用侧向力显微镜对力/电/热耦合作用下金表面力学行为的研究

对微构件力/电/热等多域场下力学行为的研究有着重要的意义,利用原子力显微镜采用纳米压痕法对样品金在力-电-热耦合作用下的表面力学性能进行了研究,实验表明在压痕过程中,无论在无电场作用下还是有电场作用下,压痕周围的金属由于挤压形成了凸起,从扫描得到的形貌图中可以明显的看出,压痕周围的亮区为材料被挤出的区域.此外,在外加直流电场作用下,随电流的增大,硬度值有增大的趋势,而残余压痕和弹性模量都呈现减小的趋势.     

一种Stewart结构六维力／力矩传感器参数辨识研究

介绍了一种大量程Stewart结构六维力／力矩传感器系统．建立了传感器力／力矩测量数学模型,构建了基于运动学逆解的优化目标函数．提出了一种新的参数标定法,称作分支轮换标定法．基于所研发的六维力／力矩传感器系统进行了实验研究,实验结果表明分支轮换法可以有效地辨识出传感器的结构参数,提高了测量精度．该方法可用于类似结构的六维力／力矩传感器参数标定．     

无标度网络上分片线性传染力与免疫作用下的流行病动力学

本文研究了含有免疫作用的易感染者-感染者-移出者传染病模型（即SIR模型）在复杂网络上的动力学行为,讨论了免疫作用对疾病传播的影响．当接种比例大于零时,传染率需要跨越更大的传染临界值疾病才能流行,且随着时间的增大传染临界值也增大．所以通过接种疫苗确实可以起到预防和控制疾病在复杂网络上传播的作用．具体讨论了具有分片线性传染力的SIR模型在无标度网络上的流行病传播阈值,并运用分片线性传染力得到了传播阈值为正的条件．接着分析了各种免疫策略的SIR模型,得出各类免疫后的传播阈值,并进行了数值模拟和比较．在相同的免疫概率下,目标免疫比随机免疫、近邻免疫、主动免疫更为有效．     

机器人力／位置自适应模糊控制

在机器人力／位置混合控制的基础上，本文提出了一种对力控制回路采用自适应模糊控制的方法，有利于提高系统对机器人末端操纵器五外界工作环境接触时，其接触刚度不确定性的自适应能力，仿真结果表明，该控制方法与常规ＰＩＤ控制相比，系统的自适应能力和鲁棒性有显著的改善。     

面向应用需求的力／力矩传感器技术发展动向

本文论述了面向应用需求的力/力矩传感器发展现状和趋势，从机器人学、特种机器 人及机器人化机器几个方面讨论了力传感器研究的现状和应用需求，并指出力传感技术发展 的总趋势为利用新材料、新工艺实现微型化、集成化，利用新原理、新方法实现更多种类的 信息获取，再辅以先进的信息处理技术提高传感器的各项技术指标，以适应更广泛的应用需 求．     

基于可视外部力/力矩隐喻工具的虚拟样机动力学交互分析方法

在虚拟样机动力学分析中，对施加的外部力／力矩的属性和作用进行了分析，实现了力／力矩隐喻(metaphor)工具在虚拟环境中的直观定义，并基于多刚体Lagrange动力学模型提出直观驱动的交互仿真方法，建立了可视化隐喻工具同虚拟样机间交互分析过程的动力学广义模型．简化了虚拟环境中用户同虚拟对象间的交互行为模型．最后．通过对汽车发动机曲柄活塞部分建立Lagrange动力学模型．并以建立的隐喻工具进行交互分析的实例论证了该方法的有效性以及隐喻工具的直观性．     

6-DOF并联机器人修正位置/力控制系统的研究

该文在６－ＤＯＦ并联机器人运动控制系统的基础上，研究了一种修正位置／力控制系统，讨论了系统设计与实现中一些关键性技术问题．文中内容对改善并联机器人控制质量与性能大有益处．     

附加力外环的机器人力／位置自适应模糊控制

提出一种由神经网络训练模糊控制规则的自适应模糊控制器,并应用附加力外环的机器人力／位置控制。在不改变一般工业机器人原有位置控制的前提下,实现力／位置自适应模糊控制。实验结果表明,该方法可使机器人控制系统对工作环境接触刚度的自适应能力得到显著改善。     

