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Most manipulator motion controllers require joint velocity feedback. Whenever joint velocities are not measurable, they are estimated from the joint positions. However, ve-locity estimates tend to be inaccurate under low-speed motion or low sensor resolution conditions. Moreover, velocity estimators may either be susceptible to model uncertain-ties or introduce additional dynamics (e.g., phase lag) to the control loop. Consequently, direct substitution of velocity estimates into the controller results in the deterioration of the control peiformance and robustness margin. Therefore, this paper proposes a robust position-feedback motion controller which gets rid of the problems of uncompensated dy-namics and model uncertainties introduced by velocity estimators. Furthermore, a glob-ally asymptotically stable system, which is robust with respective to model parameter variations, is guaranteed. Theoretical analysis and experimental verifications are carried out. The results demonstrate that the proposed controller is robust and outperforms the conventional computed torque plus proportional integral differential (PID) controller. [ABSTRACT FROM AUTHOR]

Abstract: Modern robotic systems perform elaborate tasks in complicated environments and have close interactions with humans. Therefore fault detection and isolation (FDI) schemes must be carefully designed and implemented on robotic systems in order to guarantee safe and reliable operations. In this paper, we propose a hierarchical multiple-model FDI (HMM-FDI) scheme to detect and isolate actuator faults of robot manipulators. The proposed algorithm performs FDI in stages and refines the associated model set at each stage. Consequently only a small number of models are required to detect and isolate various types of unexpected actuator faults, including abrupt faults, incipient faults, and simultaneous faults. In addition, the computational load is alleviated due to the reduced-sized model set. The relation between the fault detection stage of the HMM-FDI scheme and the likelihood ratio test is explicitly revealed and theoretical upper bounds of the false alarm and missed detection probabilities are evaluated. Then we conduct experiments to demonstrate the ability of the HMM-FDI scheme in successful and immediate detection and isolation of actuator faults. [Copyright &y& Elsevier]