A saddle curve is formed at the intersection of
nozzle to the header. The welding torch needs three degrees of
freedom to go through this curve:
A revolute movement around the nozzle (φ movement).
A prismatic movement along the nozzle axis ( Z
In addition, since the nozzles have variable
diameters, a third degree of freedom is used to compensate this
movement which moves the torch along the nozzle radius (r movement).
These three movements are supported by 3 gear groups.
A general view of this mechanism is shown in the figure