Colorbar question

[fiatlux]

Just making sure...on a sheetfed press the colorbar goes at the tail of the sheet not the lead edge. Correct?

 

[dabob]

Thats the way we run it . . . . to me it wouldn't make sense to put it on the lead edge . . . the inkers would have a chance to recover in the plate gap . . . .

 

[lazzz]

It depends on your control device. Some old/simple strip readers such as HDM's oldest Axis Control can measure only at tail. Inpress control reads the image near gripper bar inside the press. Modern Axis Control have 3 fixed positions: top, center and bottom. But you can choose every position manually. Image Control reads all the sheet, so you don't need color bar. Small control elements could be placed everywhere. Or it can use parts of image as control elements.
If you use msnual control device you can place it everywhere you want. Just make sure that you have enough elements.
Placing grey balance fields at the tail may provide uneven results cause of paper deformation.
Actually i think the best place for colorbar is in the center of sheet. It is most stable and saves most of sheet space.

 

[aqazi81]

@alibryan... What is the tolerance for lead to tail edge density difference?

 

[Deleted member 16349]

I would say an acceptable number is 5 points +/-. There will always be varying factors such as press make and model and also the condition of the rollers, but when everything's set correctly, it's definitely achievable.

The variation you state is probably correct but I would not say it is "acceptable".

This variation is surely related to press design. I would not expect the Anicolor press to have such a variation. There are other press designs that I would not expect that kind of variation.

It always amazes me when many types of variation are said to be acceptable or normal. Why does the industry accept variation that is visible as being OK?

In 2004, I visited a press manufacturer in Europe, where I was giving a seminar on density control related to the design of offset presses. In talking to one of the engineers there, we were discussing starvation ghosting of their presses. (Not the same as the head to tail variation but related) He said that they had a well known expert from the US who looked at their ghosting results and even though it was visible, he stated that that level of ghosting was normal and OK. That kind of statement shocks me since if it is visible, it is certainly not OK. It needs to be understood and designed out of the press.

There is too much "accepting" poor performance going on.

 

[Johu]

Then again on a perfecting press it is quite usual to have it in the middle (depending on the measuring system of course). XRite based Komori systems also read the strip from the bottom, but in most cases the sheet was turned upside down to make the measurement. The system obviously was set to turn the info in to correct orientation.

 

[Alois Senefelder]

Variation of Colour on Sheet- fed Presses,

Erik,

How do you propose to eliminate the de facto variation of present day Sheet-fed Printing Presses.....

roller train inking systems --- when the main culprit is the Plate Cylinder Gap?

The problem...... because X degrees of cylinder rotation are needed to allow for

the Mechanics of Sheet Insertion.


Regards, Alois

 

[gordo]

Variation of Colour on Sheet- fed Presses,

Erik,

How do you propose to eliminate the de facto variation of present day Sheet-fed Printing Presses.....

roller train inking systems --- when the main culprit is the Plate Cylinder Gap?

Sorry, couldn't resist!

 

[Deleted member 16349]

Variation of Colour on Sheet- fed Presses,

Erik,

How do you propose to eliminate the de facto variation of present day Sheet-fed Printing Presses.....

roller train inking systems --- when the main culprit is the Plate Cylinder Gap?

The problem...... because X degrees of cylinder rotation are needed to allow for

the Mechanics of Sheet Insertion.


Regards, Alois

Eliminating variation totally is not a practical goal with offset but reducing it so it is not noticeable is a practical goal. The first step is to understand what causes variation of the inking of the plate. There are many issues, which I will not go into here but generally the problem is delivering the right about of ink to the form rollers in the right locations. Besides the problems of lateral inking variation there is also the problem of reinking and smoothing the form roller surfaces on each cycle as the plate takes ink from the form rollers.

Some presses do this better than others. The Anicolor press should do this well but there are also more conventional presses that press designs that result in low levels of ghosting and top to bottom variation. This is a problem that can be analyzed and a press can be designed to perform well based on rules of how ink is transferred, stored and laterally distributed in the roller train.

There is the concern about the gap but I don't see this as being such a big issue. Any press can have a variety of inking patterns on the plate cylinder. The gap is basically a non image area and as far as the inking system goes, a non image area caused by the gap or by no image on the plate is similar. The application of water is different and presses that apply water directly to the plate might be more affected by a gap. But I also view the way water is applied to the roller train is an issue that has opportunities for improvement but the ink feed problem would need to be addressed properly first.

