Adaptive Robust Constrained Motion Control of an Independent Metering Electro-Hydraulic System Considering Kinematic and Dynamic Constraints

Independent metering systems (IMSs) have shown superior performance in hydraulic industrial applications because of the high power density, large force output, and high control freedom. However, the presence of mechanical safety structures, such as relief valves and replenishing valves, introduces complex constraints that significantly limit performance improvements of the IMS. If the constraints are violated, then some undesirable phenomena, such as cavitation, overflow, and pressure surge, will occur to make the system lose accuracy and stability. In this article, a double-loop control strategy, which combines theouter loop constrained trajectory planner and the inner loop adaptive robust motion controller (ARC), is developed to realize the constrained motion control of the IMS. In the outer loop, both kinematic and dynamic constraints are transformed into time-varying constraints on the replanned trajectory, which are calculated based on the state feedback online to optimize the planner's performance. A time-optimal motion trajectory is planned using a third-order nonlinear filter, ensuring convergence to the original reference while meeting the assigned constraints. In the inner loop, the high-performance ARC controller is designed to make the IMS track the replanned trajectory despite uncertainties and nonlinearities. To demonstrate the constrained performance of the proposed double-loop control framework, experiments with different control strategies are conducted on an IMS test bench.