Optical EngineeringIn-process inspection of surface-profile properties by detecting laser beam deflection
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An inspection system for the surface-profile properties of an organic photoconductor (OPC) drum substrate is studied. Defective substrates have approximately 1-mm-period waves in their surface profiles along the axial direction. The slope distribution of the surface profile is measured with an optical inspection system, which detects the angular deflection of a laser beam scanned over the surface at a high speed of 15 mm/ms. To discriminate between good and defective substrates, a threshold decision is made on components of the experimentally measured power spectrum of the slope distribution around 1-mm spatial period. The inspection system provides the same results as visual inspection with an accuracy better than 6σ. The setup dose not require any vibration isolators, because of its short inspection time of 2 ms.