Jørgen Rheinlænder, Company Director and Silvia Morar, International Marketing and Sales Coordinator, InnospeXion ApS discuss X-ray contamination detection of large products and packages.
X-ray systems are widely applied for numerous applications relative to foreign body contamination of products. Typically, inspection is aimed at un-packaged and minor products. The problem is, that large products requires a higher energy and the detector must cover a larger area. This leads to lower contrast and reduced resolution.
A novel low-energy X-ray imaging technology offers a higher resolution and a higher contrast, while retaining a high speed of scanning.
This imaging principle has now been implemented into a large product X-ray inspection system. This system aims at detecting non-conforming products, such as wrapped cheese blocks, stacked fish blocks, meat blocks, carton boxes with multiple packages, large sealed bags and pouches, etc. The solution integrates a reject system with full control of in- and out-feeding, and is designed in conformity with EHEDG guidelines for unpackaged as well as packaged products.
An X-ray system image displays the attenuation of the X-rays having passed the scanned item. The attenuation depends on the composition and thickness (or density). Therefore, the grey level value of a pixel can be correlated to details in the item that are relevant to control, or monitor. This may e.g. concern the distribution of various compounds in a mixture, to ascertain the homogeneity of a product. It may also be used to quantify the structure and the dimensions of holes, voids or cavities in cheese, in order to provide a measure of the maturity development of the cheese.
In general, the X-ray image information content is large and it can enable a close monitoring of the product tolerances being satisfied, and provide an alarm at the moment one or more parameters reach the boundary tolerance limits. This enables the on-time reaction and correction of a process, avoiding faulty production.
There is a large demand for X-ray scanning of finished boxes with product/packages. The X-ray inspection of packaged carton boxes may provide very valuable information:
- the number of packages in the box;
- the integrity, completeness, and the weight of each package;
- the presence of non-conforming packages or objects in the box;
- any contamination in each package or outside the individual packages;
- the overall packaging integrity.
In the case of large individual products, e.g. large pouches, products in bags or sacks, or products in blocks (such as cheese blocks), the need is particularly to:
- assess the contents for contamination (foreign object detection);
- verify the overall structural conformity of the product (e.g. holes in cheese);
- verify correct product representation and correct product distribution;
- verify packaging conformity and integrity (e.g. seal inspection).
X-ray inspection is an obvious choice for these applications. However, the problem is that ordinary X-ray systems offers an X-ray image quality that compromises the detection capability, and which provides too poor contrast and definition to quantify the required details of the product. The new low-energy X-ray technology provides a detection capability down to the pixel size of 0.1 mm, and with the highest sensitivity (i.e., a 40-50 per cent improved contrast that gives the ability to discriminate between different compositions and their quantitative distribution, inside the product).
The tailoring of this technology facilitates a wide conveyor inspection capability. Optimised X-ray source emission characteristics provides a high quality X-ray image of even tall and thick packaged items and products. The result is a system that detects non-conformities down to 0.2 mm even in thick and compact products (such as cheese blocks).
A modern X-ray inspection system is not necessarily a stand-alone system. In most applications, it is a requirement that the X-ray system is integrated in the production line. This requires a control of the in- and out-feed and careful consideration of the product flow. The X-ray system may be based on a specific timing control, which may be devised and monitored by the production line central control. Therefore, there are handshakes and timing parameters in accordance with the overall production line control.
When the X-ray system encounter a non-conforming sample, it will be rejected. The reject reasons (X-ray image details) will be saved, and the sample is conveyed onto a reject conveyor. The reject conveyor status is monitored and reported to the X-ray system PLC for local action, and to the central line control. The latter may issue an alarm if multiple rejects occur, or if the reject lane is in risk of being full.
This automatic functioning can be tailored to any application and any line control lay out. In some applications, intelligent usage of the X-ray system product diagnosis may be used as early warning of processes that are in danger of reaching their outer tolerance boundaries. This functionality brings savings since defects are corrected for before they emerge.
X-ray systems placed on the production floor will today acquire a very substantial amount of information which relates to the products passed through the system.
Unfortunately, X-ray systems are mainly used for detection of foreign objects of various sorts, and typically used in the food sector where retailers impose a demand for inspection, owing to consumer safety and the costs of recalls. Traditionally, there has been very little interest in using information pertaining to the products, and the X-ray systems have not had significance for the process control, only for (final product) quality control.
The novelty is that the significant improvement in contrast and resolution has opened for new applications for X-ray systems. The special low-energy X-ray systems have thus proven their capability integrated to the production line, where non-conformities are detected, before they end up as a defect. In some applications, the ability to make a quantitative quality assessment has implied a better use of the raw materials, leading to a more rational manufacturing.
These benefits of new technology is that the X-ray technology now offers much more than a final “go/no go” inspection tool. The commercial value of using the technology for control rather than discard, is substantial. Deviations can be corrected for, before they end up as defects. This leads to savings, higher product value, less scrap, better use of resources, and less downtime.
