复合伺服驱动压边力控制执行机构建模与优化

将伺服电动机驱动与双滑块六杆机构复合,利用伺服电动机的可控性和六杆机构的速度特性,实现拉深过程的变压边力控制。在综合考虑机构输出位移中的弹性位移和刚性位移基础上,建立压边机构输入输出关系的数学模型。当机构几何参数一定时,可根据压边力与滑块位移的关系并考虑机构的变形,确定压边机构的输入速度。为优化杆系尺寸,在考虑压边工作行程和传动效果良好的基础上,以机构输出速度与压力机滑块速度相差最小(在压边力施加阶段),及机构总体尺寸最小为目标函数,优化确定了双滑块六杆机构的杆系尺寸。利用仿真软件,由前面建立的输入输出关系数学模型确定仿真输入速度,仿真结果表明,采用复合伺服驱动双滑块六杆执行机构实现压边力控制是可行的。     

基于疲劳强度的柔性曲柄滑块机构优化设计

基于伪刚体模型,以机构疲劳强度为优化目标函数,考虑各个随机变量的影响和各种约束条件的概率形式,建立了一种柔性曲柄滑块机构的优化设计模型.算例表明,该模型正确可靠,计算结果显示机构的结构尺寸和材料特性对疲劳强度影响较大.     

基于柔度比优化设计杠杆式柔性铰链放大机构

分析与研究了柔性铰链的柔度特性,用于柔性放大机构的优化设计。提出了一个通用的柔度比参数λ,探讨了具有不同柔度比λ的柔性铰链主要输出位移形式的灵敏度,分析了它对常用柔性铰链的柔度特性的影响规律。然后,以柔性铰链的柔度比λ为基本参数,在考虑柔性铰链转动中心偏移量的基础上,推导了二级杠杆式柔性铰链放大机构放大率的理论计算方法,并依据柔性铰链的柔度比特性提出了柔性放大机构的优化设计方法。开展了有限元仿真和实验研究。结果显示,优化后的柔性放大机构的放大率比优化前的放大率分别提高了0.234和0.23。实验表明,依据柔性铰链的柔度比λ对柔性放大机构进行优化设计能够有效地提高柔性放大机构的位移放大率与工作行程,进而提高放大机构的末端运动及定位精度。     

含有Heaviside密度映射的构型平稳变化的柔性机构拓扑优化设计

现有柔性机构拓扑优化方法在解决柔性机构拓扑优化的类铰链和灰度问题仍存在一些困难。为获得清晰和不含类铰链的优化拓扑,提出了一种构型平稳变化的结构拓扑优化求解方法。首先,构建了一种能综合表征柔性机构输入和输出端的局部刚度特性的加权组合柔顺度函数;而后,引入加权组合柔顺度的小量变化约束、Heaviside密度映射和变约束限方案,建立了柔性机构构型平稳变化的优化模型;最后结合MMA算法,形成了一种构型平稳变化的柔性机构拓扑优化方法。给出的算例结果表明,相比于现有方法,该方法计算公式简单,可获得清晰且无类铰链的拓扑构型。     

考虑不确定性的柔性机构拓扑优化设计

柔性机构在制造和运行过程中会存在各种不确定因素。基于多椭球凸模型描述,考虑荷载及材料属性的不确定性,采用人工弹簧方法和几何非线性有限元分析手段,提出以输出端位移最大化为目标、具有最小输入端性能约束的柔性机构拓扑优化数学模型。采用伴随法给出设计变量灵敏度计算公式,提出数值计算不稳定性的简易处理方法,利用数学规划法实现优化问题的求解。反向器机构和微夹钳机构的设计算例验证了所提出优化模型的正确性及算法的有效性,并通过与确定性设计结果的比较,说明了在柔性机构拓扑设计阶段考虑不确定性的重要意义。     

模式选择阀门可调机构运动仿真分析

利用几何方法建立了基于曲柄滑块构型的模式选择阀门可调机构的滑块位移输入与阀门角度输出的关系,并对其进行了运动分析及精度分析。应用多体动力学仿真软件ADAMS建立了模式选择阀门可调机构的仿真模型,对其进行了刚体仿真,仿真结果与理论分析结果几乎一致,互相验证了数学模型与仿真模型的正确性。另外,当联动环为柔性时对其可调机构进行了柔性体仿真,分析了联动环在不同刚性下对各阀门输出同步性的影响,仿真结果表明,提高联动环的刚性能够提高各阀门输出的同步性。     

