Patent ID: 7060161

Claim:
A method for restraining deformation of a nip roll, which is used to restrain deformation of first and second nip rolls which nip a sheet material, the method comprising: setting a diameter ratio between said first and second nip rolls at a value different from 1; and setting the diameter ratio between said first and second nip rolls so that when a number of polygon sides of polygonal deformation of said first nip roll, which is defined by a ratio of the frequency of a vibration system including said rolls to a rotational speed of said first nip roll, is an integer N 1 , a number of polygon sides of said second nip roll, which is defined by the ratio of the frequency of said vibration system to a rotational speed of said second nip roll, has the following value: N 1 ≠j+a where, j=0, 1, 2, 3, . . . 0<a<1.