Optical Measurement
Non-contact gauging for delicate, soft or high-precision parts - chromatic confocal, focus-variation, interferometric and laser-line sensors, matched to the tolerance in front of them.
How it works
Optical measurement covers a family of non-contact techniques. Chromatic confocal sensors use wavelength-encoded focal distance to measure surface height. Focus-variation microscopy (Alicona) stitches sharpness across focus steps. White-light interferometry (Zygo, Bruker) measures nanometre-scale surface form. Laser triangulation and conoscopic holography give micron-level ranging for gauging tasks.
Typical accuracy
Chromatic confocal: sub-micron vertical resolution over ranges of 0.1-25 mm. Focus variation: 100 nm vertical, ~2 micron lateral. White-light interferometry: sub-nanometre vertical over millimetre lateral areas.
Applications
- Cutting-tool edge geometry and wear
- Surface finish and Sa/Sq areal roughness
- Micro-feature measurement on medical and electronic parts
- Wafer and MEMS metrology
- Delicate or soft parts unsuitable for contact probing
- In-line gauging where a probe would slow the line
Strengths
- • Non-contact, non-destructive
- • Nanometre-scale vertical resolution on the best techniques
- • Fast for small areas - suits in-line and automated cells
- • Combines dimensional and surface metrology in one dataset
Limitations
- • Small measurement volumes - not a general-purpose CMM replacement
- • Sensitive to surface reflectivity and colour
- • Calibration and traceability need specialist attention
- • Capital cost per volume measured is high
Choosing the right optical technique
Chromatic confocal is the pragmatic default for micron-level height measurement in an automated cell. Focus variation dominates cutting-tool edge and micro-feature work. White-light interferometry is the reference for nanometre-scale surface form. Laser triangulation trades resolution for speed and stand-off in gauging applications.
Areal surface metrology, not just Ra
Modern surface metrology has moved from single-line Ra to areal Sa/Sq/Sk parameters (ISO 25178). Optical areal instruments capture full 3D surface topography and give a much richer picture of how a surface will function - critical for sealing, coating, wear and additive-manufactured surfaces.
Buying considerations
- Match the sensor family to the tolerance and feature size
- Traceable calibration against certified step-height and areal standards
- Integration with a CMM, robot or dedicated stage
- Software: MountainsMap, LeicaMap, Alicona MeasureSuite, Zygo Mx
FAQs
Do we need optical measurement or a standard CMM?+
For sub-micron surface features, cutting-tool edges and delicate parts, optical wins. For general dimensional inspection above ~5 microns, a CMM (possibly with a chromatic sensor fitted) is usually more cost-effective.
Can we integrate optical sensors on our existing CMM?+
Often yes - chromatic and laser sensors are available for most modern CMMs. We'll advise whether a retrofit or a dedicated system is the right route.