Type Synthesis And Evaluation Of Redundant Parallel Machanism With Actuation Fault Tolerance

The movement of the parallel mechanism depends on the joints driving action of multiple branches.A drive failure in any branch drive would adversely affect the operation of the parallel mechanism.It is the problem that needs to study the actuation fault tolerance for reducing the influence of the drive failure on the machanism.Therefore,the problems of drive failure and mechanism actuation fault tolerance are very important issues in the research field of the parallel mechanism.Driving force invalidity is one of the main drive failures of the parallel mechanism,and it is very necessary to study the driving force invalidity and improve the actuation fault tolerance of the parallel mechanism accordingly.The object of this dissertation is to establish a new index that can evaluate the influence of the branch driving force invalidity on the operability of the parallel mechanism based on the screw theory and the index,which could lay a foundation of the evaluation for the actuation fault tolerance of the parallel mechanism.Moreover,a practical type synthesis method of parallel mechanism is proposed based on the screw theory,which can synthesize a new type of redundant parallel mechanism with actuation fault tolerance for the branch driving force invalidity,which provides a reference for studying the actuation fault tolerance of the parallel mechanism.Firstly,the common drive failures and causes of parallel mechanisms are sorted out in this dissertation,meanwhile common actuation fault tolerance methods for drive failures are summarized.The properties of the constraint space and the driving space of the parallel mechanism is studied based on the screw theory,the operability failure index reflecting the failure degree of the driving force based on the Jacobian matrix is proposed.Secondly,the operability invalidity analysis of the non-redundant parallel mechanism is carried out with the case of 3-RPS parallel mechanism.The common forms of actuation wrenches are also summarized,which are prepared for the type synthesis method proposed later.The actuation“identity”condition is proposed for analyzing the driving force failure based on the characteristics of the actuation space.Furthermore,a type synthesis method of redundant parallel mechanisms with actuation fault tolerance for driving force failure is proposed.Then,parallel mechanisms with 3R-DOF and 2R1T-DOF are selected to conduct type synthesis analysis for the driving force invalidity of any single branch based on the proposed type synthesis method,And two new types of 3R-DOF and one new type of 2R1T-DOF redundant parallel mechanisms are obtained.Finally,The obtained redundant parallel mechanisms,(4-RRR)_I,4-UPS/S and 3-UPU/UPS redundant parallel mechanisms are selected as cases.The kinematics models of these parallel mechanisms are established.The actuation fault tolerance of the cases is analyzed by using the proposed operability invalidity index,when the driving force of any single branch fails.