Passive fault-tolerant control design for robotic arm using robust fractional order sliding mode controller

Enhancing the technological autonomy, controllability, and intelligence of manipulator robots can enable companies to achieve their increasing production requirements. The demand for fault-tolerant control (FTC) research is increasingly realized in manipulator robots. This work describes the design and assessment of a Fractional-Order Sliding Mode Controller (FOSMC) for precise trajectory tracking of a PUMA560 robotic manipulator. The proposed control strategy is validated using a reduced-order three-degree-of-freedom (DOF) model and considering only the first three joints. The traditional Sliding Mode Control (SMC) is first implemented on a reference model in order to develop a performance baseline. Despite having sufficient robustness, SMC produces chattering and increases tracking inaccuracy due to its high-frequency switching. The authors overcome these constraints by employing a fractional-order sliding manifold, which enhances the dynamic responsiveness and smoothness of the control action. To improve robustness against time-varying disturbances and nonlinear uncertainty, the suggested FOSMC design includes fractional derivative filtering, equivalent control compensation, and a saturation-based switching function. Further results show that the FOSMC works better with additional disturbances and actuator faults. The work shows that the high-precision and fault-rejection capabilities of robotic manipulators can be successfully replaced by fractional-order control.