Design and fabrication of miniature compliant hinges for multi-material compliant mechanisms

Multi-material molding (MMM) enables the creation of multi-material mechanisms that combine compliant hinges, serving as revolute joints, and rigid links in a single part. There are three important challenges in creating these structures: (1) bonding between the materials used, (2) the ability of the hinge to transfer the required loads in the mechanism while allowing for the prescribed degree(s) of freedom, and (3) incorporating the process-specific requirements in the design stage. This paper presents the approach for design and fabrication of miniature compliant hinges in multi-material compliant mechanisms. The methodology described in this paper allows for the concurrent design of the part and the manufacturing process. For the first challenge, mechanical interlocking strategies are presented. For the second challenge, the development of a simulation-based optimization model of the hinge is presented, involving functional and manufacturing constrains. For the third challenge, the development of hinge positioning features and gate positioning constraints is presented. The developed MMM process is described, along with the main constraints and performance measures. This includes the process sequence, the mold cavity design, gate selection, and runner system development. A case study is presented to demonstrate the feasibility of creating multi-material mechanisms with miniature hinges serving as joints through MMM process. The approach described in this paper was utilized to design a drive mechanism for a flapping wing micro air vehicle. The methods described in this paper are applicable to any lightweight, load-bearing compliant mechanism manufactured using multi-material injection molding.     

Manufacturing multi-material articulated plastic products using in-mold assembly

In-mold assembly can be used to create plastic products with articulated joints. This process eliminates the need for post-molding assembly and reduces the number of parts being used in the product, hence improving the product quality. However, designing both products and molds is significantly more challenging in case of in-mold assembly. Currently, a systematic methodology does not exist for developing product and processes to exploit potential benefits of in-mold assembly for creating articulated joints. This paper is a step towards creating such a methodology and reports the following three results. First, it presents a model for designing assemblies and molding process so that the joint clearances and variation in the joint clearances can meet the performance goals. Second, it describes proven mold design templates for realizing revolute, prismatic, and spherical joints. Third, it describes a mold design methodology for designing molds for products that contain articulated joints and will be produced using in-mold assembly process. Three case studies are also presented to illustrate how in-mold assembly process can be used to create articulated devices.     

A multi-material part design framework in additive manufacturing

Additive manufacturing (AM) technologies provide more freedom to functional part design in various industries. One of the unique capabilities of AM is that multi-material parts can be produced with material compositional and geometric complexity. Multi-material parts have the advantage of achieving multiple performance requirements. In the research, we propose a framework for designing multi-material parts using AM processes. The proposed framework is composed of four interacting modules, including design requirement identification, primary material selection, AM process selection, material composition, and part geometry determination. Rules and guidelines for AM are integrated into the proposed framework with AM processes’ capabilities and constraints compiled in databases. We also introduce databases to assist in decision-making and ensure manufacturability of the designed multi-material part in various product design phases. The proposed framework is applied to a case study involving a conceptual design of a multi-material battery pack cooling plate.     

全柔性机构与MEMS

柔性机构是一种新型机构。首先描述了柔性机构和全柔性机构的概念及特点,论述了它们与MEMS之间的关系。然后详细介绍了全柔性机构在MEMS领域内包括微装配、微操作等应用背景下的状况及前景。最后就对全柔性机构研究中的几个关键技术问题如机构的分析、设计及加工,柔性铰链的选择与设计,驱动器的选择及设计等进行了探讨。     

基于并行策略的多材料柔顺机构多目标拓扑优化*

多材料柔顺机构能够让设计者充分利用各种材料的优良属性,在力,位移,以及能量转移等方面获得更大的设计自由度,因而受到重视。针对受到广泛研究的柔顺机构,结合多目标拓扑优化的方法,提出相应的基于并行策略的求解模型。该方法的核心是将一个复杂的多材料多目标问题离散成为单材料子问题,然后并行求解,再根据整体目标的需要,对所有子问题的解进行调整以得到原始问题的解。针对多目标情形,提出新的材料与输出目标关系,从而在将多材料问题离散成单材料子问题的同时,也将多目标问题离散成单目标子问题。对所有的单材料单目标子问题采用各向同性材料的刚度插值-惩罚法并行独立求解。以上方法有其独特优势：在理论和实践上都比较简单,可以处理任意多种材料,可以避免零碎的拓扑结构因而有利于制造。通过算例说明了此方法的有效性。研究结果表明,该方法在某些输出需要特定材料的设计场合更具优势。     

电火花加工多材质电极制备方法及试验研究

随着电火花加工技术的不断发展,利用多材质电极来实现微小复杂曲面的电火花成形加工,具有加工速度快、一次成形等特点而被广泛应用。针对多材质电极的制备,以黄铜、紫铜、铁、钼及铜钨合金等材质电极在模具钢上进行了加工试验,以研究的电极损耗及形状变化规律为基础,根据复杂曲面加工需求设计多材质电极,运用热镀法制备多材质电极,通过扫描电镜对多材质电极的成分和粘结效果进行检测,并以制备的黄铜-铁、紫铜-铜钨及黄铜-紫铜多材质电极进行试验加工,用电子放大镜观测多材质电极的损耗形貌和黏结质量。结果表明,运用热镀法制备的多材质电极连接紧密,在加工过程中不会出现开裂,能够良好地完成电火花加工。     