全柔性微位移放大机构的设计与分析

微机械放大器中常采用全柔性微位移放大机构来实现输出位移的放大,且大多采用短臂柔性铰链连接各构件。设计了一种对称的长柔性杆微位移放大机构,结合弹性力学和Bernoulli-Eu-ler假设,推导出该放大机构的力位移计算公式及放大比公式。对影响该机构放大比的关键因素进行了分析,通过实例分析得到该机构中的长柔性杆角度与输出位移之间的关系。同时用有限元方法对该实例进行了仿真分析,并对两种方法所得结果进行了分析比较。     

柔性机构的研究现状及其在仿生领域的应用前景

柔性机构是一种依靠构件元素所具有的柔性来输出全部(或部分)运动或力的机构.由于柔性机构所具有结构紧凑、重量轻、无间隙、无摩擦等优点,使其微定位、MEMS等领域得到广泛的应用.本文介绍了柔性机构理论研究现状和其在实际中的应用情况,以及目前还存在的问题.最后,展望了柔性机构在仿生领域的应用前景.     

六自由度微位移定位平台的设计与试验

压电叠堆与柔性机构构成了微位移的基本形式,其行程与精度、输出力的矛盾需要结合应用要求对结构进行综合设计。针对所构建的超精密加工工具对六自由度微位移的需求,提出了一种以压电叠堆作为驱动元件,以柔性铰链和楔形机构作为传动机构的空间六自由度微位移定位平台。由于压电叠堆需要一定的预紧力才能发挥其微位移精度和输出力的优势,通过静力分析,得出了微位移平台各个自由度驱动力和位移输出关系的表达式及刚度表达式,对结构进行了优化。试验表明,各自由度的行程与分辨率如下:x,y,z方向的最大位移分别为7.48,8.33和4.14μm,分辨率为0.01μm;沿θ_x,θ_y,θ_z方向的最大旋转角度均为0.13°,分辨率为0.01°,满足所构建的超精密加工工具定位的精度要求。试验获得了微位移定位平台的激励电压与各自由度位移输出曲线,为平台的运动、定位控制提供了依据,也为柔性铰链机构和楔形机构在其他结构中的应用提供了理论依据和试验基础。     

考虑屈曲约束的无铰链多输入多输出柔性机构拓扑优化设计方法

针对柔性机构的稳定性要求,基于Heaviside三场映射方案和柔顺度变化率约束措施,研究了屈曲约束下无铰链多输入多输出柔性机构柔度最小化的拓扑优化问题。首先,为解决低密度单元引起的伪屈曲模态和计算效率等问题,构建了单元刚度矩阵和应力矩阵的光滑惩罚函数,提出了解决低阶伪屈曲模态问题的综合措施。其次,结合Pian混合应力单元公式、凝聚函数法、Heaviside三场映射方案和柔顺度变化率约束措施,构建了考虑屈曲的无铰链多输入多输出柔性机构拓扑优化模型。而后,推导了目标函数和屈曲约束的灵敏度,并利用MMA(Method ofMoving Asymptotes)算法进行优化求解。最后,给出的数值算例,说明了此方法的可行性和有效性。     

Transmission angle in compliant slider-crank mechanism

The transmission angle is an important parameter for the quality of motion transmission in a mechanism. However, in the literature there is no study available on compliant mechanisms regarding their transmission characteristics. In this paper, the transmission angle of a compliant slider-crank mechanism is introduced. Similarity conditions for the transmission angle of the compliant slider-crank and its rigid body counterpart are devised via two theorems. A real model is manufactured and one of these theorems is verified experimentally. Finally, the effect of eccentric slider on motion transmission quality is discussed. It is believed that newly proposed theorems will find use in the design of compliant slider-crank mechanisms.     

多输入多输出柔顺机构拓扑优化及输出耦合的抑制

多自由度柔顺机构在微动精密定位和精密操作等领域有广泛的应用,因而研究多自由度柔顺机构的拓扑优化方法就显得十分必要。给出了一种多输入多输出柔顺机构拓扑优化设计的新方法。首先,推导了描述多输入多输出柔顺机构柔性的互应变能公式和描述机构刚性的应变能公式,研究了抑制耦合输出的策略,进一步给出了描述输出耦合效应的计算公式,在此基础上建立了考虑抑制输入输出耦合效应时柔顺机构的多目标拓扑优化设计模型。其次,基于改进的优化准则法给出了优化模型的有效求解算法。最后,通过算例说明了该方法的正确性和有效性,研究结果表明,拓扑优化后柔顺机构可以按照预定的要求运动,其输出耦合现象得到了有效抑制。     

