Tech Update: Vision and X-ray Inspection

May 1, 2008
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Be it X-ray, optic or laser, vision systems are finding new applications in food and beverage plants.

Hamburger buns pass through an optical inspection and sorting machine. Source: Dipix Technologies Inc.


What can be seen and what is unseen by the human eye are laid bare by vision-based inspection systems for food and beverage manufacturing, and the capabilities of the technology are expanding.

Optical and laser-based inspection had dominated the field until recent years, when X-ray became a serious option to metal detectors for final-package inspection. Increasingly, machine-vision technologies are being used in combination to optimize performance and improve both manufacturers’ processes and the integrity of finished goods.

Whether they emulate the human eye or replicate the powers of the Man of Steel, vision systems make tradeoffs in what they can and cannot detect. To overcome those limitations, technology providers are bundling two vision technologies and even exploring a cocktail of all three to improve detection performance without boosting false-positive levels.

“Inspecting for precise fill levels in cans or bottles requires X-ray,” notes Bob Ries, product manager-metal detectors and X-ray systems for Thermo Fisher Scientific Inc., “but label placement and cap position is a job for optics.” The firm incorporates Cognex cameras and X-ray tubes in inspection systems for some beverage and food companies.

Similarly, Key Technology combines fluorescence-sensing lasers with color or visible-infrared cameras in a new sorter with a two-meter wide scan area for high-volume processing. Up to eight cameras and two lasers can be configured. A few years ago, the Walla Walla, WA-based firm tried to incorporate X-ray in a more robust vision system, but X-ray’s field of vision wasn’t as great as the other technologies. The concept was ahead of its time, suggests Bret Larreau, product manager-optical inspection systems. Nonetheless, multiple vision technologies have a role to play. “No one technology is going to solve all your problems,” Larreau points out.

Inspection is a major function for vision, though not necessarily the best application. Some technology providers that originally applied vision to quality assurance have gravitated to in-process and material-handling challenges. “Quality assurance alone doesn’t give people much return on investment,” observes Laura Dierker, marketing director at Dipix Technologies, Ottawa, Ont. and a former process-monitoring specialist. Camera-based hamburger bun inspection was an early focus, but the firm has gravitated toward high-speed material handling issues, focusing on item counts, orientation and flow-management of bakery items en route to packaging. Of course, manufacturers aren’t opposed to technology with more than one function: “The one thing you can’t get with gray scale is hue,” Dierker says, and Dipix is beginning to incorporate color cameras that also help with process control by monitoring color shifts and signaling a needed change in oven time or temperature.

Multi-tasking is a particular strength of X-ray. Depending on the product, X-ray units can come within 2% of a product’s weight by applying density and size calculations, according to Hermann Fleps, technical manager at Carol Stream, IL-based Loma Systems Inc. Two years ago, the margin of errors was closer to 4%, he adds. As safety fears abate and prices drop, X-ray systems are being installed in more food plants and are doing much more than contaminant detection.

Laser and optical technologies come into play in Key Technology’s vision-based inspection systems. Source: Key Technology.

Nondestructive inspection

Fear of radiation exposure used to be enough to keep companies from considering X-ray, but those days are past, equipment providers insist. Most of the electron beam generators found in food plants operate in the 50-70 kV range, comparable to a dental X-ray. Stringent safeguards against leakage and human exposure are a given. Testing for radiation is done at the time of installation, to verify levels are incidental and don’t require radiation badges on personnel. Radiation cannot exceed 0.5 milliroenigens per hour within 5cm of the cabinet surface.

Simple systems available for as little as 40% more than metal detectors are drawing interest from food companies that see added value in the nondestructive inspection X-ray offers. While a number of suppliers are jumping in with low-cost systems, only a handful have engineered systems for high-speed production lines. Those systems also justify their higher costs with greater functionality.

Alcoa, TN-based Smiths Detection, a major supplier of airport screening and other security equipment, recently adapted a dual-energy X-ray unit built for plastic-explosives detection for real-time fat analysis of ground beef and poultry. One beam operates at a conventional 70 kV power level, while the second is 140 kV, according to Marketing Manager Christopher Young. By utilizing dual-energy X-ray absorptiometry, “you can find contaminants that might not be detectable with one, as well as analyze the chemical composition of the product,” he says.

