基于物理属性的虚拟装配过程

针对虚拟装配系统中存在仿真程度不够高的缺点,提出基于物理属性的虚拟装配过程研究。通过分析虚拟装配过程对零部件物理属性的需求,建立零部件物理属性模型,给出确定零部件各物理属性以及自由运动状态的方法,分析碰撞响应对运动状态的影响。研究虚拟装配系统中装配对象间的交互过程,使用多刚体系统动力学分析方法对零部件装配过程中的动力学以及运动学进行分析,给出装配对象的运动学与动力学方程。通过把抽象的约束关系转换为基本约束方程表达运动副约束,并把运动副约束用于装配对象的运动分析。提出基于碰撞与静力学的稳态分析方法研究零部件达到稳定状态的条件。应用实例表明上述方法有效可行。     

Force Feedback Coupling with Dynamics for Physical Simulation of Product Assembly and Operation Performance

Most existing force feedback methods are still difficult to meet the requirements of real-time force calculation in virtual assembly and operation with complex objects. In addition, there is often an assumption that the controlled objects are completely free and the target object is only completely fixed or free, thus, the dynamics of the kinematic chain where the controlled objects are located are neglected during the physical simulation of the product manipulation with force feedback interaction. This paper proposes a physical simulation method of product assembly and operation manipulation based on statistically learned contact force prediction model and the coupling of force feedback and dynamics. In the proposed method, based on hidden Markov model(HMM) and local weighting learning(LWL), contact force prediction model is constructed, which can estimate the contact force in real time during interaction. Based on computational load balance model, the computing resources are dynamically assigned and the dynamics integral step is optimized. In addition, smoothing process is performed to the force feedback on the synchronization points. Consequently, we can solve the coupling and synchronization problems of high-frequency feedback force servo, low-frequency dynamics solver servo and scene rendering servo, and realize highly stable and accurate force feedback in the physical simulation of product assembly and operation manipulation. This research proposes a physical simulation method of product assembly and operation manipulation.     

机器人轴孔装配状态的分析

利用旋量理论和虚功法对机器人装配过程点接触、面接触的力约束进行理论分析。以轴孔装配为例 ,得出了判断接触状态的条件 ,并设计了仿真算法。从分析中可以看出 ,旋量法比常规的几何方法简洁 ,可用来分析接触状态     

Elimination of unnecessary contact states in contact state graphs for robotic assembly tasks

It needs much computation to develop a contact state graph and find an assembly sequence because polyhedral objects consist of a lot of vertices, edges, and faces. In this paper, we propose a new method to eliminate unnecessary contact states in the contact state graph corresponding to a robotic assembly task. In our method, the faces of polyhedral objects are triangulated, and the adjacency of each vertex, edge, and triangle between an initial contact state and a target contact state is defined. Then, this adjacency is used to create contact state graphs at different priorities. When a contact state graph is finished at a higher priority, a lot of unnecessary contact states can be eliminated because the contact state graph already includes at least one realizable assembly sequence. Our priority-based method is compared with a face-based method through statistically analyzing the contact state graphs obtained from different assembly tasks. Finally, our method results in a significant improvement in the final performance.     

板带轧机预应力机架的装配接触分析

由于预应力机架是多体装配结构,各零件配合面是非线性的接触关系,采用常规的解析法不易准确计算预应力机架的整体刚度及各零件内部的应力分布状态.笔者借助大型有限元分析软件ANSYS,对预应力机架进行装配分析,对各零件重要配合面进行面-面接触分析.     

Surface contact stress-based nonlinear virtual material method for dynamic analysis of bolted joint of machine tool

The components of machine tools are mainly fixed and connected by bolts. The performance of the assembly can be affected by the dynamic characteristics of the bolted joints. This paper presents a nonlinear virtual material method based on surface contact stress to describe the bolted joint for accurate dynamic performance analysis of the bolted assembly. Fractal geometry theory is used to describe the surface topography. The elastic modulus and shear modulus of one micro-contact are derived based on fractal contact theory. The equivalent elastic modulus, Poisson ratio, and density of the bolted joint can be obtained through the weighted mean method. In order to obtain the stress distribution, the contact surface is assumed flat in the macro-scale, and the uneven distribution of contact stress can be obtained by the finite element method (FEM). The contact surface can be divided into several sections, and the parameters of a virtual material layer can be determined based on the mean contact stress. Both theoretical and experimental results for a bolted joint are obtained for a box-shaped specimen under equal pre-tightening force and bending moment effect. The results show that the theoretical mode shapes are in good agreement with the experimental mode shapes. The relative errors between the theoretical and experimental natural frequencies are less than 4.41%, which indicates that the present nonlinear virtual material method is appropriate for the bolted joint in modeling CNC machine tools.     

