Method and Apparatus for Controlling a Coating Head, and a Coating Head

A method for controlling a coating head configured to exert a nip pressure profile to a fibrous web to be coated while the fibrous web is supported by a backing roll, comprising the steps of:

• reading an output signal of a sensor integrated within the backing roll in the cross direction, and producing a measured indication of the nip pressure profile of the coating head in the cross direction;
• deriving a plurality of actuator control values at least partly from said measured indication of the nip pressure profile;
• and
• delivering said actuator control values as commands to a plurality of respective actuators that contribute to creating the nip pressure profile, by pressing indirectly on a coating blade through a profiler bar to control an amount of a coating substance on the fibrous web.

An arrangement for controlling a coating head configured to exert a nip pressure to a fibrous web to be coated while the fibrous web is supported by a backing roll, wherein the arrangement comprises:

• a sensor integrated within the backing roll,
• a plurality of actuators configured to contribute to creating the nip pressure;
• a reading system configured to read an output signal of said sensor and to produce a measured indication of the nip pressure;
• and
• a control unit configured to derive a plurality of actuator control values at least partly from said measured indication of the nip pressure, and to deliver said actuator control values as commands to said plurality of actuators arranged to press indirectly on a coating blade through a profiler bar, thus controlling an amount of a coating substance on the fibrous web in the coating head.

A method for controlling the coating of a fiber web, comprising the steps of:

• applying a coating to a fiber web supported by a backing roll, the applied coating defining a thickness;
• passing the coating and the fiber web through a cross direction coating metering nip;
• controlling the pressure in the metering nip so as to control the thickness of the applied coating on the fiber web in a cross direction and a machine direction;
• wherein the step of controlling the pressure in the metering nip is accomplished with a multiplicity of digital hydraulic actuators impinging on a doctor blade, a profiler bar engaging a doctor blade, or a rod which is pressed toward the fibrous web, creating a distribution of nip pressure along a linear region of the fibrous web that is passing through the metering nip;
• measuring the pressure in the nip in a cross direction and circumferential direction with pressure sensors integrated within the backing roll;
• reading an output signal from the pressure sensors and producing a measured indication of the nip pressure profile of the coating head in the cross direction;
• deriving a plurality of actuator control values at least partly from said measured indication of the nip pressure;
• driving each of said multiplicity of digital hydraulic actuators with a plurality of digital valves;
• and
• delivering said actuator control values as commands to the plurality of digital valves of each of the digital hydraulic actuators.