Technology transfer - seeing the light

24 October 2011

CEE looks at a quality-control technology which is being transferred from its traditional applications in pulp and paper to the metal industry.

Having acquired the machine vision business operations of Viconsys Oy in Finland Metso is now expanding machine vision applications beyond its traditional fields of pulp and paper.
Machine vision systems using analogue tape-based cameras have been used in the paper industry for analysing track breaks since the early 1990s. In 1995, data storage was first digitised, followed by the cameras themselves. Viconsys is believed to be the first to integrate process cameras and fault detection into one system in which all cameras are able to identify and save both process incidents and faults.

Lighting is key in machine vision systems and lights working at a direct current level, that are constantly switched on, are usually employed. However, with fault detection in particular, lights fight each other when filming and picture quality can be poor. To counter this Viconsys developed a pulsating LED light as a replacement. The pulse is so short and sharp that the LEDs do not generate heat.

“Normal LED light burns constantly at an equal voltage. An LED pulsating with an electrical impulse is only switched on for 1-2% of the time”, said product manager Niko Niemelä. The pulsating light is reflected from above and below and as transilluminating light, which produces a different kind of response from the monitored surface. Pulsating LEDs have been synchronized with digital cameras so that the camera beam takes a picture from each light angle. The cameras capture 100–300 black-and-white images per second.

Real-time images are processed in a power processor. If the system discovers a sufficiently notable change in a process, it will automatically save the images. An analysis based on the image data helps classify faults.

Matrix camera
The digital matrix imaging systems, developed for the observation of processes in the pulp and paper industry can be applied in the metal industry almost as they are, we are told. The matrix camera is the most important part of Metso’s capability to export this technology into other industries. Many competing pulp and paper equipment providers do not offer their own systems, and many fault detection solutions developed for quality inspection applications in the metal industry rely on traditional linescan technology.

The core of the system is a processor card that has two DSP processors and one gigabyte of memory per camera. Data is transferred with optical fiber to the processor card to minimise electromagnetic disturbances from motors.

The movable system with a couple of cameras can be joined to a portable computer. Some larger systems supplied for paper machinery have had as many as 250 cameras. In such cases, data storage requires its own server. Fault/quality charts can be transferred from these systems either for the operator to view or can be printed for the customer with the delivery of goods.

Viconsys and Metso have already jointly delivered many systems. One project involves a fault detection system delivered to an aluminum manufacturer, and it uses a reflection survey on the metal surface to look for scratches, dents, abrasions, and material transported from outside.

Niemelä estimates that Metso machine vision at this stage is best suited for metal surfacing processes, in industries that use ready-painted steel or galvanizing. Machine vision technology can also be used for the quality control of metal used in the car industry. Other promising areas are strip-like processes with variable speeds, such as rolling.

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