Observer Based Sliding Mode Control for Hydraulic Driven Barrel Servo System With Unknown Dynamics

The position tracking control of a barrel system driven by a two-stage hydraulic cylinder with long transmission lines was addressed in this paper. First, an active balancing system was designed to balance the gravitational torque which may deteriorate the performance of the barrel control system. The active balancing system is totally isolated from the barrel control system; thus the dynamics of the barrel servo system is significantly simplified. The effects of the long transmission lines were also considered during the modeling of the barrel servo system. In order to exactly estimate the unmeasured states and the mechanical disturbance, an extended state observer was designed by employing the Levant's Differentiator, thus the estimation errors would converge to zero exponentially. Then, based on the estimated signals, the barrel system was transformed into the pure integration chain form, thus the sliding mode technology can be directly utilized. After that, a sliding mode controller is designed to make the position output of the barrel to track different motion trajectories as close as possible in the presence of model uncertainty and unknown dynamics. The closed loop system was proven to be asymptotical stable in the sense of Lyapunov theory. Three different motion trajectories were tested to verify the effectiveness of the proposed controller.