Product Reviews

Web Inspection

May 7, 2009

The perfect printed image must pass ever more stringent quality standards, and the industry is meeting the challenge.

Web Inspection

The perfect printed image must pass ever more stringent quality standards, and the industry is meeting the challenge.

By Jack Kenny

The Shark inspection system from BST Pro Mark
Many a converter employs a strobe lamp to keep track of defects in the printed web. These can be handheld models or mounted on the press to give a stop-action view of the image on the moving substrate. High speed rewinders also can be outfitted with strobe lamps. This method of web inspection has proven to be reliable over the years, or else it would no longer be used. It is, however, the simplest form of inspection available today, and for some label buyers it just doesn’t provide the level of inspection desired in a world of increasingly complex and critical graphics.

The stroboscopic light relies on the human eye, a sensitive yet limited organ. (Fact: A solid majority of rewind personnel in the label business are female. Better vision?) The adaptation of the camera into web inspection has raised the ability to inspect to a much higher level. This second tier involves the use of electronic sensors, area scan cameras and a programmable logic controller. This type of system also makes use of the human eye, but presents a view of the web that is magnified on a screen, rendering the operator’s visual capability more effective.

The third plane of inspection devices provides 100 percent inspection of the web. The process involves line scan camera technology that can be adjusted to detect defects on the printed web to a high degree of sensitivity.

“Area scan vision systems are automated, computer based inspection systems that use a digital matrix camera,” explains Todd Guzzardo, North American sales and marketing manager for Erhardt + Leimer (E+L), Duncan, SC, USA. “The camera is configured to see an area defined by the full web width and a maximum web length. The camera is triggered to take an image by a sensor and the image is compared by the computer to the reference image to identify non-compliant areas. Often retrofitted to finishing machines, they work for some applications but generally they lack the resolution necessary for more demanding inspection on webs wider than 10". They also suffer from speed limitations caused by the camera. Their major advantage is they can allow for objective application of inspection criteria without direct operation intervention.

“Most new label inspection systems are line scan camera based and are significantly automated,” he notes. “They are computer based and offer speed, inspection robustness and control that were previously unavailable. The systems use one or more line scan cameras each of which has a single row of pixels. By moving the web under the camera and triggering the camera at regular intervals with a web driven encoder, an image is ‘read’ by the computer. The image that is read is then compared to a reference, and non-compliant defects are identified. This allows the entire web to be inspected, thereby providing 100 percent print inspection.”

Guzzardo says that another type of system is sensor based. “Using a row of optical sensors similar to a flatbed scanner, sensor based vision systems provide an automated, low-resolution method to inspect a moving web. The sensors are interfaced to a computer and a trigger sensor causes the image from the sensors to be read by the computer. The image is then compared to the master image established for the job. As the images are processed by a computer, operator dependence for a decision on compliance is significantly reduced. However, because the system’s resolution is low, sensor based vision is not used in more demanding inspection applications.”

A recently completed project by AB Graphic International provided an inline 100 percent inspection solution to Innovative Labeling Solutions, Hamilton, OH, USA. The system is composed of a press mounted, PC-based vision system (FlyVision) operating in conjunction with a Vectra turret rewinder, automated take off conveyor and core loader.
AB Graphic International (ABG), a Britain based company that has its US headquarters in Ontario, CA, supplies inspection devices in all three of the functional tiers. “We manufacture solutions to meet all budgets and levels of sophistication required by any label converter,” says Al Spendlow, chief operating officer. “Some are customized solutions, but most are readily available out of the box. Solutions range from high speed electronic strobes, flag and splice detectors, and missing label detector arrays integrated with horizontal (Omega SR range) or vertical rewinders (Omega VSR range) to area scan or line scan vision systems capable of detecting minute defects.

