基于VRML的机器人构型及模型控制的研究

分析了虚拟现实建模语言(VRML)坐标系与传统机器人连杆坐标系之间,在坐标轴规定方法上的区别,建立了与VRML坐标系一致的机器人连杆坐标系,推导出与之对应的连杆变换矩阵,并说明了机器人造型及模型控制的VRML实现方法。用所提出的方法对六自由度旋转关节机器人进行构型及模型控制,证明了该方法的有效性。     

基于并行计算的平面可调七杆机构动力学解析模型研究

基于运动学分析、凯恩动力学方程及数字-符号法,提出采用并行计算建立平面可调七杆机构动力学解析模型的方法,并研究了构件杆长及惯性参数变化对驱动力/力矩的影响.利用封闭矢量法对平面可调七杆机构进行运动学分析,得到各构件的速度和加速度表达式;将独立广义坐标、杆长及惯性参数作为符号量,其余参数处理为数值量,导出动力学解析模型的数字-符号表达式,并构造了解析模型的并行算法.由于动力学模型及实时代码优化是离线建立的,并且采用并行计算结构,减少了在线计算时间,从而为实时控制打下了基础.给出的仿真实例证明了此方法的有效性.     

工业机器人仿真系统碰撞检测快速算法

根据6R机器人杆系的特有结构，提出了三角形包围法和端点矢量投影法来提高双机器人协调工作时连杆碰撞检测的效率。通过改进公共面法来进行几何元素的碰撞和干涉检测，给出了相关的数值仿真结果。     

Modified Smith predictor based cascade control of unstable time delay processes

An improved cascade control structure with a modified Smith predictor is proposed for controlling open-loop unstable time delay processes. The proposed structure has three controllers of which one is meant for servo response and the other two are for regulatory responses. An analytical design method is derived for the two disturbance rejection controllers by proposing the desired closed-loop complementary sensitivity functions. These two closed-loop controllers are considered in the form of proportional-integral-derivative (PID) controller cascaded with a second order lead/lag filter. The direct synthesis method is used to design the setpoint tracking controller. By virtue of the enhanced structure, the proposed control scheme decouples the servo response from the regulatory response in case of nominal systems i.e., the setpoint tracking controller and the disturbance rejection controller can be tuned independently. Internal stability of the proposed cascade structure is analyzed. Kharitonov's theorem is used for the robustness analysis. The disturbance rejection capability of the proposed scheme is superior as compared to existing methods. Examples are also included to illustrate the simplicity and usefulness of the proposed method.     

Damping analysis of beams covered with multiple PCLD patches

An analytical approach for vibration damping analysis of beams with partial passive constrained layer damping (PCLD) treatments is extended to the case where the structure is covered by multiple patches. The energy-based approach and assumed-mode method are used to derive the equations governing the vibration displacement responses of the system, which is characterized in terms of the identical transverse displacement of all layers, and the longitudinal displacements of the base beam and the constraining layers. Furthermore, the longitudinal displacements of the base beam and constraining layer are independent of each other, which is in contrast to Kerwin's weak core assumption. The direct frequency response method is employed to determine the modal loss factors of the damped beam in a frequency range of interest. A convergence study is made on the damped beam to determine appropriate numbers of the mode functions for frequency response function (FRF) calculations. Parametric studies are performed with the established analytical approach and the determined numbers of mode functions to study the effects of dividing a PCLD patch into two pieces in different length ratios and also the spacing between the patches on the damping performance of a simply supported beam.     

Modal testing of nanocomposite materials through an optimization algorithm

An efficient identification method for modal testing of viscoelastic composite materials is demonstrated in this paper, through the analytical–experimental transfer function method. The procedure for the identification of analytical–experimental transfer functions is carried out using a genetic algorithm (GA) by minimizing the difference between the measured response from tests and the calculated response, which is a function of the modal parameters. The analytical transfer functions provide a sub-structuring process to identify modes, as a function of damped natural frequencies and loss factors of a complex structure and it is insensitive to experimental noise as well as the modal coupling effect. The proposed method is verified with the calculation of the elastic modulus and modal properties of a cantilever steel beam with the FEM and compared with the identification results of the proposed algorithm. The effectiveness of the proposed method is demonstrated by investigating the static and dynamic behavior of epoxy cantilever beam specimens reinforced with silica nanoparticles. Analytical–experimental transfer functions accurately identified the viscoelastic and dynamic response of the studied specimens, while the results indicated that the inclusion of nanosilica particles increased the stiffness of the epoxy network and the damping response of the reinforced specimens is improved.     

