DIGITAL CORRELATOR FOR MEASURING THE VELOCITY OF SOLID-SURFACES

Correlation techniques offer a good possibility for contactless measur ement of the velocity of solid surfaces, The system presented consists of an optical sensor unit, which transforms the stochastic roughness of the object into two signals with a delay time tau, and of a correl ation unit, which extracts the delay time from the signals and calcula tes the velocity of the surface, The main algorithm of that digital co rrelator, representing an identification problem of the delay time tau , is realized by a closed-loop with the advantage of estimating only one point of the correlation function. The dynamic response is mainly dependent on the bandwidth of the sensor signals and the sampling freq uency of the correlator, but not on its arithmetic speed, The mathemat ical description of the correlator is discussed both in the time-domai n and the z-domain. Based on a linearized system, this allows one to d etermine the dynamic response and the stability of the closed-loop cor relator. Two different applications are presented: the measurement of the velocity of paper webs and the measurement of the length of textil e yarns during a winding process.