Apparatus and method for controlling the thickness of coatings on paper or other materials

In a system for applying a coating material to web material, the system of the type in which web material from a continuous roll on which coating material has been placed is transported through a slot formed between a surface and a metering element, the metering element for pressing the web material on which coating material has been placed against said surface and removing excess coating material, the slot oriented in a cross-direction relative to the direction of transport of the web material and having a width at each cross-directional position that determines the thickness of the web material and coating material at said cross-directional position that is transported through said slot, the improvement, by which a preselected thickness of coating material is applied to the web material with the thickness regulated at a plurality of selected cross-directional positions while web material is being transported through said slot, comprising:

• a metering element capable of flexion at said plurality of cross-directional positions so that the displacement of said metering element from said surface and hence the width of the slot is adjustable at least to some extent independently at each of said plurality of selected cross-directional positions;
• control means for generating, as web material is transported through said slot, a plurality of control signals corresponding to said plurality of selected cross-directional positions, each control signal having a value dependent upon the difference in thickness of the web material before it is transported through said slot and the coated web material after it is transported through said slot at one of the plurality of selected cross-directional positions and dependent upon the preselected thickness of said coating material;
• and
• adjusting means coupled to said metering element and coupled to said control means for adjusting, at least to some extent independently, as web material is transported through said slot, the flexion of the metering element and thereby the width of the slot at each of said plurality of selected cross-directional positions, said adjusting means acting in response to the corresponding control signals in order to regulate the thickness of the coating material on the web material as it is transported through said slot.