Sliding Mode Control For Trajectory Tracking Of Uncertain Robot Manipulators

Robot manipulators are dynamic systems with highly nonlinear and strong couplings.Highprecision trajectory tracking control of robot manipulators is a popular topic in the control field and has been widely studied in the past years.It is well-known that sliding mode control is insensitive to unmodeled dynamics and bounded external disturbances.Moreover,it is an effective robust control for trajectory tracking of systems with features such as easy implementation,simple structure and strong robustness.Since the uncertain part of robot manipulators includes the joint acceleration information,the most existing terminal sliding mode controls and fast terminal sliding mode controls suffer from the algebraic loop problem.The dissertation proposes several sliding mode controllers for high-precision trajectory tracking of uncertain robot manipulators.The main works can be described as follows.Taking into account the algebraic loop of the most commonly-used sliding mode control in the trajectory tracking of robot manipulators,the third chapter develops a linear sliding mode control and terminal sliding mode control without algebraic loop for uncertain robot manipulators.The convergence characteristics of the proposed two sliding mode controls are analyzed in detailed and the explicit convergence time of terminal sliding mode control is given.The proposed scheme provides an effective method to solve the algebraic loop for the sliding mode control of uncertain robot manipulators.The fourth chapter proposes a novel terminal sliding mode control constructed by a powerlike function featuring with amplifying small errors.It is proved that the proposed terminal sliding mode control first ensures that the sliding variable converges to the origin within a finite time and then the tracking errors on sliding phase converge globally to an arbitrary small domain of the origin within a finite time and thereafter arrive at the origin asymptotically.The appealing feature of the proposed control is that its convergence time can be explicitly given.The proposed sliding mode control offers an alternative improved design for trajectory tracking of dynamical systems with features such as easy implementation,simple structure and strong robustness.The fifth chapter develops a fast terminal sliding mode control.Combined the fast terminal sliding surface and the exponential reaching law,the proposed sliding mode control further improves the convergence performance of the trajectory tracking robotic system in the reaching phase and the sliding phase.Compared with the terminal sliding mode control proposed in Chapter 4,the proposed fast terminal sliding mode control has faster convergence speed.A fixed-time sliding mode controller is developed for trajectory tracking of robotic systems in Chapter 6.It is proved that the proposed fixed-time sliding mode control first ensures that the sliding variable converges to the origin within a fixed time and then the tracking errors on sliding phase converge globally to the origin within a fixed time.The appealing feature of the proposed fixed-time sliding mode control is that its convergence time can be explicitly given and is independent of the initial states of uncertain robot manipulators.The proposed fixed-time sliding mode control has better convergence performance in comparison with the finite-time sliding mode control.The finite/fixed-time stabilities of the all proposed sliding mode controllers are proved by the finite-time and fixed-time Lyapunov stable theory.The numerical simulations and experimental results of the robot manipulators verify the effectiveness of the proposed controllers including fast transient and high steady-state tracking precision.