METHOD AND APPARATUS FOR MEASURING AND CONTROLLING THE SURFACE CHARACTERISTICS OF SHEET MATERIALS SUCH AS PAPER

摘要

An on-line laser triangulation position sensing system provides measurements of the surface features of a moving sheet such as paper. The measurements ar e correlatable with measurements made with standard laboratory surface smoothness testers and provide predictions of the printability of paper duri ng its fabrication. The sensing system includes a segmented balance detector having a high frequency response. The sensing system further includes signal processing circuitry comprising a plurality of channels, each channel including a filter. The various filters have different cutoff frequencies fo r passing different frequency spectra representing ranges of surface feature scale sizes. The cutoff frequency of each filter is varied in response to variations in sheet speed. The sheet sensing system further includes a sheet stabilizer to minimize flutter in the measurement region and a standardizing member permitting performance verification of the sensor system at at least one scale size spectrum. The sensing system may also be provided with a shee t compressor to compress the sheet in the measurement region so as to simulate the pressures applied to sheet samples by laboratory air leak smoothness testers. The output of the position sensing system may be used in conjunctio n with various kinds of papermaking machines to control one or more of the man y papermaking process parameters that determine the smoothness or texture of t he final product. The sensing system can be used to measure tissue crepe and su ch measurement can be utilized to control various crepe-determining stages in a tissue making machine and to monitor the condition of the creping or doctor blade in such a machine.