关键词： 七自由度机械臂   运动学   动力学   ADAMS  

摘要： 针对七自由度机械臂(KUKA LBR IIWA机械手臂)的动力学模型正确性问题,对其关节1进行动力学分析。首先,采用DH法进行结构建模,得出正运动学方程,依据七自由度机械臂自运动特性,计算出机械臂各关节角。然后,采用牛顿—欧拉方法对机械臂进行动力学建模,推导出机械臂各关节约束力/力矩方程。最后,采用ADAMS动力学仿真和实物实验论证,分别对机械臂关节1在静态和动态两种情况所受到的力/力矩进行比较。结果表明:运用理论公式推导、ADAMS仿真和实验验证,综合分析出机械臂关节1受力/力矩结果误差不大,具有一致的,为后续机器人控制、机器人动态分析和机械臂动力学优化等问题研究奠定基础。

关键词： 工程机械臂   系统结构   动力学  

摘要： 在计算机技术、控制技术不断发展的背景下,机械产品也呈现出高速化、精准化、环保化的发展趋势,这就需要对机械产品特性进行分析和研究,为机械产品设计提供可靠依据。在工程机械领域中,工程机械臂占据着重要地位,其工作环境较为恶劣,受到的负荷情况较为复杂。为保证机械臂安全、可靠地工作,本文分析了工程机械臂系统结构的动力学原理,探讨了其动力学特性分析方法。

关键词： Brain state   Sleep   Whole brain modeling   Perturbation  

摘要： Human neuroimaging research has revealed that wakefulness and sleep involve very different activity patterns. Yet, it is not clear why brain states differ in their dynamical complexity, e.g. in the level of integration and segregation across brain networks over time. Here, we investigate the mechanisms underlying the dynamical stability of brain states using a novel off-line in silico perturbation protocol. We first adjust a whole-brain computational model to the basal dynamics of wakefulness and deep sleep recorded with fMRI in two independent human fMRI datasets. Then, the models of sleep and awake brain states are perturbed using two distinct multifocal protocols either promoting or disrupting synchronization in randomly selected brain areas. Once perturbation is halted, we use a novel measure, the Perturbative Integration Latency Index (PILI), to evaluate the recovery back to baseline. We find a clear distinction between models, consistently showing larger PILI in wakefulness than in deep sleep, corroborating previous experimental findings. In the models, larger recoveries are associated to a critical slowing down induced by a shift in the model's operation point, indicating that the awake brain operates further from a stable equilibrium than deep sleep. This novel approach opens up for a new level of artificial perturbative studies unconstrained by ethical limitations allowing for a deeper investigation of the dynamical properties of different brain states.

关键词： Waxy maize   Swelling kinetics   Granule size distribution   Polymer swelling theory   Second virial coefficient   Cryo SEM  

摘要： The evolution of 8% suspension of waxy maize starch granule size distribution when subjected to heating to 65, 70, 75, 80, 85 and 90 degrees C at a heating rate of 15 degrees C/min were measured. Granule swelling was more pronounced at higher temperatures with an increase in the average size from 13 gm to 25-28 mu m, eventually approaching equilibrium. Cryo SEM images revealed porous structure of swollen granule. The proposed model for starch swelling accounts for entropy of mixing, enthalpy of water-starch interaction and elastic restoring force. The second virial coefficient of waxy maize in aqueous medium was characterized by static light scattering. Chemical potential profile as well as the temperature profile within the granule were predicted from the solution of unsteady state diffusion and heat conduction respectively. The granule size was then inferred from the chemical potential profile. The proposed model predicts the evolution of average granule size and granule size distribution accurately. (C) 2017 Elsevier Ltd. All rights reserved.

关键词： Thermoresponsive hydrogel   Cryogels   Nanocomposite   N-Isopropyl acrylamide   Superporous  

摘要： The superporous thermosensitive PNIPA/clay hydrogels were prepared by the advanced two-step freezing polymerization. The formation and properties of the cryogels were controlled by freezing conditions, such as time of freezing during the two-step polymerization and the rate of cooling. The freezing of the reaction mixture in different well-defined stages of structure evolution during polymerization made it possible to fine tune the structure, morphology, and properties of cryogels. The development of structure during polymerization was followed by NMR and chemorheology, and moreover, the morphology, porosity, swelling behavior, and mechanical properties of the cryogels were determined. The results contribute to the basic understanding of the structure evolution under freezing conditions and to the knowledge of the mechanism of a cryogel formation. The smart thermoresponsive gels with a wide variety of properties were prepared, ranging from the weak ultrafast responding cryogels (deswelling in 30 s, reswelling in 8 min), prepared by the early freezing, up to the porous gel with extraordinary mechanical properties (sigma (b) = 320 kPa, epsilon (b) = 900%) still displaying a relatively fast thermal volume transition. The advanced two-step freezing polymerization is shown to be a suitable general approach to controlling and tuning porosity, as well as swelling and mechanical properties of porous gels.

