There’s an old management adage: “Inspect what you expect.” In the printing industry, that means examining what your press is supposed to be producing, but the days of manual inspection with a loop are long gone for most printers.
In today’s fast-paced commercial printing, the verification of press performance relies on the advanced technology of cameras and sophisticated software to detect, verify and/or register more print detail than humanly possible.
This kind of quality assurance equipment can be critical to customer satisfaction as well as profit margins. Some printers make this investment as part of a new press purchase—after all, the OEM’s inspection equipment costs a fraction of a new multi-million dollar press. Others bring this technology into their printing operation through the addition or retrofit of inspection equipment.
In any case, inspection technology has come a long way from where it was even a few years ago. A lot of that magic comes from advancements in software—interpreting what and how the system is reading. Like laptops and smartphones, advances in the software or operating systems have continued to give these devices greater functionality. That includes both spot as well as 100 percent inspection solutions.
Spot, or area, inspection systems typically employ optical cameras to monitor a limited area of the web or sheet. This technology utilizes a camera with a high-speed strobe to capture an image of the web with each flash. The image can then be examined and enlarged to verify print detail, whether registration marks, dot patterns, security features or the like.
These systems can be programmed to automatically move the camera to random or designated positions. This may essentially result in examining 5 percent to 10 percent of the web. Operators can also manually move the camera to a desired location through the system HMI (human/machine interface).
Some systems can zoom in close enough to see the hair on a fly (it wouldn’t be the first time an insect ended up on a print job). Likewise, systems designed for 100 percent inspection also allow captured printed areas to be closely examined.
Full Web Watched
Inspecting the entire web edge—100 percent of it—may require deployment of multiple cameras. The number of cameras and system parameters are based on how much detail verification is needed.
Today’s 100 percent inspection systems employ digital cameras to capture everything being printed. A single camera may be viable for narrow webs up to 22-in. More cameras may be positioned in an array for wider and/or faster webs.
It’s important the cameras and software can handle the speed of the press in order to avoid “seeing” an elongated dot. More cameras may also be needed on narrow webs when high detail inspection is required.
Typically, in 100 percent print inspection, the operator “pulls” or identifies a master image. The system will then flag the operator at any point the web image does not compare to the master. That print issue could be random, like an intermittent ink splatter. Or, it could be a repeating error from a worn or damaged print plate or cylinder.
Dealing with Defects
We’re seeing more inspection system retrofitting now in the label industry. Here, resolving print defects might be as simple as replacing defective labels on the web.
Defects on flexible packaging runs, however, can be a bit more complicated, like when 100 feet of printed web needs to be removed. In either process, depending on the operation, the inspection and resolution might be done right on press, or on a separate doctoring or winding unit.
Ultimately, inspection systems capture run data for various quality control (QC) procedures, including possible defect removal, such as triggering a flagging system. In the mix, operators have options on both degrees of inspection, as well as alerts.
Programmable defect alerts can be audible as well as on-screen. In addition, 100 percent inspection systems can be set to different levels of inspection, or tolerances, for different areas of the web. The higher the tolerances, the more the system sees. The reverse is true for lower tolerances.
Some operators start to ignore alerts when the inspection system finds too many defects. In these instances, the system sensitivity is set too high. Settings too high will generate too many unnecessary alerts. Set the system too low and print issues can start slipping through.