“The vision systems, called FleyeVision, are manufactured by ABG under the brand name Flytec and are available in 2K, 4K & 6K grayscale or full color with touch screen operator interfaces. Options for the vision systems include optical character recognition used to check sequential numbers or characters, bar code recognition and grading to industry standards, printable reports, Braille reading, comparisons through golden image or PDF files. Jobs can be saved and recalled. When the FleyeVision systems are integrated with inspection rewinders, a defective label is catalogued and presented in an area for operator scrutiny and editing or removal. More sophisticated rewinders equipped with the FleyeVision can reverse direction back through the inspection area which is then rechecked after editing to guarantee true 100 percent inspection without human error becoming a factor.”

Morphing technology

BST Pro Mark, Elmhurst, IL, USA, also offers systems across the range. According to VP of Marketing John Thome, the company manufactures nine basic models in various configurations that can inspect on press or on the rewinder. These include HandyScan, Powerscope, Premius, and Shark systems.

The basic visual system, Thome says, has morphed into something far more capable than a simple camera magnifying part of a web on a screen. “They have become print process management systems (PPM), using area scan technology, and beyond visual inspection they offer defect detection and color monitoring. The systems have a virtual repeat. If a customer says he wants to see the whole web on the monitor, we can show him the whole web using our Super HandyScan. The interface is different now, and features a touch screen that sends you to different views of the web. It’s easier to use, and much more intuitive. For 20 years customers have been asking for this.”

BST’s 100 percent inspection systems, featuring line scan technology, can operate on web widths to 80" and press speeds to 2,600 fpm. They can be integrated with PPM systems, says Thome. The Lector workflow software generates reports and integrates the press with the rewinder. “Lector is the reporting software for our high end systems,” he says. “Now we can save a reporting document from the press and send that information to the rewinder, which will stop at the predetermined defect.”

Thome points out the strengths and weaknesses of 100 percent inspection systems. Besides the obvious strength of full inspection of the material produced, he says it is effective for finding random defects, bugs, hairs, web creases, and splash; it’s effective for repeated defects, such as register, streaks, fill-in, missing print, and hickeys; and it is “very effective for identification and sorting of good from bad material.”

He lists the weaknesses as “press speed sensitive; ineffective for color or color related defects; ineffective at identifying small, gradually developing defects; some inability to verify bar codes to ISO/ANSI standards; ineffective as a process management tool; no viewing capability or image magnification; and not usable during job startup or make-ready.”

An offline inspection system from PC Industries
PC Industries, of Gurney, IL, USA, is another company with a full range of systems. “The RX Series web viewers provide cameras from 1.2 to 5 megapixels, and features from simple viewing to sample defect detection,” says Jack Woolley, general manager. “The Guardian family offers both area scan and line scan cameras, depending on the application. Solutions include color or grayscale cameras configured in single camera or multi camera arrays. The Guardian PQV systems provide inspection of print quality, measurement and gauging, bar code grading, variable information, and color variation. Our Guardian OLP systems provide offline proofing utilizing a range of scanners, including duplex, small and medium flatbed scanners, card scanners, and wide format 42" feed-through scanners.”

Linking the workflow

Advanced Vision Technology – AVT – an Israeli company with US headquarters in Atlanta, GA, focuses on the high end of web inspection. For the narrow web converter the product is called Helios. “The Helios system uses line scan cameras with a choice of resolutions,” says Lance Shumaker, president of AVT’s North American operation. “The higher the resolution, the more the detail. But also, the higher the resolution, the slower the speed.”

Line scan cameras can be used on rewinders, says Shumaker, but this is specifically for quality control purposes. “On a rewinder you are really just looking at a product, and if there’s a problem that becomes waste. A line scan inspection system on press can do process control, it can look at what you are printing, and if you find a skip-out or a defect or missing text – particularly in pharmaceutical labels – you can find and correct it right away and not waste a whole roll.

“We have a new product called Workflow Link, which allows you to track every defect on press,” says Shumaker. “The camera gathers the information and puts it into the Workflow Link, then the team reviews the whole roll for defects electronically, and then can make decisions about whether they want to take action or ignore it. The information is sent to the rewinder, which is being controlled by this data. When it gets to the defect it stops. The operator replaces it or splices it out, then the rewinder continues until it comes to another defect.”

