Welding apparatus with automatic following of the joint to be welded

Welding apparatus for welding a joint between two plates, said apparatus comprising a frame, at least one transverse guide carried by the frame, a welding torch mounted for movement along the guide transversely of the joint, drive means for adjusting the position of the torch along the guide, a further guide, said further guide being fixed on the torch, a carriage mounted on said further guide for movement therealong with respect to the torch transversely of the general direction of the joint to be welded, further driving means for regularly reciprocating the carriage along said further guide, optical sensor means for optically sensing said joint, said optical sensing means being carried by said carriage and being arranged to supply an electrical pulse each time said optical sensor means passes over the joint, reference sensor means for sensing a central reference position to thereby supply a pulse when the optical sensor means passes the axis of the torch, a measuring circuit for developing an algebraic measurement of the difference in time between the said pulses in each reciprocation cycle of the movable carriage, and a control circuit connected to the measuring circuit and arranged to actuate the torch-driving motor in a sense which leads to a reduction in said difference in time.