Indirect Force Control in Hardware-in-the-Loop Simulations for a Vehicle Axle Test Rig

For test rigs with multiaxial excitation of the specimen, the realization of a Hardware-in-the-Loop (HiL) simulation is a challenging task. In general, the excitation unit is a serial or parallel kinematic manipulator and the dynamic properties of the specimen vary in different spatial directions. Hence, the contact situation between the manipulator and the specimen requires extensive consideration. System instabilities and damage are possible. In this paper, it is demonstrated how indirect force controlled manipulators are used to provide realistic and safe HiL simulations. In this context, a HiL controller is developed for a highly dynamic vehicle axle test rig with a hydraulically actuated hexapod used as the excitation unit. The models of the HiL subsystems are shown first, and afterwards the design of the HiL controller is presented. A theoretical system analysis is provided, which includes the investigation of stability, bandwidth limitations and disturbance rejection. Simulation results are provided to emphasize the high quality of the HiL simulation.