Displacement measurement device, displacement measurement method, and displacement measurement program

A displacement measurement method comprising:

• receiving signals from a plurality of light receiving elements, the signals being 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;
• performing a 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;
• calculating a phase of the interference fringe on the basis of the signals output from the plurality of light receiving elements;
• and
• selecting 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.

A non-transitory computer-readable storage medium storing a program causing a computer to execute a procedure, the procedure comprising:

• receiving signals from a plurality of light receiving elements, the signals being 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;
• performing a 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;
• calculating a phase of the interference fringe on the basis of the signals output from the plurality of light receiving elements;
• and
• selecting 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.