Adaptive Trajectory Tracking Control for Nonholonomic Wheeled Mobile Robots:A Barrier Function Sliding Mode Approach

The trajectory tracking control performance of nonholonomic wheeled mobile robots(NWMRs)is subject to nonholonomic constraints,system uncertainties,and external disturbances.This paper proposes a barrier function-based adaptive sliding mode control(BFASMC)method to provide high-precision,fast-response performance and robustness for NWMRs.Compared with the conventional adaptive sliding mode control,the proposed control strategy can guarantee that the sliding mode variables converge to a predefined neighborhood of origin with a predefined reaching time independent of the prior knowledge of the uncertainties and disturbances bounds.Another advantage of the proposed algorithm is that the control gains can be adaptively adjusted to follow the disturbances amplitudes thanks to the barrier function.The benefit is that the overestimation of control gain can be eliminated,resulting in chattering reduction.Moreover,a modified barrier function-like control gain is employed to prevent the input saturation problem due to the physical limit of the actuator.The stability analysis and comparative experiments demonstrate that the proposed BFASMC can ensure the prespecified convergence performance of the NWMR system output variables and strong robustness against uncertainties/disturbances.

Predefined-Time Sliding Mode Control with Prescribed Convergent Region

Dear editor,K1 In recent years,the finite-time and fixed-time control techniques have drawn much attention.This letter will present a new method for designing a predefined-time adaptive sliding mode controller with prescribed convergent region.More specifically,class function is used to construct the sliding function,and to achieve a real sliding mode,the function is also adopted in designing the adaptive gain without knowing the disturbance’s upper bound(DUB).Compared to the existing finite-time and fixed-time controllers,the key superiority of the proposed method is that the system can converge to a prescribed arbitrarily small region in predefined time irrespective of the initial condition.In addition,the control signal is bounded along the settling period,where the settling time instance can be estimated without conservation.

Precise trajectory tracking of mecanum-wheeled omnidirectional mobile robots via a novel fixed-time sliding mode control approach

This paper proposes a novel fixed-time sliding mode control approach for trajectory-tracking tasks of a mecanum-wheeled omnidirectional mobile robot.First,the idea of two-phase attractors is introduced into the domain of sliding mode control,and a new fixed-time sliding surface is proposed.Then,according to this sliding surface,a new type of nonsingular fast terminal sliding mode control algorithm is designed for the omnidirectional mobile robot,which can realize a fast fixed-time convergence property.The stability of the control system is proven scrupulously,and a guideline for control-parameter tuning is expounded.Finally,experiments are implemented to test the trajectory-tracking performance of the robot.Experimental results demonstrate the superiority of the proposed sliding surface and the corresponding control scheme in comparison with benchmark controllers.

Active steering control for vehicle rollover risk reduction based on slip angle estimation

In this study,a robust controller is proposed for rollover risk suppression in automatically-driven vehicles by reducing the lateral acceleration through a steer-by-wire system equipped on the vehicles.First,since the slip angle is difficult to measure directly,a sliding mode observer combining an add-on switching term with a linear observer is developed to provide more robust estimation of slip angle in the presence of system uncertainties.Second,an adaptive sliding mode control method is proposed,in which the control gain is adaptively tuned to compensate for the system uncertainties.Lastly,simulation is conducted and the results verify that the proposed estimator and controller can reduce the vehicle rollover risk efficiently and robustly.

Second-order terminal sliding mode control based on perturbation estimation for nanopositioning stage

This study proposes a robust second-order terminal sliding mode control with perturbation estimation(2OTSMCPE)strategy with application to trajectory tracking control of the flexure-based nanopositioning system.The proposed controller advantages not only lie on its finite-time convergence but also can provide a high tracking precision with a chattering alleviation which is attend by employing a second-order sliding surface with the switching function.The model of the piezo-driven nanopositioning system is presented first.Second,the sliding variable is designed such as proportional-integral-derivative form to enhance the dynamic response of the control system.Then,a non-singular terminal sliding function(NTSM)is used to achieve the finite-time convergence of the linear sliding variable.Next,a perturbation estimation technique is integrated with the control structure for online estimation of the system uncertainties,thus the prior knowledge of the bounds of system uncertainties are not needed in the proposed control design.Afterwards,the theoretical analysis of the 2OTSMCPE with stability proof is investigated herein.Finally,the system performance with the proposed controller is experimentally verified.The results reveal that the 2OTSMCPE has stronger robustness and also has smoother control signals in comparison with both conventional sliding mode control and the NTSM controller.