Fixed-Time Adaptive Fuzzy Constraint Control for Stochastic Nonlinear Systems With Dead Zone and Its Application to Flexible-Joint Robot

This paper studies a fixed-time (FT) adaptive fuzzy constraint control strategy based on the command filtered control technique for a class of strict-feedback stochastic nonlinear systems (SNSs) subject to dead-zone input. Firstly, by combining the command filtered backstepping technique with FT control, the proposed strategy not only reduces the computational burden and compensates for filtering errors, but also guarantees FT stability for the SNSs. Secondly, by designing a nonlinear transformation function that only depends on the output of the SNSs, the asymmetric time-varying output constraint problem for the SNSs is solved. This approach reduces the complexity of system stability analysis and relaxes the constraint on the initial output value. Thirdly, the fuzzy logic system is effectively utilized to counteract the detrimental effects caused by unknown stochastic disturbances. Furthermore, by utilizing the boundary information of dead-zone slopes, the adverse impact of the dead-zone input on control efficacy is effectively compensated. Finally, the effectiveness of the proposed control strategy is validated through simulations of a flexible-joint robot system.