Example: Trapezoidal/pillow sheet growth profile
With some of the newer sheetfed printing presses, the required sheet
growth compensation is not necessarily linear; it may be trapezoidal
(as pictured on the left) or pillow (the left and right black edges are
bowed out or in, creating a pillow-like shape, as pictured on the right).
In the examples shown, the red box is the desired size and shape of the
printed sheet. The black box is the size and shape that may result if no
sheetfed compensation is applied. The lower edge of the content
bounding box is the gripper edge of the printing press.
Both examples show non-parallel growth in the horizontal direction,
and parallel growth in vertical direction.
Notice that the top and the bottom sides of the bounding box remain
unrotated and parallel to each other. In other words, trapezoidal
sheetfed compensation cannot be performed in a vertical direction
(that is, parallel to the gripper edge). However, it is possible to apply
linear sheetfed growth or contraction in a vertical direction.
This topic provides an explanation of the required format and an
example of a trapezoidal growth profile.
Format
To specify trapezoidal sheetfed compensation in the web growth
profile, specify two or three points in the following format:
<fanout y="<#>" fanoutvalleft="<#>"
fanoutvalright="<#>" dy="<#>" />
●
y
is the vertical position of the point being sampled.
●
fanoutvalleft
is the amount of growth/shrinkage on the left
side.
○
Use positive values when the measured, uncompensated output
is expanding (growing) to the left.
○
Use negative values when the measured, uncompensated output
is contracting (shrinking) to the right.
●
fanoutvalright
is the amount of growth/shrinkage on the right
side.
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Chapter 12—Outputs
