What is the direction discrimination principle of displaceme

What is the direction discrimination principle of displacement detection sensor?
In practical application, the displacement has two directions, that is, after selecting a direction, the displacement can be divided into positive and negative, so the displacement direction can not be determined by measuring the Moire fringe signal with a photoelectric element. In order to distinguish direction, the Angle displacement sensor needs two Mohr fringe signals with π/2 phase difference. As shown in FIG. 2, two photoelectric elements are placed at a position 1/4 apart from the fringe spacing, and two electrical signals U01 and U02 with phase difference π/2 are obtained. After shaping, two square wave signals U01 'and U02' are obtained. When the grating moves forward, U01 is 90 degrees ahead of U02, and when the grating moves backward, U02 is 90 degrees ahead of U01. Therefore, the direction of grating motion can be determined by circuit phase discrimination.