TPT September 2012

Technology News

CNN camera for 100 per cent surface inspection at high speed

the first image based system capable of completely surveying surfaces at production speeds in the order of 10m per second. The inline inspection system uses pixel-parallel image processing based on cellular neural networks (CNN), which allow image evaluation up to 10kHz. A recent implementation of the technology is an inspection system for wire production, which has just been put into operation. Typical surface defects in wire production processes are cross dents, drawing marks and so-called chatter marks. Wires with diameters from 0.4 to 2mm typically show such defects ranging from a few millimetres to 50m. Ordinary image processing systems miss these defects when inspecting the fast-moving wire surface. In FlexFormCNN, Fraunhofer IPM has developed an inline image processing system which is able to recognise a 50m scratch on a wire whizzing by at speeds of 10m/s and evaluate it at the same time. This is possible thanks to camera-internal pixel-parallel image processing and a specially adapted lighting system. The image processing system relies on a CNN camera in which each pixel has its own processor. The camera processes up to 10,000 images per second at a 176×144 pixel resolution. To inspect moving surfaces, an image processing system’s lens must fulfil many criteria: first, the defects must be shown at such high contrast and so brightly that the exposure time is short enough to prevent blurring. Secondly, both the depth of field and the optical resolution must be sufficient for the smallest relevant defects to be shown sharply over the whole measurement area. Thirdly, especially on uneven metallic surfaces, disturbing reflections must be prevented so that the light intensity is uniformly distributed on the object surface. Thus, the right lighting is crucial for processing images of moving objects. To guarantee sufficient light intensity on a defined focal area, special optics using dark field illumination and high-power LEDs with a pulse length of 10 µsec are employed.

up or damaged tools, for instance, may concern every single work piece of a whole production batch – which boosts the reject rate. In this case, an effective inline-control of production processes is necessary to identify errors immediately after they occur in order to be able to fix the problem in due course. Random defects such as scratches or disposals may be reason enough for the customer to reject the complete delivery. A 100 per cent surface inspection makes it possible for manufacturers of wires, tubes or steel sheet to identify and document errors and thus reduce the error rate in further production steps. The German Fraunhofer IPM, an institute for applied research with a focus on optical measurement techniques, has developed an inline measurement system, which guarantees 100 per cent quality control of surfaces at high production speeds. FlexFormCNN is

QUALITY control in high-speed production processes poses a challenge in many industrial areas such as electronics, medical or automotive. Tubes, wires or rods produced for medical, telecommunications or aerospace applications, for instance, have to comply with high quality standards. Here, immaculate surfaces are required for functional or aesthetic reasons and have to be achieved at very high production rates. Fraunhofer IPM has developed an inline measurement system that guarantees 100 per cent quality control of surfaces at high production speeds. Signal processing and camera speed are the bottlenecks of a 100 per cent quality control in such processes. Even today, many manufacturers of high-tech materials and components rely on visual inspection at the end of the production chain. Defects, which result from used-

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S eptember 2012