Finite-time Fuzzy Fault-tolerant Control Of A Manipulator Considering Output Constraint

With the development of modern society,the application of robots is becoming more and more widespread,and the application scenarios are also becoming more diverse.Some special work scenarios have higher requirements for the reliability and safety of robots.For example,space robots and deep-sea robots require long-term stable operation in harsh working environments,and service-oriented robots that interact frequently with humans need to maintain a safe and reliable state.As one of the most important executing mechanisms of robots,robotic manipulators are widely used in various fields of robot equipment.However,during the working process,robotic manipulators inevitably encounter problems such as actuator faults,unknown dead-zones,and constraints.In addition,the model parameters of robotic manipulators are often inaccurate or difficult to obtain.Finally,in addition to ensuring the high reliability and safety of the robotic manipulators during its operation,improving its convergence speed and control accuracy is one of the urgent issues that need to be addressed to achieve the current high standard working requirements of the robotic manipulators.In this paper,a finite-time adaptive fuzzy fault-tolerant control method for a manipulator with output constraints is presented,which combines adaptive control,disturbance observer(DO),fault-tolerant control(FTC),barrier Lyapunov function(BLF)and finite-time backstepping.The main research results of this article are as follows:(1)An adaptive fault-tolerant control method for rigid manipulators with time-varying output constraints and actuator faults is presented.Firstly,Adaptive technique is used to estimate the loss of system effectiveness caused by actuator faults and compensate for the losses caused by actuator faults.Secondly,the logarithmic BLF is designed to constrain the output of the system within the preset bounds,and combined with the finite-time backstepping method,the convergence speed of the control system is improved.Moreover,adaptive fuzzy control is adopted to dynamically estimate the system,so that the control law does not require model parameter information,which increases the portability of the control method.The simulation results show that the proposed control method can achieve better tracking performance without violating the output constraints in case of actuator faults.(2)A finite-time fault-tolerant output constraint control scheme based on command filtered is presented,considering the actuator faults of the manipulators and the unknown dead-zones characteristics of the mechanical structure.Firstly,in the case of actuator faults and unknown dead-zones,adaptive compensating control is used to ensure the control effect of the controller.Secondly,a finite-time command filter with error compensation is designed,which solves the problem of "explosion of complexity" in the backstepping design of controller and saves the burden of on-line calculation.The simulation results show that the proposed control method can estimate and compensate the actuator faults to varying degrees for a manipulators with unknown dead-zones,so that the system output can track the given trajectory in a finite time.(3)The influence of unknown non-linear disturbance on the system is further considered,and a fault-tolerant output constraint control scheme for a manipulators based on disturbance observer is presented.Firstly,the fuzzy logic system is combined with the disturbance observer to estimate unknown external nonlinear disturbances.Secondly,the combination of fuzzy disturbance observer and FTC technique reduces the influence of external disturbance on the slope of unknown dead-zones and the estimation of actuator faults degree,and makes the control system have better tracking effect,and improves the accuracy of the disturbance observer estimation.Then,the finite-time technique is introduced into the controller design,which makes the system response speed faster than that under the asymptotic stability control method.The simulation results show that the proposed method has faster response speed and better tracking performance when the manipulators have different degrees of actuator faults and unknown dead-zones.