Apply of digital speckle projection in measurement of paper sheet thickness

Traditional measurement methods of paper sheet thickness can only measure the thickness of paper sheet at a certain single point, leading to the measurement error due to the uneven distribution of the paper sheet thickness. A new approach of paper sheet thickness measurement using digital speckle projection was proposed to address the problem of single-point measurement. The thickness and contour of paper sheet could be determined by executing the three-dimensional digital image correlation algorithm, after the speckle pattern was projected to the tested paper sheet and a speckle projection experimental system was built. The experimental result is 0.177 mm for measuring the paper which nominal value of thickness is 0.180 mm, and the repetitive experimental results show that the relative difference is less than 4%. Moreover, the full-field distribution of the paper sheet thickness is shown intuitively. In addition, the proposed method of paper sheet thickness measurement has the advantages of simple structure, non-contact full-field measurement, etc., which make the proposed means a promising approach for the measurement of paper sheet thickness during the paper production.