关键词： 空间漂浮基机械臂系统   动力学   耦合机理   解耦方法   路径规划  

摘要： 空间漂浮基机械臂技术是空间机器人领域的关键技术之一，在过去的四、五十年间取得了突飞猛进的发展。它将空间感知，自主机动和复杂操作能力集于一身，通过自主或人为操作、在轨或地面遥操作等方式执行空间站在轨组装维修，非合作目标捕获，组件更换，燃料加注，轨道更迭等任务。尤其是近年来，随着计算机科学和人工智能等热门学科的发展，机器人技术迎来了新一轮的研究热潮。当一个个最新研究成果应用于空间机器人领域当中去的时候，有理由相信，在不远的将来，空间机器人技术将会成为空间探索科学中一个显著的亮点，它也将更为高效地推动人类宇宙探索事业向前进步。\n 空间漂浮基机械臂系统耦合动力学与解耦研究是研究者们长期以来最为关注的理论问题之一，它也是解决基体位姿控制系统能力饱和问题和能源消耗问题的最基本、最有效的手段。辅之以动力学建模、工作空间分布和路径规划方面的研究工作，使得动力学解耦方法在实际的任务执行过程中被更为有效的应用。本文是以航天预研课题“空间XXX科学实验平台”、商业航天预研项目“XXX电池阵和天线展开机构”、国家自然科学基金项目“重载灵巧高刚度搅拌摩擦焊机器人动态特性分析及优化设计”(项目编号51505470)等为依托而进行的。本文将围绕空间漂浮基机械臂系统动力学建模理论新方法、工作空间分布特点及其组成、机械臂与基体之间的动力学耦合原因、性质及其解耦方法、考虑解耦要求的路径规划与避障和相关仿真实验等方面，依次开展了以下几个方面的研究工作:\n (1)漂浮基空间机器人自上世纪七、八十年代开始逐渐进入人们视野，目前，以位姿可控的卫星或航天器上搭载单个或多个机械臂形式存在居多。机械臂在执行任务过程中，如何减少对基体位置、姿态的影响是本文研究的核心问题。因此，一方面，对前人关于空间漂浮基机械臂建模、动力学耦合分析等方面的工作进行调研，并总结其中存在的不足之处，另一方面，搭建文章研究框架，为后续的研究工作提供路线依据。\n (2)数学模型是一个物理系统所要面对的实际问题与数学工具之间的必不可少的沟通桥梁。文中分别从坐标系选择、模型描述方法、非完整性分析等角度对系统进行了梳理;提出了容许运动空间的概念，并以此为依据，引出了一种针对空间漂浮基机械臂系统的建模新方法。\n (3)工作空间是反映系统工作能力的一个重要特征，工作空间分析也是机器人执行任务过程中必不可少的一环。与固定基机械臂系统相比，漂浮基系统工作空间分布更加复杂，这是由系统的非完整性所导致的。当系统进行逆向运动学、动力学控制时，系统的动力学奇异性也会给整个过程带来困难。因此，通过工作空间分析和动力学奇异分析过程，寻找出一个可以成功规避动力学奇异现象的路径无关工作空间是本文的又一目的。这也是耦合动力学解耦过程的一个必要前提。\n (4)动力学耦合机理与解耦方法是本文研究的重中之重。为了显式的描述这一问题，提出了动力学耦合度的概念，并介绍了耦合度的度量方法。用耦合度椭球这个概念几何体还可以从感官上给出一种定性的耦合度大小的表达。通过对系统的约束和任务分类，运用响应零空间方法，将动力学解耦问题转化为非奇异线性方程的求解问题。然后，结合路径无关工作空间分析结果和虚拟机械臂方法，验证路径无关工作空间中运动分解速度控制方法成功避免动力学奇异问题的可行性。\n (5)动力学解耦的效果取决于系统的任务约束种类和个数，换句话说，有时任务约束可能存在矛盾，并不能顾此即彼，动力学解耦过程可能存在无解的情形。所以，文中提出了将动力学解耦作为优化目标之一的路径规划方法来解决这一问题。其中，从关节空间中进行路径规划避免了系统遇到非奇异性问题的影响;量子遗传算法的应用体现出其收敛速度快、搜索能力强的优点;Pareto最优解为相互矛盾优化目标提供了解决方案;多约束避障问题的路径规划为解决实际问题提供了重要的解决思路。\n (6)运用SpaceDyn仿真平台，进行相关仿真试验。为了说明机械臂与基体之间存在动力学耦合现象，进行仿真实验一:正向运动学仿真实验，观察基体位姿所受影响，以及末端位置变化曲线;为了说明动力学解耦方法的有效性，进行仿真实验二:动力学解耦过程仿真，观察基体位姿响应。

