Patent ID: 7945420
Filing Date: 2011-05-17
Classification: G01D

Abstract:
1. An absolute position measurement apparatus, comprising: an output unit configured to output a plurality of first signals having a phase that changes in accordance with a position of an object to be measured and a plurality of superimposed signals formed by superimposing each of a plurality of second signals on each of the plurality of first signals, wherein a phase of the plurality of second signals changes in accordance with the position of the object to be measured, and the plurality of second signals have a different cycle from that of the plurality of first signals; a phase computing unit configured to calculate the phase of the plurality of first signals during a first period in which the output unit outputs the plurality of first signals, and calculate the phase of the plurality of second signals during a second period in which the output unit outputs the plurality of superimposed signals; a regression computing unit configured to calculate a regression coefficient of the phase of the plurality of first signals; a phase difference computing unit configured to calculate a phase difference between the phase of the plurality of first signals and the phase of the plurality of second signals calculated by the phase computing unit during the second period, wherein the phase difference is calculated using the regression coefficient; an origin position computing unit configured to determine an origin position of the object to be measured based on a position where a sign of the phase difference that is output from the phase difference computing unit is inverted; and an absolute position calculating unit configured to calculate an absolute position of the object to be measured based on the origin position, wherein the regression computing unit calculates the regression coefficient by multiplying an exponential weighting factor in accordance with time that has passed from a time point of measurement to the phase of the plurality of first signals calculated by the origin position computing unit.