Inline Versus Offline Inspection
Consumers are probably as smart as you think they are, and when it comes down to one vendor’s package versus another’s, they notice everything. They’ll notice print and graphics on the package that are out of registration, and they’ll definitely notice when the bar code isn’t printed correctly as they wait at the checkout for an item to scan properly. You’ll see it in your bottom line if the vendors to whom you print packaging aren’t completely happy with the end result, especially if what you printed doesn’t match what they approved at the tail end of press qualification. Today’s web inspection systems have increased in sophistication to address the very specialized needs of several packaging categories, from food to pharmaceutical. There are various criteria converters must consider when selecting a web inspection system, beginning with which type to specify—inline, offline, or both.
Inline vs. offline inspection systems
Inline inspection systems are used while printing on a press to show issues with registration , streaking, or voids so they can be corrected quickly and have minimal impact on the job, according to Scott Durfee, district manager for Fife Corp. These systems look for printing defects and continuous style problems. Offline inspection is suitable for a slitter/rewinder where the converter slits a printed roll down to the required size. “[Operators] will use this system to detect a hickey, spot, or some other intermittent style problem,” says Durfee. “Once it’s detected, they’ll stop the machine, flag the issue, or splice it out.”
Gal Shamri, vice president of marketing, AVT, says that on-press automatic inspection is used mainly for process control, meaning to assist operators controlling quality during printing in order to reduce material waste. As the rewinder is typically the last stage before shipment, the printer’s main target when installing an AIS (automatic inspection system) is to perform quality assurance, meaning to detect all waste defects so they can be removed before shipment to customers.
According to Jack Woolley, PC Industries, online press inspection typically provides a method to locate and mark defects without stopping the press. Press corrections are made on the fly to eliminate problems. When major or continuous defects occur, the press might be stopped to reduce material loss. Offline “rewind inspection” operations are performed on a horizontal, vertical, or tabletop machine. The system presents defects to the operator, and the machine is stopped with the defect placed for operator action. Material is spliced or the label is replaced.
Tim Lydell, Label Vision Systems, Inc., states that offline inspection is usually carried out in a QC/QA typical operation. “They are either doing inspection to test the quality of the images prior to use (prepress image) or inspect as a statistical sampling of the finished product.” He adds that what is inspected is a sample, not all of the images. Offline inspection gives time to analyze what may be wrong with an image that has been pointed out by the inline system as an unacceptable image. Inline systems are performing 100 percent inspection of the printed image, which, according to Lydell, offers assurance that all images are properly inspected.
“Inline is on press—that’s for quality control in the printing process. Offline is for security. So after it’s printed, the offline examines every label after it’s printed,” says Kevin Gourlay, sales manager, Rotoflex. “Principally, when you’re running the press, you can’t stop the press. When it [inspection system] triggers, and you see it’s off, you mark it—electronically, automatically, or by hand. So it makes the operator aware that it’s out of register, so he pays attention to it; or something’s not right, so he looks at it. So you hope you reduce the amount of waste by him being more attentive.”
“The biggest difference between inline and offline is the stage or condition of the printed product at the point of inspection,” says Jim Doerr, president and CEO, TruColor Vision Systems, Inc. He continues, “Inline inspection typically occurs during the production of the printed product at some point inline, while the product is being printed. Offline inspection typically will take place post print, after the product has been produced. This is a way to reduce or eliminate defective product from reaching the end users.”
Advantages to both
Each type of web inspection system has advantages depending on how it’s used. According to Durfee, inline inspection systems cut down on the makeready for a job. “Without inspection, the operator will have to stop the press to look for defects, wasting time and material,” he says. He adds that an inspection system will identify the issue on a press moving at speeds of 500-1500 fpm. Offline inspection systems, on the other hand, are suitable for converting rolls to an acceptable size. To make the process more efficient, a converter will run a larger master roll and rewind it offline to the size needed. When a problem is identified, the operator will flag it for the customer or splice it out right away. “Just like with inline systems,” adds Durfee, “detection by the naked eye requires a slower moving machine.”
There are two types of camera inspection being used for inspection today: area scan and line scan. Area scan camera systems inspect one area in each picture. Taking and processing a new picture takes 1-2 seconds. Line scan camera systems inspect 100 percent of the material, 100 percent of the time by inspecting across the web in one long line, at rates to 14,000 lines per second.
On the rewinder, states John Thome, general manager, BST Promark, 100 percent line scan systems are viable inspection tools. They are more reliable than humans, more consistent in their evaluation or quality, and more accurate. The payback from using line scan inspection systems on rewinders results from eliminating reruns and returns.
On press, 100 percent line scan systems have advantages over area scan systems. They inspect all the material, are very effective for random defects, most, but not, all are effective at identifying repeating defects, and most, but not all, are effective for identifying gradually developing defects. Area scan systems have two shortcomings though: they do not find random defects, and they do not inspect 100 percent of the material.
On rewinders, there are two basic inspection systems available, according to Michael Simonis, president, Unilux, Inc. “One is video, which allows micro analyses, and the other is stroboscopic, which allows macro analysis.” Brian Ivens, manager, marketing and sales, Arpeco, adds that stroboscopic visual inspection is relatively inexpensive, but requires that the web be travelling at approximately 100 fpm for each one inch of label length in order to provide a suitable number of flashes per second to freeze the image.
