Absolute position measurement apparatus

• US 7,945,420 B2
• Filed: 09/09/2008
• Issued: 05/17/2011
• 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
• Primary Examiner(s): TEIXEIRA MOFFAT, JONATHAN CHARLES
• Application Number:
  US12/206,822
• Publication Number:
  US 20090076768A1
• Time in Patent Office: 980 Days
• Field of Search: 702/150
• 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, a phase computing unit, a regression computing unit, a phase difference computing unit, an origin position computing unit, and an absolute position calculating unit. The output unit outputs first signals and superimposed signals formed by superimposing second signals on the first signals. The first signals relate to a position of an object to be measured and the first and second signals have a different cycle. The phase computing unit calculates the phase of the first and second signals. The regression computing unit calculates a regression coefficient of the phase of the first signals. The phase difference computing unit calculates a phase difference between phases of the first and second signals. The origin position computing unit determines an origin position of the object to be measured. The absolute position calculating unit calculates an absolute position of the object to be measured.

Claims

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.

2. An absolute position measurement apparatus according to claim 1, further comprising an amplitude detector configured to detect an amplitude size of the plurality of 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 plurality of first signals and the phase of the plurality of second signals and the amplitude size of the plurality of second signals.

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

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

wherein the origin position 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.

4. 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 plurality of first signals and the plurality of superimposed signals output from the output unit are input to an analog/digital converter,

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

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

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

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

5. An absolute position measurement apparatus according to claim 4, further comprising an amplitude detector configured to detect an amplitude size of the plurality of 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 plurality of first signals and the phase of the plurality of second signals and the amplitude size of the plurality of second signals.

6. An absolute position measurement apparatus according to claim 4,

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

wherein the origin position 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.