Research On Modeling And Fault-tolerant Control Of Redundant Robot Under Single Joint Failure

Redundant space manipulators own variety of advantage in avoiding singularityand obstacle, and is widely used accordingly. However, when a joint is locked inarbitrary position due to some failures, the7R manipulator degrades to a6Rmanipulator, which will exert detrimental influence upon for the function of themanipulator, even make the manipulator unable to accomplish the mission. In order tomake sure the manipulator with joint failure is still able to accomplish the fundamentalmissions, this work conduct the research focusing on the modeling and fault-tolerantcontrol for the redundant manipulator with single joint failure.Regarding to a specific kind of non-spherical-wrist redundant space manipulator,the fault-tolerant properties are analyzed under the situation of different configuration,different joint, different angle of the manipulator. According to these analysis, we canfind which joints have the major effect on the fault-tolerant properties, also can findwhich angle is the singularity position for the manipulator. Thus, it paves the way forthe kinematics analysis and fault-tolerant control.The universal D-H parameters table of the new6-DOF manipulator formed bylocking a joint in an arbitrary position is established; the inverse kinematics problem isanalyzed based on the unified D-H table; the specific examples are given. When one ofthe joints from1,2,6,7is failure, the D-H parameters are easy to obtain, the inversekinematics can be acquire using the matrix transformation. When one of the joints from3,4,5is failure, the configuration of the manipulator is not satisfied with the condition ofanalytic solution. The D-H parameters can be obtained with the help of the top view ofthe links projecting to the undersurface. The Offset modification method is presented tosolve the inverse kinematics equations for locking joint3,4or5. The specific examplesare given to verify the expressions.The parameters for dynamic property are deduced for the non-spherical-wristredundant space manipulator; the dynamic model is reconstructed under single jointfailure for this type of manipulator; ADAMS is used to verify the dynamic model. Whenone of the joints is failure, two related links would combined to be a new link, thedynamic parameters of the new link is related to the fault angle. We deduced all kinds ofthe expression of dynamic parameters under any joint failure, and built the dynamicmodel based on these expressions.Path planning based on self-motion is conducted for the non-spherical-wristredundant space manipulator with the single joint failure. Then, the tolerant controlmethod of H∞robust control is conducted on the redundant manipulator utilizing the dynamic coupling properties. At the end, MATLAB is used to verify the validity of thecontrol algorithm.The research result plays a great important role in the development of the spacestation manipulator: be able to assist the designer to project a manipulator avoiding theinappropriate position; be able to assist the real-time control of the manipulator; be ableto ensure the basic mission is accomplished under the single joint failure.