Each pair of rollers is moved by their own frequency-regulated drive via a HTD belt that is toothed on both sides. The rollers can be moved far apart with a quick ventilation stroke and can be braked in a controlled manner during the ventilation process. To compensate for diameter tolerances, the upper roller is driven frictionally via the belt. This important compensation is difficult to achieve with toothed and chain drives and leads to an excessive wear of the drive wheels and rolling bearings.
