Technology transfer - seeing the light

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 MJ-808 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 Niemela. 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.

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.