How often do I have to Calibrate? Not as often as you think.
By: Cory Sawatzki
Almost every company I visit has a similar set of questions regarding calibration. “How often should we be calibrating” is the question I hear most often. The answer really is as often as you must, and probably not as often as you are currently.
In today’s industry, there are so many different manufacturing processes and capabilities. You have different print technologies from inkjet, to toner based, and back to offset. You have both large and small production devices that are made to handle everything from paper rolls, cut sheet and label stock to plastics and banner. To try and understand how stable each print condition is could be mind boggling. So while some of the older, more sturdy equipment may be more stable , they could also have more fluctuation based on maintenance or a lack of technology. On the other hand, some of the newer equipment might have a lack of stability based on cheap parts or a sensitivity to environment. Yet another variable to take into account is the substrate itself.
As you order and store more and more paper, the amount of possible flux in those materials as great as some of the equipment variables. This could be based on a white point shifting over time, coating being affected by storage, or a simple surface change based on a physical defect. The bottom line is that things change. Sometimes this happens quickly, and sometimes it happens slowly over time. When this happens, it is only slightly predictable.
In the end, the answer to “When do I calibrate” is not so simple as a timeframe.
VALIDATE, BEFORE YOU CALIBRATE
The word “calibrate” can mean different things to different people. Let’s talk about those different meanings first. Most often it is “calibration” which is bringing that device back to a base level or “stake in the ground.” This is typically determined by the manufacturer as some sort of match to a dependably known measure. Some people will use “linearization,” which is really using 4 1-D curves to simply make sure a 50% reads a 50% and a 75% reads a 75% and so on. There are many other forms of calibration ranging from reading a single number patch to running an entire iT8 to make sure you are in conformance with the GRACoL standard or P2P to check to G7. Like I said, it can be many things.
Alright, now I am going to stick a term in your head that I hope will stay. “Validate, before you Calibrate.” The idea of this is to read a standard set of patches that will tell you a story about your device. This will range all the way from indicating you are within a standard, to seeing how much variance you have had since your last validation.
If you simply read in a set of strips (possibly once a shift), this is something that is easy for the operator to do, and can give them a simple go, clean, or stop warning. On top of that, it is going to tell you a story over time about what variables you may want to pay more attention to.
In some cases, as I mentioned before, your substrate may vary greatly. When you do a validation, this will tell you if that is the issue. This will keep you from tearing apart your press and replacing expensive parts that have nothing to do with the actual issue. Sometimes it could be a machine just needed to be warmed up before running a job. This might be identified by an overall dip in density when the printer has not yet come up to temp (we all start slow some mornings.) It could identify a spike or dip in a single color that would typically be pointing at a single cylinder or drum.
Last, and probably most powerful, is the trend of data over time. If you can see how a press performs over time, you can start to be more proactive about certain types of maintenance on your presses, and in the end, find out “how often should I calibrate.”
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