Reconfiguration Identification And Kinematic Coupling Analysis For Reconfigurable Mechanisms

Reconfigurable mechanisms have varying configurations and variable numbers and types of mobility to meet the requirements of multiple tasks,multiple working conditions and multiple functions in comparison to conventional mechanisms with fixed mobility.This dissertation deals with the key issues relevant to reconfiguration identification and kinematic coupling of reconfigurable mechanisms when these mechanisms are applied in advanced manufacturing and next generation robotic system,and focuses on reconfiguration identification of single-loop reconfigurable mechanisms,reconfiguration identification of multiloop reconfigurable mechanisms and kinematic coupling analysis of reconfigurable parallel mechanisms.The main contents of this dissertation are summarized as follows:(1)Based on the DH parameters,the closure equations of three types of Schatzinspried 7R reconfigurable mechanisms are constructed.The configuration spaces of the mechanisms can be obtained by using the numerical approach of singular value decomposition.Then,the identification of motion branches in the three types of the mechanisms ars analyzed respectively and the motion ruled surfaces of the coupler links are gernerated to study the motion characteristics in the mechanism.Taking these novel reconfigurable mechanisms as examples,this dissertation demonstrates the general process of reconfiguration identification in single-loop reconfigurable mechanisms.(2)Compared to single-loop reconfigurable mechanisms,multiloop reconfigurable mechanisms have more loops and more complex structures.As a result,reconfiguration identification of multiloop reconfigurable mechanisms is still a challenge.Meanwhile,it is difficult to apply methods for reconfiguration identification of single-loop reconfigurable mechanisms to multiloop reconfigurable mechanisms.In this dissertation,the first-and second-order kinematics-based constraint system of multiloop reconfigurable mechanisms is established by introducing the sequential operation of Lie bracket in a bilinear form.Then,the second-order constraint equations can be expressed in matrix form and simplified easily by substituting the first-order constraint equations.This first-and second-order kinematics-based constraint system lays the foundation for reconfiguration identification of multiloop reconfigurable mechanisms.(3)Based on the first-and second-order kinematic constraint system of multiloop reconfigurable mechanisms,this dissertation analyzes reconfiguration identification of the queer-square mechanism,which is a typical multiloop reconfigurable mechanism.By obtaining the solutions of the constraint system,six motion branches of the queersquare mechanism are identified and their corresponding geometric conditions are presented.Moreover,the initial configuration space of the mechanism is attained.In a word,a method based on first-and second-order kinematic constraint equations for reconfiguration identification of multiloop reconfigurable mechanisms is proposed.(4)The first-and second-order kinematic constraint equations can also be applied to reconfiguration identification of single-loop reconfigurable mechanisms.Through the analyses of reconfiguration identification of several single-loop reconfigurable mechanisms,the correctness of this method for identifying different motion branches is verified.Meanwhile,the universal applicability of the first-and second-order kinematic constraint equations in reconfiguration identification is proved by comparing with other analysis results.(5)There exsists kinematic coupling between limbs in reconfigurable parallel mechanisms,which makes it difficult to analyze these mechanisms with existing methods for reconfiguration identification.This dissertation presents a new method to deal with kinematic coupling between limbs based on the transferability of limb constraints and their degree of relevance to the reconfigurable platform constraints.Setting up the geometric model of the mechanism and adopting the screw system theory to verify the degree of relevance between limb constraint wrenches and platform constraint wrenches,the transferability of limb constraints is revealed.The final resultant wrenches and twists of the end-effector are then obtained.Finally,the proposed method is extended to parallel mechanisms with planar n-bar reconfigurable platforms,spherical n-bar reconfigurable platforms and other spatial reconfigurable platforms.