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Peeking inside the package.

Wide array of technologies, capabilities vie to become last defense in quality control.

It can take only one empty or misfilled package to alienate a consumer for life. It can take only one metal or glass fragment in a package to permanently tarnish a brand's image among millions of consumers or create a multimillion-dollar liability exposure for a manufacturer.

As production line speeds increase, however, no human inspector can possibly examine every package that comes off the line. And even if inspectors could, they couldn't see inside opaque packages or reliably record inspections for eternity.

That's why increasing numbers of food manufacturers are turning to electronic technology that can take a peek inside packages at the end of the line. Inspection systems using metal detectors, X-rays, gamma rays, laser beams, acoustical pulses and, most recently, capacitive resistance offer manufacturers a growing range of ways to form their final line of quality control defense.

Not all the technologies, however, handle both of the primary end-of-line inspection jobs - checking for foreign objects and monitoring product quality. Only X-rays and capacitive resistance can do both. Metal detection looks only for foreign objects. And acoustical and gamma ray systems are designed only to inspect for proper fill and other quality issues.

Either as part of the detection system or integrated with a previously installed rejection mechanism, the systems eject the defective product and create permanent records to document that packages were inspected and that the inspection system was functioning properly.

Metal detection

One of the oldest and least expensive ways to peek inside a package remains metal detection. About 70 percent of food industry applications of metal detectors are for inspecting the finished product, says Chuck Morgan, product manager for Advanced Detection Systems, a Milwaukee-based manufacturer of metal detection systems. Meat processors are among the biggest users, seeking ways to find sausage clips, meat hooks or fragments from metal parts in ground meat, Morgan says.

While end-of-the-line inspections are important, adding a metal detector earlier in the process can prevent even more trouble - and rejects - later, Morgan says. "Often (a metal detector) will be installed right before the grinder. If a sausage clip or meat hook gets into the grinder, not only does it ruin the grinder, but it also ends up chopping the metal into finer pieces that are harder to find later."

One big advantage of metal detection over X-ray technology - the major alternative form of looking for such foreign objects in food packages - is cost, Morgan says. While a metal detector can cost as little as $6,000 to $10,000 per line to install, an X-ray machine can cost $100,000 to $150,000.

One shortcoming of X-rays is where the product density is similar to that of the potential contaminant, Morgan says. Metal detection, on the other hand, may be useless in finding problems inside metal cans or even some metallic-film packages. Ferrous detectors can be used to find ferrous metals inside non-ferrous cans or film, however, Morgan says.

X-rays have the advantage of being able to search for a wider variety of contaminants, including bone, wood, plastic and glass. But in the meat industry at least, metal is by far the biggest threat, Morgan says, "and the possibility of glass or plastic contamination is virtually non-existent, unless you have sabotage."

The primary advantage of X-ray machines for meat inspections is in detecting bone, Morgan says. But he adds that bone generally presents less of a risk and can be ground into relatively harmless small pieces.

X-ray technology

Perhaps the biggest problem with X-ray technology has been its cost. But EG&G Astrophysics Inspection Systems, Oak Ridge, Tenn., has tried to overcome that objection by introducing late last year its PakScan line of inspection systems for the food industry at a cost of around $50,000, half or less what other X-ray inspection costs.

EG&G can afford to slash prices so dramatically, says sales director Art Isham, because it can take advantage of the economy of scale inherent in being the world's largest producer of airport X-ray security systems. The company combined its airport security and manufacturing quality control operations last year.

PakScan actually performs a form of metal detection in addition to X-ray inspection, Isham says, using a dual-energy detector that distinguishes organic from inorganic material. The system also looks for foreign objects of any kind by searching for density variations with X-rays. Line speeds are comparable to these metal detectors can work with - up to 200 linear feet per minute.

PakScan also performs a missing product inspection that's more sensitive than conventional checkweighing, because the system tracks weight changes of the product at various points throughout the production process, he says, While a conventional checkweigher wouldn't detect a missing flavor packet in a box of macaroni and cheese because the variation in weight wouldn't be large enough, he says PakScan would detect the problem.

"A lot of people are looking for missing product inspection," Isham says. "And if you can do that at the same time [you do other quality control inspections], it's just a better way to justify the cost."

Capacitive resistance

The latest technology for peering inside food packages is capacitive resistance, used in the recently introduced Closed Pack Inspection System made by Cintex of America, Kenosha, Wis. The Cintex CPI uses an energy field created by a drive oscillator to form an image of the product inside the package based on the electrical absorption of various components inside.

