Robust Translational Force Control of Multi-Rotor UAV for Precise Acceleration Tracking

In this article, we introduce a translational force control method with disturbance observer (DOB)-based force disturbance cancellation for precise 3-D acceleration control of a multi-rotor unmanned aerial vehicle (UAV). The acceleration control of the multi-rotor requires conversion of the desired acceleration signal to the desired roll, pitch, and total thrust. However, because the attitude dynamics and the thrust dynamics are different, simple kinematic signal conversion without consideration of those difference can cause serious performance degradation in acceleration tracking. Unlike most existing translational force control techniques that are based on such simple inversion, our new method allows controlling the acceleration of the multi-rotor more precisely by considering the dynamics of the multi-rotor during the kinematic inversion. By combining the DOB with the translational force system that includes the improved conversion technique, we achieve robustness with respect to the external force disturbances that hinder the accurate acceleration control. \mu -analysis is performed to ensure the robust stability of the overall closed-loop system, considering the combined effect of various possible model uncertainties. Both simulation and experiment are conducted to validate the proposed technique, which confirms the satisfactory performance to track the desired acceleration of the multi-rotor. Note to Practitioners - This article presents a method for controlling the acceleration of a multi-rotor accurately under the presence of translational force disturbance. Unlike the existing methods, the new signal conversion technique that considers the dynamics of the multi-rotor in the process of converting the target translational acceleration signal to the target roll, pitch, and thrust signal enables a more accurate translational force control. The DOB structure applied to the translational force control system overcomes the acceleration control performance deterioration caused by external translational force disturbance. Through the combination of the two techniques, the acceleration of the multi-rotor can be accurately controlled not only in the nominal environment but also in the presence of translational force disturbance.