Metamorphic Joints Research Articles

Design, Configuration Synthesis, and Experimental Study of Side-Rolling Metamorphic Mechanism for Metal Additive Manufacturing

Arc additive manufacturing (AAM) has the advantages of fast deposition speed and good surfacing quality. It is a promising additive manufacturing (AM) method. However, arc additive manufacturing is difficult to use widely in industry due to its poor deformation, microstructure, and mechanical properties. Since the mechanical properties of materials can be greatly improved by rolling, a method for configuration synthesis of the side-rolling mechanism by using metamorphic mechanism theory is presented in this paper. Firstly, by analyzing the operational demands of the side-rolling mechanism, we obtained the motion cycle diagram for the metamorphic mechanism in addition to the corresponding equivalent resistance gradient matrix. Secondly, according to the motion cycle diagram and equivalent resistance gradient matrix of the metamorphic mechanism, the structure and constraint form of the metamorphic joints were established, and the relationship between the force variation and the structure and the constraint form of the metamorphic joints was also obtained. Then, the structures of all 12 corresponding constrained metamorphic mechanisms were synthesized. Ultimately, one among the twelve mechanisms was chosen as the side-rolling metamorphic mechanism. The topological transformation of its working configuration was examined. The results confirmed the feasibility and practicality of the proposed structural synthesis method in this study.

Task-Oriented Topology System Synthesis of Reconfigurable Legged Mobile Lander Integrating Active and Passive Metamorphoses

To explore hostile extraterrestrial landforms and construct an engineering prototype, this paper presents the task-oriented topology system synthesis of reconfigurable legged mobile lander (ReLML) with three operation modes from adjusting, landing, to roving. Compared with our preceding works, the adjusting mode with three rotations (3R) provides a totally novel exploration approach to geometrically matching and securely arriving at complex terrains dangerous to visit currently; the landing mode is redefined by two rotations one translation (2R1T), identical with the tried-and-tested Apollo and Chang’E landers to enhance survivability via reasonable touchdown buffering motion; roving mode also utilizes 2R1T motion for good motion and force properties. The reconfigurable mechanism theory is first brought into synthesizing legged mobile lander integrating active and passive metamorphoses, composed of two types of metamorphic joints and metamorphic execution and transmission mechanisms. To reveal metamorphic principles with multiple finite motions, the finite screw theory is developed to present the procedure from unified mathematical representation, modes and source phase derivations, metamorphic joint and limb design, to final structure assembly. To identify the prototype topology, the 3D optimal selection matrix method is proposed considering three operation modes, five evaluation criteria, and two topological subsystems. Finally, simulation verifies the whole task implementation process to ensure the reasonability of design.

Practical Structural Design Approach of Multiconfiguration Planar Single-Loop Metamorphic Mechanism with a Single Actuator

As a type of multiconfiguration mechanism that can operate in an under-actuated state, metamorphic mechanisms were proposed more than two decades ago and attracted significant interest. Studies on structural synthesis of metamorphic mechanisms tend to focus more on metamorphic techniques and the structural synthesis of source mechanisms for metamorphic mechanisms. By designing different constraint architectures of metamorphic joints, multistructures can be obtained from the same source metamorphic mechanism. To determine the constraint architectures of metamorphic joints and their different assembly combinations, a kinematic status matrix and a corresponding constraint status matrix are constructed based on the metamorphic cyclogram of a source mechanism. According to the equivalent resistance gradient model and the constraint status matrix, an equivalent resistance matrix for the metamorphic joints is proposed. A structural synthesis matrix of the metamorphic mechanism is then obtained from the equivalent resistance matrix by deducing the constraint form vectors of the metamorphic joints. Furthermore, a kinematic diagram synthesis of the source metamorphic mechanism of a planar single-loop metamorphic mechanism is proposed, which is based on only the 14 one- or zero-degrees-of-freedom linkage groups. The entire structural design method of a metamorphic mechanism is based on the structural synthesis matrix and is presented as a systematic process. Finally, the proposed structural design approach is illustrated by two examples to verify its feasibility and practicality. This study provides an effective method for designing a practical multi-mobility and multiconfiguration planar single-loop metamorphic mechanism with a single actuator.

Research on Dynamics Modeling and Simulation of Constrained Metamorphic Mechanisms

This paper presents a method for establishing a unified dynamics model of constrained metamorphic mechanisms. Based on the equivalent resistance, the influences of geometric constraints and/or force constraints on metamorphism are discussed, and the kinematic characteristics of metamorphic joints are described and analyzed in detail. On this basis, the metamorphic configurations of augmented Assur groups can be classified into three types, including non-collision, internal collision and external collision configurations, and the configuration complete dynamics models of augmented Assur groups are established. Then, the dynamics models of active parts, Assur groups and augmented Assur groups are summarized into a unified mathematical framework, and the unified dynamics model of constrained metamorphic mechanisms can be obtained. Based on the research mentioned above, the initial conditions of all components and the motion law of the active parts are given. The motion laws of all components, the driving force/torque of the active parts and the constraint force/torque of the metamorphic joints can be obtained by iteration and solution based on the theory that velocity and acceleration are same in an extremely brief period. Taking the planar double-folded metamorphic mechanism and the metamorphic nipper swing mechanism as examples, the computer numerical analysis and dynamic simulation are carried out to verify the correctness and effectiveness of the proposed theory and method.

