Components of a Closed-Loop Color Control System and How They Work Their Magic
Adding a Closed-Loop Color Control System is often the best and most effective way to breath new life into an older offset press. The result is automation which decreases job make-ready times for instant time and material savings but it’s also the “great equalizer” too, which increases the color consistency across individual press runs, over time, and even across multiple presses or different shifts of press operators. However, to better understand how the closed-loop system works its’ magic, let’s start with understanding the various system components and the part each one plays in the workflow.
A full closed-loop system and workflow consists of the following sub components: file conversion, ink pre-setting, scanning, automated closed-loop, and optimization. Now here comes the deeper dive into each piece.
The first step in a closed-loop workflow actually begins in the pre-press department during the plate making process. Here, in addition to outputting a high resolution file used for plate making, an additional, low resolution file is also created for use in the closed-loop system. This file can be output as a CIP3/CIP4 file or as multiple 1-Bit TIFF files. These low resolution files are then moved into the file conversion “hot folder” which is located on server that is also accessible to computers in the pressroom.
The file conversion process is a fairly simple task that runs in the background and converts the low resolution ripped files into a format that the main software application can use. The conversion happens when the low resolution image file is saved into its’ queue or hot folder and it then merges the image data with press specific data like number of ink keys, maximum sheet size, etc. The resulting, converted, file is then saved into a different network location that is accessible to press-side PC’s. The nice thing about the file conversion software is that one license can perform this task for an entire company. For example, if you have a central pre-press location, you can create ink-presetting ready files for all of your press side PC’s (assuming they all have access to the network location).
Now, we are ready to move into Ink-Presetting. So far, the process has involved computers and networking that you already have and some new software to perform the file conversion. Now, for the ink pre-setting process, we need special hardware called a “DPI” (Direct Press Interface) which works for most presses. The DPI is a small silver box that connects either directly to the press console computer or circuit boards to a press-side PC (running either Windows 7 or Windows 10). This box has electronics and special firmware inside that allows our PressLink software to talk directly to the console in a manner very similar to how the original manufacturer talks to it. (NOTE – Heidelberg presses require a slightly different approach where the converted file or job data is loaded via a card or disk drive simulator instead of the DPI). One more note to consider, we recommend that you get a good VESA mount, adjustable, monitor stand to mount the supplied touch screen display. This allows the monitor to always be in an assessable position for use and viewing.
PressLink software allows the user to browse a list of jobs that have been converted and are ready to run on press. Upon selecting one, the user will assign and specify things such as colors in each press unit, if the job is perfecting or not, etc. Next, the user simply selects the substrate that they will be using and the PC analyzes the input data, combines it with the pre-configured settings for density or Lab targets, and computes the appropriate ink key and sweep positions (sweeps on most presses). This ink key information is then automatically sent to the console. Typically, an operator will then just need to confirm these ink key changes at the console before the actual changes are made. Just another note, for all press types, the software only sets the ink sweeps during the initial ink-presetting. Therefore, if further changes to the ink sweeps are required, the operator would make these changes manually.
At this point, we now have ink on paper, the registration is close, and it is time to start scanning sheets to determine what specific ink key adjustments are needed. This brings us to the next piece of hardware that is required, the Techkon SpectroDrive. Typically, we mount this on the console directly above the ink key display which allows the press operator a seamless view of what is happening on press. As an alternative, we can also mount the SpectroDrive on separate tables if that is preferred by the customer. In some cases, the console top is not designed or sized to accommodate the scanner. Therefore, in such cases, we typically mount a sheet of melamine over the console top to expand the length of the top to better accommodate the scanner. In reality, any smooth uniform white or black, cleanable, surface will do just fine. To start the scanning process, the press operator pulls a sheet and lays it down on the console or table. Next, the operator starts the scan by just pressing the big green button on top of the SpectroDrive or by touching the scan icon on the screen. The SpectroDrive measurement head then immediately scans accross the sheet measuring the color bar and returns to its’ home position after the scan.
When the scan is done, the results are displayed on screen so the operator can then review the suggested ink key changes. Then, with the press of button, the operator simply sends the corrections to the console/press (or they make additional manual adjustments if they like). At this point, the ink keys will either open or close as needed based on the scan, results, and calculated corrections. Another noteworthy point, similar to the ink-presetting point made earlier, is that the closed-loop portion of this system ONLY ever adjusts the ink keys. Therefore, if the blankets are worn, or if impression cylinders are old or not aligned, or if the water balance is not correct, there is nothing that the closed-loop system can do about those issues. Often times on an installation, we will see in a matter of hours just how well or poorly a press has been maintained and this ends up having a huge impact on the effectiveness of the ink presetting and closed-loop automation process.
Finally, the press is being controlled by a closed-loop system! Now, the final step is system optimization. This is the last step in the set-up process where our trained staff reviews the ink preset data, closed-loop scans, & the final ink key positions and they make adjustments to the system to improve or optimize its’ performance. This optimization process can usually take place after only a few jobs have been run through the system and the results typically change from 70% efficiency (on the first run) to about 90% efficiency on all future press runs. Then going forward, we recommend that periodically you contact us to re-optimize your closed-loop system to accommodate for drifting changes in the press, paper, ink, plate curves, etc.
So there you have it! This should give you a better idea regarding the installation and implementation details of the various system components of our Techkon PressLink Closed Loop product. I hope the benefits of a closed-loop color control solution are clear for you. If not, please contact us directly and we would be happy to explain or stay tuned for a future blog post where we tackle the solution benefits and show you how the system can pay for itself in only a matter of a few months!