Absolute displacement detection method and absolute displacement sensor using the method

An absolute displacement sensor comprising:

• a mass body which is supported by a detection object with a predetermined spring coefficient and a predetermined damping coefficient;
• detecting means which detects a relative velocity of the detection object with respect to said mass body;
• a closed feedback loop having a feedback control means which controls a displacement of said mass body attributable to an absolute displacement of the detection object by positively feeding back a relative displacement obtained by integrating the detected relative velocity and by negatively feeding back a relative acceleration obtained by primarily differentiating the detected relative velocity, respectively;
• and phase lag compensation means which performs phase lag compensation in a required frequency region including a natural frequency of the closed feedback loop with respect to the relative displacement obtained by the integration to make a phase lead into zero in a detection region within which the absolute displacement of the detection object is detected, wherein the relative displacement subjected to the phase lag compensation by said phase lag compensation means is outputted as the absolute displacement of the detection object.