The global market for seafood is predicted to reach $134 billion by 2026, with a greater variety of products than ever before. But, for many people, there remains one big drawback – the presence of fish bones. Often long, thin and sharp, bones in fish are not just an annoyance – they can pose a serious health risk if they are swallowed and get stuck in the throat.
Automatic deboners swiftly and efficiently take care of most of the problem for processors – but even the very best machines inevitably let the odd bone through. Often the deboner lifts the bone and removes a section of it, leaving a smaller section behind – making it even more challenging to detect. That’s when the latest generation of X-ray inspection technology can come to the rescue.
When low-energy X-rays are passed through a product, different elements absorb different amounts of X-ray – so, in the resulting images, metals, glass and bone appear darker than the surrounding fish. However, because fish bones are very thin and low density, with low mineral content, they are difficult to detect and likely to be missed by standard end-of-line X-ray inspection equipment that uses a 0.4 mm or 0.8 mm resolution sensor to detect contaminants.
The detection of tiny bones and other sub-mm diameter bones requires a 0.05 mm (50 micron) resolution area sensor more typically seen in the medical or electronics industries. This unparalleled level of resolution, combined with low-energy X-ray generators, gives rise to images which can reliably show even the smallest of bones in fish.
These high-quality images are then processed via automatic inspection software that looks for dark features that follow a straight line – taking into account the natural muscle patterns in fish, which would otherwise lead to false rejects. The software must therefore be able to differentiate between the dark features which are caused by bone and the lighter features caused by the natural texture of the fish. This process is made more difficult if the fish has been frozen and then defrosted – or has been excessively processed – as this can cause separation of the muscle, giving rise to false rejects.
The production line can be programmed to reject any products where bones over a certain size have been identified. It’s also possible to count the number of bones and so allow through a certain number of small bones that pose little risk to health. This information can also be used to grade fish – sending truly bone-free fish along lane one, for example, while products containing a low number of bones go to lane two, leaving fish with a large number of bones to go to lane three and be reworked.
If fish is reworked, the X-ray image can be provided to a rework station – providing operators with an image showing the location of the bone, and so speeding up the process. A return conveyor can then be used to reinspect the fish, ensuring all the bones have been removed correctly.
Metal contaminant detection has long been the main target of X-ray equipment on the production line. But the ability to detect ever-smaller bones is now crucial in the battle to improve the quality of fish products.
www.sapphire-inspection.com