分布式柔性机构拓扑优化设计的理论和算法

将连续体结构的拓扑优化技术应用到分布式柔性机构的设计中,基于变密度法和优化准则法推导并建立柔性机构拓扑优化的一种显式的设计变量收敛格式。结合分布式柔性机构优化设计的人工弹簧模型和虚拟载荷法,提出一种新型的分布式柔性机构拓扑优化设计的多准则优化模型,同时综合考虑柔性机构设计的机械效率要求和结构的刚度要求,并利用伴随敏度分析法进行敏度分析。数值算例证明研究方法的有效性,并分析和讨论优化模型和收敛格式中有关优化设计参数对柔性机构优化设计结果的影响。用激光快速成形技术验证柔性机构概念设计的合理性。     

Finding the optimal characteristic parameters for 3R pseudo-rigid-body model using an improved particle swarm optimizer

Compliant mechanisms have been used in many engineering areas where high precision and sensitivity are required. One of the major challenges of designing compliant mechanisms lies in understanding and analyzing the nonlinear deflections of flexible members. The pseudo-rigid-body model (PRBM) method, which simplifies the modeling of the nonlinear deflection by approximating it as motion of rigid links, has been accepted as one of the most important tools for synthesis and analysis of compliant mechanisms. In this paper, a review of various PRBMs is presented. The 3R PRBM whose characteristic parameters are independent of external loads is discussed in detail. For the purpose of finding the optimal set of the characteristic parameters for the 3R PRBM, a six-dimensional objective function is formulated by combining the approximation errors of both tip point and tip slope for the two extreme load cases, i.e., pure moment load and pure vertical force load. A particle swarm optimizer was employed to conduct a continuous search on the objective function. The resulting 3R PRBM with the optimized characteristic parameters shows better performance in predicting large deflections of cantilever beams over the original 3R PRBM.     

A parameter optimization framework for determining the pseudo-rigid-body model of cantilever-beams

This paper focuses on developing a framework for determining the optimal pseudo-rigid-body (PRB) model of 2D cantilever beams. PRB models are commonly used in design and analysis of compliant mechanisms since they significantly reduce the number of degrees of freedom compared with the finite element approach. Although a number of PRB models are available in literature, there is not a unified method to determine the most suitable pseudo-rigid-body model for a specific application. In this work, we first study a modified Timoshenko beam equation which accommodates shear forces and axial deformation. The numerical solution to the Timoshenko beam equation provides a baseline for comparing various models. A novel concept of “PRB matrix” is proposed for representing topologies of all PRB models in a uniform way. The optimal set of kinematic parameters (characteristic lengths and spring constants) of PRB models are determined by minimizing the error of tip deflection and comparing with the solution of the Timoshenko beam equation. To validate this formulation, we compare the results with existing PRB models and obtained equivalent if not a more accurate set of PRB parameters. At last, a case study of a compliant slider mechanism is provided to demonstrate the accuracy of two PRB models in this particular application.     

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.     

Analytical modeling and FEM Simulations of single-stage microleverage mechanism

Microleverage mechanisms have potentially wide applications in micro-electro-mechanical systems (MEMS) for transferring an input force/displacement to an output to achieve mechanical or geometrical advantages. Constrained by micro-fabrication technology, a microleverage mechanism is made of planar flexures, achieving mechanical transformation through elastic deformation. This kind of mechanism is referred to as a compliant mechanism. In this paper, the analysis and optimization of a single-stage microleverage mechanism is presented with a double-ended tuning fork as the output system in a resonant accelerometer to address the design issues. A very good agreement is obtained between the results of analytical modeling and those of FEM simulation with a SUGAR software package. Although the SUGAR data are more accurate, the analytical equations give clearer insights as to how to design a microleverage mechanism. While high axial spring constants and low rotational spring constants are desirable, the axial and rotational spring constants at pivot need to match those at the output system to achieve the maximum force amplification factor. This compliance-match concept is very important for the design of both single-stage and multiple-stage leverage mechanisms.     

柔性机构的结构拓扑特征及其自由度分析

柔性机构是利用组成元素间的相对柔性来获得运动或力的一类机构。通过分析柔性机构的结构特点 ,本文提出了一个新的拓扑图来表示柔性运动链的结构拓扑特征 ,并给出了相应的矩阵表示 ,借助该矩阵中的信息 ,可以方便地对柔性机构进行自由度分析。并且指出柔性机构是一种变自由度机构 ,其自由度的数目与机构所受外力 (矩 )的大小和方位有关。     

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。