Register compensation in Prepress
- Thread starter aqazi81
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D
Deleted member 16349
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As long as the misregistration is consistent and not randomly changing, then it can.
Alois Senefelder
Well-known member
Gentlemen,
mmm.............. "As long as the mis -registration is consistent " ----- it must be in Register
mmm.............. "As long as the mis -registration is consistent " ----- it must be in Register
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Alois Senefelder
Well-known member
Mis-registration
Gentlemen,
No matter what claims are made for so called "Mis-registration" compensation software programmes.............. Paper is an unstable material,
Regards, Alois
Gentlemen,
No matter what claims are made for so called "Mis-registration" compensation software programmes.............. Paper is an unstable material,
Regards, Alois
D
Deleted member 16349
Guest
No, two printed separated images can have different dimensions, such as one being wider than the other. If one was always wider than the other, being consistent, then one can adjust for that in prepress. It is done all the time.
mmmm...... Alois, what were you thinking?
gordo
Well-known member
Web growth. And Erik is correct. My local daily paper can't compensate because there is no consistency with the dimensional change. They try - so there's some compensation with a sense of job security by chasing a moving target.
They did switch to FM screening which did reduce the range of web growth variation while making the image degradation caused by mis-registration less visible which in turn reduced the number of charge backs.
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Alois Senefelder
Well-known member
Gentlemen,
What was I thinking of..........
Having spent 40 years..... seeing Millions of Meters of Paper put through various Web-Offset Presses and the resulting register variation at Reel Changes ,
also of the running reel.
Regards, Alois
What was I thinking of..........
Having spent 40 years..... seeing Millions of Meters of Paper put through various Web-Offset Presses and the resulting register variation at Reel Changes ,
also of the running reel.
Regards, Alois
What software are you using to output plates? We use Prinergy and their web growth compensation works great.
aqazi81
Well-known member
Hi all,
Sorry I didn't provide details. My question is specifically for sheetfed offset.
We sold a VLF CTP to a customer and they are using Founder Elecroc 6 workflow. They have KBA 145 and a 105 press. The paper stretch is causing register marks of the subsequent colors to be out of register in lateral direction. The problem is mostly on the tail edge of the sheet.
Sorry I didn't provide details. My question is specifically for sheetfed offset.
We sold a VLF CTP to a customer and they are using Founder Elecroc 6 workflow. They have KBA 145 and a 105 press. The paper stretch is causing register marks of the subsequent colors to be out of register in lateral direction. The problem is mostly on the tail edge of the sheet.
gordo
Well-known member
The Devil's in the details.
Assuming it's a press ather than a CtP issue, there's one of two kinds of misregistration that you're seeing: "back sheet flare" or "back stretch" more info is here: http://the-print-guide.blogspot.ca/2011/08/misregistration-on-press.html
gordo
Well-known member
The only ways I know is:
1 - rotate the file 180° so that the heaviest coverage is at the lead edge and the lightest coverage is at the tail
2 - use a heavier weight paper.
3 - check for excessive impression/blanket squeeze which may be stretching the paper.
I don't think you can employ any file distortion in prepress to solve this. Maybe others folks have more ideas. Sorry.
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Alois Senefelder
Well-known member
Hello aqazi8,
I suggest before we get into the "Realms of Fantasy" re - software ! THAT you visit the Printers and verify first IF the press operators know
what they are doing --- correct/incorrect of operation of these very sophisticated presses !!!!!!!!!
Question 1) ASK them..... do they know about adjusting - Print Length, via Plate/Blanket Height ???
Regards, Alois
I suggest before we get into the "Realms of Fantasy" re - software ! THAT you visit the Printers and verify first IF the press operators know
what they are doing --- correct/incorrect of operation of these very sophisticated presses !!!!!!!!!
Question 1) ASK them..... do they know about adjusting - Print Length, via Plate/Blanket Height ???
Regards, Alois
D
Deleted member 16349
Guest
In 1997, one of the two tech papers I presented at the TAGA conference was related to web tensions and repeat length in web offset presses. It was an engineering paper with equations related to the main factors affecting repeat length and this is also very closely related to print length. In the paper both web and sheetfed conditions were discussed. This paper was written from investigations I did in the mid 1980's at TetraPak Canada, where one of the critical issues was insetting, which is the process of printing to a predetermined repeat length.
