Fault-tolerant control scheme for a parallel robotic system with actuator fault

Abstract

Thanks to the rapid development of technology science and computer, robotic systems are widely used and play an increasingly important role in human life these days. They are used to perform complicated tasks in many fields such as industrial manufacturing, medicine, civil engineering, and aerospace. Nevertheless, in practice, there are some inevitable problems during the operation of robots, such as uncertainties, disturbances, and unmodeled dynamics and friction which may lead to a significant destabilization of the system. Furthermore, the occurrence of faults in systems seriously reduces the safety and reliability of robotic systems. This has caused great obstacles and challenges in designing controllers for robot manipulators. Therefore, the requirement for precise and robust control under the existence of uncertainties, disturbances and faults has attracted a massive number of researchers over the past decades. In this thesis, a fault-tolerant control (FTC) is proposed for a parallel robotic system. To obtain the robustness and a fast finite-time convergence, a nonsingular fast terminal sliding mode control (NFTSMC) is used. In addition, an extended state observer (ESO) is applied for the control scheme to estimate uncertainties, disturbances, and faults. To increase the convergence speed and alleviate the chattering phenomenon, a novel reaching law is proposed which gives the system a quick reaching speed. Finally, a novel FTC that ensures robustness to disturbances and faults is developed based on the NFTSMC, the ESO, and the proposed reaching law. Consequently, the proposed FTC has outstanding features such as high tracking performance, a decrease in the effects of disturbances and faults, a fast convergence speed in finite time, and less chattering. The simulation and experiment results demonstrate the efficiency of the proposed FTC compared to other control schemes. Besides. in the real life, the application of the Stewart Platform is very diverse and this research will investigate one of its applications, a haptic device. The haptic device based on the Stewart Platform is developed by a combination of an admittance model and the proposed FTC. The admittance model transforms a force to the desired trajectory while the proposed FTC is used to track the reference trajectory resulting from the admittance model. Accordingly, the haptic device is applied for teleoperation of a mobile robot with force feedback that helps the operator prevent the robot from colliding obstacles and improve the task performance. The experimental results will demonstrate the effectiveness of the proposed haptic device.