LIBRARY ı6ıul 0) - Cranfield University

3.3.3 Control module
In the control module (see Figure 3.25) the welding process and the position
of the welding torch relative to the joint are monitored and controlled in order to
ensure that the required weld quality is achieved. The module comprises three main
parts: a) the monitoring system; b) the control of welding torch-to-workpiece relative
position; c) the control of the welding process.
The monitoring system is responsible for continuously monitoring the state of
the process and the relative positioning between welding torch and joint line. The
welding data are acquired via suitable sensors, digitized and relayed to the main
controller, where an assessment is made about the process state and control
instructions are issued and transferred to the other control parts of the module.
The control of the welding torch-to-workpiece relative position is represented
in Figure 3.25 by the blocks surrounded by a dashed line and comprises the main
controller, the torch-to-workpiece relative position controller and the robot. In the
main controller, the deviation of the required relative positioning is estimated based
on the information acquired by the monitoring system. Such deviation is then
transferred to the relative position controller where control instructions are generated
in order to compensate for the deviations.
The control of the welding process is represented in Figure 3.25 by the blocks
surrounded by a dash-dotted line and includes the main controller and the welding
power source. In the main controller the changes in welding parameters that are
necessary to compensate for a deviation of process behaviour are issued and
transferred to the welding power source, which is responsible for ensuring that the
controlled welding parameters are implemented.
Note that in Figure 3.25, the block representing the main controller is involved
by the limiting boundaries of both the welding process control and the torch relative
position control. Such representation was adopted to show the interdependency
between torch positioning and welding process behaviour.
The control system implemented is described in detail in the next chapter.
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