Non-Singular Fast Terminal Sliding Mode Control of 6-PUS Parallel Systems Based on Adaptive Disturbance Estimation

The 6-PUS (P: prismatic joint; U: universal joint; S: spherical joint) parallel mechanism study in this paper is the core mechanism used in the rehabilitation robot for children with cerebral palsy, which has a dynamic platform that acts on the pelvis of the child with cerebral palsy to provide support for the child. The complexity of the parallel mechanism leads to complex dynamics analysis and modeling errors, and the design of the controller must consider singularities, unknown external disturbances, stability, and so on. In response to the above considerations, this paper analyses the dynamics of a 6-PUS parallel mechanism and designs a non-singular fast terminal sliding mode control based on adaptive disturbance estimation to address the modeling errors and unknown external disturbance to which the system is subjected in practical applications. Feed-forward compensation of the controller is achieved by estimating the external disturbance and modeling errors to which the system is subjected with an adaptive disturbance estimation strategy. The non-singular fast terminal sliding mode controller is used to suppress the inherent jitter phenomenon of sliding mode control while ensuring the error between the actual trajectory and the desired trajectory converges quickly. Finally, the simulation results demonstrate that the designed controller can achieve highly accurate trajectory tracking despite the presence of modeling errors and external disturbances.