Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Patent
1990-06-22
1991-11-05
Nelms, David C.
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
250237G, G01D 534
Patent
active
050632914
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.
REFERENCES:
patent: 3410976 (1968-11-01), Watson
patent: 3755682 (1973-08-01), Russell
patent: 4359688 (1982-11-01), Haville
patent: 4468617 (1984-08-01), Ringwall
patent: 4639679 (1987-01-01), Kasperkovitz et al.
patent: 4823000 (1989-04-01), Onyow
Le Que T.
Nelms David C.
Rank Taylor Hobson Limited
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