Robust H∞ Computed Torque Control of Flexible Joint TVC Systems

Abstract

Abstract Flexible Joint Thrust Vector Control (FJ-TVC) is often used to control the orientation of spacecraft and aircraft since there is no thrust loss in the nozzle and a longer lifespan is possible due to the absence of moving parts. However, the structure of the flexible material and some parameters in the system introduce uncertainties, such as misalignment of the pivot point on the nozzle and nonlinear behavior in the elastomer material, that impact negatively on high precision and tracking control. In this paper a computed torque control law together with a PD controller is first designed but the results are not sufficiently robust and stability problems could arise in the resulting control loop. To counter such effects, an H∞ based computed torque controller is designed based on norm bounded model uncertainty, where Monte Carlo based simulations have been used to model the effect of the uncertainties. Finally, the effectiveness of the new design is demonstrated by a simulation study.