprises a first array of grating lines in a first direction and a second array of grating lines in a second direction to diffract the measurement beam incident on the first and second arrays in at least one first diffracted beam in the first direction and in at least one second diffracted beam in the second direction, wherein the at least one first diffracted beam is for position measurement in the first direction and wherein the at least one second diffracted beam is for position measurement in the second direction, wherein the measurement beam has a power quantity, and wherein the grating is configured to distribute the power quantity unevenly between the at least one first diffracted beam and the at least one second diffracted beam.