关键词： 机械臂   动力学建模   凯恩迭代式算法   三维仿真平台  

摘要： 机械臂动力学是机械臂系统研究中的重要部分之一，机械臂动力学主要研究的是机械臂运动与作用力之间的关系，研究机械臂动力学对于机械臂实时控制和机械臂结构设计具有重要意义。以三自由度转动机械臂为研究对象，对机械臂的运动学进行了研究，并介绍了凯恩方法，然后以凯恩方法为基础，提出凯恩迭代式算法对机械臂进行动力学建模，并利用牛顿-欧拉方法，对机械臂动力学解算结果进行验证。\n 首先，利用D-H方法，完成机械臂的运动学模型建立，并利用广义齐次变换阵的串接性质，进行机械臂正运动学解算。然后借助于欧几里德范数，完成三自由度转动机械臂的逆运动学解算，获得其解析解，排除不合理的解。并通过逆运动学最优解方法，得到最终的机械臂各关节旋转角度。同时进行机械臂正运动学解算与逆运动学解算互验。机械臂运动学解算的结果对后续机械臂动力学仿真具有重要作用。\n 其次，基于凯恩方法，提出凯恩迭代式算法，完成机械臂动力学建模。分别就关节为转动关节和棱柱关节的两种情况进行分析，采用迭代式计算公式完成机械臂杆件速度、加速度及偏速度的计算，关节力或力矩的计算分为无负载与有负载两种状况。其次分析了该算法的计算复杂度，并与其它几种动力学方法进行了对比。然后以三自由度转动机械臂为研究对象，利用凯恩迭代式算法建立其动力学模型，完成机械臂动力学解算，得到最终的机械臂动力学解算结果。最后利用经典的牛顿-欧拉方法对凯恩迭代式算法的解算结果进行检验。\n 最后，基于VS2010与三维图形软件开发包Open Inventor建立机械臂三维仿真平台。该仿真平台包含机械臂运动学模块、机械臂动力学模块、三维仿真模块、3D渲染性能曲线模块和人机交互模块等，并利用该仿真平台进行了机械臂拾放小球的仿真实验。实验证明了机械臂运动学模型、逆运动学解算方法和动力学建模方法的正确性。然后利用MATLAB进行了机械臂的运动学与动力学仿真，将二者进行对比，结果基本一致，进一步验证了本文提出的方法的正确性。

关键词： 汽车   电子机械制动系统   制动力   检测方法  

摘要： 汽车电子机械制动系统具有环保、节能等突出优点。目前在研的电子机械制动系统中检测制动力的传感器具有安装困难、成本高等缺点,影响了其广泛应用。本文应用热力学理论和数学方法,结合实验对该系统的刹车片热性能、温度场等进行了研究,初步建立了刹车片温升和冷却条件下计算制动力的模型,并用实验进行了验证。

关键词： 120   mm迫击炮   供输弹机械手   动力学仿真  

摘要： 针对传统迫击炮自动化程度低、战场生存能力差等弱点,设计了用于120 mm迫击炮的供输弹机械手,实现3~4发/每分钟的射击速度。采用ADAMS软件进行机械手的动力学仿真,得到包括炮弹运动参数、机械手振动变形以及关节驱动等关键数据。

关键词： Ubiquitin   NuG2   Molecular Dynamics simulations   Atomic force microscopy   Non-exponential kinetics  

摘要： Protein unfolding often does not obey a simple two-state behavior. Previous single molecule force spectroscopy studies demonstrated stretched exponential kinetics of protein unfolding under a constant pulling force, the molecular origin of which remains subject to debate. We here set out to extensively sample the mechanical unfolding of ubiquitin and NuG2 by Molecular Dynamics (MD) simulations. Both proteins show kinetics best fit by stretched exponentials, with stretching exponents similar to those found in experiments, even though static disorder is absent in our short MD simulations. Instead, we can ascribe non-exponential kinetics to dynamic disorder, due to conformational fluctuations on the nanosecond timescale. Our study highlights the general role of dynamic disorder in protein kinetics on a broad range of time scales even including those probed in MD simulations. (C) 2016 Elsevier Inc. All rights reserved.

