LIBRARY ı6ıul 0) - Cranfield University

Appendix D
This Appendix shows a fibre optic based sensor concept for gap detection and
seam tracking. Figure D. 1 shows the proposed concept. This was devised after
analysing the currently available vision based seam trackers. These were observed to
have the similarity of being directional, that is, they are only effective if the projected
laser light precedes the welding torch during seam tracking. This restricts the welding
torch to determined orientations, thus reducing the flexibility of the robot.
Considering that the robot must change the orientation of the torch (rotation
around the torch axis) in order to be able to reach certain positions in its workspace
with a constant torch approach direction, a non-directional sensor would be needed.
This could be obtained by rotating a directional sensor around the torch as needed or
projecting an annular shaped laser light around the torch and sensing the intensity of
the reflected laser light. The points with low intensity would correspond to the joint
line or a gap, the number of low intensity points being an indication of the gap
dimension. The exact position of these points in the circle could be known by using a
coherent fibre bundle in the sensing ring.
Some tests were carried out to check the viability of projecting a ring of laser
using a series of optic fibres arranged in an annular shape. Although promising results
were obtained, the development of this sensor was considered to be out of the scope
of the thesis.
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