But of course, if one wants to argue that nothing can improve the process as it is, then inkjet presses are the way of the future since they do not suffer from ghosting or top to bottom variation. Those that do not think the offset process can improve are basically saying that we should get rid of all the offset press operators that can not deliver consistency and go to digital presses.

 

[Bloodsaler]

For xrite Intellitrax device, the measurement only can be done on the tail edge. But for Techkon, you can put the colorbar on any place of the sheet. And for InpressControl from heidelberg, the color bar can not be placed at the tail edge, but in middle or in lead edge both are OK. We have Intellitrax and Inpress Control, so most of our sheet have two colorbars. One on tail edge for Intellitrax, another one on lead edge for inpresscontrol

 

[chevalier]

There's some errored information on this post about Heidelberg's Dipco marks system used on ImageControl and Inpress. It varies between the different systems what is and what is not required.

https://www.heidelberg.com/global/e...surement_systems_1/prinect_dipco_elements.jsp
https://www.heidelberg.com/global/media/global_media/products___prinect_modules/Dipco.zip - See Manual.pdf for English instructions. Section "B Other" covers marks placement and requirements.

Direct copy/paste from Heidelberg Dipco Manual regarding inpress:

You can mount the quality control strip at any position
you wish between the gripper margin
(Fig. 19/1) and the center of the sheet (Fig. 19/2).
● To guarantee the measurement quality, allow
1 mm of paper white between the gripper margin
and the color measurement fields, particularly
when using micro strips.
Note
For perfecting on thin (translucent) paper:
Do not fit the quality control strips
congruently on the front and reverse
side. This can lead to measuring errors.
DP.901.0016-000UTKENU_01
Other
B.1.13
1
DP.901.0095-000GRAUND_00
Fig. 20 Position mark, Prinect Inpress Control
● For automatic detection of the quality control
strip, position marks (Fig. 20/1) are located on the
strip. It is vital that these are in place! Otherwise,
the quality control strip will not be found.
● For automatic detection and register control,
there has to be sufficient space at the top and
bottom. Therefor, there must be at least 1 mm of
paper white above and below the measurement
fields. This also applies for quality control strips
with 5 mm x 6 mm measurement fields!
Note: 1 mm of paper white above and below the
measurement fields is recommended for conventional
paper types and printing conditions. However,
in situations with highly variable or thin paper
types, particularly in connection with high ink
coverage, more than 1 mm may be necessary!
● Measurement of colored, metallized, film-laminated,
aluminized or similarly coated paper types
is generally not possible. Measurement with
opaque white is also not possible when using
opaque white under the quality control strip!
Minimum distances to the rear edge of sheet
If the quality control strip has to be arranged beyond
the center of the sheet toward the rear edge of sheet,
you need to take into account the following minimum
distances to the rear edge of sheet:
● Speedmaster CD 74 and XL 75: 120 mm
● Speedmaster SM 102: 110 mm
● Speedmaster XL 105/106 and CX 102: 150 mm
● Speedmaster XL 145 and XL 162: 35 0 mm
Gripper bite
The paper white measurement and the adjustment of
the spectrophotometer are performed in the gripper
margin. The size of the gripper margin is as follows:
● Speedmaster CD 74 and XL 75: 8 - 10 mm
● All other presses: 10 - 12 mm

 

[DeltaE]

The variation you state is probably correct but I would not say it is "acceptable".

This variation is surely related to press design. I would not expect the Anicolor press to have such a variation. There are other press designs that I would not expect that kind of variation.

It always amazes me when many types of variation are said to be acceptable or normal. Why does the industry accept variation that is visible as being OK?

In 2004, I visited a press manufacturer in Europe, where I was giving a seminar on density control related to the design of offset presses. In talking to one of the engineers there, we were discussing starvation ghosting of their presses. (Not the same as the head to tail variation but related) He said that they had a well known expert from the US who looked at their ghosting results and even though it was visible, he stated that that level of ghosting was normal and OK. That kind of statement shocks me since if it is visible, it is certainly not OK. It needs to be understood and designed out of the press.

There is too much "accepting" poor performance going on.

Hi Erik,

You mentioned about density lead-tail variation of Anicolor. Could you please tell me how it is if we compare to conventional offset machine?

All you here are very experience, could you please give me any documents or link to study about ink-train, influence of gap in plate cylinder?

