平面双稳态柔性微机构的优化设计

讨论了一种平面双稳态柔性微机构的设计问题。首先给出了机构稳定平衡位置的物理含义 ,建立了两种类型平面双稳态柔性微机构的伪刚体模型。提出了一种允许设计者随意指定稳定平衡位置点的具有较大自由度的优化设计方法 ,建立了优化数学模型及相应的约束准则 ,采用一种改进的遗传进化算法获得了全局最优解。根据所得的最优解对双稳态柔性微机构进行了分析 ,结果表明该设计方法是有效的     

基于固支-简支屈曲梁的旋转驱动双稳态柔顺机构

与传统刚体机构不同,柔顺机构通过构件变形可实现位移和力的传递与转换,这可大大减少摩擦、润滑和装配。由于具有结构简单、变形大、易于加工等特点,双稳态屈曲梁成为常见的柔顺机构设计单元,在能量吸收、软体机器人、能量收集等领域被广泛应用。以固支-简支双稳态屈曲梁为研究对象,设计一种新型旋转驱动的双稳态柔顺机构。首先,基于能量法建立分析模型,用于分析双稳态屈曲梁在简支端旋转驱动下的跳变特性,预测屈曲梁的力矩-角度曲线和变形过程,并通过有限元模型和实验结果验证了分析模型的有效性;其次,利用分析模型、有限元模型和实验分析了预压缩量和几何参数对于双稳态屈曲梁力矩-角度曲线和最大力矩的影响;最后,基于双稳态屈曲梁的研究结果设计旋转驱动的双稳态柔顺机构并对其跳变行为进行有限元分析和实验验证。     

微位移放大模块的刚度分析

刚度的优劣很大程度上影响着全柔性微动机构末端执行器的定位精度及动态特性,因而建立全柔性微动机构较为简便的、精确的刚度模型变得尤为重要。以全柔性微位移放大模块为例,采用伪刚体法并依据构件之间的弹性变形关系得到模块机构的运动方程,利用全柔性微位移放大模块在运动过程中能量的转化关系,结合功能原理建立机构的刚度模型,并通过算例对其进行ANSYS有限元仿真分析。结果表明理论计算值与仿真结果误差在5%之内,具有较高精度。     

一种新型柔性双轴微夹钳的设计与分析

针对传统的微夹钳在复杂的微操作中只能沿单轴进行夹持操作的不足，文中设计了一种柔性铰链的双轴微夹钳，结构简单又紧凑，该微夹钳由一个压电陶瓷驱动器驱动，实现夹持和旋转两种操作。采用非对称结构设计，实现左边完成向前旋转动作，右边完成夹持动作。通过左右两边两级放大机构结构设计不同，实现位移放大和运动传递。为实现抓取和搓动功能的解耦，对两部分的运动导向机构进行了正交设计。采用伪刚体法建立了机构的伪刚体模型，建立了机构的运动学和动力学模型，包括运动机构放大比、输入刚度和机构的固有频率。通过有限元分析方法验证了微夹钳的性能模型的准确性。仿真试验结果表明，左侧机构的放大比为8.01,右侧放大比为8.56,最大输出位移可达171.36μm。所设计的微夹钳具有良好的抓取和搓动的性能，可实现高精度的抓取和释放操作。     

基于动力学的双稳态机构驱动特性分析

柔性双稳态机构是一种在无外部输入的情况下,可以保持两个稳定平衡位置的机构,在MEMS和机械传动领域中有广泛的应用。对柔性机构稳态的判别一般使用能量法,但能量法无法对柔性机构的驱动特性进行分析。为此提出一种基于动力学的柔性四杆机构稳态分析方法,对只含一个柔性关节的四杆机构的驱动特性进行分析,并根据驱动特性曲线对柔性机构的稳态特性进行判断。首先,建立柔性四杆机构的伪刚体模型,利用拉格朗日方程建立动力学模型,解算出主动杆件旋转360°时驱动力的变化曲线;然后,在ADAMS中建立对应的柔性四杆机构模型,将仿真结果与动力学解算结果进行对比,验证动力学模型的准确性;最后,通过一个算例将提出的动力学分析方法与传统能量法的分析结果进行对比,证明动力学分析方法的有效性,同时还可以得到机构在稳态位置与非稳态位置转换过程中驱动力的临界值,为柔性稳态机构的设计提供一种新的方法。提出的基于动力学的双稳态驱动特性,在双稳态开关、双稳态传感器中都可以被设计和应用。     

基于AutoCAD的柔性机构伪刚体模型建立与性能分析

提出了一种在AutoCAD中建立柔性机构伪刚体模型并对其进行性能分析的方法:将柔性机构分类并单元化;利用AutoCAD提供的API,借助参数化建模技术,创建柔性机构构件库;定义构件单元属性,生成机构单元刚度矩阵,获得单元伪刚体模型;经过坐标变换等,得到机构总刚度矩阵,完成伪刚体模型的建立;通过自定义载荷,对伪刚体模型进行性能分析。基于所开发程序,以一种3-RRR平面微定位平台为研究对象,进行了伪刚体模型的建立和性能分析,并将分析结果与ANSYS仿真结果进行了对比,验证了模型的正确性及应用程序的有效性。     

