The HEUFT development team makes a breakthrough
- the detection of scuffing on misted-up PET bottles
A reliable method of inspecting scuffing on misted-up PET bottles was not possible in the past - this has changed with the latest HEUFT technology. Imagine the following situation in a supermarket: there are bottles neatly lined up on a shelf. There are bottles on the right, brand "A", with insignificant scuffing and bottles on the left, brand "B", some with and some without scuffing. We assume that to begin with the customers help themselves equally to both products. After a certain period of time approximately the same number of bottles from both products have been removed. In contrast to brand "A" where the overall appearance has hardly changed except for a few missing bottles, amongst brand "B" on the left there are practically only unattractive containers with scuffing marks remaining due to the fact that the customers have unintentionally taken the "best looking" bottles first. From this point onwards the customer´s pattern of behaviour will change decisively. Customers who previously chose brand "B" will tend to change to brand "A" with increasing frequency due to its appearance. This can result in brand "B" losing these customers in the long run.
A high-quality scuffing inspection is necessary in order to prevent this happening so that unattractive bottles do not come on the market.
The methods available for the detection of scuffing are either based on optical absorption (bright field detection) or optical deflection (dark field detection). However the evaluation of the scuffing inspection can be influenced to a great extent by ambient conditions in both these cases. The formation of drops and condensation on the bottles are at the top of the list. This effect is caused by the temperature differences exisiting between the final rinsing and the temperature in the hall. The occurrence of misted-up bottles can be reduced but not completely avoided by regulating these temperatures and by using an extraction system at the washing machine outfeed. Condensation on the outer surface can if necessary be removed by a surge of water. However there is no reliable method for removing condensation on the inner surface.
Furthermore the dwell time of the bottles between the outfeed of the washing machine and the scuffing inspection represents an important parameter. The longer this dwell time the greater the likelihood that the containers will become misted up. A short, constant dwell time also requires a short distance between the washing machine and the scuffing inspection as well as continuous production. For this reason a modern scuffing inspection monitors the production process (standstill detection) and depending on the dwell time adjusts the limit values accordingly either more insensitive or deactivates the detection completely for a certain period of time. All these measures can reduce the false rejection rate but they do not improve the detection of scuffing.
With the new HEUFT scuffing inspection the detection of scuffing must not be adjusted so that it is insensitive if misted-up bottles occur. Therefore a standstill detection is no longer required.
The HEUFT reflexx scuffing inspection can also identify scuffing on bottles which are misted up on the inside with a high degree of accuracy.
The heart of the inspection is a measuring bridge comprising an optical mirror cabinet with an image processing system. This system consists of a high-resolution camera and a fast image processor card. The image processor card is an in-house development especially optimised for the task of container inspection. The experience gained with empty bottle inspectors, sorting units and case checks over a period of more than 10 years was implemented in the development of the card design. This image processor card has already proved to be worthwhile over the past two years and is now used in all empty bottle detections.
During the evaluation process the differences between a misted-up bottle and a bottle with scuffing are worked out. In this way it is possible to identify scuffing on a dry as well as a misted-up bottle reliably.
When this detection is combined with a rejection rate control system the result is a highly effective tool for sorting out a bottle pool. Badly scuffed bottles are always rejected via a limit value because a customer cannot be expected to tolerate the appearance of such bottles. In addition other less scuffed bottles can be rejected by means of an adjustable percentage. The preset rejection rate of "old" bottles is not generally exceeded.
A reading can be taken relating to the distribution of the occurring bottles from the integrated histogram. The containers with severe scuffing are on the right. After a certain period of time the curve will shift more and more to the left because the worse bottles are being progressively removed. The bottle pool is constantly improving!
This method of sorting out the bottle pool prevents the above-mentioned shelf being "ignored". Quality pays off!