Patent ID: 7990522

Claim:
A method for operating a chromatic point sensor for measuring a distance to a workpiece surface, the chromatic point sensor including an optical pen comprising a chromatically dispersive optical system and a spatial filtering aperture, and an electronics portion comprising a wavelength detector, a calibration memory portion including data corresponding to sets of index-specific data-limiting parameters and a signal processor, the method for operating the chromatic point sensor including measurement operations comprising: operating the chromatic point sensor to output multi-wavelength light through the optical pen and focus a plurality of respective wavelengths of light along an optical axis at a plurality of corresponding respective focus distances; arranging a workpiece surface along the optical axis at a measurement distance relative to the optical pen; reflecting the respective wavelengths of light from the workpiece surface through the optical pen, and into the wavelength detector, to form a resulting spectral intensity profile distributed over a plurality of pixels along a measurement axis of a detector array of the wavelength detector; and operating the electronics portion to perform a set of operations comprising: providing a set of measurement-time profile data corresponding to the plurality of pixels along the wavelength detector measurement axis; determining a peak position index coordinate ppic based on the set of measurement-time profile data, the peak position index coordinate ppic corresponding approximately to a position of the spectral peak of the spectral intensity profile along the detector array measurement axis; selecting a set of index-specific data-limiting parameters that are utilized as part of a process for determining a distance-indicating subset of the set of measurement-time profile data, the set of index-specific data-limiting parameters corresponding to the peak position index coordinate ppic from the calibration memory portion, the set comprising at least one index-specific data-limiting parameter; determining a distance-indicating subset of the set of measurement-time profile data based on the set of measurement-time profile data and the selected set of index-specific data limiting parameters; determining a subpixel-resolution distance-indicating coordinate corresponding to the measurement distance to the workpiece surface, based on the distance-indicating subset of measurement-time profile data; and determining the measurement distance to the workpiece surface, based on the determined subpixel-resolution distance-indicating coordinate and distance calibration data that correlates known measurement distances with resulting distance-indicating coordinates from the chromatic point sensor.