On the modeling of flexure hinge mechanisms with finite beam elements of variable cross section

In this paper, a modeling technique for flexure hinge mechanisms is studied. Beam elements of variable cross sections are deployed within a finite element procedure to model a circular flexure hinge. The resulting finite element model has very few degrees of freedom and is accurate in both static and dynamic analysis. Furthermore the modeling approach is applied to an amplifier mechanism. Comparing the results of the proposed model with a 3D finite element reference model, high accuracy for a broad spectrum of hinge parameters is reported while reducing the number of degrees of freedom immensely.     

柔性平行导向机构的静刚度分析

柔性机构是一种新型机构。作为一类最简单的柔性机构 ,柔性平行导向机构被广泛应用在精密定位场合。由于在精密操作中要求机构具有很高的定位精度 ,而机构的静刚度在很大程度上决定着这一指标。针对静刚度分析的重要作用以及目前对机构静刚度分析中存在的不足 ,采用结构分析中的柔度矩阵法建立了一种新的用来分析机构静刚度的理论模型。其结果相对原有模型更接近有限元仿真的结果     

Modeling and design of planar parallel-connection flexible hinges for in- and out-of-plane mechanism applications

The paper studies the planar parallel-connection, small-deformation flexible hinge chains formed of serially-coupled individual segments with variable cross-sections. It introduces the concept of virtual flexible hinge that is quasi-statically equivalent to the actual parallel-hinge configuration. General compliance and stiffness matrices are formulated for the virtual hinge under in-plane and out-of-plane loads by combining the transformed compliances of the individual hinge segments. Two classes are specifically analyzed: one comprises geometrically parallel, straight-axis hinge designs and the other includes concentric, circular-axis hinge configurations. From each class, particular designs with identical and transversely symmetric hinges of right circularly corner-filleted geometry are further investigated. Specifically, the behavior of parallelogram mechanisms with straight-axis hinges and of stage devices with circular-axis hinges is analyzed. Their elastic responses are validated by finite element analysis and their stiffnesses are subsequently studied in terms of offset geometric parameters.     

Topology optimization of flexure hinges with a prescribed compliance matrix based on the adaptive spring model and stress constraint

This paper focuses on the configuration design of flexure hinges with a prescribed compliance matrix and preset rotational center position. A new method for the topology optimization of flexure hinges is proposed based on the adaptive spring model and stress constraint. The hinge optimization model is formulated by maximizing the bending displacement with a spring while optimizing the compliance matrix to a prescribed value. To avoid numerical instability, an artificial spring is used as an auxiliary calculation, and a new strategy is developed for adaptively adjusting the spring stiffness according to the prescribed compliance matrix. The maximum stress of flexure hinge is limited by using a normalized P-norm of the effective von Mises stress, and a position constraint of rotational center is proposed to predetermine the position of the rotational center. In addition, to reduce the error of the stress measurement, a simple but effective filtering method is presented to obtain a complete black-and-white design. Numerical examples are used to verify the proposed method. Topology results show that the obtained flexure hinges have the prescribed compliance matrix and preset rotational center position while also meeting the stress requirements.     

Nonlinear modeling of compliant mechanisms incorporating circular flexure hinges with finite beam elements

Modeling of compliant mechanisms incorporating flexure hinges is mainly focused on linear methods. However, geometrically nonlinear effects cannot be ignored generally. This work shows that nonlinear behavior plays an important role in the deformation and stress analysis, which consequently impacts the design of compliant mechanisms. In this study a nonlinear higher order finite beam element based modeling approach is presented strongly reducing the computation time of nonlinear models. Planar deformation and mechanical stress of a single circular flexure hinge under a wide range of loads is modeled and computed with the proposed approach. A comparison with a 3D-nonlinear finite element model shows very good agreement and validates the beam model. It is shown that the linear and nonlinear deformation behavior of a single flexure hinge deviate marginally so that linear modeling approaches are sufficient. Furthermore a planar displacement amplification mechanism incorporating circular flexure hinges is studied by means of the same method highlighting the distinct deviation of the behavior of the geometrically nonlinear model from its linear prediction. In conclusion the nonlinear behavior at the system level can not longer be neglected. Finally, a study shows that different designs of the displacement amplification mechanism are achieved when linear or nonlinear modeling approaches are applied.     

