Research On Fault-tolerant Control Of 7-DOF Redundant Manipulator

The study of redundant manipulators is at the forefront of robotics research.When a manipulator has n independent joints ans the dimension of task space is m and m<n,then the manipulator is redundant.The redundant manipulators currently studied are 7-DOF manipulators,and 7-DOF manipulators have one more degree than the 6-DOF manipulaiotrs,so this extra degree of freedom can be utilized to compensate for the lack of 6-DOF manipulators.Especially in some specific places such as aviation,deep sea,nuclear power plants,etc.,when a joint of a manipulator in a work task fails,it is difficult to repair the manipulator in the first time.Therefore,it is hoped that after a joint failure,the manipulator can continue to complete the original operation task.After the failure of the single-joint axis of the 7-DOF manipulator,it degenerates into a 6-DOF manipulator,and the original operation task can still be completed,thereby achieving the fault-tolerant control of the 7-DOF redundant manipulator.The first problem needs to be solved of the fault-tolerant control is the inverse kinematics of 7-DOF manipulators.The solution of the inverse kinematics is related to the configuration of the manipulator.Most researchers focus on anthropomorphic manipulator without joint offsets,and few researchers focus on anthropomorphic manipulator with joint offsets.In this paper,a self-developed anthropomorphic manipulator with a joint offset(mainly the front threeaxis bias)is used.The angle of the first joint is used as the redundancy parameter,and a combination of algebraic method and geometric method is proposed.Given the end pose,by changing the angle value of the first joint,different analytical solutions can be obtained to achieve the self-motion of the manipulator.The method has good real-time performance and high precision and is suitable for practical use in engineering.Then,in order to achieve the kinematic optimization,this paper proposes a series of faulttolerant optimization indicators including fault-tolerant space and reduced manipulability.And the influence of different indicators on the manipulative performance of the manipulator is analyzed.Considering that when a single joint fails,the other joints should still have strong operational performance.In this paper,the reduced manipulability is taken as the optimization index to realize the kinematic optimization.By adjusting the angle of the first joint,a set of kinematic inverse solutions is obtained to maximize the degraded operability.Finally,this optimization method was verified in the self-built simulation platform.Through the kinematic optimization,it can be ensured that the manipulator still has strong operational performance when a single joint fails.After the failure of the single joint,this per firstly uses the three-dimensional convex hull algorithm to analyze the influence of different joint failures on the manipulable space of the manipulator,and whether the target task is still in the operable space of the manipulator.If the target task is not in the reduced operational space,the manipulator is directly notified that the original operation task cannot be completed.If the target task is still in the reduced operational space,the kinematic replanning is achieved based on different joint failures.For the first four joint failures,the kinematic inverse solution of the reduced manipulator can still be obtained by analytical method,and the other joints can only be solved by the numerical method in the form of Jacobian iteration to complete the original operation task.To verify the effectiveness and feasibility of the fault-tolerant control scheme,this thesis is verified by the simulation platform on matlab and the physical motion platform of robot motion control based on EtherCAT.In the simulation,a simulation platform is built based on the 3D model of manipualtos,and linear motion and self-motion are completed on the simulation platform.Then the effectiveness of the kinematics optimization algorithm is verified by the fault-tolerant optimization index.Finally,the fault-tolerant control of the 7-DOF redundant manipulator is realized on the simulation platform.The simulation is carried out on the physical experiment platform,which proves the feasibility of the fault-tolerant control of the 7-DOF redundant manipulators.