A Hybrid Controller Enhancing Transient Performance for an Aerial Manipulator Extracting a Wedged Object

Autonomous aerial manipulation requires the capa- bility to handle inevitable dynamic changes during physical inter- action. Previously, very few studies have addressed the stability and transient performance of the scenarios involving abrupt changes in dynamics. This paper proposes a hybrid controller enhancing transient performance for an aerial manipulator extracting an object wedged in a static structure. This task incurs a significant jump in the interaction force on the end-effector so that the analysis using the concept of hybrid dynamical systems is required. To demonstrate the dynamic characteristics of the object-extracting aerial manipulator, we derive the dynamic equations for two flight modes, i.e., free-flight and object- extracting, and the rule of state jumps. Also, we design control strategies which enhance the transient performance during flight mode transition. Then, the stability of the proposed control law is proven, and the overshoot reduction after the object extraction is analyzed. To show the improved performance, we conduct plug-pulling experiments with a quadrotor-based aerial manip- ulator using the proposed controller and two different existing controllers. The comparative results confirm that our controller enables the aerial manipulator to maintain its stability after the flight mode transition and shows the best transient performance in overshoot minimization among three controllers. Note to Practitioners—The motivation for this article is the desire to prevent unexpected collisions between obstacles and an aerial manipulator after the vehicle extracts a wedged object from a static structure. To resolve this problem, we present a hybrid control method for such tasks while avoiding an excessive overshoot after the extraction. This method can be utilized in Manuscript received 5 April 2023; accepted 11 May 2023. This article was recommended for publication by Associate Editor Z. Pei and Editor M. Dotoli upon evaluation of the reviewers’ comments. This work was supported in part by the Unmanned Vehicles Core Technology Research and Development Program through the National Research Foundation of Korea (NRF); and in part by the Unmanned Vehicle Advanced Research Center (UVARC) funded by the Ministry of Science and Information and Communication Technol- ogy (ICT), Republic of Korea, under Grant NRF-2020M3C1C1A01086411. (Corresponding author: H. Jin Kim.) Jeonghyun Byun and H. Jin Kim are with the Department of Aerospace Engineering, Automation and System Research Institute (ASRI), and the Institute of Advanced Aerospace Technology (IAAT), Seoul National University, Seoul 08826, South Korea (e-mail: quswjdgus97@snu.ac.kr; hjinkim@snu.ac.kr). Inkyu Jang is with the Department of Aerospace Engineering and the Automation and System Research Institute (ASRI), Seoul National University, Seoul 08826, South Korea (e-mail: leplusbon@snu.ac.kr). Dongjae Lee is with the Department of Aerospace Engineering and the Insti- tute of Advanced Aerospace Technology (IAAT), Seoul National University, Seoul 08826, South Korea (e-mail: ehdwo713@snu.ac.kr). This article has supplementary material provided by the authors and color versions of one or more figures available at https://doi.org/10.1109/ TASE.2023.3277508. Digital Object Identifier 10.1109/TASE.2023.3277508 tasks involving abrupt changes in the dynamic model such as retrieving a device attached to a tall structure, reclaiming an object in disaster recovery, or pulling a plug out of a socket. Unlike existing methods, the proposed method simultaneously considers the stability and the initial overshoot right after pulling the object out of the structure, by employing a disturbance observer (DOB) in a hybrid control structure. It can be utilized for the aerial manipulator to avoid collision in a narrow space or to keep it in a safe operation envelope even though the task requires producing a relatively large pulling force.