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A two-axis gimbaled stabilization system in air vehicles must stabilize the line of sight of the payload toward a target against the external motion induced by air vehicle maneuvering and aerodynamic forces. The target tracking and pointing performances of the air vehicles are largely affected by air vehicle motion decoupling capability. In this work, the H ∞ controller design is carried out for a two-axis gimbal system. The plant model is generated using experimental frequency response data and mathematical formulation of the system. The mixed sensitivity problem is posed and weighting functions are selected so that they not only fulfill all the design goals but also accommodate the modeling uncertainties. The stabilization loop is designed and implemented in digital signal processor-based hardware for only one axis (in azimuth). [ABSTRACT FROM AUTHOR]

SUMMARY The mixed sensitivity minimization problem is revisited for a class of single-input-single-output unstable infinite dimensional plants with low order weights. It is shown that H ∞ controllers can be computed from the singularity conditions of a parameterized matrix whose dimension is the same as the order of the sensitivity weight. The result is applied to the design of H ∞ controllers with integral action. Connections with the so-called Hamiltonian approach are also established. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Real-time hybrid simulation (RTHS), dividing the emulated structure into numerical substructures (NS) and physical substructures (PS), is a powerful technique to obtain responses and then to assess the seismic performance of civil engineering structures. A transfer system, a servo-hydraulic actuator or shaking table, is used to apply boundary conditions between the two substructures. However, the servo-hydraulic actuator is inherently a complex system with nonlinearities and may introduce time delays into the RTHS, which will decrease the accuracy and stability of the RTHS. Moreover, there are various uncertainties in RTHS. An accurate and robust actuator control strategy is necessary to guarantee reliable simulation results. Therefore, a mixed sensitivity-based H∞ control method was proposed for RTHS. In H∞ control, the dynamics and robustness of the closed-loop transfer system are realized by performance weighting functions. A form of weighting function was given considering the requirement in RTHS. The influence of the weighting functions on the dynamics was investigated. Numerical simulations and actual RTHSs were carried out under symmetric and asymmetric dynamic loads, namely sinusoidal and earthquake excitation, respectively. Results indicated that the H∞ control method used for RTHS is feasible, and it exhibits an excellent tracking performance and robustness. [ABSTRACT FROM AUTHOR]