LIBRARY ı6ıul 0) - Cranfield University

aims at fine tuning the welding parameters such that the most stable situation is
always attained.
3.3 Off-line programming and control system for robotic gas metal arc
welding
Considering the positioning and process aspects mentioned in the former
sections, a strategy for integrating off-line programming with robotic welding, process
monitoring and adaptive control is proposed. It is assumed that the robot arm as well
as the welding cell are correctly calibrated. Although it is ideal to calibrate the robot
and workcell, this is not absolutely necessary since the control system provides
alignment of the welding torch relative to the workpiece. This is limited, however, by
the range of movement allowed, which implies that the control system can only
accomodate errors within this range and hence, if the robot had large geometric errors
beyond this range, then the control system would reach a limit of movement.
Therefore, the proposed system addresses mainly the off-line programming aspects
and the component and process errors.
The proposed concept aims to integrate the geometrical design of a
component (via CAD modelling) and the welding design (via weld modelling) to
generate the robot program necessary to carry out the required weld. Such a robot
program would contain the necessary communication instructions and logic necessary
for in-process monitoring and adaptive control to be performed, thus ensuring that the
required weld quality is attained. In the present work such a system has been
implemented on a personal-computer, using as its base a commercial CAD software.
The idea behind this concept was to devise a system in which the welded component
is dealt with from the design to the shop floor without the need for developing
welding procedures and without the intervention of an operator for correcting robot
path or adjusting welding parameters. The proposed system is composed of three
main modules, namely: a) CAD Module; b) Off-line Programming Module; c)
Control Module. (see Figure 3.1)
3.3.1 CAD Module
In the CAD module, the welded part is designed such that the welds are
accessible from the part's exterior. A solid model of the workpiece in its final welded
form should be provided in order to allow the off-line programming module to be
used. AutoCAD® (AutoDesk Inc., USA) was chosen to be the basis of the system
due to its flexibility in terms of programming and modelling tools and due to the fact
that it can be considered as a standard personal-computer based CAD software for the
industry.
The AutoCAD programming facilities used in this work are based on
AutoLISP®, a symbolic programming language whose functions are interpreted
during program execution. The advantage of using this programming language is that
the program becomes platform independent. It also provides modularity,
functions can be added to the program without much trouble.
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