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Experimental and Theoretical Observations of the Dynamics of Paper in a Printing Press Folder

The jaw folder is widely used in the printing and paper converting industry, having the purpose of placing a fold in a sheet or sheets of paper in a direction perpendicular to their direction of motion. The dynamics of the sheet are complex, involving the rapid reversal of motion of half of the sheet, and are not presently well understood. Through analysis of high-speed cine films of a typical jaw folder, the authors have quantified the positions and accelerations of the sheet during the folding process. These have been verified by software simulation. The surrounding air is shown to be of great significance to the effective sheet mass and the damping of its motion. Accelerations in the plane of the sheet are also demonstrated to be important contributors to its stiffness. Methods are suggested by which the design of the folder might be improved.