Evaluation of wood surface roughness by confocal microscopy
The main aim of this study is to define the usability of the confocal scanning optical microscope (CSOM) to evaluate the wood surface roughness. Therefore, systematic investigation was carried out to define the influences of CSOM on the acquisition of 2D surface roughness parameters. Mahr Perthometer was applied to get reference data to estimate the applicability of the CSOM. Because wood roughness parameters measured with stylus and optical methods are not always comparable a calibration method was conducted on a metal calibration etalon. After the calibration process, the roughness profiles taken with the optical and stylus units were much closer to each other and only the optical Rpk parameter was definitely higher due to artificial peaks generated by the optical system. In order to eliminate this measuring failure, the morphological filter option of the optical apparatus may be activated. The surface roughness parameters were measured on planed Scotch pine samples. The planed surface plains were produced with 0.2 mm parallel offset to investigate the structural influence of the single cutting plains. The obtained results show that the average values for Ra, Rq, Rz, Rk, and Rvk are close to each other for both measuring systems, only the optically measured Rpk values must be corrected. The standard deviations, however, are systematically slightly higher for optical system. This may be explained by the higher resolution of the optical system giving more fine profile details. The earlier developed and introduced dimensionless quantities, such as Abbott ratio, are also fully comparable for both systems provided that the optically measured Rpk values are also correct.