一种全柔顺六稳态机构的设计

多稳态机构因不需输入能量就可保持多个稳定平衡状态而在生产生活中得到越来越广泛的应用。全柔顺多稳态机构免装配、无摩擦、低能耗,但因为柔顺片段大变形时容易产生应力集中、输出非线性等原因,全柔顺多稳态机构的设计难度较大。提出一种全柔顺六稳态机构的设计方法,由两个临界跳转力不同的双稳态机构和一个柔顺片段组成机构,成功实现六个稳定平衡状态。对柔顺片段用伪刚体模型法建模,并通过比较两部分结构的力-位移特性给出机构具有六个稳定平衡状态的条件,从而避免了非线性分析;考虑机构的实际运动给出柔顺片段的刚度范围计算公式,设计者可据此选择合适的刚度完成全柔顺六稳态机构的设计。用ANSYS得到的输出力特性和样机测试证实了该设计方法的正确。     

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。     

具有零刚度特性的微动平台优化设计

针对传统常力机构存在的运动副间隙、装配误差和摩擦磨损等问题,设计了一种基于柔顺机构的常力微动平台。平台利用直梁正刚度和双稳态梁屈曲行为产生负刚度来实现其零刚度特性。平台由对称的直梁、双稳态梁和刚性连接块组成,直梁和双稳态梁通过连接块并联连接。采用伪刚体法和椭圆积分法相结合的建模方法,建立反映常力平台力学性能的理论模型。通过与有限元分析结果进行比较,分析结果显示所建立的模型能准确反映常力平台的力学性能。基于所建立的力学模型,提出一种提高平台常力运动范围和承载能力的优化设计方法。制作样机对该平台力学性能进行实验测试,实验结果表明,平台能在输出位移范围为[0.6~1.7]mm内能够保持约48N常力,证明了常力平台设计思路的可行性、所建模型的准确性和优化方法的有效性。     

平面双稳态柔性机构的设计

讨论了平面双稳态的物理含义以及平面双稳态柔性机构的主要分析理论;在实例模型分析的基础上提出了允许设计者调整稳定平衡位置的强迫式双稳态柔性机构设计思想,并结合实例对这一设计思想进行了理论分析。结果表明,这可极大地提高机构工作时的精确性、稳定性、可靠性。     

A 3-DOF Pseudo-Rigid-Body Model for Tension-Based Compliant Bistable Mechanisms

Compliant bistable mechanisms, devices with two distinct stable equilibrium positions, are used in a variety of applications, such as switches, clasps, and valves. Many kinds of compliant bistable mechanisms were proposed and studied during the past decade. Among them, tension-based compliant bistable mechanisms, that incorporate tension pivots as their flexible members, feature in short travel distance and low power consuming. So far, the design of this kind of bistable mechanisms is done using finite element method through trial and error, thus is time-consuming. By treating the tension pivots as fixed-guided segments and their elongation as a spring, we developed a novel three degree-of-freedom (3-DOF) pseudo-rigid-body model (PRBM) for this kind of bistable mechanisms. The principle of virtual work is used to derive the force-deflection relationship of the PRBM model. The comparison between the PRBM results and the experimental results of the force-deflection characteristics shows that the PRBM can predict not only the bistable behavior of the tension-based bistable mechanisms, but also their soft spring-like post-bistable behavior and the spring-like force-deflection characteristics when pulling in the reverse direction from the as-fabricated position, which is called reverse behavior. The 3-DOF PRBM can be used to design and identify tension-based bistable mechanisms. Using the PRBM instead of the trial-and-error method can greatly reduce the development time of this kind of bistable mechanisms.     

基于局部截面构型优化的双稳态结构跳跃阈值控制与设计*

双稳态结构正反行程跳跃阈值不相等引起的驱动困难是制约其工程应用的瓶颈问题。基于大变形有限元理论分析了影响双稳态结构跳跃过程的关键因素,引入跳跃阈值力、稳态保持力以及双稳态特征系数(二者的比值)作为描述双稳态特征的指标,提出了基于局部单元截面构型优化的双稳态跳跃阈值控制方法,建立了具有特定跳跃力学特征的双稳态结构优化设计模型,以局部单元的截面尺寸、个数及位置为设计变量,采用分步优化的方法,得到了几类具有不同双稳态特征系数的余弦梁新构型,分析了变截面单元厚度及布置方式对跳跃阈值及路径的影响关系。数值仿真结果表明,局部截面构型改变前后双稳态结构的跳跃时间及振动频率变化不大。考虑试验加载位置与夹持条件对双稳态特征系数的影响,仿真与试验结果基本一致,验证了所提出的双稳态结构跳跃力控制方法的有效性。     

