Optical grating with interpolator having multiplying means to produce quadrature signals
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United States of America Patent
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-
Nov 5, 1991
Grant Date -
N/A
app pub date -
Jun 22, 1990
filing date -
Jun 23, 1989
priority date (Note) -
Expired
status (Latency Note)
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Abstract
An interpolator, particularly for use with an optical grating for detecting position in a metrological apparatus, receives input signals in quadrature. One of the input signals is squared and the two signals are multiplied together to provide further signals in quadrature at twice the frequency of the input signals. One of the further signals is also squared and the further signals are multiplied together to provide output signals at four times the frequency of the input signals. Filtering is provided to remove DC components, such as due to drift. In the illustrated metrological apparatus, the zero crossing points of the output signals are detected to effect sampling, with high resolution, of a surface sensor output. Interpolation noise occurs at a high frequency and is removed by low pass filtering of the sample signal from the surface sensor.
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