Smiths also rolled out a quad-view system 18 months ago. “If glass contamination is a concern, four views are the way to go,” says Young. Up to 1,100 baby food jars a minute are being scrutinized with the system.

Dual-view systems are built by a handful of other suppliers. As with most technology, there are tradeoffs to be made for versatility and speed. Four views may be better than two, concedes Allan Anderson, president of Fremont, CA-based InspX LLC, but a two-beam system is much lighter. More weight translates to more stress on moving parts, he says, and that means more maintenance.

X-ray systems are more rugged and reliable than they used to be, says Anderson, but the laws of physics have not changed. If a machine must inspect at high speed, high power is required. If the item being inspected is a carton instead of a package, the distance between the tube and the receiver must be greater, increasing the power requirement dramatically. InspX has focused on equipping high-speed lines and rigid packages, and its system is engineered accordingly. The cantilevered unit swings over a conveyor belt, eliminating transfer points where containers can jam. An X-ray beam can’t be turned off and on during gaps in production, so InspX’s design employs a shutter system to prevent radiation leakage.

Baked desserts produced in Culi d’Or’s Velp, Holland plant are packaged in foil, a factor that influenced the selection of X-ray inspection units. Source: Loma Systems.

X-ray systems for beer and other bottled beverages are being introduced, but those machines direct their beams from the top or bottom. InspX and DYLOG Italia SpA direct their beams from the side, an advantage with more viscous products, according to Anderson. 

DYLOG claims to have installed more than 400 X-ray systems worldwide in food and pharmaceutical plants. It has a strategic alliance with Thermo Fisher for a high-end unit suitable for glass inspection. But the greatest demand is coming from first-time users who have switched to metalized film packaging that poses a problem for metal detectors, points out Thermo’s Ries. “Our base machine can’t find the box with the missing cookie or do checkweighing,” he concedes. On the other hand, first-time users don’t require complex machines. They simply want to inspect for contaminants with a machine guided by a logarithm that doesn’t reject a high percentage of good product.

“Marketing people love foil, and when companies change from a polybag to a foil package, they make it impossible for a metal detector to hit their metal specs,” adds Ray Spurgeon, X-ray division manager for Erie, PA-based Eriez Manufacturing Co. The magnetic specialist complemented its inspection equipment in November 2006 with a basic unit built around components and software from UK physicist Richard Parmee. Parmee’s Sapphire Alliance offers country licenses to machine builders like Eriez, which then add the controls, conveyors and cabinetry to deliver a complete X-ray system. Since the launch, Eriez has added five larger and more sophisticated units, including a pipe-inspection machine for pumpable foods.

AIB International requires metal detectors in plants seeking HACCP certification, Spurgeon says, but he expects AIB soon will take a more receptive approach to X-ray vision. Cheese, marinated meats and other products with high conductivity because of sodium levels require phase adjustments in metal detectors that hurt metal sensitivity. X-ray overcomes the problem, making it a superior detection technology in many applications.

X-ray inspection for products in glass containers and metallized film is becoming a viable alternative to metal detectors in food plants. Source: Mettler-Toledo Safeline Inc.

3D cameras, 2D codes

Photoelectric sensors are adequate for simple detection of the presence or absence of a component, be it a cookie on a belt or a cap on a bottle. For more detailed evaluation, such as the correct position of a cap or the proper date code, a camera is needed, and those vision systems are growing in sophistication.

This month, Omron Electronics will release a 3D color camera system to detect flaws in surface dimensions. The dual-camera set-up is designed for evaluating the fit and finish of automobiles and other high-ticket items and may be too pricy for food applications, but it illustrates the trail being blazed in optical inspection.

“In gray scale, you’re pretty much limited to 255 shades,” points out Thomas Kahn, product manager for auto ID/RFID/vision at Schaumburg, IL-based Omron. “Trying to discern a subtle change in cookies as they come out of an oven can be impossible,” though the change over time could be dramatic. The specialized lighting and two mega-pixel 3D cameras would be overkill for an oven PID controller, but advances in high-end optics have a residual benefit for lower-end technology, particularly in cost.

