07.20.05
We live in an imperfect world. Defects are always with us. Still, that does not stop the label customer from insisting on perfection. That’s the reason inspection equipment is with us, and the reason that it has become a necessity, in all of its complex incarnations, for the printer and converter.
Inspection equipment has been in use for years, relying heavily on the human eye aided by a strobe light or a camera. Optical and digital revolutions and evolutions have given engineers lots of technology to play with, and they have put it to good use in crafting devices that now can look at an entire web moving at full speed and spot a bad dot.
In the narrow web industry, experts say, the need for extreme defect detection is not widespread, at least not today. But the market for the advanced equipment is growing steadily, and suppliers are keeping pace with ideas.
Missing a defect — whether it’s a shift in color, a movement in registration, an ink blotch, a bruise on the printing plate that shows up on the label — can have its costs. Most dramatic is rejection by the customer; more usual, and still costly, is waste. Not catching a printing error quickly can result in hundreds of feet of expensive material rendered useless, the cost of which is eaten by the printer.
“There have been some dramatic developments,” says Lance Shumaker, president of Advanced Vision Technology Inc. (AVT), in Atlanta. “A lot of changes have taken place in the inspection field that are here today. Converters are very knowledgeable about the benefits that today’s systems offer, and the new presses being purchased today almost always are equipped with full inspection systems. There is a definite need for higher quality, and inspection is really the only way to monitor the process.”
“We are in the midst of a fairly large transition, from the inspection perspective,” says John Thome, vice president of marketing for BST Pro Mark, Elmhurst, IL. “Certainly more presses now have visual systems than those that don’t, in North America. Those that have them are producing a higher quality product more efficiently. Those without are at a competitive disadvantage.”
Still, Thome says, some printers continue to run their equipment slowly and eyeball the job. “In this day and age that’s suicide. It just doesn’t work any more.”
On the other side of that coin are the companies that have equipped their presses — not just the post-press inspection tables or inspection rewinders — with sophisticated machinery that watches part or all of the web as it whips through the press. Some press operators, reports one equipment supplier, are having a bit of fun lately with the advanced defect detection equipment: They set the tolerances of the system extremely low, so that the slightest defect will set off the alarm, and then they print — faster, faster. They want to test their mastery and deliver printed perfection that even an electronic eye cannot fault.
“Most converters want a system that is capable of the complete, ultimate solution of present and wish-list needs,” says Dave Kunz, sales manager for PC Industries, Gurnee, IL. “The budget and realistic goals determine the solution. Any system worth considering must be expandable for future needs. These systems should also carry a written money back guarantee that covers the performance and specifications. Additional applications arise after the system is installed, and a vendor who will assist in customizing the system to these new applications will help the converter realize the maximum benefits.”
Kunz says that the best way to think of inspection systems is in three groups:
• Web viewers: non-critical inspection of labels being produced on a press. The operator observes a monitor and determines the action required.
• Sampling defect detection: Inspection of labels wherein the main objective is to automatically catch recurring defects or problems. Action taken is determined by the output of the system (e.g., stop the press or sound an alarm to alert the operator). These systems are also called 100 percent repeat inspection systems.
• 100 percent inspection systems: Inspection of critical path labels (e.g., pharmaceutical) that will not tolerate occasional defects. Typically the final inspection is just prior to shipment.
The basics
“Ten years ago people got a handheld strobe that covered a small section of the web,” says Mike Simonis, president of Unilux, Saddle Brook, NJ. “They’d take a look at the web, put it down, come back a bit later to check again. Now we have strobes that can cover areas up to two meters wide.”
Strobe lamps still come in handheld styles as well as mounted versions. They vary in size by web width, and by application, depending on how close to the surface the lamp can be mounted. Some rewinders, Simonis says, are constructed such that the strobe can’t be placed too close to the print surface.
Using a strobe for inspection allows an operator to find variations in registration or color, repeated skipping, voiding or plate plugging in the print, and blotching. This type of inspection still relies heavily on the human eye, a marvelous tool but not a machine.
Strobe use is more common on rewinding machines, Simonis says, adding that more printers in the US are putting them on presses lately, as opposed to European converters, who still prefer off-press.
