Control for Pitch Motion of Underwater Gliding Snake-Like Robot Based on Disturbance Observer

Aiming at the problem that the underwater gliding snake-like robot has input constraints and unknown external disturbance during implementing gliding, the backstepping control method based on Nussbaum function and nonlinear disturbance observer is proposed to improve its pitching motion tracking performance. The vertical plane motion of the under-actuated underwater gliding snake-like robot is analyzed and conditionally simplified, and the corresponding kinematics and dynamic equations are obtained. Nussbaum function and hyperbolic tangent function are combined to deal with the problem of system control input saturations, which avoids the controller singularity of the latter, and the nonlinear disturbance observer is used to effectively observe and compensate the external complex disturbance. The backstepping controller is designed for pitching motion tracking, where the computational expansion caused by the virtual item in the backstepping method is eliminated by the dynamic surface method. The controller designed following Lyapunov stability theory ensures that the system can achieve global uniform stability of velocity and position semaphore. The results show that compared with the traditional backstepping method, the proposed scheme can improve the response time and error convergence rate to some extent, and the nonlinear disturbance observer has a good performance for observation of complex disturbances. The designed controller can effectively track the longitudinal motion of the robot under the unknown disturbance with strong robustness. © 2020, Editorial Office of Journal of Xi'an Jiaotong University. All right reserved.