Shumaker says the system has been out about a year and a half, “but it’s really just now beginning to be used. We have multiple companies using it with dramatic productivity increases. It can increase production 30 percent,” he says.

Another recent AVT product – Jobref – allows the printer to compare a customer-supplied PDF to what is being printed on the press. “There are different variations between jobs,” says Shumaker. “For example, pharmaceutical labels can have different verbiage, close but different. Jobref allows you to take the PDF and make sure that what is on the printed job matches what the customer wants. And it’s all done electronically.”

Erhardt + Leimer offers the ELSCAN product line, which uses digital matrix cameras. “ELSCAN OMS 4 is our newest offering and uses a patent pending digital camera configuration to capture images from the web,” says Guzzardo. “The camera configuration consists of two 5-megapixel cameras arranged in a concentric field of view, which allows for a full view of the print repeat. Using a digital zoom controlled by the scroll wheel of the mouse, the operator can immediately zoom in to any level required up to the maximum zoom available without delay. Coupled with a state of the art motorized traverse, the camera can be placed anywhere across the web at speeds up to 1,500 mm/second to ensure optimal repeat viewing.”

The company also markets the NYSCAN 100 percent inspection system. “The foundation module of NYSCAN is Web:Inspector:2, a 100 percent print inspection system that uses line scan cameras,” says Guzzardo. “One of Web:Inspector’s key features is our patent pending lighting system – TubeLight. Using a high intensity lamp and a tube shaped diffusion chamber, the web is evenly lit by fully diffused lighting. The diffused nature of the light allows Web:Inspector to be able to inspect foil decorated labels, labels printed on reflective substrates, embossed labels, metallic inks, thick ink films, etc., without the need for add-ons or optional extras.”

An inspection system from Lake Image Systems
Lake Image Systems, Henrietta, NY, USA, produces line-scan inspection systems that “take images of every label produced and inspects the data integrity and/or print quality to ensure the content meets minimum requirements,” says Pat Hoskins, president. “Our solution, IntegraVision PrintScan, can perform multiple inspections simultaneously and take an action (stop, trigger a tabber, trigger a printer, etc.) when a user-definable number of defects is identified. The system records all data, records the status of every piece and can also record (store) an image of every label or every defect (most common). The system outputs ‘integrity reports’ which provide an audit trail of every piece produced and all defects. This report is what can be passed on to the next segment of the product life cycle as the tracking report for applications such as ePedigree.”

The IntegraVision systems verify print quality by inspecting color matching, streak/void detection, proper location and formation of generic and variable data/graphics, completeness of graphics, and proper alignment of components which are printed by multiple processes. They perform data integrity verification, says Hoskins, including ANSI bar code grading, legibility inspection of human readable characters and bar codes (for instance, scratch off labels/tickets where the printer needs to ensure proper legibility so they can be read in the ‘field’), missing/duplicate piece detection (either by checking sequence on multiple lanes of labels or by comparing production in real time to a database), data logging and tracking (ePedigree), and scratch-off verification.”

Down the road, Hoskins sees the continued merging of print quality inspection and data integrity verification at faster production speeds. “Camera resolution, camera speeds and processing speeds have improved exponentially, and will continue to enable us to provide broader inspection capabilities at higher speeds.”

Offline or inline?

The function of inspection equipment on the rewinder is to spot a defect so that it can be removed, and/or replaced with a defect-free version of the label. This action is not corrective; in other words, the mistakes are already on the roll and must be removed. If the defect occurs among a substantial length of the web, the roll could end up in the scrap heap.

