1993

Nevala, Kalervo

In the finishing of paper, attempts are made to achieve a high quality of the roll through the optimum stress structure of the roll during the winding and through minimum damage when the roll is transferred. The greatest amounts of breakage are caused by form errors during winding and roll transfer and by damage to the roll caused by a state of faulty internal stress. Increased production speeds and paper roll sizes and increasingly strict quality requirements have made it difficult to control the winding and to achieve the paper quality expected by the customers. The quality of the roll and the amount of breakages produced in paper finishing are influenced by the properties of the paper and the accuracy of roll transfer movement and nip load control. The paper describes the development of a new control method for center winders, by means of which it is possible to reduce roll damage and to carry out the roll transfer movements more rapidly and accurately than with the methods presented previously. The control method includes a winding arm motion control based on an electro-hydraulic servo system and the control of the nip load between the paper roll and the backing roll. The control method includes the set point calculation of the winding cycle and the measurements and the control methods needed to control the winding arms motion and the nip load. The functioning of the control method has been verified experimentally using equipment containing the functions of a center winder. As the result of this work, the theory and experimental measurement results for a control method developed for the center winder, as well as for the sub-methods involved in this control are presented, including a method of calculating the set points for the winding cycle, a method to control the movements of the winding arms and a method to control the nip load. The comparison of alternative methods and the choice of the method proposed for center winders has been performed on the basis of the experimental measurement results. These results show that the control methods developed in this work can provide considerable improvements in the control accuracy in terms of the motions of the winding arms and the nip load.