Meaning
Spatial separation metrics establish the smallest horizontal distance between two distinct surface features that an optical or tactile metrology system can resolve as separate profile points. Specifying lateral spatial resolution dictates whether a surface metrology system can evaluate micro-injection moulded textures, narrow laser-ablated tool features, and subtle sink mark boundaries. The measurement capability is bounded by the optical diffraction limit in light-based systems and by the physical tip radius in mechanical stylus profilers.
When feature spacing narrows beneath this resolution boundary, adjacent structural peaks blur into a single continuous profile, destroying structural fidelity.
Optical Limit
Rayleigh criteria and numerical aperture values dictate the resolving power of optical lenses used on non-contact profilers. Fine lateral spatial resolution demands high numerical aperture objectives, which inherently reduce the working distance between the lens and the mould steel cavity. Moulded micro-fluidic channels with steep vertical sidewalls restrict objective approach, forcing metrology technicians to use lower magnification lenses that degrade horizontal resolution.
High-magnification optical heads resolve sub-micron feature spacing on polished tooling inserts but suffer from restricted fields of view that extend scanning duration.
Feature Discrimination
Accurate discrimination between adjacent structural peaks prevents false roughness reporting on micro-textured surfaces. Inadequate lateral spatial resolution averages high-aspect-ratio ribs into smooth domes, underestimating peak-to-valley height parameters on EDM-eroded tooling. Micro-injection moulders producing hydrophobic polyolefin surfaces with microscopic pillar arrays require sub-micron horizontal resolution to verify feature replication.
Incomplete mould filling due to premature gate freeze shows up as widened pillar spacing and rounded top radii under high-resolution scans.
Stylus Dimension
Physical stylus contact mechanics depend strictly on diamond tip geometry and tracking force. Mechanical lateral spatial resolution corresponds to the horizontal contact area between the diamond tip and the polymer surface. Conical styli with two-micrometre tip radii fail to penetrate narrow scratch defects or micro-crack fissures on moulded surfaces.
The resolution limit causes tip bridging over sharp valley features, delivering artificially low valley depth figures on technical datasheets. Selecting excessive stylus tracking force avoids bridging but induces plastic ploughing on soft polyolefin mouldings, distorting horizontal feature boundaries.
