This paper presents a new control strategy (AF-PID) which consists of an adaptive feedforward controller combined with a PID controller. This scheme is used for oscillation control in the nozzle of a pipeline automatic welding robot. The reference consists of both frequency and DC bias terms. In the identification block, the estimated peak-to-peak amplitude of response is compared with that of reference. Then an adaptive feedforward gain is updated. Consequently adaptive feedforward gain is regulated based on the measured amplitude error between output and reference. The system mechanical and electrical parts are mathematically modeled. The closed loop system along with the controller is symbolically modeled, in a state space expression, making the stability analysis possible in a close form. Simulation and practical results are then illustrated. After that the AF-PID control results are compared with the PID control results. The present method has practically been implemented in the professional welding robot control system. Finally, the real implementation results have been illustrated in the paper.
