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A helping hand to minimise waste

15 November 2020

Ciaran Murphy explains how X-ray inspection technology has a role to play in helping minimise waste. 

Unnecessary waste has always been the enemy of the production manager in the food industry. From overweight packs – where the extra amount cannot be charged for – to product that has to be scrapped before it leaves the factory, all of these incidences will impact a company’s bottom line. At the same time, there is a constant pressure to get product out – maximising throughput and efficiencies while minimising waste is a constant challenge.

When it comes to product quality, the line between productivity and profitability can be very fine. Sending out sub-standard packs – particularly those containing foreign bodies – will have financial implications, especially if this involves a full recall or results in a retailer fine, as well as seriously damaging a brand’s reputation. Equally true today, with food waste recognised as major environmental issue, the unnecessary loss of any product has sustainability implications as well.

However, an over-zealous inspection system that rejects too many acceptable packs will also have a detrimental impact on the bottom line, in terms of both waste product and packaging.

The challenge for inspection equipment manufacturers therefore is to provide a solution where neither speed nor detection accuracy are compromised. For X-ray inspection systems, the level of sensitivity of the machine is one of the most critical factors in avoiding too many ‘false positives’, where packs without foreign bodies are mistakenly rejected. This is vital in food applications where it is usual for rejected contaminated packs and their contents to be destroyed and not reworked, even if they have been rejected in error.

The characteristics of the product and the type of foreign bodies to be detected – or other quality checks that need to be performed such as missing items or deformed product – are critical in selecting an X-ray system with the appropriate level of sensitivity. 

X-ray inspection involves the projection of relatively low energy X-rays onto a sensor or detector. As the product or pack passes through the X-ray beam, only the residual energy reaches the sensor. Measurement of the difference in the absorption level of the X-ray energy between the product and a foreign body enables the foreign body to be detected.

The sensor is made up of small pixels similar to how a digital camera operates.  As with a digital camera, the more and smaller the pixels, the better the resolution of the X-ray image that indicates the place of a foreign body.  X-ray machines with smaller pixels will be better able to pick up softer foreign bodies and at smaller sizes.

If an X-ray inspection system is required to detect a foreign object of 1.5mm in size, then the amount of false rejects will be determined by the available head room between the ultimate performance of the machine and this target. A machine with the capability of detecting no lower than 1mm on a particular contaminant will have a lot less head room than one that can detect as low as 0.3mm. This means the first machine will have to be set close to its absolute performance limit in order to ensure it detects all foreign bodies and this can lead to many more false rejects. By comparison, the second machine can be set to be proportionally less sensitive in order to achieve the same result, meaning it will offer less false rejects and therefore reduce waste. 

The detection challenge becomes even greater with lower density objects, such as rubber or stone, where the tolerance levels are further limited. For example, a stone is roughly three times less dense than stainless steel, meaning you need three times the volume of the material to have the same effect on the density differential detected. Higher sensitivity machines therefore have greater capabilities, and this can provide invaluable future proofing if retailer standards or legislative requirements become more stringent.

The ability of the software can also contribute to the reduction of waste. For many applications, the detection of foreign bodies involves similar items. Special genetic algorithm software is able to analyse image data over a number of generations and in this way can be optimised to look for these objects. This delivers a high level of accuracy and helps to eliminate recurring sources of contamination.

Similarly, advanced software can be trained to recognise areas which can regularly result in false positives, such as the edges of cartons, and ignore items that do not need to be detected, for example clips on sausages or pre-packed loaves of bread.

Some products have particular inspection challenges. For meat and poultry, a typical quality inspection requirement is the detection of unwanted bones in fillets. Because there is a relatively small difference in density between the bone and the meat, the bone can be particularly difficult to spot. 

This has led to the development of dual energy X-ray systems, which have two line sensors, one which takes images at high energy and one at low energy. This provides a better overall image of the product with a clearer contrast between the product and the bone or other foreign bodies.

The versatility of X-ray technology contributes to waste reduction in other ways. Its wider detection abilities, which include spotting missing, deformed or broken items, mean such defects can be identified quickly and necessary steps taken to rectify these if they are a recurring issue; ease of operation with pre-setting of detection requirements and parameters minimises operator involvement for error-free set-up and changeovers to help maximise production.

And as part of the automated set up for individual products, the X-ray power required for detection can be optimised to reduce energy levels and maintain the high performance of the X-ray generator; another energy-saving feature on some machines is their ability to go into stand-by mode following spells of inactivity.

Consistent product quality is critical to a brand’s enduring success and reputation. Maximising production throughput without compromising on this is vital to continued success. An efficient X-ray system will help companies achieve both and keep unnecessary waste to a minimum. 

Ciaran Murphy is business manager EMEA – Quality Control at Ishida Europe.

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