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The robust non-singular fast terminal sliding mode (NFTSM) controller is adopted in this work to solve the problem of tracking trajectory of a mobile manipulator (MM) suffering from uncertainties. The NFTSM method has the capability to ensure convergence rate and to provide good tracking accuracy and robustness against external perturbations and parameter uncertainties (total disturbances). However, the NFTSM controller needs high discontinuous gain to reject the effect of strong disturbances, which results in vibrations in the steady-state and chattering in the control law. To solve these issues, an extended state observer–based NFTSM technique is proposed for n -degree of freedom (DoF) coupling MM. The proposed method is designed to approximate and compensate in real-time the uncertainties. It also ensures robustness against total disturbances, good convergence rate, and good tracking accuracy. The stability of the proposed control is also verified based on the Lyapunov theory. Experimental works are conducted on a 5-degree-of-freedom (5-DoF) MM where the results obtained demonstrate the effectiveness of the developed technique and prove the stability of the closed-loop system. [ABSTRACT FROM AUTHOR]

This work takes advantage of synergetic control theory and fractional calculus to develop and propose fractional synergetic control (FSC) strategy for Four Degrees of Freedom (4-DOF) robot manipulator. The proposed fractional synergetic control is designed to track a joint space as well as workspace desired trajectories. Fractional calculus gives more flexibility in the design since it has a wider stability region. Added to that, as stated in the literature, compared to a similar approach such as sliding mode control, the synergetic control approach converges faster to the equilibrium point, without chattering with a fast response. This paper proposes a new control strategy that takes advantage of fractional calculus and synergetic control theory. This proposed control strategy is tested experimentally on a 4-DOF manipulator to study the performance of the proposed control scheme. The stability of the closed-loop system is proved using the Lyapunov approach. The experimental results have shown that the proposed FSC design has achieved a good tracking performance. [ABSTRACT FROM AUTHOR]

This research work focuses on the need to provide a control scheme able to tolerate multiple robotic control challenges related to noisy measurements, unknown disturbances and uncertainties using the joint position measurements only. The proposed control scheme avails the advantages of integrating the Extended State Observer (ESO) with the synergetic control to operate n-DOF robot manipulators. The ESO is known as a powerful tool that can provide the online estimation of the uncertainties, nonlinearities and disturbances to be rejected or compensated by a feedback stabilizer. Correspondingly, implementing ESO in the control scheme makes it work with less knowledge of the system model dynamics and states. On the other hand, the synergetic control is a proper controller that can provide the desired tracking performance, but it has a high dependency on the system model which makes it sensitive to control parameters variation and operating conditions. Hence, combining both techniques in one scheme is a convenient approach to overcoming the shortcoming of each method. The proposed method is tested experimentally on the MICO 4-DOF Kinova robot and its performance is compared to the conventional synergetic control considering three case studies to validate its effectiveness. [ABSTRACT FROM AUTHOR]

Summary: Trajectory tracking of a mobile manipulator in the Cartesian space based on decentralized control is considered in this paper. The dynamic model is first rearranged to take the form of two interconnected subsystems with constraint flow, namely, a nonholonomic mobile platform subsystem and a holonomic manipulator subsystem. Secondly, using the inverse kinematics, the workspace desired trajectory of the mobile manipulator is transformed to the manipulator joint space as well as the platform desired trajectory. The kinematic control is developed from the desired trajectory of the platform. Then, the desired velocity is derived using the kinematic controller of the mobile platform, after which the velocity is used to obtain the control law of the mobile platform subsystem. Thirdly, the control law of the manipulator subsystem is developed based on the desired and real values of the manipulator, as well as the desired velocity. According to the Lyapunov stability theory, the proposed decentralized control strategy guarantees the global stability of the closed-loop system, and the tracking errors are bounded. Experimental results obtained on a 3-DOF manipulator mounted on a mobile platform are given to demonstrate the feasibility and effectiveness of the proposed approach. This is confirmed by a comparison with the computed torque approach. [ABSTRACT FROM AUTHOR]

This paper proposes a fractional-order controller for serial link manipulator to track desired trajectories in the joint space. The proposed control strategy consists of two main parts. First, a PID fractionional controller is developed using five parameters. By adding the extra degrees of freedom, the fractional order controller can achieve better control performance than the conventional PID controller. In contrast of the first part of the proposed controller which depends on the error between the desired and real values, the second part depends on the robot dynamics. This proposed control law guarantees the global asymptotic stability of the tracking errors. This global stability is proved using Lyapunov theory. The control strategy is tested ona 2 DOF robot manipulator. Simulation results and the comparison with the computed torque approach show the effectiveness of the approach with good tracking performance. Copyright © 2018 Praise Worthy Prize S.r.l. - All rights reserved. [ABSTRACT FROM AUTHOR]

This paper discusses the tracking trajectory in the workspace of rigid manipulators using distributed adaptive control strategy. This control strategy consists of two steps; first, the classical MIMO dynamical system is decomposed into a set of nonlinear interconnected subsystems. Each subsystem has one joint. Second, the distributed adaptive control strategy is introduced. This control strategy consists of controlling the last subsystem while assuming that the remaining subsystems are stable. Then, going backward to the second last subsystem, the same strategy is applied and so on until the first one. The system parameters are assumed to be unknown. An adaptive control is used to estimate these parameters. Indeed, the unknown parameters existing in the equation of motion of the last subsystem are first estimated and the control law is developed based on these estimated parameters. Then, going backward to the before last joint, the control law is developed using its own estimated parameters and the ones already estimated in the upper level subsystem. Asymptotical stability of the error dynamics is proved using Lyapunov approach. The developed algorithm is experimented on a 4 DOF hyper redundant articulated nimble adaptable trunk robot and compared with the classical computed torque approach. Good tracking in the workspace and joint space is obtained and effectiveness of the results is shown. [ABSTRACT FROM PUBLISHER]

This paper presents a nonlinear distributed control strategy for flexible-link manipulators to solve the tracking control problem in the joint space and cancel vibrations of the links. First, the dynamic of an n-flexible-link manipulator is decomposed into n subsystems. Each subsystem has a pair of one joint and one link. The distributed control strategy is applied to each subsystem starting from the last subsystem. The strategy of control consists in controlling the nth joint and stabilizing the nth link by assuming that the remaining subsystems are stable. Then, going backward to the (n − 1)th subsystem, the same control strategy is applied to each corresponding joint-link subsystem until the first. Sliding mode technique is used to develop the control law of each subsystem and the global stability of the resulting tracking errors is proved using the Lyapunov technique. This algorithm was tested on a two-flexible-link manipulator and gave effective results, a good tracking performance, and capability to eliminate the links' vibrations. [ABSTRACT FROM AUTHOR]