EuroWire July 2015

Technical article

Ultra-fast, high resolution, surface quality measurement (SQM), for wires, optical fibres and cables By Jean-François Fardeau, Gérald Novel and David Miara, Cersa-MCI, R&D division, Cabries, France

Abstract This project meets a long-time wire, cable and fibre industry requirement for efficient in-line surface quality measurement and defect detection. It was recently allowed by the very lastest technology progresses in optoelectronics. The system works like a ring linear camera around the wires. The fine wire version works from 10μm (0.4 mils) to 2mm (80mils) in two models, fine and ultra-fine. With 64 dots per circumference, about 300,000 circumferences per second (c/s), and a dot size proportional to the wire diameter, it brings surface detection performance far above all present existing technologies at a competitive cost. It includes all necessary real-time electronic computing: defect characterisation and selection, and alarms. It connects to external computers for data logging, parameter setting, and image display of the surface on PC screen, statistic computing, production quality reports and maintenance. (International patent July 2004). Other models, for larger diameters and higher resolutions but lower speed will follow by next year.

Introduction In applications where surface quality (roughness, flaw, lump, neck) is critical, like special fine stainless steel wires, gold wires and wire plating, coatings or colourings of optical fibres, enamelling of copper wires, broadband cables, there was no instrument for high resolution and high-speed whole-surface analysis. The existing surface quality instruments are based on standard camera image analysis. The limits for fine wire are the resolution on the wire, the image frequency, and the lighting system for surface analysis. With the non-contact full circumference imaging, this covers all the surface of the wire at high resolution and high speed. It becomes possible to evaluate the surface and shape of the defect. At 300,000 circumferences per second and 64 dots per circumference, at line speed of 30m/s (1,800m/min) the axial resolution (pitch) would be 0.1mm (4 mils). Including the wire feed pulses for wire length and speed measuring, the two dimensions are known: length and circumference. That gives a two-axis image of the wire for defect characterisation. Connected to a PC, this can display local images of the wire surface, especially when there is a defect, for analysis and knowledge. Using only static components, lifetime is not a problem. Maintenance of optical systems in harsh environments requires specific care.

For low maintenance action, it uses clean air pressure to avoid dust, vapour or particles deposition on the inner glass tube interface. Principle The idea came from the gleam of a spotlight on a cylinder.

▲ ▲ Figure 1

In this image, re/D is about two per cent. Then re/π*D < 1% of the circumference. The size of the gleam depends on the size of the spot source and on the angular aperture of the observer (optic of the sensor). The energy gleamed to the observer (sensor) is strongly modulated by the surface quality; roughness, colour (absorption) and flaw, but also the local shape of the cylinder. Then, rotating the light around the wire axis will also rotate the gleam on the surface referring to a fixed observer. This generates a circumference image. When the wire moves, it develops a complete surface image of the wire. If the design is well made, any small surface defect, colour or shape change will produce locally a significant reduction of the gleamed energy to the sensor.

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July 2015