Patent ID: 9200926
Filing Date: 2015-12-01
Classification: G01D

Abstract:
1. A displacement detecting device, comprising: a scale; scale marks that is provided in the scale, and that change so that an integration of pitch intervals along a measurement direction can be approximated by a third or more order polynomial expression and so that an integration of pitch intervals can be approximated by a second or more order polynomial expression along a track direction perpendicular to the measurement direction and parallel to a measurement surface of the scale; a displacement detecting section that is arranged facing the measurement surface of the scale and that detects a displacement of the scale mark; a displacement calculation section that calculates a displacement amount of the scale mark with respect to the scale, based on the displacement of the scale mark detected by the displacement detecting section; a movement detecting section that detects a movement in the track direction with respect to the scale in the displacement detecting section; a movement amount calculation section that calculates a displacement amount in the track direction with respect to the scale in the displacement detecting section, based on a signal detected by the movement detecting section; a comparison/calculation section that differentiates, when the displacement detecting section or the scale moves in the track direction, a displacement amount calculated by the displacement calculation section, based on a movement amount in the track direction with respect to the scale calculated by the movement amount calculation section, thereby calculating a second-order differential amount in the track direction; and an absolute position calculation section that calculates an absolute position in the measurement direction with respect to the scale based on the second-order differential amount calculated by the comparison/calculation section and that outputs the absolute position.