Precession electron diffraction using a digital sampling method

A software-based method for collecting precession electron diffraction (PED) patterns is described. The PED patterns are obtained on a computer controlled transmission electron microscope. A series of electron diffraction (ED) patterns are collected as still ED frames at equal intervals, while the electron beam is precessed by one period (360°) around the optical axis. A PED pattern is obtained by combining the different ED frames, which resembles the sampling of a conventional PED pattern. Since intermediate ED frames are collected, it is possible to perform different post-processing strategies on the ED data. This can be used for geometric corrections to obtain accurate integrated intensities. The alignments and data collection are fully automated and controlled by software. The data quality is comparable to what can be achieved using specialized hardware for precession. The PED data can be used for structure solution and refinement with reasonably good R-values.     

Precession electron diffraction using a digital sampling method

A software-based method for collecting precession electron diffraction (PED) patterns is described. The PED patterns are obtained on a computer controlled transmission electron microscope. A series of electron diffraction (ED) patterns are collected as still ED frames at equal intervals, while the electron beam is precessed by one period (360°) around the optical axis. A PED pattern is obtained by combining the different ED frames, which resembles the sampling of a conventional PED pattern. Since intermediate ED frames are collected, it is possible to perform different post-processing strategies on the ED data. This can be used for geometric corrections to obtain accurate integrated intensities. The alignments and data collection are fully automated and controlled by software. The data quality is comparable to what can be achieved using specialized hardware for precession. The PED data can be used for structure solution and refinement with reasonably good R-values.     

基于解析法的复杂封闭空间有源结构声控制

给出了任意凸多面体声腔在内部点源和外力激励下,腔内声压分布的解析解。该解析方法较传统的数值方法,不仅数据准备量小、速度快精度高,且能够解决目前常用的声弹性法难以解决的复杂几何形状的封闭空腔的声固耦合问题。在此基础上,结合有源结构声控制方法,建立了复杂封闭空间局部区域有源消声的模型,给出了矩阵形式的数值算法,并对一类似车辆驾驶室的复杂封闭空腔进行了有源降噪仿真分析,降噪效果良好,证明该方法可以作为复杂封闭空间有源力消声控制系统的建模基础。     

Experimental and numerical investigation of modal properties for liquid-containing structures

The dynamic response of liquid-containing structures is governed by their modal properties, which are affected by the mass of liquid and other fluid-structure interaction mechanisms. Therefore, knowledge of the effects of different parameters on modal properties is helpful in conducting a precise dynamic response analysis. In this paper, the effects of liquid on the modal properties of two structures, i.e., a pipe structure and a cylindrical storage tank, are investigated experimentally. The experimental results are then used to construct accurate analytical/numerical models for these structures. The models are capable of regenerating the experimental dynamic characteristics of the structures with an acceptable accuracy, indicating a proper modeling of the effects of liquid and the corresponding interaction mechanisms.     

Dynamic plastic deformation of rings under impulsive load

A study of the plastic response of rings of different materials to different types of dynamic load is presented.

Inertial loading of rings was obtained by allowing heavy lead rings to fall freely on to flat and pointed rigid anvils and impulsive loading was obtained by subjecting stationary lead, copper and aluminium rings to a high-speed bullet or to contact explosives. Heavy mass, low velocity impact loading was obtained by allowing a large tup to freely fall on to the ring. Collision loading was obtained by allowing one ring to fall on to one or two stationary rings.

Two types of approach are employed to analytically investigate the loading of rings. The first is a numerical one which assumes a simple approximate model for the structure of the ring; it reduces the ring to small masses concentrated around the circumference, connected to each other by weightless links possessing the strength properties of the material of the ring. The problem is then reduced to solving the dynamical equations of each mass around the ring with the help of a digital computer. The second is an energy method which utilizes Lagrange's equations for the motion of approximated links within the ring.

Results of each of these approaches are compared with experiments presented in terms of instantaneous deformation obtained from high-speed photographs.     

考虑参数不确定性的转向架构架结构强度分析

考虑工程实际中设计参数的不确定性,基于D-最优试验设计和可靠性理论对转向架构架进行结构强度分析。根据UIC 510-3-1994标准对构架进行结构强度分析,确定受力较大部位的设计参数。运用APDL语言建立构架的参数化模型,并对设计参数进行D-最优试验设计,进而计算构架的结构强度。利用最小二乘法对试验数据进行拟合,建立多项式响应面函数,并对其进行方差分析,检验响应面的精度。基于高精度响应面函数,采用Monte-Carlo拉丁超立方抽样方法对构架进行结构强度的可靠性分析。研究结果表明：设计参数的变化对结构强度的影响较大,且各设计参数的交互作用较小。转向架构架的结构可靠度为0.984 3,表明了不确定参数对构架结构强度和安全性的影响程度。基于D-最优试验设计的响应面法工作效率高,可为其他复杂结构的不确定性分析提供参考。     

