Erik,
I've been reading up on inking systems in an effort to better understand why one concept may be better than another. I have a pretty good idea of how your ITB works and also how the Goss DigiRail works. What I have gathered so far is that the traditional fountain roller and ductor roller concept leaves a lot to be desired because you can't predict how much ink is actually transferred from the fountain roller to the roller train via the ductor due to water, temperature, speed variations. Your ITB attempts to improve the situation by replacing the ductor roller with a blade and transfer roller that is capable of metering predictable amounts of ink to the roller train. The DigiRail takes another approach and digitally meters ink onto the fountain rollers, eliminating the need for ink keys and a traditional open fountain. However the same old ductor is still there doing it's thing. So between these two ideas one does away with the fountain and ink keys and one does away with the ductor. Is that a fairly accurate overview?
Could both concepts be taken a step further to produce an inking system that does away with all of the above? No fountain, no ink keys and no ductor. It would be a DigiRail like system that meters ink directly to the roller train. It seems that that would not be to difficult and could be the best of both worlds. Am I missing something? If this is feasible why has no one implemented such a system? Or have they?
This is really good. You are thinking in the right direction and basically what you have said is correct.
The Goss DigiRail has zones that do the same function as the ink keys. The purpose is to supply the ink requirements for the design that is in line with the zone. The Goss system does not have a ductor in the traditional sense but it has a continuous ductor which is a metering roller that has about a 0.004" to 0.006" gap between it and the ink fountain roller. The continuous ductor is running at press speed and shears the ink from the ink fountain roller. It is a different concept from the traditional ductor but it still suffers from inconsistent ink transfer. It might even be more inconsistent but it is used on high speed presses where having a traditional intermittent ductor, would be a problem due to the high speeds.
The DigiRail is claimed to be highly precise and I have no reason to doubt that. The problem of density control actually does not require high precision but if one has it then why not get the benefit out of it.
There have been attempts to apply ink directly into the roller train in the newspaper industry for a very long time. Before digital inkers there were mechanical positive feed inkers. There were problems with accuracy, zone size and trying to apply ink to high speed rollers. It can be very messy.
There are several positive or semi positive inkers in the newspaper industy and the trend has been to apply the ink to a slow ink cylinder like the ink fountain roller and have a continuous ductor take away that ink by shearing.
In Goss's example, we have a very accurate inker supplying ink to the ink fountain roller. The continuous ductor takes ink away inconsistently due to the affects of changes in water, temperature and press speed. Because the inker, on average is supplying ink consistently, the print on average will tend to print consistent density. The problem is that there can be larger than necessary variations in printed density from that average density and these systems also have very slow response to changes in ink feed.
Because the ink transfer is inconsistent you will have a situation where the storage of the ink in the roller train can decrease while the ink storage on the ink fountain roller increases due to the transfer rate at the ductor changing. This change is only momentary because the ink storage on the ink fountain roller will build up and eventually restore the ink transfer into the roller train. I hope you get the idea. In this case the swings in print density are due to shifts in ink storage between the roller train and the ink fountain roller due to changes in ink transfer at the ductor.
Now think of the DigiRail concept, the way it is but now having my ITB and pickup roller in place of the continuous ductor. The ITB blade itself would be a very simple scraper blade and all the ink being fed by the DigiRail would go directly into the roller train. One would get the full benefit of the accuracy of the DigiRail inker with the immediate and consistent ink transfer of the ITB. The result would be that the new combination would have very fast response, since no storage in ink would be on the ink fountain roller and changes in water, temperature and press speed would not affect the ink transfer and therefore the ink storage on the roller train, Density variations would be very small. With such a system, and with the correct algorithm for presetting the ink keys (pumps), the print would be good in about 50 impressions.
The ITB is just one way to correct the DigiRail inker but there are other ways but Goss has little interest in correcting this problem. Back in 1996 I tried to tell them this could be corrected and still they continue to not be interested.
Positive ink feed devices have been applied to presses for probably over thirty years and even now, suppliers such as Goss, do not connect the idea of having a positive ink feed with the idea of decoupling the ink/water relationship. I am the only one who is claiming this is possible. That is a sad situation for an industry that there is no interest to solve these kinds of fundamental problems.
The solution to the problem of density variation has been right in front of their faces for decades but because they don't have a theoretical understanding of the problems, they can not see where they make mistakes and how that affects performance.
You are right that the next step could be made. Certainly a positive ink feed, such as the DigiRail concept, applied in the right way would perform better than my ITB with an open ink fountain. Ideally if one was only running CMYK inks and had a positive ink feed pumping system, one would have extremely consistent density control.
At this time, the practical problem with the DigiRail inker is that it can not be used with high viscosity inks. All of the positive ink feed systems on the market that I know of can not be used with high viscosity inks. But the ITB can.
Cleaning these pump systems is a problem and going from one coloured ink to another is time consuming and requires harsh solvents. Cleaning a fountain and the ITB is easy.
I see the ITB as a transition technology to the future. It shows how the potential of the process can work. It demonstrates new science. It is cheap and simple and can be applied to existing presses. The ITB does not only transfer ink but because it meters a consistent returning ink film back to the ink fountain reservoir, it changes the existing ink fountain into a positive displacement pump. The difference between the amount of ink metered by the ink key and the amount of returned ink metered by the ITB, is equal to the ink that will be transferred into the roller train. The return ink film is the zero set ink film for the ink key. This gives the system a more accurate datum for an accurate ink key presetting algorithm and makes the system calibrate-able mathematically for different inks and paper combinations. One potentially can make the process mathematically predictable.
Press manufacturers have no clue and are losing the battle. They are ignorant and therefore they take no action. They don't want to understand and don't want to believe that some problems are simpler than they thought. As long as they take no action, they are experts.
