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ABSTRACTIn this paper, an Improved Extended State Observer-based Finite-Time adaptive sliding mode control, is investigated for trajectory tracking control of a wheeled mobile robot. First, a novel finite-time adaptive sliding mode control, based on the fractional power of the sliding surface, is developed to deal with the chattering problem. Moreover, this strategy improves the convergence rate by adjusting online the switching part in sliding mode control. Second, an improved Non-linear ESO is employed to reconstruct and compensate for the unknown disturbances. To complete the trajectory tracking control, the kinematic algorithm is introduced. Theoretically, the proposed control scheme converges within finite-time thanks to the Lyapunov method. Finally, numerical simulations show the efficiency of the designed controller.

This paper investigates a Non-singular Fast Terminal Sliding Mode control (NFTSM) for Wheeled Mobile Robot (WMR) based on a Fixed-Time Extended State Observer (FT-ESO). On the basis of the detailed dynamic model for WMR and its actuators, a fast terminal sliding mode manifold is designed to ensure a quick convergence of the system variables without a singularity problem. Then, a fixed-time sliding mode controller is designed by using an appropriate reaching law. Moreover, a fixed-time ESO is designed to reconstruct and compensate for disturbances. The Lyapunov criterion is employed to demonstrate the suggested dynamic control strategy's fixed-time stability. In the outer loop, a classical kinematic controller is used to complete the trajectory tracking control for WMR. Numerical simulations are carried out to verify the efficiency of this strategy.

This paper presents a fuzzy adaptive sliding mode controller (FASMC) for electrically driven wheeled mobile robot for trajectory tracking task in the presence of uncertainties and disturbances. First, a finite-time kinematic controller is developed to compute the auxiliary velocity vector. Second, the FASMC, based on the nonlinear dynamic model of the robot and its actuators, is used to guarantee the stability and the convergence of the closed-loop system. Moreover, by employing the advantages of the fuzzy logic systems, the developed controller ensures the robustness of the system against dynamic disturbances and uncertainties, the smoothness of the computing voltage against the chattering phenomenon, and the optimal convergence of the velocity and posture errors. The Lyapunov theory is used to analyse the stability of this algorithm. In order to evaluate the effectiveness of the developed method, numerical simulations are done in the Mahlab/Simulink environment.

The like-rubber O-ring gaskets are widely used in hydraulic and pneumatic equipments to ensure the sealing of the shaft, the pistons and the lids. The correct operation is due to the good tightening of the joint that generate a sufficient contact pressure able to confine the fluids inside rooms or to prevent their passage from one compartment to another. Several studies are carried out to model the O-ring behavior but without taking in account the effect of the relaxation and creep phenomena. In this article, an axisymmetric finite element model is proposed to study the O-ring relaxation during the first hours of its installation in the unrestrained axial loading case. The results of the numerical model are compared with an analytical approach results based on the classical Hertzian theory of the contact. The effects of the o-ring mechanical and geometrical characteristics are examined. The contact stress profiles and the peak contact stresses are determined versus the time relaxation in order to specify the working conditions thresholds.