Dual-fixed-time second order sliding mode control for hybrid robots with input saturation

This paper investigates the high precision anti-saturation control for hybrid robots with uncertainties and input saturation via a dual-fixed-time second order sliding mode control (DFx-SOSMC) strategy. With the construction of the fixed-time disturbance observer (FxDOB), lumped uncertainties such as external disturbances and modeling errors of the system are effectively estimated and compensated in a fixed time. A specific fixed-time convergent auxiliary system (FxCAS) is established by introducing fractional exponential powers with an auxiliary variable to address input saturation. By incorporating the estimation of FxDOB and the state of FxCAS into the sliding mode surface, the suggested DFx-SOSMC ensures the simultaneous fixed-time convergence of observation error and tracking error in the hybrid robot system, enhancing robustness while weakening sliding mode control chattering. Lyapunov analysis is applied and the global fixed-time convergence of the DFx-SOSMC algorithm is theoretically verified, with an upper bound on the convergence time independent of the initial conditions. Simulations and experiments conducted on industrial hybrid robots confirm the accuracy and feasibility of the presented DFx-SOSMC method.