Design of compliant straight-line mechanisms using flexural joints

Straight-line compliant mechanisms are important building blocks to design a linear-motion stage, which is very useful in precision applications. However, only a few configurations of straight-line compliant mechanisms are applicable. To construct more kinds of them, an approach to design large-displacement straight-line flexural mechanisms with rotational flexural joints is proposed, which is based on a viewpoint that the straight-line motion is regarded as a compromise of rigid and compliant parasitic motion of a rotational flexural joint. An analytical design method based on the Taylor series expansion is proposed to quickly obtain an approximate solution. To illustrate and verify the proposed method, two kinds of flexural joints, cross-axis hinge and leaf-type isosceles-trapezoidal flexural（LITF） pivot are used to reconstruct straight-line flexural mechanisms. Their performances are obtained by analytic and FEA method respectively. The comparisons of the results show the accuracy of the approach. Both examples show that the proposed approach can convert a large-deflection flexural joint into approximate straight-line mechanism with a high linearity that is higher than 5 000 within 5 man displacement. This can lead to a new way to design, analyze or optimize straight-line flexure mechanisms.     

基于多刚体离散元模型的柔顺机构动力分析新方法

柔顺机构是部分或者全部由其构件的预期弹性变形来传递运动和力,这使得构件的弹性变形一般都较大。它的分析一般属于几何非线性问题。基于弹性体的多刚体离散元模型,研究了柔顺段和柔顺机构的多刚体离散元建模方法,推导了柔顺机构系统的一般控制方程,该方程可以解决柔顺机构的特征频率和几何非线性变形问题。并给出了算例,计算结果表明多刚体离散元方法能较好解决柔顺机构的几何非线性静力学和动力学分析。     

Application of the TRIZ creativity enhancement approach to design of passively compliant robotic joint

The essence of the conceptual design is getting the innovative projects or ideas to promise the products with best performance. It has been proved that the theory of inventive problem solution (TRIZ) is a systematic methodology for innovation. The design of a passively compliant robotic joint as an engineering example is illuminated in this paper to show the significance and approaches of applying TRIZ into getting the creative conceptual design ideas. In the robotic joints with passively compliance, the joints are composed of mechanical components such as springs and dampers as internal elements, which absorb the excessive collision force. Passive compliant joints with springs and dampers ensure a smooth contact with the surroundings, especially if robots are in contact with humans, but the passive compliant joints cannot determine precisely the position of the members of the joint or direction of the collision force. The main aim of this work is to show a systematic methodology for innovation as an effective procedure to enhance the capability of developing innovative passive compliant robotic joint and to overcome the main design problems. The TRIZ method will be utilized in order to eliminate the technical contradictions which appear in the passively compliant robotic joint.     

Integrating mechanism synthesis and topological optimization technique for stiffness-oriented design of a three degrees-of-freedom flexure-based parallel mechanism

This paper introduces a new design approach to synthesize multiple degrees-of-freedom (DOF) flexure-based parallel mechanism (FPM). Termed as an integrated design approach, it is a systematic design methodology, which integrates both classical mechanism synthesis and modern topology optimization technique, to deliver an optimized multi-DOF FPM. This design approach is separated into two levels. At sub-chain level, a novel topology optimization technique, which uses the classical linkage mechanisms as DNA seeds, is used to synthesize the compliant joints or limbs. At configuration level, the optimal compliant joints are used to form the parallel limbs of the multi-DOF FPM and another stage of optimization was conducted to determine the optimal space distribution between these compliant joints so as to generate a multi-DOF FPM with optimized stiffness characteristic. In this paper, the design of a 3-DOF planar motion FPM was used to demonstrate the effectiveness and accuracy of this proposed design approach.     

A new approach for molding multi component parts

Injection molding has gained an enormous importance over the last twenty years. This is due both to the development of sophisticated products and to the efforts being generally made to the reduction of product weight specially in automobile industry. Developments aimed at creating innovative products are expected to broaden industrial implementation of their techniques. Establishment then requires the progressive development of existing mold techniques and engineering knowledge. This paper describes a successive process for molding multi component complicated products such as door trim, instrument panel and so on. Using an analytical model, the orthogonal experiment method (Taguchi method) and numerical simulation, an optimal process for simultaneous injection molding with “core-back” and “co-injection” technique is presented to produce such innovative products. Through practical tests, this process was verified in terms of applicability.     

Constraint Force Analysis of Metamorphic Joints Basedon 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 mec...     

