Design of a mixed fuzzy controller for multiple-input multiple-output systems

Multiple-input multiple-output (MIMO) systems usually have characteristics of nonlinear dynamics coupling. Therefore, the difficulty in controlling MIMO systems is how to overcome the coupling effects between the degrees of freedom. The computational burden and dynamic uncertainty associated with MIMO systems make model-based decoupling impractical for real-time control. This work develops a mixed fuzzy controller (MFC) to solve this problem and improve control performance. This study first designs a traditional fuzzy controller (TFC) from the viewpoint of a single-input single-output (SISO) system for controlling each degree of freedom of a MIMO system. Then, an appropriate coupling fuzzy controller is also designed according to the characteristics of the system's dynamics coupling and incorporated into a TFC to compensate for coupling effects between the degrees of freedom. This control strategy can not only simplify the implementation problem of fuzzy control, but also improve control performance. The state-space approach for analyzing the stability of fuzzy control systems is applied to evaluate the stability and robustness of this intelligent mixed fuzzy controller. To verify the applicability of the proposed mixed fuzzy controller, this work presents a two-link robotic manipulator with a complex dynamic model for a MIMO system to evaluate the stability and robustness of the MFC by numerical simulation, and to examine the control performance by comparing the simulation results of the MFC with those of a TFC for this MIMO system.