The optimization of numerous technological processes requires a deep understanding of the paper friction phenomena. This thesis aims to better understand these phenomena in order to improve the envelopes separation in franking machines.
First, standardized methods for measuring the paper-on-paper friction force having proved limited in terms of repeatability and experimental conditions, two measurement methods ? low and high speed ? were developed. Similarly, the friction measurement has been adapted to the different contacts encountered in franking machines. Secondly, these methods have been used to study the mechanisms of friction with the paper material including the dependency of the paper-on-paper friction to length of the displacement, the influence of both temperature and humidity on the paper-on-paper friction, and the main frictional properties of the envelope-on-envelope, rollers-on-paper, and pads-on-paper contacts, respectively. Thirdly, a comprehensive model of the envelopes separation in a franking machine was created. This process aims at displacing, with no damage, only the bottommost envelope of a stack of envelopes. This model allows to identify, characterize and propose an optimization of the main process parameters.