Feedback linearization control for a tandem rotor UAV robot equipped with two 2-DOF tiltable coaxial-rotors
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ORIGINAL ARTICLE
Feedback linearization control for a tandem rotor UAV robot equipped with two 2‑DOF tiltable coaxial‑rotors Xiongshi Xu1 · Keigo Watanabe1,2 · Isaku Nagai1 Received: 4 July 2020 / Accepted: 1 October 2020 © International Society of Artificial Life and Robotics (ISAROB) 2020
Abstract In this paper, computed torque control as one method of feedback linearization techniques is considered for an unmanned aerial vehicle (UAV) robot that has two tiltable coaxial rotors so as to realize multifunctional locomotion modes, where each rotor has 2-DOF tilt mechanism. First, a dynamical model of such an UAV robot is derived following the Newton–Euler law. Next, under the assumptions that the anti-torque of the tiltable coaxial rotors is zero and the gyro moment effect of the tiltable coaxial rotors can be ignored, a computed torque controller is derived, because the resultant model of the UAV robot can be simplified to a fully actuated model, which has six motion inputs and six generalized coordinate outputs. In addition, a control allocation problem of the system, in which the control inputs designed using the dynamical model are assigned to all motors for tilting the rotor as well as rotating it, is solvable by using a Moore–Penrose pseudo-inverse, where a coordinate transformation is used to simply the allocation problem. Finally, some simulations are demonstrated to verify the effectiveness of the computed torque control strategy for the robot. Keywords Coaxial rotor · Tilt mechanism · Computed torque control · Control allocation problem
1 Introduction Many unmanned Aerial vehicle (UAV) robots are going to be applied for human transportation, delivery of goods, infrastructure inspection, etc. [1, 2]. However, it needs for a multi-rotor type UAV to tilt the attitude of the UAV robot during level flight motion, because all the rotors in conventional multi-rotor type UAVs are fixed to the fuselage. In addition, it is difficult for drones, such as conventional quadrotors and hexacopters, to maintain a stable flight in the proximity inspections of bridges and buildings, due to the same reason.
* Xiongshi Xu [email protected]‑u.ac.jp Keigo Watanabe [email protected]‑u.ac.jp Isaku Nagai [email protected]‑u.ac.jp 1
Graduate School of Natural Science and Technology, Okayama University, Okayama 700‑8530, Japan
BAICIRS, Beijing Institute of Technology (BIT), Beijing, China
2
Therefore, several studies have been already carried out by introducing a tilt rotor mechanism to ensure fault tolerance in the event of a rotor failure, or to realize a task by using a specialized motion in the air such as dexterous motion during infrastructure inspections. For example, Rihani et al. [3] proposed to use a 2-DOF tilt mechanism for each rotor in a quadrotor, where 12 motors were mounted totally to improve system reliability and increase actuator bandwidth, but they did not discuss on a control allocation problem. Ryll et al. [4, 5] introduced a 1-DOF tilt mechanism for each rotor in a quadrotor equipped 8 motors tot
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