Abstract: An automatic welding apparatus including a robot which comprises a base, a rotary support rotatably mounted on the base, a pair of first arms pivotally movable together and rotatably supported each at its one end by the rotary support, a second arm rotatably supported by the other ends of the first arms at an intermediate portion close to its one end, and a hand connected to the other end of the second arm and rotatable about two axes intersecting each other at right angles. A core wire is supplied from a feeder to a welding torch attached to the hand of the robot. A control device controls movement of the robot, operation of the core wire feeder and power supply to the welding torch. When the forward end of the welding torch comes into contact with the work to be welded, with the core wire drawn into the torch, the resulting short-circuiting is detected to detect the position of the work.

Abstract: A synchronous motor is driven by a plurality of inverting circuits. The inverting circuits are controlled by signals from a position detecting circuit coupled to the shaft of the synchronous motor so as to produce output current signals from the inverting circuits which are shifted by a certain angle from each other.