Observer-based nonlinear control strategies for Hardware-in-the-Loop simulations of multiaxial suspension test rigs

The Hardware-in-the-Loop (HiL) simulation is a powerful and well-established approach for the development and testing of mechatronic systems. The specimen is coupled appropriately with mathematical models of the remainder of a larger system that run in parallel on a real-time computer. For test rigs with multiaxial excitation of the specimen, the realization of HiL simulations is a challenging task. The excitation units are serial or parallel kinematic manipulators and the dynamic properties of the specimen vary in different spatial directions. In particular, the interaction forces and torques at the interface between manipulator and specimen have to be considered. Thus, appropriate control strategies are necessary to drive the manipulators enabling realistic and safe HiL simulations. This article deals with the design of motion and force control strategies for a vehicle axle test rig with a highly dynamic hydraulic hexapod used as the excitation unit. The realization of motion and force control for a hexapod requires the knowledge of its current system state. Therefore, sliding mode state observation techniques using super-twisting algorithms (STA) are presented. The developed controllers, observers and HiL configurations are validated with simulation and experimental results.