Throughput volume could not be sustained with labor, which is too expensive and too scarce anyway to sustain production of fruits and vegetables. Vision inspection serves both a quarterback function for the line and a supplier grading tool. If surface defects or product dimensions exceed standards, the inspection system provides the data needed to address the problem with the supplier.
Customer requirements compel some processors to adopt zero-tolerance policies toward foreign materials. To meet those specs, the product makes multiple passes through the sorter. That raises the likelihood of product degradation. Frozen cranberries are brittle, and the less handling, the better. Emblème Canneberge in Bourgeois, Quebec, wanted to minimize damage to the 30,000 lbs. of frozen berries it sorts per hour, president Vincent Godin explains, so it recently commissioned a sorter that layers multiple images in a single pass to remove contaminants and defective berries with minimal false rejects.
Emblème Canneberge employs a sorter from Key Technology Inc. (www.key.net), Walla Walla, Wash., that combines pixels from up to eight lasers and four cameras in a single image of each piece of fruit. Emblème’s frozen cranberries arrive through a chute; if product was fed on a belt, the berries would become airborne when they reached the sorter’s field of vision, providing a 360° view. Prior generations of Key sorters required separate top and bottom image capture.
“You were able to make decisions at the object level, but you didn’t have the ability to combine that information at the pixel level,” explains Marco Azzaretti, Key’s product manager-advanced inspection systems. The firm refers to the multi-channel imaging system as pixel fusion.
The “heart of the machine” is a CPU that can process huge amounts of data in nanoseconds. “It has to be able to process instantaneously,” says Azzaretti. “It sees everything in the process but uses only a fraction of it in the sort.” Data analytics on line performance, quality trends and other metrics is pointing the technology toward predictive functions, he concludes.
What’s the frequency, Kenneth?
Contaminant detection ranks as the most automated approach to product inspection. Metal detectors and X-ray machines have a decades-long track record in end-of-line inspection, with X-ray units gradually becoming the standard for the largest food & beverage companies. X-ray’s ability to detect a wide range of contaminants is driving the shift, with factors such as increased use of metalized film adding additional impetus.
But X-ray machines can be overkill when ferrous and nonferrous metals constitute the vast majority of product contaminants. Even when final inspection is done with X-ray, metal detectors increasingly are positioned upstream in production. The good news is that metal detector technology continues to advance, with Thermo Fisher Scientific’s five-frequency machine the most recent example.
Introduced to the industry at September’s PackExpo Las Vegas trade show, Thermo’s Sentinel metal detector generates five frequencies of electromagnetic waves simultaneously. Multi-frequency metal detectors were introduced a decade ago, but they only operate on one frequency at a time, according to Bob Ries, lead product manager-metal detection & X-ray inspection at Thermo Fisher (www.thermofisher.com/us), Minneapolis. The Sentinel unit continuously scans the frequencies, switching from one to the next every millisecond. Strictly speaking, that constitutes semi-continuous scanning, but it means multiple wavelengths at each frequency scans product every second.
Ries recalls a visit to a cheese plant, where a metal detector failed to reject a chunk with a 2mm piece of metal but was able to detect smaller and larger metal fragments. This was an example of “phasing,” a phenomenon where the phase angle of the product and the contaminant align and the metal goes undetected. “The software has to be able to ignore magnetic and conductive product effects,” he explains, “and the most common way is phasing. With this new technology, we accept the fact that there is no one frequency that is going to detect everything.”
The final opportunity for automatic inspection immediately follows metal or X-ray detection: checkweighing. Deviations as minute as 10mg between measured and actual weight can be achieved with checkweighers, though that requires slow line speed. At throughput rates up to 600 packages a minute, variances of 0.5g are more realistic, a deviation most manufacturers can live with.
Sanitary design is a more immediate need for improvement. The ANSI B155.1 standard for packaging and processing equipment was revised recently to require hygienic risk assessments, along with electrical and mechanical risk assessments. Anticipating the change, some food manufacturers already were including hygienic risk in their RFPs, reports John Uber, product management leader at Mettler Toledo Checkweighing (www.mt.com).
In September, Mettler-Toledo rolled out its C series of checkweighers, a good-better-best assortment with four levels of hygienic design. An IP54 rating accompanies the base platform, the only machine with some aluminum components. The other platforms carry IP65, IP66 and IP69 ratings, depending on how aggressive the washdown conditions are. All parts are stainless steel or polymer.
“It’s our oldest automated inspection line but the first to implement sanitary design,” says Uber. Rounded or canted plains replace flat surfaces, and easy disassembly for cleaning was an engineering requirement. To provide a turnkey solution, Mettler-Toledo fabricates clear plastic machine guarding featuring a gabled cover over the product zone to draw moisture away.
The PackML standard has been embedded in the company’s checkweigher controls for nine years. “It’s a common language, and when every machine in the line is talking the same language, you get unbiased data for OEE measurement,” he points out. For food companies that have adopted PackML, there are numerous advantages.
For example, one international food company using PackML remotely downloads controls code for checkweighers placed into service anywhere in the world. “In five minutes, the checkweigher is integrated in the line,” says Uber.
Checkweighers and metal detectors lack the glamour of multi-channel vision graders and spectrometer-on-a-chip. Nonetheless, as demands for higher speeds and accuracy clash with requirements for safe and contaminant-free finished goods, the performance of automated inspection systems is advancing to reconcile them.