Force sensorless fixed-time model-free impedance coordination control for uncertain underwater teleoperation systems

Abstract New robust fixed-time model-free impedance controllers are proposed in this paper for coordination control of underwater teleoperation systems with system model uncertainties and unknown external underwater interference. Firstly, the transparency and the flexibility of the master-slave manipulators are improved without force sensor, respectively. A new terminal sliding mode force observer is designed to estimate force in fixed time by designing observer parameters. Moreover, time delay estimators are designed to compensate for the effect of model uncertainties and unknown external disturbances. Furthermore, a novel nonsingular integral terminal sliding mode (NITSM) surface and fixed-time controllers are proposed, so that master-slave coordination control can be obtained in fixed time with zero errors. The coordination performance and global stability of the underwater teleoperation systems are proved with the Lyapunov stability theory. Finally, simulation results highlight the feasibility of the proposed control scheme. The results show the super performance of the position and force coordination control for the underwater teleoperation systems.