Analysis of frequency characteristics and sensitivity of compliant mechanisms

Based on a modified pseudo-rigid-body model, the frequency characteristics and sensitivity of the large-deformation compliant mechanism are studied. Firstly, the pseudo-rigid-body model under the static and kinetic conditions is modified to enable the modified pseudo-rigid-body model to be more suitable for the dynamic analysis of the compliant mechanism. Subsequently, based on the modified pseudo-rigid-body model, the dynamic equations of the ordinary compliant four-bar mechanism are established using the analytical mechanics. Finally, in combination with the finite element analysis software ANSYS, the frequency characteristics and sensitivity of the compliant mechanism are analyzed by taking the compliant parallel-guiding mechanism and the compliant bistable mechanism as examples. From the simulation results, the dynamic characteristics of compliant mechanism are relatively sensitive to the structure size, section parameter, and characteristic parameter of material on mechanisms. The results could provide great theoretical significance and application values for the structural optimization of compliant mechanisms, the improvement of their dynamic properties and the expansion of their application range.     

Constraint-force-based approach of modelling compliant mechanisms: Principle and application

Numerous works have been conducted on modelling basic compliant elements such as wire beams, and closed-form analytical models of most basic compliant elements have been well developed. However, the modelling of complex compliant mechanisms is still a challenging work. This paper proposes a constraint-force-based (CFB) modelling approach to model compliant mechanisms with a particular emphasis on modelling complex compliant mechanisms. The proposed CFB modelling approach can be regarded as an improved free-body- diagram (FBD) based modelling approach, and can be extended to a development of the screw-theory-based design approach. A compliant mechanism can be decomposed into rigid stages and compliant modules. A compliant module can offer elastic forces due to its deformation. Such elastic forces are regarded as variable constraint forces in the CFB modelling approach. Additionally, the CFB modelling approach defines external forces applied on a compliant mechanism as constant constraint forces. If a compliant mechanism is at static equilibrium, all the rigid stages are also at static equilibrium under the influence of the variable and constant constraint forces. Therefore, the constraint force equilibrium equations for all the rigid stages can be obtained, and the analytical model of the compliant mechanism can be derived based on the constraint force equilibrium equations. The CFB modelling approach can model a compliant mechanism linearly and nonlinearly, can obtain displacements of any points of the rigid stages, and allows external forces to be exerted on any positions of the rigid stages. Compared with the FBD based modelling approach, the CFB modelling approach does not need to identify the possible deformed configuration of a complex compliant mechanism to obtain the geometric compatibility conditions and the force equilibrium equations. Additionally, the mathematical expressions in the CFB approach have an easily understood physical meaning. Using the CFB modelling approach, the variable constraint forces of three compliant modules, a wire beam, a four-beam compliant module and an eight-beam compliant module, have been derived in this paper. Based on these variable constraint forces, the linear and non-linear models of a decoupled XYZ compliant parallel mechanism are derived, and verified by FEA simulations and experimental tests.     

纳米级精度柔性机器人的设计方法及实现研究

从材料、几何结构、柔性铰链、驱动器、运动与负载及加工等几个方面总结了面向精密作业的柔性机器人设计准则。对柔性机器人的设计方法进行了探讨。以精密作业中的具体应用为例，依据这些设计方法与准则，从机械本体和驱动器控制2个方面详细描述了可实现纳米级精度的3自由度柔性机器人样机设计的具体实现过程，设计结果满足任务要求。     

Engineering signal processing based on bistable stochastic resonance

The stochastic resonance (SR) characteristics of a single bistable system and two bistable systems connected in series with small and large parameters have been investigated, respectively. The viewpoint is that a single bistable system is better than a cascaded bistable system in detecting a weak periodic signal in frequency domain, and that, in time field, a cascaded system can detect a more beautiful waveform of either a periodic or an aperiodic weak signal. However, for some detection of a special signal, the periodic pulse for instance, a single bistable system is of great benefit to the signal extraction in time domain. It can provide some important information properties that are hardly obtained in frequency spectrum. Two examples of detecting a weak signal embedded in strong noise are presented in the end to illustrate that a single bistable system and a cascaded bistable system are both powerful tools for signal processing.     

微型机械运动参数测试仪光学机械系统研究

微型机械运动参数的测试是微型机械研究工作的基础.本文介绍微型机械运动参数测试仪的工作原理和关键技术,并对仪器的精度进行了分析.     

不锈钢多轴非比例加载低周疲劳的研究

对３１６Ｌ不锈钢进行了单轴及多轴非比例加载低周疲劳试验及其微结构的观察,分析了非比例循环附加强化及低周疲劳寿命对应变路径依赖性的微观机理,基于微观机理的研究结果,以位错结构特征参量的统计平均值给出了加载路径的非比例度定义,建立了新的多轴非比例加载低周疲劳寿命估算公式。