Robust Control of Hand-held Concentric-tube Robot Based on Nonlinear Disturbance Observer

When performing nasal operations utilizing a hand-held Concentric-tube Robot (CTR), the mechanical error and tremor in hand movements significantly compromise procedural outcomes. To mitigate the susceptibility of a hand-held CTR to internal error and external disturbance, a control framework based on nonlinear disturbance observer (NDO) is proposed to enhance control accuracy and stability. Initially, a control algorithm based on inverse Jacobian is present to facilitate trajectory tracking control and resist external interference. Then, a NDO is designed to estimate hardware error in the driving module, with a feedforward control block implemented to attenuate the influence of internal error. Simulation experiments on trajectory tracking were conducted. The external disturbance was effectively reduced, and internal error was decreased by more than 60%, thereby affirming the effectiveness of the devised robust control framework based on NDO.