Product inspection systems

False rejections 'should not be underestimated' - Heuft

By Joseph James Whitworth contact

- Last updated on GMT

Heuft tackles false rejection dilemma
Heuft tackles false rejection dilemma
“Better too much than too little" is a policy that prevails worldwide when it comes to removal of supposedly faulty products from the production line, according to Heuft.

The firm said false rejections equal wastefulness and their equipment can reduce the proportion of good products removed from the production line by mistake.

Dr Thomas Jahnen, technical sales director at Heuft SystemTechnik, told false rejections are a cost factor which should not be underestimated.

Complaints or recalls

Jahnen said producers want to prevent faulty products, such as underfilled food containers or those contaminated with glass splinters, reaching the market and resulting in complaints or recalls.

He said these are generally very costly and can permanently damage brand image. 

“The readiness to remove products immediately to be on the safe side even if they are only supposedly defective is accordingly high. 

“Of course this is the case above all in such filling and packaging plants where there is an awareness that the accuracy of the equipment used for inspecting the quality is not adequate in order to reliably differentiate between harmless deviations and serious threats to the product quality. 

“For example it is perhaps better to play safe and immediately remove the full container in question once and for all from the production flow if it is not clear whether a detected object is merely an uncritical product inhomogeneity or a dangerous foreign object.”

Minimise risk

Jahnen said it is accepted that such full containers which are marketable are also rejected and disposed of so there is no risk of a faulty product leaving the plant. 

“In the meantime a change in attitude can be diagnosed even where this was formerly viewed in a slightly more relaxed manner.  This may be connected with the food scandals of the past years in the Asian region and the resulting stricter legal requirements,” ​he said.

“To put it drastically: those who accept a false rejection rate which is too high may as well throw their money straight out of the window. 

“The overall equipment effectiveness (OEE) also suffers – and with it productivity.  In other words:  an increase in false rejections always means a reduction in output. 

“Furthermore it is more than ethically questionable when food which is qualitatively perfect and can be eaten without hesitation ends up in the bin.”

Very thin line

He said the line between rejecting faulty products and removing products that are ok is ‘very thin’.

“A real-time quality inspection with maximum detection accuracy is needed particularly along high speed lines where 60,000 containers and more are filled per hour in order to ensure that only those products are rejected as far as possible which really have to be rejected. 

“We already succeeded in halving the false rejection rate of Heuft inspection systems more than ten years ago with the introduction of our first generation of high-performance image processing systems. 

“A significant reduction in the share of unwanted false rejections can be expected once more with the Heuft reflexx² and the Heuft Spectrum II device platform.”

Similar to a quality defect

He said false rejections typically occur when an object is identified which is similar to a quality defect but in reality is not one. 

Jahnen cited an air bubble in a paste-like mass such as baby food which can at first glance hardly be differentiated from a foreign object in the detection picture. 

“Integrated structures in the container design such as embossing can also be easily mistaken for glass defects or leaks if the image processing system is not powerful enough.  Supposedly dropping below the nominal filling quantity is a common cause of false rejections," ​he said. 

“Therefore the principle "better too much than too little" is also frequently applied in this case which means that more is placed in the packaging than actually belongs in it as a precaution and consequently a part of the valuable product is practically given away.” 

He said the actual fluctuations of the container material should also be mentioned. 

“For example these often exceed the specified tolerances in the case of glass packaging - for instance due to the cost pressure when purchasing and production fluctuations during the manufacture of the packaging. 

“Of course such deviations are noticed during a sensitive quality inspection and result either in unwanted false rejections or the acceptance of actual faults. 

“Only systems with a high measuring accuracy and a highly developed evaluation technology can carry out a useful classification of these actual deviations in good and faulty products.”

Related topics: Industry news

Related news

Show more