Robust adaptive control of revolute flexible-joint manipulators using sliding technique

Abstract

In this paper, we present a 3-step procedure to robustly control the revolute flexible-joint manipulator in the presence of parameter variations and bounded input disturbances such as torque ripples. By treating the difference of motor angle and link angle as the input to the rigid link part of the manipulator dynamics, our first step is to design a smooth adaptive reference signal for this input to globally stabilize the rigid subsystem. The second step is to drive the difference of motor and link angles to this desired reference signal exponentially by using sliding control. In the third step we exploit the model reduction capability of sliding control to perform the stability analysis. It is well-known that sliding control can reduce the system order by n if the number of control inputs is n. The exploitation of this property of sliding control makes our stability analysis a lot simpler than other approaches. Global stability in the sense of Lyapunov can be guaranteed and errors in link position and velocity are driven to zero when the system is in sliding mode. No weak elasticity assumption is needed.