Patent ID: 8527236

Claim:
A displacement detection apparatus comprising: a scale on which a plurality of marks are periodically disposed; a first position detection sensor and a second position detection sensor configured to detect positions of the marks; and a processor configured to perform a calculation processing of an output signal from each of the first position detection sensor and the second position detection sensor, wherein the first position detection sensor and the second position detection sensor are disposed at a distance L from each other in a relative movement direction so as to be movable relative to the scale, and wherein the processor calculates a correction value P′ of a mark pitch P of the plurality of marks using the distance L, a first time T PK required for K marks of the plurality of marks to pass a detection position by one of the first position detection sensor and the second position detection sensor, and a second time T L required for a specific mark of the plurality of marks, which is measured at the same time of the measurement of the first time T PK , to move the distance L.