Inspection Systems Strive for Balance

April 29, 2020
In-line inspection systems have to reliably weed out contamination and defective product without being too finicky.

The goals of quality-control inspection systems are simple: find stuff in the product that’s not supposed to be there, and get rid of it – while getting rid of as little good product as possible.

But “simple” doesn’t mean “easy.”

Reliably finding foreign material with as little waste as possible depends on many factors: the nature of the product and of the foreign material, line speeds, the kind of packaging used, the size of the product or package and more. The key is reliably finding foreign material while causing as little waste and downtime as possible.

“Food processors upgrading their digital sorting equipment are looking to remove all foreign material and the right amount of defects to make grade while maximizing recovery/yield,” says Karel Van Velthoven, advanced inspection systems product marketing manager at Key Technology. “They want their sorters to protect food safety by ejecting foreign material including insects, animal parts, paperboard, wood, rocks, plastics, glass and extraneous vegetative matter such as weeds without false rejects. They also want their sorters to achieve final product specifications by identifying defects based on color, size, shape, structural properties and/or chemical composition and then removing the ideal amount.”

One of the new ways Key is doing this is with the ADR EXOS, an inspection system especially for French fries. Billed as the only vision system on the market specifically for potato strips, the ADR EXOS recovers French fries with defects and turns them into “good” product, directly increasing yield.

The ADR EXOS inspects strips that are rejected by an upstream inspection system, locates the defect and cuts around it, retaining as much good product as possible. This increases yield – an important consideration when the quality of potatoes and other incoming product is becoming more variable due to changing climate and its effect on crops.

A green bean sorting system from Key Technology can sort beans according to how hard they’ll be to snip. Source: Key Technology

Key also has another new system designed to remove foreign material with minimal waste from a more challenging type of product: green beans. This system comprises Key’s Iso-Flo shakers, a Rotary Size Grader (RSG) and a Veryx digital sorter. These divide the beans into “easy to snip” and “hard to snip” streams (while removing foreign material), determined by whether the beans have already been “field-snipped” or, if not, whether they have a relatively regular shape.

The anchor of the system is the Veryx, a sorting system that blows individual beans out of a product stream launched into the air. LED lighting all around the line of sight minimizes shadows. The easy-to-snip and hard-to-snip beans are separated into two streams and routed to systems that snip the latter more aggressively; routing the easier beans away from that equipment means less product loss and faster processing.


Another way to use detection to lower waste comes from Mettler Toledo. It offers an X-ray Re-Inspection Program to take a closer look at product that has been quarantined, allowing manufacturers to recover as much of it as possible.

The re-inspection takes place off-line, with equipment that Mettler Toledo brings to the site and configures for the suspected contaminant. When the re-inspection is complete, the manufacturer will receive a full report documenting inspection results to support the company’s quality program for future audits.

One aspect of reliability is the reject mechanism that the inspection system uses to take contaminated product or packages out of the product stream. The two main options are air-blasting, for lighter products, which is fast and requires few moving parts; and pusher-arm mechanical rejecting, which is required for heavier product units or packages.

The Xtreme metal detector from Eriez comes with optional air-blast or pusher-arm rejects. Source: Eriez

Eriez is now offering its standard Xtreme Metal Detector Conveyor Systems with optional air-blast or pusher-arm rejects. The reject option is available with the company’s popular 14-in. wide by 6-, 8- or 10-in. high aperture sizes.

“These systems are now more versatile than ever with the availability of rejects as well as a great variety of other options, including lockboxes, reject confirmation, stainless steel motor/reducers, upgraded guarding and emergency stop systems,” says Ray Spurgeon, Eriez’ metal detection product manager.

What’s the target?

One of the most important aspects of specifying an in-line inspection system is ensuring that it can find the particular contaminants that are likely to occur in a given operation. This depends on the nature of the contaminants themselves, the product and its packaging.

Metal detectors can be flummoxed by odd-shaped pieces of metal, especially long, thin ones, like a needle or a piece of wire. According to Steve Gidman, president of Fortress Technology, the detector basically treats such a piece of metal as though it’s as small as its smallest dimension.

“This is why we use spheres to test a metal detector – it reflects the same amount of signal no matter where it’s pointing,” Gidman says. “But if you flatten out the metal or roll it into a needle or wire shape, there’ll be a significant difference in signal, depending on how it passes through. This is due to the physics of how it’s breaking the lines in the field. The general rule is, if any of the dimensions are less than the detectable metal’s sphere size, the machine may have trouble detecting it. Depending on the orientation in which it passes through, you may get a bigger signal than the sphere.”

X-ray systems have similar problems, Gidman says: “If the product’s very thin at its length and edge and small across the belt, even if the density is quite high, it may not be detected. Equally, if it’s very thin and flat, such as stainless steel and ferrous metal blade shapes, the total density may be too small to detect. In these scenarios, a metal detector is the top performer.”

The Profile Advantage metal detector from Mettler Toledo uses multi-simultaneous frequency technology for greater accuracy. Source: Mettler Toledo

One way Fortress solves this problem is with the Interceptor DF, which is made to handle thin, flat, metal flakes – one of the most vexing problems for Fortress’s customers. The Interceptor uses a second electromagnetic field that works in the vertical plane, looking for signals over a broad spectrum, from multiple angles, with the stronger disturbance from one field compensating for the weaker signal from another.

Mettler Toledo uses a similar approach with its Profile Advantage metal detector. The Profile Advantage uses multi-simultaneous frequency technology, which analyzes product signal data captured across a wide spectrum of frequencies simultaneously. This is processed by Mettler Toledo’s 3S software algorithm in real time, which results in a 30-50% higher sensitivity than competing technologies.

Keeping it clean

One of the biggest ongoing challenges in many food plants is to maintain sanitation while making sure that expensive equipment is safe. High-pressure or caustic washdowns often make this difficult. The key is specifying equipment that can stand up to whatever washdowns are needed.

For example, the IQ4 metal detector from Loma Systems now comes in a “Run-Wet” version. The “Run-Wet” achieves an IP-69K ingress rating by incorporating an open frame that uses multi-angled surfaces and minimal welds, as well as easily removable covers. Motors, lamp and sounder, controls and enclosed pneumatics are all high-pressure and high-temperature washdown-proof.

In-line inspection systems must adapt, not only to the nature of the product and its packaging, but the kind of contaminants most likely to appear. Photo: Loma Systems

Another challenge with inspection equipment is fitting it into the relatively small spaces available in many food plants. Loma offers the X5 SpaceSaver for production lines with space restrictions. Similarly, the Meki One from Mekitec  comes in models with widths ranging from 9.5 in. down to 5.1 in.

Another way to save space is to combine inspection with another function in the same system. Mettler Toledo accomplishes this with its Combichecker line. Previous Combicheckers have paired checkweighing with vision systems and metal detection. The latest in the line, the CX35, combines Mettler Toledo’s C35 checkweigher with its X33 X-ray inspection system.

Product inspection continues to be one of the most challenging aspects of plant automation. Equipment manufacturers offer a wide range of systems to cope with specific challenges, whether product-related, space-related or sanitation-related.

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