Structural Design Method And Performance Study Of Metamorphic Parallel Mechanism

Topological and geometrical representation of kinematic structure of mechanisms is essential in mechanism study. It's also the fundamental basis in innovation design of mechanical systems. This dissertation proposes new approaches for structural representation of mechanisms including the new developed metamorphic mechanisms. These approaches are capable to accurately represent the nature of connection among various links of a mechanism. A new methodology for mechanism design inspired by metamorphosis is introduced based on the genesis of metamorphic mechanism and the outcomes of extensively studied parallel mechanisms. New parallel mechanisms with interesting performances and a family of metamorphic parallel mechanisms are presented.The new approaches for structural representation of mechanisms integrate the essential information about which link is connected to which other link by what type of joint into the augmented adjacency matrix and three-dimensional (3D) adjacency matrix. The 3D adjacency matrix is originated from the link-to-link adjacency matrix but extends the two-dimensional link-to-link adjacency matrix by integrating 16 bits binary strings. The advantages of the 3D adjacency matrix for topological and geometrical representation of kinematic structure of mechanisms are elucidated with examples. Unified EU-elementary matrix operation for representation of transformation between parent phase and subphase (offspring phase) in metamorphic mechanisms is developed. The information of the annexed links is represented by the entry with element-1 which is embodied in the unified EU-elementary matrix operation. The matrix operation between the parent phase and a subphase can be further represented in abstract form by the digraph representation to illustrate the process of phase change.Generalized metamorphic kinematic pairs with metamorphosis are extracted based on fundamentals of metamorphic mechanisms. An 8-bar metamorphic kinematic chain is evolved from the design of the metamorphic kinematic pair. The structural evolution resorting to link annex of the metamorphic chain is addressed and a novel overconstrained 6-bar linkage is obtained in the study of phase change. The study further presents enumeration of subphases of the metamorphic chain based on Burnside's lemma and Polya enumeration theorem in combinatorics with consideration of kinematic geometry. Geometric constraints induced bifurcated motions of a metamorphic parallel mechanism are investigated based on screw theory, leading to clarification of essences of geometric induced bifurcation and the link annex induced topological variation.Based on the study of mechanisms and art, new 3-DOF parallel mechanisms with spherical metamorphic chains as chain-legs are evolved form origami. Equivalent kinematic pair of the spherical chain in each chain-leg is derived in terms of equivalent screw system. Taking the concept of generalized kinematic pair, the equivalent serial kinematic chain of the chain-leg is derived, and the motion characteristics of the parallel mechanisms are revealed based on screw theory. Kinematic analyses of the two new parallel mechanisms are addressed and workspace of the parallel mechanism with three chain-legs is investigated. The singularity criterion for each 3-DOF parallel mechanism is investigated based on constraint analysis and dependency of the corresponding screw system containing only line vectors. The existing conditions of the singular configuration and the ratio of design parameters have been further identified to reveal the platform inner singularity.Metamorphic modules with reconfigurability are constructed based on dependency of line vectors and degeneration of screw system corresponding to the evolved kinematic chains that only contain revolute joints. The design of metamorphic module further reveals the inherent properties of generalized kinematic pair extracted from origami. According to the geometric condition and constraints that must be met by proper limbs, two 3SurPSur metamorphic parallel mechanisms with subphases which can implement pure translational motion and pure rotational motion are constructed respectively. A prototype of the 3SurPSur metamorphic parallel mechanism is fabricated to implement phase change and verify the reconfigurability.