Patent ID: 9689662
Date: 2017-06-27
CPC Classifications: G01B,G01D

Claim:
1. A displacement detecting device comprising: a scale having marks whose pitch interval is approximated to a quadratic or higher-order polynomial along a measurement direction, or changes randomly; a first displacement detecting unit that is arranged facing the scale and detects a displacement in the measurement direction; a second displacement detecting unit that is arranged facing the scale and with a predetermined distance in the measurement direction from the first displacement detecting unit, and detects a displacement in the measurement direction; a first displacement computing unit that outputs first relative position information based on the displacement in the measurement direction detected by the first displacement detecting unit; a second displacement computing unit that outputs second relative position information based on the displacement in the measurement direction detected by the second displacement detecting unit; a comparing unit that calculates a difference between the first relative position information and the second relative position information per unit displacement in a position where the first displacement detecting unit is arranged, calculates absolute position information with respect to the measurement direction of the scale based on the calculated difference, and outputs the absolute position information; and an absolute position computing unit that computes an absolute position in the measurement direction with respect to the scale based on the absolute position information from the comparing unit and the relative position information of at least one of the first relative position information and the second relative position information and outputs the absolute position, wherein in the comparing unit, information indicative of a relationship between difference information between the first relative position information and the second relative position information per unit displacement in a position where the first displacement detecting unit is arranged and absolute position information of the scale is stored, and the comparing unit calculates the absolute position information based on the calculated difference and the stored information.