Evaluation of surface smoothness by a laser displacement sensor II: comparison of lateral effect photodiode and multielement array

Development of accurate surface assessment technology is of vital interest to modern wood industries. In this experiment we investigated new and fast noncontacting sensors to determine their usefulness for wood surface evaluation and to verify their accuracy. Two types of laser displacement sensors [equipped with a position sensitive detector (PSD) and a charge coupled device (CCD) detector] are compared with a conventional stylus and with theoretical profiles. Hornbeam workpieces with triangular profiles of differing slope and height were used for the evaluation. The results show that resolution of both sensors decreases as the height of the profile decreases. The error ratio of the laser-scanned profiles changes as a function of profile height, in the range 5%-33%. The CCD method is superior for accurate surface roughness evaluation, although the PSD approach can still be used for monitoring the error of form in most applications.