Food Engineering
Engineering R&D

X-ray's double take on inspection detection

Dual energy X-ray systems bring value added detection features to identify missing product, damaged product, dented or altered packaging and presence of a premium item.

February 7, 2014
Kyle Thomas, strategic business unit manager, Eagle Product Inspection.
Kyle Thomas, strategic business unit manager, Eagle Product Inspection. Source: Eagle.

Conventional single-energy X-ray inspection technology has been established as a reliable tool in detecting contaminants like stainless steel, ferrous and non-ferrous metals, glass, calcified bone, mineral stone and high-density plastics and rubber.

Yet it doesn’t do as well with inorganic contaminants such as glass shards, low-density plastics and rubber or stones and rocks. Inaccurate readings also frequently occur with single-energy X-ray systems when inspecting complex, variable-density foodstuffs.  The goal for dual-energy X-ray systems is to run at maximum sensitivity with few to no false reject activity in these applications.

To serve the burgeoning market of complex foodstuffs, Eagle Product Inspection offers its Material Discrimination X-ray (MDX) system, a dual-energy approach for general applications such as those previously mentioned.  Another type of dual-energy offered by Eagle, dual-energy X-ray absorptiometry or DEXA, analyzes the fat and lean components of meat while providing contaminant inspection (see “Two-trick pony,” FE, January 2013).

Eagle, formerly Smiths Detection PID, offers single X-ray and dual X-ray solutions to food processing plants.

Kyle Thomas, a strategic business unit manager at Eagle Product Inspection, is responsible for the research and development of Eagle’s product portfolio. Previously, he held various senior positions during his 28 years with Mettler-Toledo, most recently as head of marketing for Mettler-Toledo Hi-Speed in the United States. Mettler-Toledo acquired Eagle Product Inspection in 2011. Thomas earned a bachelor’s degree in marketing management from the University of Northern Iowa.

 

FE: What are the current capabilities of MDX dual-energy X-ray?

Thomas: MDX dual-energy X-ray does more than just inspect for contaminants; it simultaneously finds missing pieces, measures fill levels, estimates product mass and finds damaged or incorrectly sealed packaging. This is especially true with premium items, which can be anything from a toy in a cereal box to a salad kit that contains the dressing, seasonings and croutons within a salad bag. MDX can detect flat glass and stone in mixed nuts, a task that is difficult for conventional X-rays. Often these additional features can help pay for the cost of the system.

Unlike single-energy X-ray that uses thickness and absorption to analyze varying gray scales, MDX looks at the material’s average atomic number to distinguish organic from inorganic. This allows MDX to filter out product variation and focus on the inorganic contaminants.

There is no limit to the number of products that a dual-energy X-ray unit can identify. The software can be set up to see a contaminant, a foreign body, a product defect or product quality. Overall, X-ray performance depends on contaminant size, packaging and the existing environmental conditions. It also depends upon how the image is generated and the image processing software supporting the application.

Metal or thin products down to 0.5 to 0.7mm are detectable with dual-energy X-ray, with glass detection in the 1.5 to 1.3mm range. Stones with a density similar to that of glass produce comparable results with X-ray systems. But X-ray will not cause metal detection or vision systems to become obsolete. Each has its place in the market.

 

MDX dual-energy systems from Eagle Product Inspection identify organic and inorganic items found in foodstuffs, whether it’s contaminants, foreign bodies or premium packaging.
MDX dual-energy systems from Eagle Product Inspection identify organic and inorganic items found in foodstuffs, whether it’s contaminants, foreign bodies or premium packaging. Source: Eagle.

FE: Is there an overlap between single and dual in terms of capability or application?

Thomas: With single energy, users see all the items in the bag but have to look for slight inconsistencies in material density to highlight the contaminant. This is not a density view approach, which some X-ray technologies follow. With our X-ray, we look at absorptiometry.

Eagle has supplied single- and dual-energy systems long enough to determine early on which type our customers should use. There is usually not an overlap regarding the selection of a single-energy or dual-energy technology. It is determined through the evaluation of the application.

MDX targets more detail and a wider variety of contents in the container than a single-energy approach. This makes dual-energy X-ray ideal in applications for fruits, vegetables, salad mixes, nuts, cereals and candies, which can be a challenge for standard X-ray systems since they present busy images where contaminants can be difficult to locate. Eagle’s MDX overcomes the challenges by using dual-energy technology to discriminate materials by chemical composition.

MDX features a detector array that gives values at two different energies. From these, a relative ratio of absorbed energy can be calculated to determine the composition of a material. Thus, foreign body detection is based on the atomic number rather than density variation or a product thickness calculation. Innovative packaging designs, like fold-out cardboard sandwich packaging and corrugated card encasements, also provide challenges in foreign body detection for standard X-ray technology, but these challenges are overcome with MDX and dual energy.

 

FE: How do the signals work?

Thomas: A single beam emits energy to two different detectors in the array, so one X-ray generator and one beam are emitted at two different detectors. One detector measures high gain or the energy absorption at the higher end of the energy spectrum, while the second detector measures the energy at the lower end. MDX looks at the two different energy levels or two different energy inspection points, which provides additional detail about the detected object. Certain products, such as organic materials, respond better at higher X-ray frequencies, while certain types of inorganic materials appear more clearly when the frequency is at another point along the spectrum.

MDX relies on two arrays of response diodes, sensing two spectrums of energy. One diode measures the amount of energy absorption by organic materials, whereas the second diode highlights the inorganic materials on the conveyor. Therefore, the unit paints two pictures. One is of the product we want to keep in the bag, and the other identifies items we do not want in the bag. Advanced algorithms use the two resulting 2-D images to precisely calculate content.

All materials are based on elements found on the Periodic Table. Each ingredient has its own atomic number, and the higher the atomic number, the greater proportion of X-ray energy is absorbed. We look up the reference material on the Periodic Table to determine the composition of the material. (We estimate a material’s average atomic composition.)

 

FE: Where is dual-energy X-ray being used?

Thomas: A potato grower and manufacturer in the northwestern United States is using MDX to detect and reject low-density rocks and golf balls in its process. In Poland, a cereal manufacturer deployed eight Eagle X-ray inspection systems with MDX technology after receiving complaints about glass being found in its products. The complaints have ceased in the wake of MDX being introduced.

There are also potential future uses for MDX beyond inspecting complex-density food products. The technology might also be used to measure ingredients to simplify the classification of products for food labeling.

Eagle offers MDX dual energy as an option for many of its standard models including the Eagle Pack 550 Pro unit, which has a footprint 72.2-in. long, 91.3-in. high and 50.6-in. wide, similar to or more compact than conventional single X-ray units.

Products up to 21-in. wide and 7-in. high can be inspected on the conveyor, which is 24-in. wide and either 72-  or 108-in. long and operates with a maximum load of 100 lb. at speeds from 50 to 295 ft./min. Beam width varies with package height. For example, a belt-high product is inspected with a 21.6-in. wide beam, while a 10-in. high product is scanned with a 12.5-in. wide beam.

 The unit operates in a 32°F to 104°F range with 24 to 90 percent relative humidity.  Users can select detection modes for contaminants; missing items; clip, void and premium; mass weight; shape/position; and fill level and filler feedback.