Reconfiguration-aimed and manifold-operation based type synthesis of metamorphic parallel mechanisms with motion between 1R2T and 2R1T

This paper presents a novel approach for synthesizing metamorphic parallel mechanisms with an ability of reconfiguring motion between 1R2T and 2R1T based on quotient operation of manifolds. With the theoretical fundamentals of Lie subgroups and submanifolds, the principle of configuration change is proposed in the synthesis with a submanifold switch, that reconfigures the mechanism to provide a various motion, leading to reconfiguration of the metamorphic parallel mechanism platform. The synthesis starts from a quotient operation of manifolds to generate a manifold subchain, the synthesis of these subchains is aiming at the reconfiguration of the platform between 1R2T and 2R1T based on the same composition form of submanifold subchains with various motions. Three new subchains are synthesized with metamorphic joints, revolute joints and prismatic joints based on manifold-operation, which leads to a configuration switch of each subchain in terms of the phase change of the metamorphic joint with respect to relative positions of rotational axis and links, resulting in different constraints and motions of the subchains, leading to a platform with an ability to realize multiple motions. The design of new metamorphic joints is a key factor to realize the different motion of platform in terms of the principle of configuration change and manifold-operation. Further, the special geometrical properties and several specific phases of the metamorphic joint are analyzed. The approach of synthesis based on manifold-operation provides a distinct rationale for this paper. Under this guidance, analysis of motion and constraint conditions transmitted to the platform through subchains is essential, to enable the reconfiguration aimed type synthesis of metamorphic parallel mechanisms.

Method for configuration synthesis of metamorphic mechanisms based on functional analyses

Metamorphic mechanisms could change their configuration continually to accommodate different task requirements. From the perspective of the entire working cycle, the metamorphic mechanism is responsible for the synthesis of all working-phase mechanisms. The source-metamorphic mechanism, which is obtained by the aggregation of a series of working-phase mechanisms, is focal to the configuration synthesis of these mechanisms and to metamorphic joint design. The metamorphic modes can be classified into five types, including the geometry, motion, force, driving joint, and combined metamorphic mode. Based on the above, a method for configuration synthesis of metamorphic mechanisms is introduced herein. Firstly, the number and types of the degrees-of-freedom (DOFs) of the source-metamorphic mechanisms can be acquired based on an aggregated operation applied on the DOFs of the working-phase mechanisms. The possible configurations of the source-metamorphic mechanism can be obtained using traditional synthetic methods. The metamorphic joints and source-metamorphic mechanisms are then obtained by selecting and integration operations. Finally, the entire working process of the metamorphic mechanism is described using metamorphic equations. The mechanism of a loading manipulator for a garbage truck was developed to demonstrate the proposed method. The results showed that the proposed method is practical and simple.

A representation of the configurations and evolution of metamorphic mechanisms

Abstract. Metamorphic mechanisms are members of the class of mechanisms that are able to change their configurations sequentially to meet different requirements. The paper introduces a comprehensive symbolic matrix representation for characterizing the topology of one of these mechanisms in a single configuration using general information concerning links and joints. Furthermore, a matrix representation of an original metamorphic mechanism that has the ability to evolve is proposed by uniting the matrices representing all of the mechanism's possible configurations. The representation of metamorphic kinematic joints is developed in accordance with the variation laws of these mechanisms. By introducing the joint variation matrices derived from generalized operations on the related symbolic adjacency matrices, evolutionary relationships between mechanisms in adjacent configurations and the original metmaorphic mechanism are made distinctly. Examples are provided to demonstrate the validation of the method.

Task-based structure synthesis of source metamorphic mechanisms and constrained forms of metamorphic joints

One of the key works in applied metamorphic mechanism design is to obtain the source metamorphic mechanism and the constraint forms and structures of metamorphic joints to carry out given working tasks. The metamorphic cyclogram and the types and combinations of the constraint metamorphic joints for the tasks are presented according to the task-based kinematic rules. The augmented Assur groups are further classified based on the output movement combinations so that the corresponding relationships between the task-based kinematic requirements and the structures of the augmented Assur groups are established, thereby providing a simple way to the synthesis of topological structures of source metamorphic mechanisms based on the augmented Assur groups. The equivalent resistance matrix of the metamorphic joints is introduced from the metamorphic cyclogram and equivalent resistance gradient of the metamorphic joints. The constraint structure matrix is then obtained using the resistance matrix and the constraint forms and structures of the metamorphic joints. The synthesis method of metamorphic mechanisms with the constraint forms and structures of metamorphic joints is described in steps. The task-based design approaches are demonstrated for a reposition metamorphic mechanism for broken strands of the repair robot used in extra-high-voltage power transmission lines. The results show that proposed design theory and method are feasible and practical.

Constraint force analysis of metamorphic joints based on the augmented Assur groups

In order to obtain a simple way for the force analysis of metamorphic mechanisms, the systematic method to unify the force analysis approach of metamorphic mechanisms as that of conventional planar mechanisms is proposed. A force analysis method of metamorphic mechanisms is developed by transforming the augmented Assur groups into Assur groups, so that the force analysis problem of metamorphic mechanisms is converted into the force analysis problems of conventional planar mechanisms. The constraint force change rules and values of metamorphic joints are obtained by the proposed method, and the constraint force analysis equations of revolute metamorphic joints in augmented Assur group RRRR and prismatic metamorphic joints in augmented Assur group RRPR are deduced. The constraint force analysis is illustrated by the constrained spring force design of paper folding metamorphic mechanism, and its metamorphic working process is controlled by the spring force and geometric constraints of metamorphic joints. The results of spring force show that developped design method and approach are feasible and practical. By transforming augmented Assur groups into Assur groups, a new method for the constraint force analysis of metamorphic joints is proposed firstly to provide the basis for dynamic analysis of metamorphic mechanism.

Type Synthesis of Constrained Metamorphic Mechanisms with Structural Forms of Metamorphic Joints

Type Synthesis of Constrained Metamorphic Mechanisms with Structural Forms of Metamorphic Joints