	US 7,551,290 B2
	Absolute position measurement apparatus
Hidejiro Kadowaki, Kanagawa-ken (Japan); Ko Ishizuka, Saitama-ken (Japan); and Shigeki Kato, Tochigi-ken (Japan)
Assigned to Canon Kabushiki Kaisha, Tokyo (Japan)
Filed on Jul. 25, 2006, as Appl. No. 11/459,851.
Claims priority of application No. 2005-218980 (JP), filed on Jul. 28, 2005.
Prior Publication US 2007/0024862 A1, Feb. 01, 2007
Int. Cl. G01B 9/02 (2006.01)

U.S. Cl. 356—493

9 Claims

1. An absolute position measurement apparatus comprising:

a first light source configured to emit a first beam having high coherence;

a second light source configured to emit a second beam having low coherence;

a multiplexing unit configured to multiplex the first beam and the second beam onto the same optical axis to obtain a first multiplexed beam;

a polarization beam splitting unit configured to split the first multiplexed beam into a second multiplexed beam and a third multiplexed beam, and to multiplex the second multiplexed beam reflected from a measurement reflection plane of an object and the third multiplexed beam reflected from a reference surface;

a wave plate allowing the first beam of the second multiplexed beam and the first beam of the third multiplexed beam to interfere with each other, and allowing the second beam of the second multiplexed beam and the second beam of the third multiplexed beam to interfere with each other;

a light-receiving unit configured to detect a first interference beam obtained from the first beams and a second interference beam obtained from the second beams; and

a calculation unit configured to determine the position of a measurement origin from a first and second interference signals obtained from the first and second interference beams at the light-receiving unit and to obtain the absolute position of the object on the basis of the position of the measurement origin.