关键词： Isomerization   Solvents   Vacuum   Computational chemistry   Computer simulations  

摘要： Azobenzene-based molecular photoswitches are becoming increasingly important for the development of photoresponsive, fast interconversion between a more stable trans and a metastable cis configuration can be established resulting in pronounced changes in functional soft-matter material systems. Upon illumination with light, conformation, dipole moment or hydrophobicity. A rational design of functional photosensitive molecules with embedded azo moieties requires a thorough understanding of isomerization mechanisms and rates, especially the thermally activated relaxation. For small azo derivatives considered in the gas phase or simple solvents, Eyring's classical transition state theory (TST) approach yields useful predictions for trends in activation energies or corresponding half-life times of the cis isomer. However, TST or improved theories cannot easily be applied when the azo moiety is part of a larger molecular complex or embedded into a heterogeneous environment, where a multitude of possible reaction pathways may exist. In these cases, only the sampling of an ensemble of dynamic reactive trajectories (transition path sampling, TPS) with explicit models of the environment may reveal the nature of the processes involved. In the present work we show how a TPS approach can conveniently be implemented for the phenomenon of relaxation isomerization of azobenzenes starting with the simple examples of pure azobenzene and a push pull derivative immersed in a polar (DMSO) and apolar (toluene) solvent. The latter are represented explicitly at a molecular mechanical (MM) and the azo moiety at a quantum mechanical (QM) level. We demonstrate for the push pull azobenzene that path sampling in combination with the chosen QM/MM scheme produces the expected change in isomerization pathway from inversion to rotation in going from a low to a high permittivity (explicit) solvent model. We discuss the potential of the simulation procedure presented for comparative calculation of r

关键词： ATC manipulator   digital prototyping   double-globoid cam   rigid-flexible coupling analysis   刚柔耦合分析   双弧面凸轮   数字化样机   ATC机械手   Language of Keywords: English   Chinese  

摘要： Aiming at the double-globoid cam-type ATC manipulator, 3D model was completed;the multi-degree ridge-flexible coupling dynamic model of ATC device was established based on the theoretical basis of mechanical system dynamics. And the input shaft, fork shaft,sleeve and fork of ATC manipulator were flexed through ANSYS and established the rigid-flexible coupling digital prototyping; the dynamic performance of ATC arm up, down and rotary motion was analyzed based on ADMAS. The analysis process simulated the actual working situation of ATC manipulator as much as possible. And the result has a reference value to ATC device desigmproduction and rigid-flexible coupling analysis in the future. [ABSTRACT FROM AUTHOR]

关键词： Mechanics on Lie algebroids   Higher order mechanics   Lagrangian mechanics   Lagrangian submanifolds  

摘要： The study of mechanical systems on Lie algebroids permits an understanding of the dynamics described by a Lagrangian or Hamiltonian function for a wide range of mechanical systems in a unified framework. Systems defined in tangent bundles, Lie algebras, principal bundles, reduced systems, and constrained are included in such description. In this paper, we investigate how to derive the dynamics associated with a Lagrangian system defined on the set of admissible elements of a given Lie algebroid using Tulczyjew's triple on Lie algebroids and constructing a Lagrangian Lie subalgebroid of a symplectic Lie algebroid, by building on the geometric formalism for mechanics on Lie algebroids developed by M. de Leon, J.C. Marrero and E. Martinez on "Lagrangian submanifolds and dynamics on Lie algebroids".

关键词： 制造业   机械制造技术   现状与前景  

摘要： 制造业是国民经济的主体,是立国之本、兴国之器。机械产品制造技术的发展,在制造业中具有举足轻重的地位,是我国制造业实现创新发展的驱动力。多元化的发展条件,促使我国机械制造业拥有广阔的发展前景。