直接在位置控制机器人上实现力/位置自适应模糊控制

本文提出一种直接在位置控制机器人上实现力／位置自适应模糊控制的方案，使得对于一般工业机器人，在不改变其原有位置控制器的前提下，实现力／位置控制．仿真结果表明，该控制方法使机器人控制系统对工作环境接触刚度的自适应能力得到显著的改善．     

基于迭代学习的机械手操作空间力/位置混合控制算法

基于对常规机械手操作空间力／位置混合控制算法的简单回顾，及对该算法所遇到困难的分析，提出了一种基于迭代学习的机械手操作空间力／位置混合控制算法，来改善机械手同高刚度环境接触时，机械手力／位置混合控制的动态控制性能．给出了学习算法的收敛条件及其证明．实验表明该算法具有快速的收敛性，能达到很高的力／位置动态控制精度．     

Vortices around Janus droplets under externally applied electrical field

In this study, the Janus droplet is an oil droplet covered with aluminum oxide nanoparticles on one side of the droplet surface under applied DC electrical field. The vortices around Janus droplets fixed on a horizontal surface were studied in this paper. A numerical model was set up to simulate the vortices around the Janus droplet in electric field. The simulation results illustrate that the electric field determines the strength of the vortices around a fixed Janus droplet, and the surface coverage of the positively charged nanoparticles on a Janus droplet affects the size and location of the vortices. The numerically predicted results were further validated experimentally by visualizing the vortices around Janus droplets in an externally applied DC electric field. Furthermore, as the Janus droplets are generated in electric field, the surface coverage by the nanoparticles depends on the strength of the electric field; therefore, the effect of the electric field on the nanoparticle covered surface area of a Janus droplet and the vortices was analyzed.     

Tuning PID control parameters for micro-piezo-stage by using grey relational analysis

The materials used in piezo-actuators, which ferroelectric, demonstrate inherent hysteresis behavior in an applied electric field. Unfortunately, this behavior typically results in control problems, with severe inaccuracy and degraded tracking performance. This work focuses on the control of the piezoelectric positioning stage. The hysteresis function is expressed as an external disturbance. Grey relational analysis is proposed to examine the sensitivity of the tuning of the PID parameters for such system, to achieve the desired performance. Accordingly, the PID parameters can be tuned to handle uncertain information. The experimental results of the proposed grey relational approach also indicate that developing a low-cost, reliable, automatic, less time-consuming controller than conventional PID control for a piezoelectric positioning stage is technically and economically feasible. Hence, the results obtained using this proposed methodology can be applied to various mechanical systems, such as positioning control subjected to external disturbances.     

Deflection of coupled elasticity–electrostatic bimorph PVDF material: theoretical,FEM and experimental verification

Piezoelectric materials have wide applications in the field of mechanical, aerospace and civil engineering because of its voltage dependent actuation. Piezoelectric material goes through voltage generation whenever deflection is induced in it and vice versa. Piezoelectric bimorph beam has been widely used for sensing and actuating. In the actuation mode, an electric field is applied across the beam thickness, one layer contracts while the other expands. This results in the bending of the entire structure and tip deflection. In the sensing mode, the bimorph is used to measure an external load by monitoring the piezoelectric induced electrode voltages. In this research work, a 2D bimorph piezoelectric actuator model having two layers made of polyvinylidene fluoride (PVDF) material was developed to examine the inverse piezoelectric effect. Finite element analysis (FEA) was carried out on specially designed actuator model by using MATLAB Partial Differential Equation (PDE) Toolbox™. Theoretical analysis has been carried out to measure the tip deflection under applied electric field. The laboratory test was performed to investigate the deformation behavior of piezoelectric actuator. It is observed that, more the electric field applied, more the material would be deformed in a particular direction. The experimental results are in good agreement with numerical results.

     

Micro-PIV measurements of induced-charge electro-osmosis around a metal rod

A cylindrical gold-coated stainless steel rod was positioned at the center of a straight microchannel connecting two fluid reservoirs on either end. The microchannel was filled with 1 mM KCl containing 0.5 μm diameter carboxylate-modified spherical particles. Induced-charge electro-osmotic (ICEO) flow occurred around the metallic rod under a sinusoidal AC electric field applied using two platinum electrodes. The ICEO flows around the metallic rod were measured using micro particle image velocimetry (micro-PIV) technique as functions of the AC electric field strength and frequency. The present study provides experimental data about ICEO flow in the weakly nonlinear limit of thin double layers, in which, the charging dynamics of the double layer cannot be presented analytically. The measured ICEO flow pattern qualitatively agrees with the theoretical results obtained by Squires and Bazant (J Fluid Mech 509:217–252, 2004). Flow around the rod is quadrupolar, driving liquid towards the rod along the electric field and forcing it away from the rod in the direction perpendicular to the imposed electric field. The measured ICEO flow velocity is proportional to the square of the electric field strength, and depends on the applied AC frequency.     