ANALYTICAL MODEL ALGORITHM FOR DYNAMICS OF ROBOTIC MANIPULATORS

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基于广义几何误差模型的微机器人精度分析

提出了一个用于微机器人精度分析的通用方法,该方法以广义几何误差的形式描述各种误差源对机器人本体产生的影响,通过任两座标系间的向后微分关系,利用运动学方程以及并联机构的环路特性,建立了微机器人的广义几何误差模型。基于此模型,对工作空间中的位姿误差进行了仿真分析,验证了该法的有效性。此方法虽然是针对微机器人,但可推广应用到一般并联机器人的误差建模和精度分析。     

子结构界面连接参数识别的波传播法

提出一种基于波传播法识别子结构连接界面刚度和阻尼的新方法。以子结构在平面内的弯曲振动为例,将单元的状态变量与波模式联系起来。通过单元波幅系数的识别,得到连接界面的位移和力向量,再由结点上位移连续及力平衡条件,求得连接界面各个自由度上的动刚度。在识别过程中,将动刚度分离为实部和虚部,以便于连接刚度和阻尼的独立识别。为了提高识别精度,选择一定的频率范围,在每一频率下求得连接界面的刚度和阻尼,最后求出统计平均值作为界面的连接参数。数值仿真算例表明本方法具有良好的识别精度和数值稳定性,是一种极有潜力的参数辨识方法。     

从任意格式的标题栏和明细表中提取零部件信息的方法

针对制造信息化过程中,企业只能从固定格式的标题栏和明细表中提取信息的不足,通过分析标题栏、明细表在工程图样中的结构特征和数据存储特点,使其按拓扑结构进行分类,并存入数据库。利用不同语义的数据在拓扑结构相同的表格中分布相似的特性,从数据库中检索与目标数据表格有相同拓扑关系的记录,并按记录中各语义数据的分布情况来提取目标数据表的信息,从而有效地解决了任意格式的数据表中零部件信息的提取问题。     

基于有限元的发电机U型架结构动力特性分析

针对某机型发电机U型架结构,运用有限元分析软件ANSYS,对发电机U型架及连接部件进行精确的数值建模,然后利用ANSYS动力学分析的完全法对该结构在交变载荷作用下的动力特性进行数值模拟分析,并运用后处理对数值分析结果进行图形及曲线描述,最后对U型架及连接部件的力学性能进行评估.通过分析该结构的动力响应及力学性能,得出该结构容易失效或疲劳的部位,为U型架结构的改进设计和日常维护提供了有力依据.     

Local POE model for robot kinematic calibration

A robot kinematic calibration method based on the local frame representation of the product-of-exponentials (Local POE) formula is introduced. In this method, the twist coordinates of the joint axes are expressed in their respective local (body) frames. The advantages of this new approach are threefolds: (1) revolute and prismatic joints can be uniformly expressed in the twist coordinates based on the line geometry; (2) the twist coordinates of the joint axes can be set up with simple values because the local frames can be arbitrarily defined on the links; (3) the kinematic parameters described by the twist coordinates vary smoothly that makes the method robust and singularity-free. By assuming that the kinematic errors exist only in the relative initial poses of the consecutive link frames, the kinematic calibration models can be formulated in a simple and elegant way. The calibration process then becomes to re-define a set of new local link frames that are able to reflect the actual kinematics of the robot. This method can be applied to robot manipulators with generic open chain structures (serial or tree-typed). The simulation and experiment results on a 4-DOF SCARA type robot and a 5-DOF tree-typed modular robot have shown that the average positioning accuracy of the end-effector increases significantly after calibration.     

采用三点定位原理的反射镜支撑结构设计

在选择空间反射镜的支撑形式时,大口径反射镜一般采用柔性支撑结构加背板的支撑结构;小尺寸反射镜采用周边支撑的结构,但支撑结构质量都较大。为了降低反射镜支撑结构质量,通过对三点定位原理的自由度分析,设计了3个柔性铰链结构,通过柔性铰链的结构参数分析及有限元分析计算,设计出参数为R=1mm,t=2.5mm的三点柔性铰链,实现400mm口径反射镜的周边支撑,并使支撑反射镜的三个铰链直接与相机机身连接,省略了常规反射镜支撑的背板及边框,大大降低支撑结构质量;且该支撑结构具有较好的动态刚度和力、热环境适应能力。     

Study of the field around magnetic force microscopy probes using electron holography

We have used electron holography to perform quantitative investigations of the leakage flux of thin film tips used as probes in magnetic force microscopy. A method to deduce an arrangement of magnetic domains in a thin magnetic whisker from the knowledge of the stray flux is also described. A simple analytical model of the magnetic properties of the probes allows the extraction of computer images, which simulate the experimental results satisfactory. The reliability of the recorded experimental maps of the magnetic flux arising from these kinds of sensors allows an evaluation of the total flux affecting the sample and the calculation of the magnetic field profile along the tip axis.