Research ArticleRobust H∞ positional control of 2-DOF robotic arm driven by electro-hydraulic servo system

•A robust H∞ positional controller in electro-hydraulic servo system (EHSS) is proposed.•Three parameters uncertainties including the flow gain of the servo valve Kq, the cylinder volume Vt, the viscous damping coefficient of cylinder Be are considered in proposed method.•The external loads FL is considered as a structural uncertainty which is quantitatively analyzed by Lagrange method.•Effectiveness of proposed method is demonstrated on 2-Dof robot arm.

In this paper an H∞ positional feedback controller is developed to improve the robust performance under structural and parametric uncertainty disturbance in electro-hydraulic servo system (EHSS). The robust control model is described as the linear state-space equation by upper linear fractional transformation. According to the solution of H∞ sub-optimal control problem, the robust controller is designed and simplified to lower order linear model which is easily realized in EHSS. The simulation and experimental results can validate the robustness of this proposed method. The comparison result with PI control shows that the robust controller is suitable for this EHSS under the critical condition where the desired system bandwidth is higher and the external load of the hydraulic actuator is closed to its limited capability.