(57) The present invention provides an apparatus (13) for straightening sheet curls in
which a wrap angle ϑ is provided for a sheet (20) wound off from a winding roll (19)
by applying a decurler bar (31) to the sheet (20) between two backup rolls (32), the
apparatus (13) comprising a wrap angle adjusting device (34) for adjusting the wrap
angle (ϑ) of the sheet (20) by relatively displacing the backup rolls (32) and the
decurler bar (31), and a controller (16) which serves to calculate an optimum wrap
angle (ϑ) in accordance with changes in the diameter of the winding roll (19) using
the logical equation: ϑ = A/Dq + B (wherein A, B, q are constants which are previously determined) from which the
optimum wrap angle ϑ can be calculated for the diameter D of the winding roll (19),
and to control the wrap angle adjusting device (34) on the basis of the results of
this calculation. In consequence, the present invention is able to realize automatization
of straightening of curls with a simple configuration and in a rapid and highly precise
manner.
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