ABSOLUTE POSITION MEASUREMENT APPARATUS

• US 20090076768A1
• Filed: 09/09/2008
• Published: 03/19/2009
• Est. Priority Date: 09/14/2007
• Status: Active Grant

• Current Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Original Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Inventors: Seo, Yuzo
• Granted Patent: US 7,945,420 B2
• Time in Patent Office: Days
• US Class Current: 702/150
• CPC Class Codes: G01D 5/2457 Incremental encoders having reference marks
• CPC Class Codes: G01D 5/266 by interferometric means G01D5/353 takes precedence

Abstract

An absolute position measurement apparatus includes an output unit outputting a plurality of first signals and a plurality of superimposed signals formed by superimposing each of plural second signals on each of the plural first signals, a phase computing unit calculating phases of the first signals during a first period in which the output means outputs the plural first signals, and calculating phases of the second signals during a second period in which the output means outputs the plural superimposed signals, a regression computing unit calculating a regression coefficient of the phase of the first signals calculated during the first period, a subtracter calculating a phase difference between the phase of the first signals and the phase of the second signals during the second period, a phase difference computing unit determining an origin position of the object to be measured based on a position where a sign of the phase difference output from the subtracter is inverted, and an absolute position calculating unit calculating an absolute position of the object to be measured based on the origin position.

Claims

1. An absolute position measurement apparatus comprising:

an output unit configured to output a plurality of first signals whose phase 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, a phase of the plurality of second signals changing in accordance with the position of the object to be measured, and the plurality of second signals having a different cycle from that of the first signals;

a phase computing unit configured to calculate the phase of the first signals during a first period in which the output unit outputs the plurality of first signals, and calculate the phase of the 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 first signals calculated by the phase computing unit during the first period;

a subtracter configured to calculate a phase difference between the phase of the first signals calculated using the regression coefficient and the phase of the second signals calculated by the phase computing unit during the second period;

a phase difference 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 output from the subtracter 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 determined by the phase difference computing unit.

2. An absolute position measurement apparatus according to claim 1,

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 first signals calculated by the phase difference computing unit.

3. An absolute position measurement apparatus according to claim 1,

wherein the first signals and the superimposed signals output from the output unit are input to an analog/digital converter,

wherein the first signals are always input to the analog/digital converter,

wherein the superimposed signals are input to the analog/digital converter every constant period by superimposing the second signals on the first signals,

wherein the analog/digital converter temporally alternately processes the first signals and the superimposed signals, and

wherein the second signals input to the phase computing unit are calculated by subtracting the first signals that are calculated using the regression coefficient from the superimposed signals.

4. An absolute position measurement apparatus according to claim 1, further comprising an amplitude detector configured to detect an amplitude size of the second signals,

wherein the absolute position measurement apparatus determines the origin position of the object to be measured utilizing the phase difference between the phase of the first signals and the phase of the second signals and the amplitude size of the second signals.

5. An absolute position measurement apparatus according to claim 1,

wherein the phase difference computing unit stores a plurality of values obtained by adding up or averaging the phase differences between the first signals and the second signals over one cycle of the first signals per every cycle of the first signals, and

wherein the phase difference computing unit determines the origin position of the object to be measured by detecting an inversion of signs of the added-up or averaged values of adjacent cycles.