Advanced Welding Processes: Technologies and Process Control

Welding automation and robotics 239
Adaptive control (see Chapter 10) techniques may be used to improve the
tolerance of automation systems to normal variations in component dimensions,
joint position and material characteristics. These techniques should not,
however, be regarded as the first or only solution to problems of this type;
redesign of the joint or improved component preparation are often more cost
effective. Major developments have, however, been made in adaptive control
and a large number of alternative options are available, as already discussed
in Chapter 10.
Flexible manufacturing systems (FMS) are used in many non-welding
applications; 6 they enable reductions to be made in work in progress by
automatically scheduling the production operations to suit component
availability and demand. A simple but effective example of this system is the
Autotech flexible welding system. [284] In this system, a conveyor is used
to transport standard 750 mm ¥ 1200 mm pallets, containing the components
to be welded, from the loading station to the robot. Each pallet has jigging
suitable for a specific component mounted on it and is identified by a unique
arrangement of five plugs on its side. When the pallet enters the robot station,
the position of the plugs is read by proximity switches and fed to the robot
controller which selects the appropriate welding program. The pallets may
be loaded onto the system in any sequence and the throughput may be varied
to suit the availability of parts.
This approach has been extended by the use of AGVs (automatic guided
vehicles) to transport the workpiece and alternative methods of component
identification. [285] The use of typical FMS systems in the fabrication of
heavy construction equipment is reported to have resulted in cost savings of
28%. [286] The FMS approach is not restricted to robotic welding and may
be applied to dedicated and modular systems, which are equipped with suitable
programmable controllers.
11.9.1 Simulation and off-line programming
Programming of robotic systems may take a significant amount of time and
this results in lost production. Off-line programming allows the robot program
to be developed on a remote workstation and transferred to the robot controller
almost instantaneously. Various systems are available for off-line programming
(e.g. GRASP, IGRIP and ROBCAD), but these share the following
characteristics:
∑ A graphic and kinematic model of the robot is stored as a library file in a
6 Flexible manufacturing systems are systems which are able to accept a variety of components
or tasks, often in a random order, and are able to identify the component and automatically
adapt the manufacturing operations to produce the required end result.