Influence of part material and sensor adjustment on the quality of digitised point-clouds using conoscopic holography

• We analysed a conoscopic holography sensor for digitising 12 different materials.
• We tried all feasible combinations of power and frequency for sensor tuning.
• Quality indicators used: SNR, Measurement Dispersion, Flatness Deviation.
• Work reveals there is not a link between signal quality and measurement quality.
• Adjustment parameters are proposed for digitising different metals and plastics.

Conoscopic holography is an interferometric measurement technique commonly used for non-contact surfaces digitising in quality assessment, in-process inspection and reverse engineering. Among other factors, accuracy of measurements provided by this technology is influenced by the surface optical properties. Parameters such as laser power (P) or frequency of acquisition (F) are commonly used to adjust the sensor until a quality indicator of the signal acquired (Signal-to-Noise-Ratio) is maximised. Nevertheless, measurements taken under this adjusting criterion does not necessarily ensure the most accurate results from a metrological point of view. Taking this into account, the present work proposes two additional indicators to analyse the influence of sensor setting parameters on the quality of digitised point-clouds for different metals and polymers. Digitising tests have been performed on flat specimens of each material by means of a conoscopic holography sensor integrated on a Coordinate Measuring Machine. In order to meet an optimal scanning of each material, the study provides a series of recommendations about adjustment of the sensor as well as the most suitable indicator to be used in each case.