Robust force control with a feed-forward inverse model controller for electro-hydraulic control loading systems of flight simulators

A hybrid control strategy for an electro-hydraulic control loading system (EHCLS) of a flight simulator in the presence of a control mechanism kinetic parameter perturbation is proposed to improve the force tracking accuracy and guarantee robust stability of the EHCLS system. A double-loop model of the EHCLS, including the control mechanism and the hydraulic mechanism, is established and analyzed from the force-displacement impedance perspective. A force closed-loop parameter model of the EHCLS is identified by a recursive-least-squares (RLS) algorithm and its inverse model is designed using a zero phase error compensation technology to expand the frequency bandwidth of the force closed-loop system of the EHCLS. A μ theory of robust control is employed to design a stable controller for enhancing robust stability of the EHCLS in the presence of uncertainties of the inner loop, the control mechanism and the high frequency disturbance force. Simulation and experimental results show that the proposed hybrid control approach can greatly improve the control performance of the EHCLS by expanding the frequency bandwidth of the force closed-loop system and enhancing stability of the EHCLS, which can decrease displacement output response error of the EHCLS from 10.34% to 3.1%.