LIBRARY ı6ıul 0) - Cranfield University

Although only linear joints were implemented in this work, it should be noted
that non-linear joints could also be included for off-line programming by sub-dividing
the non-linear curves obtained from the intersection between two adjacent surfaces
into small linear segments and treating these as a series of successive linear joints.
This could increase the application scope of the program to deal with, for example,
fillet welds in pipe sections. It should also be noted that the currently available robots
are limited to linear and circular interpolation. That is, they can only perform ruled
paths either passing through specified points in the form of a line between two teach-
points or an arc passing through a third teach-point located between the teach-points
which define the start and end of the arc. Hence, a non-linear non-circular robot path
can only be defined as a series of successive linear paths with the torch orientation
changing linearly between the teach-points.
The benefit of integrating the welding procedure generation and the
geometrical data extraction for off-line programming into the CAD software is that
the resulting welding data2 and the weld positional data3 can be stored in the same
CAD drawing file in the form of data associated with the line segment which defined
the weld joint. Therefore, if a different welding cell and robot is used, the only
modification needed for generating the new robot teach-points would be the definition
of the CAD-to-Robot transformation matrix. It should be noted that the definition of
this transformation matrix depends on a set of points which are located using the
robot. The orientation of the torch relative to the joint line was set by default as
being perpendicular to the joint line at the point being defined (start or end point) and
contained in the joint bisection plane. For example, for a 90 deg included angle flat
position fillet joint, the default orientation would be parallel to the gravitational
vector. This orientation could be changed by the user if required.
Also, an offset for the position of the weld start and end points along the joint
line was introduced to ensure that there would always be base material to receive the
weld metal. No transversal tolerance was allowed, however this could be easily
implemented. This could be necessary for welding steels with different heat sink
characteristics in each side of the joint.
The rules used to generate the orientation necessary for the welding torch to
achieve different joint approach and withdrawing directions were devised from prior
on-line programming experience of a welding robot with a specific torch
configuration. Therefore, for a different robot/welding torch combination, a
modification in the angles of the planes defining the different orientation regions
would be necessary (see section 3.3.2.2).
The teach-points defining the welding torch approach and withdrawing paths
relative to the joint were generated based on the assumption that the component, once
fixed in the jigging system, would not be moved until the completion of the welding
operation. This implies that the component clearance box (see section 3.3.2.2) would
also be fixed and, therefore, the approach and withdrawing points and vectors.
However, different rules could be defined in situations where the component
2 Required welding quality and chosen welding procedure
3 Relative to the CAD coordinates frame.
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