Quasi fixed-time fault-tolerant control for nonlinear mechanical systems with enhanced performance

A novel quasi fixed-time prescribed performance control approach is investigated for mechanical systems with consideration of unknown dynamics and actuator faults. First, a fixed-time stable performance function is developed to quantitatively characterize the transient and steady-state responses. Then, a quasi fixed-time adaptive controller with a pretty simple computational structure is devised based on the developed performance function. Different from the existing finite-time/fixed-time control schemes, the prominent advantages are twofold: (1) no fractional-order state or output information is required, wherein, the order of the states involved in the developed controller just equals to one. (2) the fixed convergence time can be prespecified by the uses instead of relying on several parameters. Finally, applications to a 2-link robotic manipulator are employed to validate the effectiveness of the proposed control approach.