胶囊内窥镜机器人的外磁场驱动方法

研究了利用外部磁场驱动胶囊内窥镜机器人的方法. 我们将梯度线圈和匀场线圈进行组合，通过调整线圈加载电流以及线圈绕可平移病床的旋转来合成空间上梯度均匀、低场强区域可动态调整的驱动磁场，作用于机器人内置的永磁体,从而获得期望的驱动力和辅助转矩.仿真表明组合线圈构成的磁场环境对于驱动相当有利. 我们提出的驱动方法具有良好的可控性和安全性，为进一步研究梯度磁场驱动适于体内各种腔管的微机器人奠定了基础.     

The Dirichlet-to-Neumann map for two-dimensional crack problems

A coupled analytic/finite-element method is presented for two-dimensional crack problems. Two classes of problems are studied. The first considers problems where non-linear constitutive processes occur in a region near the crack tip and the remotely applied loading can be characterized by the linear elastic K-field and perhaps the T-stress. In this case, the finite-element method is applied in a circular region around the crack tip where non-linear constitutive response is occurring, and stiffness contributions associated with a numerically implemented Dirichlet-to-Neumann map are imposed on the circular boundary to account for the large surrounding elastic domain and the remote applied loading. The second class of problems considers entirely linear elastic domains with irregular external boundaries and/or complex applied loadings. Here, the discrete Dirichlet-to-Neumann map is used to represent a circular region surrounding the crack tip, and finite-elements are used for the external region. In this case the mixed mode stress intensity factors and the T-stress are retrieved from the map.     

A reduced integration finite element technology based on a thermomechanically consistent stabilisation for 3D problems

In this paper we suggest a new finite element technology for thermomechanically fully coupled problems. It is based on the method of reduced integration with hourglass stabilisation. The proposed formulation allows the evaluation of the additional thermal field at one Gauss point, e.g. in the centre of the element. One crucial aspect is the Taylor expansion of all constitutively dependent variables, as e.g. the heat flux, the internal and the external rates of dissipation, with respect to the centre of the element. In this way a so-called thermal hourglass stabilisation, analogously to the classical mechanical hourglass stabilisation, is derived. The thermal stabilisation parameters are defined well and the computational efficiency which comes along with the consistent formulation is very high. The new element formulation is applied on thermomechanically coupled problems of finite elastoplasticity. It can be also easily used in the context of other multi-field problems.     

Random vibrations with MACSYMA

The symbolic manipulation code macsyma is applied in this paper to five problems in the field of random vibrations of mechanical systems. These include cumulants of a distribution, single degree of freedom deterministic and random parameter oscillator excited by an external colored noise random force, the infinite degree of freedom beam under space-wise random loading, and a differential equation of order N with random coefficients. In these cases, application of macsyma is shown to greatly extend the researcher's ability to derive closed-form or approximate analytical solutions. In more complicated problems such as the single degree of freedom system with stiffness treated as a stationary random forcing function, and subjected to random excitation, macsyma is applied to transform intermediate analytical results into a fortran code for subsequent numerical analysis.     

电场作用对改进的HR神经元模型的同步影响

MSF,即主稳定函数,是一种使用Lyapunov指数理论来确定复杂同型网络同步状态的稳定性的工具.负的MSF值表明网络可以同步.我们构建了一种双变量HR模型来描述神经元在电场作用下的同步行为,将神经元尺寸和外加电场作为影响电场作用的调控因素,利用简化的MSF方法,研究主稳定函数MSF和电荷尺寸及外加电场的关系.结果显示,电场效应对神经网络同步的作用是丰富的.施加较强的恒定电场可以促进网络同步,而施加交变电场则会抑制同步.另外,神经元半径也会影响电场效应的作用结果,在较大的神经元半径下,神经网络会更容易同步.