A Variable Structure Observer for the Control of Robot Manipulators (original) (raw)
Related papers
Observer Based Variable Structure Controller Nonlinear Systems
This paper discusses a new observer based intelligent variable structure state tracking controller for nonlinear systems in which the states of the subsystems are assumed to be unavailable for measurement. It is assumed the functions of the system and the interaction terms are unknown. Ultimately boundedness of both observer and tracking errors, boundedness of the controller and observer parameters, Robustness against approximation error and external disturbances are the merits of the observer-based controller design procedure. The simulation results illustrate the good performance of the proposed algorithm.
Robotica, 2015
SUMMARY In this work, we propose the development and the corresponding stability analysis of a novel, observer-based output feedback (OFB), tracking controller for rigid-link robot manipulators. Specifically, a model-independent variable-structure-like observer in conjunction with a desired dynamic compensation technique have been utilized to remove the link velocity dependency of the controller formulation. Asymptotic stability of the observer--controller couple is then guaranteed via Lyapunov-based arguments. An adaptive controller extension is also presented to illustrate the expansiveness of the proposed scheme. Experimental studies performed on a two-link planar robot with dynamical uncertainties are included in order to demonstrate the performance and feasibility of the proposed method.
Observers in the control of rigid robots
Lecture Notes in Control and Information Sciences, 1991
In this paper we propose a simple observer, with linear and decoupled structure, for the estimation of the generalized velocities of a rigid robotic manipulator. High-gain output injections are used in the attenuation of the effects of the non-linearities characterizing the dynamic behaviour of the robot upon the dynamic behaviour of the estimation errors. The Liapunov stability theory has been used to prove the practical stability of the error dynamics, in case of open-loop observers, and the asymptotic stability of the closed loop robotic system, in case of observer-based control laws.
The problem of observer design for nonlinear systems has got great attention in the recent literature. The nonlinear observer has been a topic of interest in control theory. In this research, a modified robust sliding-mode observer (SMO) is designed to accurately estimate the state variables of nonlinear systems in the presence of disturbances and model uncertainties. The observer has a simple structure but is capable of efficient observation in the state estimation of dynamic systems. Stability of the developed observer and its convergence is proven. It is shown that the estimated states converge to the actual states in a finite time. The performance of the nonlinear observer is investigated by examining its capability in estimation of the motion of a two link rigid-flexible manipulator. The observation process of this system is complicated because of the high frequency vibration of the flexible link. Simulation results demonstrate the ability of the observer in accurately estimating the state variables of the system in the presence of structured uncertainties along with different initial conditions between the observer and the plant.
Nonlinear disturbance observer design for robotic manipulators
Control Engineering Practice, 2013
Robotic manipulators are highly nonlinear and coupled systems that are subject to different types of disturbances such as joint frictions, unknown payloads, varying contact points, and unmodeled dynamics. These disturbances, when unaccounted for, adversely affect the performance of the manipulator. Employing a disturbance observer is a common method to reject such disturbances. In addition to disturbance rejection, disturbance observers can be used in force control applications. Recently, research has been done regarding the design of nonlinear disturbance observers (NLDOs) for robotic manipulators. In spite of good results in terms of disturbance tracking, the previously designed nonlinear disturbance observers can merely be used for planar serial manipulators with revolute joints (Chen, W.H., Ballance, D.J., Gawthorp, P.J., O'Reilly, J., 2000. A nonlinear disturbance observer for robotic manipulators. IEEE Trans. Ind. Electron. 47, 932-938), (Nikoobin, A., Haghighi, R., 2009. Lyapunov-based nonlinear disturbance observer for serial n-link manipulators. J. Intell. Robot. Syst. 55,[135][136][137][138][139][140][141][142][143][144][145][146][147][148][149][150][151][152][153]. In this paper, a general systematic approach is proposed to solve the disturbance observer design problem for robotic manipulators without restrictions on the number of degrees-of-freedom (DOFs), the types of joints, or the manipulator configuration. Moreover, this design method does not need the exact dynamic model of the serial robotic manipulator. This method also * Corresponding author, Tel.: +1 (647)978-0140 unifies the previously proposed linear and nonlinear disturbance observers in a general framework. Simulations are presented for a 4-DOF SCARA manipulator to show the effectiveness of the proposed disturbance observer design method. Experimental results using a PHANToM Omni haptic device further illustrate the effectiveness of the design method.
Meccanica, 2016
This paper deals with trajectory tracking control for rigid robot manipulators with model uncertainty and subject to external disturbances. The approach suggested herein does not require velocity measurement, because these robots are not equipped by tachometers for velocity measurement. For this purpose, two observers are proposed. The first is a velocity observer to estimate the missing velocity, and the second one is a disturbance observer to estimate the disturbance. Thereafter, these observers are integrated with the controller. Furthermore, semi-global asymptotic stability conditions of the composite controller consisting of a nonlinear controller, the velocity observer and the disturbance observer are established, and an estimate region of attraction is also given. This proof is based on Lyapunov theory. Finally, simulation results on two-links manipulator are provided to illustrate the effectiveness of the velocity observer based control using disturbance estimation (namely VOBCDE), when the Coulomb and viscous friction is considered as an external disturbance.
DISTURBANCE OBSERVER-BASED TRAJECTORY FOLLOWING CONTROL OF NONLINEAR ROBOTIC MANIPULATORS
2011
Robotic manipulators are highly nonlinear and coupled dynamic systems, which may be subject to different types of unknown disturbances such as joint frictions and end-effector external payloads. Such disturbances, when unaccounted for, cause poor tracking performance of the robot and may even destabilize the robot control system. In this paper we propose a novel nonlinear control scheme for robotic manipualtors subject to disturbances using the concept of disturbance observer-based control by modifying the disturbance observers proposed in [1] and . The proposed control scheme and disturbance observer guarantee global asymptotic position and disturbance tracking and remove the previous restrictions on the number of degrees of freedom (DOFs), joint types, or manipulator configuration. Computer simulations are presented for a 4-DOF SCARA manipulator to show the effectiveness of the proposed disturbance observer-based control scheme.
Reduced-order observer for dynamic output feedback of variable-structure control systems
2008 International Workshop on Variable Structure Systems, 2008
In this paper nonlinear non-affine systems, for which the state vector is not completely available, are considered. It is assumed that the system's mathematical model is perfectly known and conditions hold, which assure the global injectivity of any required state transformation. The proposed strategy combines two approaches and designes a reduced-order observer, which relies on second order sliding mode differentiators just to provide the necessary, otherwise unavailable, artificial outputs exploited to steer to zero a lower dimensional estimation error vector under an simplified set of convergence conditions.
Design of a nonlinear disturbance observer
IEEE Transactions on Industrial Electronics, 2000
This paper presents a new disturbance observer based on the variable structure system theory for minimum-phase (with respect to the relationship between the disturbance and output) dynamical systems with arbitrary relative degrees. The model uncertainties and the nonlinear parts of the system are merged into the disturbance term and are regarded as a part of the disturbances. The upper and lower bounds of the disturbance are assumed to be known as a priori information. Simulation results are presented to show the robustness and effectiveness of the new disturbance observer. Experiment results show the practicality of the new observer.