Composite QFT controller design for flexible joint robots

In this paper, a practical method to design a robust controller for a flexible joint robot (FJR) using quantitative feedback theory (QFT) is proposed. In order to control fast and slow dynamics of the FJR separately, composite control scheme is considered as the basis for the design. A simple PD controller is used to stabilize the fast dynamics, and a QFT controller is used in addition to an integral manifold corrective term to perform on the slow dynamics. Because of the nonlinear dynamics of FJR and the proposed controller scheme, linear time invariant equivalent (LTIE) technique is used to assign a nominal model for the system with uncertainties templates. Design of the QFT controller, as slow part of the composite control law is performed to compromise between the required bandwidth and the controller order. Comparisons with previous works on FJR, such as robust PID and composite H_infin, illustrate the effectiveness of the proposed controller to reduce the tracking errors despite actuator limitations