Research On Motion Control Of Underwater Multi-legged Robots

In recent years,the development of offshore wind power has promoted the applications of underwater multi-legged robots in the maintenance of underwater equipment.Underwater multi-legged robot is a kind of bionic underwater robots which can not only crawl on the surface of underwater structures but also perform underwater tasks.This dissertation studies the motion control of underwater multi-legged robot from the following aspects:Firstly,the motion control tasks of underwater multi-legged robot are analyzed,and then both the tracking control model of walking leg considering actuator faults and the bilateral teleoperation model of manipulator considering input saturation are established.For the underwater multi-link system whose dynamics characteristics are similar to those of underwater multi-legged robot’s walking leg and manipulator,a prescribed performance controller and a barrier Lyapunov function controller are designed based on performance constraints control method,moreover,a finite-time controller and a fixed-time controller are proposed based on finite-time control method.Numerical simulations of those controllers are presented.Combining the advantages of performance constraints control method and finite-time control method,prescribed performance terminal sliding surface(PPTSS)is proposed and the mathematical definition of PPTSS is given.Secondly,the fault-tolerant tracking control issue of underwater multi-legged robot’s walking leg is studied based on PPTSS.An interval type-2 fuzzy neural network approximator is designed to tackle the uncertainties including actuator faults,hydrodynamic disturbances,model uncertainties and unmodeled dynamics.A nonsingular PPTSS is proposed and a nonsingular performance constraints fixed-time fault-tolerant tracking control strategy is designed for underwater multi-legged robot’s walking leg.To further reduce the steady-state errors,an improved integral PPTSS is proposed and an integral performance constraints fixedtime fault-tolerant tracking control strategy is designed.The effectiveness of control strategies based on PPTSS is demonstrated by the simulation results of underwater multi-legged robot’s walking leg fault-tolerant tracking control.Finally,the anti-saturation bilateral teleoperation issue of underwater multi-legged robot’s manipulator is studied based on PPTSS.To handle the transient input saturation of bilateral teleoperation system,an auxiliary saturation compensation system is designed and the system is transformed into an equivalent one without input saturation through auxiliary error variables.A novel PPTSS is proposed and a symmetrical performance constraints fixed-time antisaturation bilateral teleoperation strategy is designed for underwater multi-legged robot’s manipulator.What’s more,an improved asymmetrical PPTSS is proposed and an asymmetrical performance constraints fixed-time anti-saturation bilateral teleoperation strategy is designed.The simulation results of underwater multi-legged robot’s manipulator anti-saturation bilateral teleoperation demonstrate the effectiveness of the control strategies based on PPTSS.