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I am printing to the outside of bowls in an industrial setting by transferring an image from a flatbed live paint print station via an silicone pad printing head. The image distorts quite a bit growing outward as it moves down the bowl but compressing cylindrically at the same time.

Because the artwork is constantly changing to new designs but the area on the ware to be decorated remains the same, how do I pre-distort the image no matter what it is, to become the same shape every time? I believe that others must have the same dilemma.

I am using both Photoshop or Illustrator to develop images based on what elements are needed but they seem limited and time consuming to distort every image. There are a lot of the. and they need to be repeatable.

Can someone help?

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  • Question: is the printhead applying pressure normal to the surface or is it horizontal pressure only? Sep 5, 2018 at 18:26
  • The pressure is down while wrapping around the bowl as it rolls along the surface from the pressure. The transfer head is 45 shore A solid silicone.
    – user115857
    Sep 5, 2018 at 20:06

2 Answers 2

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This is a layman's answer as I am not sufficiently familiar with Illustrator or related graphic editors, but this may give you a head start on the answer.

Consider to create an image of a grid of lines, or a checkerboard of squares. Apply that image to your print pad and execute a print. Obviously, the previously rectangular image will be distorted. Take a photograph of the distortions on the bowl with the camera as square as possible to the flat surface of the bowl. I believe to minimize distortion, a zoom lens used from some distance away will give the least parallax distortion.

I use Paint Shop Pro and have had to perform "undistortion" features to clean up an image.

I understand that Illustrator (and possibly Photoshop) allow for scripting. I'm aware also that Paint Shop Pro also supports scripting.

Import the photo into your desired software and manually apply the distortion necessary to "square up" the image. Note that this adjustment is the opposite of that which will be required to pre-distort your desired image.

As a test, create a new set of grid lines or checkerboards and apply your inverse adjustments, then perform a test print.

I believe that this process will result in a set of parameters that can then be transferred to a script to automate your goal.

I am envisioning a transfer press which uses a hemispherical application pad and presses in a vertical direction on the item being printed. If the process is more of a linear action, the concept is the same, but the distortions will be biased more in one direction rather than in a radial manner.

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I found a useful PDF guide called Understanding pad printing by Peter Kiddell

It lists various methods to limit distortion. Distorting the image itself is described as a "last resort". Here's a quote from the relevant section in the PDF, the last point being applicable to your situation.

Use these guidelines when choosing a pad shape for a particular job:

• First, try your standard pads that you think would do the job for this particular part. Do a test print to verify that the proposed print area is imaged accurately.

• If the pad shape you have chosen provides a satisfactory print over just a part of the area, look for similar pad shapes that extend the prole in a way that will cover the entire image. Distortion at the image edges is almost always caused by undersized pads.

• If the obvious pads fail, try ones that appear to be unsuitable. Maybe the pad has a sharper angle than would seem to be appropriate, or is clearly too large for the image. It still may solve the problem.

• Irregular ink pickup during the test print usually means that air is being trapped between the pad surface and the cliché. Watch carefully as the pad is being imaged to be sure that a rolling action is occurring.

• Whenever possible, ensure that the point or apex of the pad does not come into contact with the image area of the cliché. This tends to thin the ink at that point, causing an inconsistent ink deposit.

• If the pad is "overstressed" (that is, too small for the image) or the image is too close to the edge of the pad, distortion is likely to occur. Always use as little pressure as possible to pick up and print the image. If the machine is running too fast, excessive pad pressure can cause distortion as well as poor ink transfer.

• If your experimentation doesn't reduce the print distortion to an acceptable level, and a custom pad is out of the question, your last resort is to distort the image on the cliché to compensate. This is often done by printing a grid onto the substrate and measuring the distortion of the grid to guide you in the alterations that must be made to the original artwork. This will shorten the time it takes you in test printing, but it won't eliminate the trial-and-error altogether. This method also leads to ongoing problems since positioning of the part and the pad (relative to the image on the cliché) must be absolutely dead on each time the job is set up to avoid distortion. We have heard that computer software packages are available that will do this work, but none are known to us.

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