Side Viewing Interferometric Probe Alignment for near Vertical Steel Sidewalls
Aligning side-viewing optical probes on vertical steel sidewalls requires tip-tilt control within 0.05 degrees to preserve coherence fringe visibility.
Low Coherence Probes
Meaning
Non-contact optical sensors utilizing light with a short coherence length measure the thickness of multi-layer polymer films and molded walls. In co-extrusion plants, low coherence probes determine the individual layer boundaries of barrier packaging without destructively slicing the material. This technique uses the light reflections from the refractive index changes at each polymer boundary to calculate the dry thickness of the individual layers.
Optical Metrology
Molding operations deploy these specialized fiber-optic sensors to monitor wall dimensions in real time. Because the light source has a broad spectral bandwidth, low coherence probes avoid the spurious interference that occurs with lasers, giving clean sub-micron resolution on thin walls. This metrology method provides instant feedback to the extruder or molding machine control loop, enabling immediate adjustments to the melt flow or nozzle pressure.
Thickness Measurement
Managing the layer thickness of expensive barrier polymers like ethylene vinyl alcohol ensures the container preserves food freshness while minimizing material costs. If a barrier layer drops below the specified tolerance, the shelf life of the packaged product degrades rapidly. Regrind layers can also be monitored for consistency, preventing the contamination of virgin food-contact layers by ensuring the barrier boundary remains intact.
Production Integration
Mounting these sensors directly inside the tooling or downstream from the mold gate allows for automated quality tracking. This inline configuration removes the need for manual sampling and laboratory testing.