Patent ID: 8532560

Claim:
A sheet de-curling device, comprising: a first de-curling roller, structured of a round axial shaft and a long bar-shaped member, wherein the long bar-shaped member is spiraled on the round axial shaft clockwise from a predetermined portion of a center of the round axial shaft toward a left end of the round axial shaft, and counterclockwise from the predetermined portion of the center of the round axial shaft toward a right end of the round axial shaft with the same spiraling pitch; a second de-curling roller, having the same size as the first de-curling roller, to be paired with the first de-curling roller, structured of a round axial shaft and a long bar-shaped member, wherein the long bar-shaped member is spiraled on the round axial shaft in opposite spiraling directions against the first de-curling roller; an initial phase-angle changing section which is configured to change an initial phase-angle difference between the first de-curling roller and the second de-curling roller, a control section which is configured to control the initial phase-angle changing section, based on a sheet size, a sheet weight, a sheet type, a sheet curling shape, and a sheet curling amount, to change phase-angles of the first de-curling roller and the second de-curling roller in such conditions that: (i) a top of a thread section of a spiral of the first de-curling roller faces a top of a thread section of the second de-curling roller; (ii) the top of the thread section of the spiral of the first de-curling roller faces a center of a root section of the second de-curling roller, and (iii) the top of the thread section of the spiral of the first de-curling roller faces a portion other than the center of the root section of the second de-curling roller; and a driving mechanism which is configured to rotate the paired first and second de-curling rollers in such a way that, when a sheet is introduced to be nipped between the paired first and second de-curling rollers, and when the paired first and second de-curling rollers are rotated, plural contacting points, on which the sheet comes into contact with the long bar-shaped members of the first and second de-curling rollers, are configured to shift in a direction from the center to both edges of the sheet.