Press Parameters: Heidelberg MOV 19 in. x 25 in. press No of ink zones: 20 at 31.75 mm spacing
For setting up I use press sheet size : 18 in. x 25 in.
I split the sheet in 20 parts horizontally at 31.75 mm spacing and make bar's of different heights (indicating different ink coverage ratio's eg 10% on left to 100% on right)
Then I feed this data to PessPerCent software, the software gives different ink zone numbers for CMYK and a sweep setting value.
a) I print this target using these values on press
b) If I achieve a target density eg 1.8 for black then I let the settings as it is for future jobs
c) If I don't get the target density eg 1.8 for black then I tweek either the ink zone values or sweep values or both to get my target density on press and then apply a curve on PressPerCent so that I get desired values on press (based on my observation on the press while trying to get the desired density value)
Now theoretically this is the co-relation I was saying in the previous message ie. if a co-relation of ink coverage to inkzone release values and sweep settings are correct then these settings should be valid for all situations. I am not worried about TVI at this point of time because TVI will be set via the rip at a later point of time. Right now the aim is to get target densities correct for specific ink coverages.
Does this make any sense to you !!!!!
Thanks
Tarun,
I will start with your last statements first. Your view of what is theoretically correct is wrong. It will not be valid for all situations. That was my point before. Don't expect it to be valid because if you do, you will just get frustrated. Yes, TVI has nothing to do with ink key presetting so don't worry about it.
Before you do anything, you should try to see if the ink keys are even across the width of the press. This is related to the zero setting concept but since it is impossible to accurately set the zero set point on presses with ductor rollers, I will suggest a step that might help.
Make a plate that has a 20% bar across the with of the plate. Set your ink keys to 20%. Do this for all CMYK units but be sure to not overprint any bars. The goal here is to see how even the ink keys are across the press. If printing the bar is even across the press then at least you know at the 20% point the keys are OK. If a zone is too dense or not dense enough, hopefully there is the ability to adjust the ink key so that the 20% will result in even density on the bar. If you had a press that could be zero set properly, this step would not be needed.
Now do the step you outlined. I think it would be 5%, 10%, 15% .....90%, 95%, 100% for 20 keys or
10% for keys 1 and 2, then 20% for keys 3 and 4, .......100% for keys 19 and 20.
Just be sure that you have the zones lined up with the imaged that has these steps. Don't assume that the edge of your paper starts exactly at the edge of the first key.
I am not sure why you are aiming at a black density of 1.8. My view is that this calibation is done for each CMYK colour with that type of plate and run one at a time. No over printing. I would also aim the density at the normal densities for the CMYK inks.
If your plan is to calibrate using only black and then apply that information to other units, that might be simpler to do but be aware that the sweeps will be different for the different inks and for different papers.
The purpose of the 10% to 100% test plate image is to check for linearity of ink key output. There are a lot of issues that you are not aware of that will affect this test so don't be too picky about it.
From past experience with a web press with a continuous ductor, the biggest impact on improving performance of presetting, with a not so perfect presetting situation, was to have the zero setting done properly. The zero setting point is the datum for the ink key values. If one does not have a predictable datum, the presetting values are not going to be predictable. The 20% bar test is a practical way to try to account for the lack of zero setting capability.
Don't expect low coverage accuracy at all. The equipment is just not capable. Don't let that frustrate you.
Good luck and I hope this helped.
