A Unified Finite-Time Sliding Mode Quaternion-based Tracking Control for Quadrotor UAVs without Time Scale Separation

This paper presents a novel design for finite-time position control of quadrotor Unmanned Aerial Vehicles (UAVs). A robust, finite-time, nonlinear feedback controller is introduced to reject bounded disturbances in tracking tasks. The proposed control framework differs conceptually from conventional controllers that utilize Euler angle parameterization for attitude and adhere to the traditional hierarchical inner-outer loop design. In standard approaches, the translational controller and the corresponding desired attitude are computed first, followed by the design of the attitude controller based on time-scale separation between fast attitude and slow translational dynamics. In contrast, the proposed control scheme is quaternion-based and utilizes a transit feed-forward term in the attitude dynamics that anticipates the slower translational subsystem. Robustness is achieved through the use of continuously differentiable sliding manifolds. The proposed approach guarantees semi-global finite-time stability, without requiring time-scale separation. Finally, numerical simulation results are provided to demonstrate the effectiveness of the proposed controller.