The system works only with products under four inches thick. The degree of resolution of the image depends on the number of cells in the equipment, with options ranging from 16 to 64 cells, each corresponding to a pixel on a video screen, says division manager Tim Baxter. Software is custom-written for each application, so the system can scan for the proper picture specification for each product and reject products that don't meet specs.

"If you have a stack of crackers like an Oscar Mayer Lunchables product and you're missing one cracker in the stack of four, you would get a different grayscale count in that position of product and know it's bad," Baxter says. "One cracker amounts to less than the (average) deviation of the product [weight], so you can't checkweigh for that."

Similarly, the system can monitor whether bakery pies are filled uniformly or whether filling has leaked out of the shell, or it can ensure all the pieces in a box of chocolates are in their proper places.

With the system still in beta testing in the United Kingdom, some details remain to be worked out, Baxter says. One is the minimum size of foreign object the system can detect.

At a cost of $60,000 to $65,000, a Cintex CPI system falls somewhere between the average cost of a metal detection system, which Baxter pegs at $20,000, and most X-ray systems, which he estimates at around $120,000. The system can do much more than a metal detector, he says, including checking for a full array of foreign materials and creating an image of the finished product, much like an X-ray would. And it handles line speeds of up to 400 packages per minute.

Gamma ray technology

Though they don't check for foreign objects, gamma-ray detectors made by Industrial Dynamics, Torrance, Calif., do go beyond the beverage fill-level inspection duties for which they're primarily designed. The FT-50 Fill Level Inspection System also can be configured to check for missing caps or lids, cocked or high caps, bulged cans, low foam in glass containers and down cans on can lines. The system also can be set up to check for presence and proper positioning of labels and bar code verification.

The major application is in the beverage industry, such as the Anheuser-Busch brewery in St. Louis. But the FT-50 is also used in canning lines, such as for Del Monte and Stokely vegetables, says technical sales manager Dave Kriebel. A base FT-50 system that checks fill level costs only around $15,000, according to Kriebel, with fully loaded systems costing as much as $30,000 or more.

The system works by passing a gamma ray across the tunnel through which the package passes. Depending on whether the proper level of product is present, it will either block or not block the ray before it reaches the detector on the other end. Proximity, optical and ultraviolet sensors are used to detect seal and labeling problems.

Acoustical and laser sensors

Handling roughly the same duties as the FT-50 gamma ray system is the Tracker series of TapTone, a division of Benthos Inc., North Falmouth, Mass. Rather than sending a gamma ray across the package, however, TapTone sends an electromagnetic pulse off the top of each container, which magnetises the metal and creates a tapping sound. Based on the frequency of the sound, the machine determines the internal vacuum pressure of the container to identify possible sealing problems, says TapTone spokesman Peter Zentz.

Tracker systems may also be outfitted with proximity sensors, which measure the shape of packages. In addition, a laser version of the system measures lid shape. All the systems are non-contact, so they can be used on high-speed lines running at up to 2,000 packages per minute.

In all cases, the company's system is based entirely on monitoring internal package pressure.

"One of the things we've been able to find on beer bottles are very small imperfections that cause slow leaks," he says. "We can also find small defects in the sealing of caps, as well as if the cap is misapplied or missing entirely."

An additional benefit over gamma or X-ray detectors is that acoustical and other systems marketed by TapTone don't require the added precautions and cost of dealing with radioactive materials, Zentz says. As with gamma ray systems, TapTone systems start in the $15,000 range, and may cost as much as $40,000 per application.

Beer bottlers have been the biggest users of the TapTone systems, with installations at Miller, Molson, Stroh's, Labatt's, Kronenbourg and Heineken breweries so far. But the system also can be used on cans and jars of other types of products, Zentz says.

Regardless of the type of detection used for end-of-the-line inspections, keeping records of those inspections is increasingly important to manufacturers. Linking detection systems to computer systems that can generate permanent records is important not only in helping identify trouble spots in the process, but also in providing documentation of proper quality control procedures if litigation ever arises, says Morgan of Advanced Detection Systems.

"Probably the most important feature that has come along recently," he says, "is report capability to monitor status, routine and memory from past triggers to store that somewhere and be able to dump it into a mainframe or print it."
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Title Annotation:food packaging inspection technologies
Author:Neff, Jack
Publication:Food Processing
Date:May 1, 1997
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