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Seeing further and understanding more

Viconsys technology brings together a range of previously unconnected image data when a paper machine is running to provide an accurate overview of the entire chain of events from when a problem first begins to develop to when a defect or break occurs. The result is that a Viconsys Process and Quality Vision system allows a mill to gain much better control over the performance of its machines and the quality of its output.

The paper industry has traditionally used two different machine vision systems: Web Inspection (WIS) and Web Break Analysis (WBA). While these systems provide high-resolution images in real time and cover all the critical locations on a machine, combining the information they generate has been largely impossible up until recently – despite the obvious benefits this would bring.

Most defects are the result of process problems, stock impurities, or system malfunctions. Collecting information on these events, linking them together, and displaying this data to operators would be very useful and deepen their understanding of actual process conditions, and help them recognise acceptable conditions from ones likely to result in bigger problems down the line.

If they can access this information in real time without the need to gather the data concerned manually, they can start any proactive action needed in good time.

Viconsys LEDs and camera fitted on an 8.6 metre-wide newsprint machine.

Bringing it all together

Drawing on extensive past experience with both WIS and WMS technologies and the latest developments in machine vision, Viconsys has successfully developed the first solution combining the advantages of both into one better system.

An ultra high-capacity 1-teraflop image analysis processor lies at the heart of the new Viconsys Process and Quality Vision (PQV) system. This has been specifically designed for use with paper machines and is capable of handling any stream of images and providing comprehensive image analysis in real time for every image. Each processor is linked to a 1 GB LAN, and camera images are received via fibre optics at 10-bit grey-level accuracy.

Analysis covers disturbance detection and sequence building, formation analysis, classification, defect detection, specific analysis of machine elements, and variables such as edge, width, and flutter.

A number of application-specific cameras can be specified for optimum image capture. Where high speed is a priority, frame rates of up to 1,000 fps can be used to allow lossless capture of the web at any required resolution.

To generate high-resolution defect images, Viconsys has developed a modular light source based on LEDs, creating an illuminated area 200 mm in MD across the web. These LEDs are used like stroboscopic lights, and are switched on for 5-10 microseconds for the requested exposure to give smear-free, crystal-clear images. These high-quality images are then analysed using sophisticated image analysis algorithms. A number of distribution analysis, adaptive median filtering, and other algorithms are applied to each image in real time, together with true event classification.

Using learning classification techniques, operators can teach the system to recognise new events by name, such as ‘edge crack at centre roll’ or ‘stock lump’. Analysis can help detect defects that are hidden within the paper formation process, with the help of advanced wrinkle detection capable of dealing with even low-contrast, narrow wrinkles.

Image analysis can also deal with dirt build-up on trim squirts, release points, edge positions, edge stability, and web width; and the system includes an easy-to-use performance image analysis library, which can be used for customised image analysis.

Viconsys has optimised the entire optical path based on the latest know-how on light sources, beam focusing, clear-glass technology, window washers, and fibre optics-based signal routing. Housings are fabricated from stainless steel (AISI316) and cleaning is fully maintenance-free, based on small amounts of water rather than expensive instrument air.

Everyone benefits

A Viconsys PQV system automatically generates disturbance event sequences for the papermaker. When a disturbance, such as a tear hole, is detected the system will open the first image in the sequence automatically. Knowing the time delays between the cameras installed, the system will then add information from subsequent cameras to provide a high-resolution review of the defect or web break. Only images meeting the appropriate time synchronisation conditions and within a given tolerance, typically +/- 2 frames, will be displayed in the same event sequence.

Several sequences can be displayed simultaneously and key information accessed quickly and conveniently by all relevant personnel over a company’s network.

Operators can follow up hundreds of events on a reel without the need to carry out any manual checking, and quickly build up an understanding of when things are running within acceptable limits and when action is called to prevent a small problem developing into a big one, such as a web break. This can translate into valuable savings in areas such as downtime, and result in better overall quality and improved customer satisfaction – and that is something that every papermaker wants.

A typical Viconsys PQV operator interface. The system has identified an edge crack and shows its root cause at the centre of the roll.
> Hannu Ruuska
(Published in HighTech Finland 2008)