Patent ID: 8941841
Filing Date: 2015-01-27
Classification: G01B,G01D

Abstract:
1. A displacement measurement device comprising: a light receiving unit including a plurality of light receiving elements each of which outputs a signal corresponding to illuminance of interference fringe, the plurality of light receiving elements being arranged in a range of two periods of the interference fringe and being arranged with an interval based on the period of the interference fringe in a movement direction of the interference fringe, a degree of the interference fringe being a second degree or higher, the interference fringe being so that illuminance of a bright portion of the interference fringe switches alternately and formation position of the interference fringe moves in response to a displacement; a differential processing unit configured to perform differential processing on predetermined combinations of the signals output from the plurality of light receiving elements to generate four signals, phases or waveforms of the four signals being different from one another; a phase calculation unit configured to calculate a phase of the interference fringe on the basis of the signals output from the plurality of light receiving elements; and an output signal selection unit configured to select two signals from among the four signals on the basis of the phase of the interference fringe and select, as an output signal corresponding to the displacement, a signal of which absolute value is larger from among the two selected signals.