An adaptive control system for off-line programming in robotic gas metal arc welding.

Abstract

The aim of this work was to develop an integration concept for using off-line
\nprogramming in robotic gas metal arc welding of thin sheet steel. Off line
\n-welding
\nparameter optimization and on-line monitoring and adaptive control of process
\nstability and torch-to-workpiece relative distance were used to ensure weld
\nconsistency.
\nThe concept developed included four main aspects: a) the use of a CAD
\nsystem to design the workpiece; b) the use of a welding off-line programming system
\nto design the welds, generate the welding parameters and to extract geometrical
\ninformation from the CAD models to generate a robot program; c) the use of a
\ngraphical simulation system to simulate the robot movements; and d) the use of
\nmonitoring and adaptive control for ensuring that the required weld quality is
\ndelivered.
\nThe CAD system was chosen to be the basis for the development of the
\nwelding off-line programming system. The generation of optimized welding
\nparameters was based on empirical welding models and the robot program generation
\nwas based on on-line programming experience.
\nA PC based monitoring and control system was developed to provide on-line
\nposition and process control. The position control was carried out by pre-weld
\nadjusting the initial position of the workpiece using a wire touch sensor and on-line
\nadjusting the torch-to-workpiece distance by moving the workpiece based on the
\ninformation provided by a through-the-arc sensor. The process control was carried
\nout by automatically trimming the welding voltage such that the most stable process
\ncould be obtained. The stability of the process was estimated by using previously
\nestablished monitoring indices. It was assumed that the off-line welding parameter
\noptimization would provide the deposition rate necessary to produce the required
\nweld quality.
\nSuccessful welding control trials were performed showing the effectiveness of
\nthe adaptive control strategy.
\nAn off-line programming system has been developed and the programs
\ngenerated have been tested by simulation. This showed that simulated positioning
\nerrors, produced by deliberate wrong path data, were successfully compensated for by
\nthe control system developed in this work.