MODELLING THE BELT – ENVELOPE INTERACTIONS DURING THE POSTAL MAIL CONVEYING BY A SORTING MACHINE
Résumé
The purpose of this study is to predict the trajectory of an envelope when conveyed between two flat belts in a mail sorting machine, as it is often the case in postal centers. Each of the two sides of the envelope is in contact with one belt. The friction coefficient can vary between the two sides, e.g. for the cases of a postcard or a plastic windowed envelope. The two belts are assumed to travel horizontally with the same velocities, but in real world small velocity differ-ences can occur. Also, some deviation from the horizontality of the belts can be observed. These phenomena can lead to unexpected situations where the relative position of the envelope to the belt changes during transportation. The work focuses on the belt-envelope mechanical interac-tions in order to predict the envelope position during its conveying. A 2D model is developed which considers the dynamic equilibrium of the envelope and simulates the transient behavior at different locations in the sorting machine. In the dynamic friction model, the contact surfaces between the envelope sides and the belts have to be determined at each time step. The belt/envelope friction forces are applied at the centers of these contact surfaces One side of the envelope is considered stuck (in adhesion) to the belt while the other is considered slipping. The position of the envelope center of gravity and the angle with the horizontal axis are calculated. For evaluation of the proposed dynamic model, several cases of operation are simulated. The results obtained are consistent with observations made on a real sorting machine. The influence of multiple driving parameters are highlighted: the plastic window location on the envelope, the friction coefficient and the speed difference between belts.