基于伪刚体模型法的全柔性机构位置分析

柔性机构是一种依靠构件元素的弹性变形传输所希望运动的机构。具有集中柔度的全柔性机构是其中的一种类型，其特征是机构中传统形式的铰链全部被柔性铰链所代替。对它的研究，近年来也已成为一个热点。为探索这类全柔性机构的运动学问题，首先建立起柔性铰链变形刚度模型。在此基础上，提出了一种扩展的伪刚体模型法，很好地解决了机构的位置正、反解问题。     

Compliant thin-walled joint based on zygoptera nonlinear geometry

This paper introduces a Compliant thin-walled joint (CTWJ) that expands the group of existing compliant joints. The CTWJ design is based on the nonlinear geometry of the zygoptera animal. With a thin-walled structure, the CTWJ allows a considerably large range of motion in the x-and-y axes. In addition, the thin-walled structure is then filled by polydimethylsiloxane material to reinforce the stiffness of the CTWJ. First, design of experiment methodology is used for the sensitive analysis of the width and the thickness to the strain of joint. The range of motion, the strain, the buckling behavior, and the first natural frequency of CTWJ are investigated via finite element analysis and experiments. The behavior of the CTWJ is subsequently compared with the conventional compliant joints to realize the efficient performance of the CTWJ. The results revealed that the CTWJ has a range of motion and strain energy larger than those of traditional compliant joints. Finally, an example of vibration isolator is modeled by using the CTWJ as planar spring. It is believed that the CTWJ has a great potential for the development of compliant mechanisms in terms of large range of motions in mutliple axes.

     

A new type of compliant spatial four-bar (RSSR) mechanism

This paper presents a novel study on the analysis and design of a new type compliant spatial four-bar (RSSR) mechanism. To the best of our knowledge, any research on compliant spatial mechanisms which possesses out of plane motions is not available in the literature. This study introduces enumeration and novel approach for the analysis and design of such mechanisms. The analysis and design are performed with the pseudo-rigid-body model (PRBM). Since there are numerous applications of rigid spatial four bar mechanisms, it is strongly believed that a compliant version of such mechanisms may find many applications.     

Spring-joint method for topology optimization of planar passive compliant mechanisms

There is seldom approach developed for the initial topology design of flexure-based compliant mechanisms. The most commonly-used approaches, which start with an existing rigid-body mechanism, do not consider the performances between different topologies. Moreover, they rely heavily on the rigid-body topology, therefore limit the diversity of compliant mechanisms topology. To obtain the optimal initial topology of such mechanisms directly from problem specifications without referencing to the existing mechanism topologies, a spring-joint method is presented for a restricted class of the serial passive flexure-based compliant mechanisms, which are the building blocks of parallel compliant mechanisms. The topology of the compliant mechanisms is represented by a serial spring-joint mechanism（SSJM） that is a traditional rigid-body mechanism with a torsional spring acting on each joint, and is described by position vectors of the spring-joints. A simplified compliance matrix, determined by the position vectors, is used to characterize the tip of the SSJM kinematically, and is optimized to ensure the desired freedoms of the compliant mechanisms during optimization. The topology optimization problem is formulated as finding out the optimal position of the spring-joints in a blank design domain with an objective function derived from the simplified compliance matrix. In design examples, syntheses of the compliant mechanisms with both single freedom and two decoupled freedoms are presented to illustrate the proposed method. The proposed method provides a new way for the initial design of flexure-based compliant mechanisms.     

Stiffness Analysis of Corrugated Flexure Beam Used in Compliant Mechanisms

Conventional flexible joints generally have limited range of motion and high stress concentration. To overcome these shortcomings, corrugated flexure beam(CF beam) is designed because of its large flex...     

双色笔杆注射成型模具设计

文中介绍了双物料单模注射成型工艺,分析了双色笔杆的结构特点,设计了双物料成型模具。解决了模具旋转换腔、型芯冷却、脱模系统、浇注系统设计等难题。     

Failure prediction for multi-material creep test specimens using a steady-state creep rupture stress

The steady-state stress distributions in single- and multi-material notched and waisted specimens were investigated for practical creep test specimens using material properties obtained for materials from a service-aged CrMoV pipe weldment. The tri-axial stress conditions existing in notched and waisted specimens machined from welded pipes were identified. By using a steady-state effective failure stress, it has been shown that an approximate method, based on steady-state stress, for the prediction of rupture life and failure position can produce reasonably accurate results. The applicability of the approximate method was confirmed by comparing the results obtained using it with those obtained from corresponding creep continuum damage modelling. These results indicate that use of steady-state stress analysis, as an approximate technique, may be useful for assessing creep failure behaviour, for determining the effect of specimen size and for generating material properties for welded components.     

A novel analytical model for flexure-based proportion compliant mechanisms

This paper proposes a novel analytical model for flexure-based proportion compliant mechanisms. The displacement and stiffness calculations of such flexure-based compliant mechanisms are formulated based on the principle of virtual work and pseudo rigid body model (PRBM). According to the theory and method, a set of closed-form equations are deduced in this paper, which incorporate the stiffness characteristics of each flexure hinge, together with the other geometric and material properties of the compliant mechanism. The rotation center point for a corner-filleted flexure hinge is investigated based on the finite element analysis (FEA) and PRBM. An empirical equation for the rotational angle is fitted in this paper in order to calculate accurately the position of the end-point of the flexure hinge. The displacement proportion equation for such mechanisms is derived according to the new approach. Combining the new proposed design equation and the existed stiffness equation, a new proportion compliant mechanism with corner-filleted flexure hinges is designed by means of the least squares optimization. The designed models are verified by finite element analysis.