Automatic welding device for external weld joints of curved U-shaped ribs

The utility model provides an automatic welding device for an external weld joint of a curve U rib, which comprises a portal frame capable of moving along a fixed track, a mechanical arm capable of moving along the horizontal and vertical directions, a capacitive sensing tracking system mounted at the lower end of the mechanical arm, a welding system mounted on the mechanical arm, and a PLC (Programmable Logic Controller) system, a bridge deck slab to be welded is arranged between the fixed rails, the bridge deck slab comprises a deck slab body and a U-shaped rib, and one side of the bridge deck slab body is obliquely placed on the support; the capacitance sensor and the bridge deck are connected with the positive electrode and the negative electrode of a power supply respectively, so that capacitance is formed due to the fact that gaps exist between the sensing probe and the U-shaped rib and between the sensing probe and the bridge deck; and the PLC system comprises a PLC control system and a servo motor dri