Optical Coherence Scanning Measurement Limit Boundaries on Vertical Tooling Cavity Sidewalls
Side-viewing prisms and polarized optical coherence gating extend sidewall slope scanning limits beyond eighty-five degrees in deep tooling cavities.
Spatial Speckle Noise
Meaning
Granular interference pattern produced when coherent light, such as a laser beam, reflects from a surface that is rough on the scale of the wavelength. In the optical measurement of moulded plastic parts, this noise appears as a random flickering in the image that can obscure fine details. The intensity of the effect depends on the surface texture of the resin and the angle of the incident light.
Signal Degradation
Accuracy of a laser displacement sensor is reduced when the speckle pattern shifts as the probe moves across the part. The spatial speckle noise of a matte-finished dashboard component can introduce a jitter in the height data, making it difficult to distinguish between the intended grain and a measurement error.
Noise Mitigation
Various techniques, such as using a broad-spectrum light source or averaging multiple frames, are employed to reduce the impact of these artifacts. By smoothing the data, the software can extract the true topography of the surface from the random fluctuations caused by the interference.
Relationship Consistency
Connection between the speckle size and the roughness of the plastic allows for the estimation of the finish without a full profilometer scan. If the spatial speckle noise is properly characterized, it can be used to monitor the consistency of the tool texture across a long production run.