“If anything, the strobe light has enhanced people’s knowledge of what they need to accomplish. It is used in conjunction with a camera, and it gives a quick reference point. It’s also a reliable back-up when the automatic systems go down.” Simonis adds that the arrival of large, expensive and highly capable automatic inspection systems “has not, in any way, shape or form, taken away from our business. On the contrary, we have grown. A lot more people can afford a strobe light than one of those systems.”
On the press
Camera inspection systems mounted on the press come in a variety of capabilities. BST Pro Mark’s Super Handyscan offers a split screen function (horizontal or vertical) as well as picture-in-picture to compare parts of the web. Thome says the new model has a quick zoom and positional memory, which allows the user to program a register mark and zoom to that spot with the push of one button.
The company is also re-introducing its Genius digital process management system as Premius.
| AVT’s Helios |
The high-end TG4000 from TruColor “is an active inspection system, for UPC bar code print quality, or monitoring color to ³E specifications,” Doerr says. “We can alarm our system so that when it detects a drift beyond the ³E tolerance on a color bar, the system will let the operator know.”
Thome offers some advice for press operators who have been asking for flat screens (TFT: Thin Film Transistor) with their inspection systems: “You do not want to do that — yet. It’s possible, but the picture quality today is not acceptable. The images are staircased, and the viewing angle presents problems. When you get 45 degrees to the side the image starts to blur, like there’s a fog over it. When it comes to graphic applications they are just not accessible, but they are coming in the future.”
Off the press
Off-line inspection systems are widespread throughout the industry. They range from the table models manufactured by Web Techniques and Lederle, among others, to large inspection slitter rewinders such as those made by Rotoflex.
“We supply the gamut, from the very basic to the very complex,” says Val Rimas, vice president of marketing and sales for Rotoflex, of Mississauga, ON. The company manufactures high speed stand-alone machinery that can undertake basic web viewing inspection or 100 percent, depending on the converter’s need.
“There are area scan cameras and line scan cameras — and both have their strengths and weaknesses. Some users say that area scan cameras detect text flaws better than the line scan cameras. We have systems that can match color and inspect for color integrity within specified tolerances. At this point there is not a lot of that in narrow web, unless you are dealing with companies such as Coca-Cola or Procter & Gamble, where color is part of their image.”
Area scan cameras, also called sampling or matrix cameras, look for repetitive defects, according to Shumaker of AVT. “It’s not looking for the one-up defect; instead it’s finding process defects. Our Jupiter system uses a sampling camera, which views a 7" x 9" area and breaks the web into a matrix. It goes around the whole repeat, monitoring and comparing against a master image.
“If you have a color problem,” he adds, “it’s usually global, across the whole repeat. If it’s a registration problem it’s probably global, and the camera picks it up right away. If a line or a streak appears, the camera will pick it up in about four seconds as it moves across the web.”
| AVT’s Helios |
According to Rimas, Rotoflex and AVT are working today on a defect detection system that will flag an error on press, and when the finished roll is moved offline to the inspection rewinder the system will stop at exactly the point on the web where the flaw was detected during printing.
Print Vision Systems, based in Lewiston, NY, also manufactures a range of inspection systems, including 100 percent inspection machines. According to President Ignatius Manning, the term is used loosely in the industry today.
“100 percent inspection means just that. Proponents of sampling based technology might try to equate it with 100 percent inspection technology, but this is not so. 100 percent inspection technology is the only method that can identify both random and repetitive errors.
“The performance of 100 percent inspection technology, in terms of web speeds achieved and/or defect sizes identified, is dependent on several factors. Users can define variable operational parameters to create the sought after results, as long as they are within a particular system’s operating range. Thus, 100 percent inspection does not equate with a particular defect size that the machine will identify.
“However, a properly selected system will always allow a user to set system operation variables to detect a defect of pre-defined size each and every time, systematically, and without fail.”
Manning recently published a white paper on the subject titled “The ABCs of 100 Percent Print Quality Inspection”, which is available at www.printvisionsystems.com.
Converters with doubts about their inspection needs might benefit from John Thome’s basic advice: “Study your waste stream. Does 90 percent of your waste come from color errors? From registration errors? Take the time, spend a couple of months, analyze the waste.”