关键词： FOCAL adhesion kinase   CELL adhesion   CELL physiology   ATOMIC force microscopy   VINCULIN   MECHANOTRANSDUCTION (Cytology)  

摘要： The adhesion of cells to the extracellular matrix is a hierarchical, force-dependent, multistage process that evolves at several temporal scales. An understanding of this complex process requires a precise measurement of forces and its correlation with protein responses in living cells. We present a method to quantitatively assess live cell responses to a local and specific mechanical stimulus. Our approach combines atomic force microscopy with fluorescence imaging. Using this approach, we evaluated the recruitment of adhesion proteins such as vinculin, focal adhesion kinase, paxillin, and zyxin triggered by applying forces in the nN regime to live cells. We observed in real time the development of nascent adhesion sites, evident from the accumulation of early adhesion proteins at the position where the force was applied. We show that the method can be used to quantify the recruitment characteristic times for adhesion proteins in the formation of focal complexes. We also found a spatial remodeling of the mature focal adhesion protein zyxin as a function of the applied force. Our approach allows the study of a variety of complex biological processes involved in cellular mechanotransduction. Published by AIP Publishing.

关键词： CL-20/HMX cocrystal explosive   Mechanical properties   Binding energy   Detonation performance   Materials Studio   Molecular dynamics  

摘要： To research and estimate the effects of molar ratios on structures, stabilities, mechanical properties, and detonation properties of CL-20/HMX cocrystal explosive, the CL20/HMX cocrystal explosive models with different molar ratios were established in Materials Studio (MS). The crystal parameters, structures, stabilities, mechanical properties, and some detonation parameters of different cocrystal explosives were obtained and compared. The molecular dynamics (MD) simulation results illustrate that the molar ratios of CL-20/HMX have a direct influence on the comprehensive performance of cocrystal explosive. The hardness and rigidity of the 1:1 cocrystal explosive was the poorest, while the plastic property and ductibility were the best, thus implying that the explosive has the best mechanical properties. Besides, it has the highest binding energy, so the stability and compatibility is the best. The cocrystal explosive has better detonation performance than HMX. In a word, the 1:1 cocrystal explosive is worth more attention and further research. This paper could offer some theoretical instructions and technological support, which could help in the design of the CL-20 cocrystal explosive.

关键词： Coarse-grained   Uniaxial tension   Multi-layer graphene   Mechanical properties  

摘要： In this work, we investigate the effect of temperature, defect, and strain rate on the mechanical properties of multi-layer graphene using coarse-grained molecular dynamics (CGMD) simulations. The simulation results reveal that the mechanical properties of multi-layer graphene tend to be less sensitive to temperature as the layer increases, but they are sensitive to the distribution and coverage of Stone Wales (SW) defects. For the same number of defect, there is less decline in the fracture stress and Young's modulus of graphene when the defects have a regular distribution, in contrast to random distribution. In addition, Young's modulus is less influenced by temperature and defect, compared to fracture stress. Both the fracture stress and Young's modulus have little dependence on strain rate. (C) 2016 Elsevier B.V. All rights reserved.

关键词： mechanically renewed silver electrode   kinetics of electroreduction of anions   impedance method   voltammetry   modeling  

摘要： The kinetics of electroreduction of peroxodisulfate anions on a mechanically renewed silver electrode is studied by voltammetric and impedance methods. Impedance diagrams obtained in the region of negatively charged metal surface are successfully modeled by the equivalent circuit formed by the solution resistance and also the reaction resistance connected in parallel with the constant-phase element substituted for the double layer capacitance. The analysis of experimental data carried out in terms of this circuit and their comparison with the literature data makes it possible to assume that the reduction kinetics of S2O (8) (2-) anions on this electrode can be adequately described in the framework of the phenomenological theory of slow discharge. The reasons for deviation of the literature data on the kinetics of this reaction on polycrystalline Ag electrode from the relationships following from the slow discharge theory are put forward and substantiated.