Design and forward kinematics of the compliant micro-manipulator with lever mechanisms

This paper presents the forward kinematics of a five-bar compliant micro-manipulator. To overcome the limited displacement of such a flexure-based mechanism driven by piezoelectric actuators, lever mechanisms are utilized to enlarge the working range. The mechanical design of the micro-manipulator is firstly described. Mathematical formulations for the five-bar mechanism are described and the solutions are developed to decide the end-effector position in Cartesian space. The amplification factor of the lever mechanism is also derived based on the analytical solution of the four-bar linkages. The velocity of the end-effector is obtained by differentiating the forward position kinematic equation, and the local mobility index of the five-bar compliant mechanism is determined and analysed. Based on linearization of trigonometric functions and constant Jacobian matrix, numerical simulations are carried out to investigate the performance of the five-bar compliant manipulator and to determine the optimal geometric parameters for the configuration. The comparisons between the exact solution and simplified methodologies are conducted. Experiments are carried out to validate the established model and the performance of the developed micro-manipulator.     

Design and development of compliant mechanisms for electromagnetic force balance sensor

Compared with the lever-type amplifier, the rhombus-type amplifier has attracted more attention by virtue of large displacement amplification ratio, compact structure, and linear output displacement. In this paper, a novel electromagnetic force balance sensor (EFBS) based on the rhombus-type amplifier is presented to measure the mass with high precision. First, the structure and operating principle of the EFBS are described, and the requirements for the design and manufacture of the amplifier are put forward. Then, the analytical models of the two-stage rhombus-type amplifier are given out, and two guiding mechanisms are analyzed and modeled. Furthermore, the validity of the established model is verified by finite element analysis (FEA). Thanks to the theoretical guidance, an electromagnetic force balance sensor based on the two-stage rhombus-type amplifier and double parallelogram flexure mechanism is designed and tested. The experimental results demonstrate that the developed EFBS can measure the mass of the objects with high precision, and also verifies the correctness of the analytical model. This provides a new concept for the structural design of the EFBS.     

The influences of the residual forming data on the quasi-static axial crash response of a top-hat section

In this paper the influences of residual effects of a deep drawing forming process on the axial quasi-static crash behaviour of straight thin-walled top-hat section were numerically investigated. The residual forming data on the plastic strains, residual stresses and thickness variations were transferred to crash models, which include both deformed and nominal meshes. The influence of spring-back or spring-in on crash performance of the member was also considered. Numerical simulations were carried out by using the nonlinear finite element code LS-DYNA. As a result of these analyses it appears that the residual forming data and the effects of spring-back significantly influence the crash response and they should be considered in computational impact simulations.     

基于VB6.0串行通信中的错误预防方法

在串行通信中常出现数据传输错误的情况，本文介绍了基于VB的串行通信中的错误预防方法，并给出了相关实例。     

Accurate low DOF modeling of a planar compliant mechanism with flexure hinges: the equivalent beam methodology

A methodology for accurate and efficient finite elements method (FEM) simulations of planar compliant mechanisms with flexure hinges is presented. First, using symmetry/antisymmetry boundary conditions and 3D elements, one-eighth of a single hinge is simulated to determine its true stress/stiffness characteristics. A set of fictitious beams is derived, which have the identical characteristics. This set is used in conjunction with other beams that model relatively stiff links to generate an equivalent model of an entire mechanism consisting of the beam elements only. The model has a low number of degrees-of-freedom (DOF) and appears to be more accurate than any 2D FEM models, even those with very large number of DOF. The methodology has been developed specifically for the right circular flexure hinge; however, it can be applied to all types of revolute flexure hinges.     

