Modeling, control and experimental investigation of horizontal hydraulic flight motion simulator*

The horizontal hydraulic flight motion simulator (HHFMS) is widely applied in the hardware-in-the-loop (HWIL) simulation of the aircraft attitude attributing to high dynamic response and large power density when a heavy load is tested. In order to achieve a high-precision control performance of the HHFMS, some serious mismatched uncertainties consisting of nonlinear friction torque, unbalanced gravity torque, inertia variation and unmodeled dynamics have to be taken into account. In particular, gravity torque, as an asymmetrical load, will degrade the control performance at the starting moment. In this paper, via transforming mismatched uncertainties into matched uncertainties as a unified disturbance, a cascaded model was firstly established, which can not only avoid designing the complex virtual control laws but also help indirectly reduce the asymmetrical effect of gravity torque. Then, a linear extended state observer (LESO) based continuous sliding mode control (SMC) was proposed. LESO is expected to realize a good suppression of disturbance, as well as convenient acquisition of states signals such as velocity and acceleration. In addition to ensuring the control accuracy and the robustness, continuous SMC without sign function also frees from worrying about possible chattering. Moreover, a setting criterion of two parameters that satisfy Hurwitz's Condition in the third-order SMC was also provided. Finally, experimental investigation shows the effectiveness of dynamic modeling and the practicability of the proposed control method.