Message-ID: <632363757.180.1611707370480.JavaMail.j2ee-workflowhelp@kodak01.managed.contegix.com> Subject: Exported From Confluence MIME-Version: 1.0 Content-Type: multipart/related; boundary="----=_Part_179_2017803087.1611707370479" ------=_Part_179_2017803087.1611707370479 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Content-Location: file:///C:/exported.html Calculating web growth

# Calculating web growth

This topic gives examples for calculating the percentage of web = growth from measurements on press sheets or traditional page-shifts.

The standard process for determining web growth compensation parameters = is to print press sheets with no compensation, and then measure the discrep= ancies between the separations at different points on the surface. The grow= th percentage for one separation relative to another is then calculated by = adding the discrepancy at the farthest left pair of marks, to the discrepan= cy at the farthest right pair of marks, and dividing by the distance betwee= n the pairs.

Once calculated, the percentages are entered into the web growth profile= file. Prinergy uses the percentages from the web growth profile in an algo= rithm to compensate for web growth.

Example 1: Measuring the displacements from the yellow separ= ation across a grid

Table 1 is a table of measurements from a press sheet of grids printed w= ith the ink order KCMY. Each column of numbers corresponds to the vertical = grid line at a particular horizontal position. (This is only an example. In= reality, a grid would contain far more lines.) Yellow is the last ink down= , so it is the base separation against which other separations are measured= .

Table 1: Displacements from the yellow separation across a grid

 Distance in mm Negative numbers indicate distances to the left. Non-negative numbers indicate distances to the righ= t. Page Growth<= /p> X -886.8 -584.0 -252.0 -12.7 12.7 315.5 584.0 886.8 N/A K-Y -1.38 -.82 -.36 .1 .13 .64 .95 1.40 (1.38 + 1.40)/(2 x 886.8) =3D .157% C-Y -1.04 -.66 -.36 .10 .10 .30 .46 .78 (1.04 + .78)/(2 x 886.8) =3D .103% M-Y -.52 -.30 -.08 .10 .08 .12 .23 .40 (.52 + .40)/(2 x 886.8) =3D .052%

X measures the horizontal distance (across the web) of the vertical grid= line from the horizontal center of the sheet. The first column corresponds= to the left-most grid line, which is 886.8 mm to the left of the center. T= he last column corresponds to the right-most grid line, which is 886.8 mm t= o the right of the center.

The figures in row K-Y measure the displacement from the black separatio= n to the yellow separation for corresponding grid lines.

The figure in row C-Y measure the displacement from the cyan separation = to the yellow separation.

The figures in row M-Y measure the displacement from the magenta separat= ion to the yellow separation.

Looking at the K-Y row in detail, the -1.38 in the column where X is -88= 6.8 indicates the black separation is 1.38 mm to the left of the yellow sep= aration at the left edge of the sheet. The 1.40 mm in the column where X is= 886.8 indicates the black separation is 1.40 mm to the right of the yellow= separation at the right edge of the sheet. Thus, the black separation is l= arger than the yellow (by about 1.38 + 1.40 =3D 2.72 mm). This is expected = because the black was printed before the yellow, and the paper grew while t= raveling from the black ink unit to the yellow ink unit. The growth of the = black separation, relative to the yellow, is (1.38 + 1.40) / (2 x 886.8) = =3D .157%, as shown in the Page Growth column at the right of the table.

Similarly, for the C-Y and M-Y rows, the growth of these separations rel= ative to yellow is calculated in the same way and shown at the right of the= table. The growth of the cyan is about twice that of the magenta, while th= e growth of the black is about three times that of the magenta. This is nor= mal for equally spaced ink units.

Note: The only data used to compute the growth was the = displacements at the outer edges.

After you calculate web growth, you enter the percentages into the web g= rowth profile for the press and paper to which this growth applies. You mus= t enter values for both the upper and lower surfaces in the same web growth= profile. Prinergy takes the percentages from the web growth profile and us= es an algorithm to compensate for the web growth. The numbers in the web gr= owth profile should decrease from the first ink tower (first down, so large= st growth) to the last ink tower (last down, so no growth).

Example of a w= eb growth profile

Example of a tow= er-color file

Note: Only horizontal percentages appear in the file. I= f a percentage is missing, as it is for all the y (along-the-web) parameter= s, it is assumed to be zero. The growth for tower 4 (corresponding to yello= w, according to the `TowerColorMap.txt` file) could therefore be= left out, given that it is zero. For true web growth, the percentage growt= h values for the lower surface (side=3DL) are the same as for the upper sur= face (side=3DU) to avoid the paper curling.

Example 2: Measuring page shifts

In this example, the page shifts used to compensate for web growth are s= pecified instead of grid measurements, as might appear in a table in the jo= b jacket when traditional compensation methods are used. In this example, t= he ink order is KCMY, measurements are in inches, the imposition is four ac= ross, and pages are 12.5 inches wide.

Table 2: Page shifts to compensate for web growth

Page

Left Outer

Left Inner

Right Inner

Right Outer

K

0.005

0.002

-0.002

-0.005

C

0.003

0.001

-0.001

-0.003

M

- - - -

Y

-0.004

-0.002

0.002

0.004

The left outer black page is moved right by .005 in. towards the center.= The right outer page is moved left by .005 in. towards the center. The yel= low pages are moved out. The magenta separation is not adjusted.

While Table 1 specified the displacement on press, Table 2 specifies the= compensation to be applied. In Table 2, magenta is used as the base separa= tion. However, the web growth profile always uses the last ink down as the = base separation.

Table 3 below reexpresses the data of Table 2 in the format of Table 1. = Consider the left outer page: the black is shifted .005 inches to the right= , and the yellow .004 to the left. As a result, relative to the yellow, the= black page is shifted .009 inches to the right. Because Table 2 indicates = how much to shift each page to align the centers of the pages, and the page= s are 12.5 inches wide, the page center of the left outer page is at 1.5 x = 12.5 inches =3D 18.75 inches left of the signature center. The displacement= of the black relative to the yellow at -18.75 inches from the center, then= , is -.009 mm.

Table 3: Displacements from the yellow separation at page centers

 Distance in inches Negative numbers indicate distances to the left. Non-negative numbers indicate distances to the = right. Page Growth X -18.75 -6.25 6.25 18.75 N/A K-Y -.009 -.004 .004 .009 (.009 + .009) / (2 x 18.75) =3D .048% C-Y -.007 -.003 .003 .007 (.007 + .007) / (2 x 18.75) =3D .037% M-Y -.004 -.002 .002 .004 (.004 + .004) / (2 x 18.75) =3D .021%

To compute the growth, we again use only data for the outer pages. The d= isplacements are accurate to only one significant figure, so there's no nee= d to use more than two figures for the growth percentage.

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