Meaning
Optical non-contact profiling systems split polychromatic white light into distinct focal planes along the optical axis through hyperchromatic objective lenses to measure vertical distances without mechanical surface contact. Applying a confocal chromatic sensor enables non-destructive surface texture evaluation and dimensional verification across transparent polymer optics, specular mould steel cavities, and micro-featured part geometries. Reflected wavelengths return through a confocal pinhole aperture toward a spectrometer, converting the detected spectral peak directly into a calibrated vertical height position.
The operating window reaches physical limits when surface slope angles exceed the numerical aperture collection angle of the objective lens, which scatters reflected light away from the optical path and induces measurement dropout.
Optical Dispersion
Chromatic dispersion separates broadband light into continuous spectral bands across a defined measurement range. A confocal chromatic optical head projects shorter wavelengths closer to the objective face while longer wavelengths focus deeper into micro cavity features. High-frequency reflections from polished steel cores produce sharp spectral returns that isolate height variations under two nanometres.
Signal intensity drops rapidly on black textured polymer surfaces, requiring longer integration times on the internal spectrometer. Transparent mouldings yield two distinct spectral peaks, corresponding to front and back surfaces.
Focal Calibration
Wavelength-to-distance transfer functions require rigorous factory calibration against certified optical references. Operating a confocal chromatic pen across variable thermal environments introduces sensor drift if housing expansion alters the pinhole alignment. Periodic verification with calibrated step height blocks guarantees vertical measurement linearity over the entire dynamic range.
Industrial production cells mount these sensors directly on automated motion axes to screen microfluidic channels and micro-moulded connector pins without cycle time penalties.
Topography Metrology
Optical inspection systems capture surface roughness parameters and microscopic defect depths across polymer mouldings without imparting mechanical scratches. Diamond-turned mould cavities transfer sub-micron optical finishes to polycarbonate lenses, demanding non-contact profile verification before part release. Surface defects such as sink marks, weld line notches, and micro-pitting yield measurable depth deviations under focused chromatic illumination.
The sensor configuration remains valid for in-line quality verification provided vibration isolation dampers isolate machine harmonics from the optical assembly.
