Patent ID: 9423276
Filing Date: 2016-08-23
CPC Classification: G01D

Claim Text:
1. A measurement apparatus of measuring a position of a target object, the apparatus comprising: a detector configured to detect modulated light from the target object having a periodic pattern, and to output a periodic pattern signal with at least two periods; and a calculation unit configured to calculate the position of the target object based on the output of said detector, wherein said calculation unit determines positions of two extreme values each of which appears as a constant value for each period of the periodic pattern from the periodic pattern signal output from said detector, calculates a first total sum by multiplying the periodic pattern signal by first reference waveform data of a sinusoidal waveform with the same period as that of the periodic pattern signal in a region between the positions of the two extreme values, and adding the multiplication results, calculates a second total sum by multiplying the periodic pattern signal by second reference waveform data of a sinusoidal waveform with a phase difference of 90° with respect to the first reference waveform data in the region, and adding the multiplication results, calculates a phase of the periodic pattern signal based on the first total sum and the second total sum, and calculates the position of the target object based on the calculated phase.