MEASUREMENT APPARATUS

• US 20090132192A1
• Filed: 11/14/2008
• Published: 05/21/2009
• Est. Priority Date: 11/19/2007
• Status: Active Grant

• Current Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Original Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Inventors: Seo, Yuzo
• Granted Patent: US 7,966,158 B2
• Time in Patent Office: Days
• US Class Current: 702/94
• CPC Class Codes: G01D 3/028 mitigating undesired influences, e.g. temperature, pressure

Abstract

A measurement apparatus of the present invention is a measurement apparatus 100 configured to measure a position of an object to be measured using a plurality of signals representing the position of the object to be measured. The measurement apparatus 100 includes a distortion correcting part 2 configured to generate a plurality of correction signals by correcting the plurality of signals using a distortion coefficient which is stored in the measurement apparatus, a distortion coefficient arithmetic unit 11 configured to correct and update the distortion coefficient by comparing each of the plurality of correction signals with an ideal signal waveform, a square-root of sum of squares arithmetic unit 3 configured to calculate a square-root of sum of squares of the plurality of correction signals generated by the distortion correcting part 2, a first normalizing part configured to generate a plurality of first normalized signals by dividing each of the plurality of correction signals by the square-root of sum of squares, and a phase arithmetic unit 6 configured to calculate the position of the object to be measured based on the plurality of first normalized signals calculated by the first normalizing part.

Claims

1. A measurement apparatus configured to measure a position of an object to be measured using a plurality of signals representing the position of the object to be measured, the measurement apparatus comprising:

a distortion correcting part configured to generate a plurality of correction signals by correcting the plurality of signals using a distortion coefficient which is stored in the measurement apparatus;

a distortion coefficient arithmetic unit configured to correct and update the distortion coefficient by comparing each of the plurality of correction signals with an ideal signal waveform;

a square-root of sum of squares arithmetic unit configured to calculate a square-root of sum of squares of the plurality of correction signals generated by the distortion correcting part;

a first normalizing part configured to generate a plurality of first normalized signals by dividing each of the plurality of correction signals by the square-root of sum of squares; and

a phase arithmetic unit configured to calculate the position of the object to be measured based on -the plurality of first normalized signals calculated by the first normalizing part.

2. A measurement apparatus according to claim 1, further comprising:

an averaging arithmetic unit configured to calculate an average square-root of sum of squares in which the square-root of sum of squares of the plurality of correction signals is averaged in one cycle of the signal; and

a second normalizing part configured to generate a plurality of second normalized signals by dividing the plurality of correction signals by the average square-root of sum of squares calculated by the averaging arithmetic unit,

wherein the distortion coefficient arithmetic unit corrects the distortion coefficient based on the second normalized signal.

3. A measurement apparatus according to claim 2, further comprising:

a first memory configured to store the second normalized signal as a maximum value of the second normalized signal when a phase calculated by the phase arithmetic unit is a first phase;

a second memory configured to store the second normalized signal as a minimum value of the second normalized signal when the phase calculated by the phase arithmetic unit is a second phase;

an amplitude error coefficient correcting part configured to correct an amplitude error coefficient of the second normalized signal based on a difference between the second normalized signals stored in the first memory and the second memory; and

a zero point error coefficient correcting part configured to correct a zero point error coefficient of the second normalized signal based on an average of the second normalized signals stored in the first memory and the second memory.

4. A measurement apparatus according to claim 3, further comprising:

a third memory configured to store the second normalized signal as a zero cross point of the second normalized signal when the phase calculated by the phase arithmetic unit is a third phase;

a fourth memory configured to store the second normalized signal as the zero cross point of the second normalized signal when the phase calculated by the phase arithmetic unit is a fourth phase; and

a phase error coefficient correcting part configured to correct a phase error coefficient of the second normalized signal based on a difference between the second normalized signals stored in the third memory and the fourth memory.

5. A measurement apparatus according to claim 4,

wherein the phase error coefficient correcting part corrects the phase error coefficient with respect to all signals of the plurality of second normalized signals so that total of correction amount of the phase error coefficient with respect to all signals of the plurality of second normalized signals is zero when correcting the phase error coefficient with respect to each of signals of the plurality of second normalized signals.