Offset Printing without density bars

[Benk]

Good Morning PrintPlanet,

This is my dilemma, we have two muller martini presses (alprinta & progress). Our graphics no longer contain the colour bars and the camera that read them has been broken for some time.

What options are left for the printer to gauge whether or not he is printing with the correct amount of colour?

My other option is include preparing an accurate simulated proof in prepress to allow the printer to make a visual assessment under a D50 lighting booth.

I would be extremely grateful for some other ideas if you may have any.
By the way, our workflow does not allow for colour bars since we use single blade cutting whereby, if colour bars are present, they would be seen on the edge of the final product.

Look forward to you replies.

Good day everybody

Ben

 

[Cornishpastythighs]

Are you running roll to roll or roll to sheet? Roll to roll makes it very difficult for the operator to visually judge colour without some form of electronic eyes as he can only get to see the colour during a roll change, this makes for very poor control of the process. Roll to sheet allows him at least to take samples and use some form of colour/density scanner to adjust the colour during the run. Making a colour perfect proof only gets him to colour it does nothing to assist in maintaining the colour throughout the press run. I would say unless your company either purchases a very expensive in-line colour control system or some form of offline scanning device your operators are going to have to judge using the old fashioned 'eyeball' method. Investigating the ITB might be another option for you.

 

[Benk]

Thanks for the response.

Sorry but what is ITB ?

Ben

 

[Al Ferrari]

http://printplanet.com/forums/color...transfer-blade-will-obtaining-canadian-patent

 

[gordo]

What options are left for the printer to gauge whether or not he is printing with the correct amount of colour?

Ink key presetting software is very helpful in getting the presswork close to being in the right place. That coupled with ink optimization software (reseparating using heavy GCR techniques) so that SID moves (variation) have minimal effect. That's how some newspaper printers work.

best, gordo

 

[Deleted member 16349]

Ink key presetting software is very helpful in getting the presswork close to being in the right place. That coupled with ink optimization software (reseparating using heavy GCR techniques) so that SID moves (variation) have minimal effect. That's how some newspaper printers work.

best, gordo

Gordon, I would think Ben could also measure some locations in the image as reference points that might help during the run.

 

[Al Ferrari]

By the way, our workflow does not allow for colour bars since we use single blade cutting whereby, if colour bars are present, they would be seen on the edge of the final product.

What do you mean by this? Is it that pages are butted up with no gutters? And why is it that there is no room across the tail of the press sheet, between the end of the imposed pages and the tail edge of the sheet?

Al

 

[Cornishpastythighs]

Gordon, I would think Ben could also measure some locations in the image as reference points that might help during the run.

\Not much help if he's running Roll to Roll. He did not answer that question. I did see he says single knife, is that inline or does he run roll to roll and cut offline

 

[Deleted member 16349]

\Not much help if he's running Roll to Roll. He did not answer that question. I did see he says single knife, is that inline or does he run roll to roll and cut offline

Yup, you are right. His presses are web presses (Alprinta, Progress) and that would be a problem if he does not have a sheeter on the end.

My experience with web presses was with printing board and the roll length was not so great. One had to wait for the end of the roll to get measurements. That was 20 years ago. If Ben is running light weight paper there could be a long time before the end of the roll.

 

[Benk]

Hi Everyone,

Thank you for the feedback. We do run Roll 2 Roll on lightweight paper. The cutting is done on-line. There is no room for colour bars. I did also think of placing reference squares hidden in the graphics but since our graphics never stay the same, our clients may not be so happy with this solution. I am thinking that the only professional solution is to read colours in real time during printing. Only then can the operator adjust ink where required. If he only checks after the job is printed then nothing can be done, it would be too late.

Thanks again everyone.

Ben

 

[Cornishpastythighs]

Just one last note from me on this. Real time ink density/colour control or scanning gets very expensive. It costs even more if you actually want the camera/scanning system to close loop the ink density and adjust the inks keys. If you run lightweight paper and there is any tension variations the camera system becomes somewhat unstable and the readings may be unreliable. I would research an offline scanner that you can scan the a sheet after cutting. I dont think the newest technology requires colour bars (I think the Heidelberg image control system works like this) Also as part of this project you should determine the stability of your printing process (process capability)

 

[Alois Senefelder]

Synchroscope Viewer made by Crosfield (UK) Ltd.

Synchroscope Viewer made by Crosfield (UK) Ltd.

Gentlemen and Benk,

Way back in the mists of printing history (1960s) long before RGS sytems and Closed Loop

Colour sytems! - I ran a Baker Perkins C.I.C Press, printing Reel to Reel preprints on 45GSM Newsprint.

We achieved perfect register and colour control (for the time) using a Stroboscopic Viewer made by

John Crosfield UK Ltd , the Synchroscope



Regards, Alois

 

[Deleted member 16349]

Hi Everyone,

Thank you for the feedback. We do run Roll 2 Roll on lightweight paper. The cutting is done on-line. There is no room for colour bars. I did also think of placing reference squares hidden in the graphics but since our graphics never stay the same, our clients may not be so happy with this solution. I am thinking that the only professional solution is to read colours in real time during printing. Only then can the operator adjust ink where required. If he only checks after the job is printed then nothing can be done, it would be too late.

Thanks again everyone.

Ben

There are systems on the market that claim to be able to read the image and then adjust ink levels. Besides Heidelberg's in image measuring system (off press), Eltromat and Quadtech have such "in press" systems. They also seem to have had patent infringement issues between them.

There was also another system which had some units running on presses about ten years ago. I had some interesting correspondence with the inventor at that time but in trying to find current info on that system, it seems there is none available. I am guessing that it did not become commercially successful. I might be wrong.

The general problem of trying to determine the inking levels with only the image information is not a trivial problem. There is no direct or convenient mathematical relationship with the printed image and the individual CMYK ink settings.

I can see that with some clever algorithms that could use an iterative method to determine what inks to move and in which direction to move them, control of inking from image information could be done but I would expect that it would be slower than a closed loop control from solid patches.

Good luck with your efforts.