Combining both
The idea of combining both types of systems so that the two communicate with each other is gaining headway in the industry. Shamri states, “It is now possible to use the data detected by a 100 percent, on-press AIS, transferring it to the rewinder machine and controlling the rewinder based on that information, enabling efficient removal of defective material. This type of workflow solution is already in operation in production sites, enabling printers to enjoy a complete control over quality, ensuring reduction of production costs and a high level of customer satisfaction.”
Another approach, says Ivens, is to combine inline inspection and offline finishing in the following way. First, web inspection is performed via a 100 percent vision inspection system on the press where it assists the operator to quickly resolve problems that cause waste. The defects are logged into a digital file. The digital files are reviewed by a quality control department which determines if any noted defects are acceptable, and edits the file accordingly. The rolls of material are run through the offline finishing machine, which, by using the edited files of information, automatically stops where defects are noted for correction, and displays the corresponding defect images to the operator.
Selection criteria
As with any piece of equipment you spec out, the application is going to determine the extent to which you add options. Some industries require redundant inspection, while some converters may offer redundant inspection as a measure of quality to their customers. According to Doerr, the first criteria in selecting an inspection system should revolve less around the actual system specifications, but more toward determining what type of solution best fits the application, your operators, your company, and your overall quality objectives. “Criteria should include an evaluation of a system feature/capability set that matches the practical production situation,” he asserts.
Businesses change, as well as customer demands. Specing your web inspection system based on current end-user requirements is a must, but also plan your system around future needs. Lydell suggests asking if the system will meet the potential range of inspection criteria currently required, as well as anticipated requirements. “Checking for blemishes is a normal need for an inline inspection system,” he says. “However, various markets are requiring that printed bar codes meet international standards for print quality. The converter may not be inspecting for bar code quality or variable images today, but may be required to do it tomorrow.”
Ease of use is also important. “Operators have a lot of work to do to get a printer functioning correctly to get high-quality output,” says Lydell. “The last thing you want to do is have a complicated system for them to master and monitor. Or even worse, have two systems on the press that are checking for print quality.” He asserts that this can happen when one system is checking for blemishes and another system is checking bar codes to ISO standards, or there are other variable images needing validation. “The converter should insist on a system that can do both functions at the same time so there is less work for the operator,” he adds.
Determine your strategy
Knowing your existing system inside and out will go a long way toward defining what it is you want to do when specifying your next web inspection system.
“Defining an effective quality management policy is no longer a simple process,” says Thome. “One must be prepared to clearly define quality control and print management objectives, analyze and quantify the waste stream, and fully understand the strengths and limitations of the two technologies on the market.”
Durfee says, “Regardless of the system you choose, the supplier should offer training tools to get an operator up and running in minimal time. Look for online videos and manuals that are easy to follow and clearly illustrate how to operate the equipment.”
Shamri adds, “Packaging and label printers are looking more and more for complete quality management solutions, that will handle quality issues from the first beginning of production until finishing. High-end automatic inspection platforms [can] perform defect detection at the different production stages, however, the most important component for complete workflow support is the flow of quality information and the ability to use it efficiently for quality management purposes.” pP
Case in point—The Control Group installs Advanced Machine Vision System
Over the past few years, FDA and other regulatory agency requirements have become increasingly stringent, requiring the highest accuracy and security in pharmaceutical and medical product labeling. The Control Group, a New Jersey-based pharmaceutical manufacturer of flexographic labels and flexible packaging has met this challenge by installing Advanced Machine Vision Technology from Rotoflex International.
The Control Group has three divisions and 10 presses. Major product categories include flexible packaging films, labels, and package inserts for pharmaceutical, health care, cosmetic, and consumer packaging applications.
Advanced Machine Vision System uses a reference-based inspection method for quality control. During a “Learn” process, the system stores a known good image and then compares it with each consecutive image using tolerance for color deviation, registration, and defect size.
All interaction with the vision system is done via an intuitive Human Machine Interface (HMI). The system identifies the defects on a monitor, so the operator can quickly locate and verify the problem. The vision system provides high-level quality control by identifying various faults including color defects, oil defects, missing print, color changes, register movement between colors, register movement print to diecut, missing labels, matrix, splice, and flags. The Control Group uses the vision technology mounted directly on a Rotoflex VSI eDrive inspection rewinder.
Case in point—French printer Saint Andre Plastique employs AVT’s press control solutions
The AVT Presco module for pressure control and pRegister module for register control have been installed for more than a year in the French printing plant of Saint Andre Plastique. This printer specializes in flexible packaging for fresh produce for leading food retail chains. Its packaging products include patented technologies such as perforated materials that open automatically during microwave cooking, and packaging that prolongs the life of fresh produce. In order to keep its quality up and costs down, Saint Andre Plastique was looking for a complete on-press solution to reduce waste and improve quality and consistency, both during press set up and run time.
The Presco and pRegister are add-on modules to AVT’s PrintVision/Jupiter Automatic Inspection System, which reduces both waste and valuable press time during set up for Flexo CI presses. The modules work automatically and simultaneously for up to 10 color stations, using small color targets and a communication link to the press. First, pRegister automatically sets the color plates into registration, both along and across the web. pRegister’s range of operation can bring a very large initial mis-register error to a fine accuracy down to 15 microns quickly, while reducing set-up time and related waste. Then Presco automatically brings plate and anilox to optimal pressure for all colors in parallel.