A new optical sensor for measuring the velocity of webs by correlation techniques

A newly developed measurement system is presented allowing us to measure the velocity of different two-dimensional (2-D) objects. The measurement system has already been tested for paper-, rubber-, and textile-webs, sheet metal, and road surfaces with a relative measurement error of typically less than 1% dependent on the dynamic response of the correlator. The measurement system consists of a sensor unit, transforming the stochastic characteristics of the moving object into two signals with a delay time t*, and a correlation unit, extracting the delay time from the signals and calculating the velocity of the surface. Different measurements at a test stand and at an industrial paper machine are presented to demonstrate the accuracy of the measurement system and its flexibility and robustness. The measurements include the velocity of the paper web in different sections of the machine and velocity fluctuations of the web.