The robustness of adaptive controllers with respect to uncertainty is examined. The uncertainties include bounded input disturbances, unknown and time-varying plant parameters, and unmodeled dynamics. A simple example shows instability of a recent manipulator control scheme in the presence of bounded disturbances. The adaptive laws for updating the controller parameters are modified so that instabilities are counteracted and robustness is guaranteed. >

Instability analysis and robust adaptive control of robotic manipulators

https://research-information.bris.ac.uk/ws/files/74384029/ROBOT_D_12_00342_RAS_nasir.pdf

A novel robust adaptive control algorithm with finite-time online parameter estimation of a humanoid robot arm

The robustness of adaptive controllers with respect to uncertainty is examined. The uncertainties include bounded input disturbances, unknown and time-varying plant parameters, and unmodeled dynamics. A simple example shows instability of a recent manipulator control scheme in the presence of bounded disturbances. The adaptive laws for updating the controller parameters are modified so that the instabilities are counteracted and robustness is guaranteed. >

A new adaptive-control scheme for direct control of manipulator end effector to achieve trajectory tracking in Cartesian space is developed in this article. The control structure is obtained from linear multivariable theory and is composed of simple feedforward and feedback controllers and an auxiliary input. The direct adaptation laws are derived from model reference adaptive control theory and are not based on parameter estimation of the robot model. The utilization of adaptive feedforward control and the inclusion of auxiliary input are novel features of the present scheme and result in improved dynamic performance over existing adaptive control schemes. The adaptive controller does not require the complex mathematical model of the robot dynamics or any knowledge of the robot parameters or the payload, and is computationally fast for on-line implementation with high sampling rates. The control scheme is applied to a two-link manipulator for illustration.

Direct adaptive control of manipulators in Cartesian space

Adaptive control of robotic manipulators in task space coordinates is considered in this paper. A new composite adaptive control law, which uses the prediction error and tracking error to drive parameter estimation, is developed based on sliding mode and a general Lyapunov-like concept. It is shown that global stability and convergence can be achieved for the adaptive control algorithm. The algorithm has the advantage that inverse of Jacobian matrix and the bounded inverse of the estimated inertia matrix are not required. The algorithm is further modified so as to achieve robustness to bounded disturbances. A simulation example is provided to demonstrate the performance of the proposed algorithm. >

M. Vukobratovi

Papers

Paper: An approach to adaptive control of robotic manipulators