基于ADAMS的PRS—XY型混联机床机构运动学仿真分析

应用ADAMS软件对PRS—XY型混联机床机构进行运动学仿真分析,使用测量工具求得混联机构逆解,然后通过样条曲线和样条函数求得正解。借助于仿真软件快速准确地求出运动学正逆解,为实际的样机调试提供了有意义的借鉴。     

A new method for the reconstruction of micro- and nanoscale planar periodic structures

In recent years, the micro- and nanoscale structures and materials are observed and characterized under microscopes with large magnification at the cost of small view field. In this paper, a new phase-shifting inverse geometry moiré method for the full-field reconstruction of micro- and nanoscale planar periodic structures is proposed. The random phase shift techniques are realized under the scanning types of microscopes. A simulation test and a practical verification experiment were performed, which demonstrate this method is feasible. As an application, the method was used to reconstruct the structure of a butterfly wing and a holographic grating. The results verify the reconstruction process is convenient. When being compared with the direct measurement method using point-by-point way, the method is very effective with a large view field. This method can be extended to reconstruct other planar periodic microstructures and to locate the defects in material possessing the regular lattice structure. Furthermore, it can be applied to evaluate the quality of micro- and nanoscale planar periodic structures under various high-power scanning microscopes.     

平面机构运动分析的有限元件法

要使用一种特殊有限元的方法进行平面机构的运动分析,需首先对组成平面机构的常用单元进行分析,并给出了描述单元的变形模态参数与单元节点坐标之间的函数关系,进而用传递函数的概念对机构的位置,速度和加速度进行分析,在此基础上,编制了计算机程序,对ＺＬ５０装载机的工作装置的运动进行了计算给出了数值模拟结果。     

基于ADAMS的PRS-XY型混联机床机构运动学仿真分析

应用ADAMS软件对PRS-XY型混联机床机构进行运动学仿真分析,使用测量工具求得混联机构逆解,然后通过样条曲线和样条函数求得正解。借助于仿真软件快速准确地求出运动学正逆解,为实际的样机调试提供了有意义的借鉴。     

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.     

仿真直动式溢流阀瞬态响应的键合图法

介绍了用键合图法仿真直动式溢流阀的瞬态响应。将直动式溢流阀接入一个易于反映阀的动态特性的液压系统,绘出系统的键合图。根据键合图推导出系统的状态方程,从而仿真出直动式溢流阀开口瞬时系统的压力和阀芯位移随时间的变化曲线。     

Reduction of the joint clearance effect for a planar flexible mechanism

When the operating speed of mechanical systems is increased, unpredictable dynamic problems are induced due to joint clearances and link elasticity. To solve these problems, quantitative prediction of the effects of joint clearance and link flexibility on the system is needed. This study has two principal objectives. The first is to develop a design method for eliminating the loss of contract at joints with clearance. The method utilizes three dimensionless parameters which govern the dynamic behavior at the instance when contact loss is predicted. These parameters are determined to maintain joint contacts throughout the operating cycle. The links in this mechanism are assumed to be rigid. The second objective of this study is to investigate the influence of the flexibility of the links. Using a finite element method, we found that link flexibility decreases the possibility of contact loss as well as the impact force at joints with clearance.     

一种求解复杂平面机构奇异位置的分析图解法

提出了复杂多环路平面机的奇异位置分析的一种简明的分析图解方法,即先将机的分解为基本运动链,再导出基本运动链的奇异性条件,后由其相应的奇异几何图形,解出其机构的奇异位置。揭示了机构奇异分析的三个重要结论。还给出了任意复杂多环路平面机构可能产生奇异位置的上限计算公式。最后举例说明了一个双环复杂机构的奇异位置求解过程,此外提出的方法可推广至空间机构的奇异性分析。     

An integrated knowledge representation model for the computer-aided conceptual design of mechanisms

An integrated knowledge representation model, namely the topology structure behaviour function (TSBF) model, is presented for the computer-aided conceptual design of mechanisms (MCACD) in this paper. The model covers both qualitative and quantitative knowledge representations of generic mechanisms. A class hierarchy consists of the abstract mechanism, the embryo mechanism, and the concrete mechanism is then proposed for object-oriented modelling. Based on the TSBF model, several reasoning techniques are integrated to achieve a relatively comprehensive environment for MCACD. The corresponding reasoning process is mainly based on a backward chaining of solutions representation and retrieval, a forward chaining of compositional behaviour reasoning with constraint propagation and satisfaction, and a forward chaining of type synthesis. Coarse optimizations for certain mechanisms are also integrated on the quantitative level. The applicability of the new model is demonstrated by the conceptual design of a zigzag mechanism.