By the way, I know some Heidelberg machine has short ink train, in that case machine will switch off 2 ink form rollers, how could you use that function in real job, how benefit?

Thanks a lot!

Regards,

Delta

 

[Deleted member 16349]

Hi Erik,

You mentioned about density lead-tail variation of Anicolor. Could you please tell me how it is if we compare to conventional offset machine?

All you here are very experience, could you please give me any documents or link to study about ink-train, influence of gap in plate cylinder?

By the way, I know some Heidelberg machine has short ink train, in that case machine will switch off 2 ink form rollers, how could you use that function in real job, how benefit?

Thanks a lot!

Regards,

Delta

Hi Delta,

The Anicolor form roller (blanket) is inked with a anilox inking roller and therefore the inking is continuous and consistent from lead to tail. The form roller is not evenly inked though since there is a difference in the amount of ink on the image areas relative to the non image contacting areas of the roller. Since the form roller is rotated in register with the plate, then the image areas, in principle, only see a consistent ink film being applied to it.

On conventional presses, the ink films on the form rollers can have a variety of ink film thicknesses, depending on the total coverage and the specific location of the image on the plate relative to the rotating form rollers. Computer simulations can show this. Computer simulations can also show how the variations can be periodic and non periodic.

Goss had some interesting papers presented at TAGA in the mid 1990s but they don't do them now. They were interesting papers but they missed the important issues. Most info on roller trains that you will find are limited in value.

I am an engineer and since the mid 1980s, I have looked at causes of variation in offset presses and have developed my own science to explain some of the issues related to density/colour control in offset presses. Back in 1996, I analyzed a Goss press concept called a Positive Keyless Inker and it only took me about 1/2 an hours to find out what was wrong with it. I sent them a letter with my analysis and I did get a response. They acknowledged that there was an issue but since that press was designed for newspapers which had weaker inks, it was not such a serious issue. That answer has some validity but it was still a poor concept. Anyhow they sold about four presses with this concept and I think all four failed and had to be reconfigured with conventional inkers of some kind.

The point here is that basically press manufacturers do not understand how to design press roller trains because they don't know what the rules are and which problems have to be corrected in order to obtain a predictable machine. This is why they build the same press over and over. Some refinement but no innovation.

Shortness of a roller train is not the issue. The issue is how the ink films are managed on that roller train with respect to ink storage, evening of ink films in both the machine direction and laterally. Each press configuration needs to be analyzed on its own.

I find the whole topic of variation and predictability of offset to be very interesting but I don't see it being of interest to this industry. :-(

 

[aqazi81]

I find the whole topic of variation and predictability of offset to be very interesting but I don't see it being of interest to this industry. :-(

What about your ITB ? Is it still in experimental phase or you have retrofitted it on any press that is in production?

 

[Deleted member 16349]

What about your ITB ? Is it still in experimental phase or you have retrofitted it on any press that is in production?

"Experimental phase" is probably not the right term. The first ITB, tested on press back in 1991, proved on day one, the science that the ink water balance problem was due to inconsistent ink feed. It has demonstrated that the science is valid on three other presses. So the issue is not about experimenting but about developing the technology for commercial use. Doing that takes money and a commitment from groups that are capable of following through with a program to solve this and other problems in the process. Unfortunately, I have never found such a group. Some engineers have been interested but their management has not supported that interest.

I am not a manufacturer and had no intention of being one. I basically don't make any money from the printing industry. My patents are getting old and therefore will have little financial value in the near future. It gets more and more expensive to maintain (fees) a patent as it gets older and I see no reason to continue to do that when there is no interest from press manufacturers or other groups. So it is likely that the US and Canadian patents will be abandoned early next year.

The patents have not been a barrier to the development of the ITB since they only applied to the US and Canada. The ITB could have been developed anywhere else and I wish someone would have but again, there was no interest.

Closed loop colour control systems work but are mainly used on larger presses and by printers who can afford them. Think of all the small presses around the world, in third world countries, that could have benefit from a very low cost solution to density variation and other related problems, if the press manufacturers bothered to spend a small fraction of their R&D budget on the ITB. Not only would it have given them a reasonably priced technology to help their customers but they would have learned something new about the process that they still do not want to know now.

So I do not expect that there will be anymore tests on press. I certainly will not finance any. Lost opportunities are not always lost because they are not workable but because their is no one to support them.