Research Article Adaptive Observer-Based Output Feedback Control for Two-Wheeled Self-Balancing Robot Ines Jmel, 1 Habib Dimassi , 1,2 Salim Hadj Said, 1 and Faouzi M’Sahli 1 1 University of Monastir, Ecole National d’Ing´ enieurs de Monastir, LAS2E 5019, Monastir, Tunisia 2 University of Sousse, Institut Sup´ erieur des Sciences Appliqu´ ees et de Technologie de Sousse, Sousse, Tunisia Correspondence should be addressed to Habib Dimassi; dimassihabib2013@gmail.com Received 2 June 2019; Accepted 10 December 2019; Published 29 January 2020 Academic Editor: J.-C. Cort´ es Copyright © 2020 Ines Jmel et al. is is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Inthispaper,anoutputfeedbackcontrolapproachbasedonanadaptiveobserverisdevelopedforthetwo-wheeledself-balancing robotsubjecttounknownparameters(withnonlinearparameterization).Firstly,ahighgaincontrolmethodwithstatefeedbackis proposed.en,anadaptiveobserverisdesignedtoestimatetheunknownstateandtheunknownbodymassoftherobotwhich influences the height of the center of mass. Next, the adaptive observer is combined with the designed high gain controller: a Lyapunov-basedstabilityanalysisoftheclosedloopsystemisdevelopedtoestablishtheconvergenceofthetrackingerroraswell as estimation and adaptation errors. Simulation results assert the performance of the developed tracking control scheme for the two-wheeled self-balancing robot subject to mass variation. 1. Introduction Control problem investigation on self-balancing robots has grown over the past decade in a number of robotic labo- ratories around the world. is is due not only to the dy- namics of the inherent instability, nonlinearity, and under- actuation of these systems but also to the presence of dis- turbance and parameter uncertainties. ese robots are characterized by their ability to balance only on two wheels and to turn on the spot. erefore, many researchers have conducted extensive studies, which can be proven how successful they were, to master the problems of modeling and control and appli- cation of the self-balancing robots. In [1], a robust tracking control scheme, employing the sliding mode method and based on nonlinear observer to estimate the unknown disturbances, is developed for two-wheeled self-balancing robot. In [2], the authors have proposed a nonlinear dis- turbance observer to estimate the uncertain disturbance torques with exponential convergence. More recently, a robusttrackingcontrolschemebasedonafuzzydisturbance observer was proposed for wheeled mobile robots with slipping and skidding in [3]. e sliding mode control (SMC) has proved its ro- bustnessonthecontroloftheself-balancingrobots.In[4], arobustslidingmodecontrollerhasbeendesignedtodeal with disturbances and instability of the self-balancing robot. An adaptive neural sliding mode controller for nonholonomic wheeled mobile robots with external dis- turbancesandmodeluncertaintieswasinvestigatedin[5]. e robustness and the efficiency of this control system were proven by the simulation results. Furthermore, a slidingmodecontrollerwasdevelopedin[6]toachievea trajectory tracking of mobile robots with parametric variations and external disturbances. e asymptotic convergence of tracking errors was shown using Lyapu- nov’s theory. More recently, in [7], a new sliding mode control strategy based on a high-order disturbance ob- server has been developed for a mobile wheeled inverted pendulum.eoreticalstabilityresultsofbothestimation and tracking errors have been established and validated experimentally. On the contrary, thanks to its robustness in pre- serving system performances; adaptive control repre- sents the main motivation of several works notably the controlofself-balancingrobots.In[8],theauthorshave Hindawi Mathematical Problems in Engineering Volume 2020, Article ID 5162172, 16 pages https://doi.org/10.1155/2020/5162172