System for controlling the nip pressure profile in a roll press

A method for regulating the transverse distribution of pressure applied to a web passing through a nip by utilizing a first number (K) of separately adjustable zone power means for a first number (K) of actual pressure zones of the nip, the number of power means loading the nip being sufficiently high to permit the formation of a desired transverse pressure distribution, and wherein said method further utilizes a control system for separately regulating the load applied to the nip by each of said power means, comprising the steps of:

• (a) creating a mathematical model of said nip whose transverse pressure distribution applied to said web is to be regulated;
• (b) determining a setting zone set value distribution or profile corresponding to a desired pressure profile of said nip comprising a second number (N) of setting zone set values for a corresponding second number (N) of setting zones, said second number (N) of setting zones being substantially larger than said first number (K) of separately adjustable zone power means;
• (c) inputting said setting zone set values obtained in step (b) into a zone conversion means for obtaining as an output therefrom a first number (K) of pressure zone set values, so that the deviation of the actual transverse pressure profile acting on the web passing through the nip from the setting zone set value distribution or profile is substantially minimized;
• (d) inputting said pressure zone set values into a means of said control system for separately regulating each of said power means as a function of a respective one of said pressure zone set values.

In apparatus for treating a web, such as a paper web, passing through an adjustable nip, such as a dewatering nip or a calendering nip, said apparatus including a zone-adjustable device and a counter-member forming said nip, said pressure zone-adjustable device including a first number (K) of nip loading means defining a first number (K) of actual pressure zones in said nip, each of said loading means being loaded by a separately controlled zone pressure which is controlled by a zone pressure controller and a regulating system including a set value unit, a regulator unit, and an actuator unit including a series of said zone pressure controllers and a series of pressure-current converters from which feedback signals are passed to said regulator unit, the improvement comprising:

• said set value unit including setting zone means in which a distribution of a second number (N) of separate setting zone set values corresponding to a desired pressure profile in said nip are provided, said second number (N) of separate setting zone set values being substantially greater than said first number (K) of actual pressure zones of said pressure zone-adjustable device, and
• said set value unit further including zone conversion means for converting said second number (N) of setting zone set values to a first number (K) of pressure zone set values on the basis of a mathematical model of the adjustable nip, whereby the deviation of an actual transverse pressure distribution applied to the web passing through the nip from the setting zone set value distribution is substantially minimized.