“Traditionally, inspection would occur offline in the finishing stage as this process would take longer to complete than to initially print with starts and stops, etc.,” says Al Spendlow of AB Graphic. “The obvious advantage here is that the press can operate at a maximum uninterrupted speed. One disadvantage to offline inspection is that defects can be printed throughout the press run and discovered too late. Combinations of inline and offline inspection are common today, making for a best of both worlds scenario. Emphasizing this combination, a recently completed project by ABG provided an inline 100 percent inspection solution to Innovative Labeling Solutions, based in Hamilton, OH. It is composed of a press-mounted PC based vision system (FlyVision) operating in conjunction with a Vectra turret rewinder, automated take off conveyor and core loader. The vision system would detect an error or defect and alert the operator to corrective action. Defect positions, type and quantity details were logged within the database and labeled automatically by the turret rewinder on the applied roll closure label. The take-off conveyor would then segregate the 100 percent good rolls from those with defects, and defective rolls could be sent for rework. This system enables a high-speed single pass process from roll to box, finished and inspected with zero wastage from unnecessary overrun or re-runs from order shortfalls.”

“Inline inspection provides the first level of inspection to allow for remedy with the least a mount of waste,” says Woolley of PC Industries. “The printer is alerted when the print changes, which will provide the opportunity to correct the error. Current systems can provide roll maps detailing the type and location of defects. The roll map can then be edited to ignore minor blemishes that are acceptable. It can be transferred to an offline machine and will present the defect to the operator. Inline applications typically are supplied with color cameras to provide the operator a true representation of what is being printed.”

Shumaker of AVT is a promoter of on-press inspection. “The only advantage of inspecting on a rewinder is quality assurance,” he says. “On-press is a cost benefit, because you can stop printing defects. You also have speed increases, because once operators have inspection on press they turn up the speeds. They are able to run faster because they are more confident they have something that will find the defects for them. With an inspection system on the press you have waste savings, increased production speeds, and all-around increased productivity.”

On-press inspection among new and retrofitted presses today, Shumaker says, is about 65 percent of all machines. “Two years ago it was reversed. This is a big change.”

“The biggest difference between inline inspection and off-line inspection is the impact on the profit margin of a job,” says Guzzardo of E+L. “With inline inspection, the profit margin can be maximized because the press operator knows immediately what is happening. This lets him respond to print problems as they happen, thereby reducing their duration and maybe their severity while at the same time knowing how much good product has been produced to meet the requirements of the job. Both of these positively impact a job’s margin by preventing costly reruns and through the minimization of waste.

“The second big difference between on-press and offline inspection is productivity improvement through visibility of the process to the operator. Typically, a press operator is fully occupied during a press run to the point where observation of print quality is jeopardized. An on-press inspection system notifies the operator when there is a quality issue, so he can respond quickly even if he is busy doing something else when the notification comes in.

“From a challenge standpoint,” notes Guzzardo, “implementing on-press inspection requires the cooperation of the printer, QC and management. With an on-press system, the quality of the printer’s work will become significantly more visible and unless he is confident of his abilities, the effectiveness of the system may be compromised. Also, regardless of how quickly the inspection job can be set up, there needs to be adequate training done to ensure the operator is being as efficient yet effective as possible. The training must also extend to QC and management so that all parties understand what the system is going to do and what to do with the defects it finds.”

John Thome of BST Pro Mark is also a proponent of on-press inspection, but he points out some aspects of the process that converters might find useful. “If you put a 100 percent defect detection system on press, your waste doesn’t necessarily go down. One of the limitations of 100 percent inspection on press is that it is not as good as a first-alert system. With a 100 percent system you have to draw the line; you don’t have the same level of sophistication to define the warning area. With 100 percent inspection, you have to know what your minimum defect size is. There’s a real learning curve with that technology. What’s the minimum size? Sometimes the converter has to learn at the school of hard knocks.”

Thome says that full visual capability “is one of the biggest weaknesses of 100 percent inspection. It uses a fixed lens. You can’t pick a spot on the web and magnify it 30 times, only eight to 10 times, and it’s digital magnification, not optical. Some wide web converters today put both area scan and line scan systems on the press. It will happen in narrow web soon.”
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