Patent ID: 8763945

Claim:
A method in connection with a continuous material web, the material web running from an unwinder to a winder, at least one of the winders being a center winder, wherein the center winder is controlled by an electric drive provided with a torque control, the method comprising: providing an initial value for density of a material on the center winder; calculating a moment of inertia for a roll of material on the center winder; determining tightness of the material web by a mechanical sensor; producing, by a tightness controller, a correction term for torque calculation on the basis of a material web tightness reference, the determined material web tightness and the calculated moment of inertia of the roll of material on the center winder; calculating a torque reference on the basis of the correction term produced by the tightness controller and the calculated moment of inertia of the roll of material on the center winder; controlling the torque of the center winder on the basis of the torque reference; and correcting a density value of the material on the center winder on the basis of the correction term produced by the tightness controller.