WCA September 2015

Wire & Cable ASIA – September/October 2015

www.read-wca.com

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.

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

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.

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.

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Figure 6

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Figure 5

Front view of the system

Source/Photo-sensor locations

Zone 1/sensors A+C

Zone 2/sensors B+A

Zone 3/sensors C+B

Photo-sensor A

Ring of elementary light

sources

Measurement area

Photo-sensor C

Photo-sensor B

Zone 1

Zone 2

Zone 3

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Figure 7

First case, one large side inked mark. Reading at

25kHz