MODELING OF A SPOT WELDING GUN The thesis applied a system identification method named nonlinear Hammerstein-Wiener to identify an electronic motor system based on the limited measurement of input current and the output displacement. The electronic motor is a servo motor embedded in the arc robot, by define the current, the arc robot moves the corresponding arc head with certain displacement. As long as the motor system is not a linear system, and the number of measurements is limited, the thesis tries to find an effective way to identify a reliable model based on the measurement combination and decreasing of the cost indicator RMSE.