Composite-H∞ controller synthesis for flexible joint robots

In this paper a robust composite control algorithm is proposed for flexible joint manipulators, with the emphasis on satisfying control effort limitations. An H∞ framework is used for the slow subsystem controller design, instead of robust PID synthesis introduced in the literature. Linear identification techniques are used to represent the nonlinear dynamics of the system into a linear model plus multiplicative uncertainty. An H∞ controller is designed in the framework of composite control, in order to optimize the required control effort, along with satisfying robust stability and desirable performance. The effectiveness of the proposed control law is compared with other methods through a simulation study. The comparison results show a significant improvement in control effort, while satisfying both stability and performance requirements.