WCA September 2015

Image computing The sensor must be able to characterise the size and the shape of the defect according to the requirements of the user. The SQM computes in real time the perimeter (P) and the surface (S) of the defect. The ratio R = k*S/P 2 gives information on the shape of the defect. k = 4π. In this case, R = 1 for a circular defect. It tends toward zero when the defect elongates. Then R and S are two key detection parameters. In order to have homogeneous resolution, the line speed is measured by the SQM (pulse counting) and the diameter is a user parameter. Then the scanning frequency is adjusted automatically. Test results At the time of writing, the authors were just at the start of application and conducting industrial tests.

Photo-sensor A Ring of elementary light sources Measurement area

Zone 1

Zone 2

Zone 3

Photo-sensor C

Photo-sensor B

Source/Photo-sensor locations Zone 1/sensors A+C Zone 2/sensors B+A Zone 3/sensors C+B

❍ ❍ Figure 5 : Front view of the system

❍ ❍ Figure 6

Figure 6 , caught by a CCD matrix at the place of the wire, shows the size of the (white) light line perpendicular to the wire axis. The Gaussian shape of the energy density in the light line makes the efficient width at about 20μm. Then the spot size along the wire axis (Line Resolution: LR) is about constant, but on the circumference (Circumference Resolution: CR), it fluctuates proportionally to the wire diameter (r*α). The line resolution on the wire depends only of the light source system, not of the sensor. To succeed in this development, one key point was the light sources. They must be small and fast, but generate very homogeneous light beams with uniform characteristics. They have been specially and successfully developed for this application. Another key point was the sensor technologies. For the smallest range, it was necessary to use a highly sensitive sensor but one that was also very fast. The movement of the wire with the rotation of the light source generates an elliptic scan of the surface and a continuous image on the sensor.

Still in laboratory conditions, a stainless steel wire 0.38mm in diameter (15mils) was moved and this generated marks or scratches. In both cases the blue line determines the periphery of the defect. Unfortunately the display is cut right on the top of the wire where the marks are. Nevertheless, it shows the computing analysis that works all around the wire. The surface quality of the wire can also be seen. Image calibration must be made on a smooth surface of the wires. This is also a process to develop to be able to deliver the reference wires. ❍ ❍ Figure 7 : First case, one large side inked mark. Reading at 25kHz

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Wire & Cable ASIA – September/October 2015