A methodology for synthesis and configuration design of metamorphic mechanisms is developed in this paper based on biological modeling and genetic evolution with biological building blocks The goal is to conceive an appropriate source-metamorphic-mechanism configuration when the multiple phases of kinematic functions are given The key enabler is the way of developing genetic evolution in modeling and design by capturing the metamorphic configuration characteristics With the unique characteristic of achieving multiple working-phase functions in a mechanism, the metamorphic mechanism possesses two features: one, the ametabolic feature referring to the specified working phases that can be accomplished by a number of traditional mechanisms; two, the metamorphic feature occurring in transition between different working phases, resulting in change of topology of the mechanism Based on this transition between phases, the concept of mechanism evolution is for the first time introduced in this paper based on biological building blocks in the form of metamorphic cells and associated intrinsic elements as the metamorphic gene This leads to development of cell evolution and genetic aggregation with mechanism decomposition and evolutionary operation based on mapping from the source-metamorphic mechanism to multiphase working configurations Examples are given to demonstrate the concept and principles

Biological Modeling and Evolution Based Synthesis of Metamorphic Mechanisms

A new family of reconfigurable parallel mechanisms with diamond kinematotropic chain

This paper presents a new way of structure composition of single-driven metamorphicmechanisms to develop a systematic and modularized structure synthesis methodology ofmetamorphic mechanisms based on augmented Assur groups (AAGs). Planar metamor-phic mechanisms can hence be constructed based on the developed AAGs by applying thestructure composition rule of general planar mechanisms formed by Assur groups (AGs).First, the one-mobility AAGs are introduced based on class II and class III AGs; thestructure formulation and composition methodology of planar metamorphic mechanismsare then proposed based on the AAGs, and the basic problems including mobility andsynthesis of constrained metamorphic working mobility-conﬁguration are investigated.This leads to the investigation of the degenerated equivalent AGs of AAGs in the meta-morphic process and the corresponding kinematic characteristics, providing referencesfor kinematic synthesis of metamorphic mechanisms. Further, a typical spatial metamor-phic group is introduced based on the concept of AAGs, and the structure formation andcomposition of spatial metamorphic mechanisms are presented. Examples show that bothplanar and spatial metamorphic mechanisms can be constructed by utilizing the one-mobility blocks extended from the AGs. [DOI: 10.1115/1.4006741]Keywords: augmented Assur group, structure synthesis, metamorphic degeneration, con-strained conﬁguration

Structure Synthesis of Single-Driven Metamorphic Mechanisms Based on the Augmented Assur Groups

This paper investigates reconfiguration of metamorphic mechanisms as a typical character of topological change of the mechanisms. Metamorphic mechanisms with reconfigurable topology provide changed topological states and subsequently change the mobility to give various subphase mechanisms. This paper investigates the built-in spatial modules extended with metamorphic characteristics to develop a metamorphosis operation based on building blocks in the form of spatial kinematic pairs and associated links. The composition principle of a metamorphic mechanism gives the mechanism characteristics and generates subphase working mechanisms. These working mechanisms change and develop into different forms in an evolutionary process of topological change and the proposed module composition principle in metamorphic mechanisms leads to the development of module topology variation and reconfiguration operations based on algebraic properties of Lie displacement-subgroup. The topology transformation is further used for configuration aggregation and degeneration and all the linkage operations are based on set theoretic, leading to topological reconfiguration of metamorphic mechanisms that maps a source metamorphic mechanism into various subphase configuration. This paper demonstrates the principle with case studies from a metamorphic mechanism generator to subphase mechanisms and vice versa.

Reconfiguration of Spatial Metamorphic Mechanisms

Background: Additive manufacturing (AM), or 3D printing, is drawing considerable contemporary interest due to characteristic of high material utilization, great flexibility in product design and inherent mouldless process. Arc-based additive manufacturing (AAM) is a promising AM method with high deposition rate and favorable build-up quality. Components made by AAM are fabricated through superimposed weld beads deposited from metal wire. Unlike laser-based additive manufacturing (LAM), AAM is more difficult to control. Because of the large energy input of the energy source and the liquidity of the melting metal material, bottleneck problems like shrinkage porosity, cracking, residual stresses and deformation occur. Resultant poor geometrical accuracy and mechanical property keep AAM from industrial application. Especially in the aerospace industry, structural and mechanical property specifications are stringent and critical. Method of approach: This paper presents a novel hybrid manufacturing method by using hot-rolling process to assist the arc welding to solve above problems. Initially, a miniature metamorphic rolling mechanism (MRM) was developed using metamorphic mechanism theory. Configuration and topology of the MRM can change according to the feature of the components to roll the top and lateral surfaces of the bead. Subsequently, three single-pass multi-layer walls were built respectively for comparison. Results: For top surface rolling, accumulated maximum height absolute error was reduced from 2.4 mm to 0.2 mm. For lateral surface rolling, maximum width absolute error was reduced from 0.45 mm to 0.12 mm. The thickness of each layer is 1.55 mm, controlled accurately under hybrid manufacturing method. The mechanical properties were improved by 4.0% for yield strength, 6.6% for ultimate tensile strength and 7.4% for elongation in travel direction compared with AAM specimens. The improved mechanical properties were superior to wrought material. In vertical direction, the improvement is 9.3% for yield strength, 1.8% for ultimate tensile strength and 10.4% for elongation. Conclusions: The rolled results show significant improvement in geometrical accuracy of the built features. Tensile test results demonstrate improvement in mechanical properties. The improved mechanical properties of rolled specimens are superior to wrought material in travel direction. Microstructure comparisons indicate columnar grains observed in vertical direction and fusion zones were suppressed. Eventually, fabrication of a large-scale aerospace component validates the feasibility of industry application for the hybrid manufacturing technology. Keywords: Arc-based additive manufacturing, hot rolling, metamorphic mechanism

Improvement in Geometrical Accuracy and Mechanical Property for Arc-Based Additive Manufacturing Using Metamorphic Rolling Mechanism

The metamorphic mechanism is defined by three characteristics in multi-stage,multi-topological structure and multi-degree of freedom.The properties and boundary of metamorphic mechanism are discussed and clarified for the mechanism with multi-degree of freedom,combined symmetrical mechanisms,and kinematropic mechanisms.A way to describe a metamorphic mechanism is proposed.A new concept of the work-stage mechanism and the origin mechanism for metamorphic mechanism,which can be expressed by metrics,are presented.Meanwhile,a mathematic model of a metamorphic mechanism is set up by a metamorphic equation,which indicates the relationship among a work-stage matrix,an origin metamorphic matrix and a metamorphic matrix.The type synthesis of metamorphic mechanism can be converted into solving the group of metamorphic equations,which leads to form all work-stage matrices,an origin metamorphic matrix and metamorphic matrices.Therefore,the metamorphic mechanism, including the series work-stage mechanism and origin mechanism, is readily located by the corresponding matrices.An example is given to demonstrate the process of the synthesis of a metamorphic mechanism.A groundwork for the theoretical basis of synthesis of metamorphic mechanisms is presented.

D. Wang

Papers

Theoretical foundation of metamorphic mechanism and its synthesis