SUPER-TWISTING CONTROL WITH QUATERNION FEEDBACK FOR LINE-OF-SIGHT STABILIZATION AND TRACKING

Abstract

The majority of works in line of sight (LOS) stabilization and tracking using inertially stabilized platforms (ISP) apply simple linear controllers to achieve the required performance. Commonly, linear models such as a double integrator with an inertia gain are employed to describe the relationship between torque and position of the ISP joints. However, these techniques do not provide ideal disturbance rejection or finite-time convergence, which are desired characteristics for these type of systems in the context of high-accuracy applications. In this work, we propose a novel Sliding Mode Control (SMC) strategy for both stabilization and orientation tracking for a 3-DOF ISP. Full state feedback and output feedback cases are considered. In the latter case, a High-Order Sliding Mode observer (HOSMO) is proposed for the estimation of the ISP joint velocities. In each case, two Super Twisting Controllers (STC) are employed in a cascade topology. The inner controller ideally rejects the \textit{dynamic} disturbances acting on the ISP joints, reducing the system to an ideal double integrator. The outer controller ensures orientation tracking in quaternion space, ideally rejecting all remaining kinematic disturbances. Numerical simulations show the efficiency and performance of the proposed controller and observer.