MEASUREMENT APPARATUS AND MEASUREMENT METHOD
First Claim
1. A measurement apparatus, which obtains a reference signal from reference light modulated by a first frequency, obtains a measurement signal from measurement light, which is modulated by a second frequency due to movement of a target object in addition to modulation by the first frequency, and measures a position of the target object by calculating a phase difference between the reference signal and the measurement signal, said apparatus comprising:
- letting fd be the second frequency,a demodulation unit which generates, by demodulating the measurement signal by the first frequency, a signal including a component of the second frequency, and periodic error components having frequencies n×
fd (for n=½
, 2, 3, . . . ), and harmonic components of the second frequency;
a decimation filter which outputs a signal including the component of the second frequency and the periodic error components by removing the harmonic components from the signal generated by said demodulation unit;
a detection unit which detects the periodic error components included in the signal output from said decimation filter;
a removing unit which outputs a signal of the component of the second frequency by removing the periodic error components detected by said detection unit from the signal output from said decimation filter; and
a calculation unit which calculates the position of the target object based on the signal output from said removing unit.
1 Assignment
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Accused Products
Abstract
A measurement apparatus obtains a reference signal from light modulated by a first frequency, obtains a measurement signal from light modulated by the first frequency and a second frequency, and measures a position of a target object by calculating a phase difference between the reference signal and the measurement signal. The apparatus includes: a demodulation unit which demodulates the measurement signal by the first frequency; a decimation filter which removes harmonic components from the signal generated by the demodulation unit; a detection unit which detects periodic error components included in the signal output from the decimation filter; a removing unit which removes the periodic error components from the signal output from the decimation filter; and a calculation unit which calculates the position of the target object based on the signal output from the removing unit.
10 Citations
15 Claims
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1. A measurement apparatus, which obtains a reference signal from reference light modulated by a first frequency, obtains a measurement signal from measurement light, which is modulated by a second frequency due to movement of a target object in addition to modulation by the first frequency, and measures a position of the target object by calculating a phase difference between the reference signal and the measurement signal, said apparatus comprising:
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letting fd be the second frequency, a demodulation unit which generates, by demodulating the measurement signal by the first frequency, a signal including a component of the second frequency, and periodic error components having frequencies n×
fd (for n=½
, 2, 3, . . . ), and harmonic components of the second frequency;a decimation filter which outputs a signal including the component of the second frequency and the periodic error components by removing the harmonic components from the signal generated by said demodulation unit; a detection unit which detects the periodic error components included in the signal output from said decimation filter; a removing unit which outputs a signal of the component of the second frequency by removing the periodic error components detected by said detection unit from the signal output from said decimation filter; and a calculation unit which calculates the position of the target object based on the signal output from said removing unit. - View Dependent Claims (2, 3, 4, 8, 9, 12)
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5. A measurement apparatus, which obtains a reference signal from reference light modulated by a first frequency, obtains a measurement signal from measurement light, which is modulated by a second frequency due to movement of a target object in addition to modulation by the first frequency, and measures a position of the target object by calculating a phase difference between the reference signal and the measurement signal, said apparatus comprising:
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letting fr be the first frequency and fd be the second frequency, and n=½
, −
1, 2, 3, . . .a demodulation unit which generates, by demodulating the measurement signal by the first frequency, a signal including a component of the second frequency, and periodic error components having frequencies n×
fd, and harmonic components of the second frequency;a decimation filter which outputs a signal including the component of the second frequency and the periodic error components by removing the harmonic components from the signal generated by said demodulation unit; a detection unit which detects the periodic error components by demodulating the measurement signal by frequencies (fr+n×
fd);a removing unit which outputs a signal of the component of the second frequency by removing the periodic error components detected by said detection unit from the signal output from said decimation filter; and a calculation unit which calculates the position of the target object based on the signal output from said removing unit. - View Dependent Claims (6, 7, 10, 11, 13)
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14. A method of measuring a position of a target object by obtaining a reference signal from reference light modulated by a first frequency, obtaining a measurement signal from measurement light, which is modulated by a second frequency due to movement of a target object in addition to modulation by the first frequency, and calculating a phase difference between the reference signal and the measurement signal, said method comprising:
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letting fd be the second frequency, a demodulation step of generating, by demodulating the measurement signal by the first frequency, a signal including a component of the second frequency, and periodic error components having frequencies n×
fd (for n=½
, 2, 3, . . . ), and harmonic components of the second frequency;a decimation step of outputting a signal including the component of the second frequency and the periodic error components by removing the harmonic components from the signal generated in the demodulation step; a detection step of detecting the periodic error components included in the signal output in the decimation step; a removing step of outputting a signal of the component of the second frequency by removing the periodic error components detected in the detection step from the signal output in the decimation step; and a calculation step of calculating the position of the target object based on the signal output in the removing step.
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15. A method of measuring a position of a target object by obtaining a reference signal from reference light modulated by a first frequency, obtaining a measurement signal from measurement light, which is modulated by a second frequency due to movement of a target object in addition to modulation by the first frequency, and calculating a phase difference between the reference signal and the measurement signal, said method comprising:
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letting fr be the first frequency and fd be the second frequency, and n=½
, −
1, 2, 3, . . .a demodulation step of generating, by demodulating the measurement signal by the first frequency, a signal including a component of the second frequency, and periodic error components having frequencies n×
fd, and harmonic components of the second frequency;a decimation step of outputting a signal including the component of the second frequency and the periodic error components by removing the harmonic components from the signal generated in the demodulation step; a detection step of detecting the periodic error components by demodulating the measurement signal by frequencies (fr+n×
fd);a removing step of outputting a signal of the component of the second frequency by removing the periodic error components detected in the detection step from the signal output in the decimation step; and a calculation step of calculating the position of the target object based on the signal output in the removing step.
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Specification