Illumination options are very product dependent, Key’s Larreau notes. LEDs are solid state and very stable, “and we’re taking advantage of the huge technological improvements that are happening” when engineering sorters. Pentium processors with software that can analyze 50 million pixels per second and self-adjust the system give today’s systems unprecedented capabilities. “They’re not just sorters; they’re process-control tools,” says Larreau.

A 360° image of cylindrical containers is generated by a four-camera technology from Cognex Corp., Natick, MA. Dubbed OmniView, the system resolves object-orientation issues on high-speed lines. The technology records surface features of up to 1,200 bottles and cans a minute, Cognex’s John Lewis says, and can interface with other machine-vision software tools such as optical character recognition and barcode reading. Those applications have opened up in recent years not because of technological advances as much as legal decisions (see related story on page 72.)

Three-dimensional images of jelly beans is probably overkill, but 3D color cameras are becoming available for quality inspections in automotive and other manufacturing industries. Source: Omron Electronics LLC.

Allergen control is nurturing another application for machine vision. Ice cream manufacturers are using 2D codes on cartons to make sure flats for ice cream without an allergenic ingredient don’t feed a filler with that ingredient. Line-scan technology demands lenses without edge distortion, and Cognex supplies cameras with those lenses to carton-formers like Hutamaki, along with frame grabbers, lights and software. Half a dozen such systems are running on multi-product lines for ice cream, baby food and soup.

Between optics, lasers and X-rays, there are huge opportunities for vision-based systems in food production. As more opportunities in both processing and inspection are identified, applications for vision technology will expand. 

For more information:
John Lewis, Cognex Corp., 508-650-3140, john.lewis@cognex.com
Laura Dierker, Dipix Technology, 613-596-4942, ldierker@dipix.com
Ray Spurgeon, Jr., Eriez Manufacturing Co., 814-835-6298, rspurgeon@eriez.com
Carl Bonnan, Heuft USA Inc., 630-968-9011, carl.bonnan@heuft.com   
Allan Anderson, InspX LLC, 510-226-6686, anderson@inspx.com
Bret Larreau, Key Technologies Inc., 509-394-3291, blarreau@key.net
Hermann Fleps, Loma Systems, 630-681-2058, hermann.fleps@loma.com
Thomas Kahn, Omron Electronics LLC, 847-285-7313, tom.kahn@omron.com   
Christopher Young, Smiths Detection, 847-395-9993, chris.young@smithsdetection.com
Bob Ries, Thermo Fisher Scientific Inc., 763-783-2794, bob.ries@thermofisher.com

Inventor's defeat spells machine-vision relief

Hailed by inventors and reviled by industry, Jerome H. Lemelson cast a long shadow over the fields of machine vision and automatic identification. Love or hate his memory, the defeat of the Lemelson Foundation by corporations led by Symbol Technologies and Cognex Corp. paved the way for expanded use of vision technology in food and other manufacturing.

One of the most prolific inventors and patent holders in US history, Lemelson took the novel approach of suing end-users of machine-vision and other technologies, rather than the companies that used his patented concepts in the barcode readers and other equipment they made. He then negotiated licensing fees with auto manufacturers and other end-users, collecting fees worth more than $1.3 billion. His philanthropic foundation dispersed more than $130 million in fellowships and prize money to inventors and other innovators.

After Lemelson’s death in 1997, Cognex initiated a legal challenge of some of his machine-vision patents, arguing their issuance was unreasonably delayed. Symbol and Cognex prevailed in 2004 in a verdict that found 76 of Lemelson’s machine-vision patents were unenforceable. The ruling was upheld in 2005 by the US Court of Appeals.

Uncertainty over the licensing status retarded wider adoption of vision inspection systems, some argue. Downers Grove, IL-based Heuft USA Inc., for example, reports a seven-camera empty-bottle inspection system it supplies to bottlers suffered from lost sales while the Lemelson case was pending. General Manager Carl Bonnan says a dairy using returnable milk bottles balked at purchasing the system after he informed them about the licensing situation. When Heuft declined to indemnify the dairy against any patent-infringement claims by the Lemelson Foundation, the dairy ended the negotiations.

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