Anyhow, one of the interesting factors was blanket squeeze and shear forces in the nip. As you suggest, this might distort the paper, but squeeze on its own will affect the pulling rate of the blanket on the paper being printed. Shear forces will also have an affect. In the tech paper, these factors were provided in a model (equations) which was based on careful measurements from testing.
Sheetfed is a more difficult problem to obtain predictable answers to these issues due to the fact that with a web press, the web itself provides some stability that an unfixed sheet can not.
Around 2001, I was working with a group that was responsible for the computer software and hardware development for a CTP manufacturer. One topic that came up was a request from a press manufacturer for some software that would compensate for distortions of the print on a sheetfed press. The distortion that they wanted to address was in the shape of a trapezoid, where the head and tail had different widths. I am assuming that this kind of problem was due to differences in forces on the paper due to different coverage as the paper was released from the blanket, and therefore possibly stretching the paper unevenly. You suggest such a thing in your 1. point.
So there could be some potential for software to compensate such a distortion and at least one press manufacturer has thought of it. I don't know if the software was developed by the company I was assisting.
I also think there has been a press manufacturer, which has done some work to account for a distorted image in the press. If I remembered correctly, the ideas was to stretch the plate laterally at the tail. I might be wrong on this.
Manroland has a function where it adjusts the rate of rotation of its plate cylinder on each revolution to try to address fit problems in the machine direction. This might mean a higher or slower speed of that cylinder during the print part of the cycle and then a return to normal relative position of that cylinder in the gap part of the cycle. I don't know it they still do this.
My original point was that if some distortion was consistent, then one could adjust in prepress. Of course, as Alois has stated, it should be common knowledge by press operators on how to adjust the fit in the machine direction with changes in packing. I am not sure what the press operator could do with lateral distortion and its mis-registration.
dabob
Well-known member
Not in prepress but, and I have never personally experienced it or had to compensate for it . . . but as I recall there are some presses with a split tail clamp to enable you to make the tail of the plate just a wee little bit wider to compensate (and yes that is the technical term for it)
Also, in talking with our lead pressman he said that some presses have a method to change how the sheet is delivered into the cylinder grippers, on presses with this option the ranger drum has a adjustment so that you can make a very small change in the sheets leading edge so that it would either have a concave shape or a convex shape when delivered into the cylinder grippers - we have a Heidelberg 4/c 72 perfector that has is and a 2/c 72 perfector that doesn't . . .
Also, in talking with our lead pressman he said that some presses have a method to change how the sheet is delivered into the cylinder grippers, on presses with this option the ranger drum has a adjustment so that you can make a very small change in the sheets leading edge so that it would either have a concave shape or a convex shape when delivered into the cylinder grippers - we have a Heidelberg 4/c 72 perfector that has is and a 2/c 72 perfector that doesn't . . .
Alois Senefelder
Well-known member
Hello gentlemen and dabob,
dabob, you are correct on both points you mentioned, Yes, M.A.N and many other German press manufacturers used....... Split Rear Plate Clamps and some even had
the facility adjusting the Impression Cylinder Grippers ..... they could be "Slightly Bowed" giving Concave/Convex position.
Regards, Alois
dabob, you are correct on both points you mentioned, Yes, M.A.N and many other German press manufacturers used....... Split Rear Plate Clamps and some even had
the facility adjusting the Impression Cylinder Grippers ..... they could be "Slightly Bowed" giving Concave/Convex position.
Regards, Alois
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Heidelberg offers Paper Stretch Compensation. This is a bit different then web growth which typically has x and Y adjustments for compensation. We have 9 aim points, top left, top center, top right, the same for the middle and bottom of the sheet, 3 points each. Once calibrated, this will compensate for flare. It is an option to our Prinect workflow or can work with other workflow via 1 bit tiff. You can contact your local Heidelberg office to get more information. Hope this helps.
Best,
Mark Tonkovich
Heidelberg USA
Best,
Mark Tonkovich
Heidelberg USA
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