Computational path planner for product assembly in complex environments

Assembly path planning is a crucial problem in assembly related design and manufacturing processes. Sampling based motion planning algorithms are used for computational assembly path planning. However, the performance of such algorithms may degrade much in environments with complex product structure, narrow passages or other challenging scenarios. A computational path planner for automatic assembly path planning in complex 3D environments is presented. The global planning process is divided into three phases based on the environment and specific algorithms are proposed and utilized in each phase to solve the challenging issues. A novel ray test based stochastic collision detection method is proposed to evaluate the intersection between two polyhedral objects. This method avoids fake collisions in conventional methods and degrades the geometric constraint when a part has to be removed with surface contact with other parts. A refined history based rapidly-exploring random tree (RRT) algorithm which bias the growth of the tree based on its planning history is proposed and employed in the planning phase where the path is simple but the space is highly constrained. A novel adaptive RRT algorithm is developed for the path planning problem with challenging scenarios and uncertain environment. With extending values assigned on each tree node and extending schemes applied, the tree can adapts its growth to explore complex environments more efficiently. Experiments on the key algorithms are carried out and comparisons are made between the conventional path planning algorithms and the presented ones. The comparing results show that based on the proposed algorithms, the path planner can compute assembly path in challenging complex environments more efficiently and with higher success. This research provides the references to the study of computational assembly path planning under complex environments.     

增强现实机械装配环境中装配过程的研究

分析增强现实装配中虚实零件装配过程。研究虚实装配方式、运动路径规划、装配中碰撞检测和力反馈输出。通过规划虚拟零件运动路径,采用六自由度运动方式实现虚实相对运动和装配;提出一种新颖的碰撞检测方法即：壳体检测法,通过虚拟构造虚实零件碰撞点和区域来定义碰撞检测;利用力反馈设备,实现虚拟零件坐标采集和力反馈输出。实验结果证明壳体检测法具有一定通用性,可以快速、准确地实现虚实物体间碰撞检测和力反馈输出。     

考虑界面端应力奇异性的螺栓连接支承面接触压力计算模型

将螺栓连接支承面接触问题简化为集中载荷和力矩耦合作用的有限刚度平头压模接触问题,利用BOGY特征值方程,分析双材料界面端应力奇异性发生的几何条件;依据GLADWELL接触力学理论,构建集中载荷和力矩耦合作用下平头压模接触压力计算模型,利用此模型分析螺栓预紧力、装配间隙和被连接件材料对螺栓连接支承面接触压力分布的影响规律。结果表明：在规定预紧力范围、装配等级和常用被连接件材料下,螺栓连接支承面不会发生退让接触,而界面端部出现明显的应力奇异性,其中预紧力变化对界面端应力奇异性强度影响不明显,但装配间隙和被连接件材料的变化对界面端应力奇异性强度影响显著;当被连接件材料弹性模量大于螺栓材料时,支承面内侧应力奇异性强度大于外侧,反之内侧应力奇异性强度明显小于外侧。此外,以平头压模为算例,采用有限元法验证了构建模型的准确性。     

基于约束的虚拟装配技术研究

为了实现基于约束的虚拟装配操作,给出了虚拟环境中装配约束的统一表达方法,以及约束与自由度的等价关系和运动自由度的归约等,提出了一套虚拟装配中的约束处理算法。首先,利用装配关系自动识别算法,判断两个零件几何约束元素之间的位姿关系是否在给定的误差范围内;其次,使用定位求解算法,使主动体零件在满足已经确认约束的基础上,以最小的位姿调整量满足新约束;最后,提出了基于广义坐标系的运动导航算法,根据装配零件满足的约束对其运动进行引导。这些算法已经应用于集成虚拟装配环境的系统中,实践证明它们能很好地支持集成虚拟装配环境的约束处理,实现了虚拟装配过程与实际装配过程的高度统一。     

基于虚拟装配特征的虚拟装配研究

主要研究虚拟环境中产品的虚拟装配问题。在研究以往学者对装配特征定义的基础上 ,结合虚拟装配的特点 ,提出了虚拟装配特征的概念 ,虚拟装配特征不仅描述了产品中零件间的约束关系 ,而且描述了产品的公差。在充分考虑了公差对产品装配工艺计划和产品可装配性影响的情况下 ,提出了装配工艺计划算法。     

面向虚拟装配的信息获取与应用

介绍了面向虚拟装配的信息获取和重用方法,该方法可以实现虚拟装配环境快速构建和对虚拟装配系统的数据支持。首先建立虚拟装配系统的信息模型,实现了信息源与虚拟装配系统之间的联系。根据信息源的不同,将信息源分成基于计算机辅助设计系统、基于用户输入和基于装配规划模块三种方式进行获取,并将获取的各种信息应用到虚拟装配系统的装配规划和装配验证等功能模块中。通过实例,对虚拟装配信息获取和应用流程进行了说明。     

在Solid Edge中实现虚拟装配

探讨在敏捷制造环境下,虚拟公司的各个合作伙伴如何在设计阶段就能够进行异地协调。以盟主企业为核心,各合作伙伴分别进行零件、组件、工艺、装置设计,通过虚拟装配,使得各合作伙伴能够及时了解相互之间的设计情况,达到并行工作的目的。文中探讨了在SolidEdge软件中,实现虚拟装配的方法。     

基于多基站IMMKF-DOA辅助车辆协同定位算法研究

针对传统卡尔曼滤波算法在进行车辆实时运动过程中难以精准定位问题,提出一种基于运动状态自适应的交互多模型卡尔曼滤波(Interacting multiple model Kalman filter,IMMKF)与多基站到达方向(Direction-of-arrival,DOA)相融合进行车辆位置实时估计算法。基于无偏估计器对测量噪声协方差进行实时更新并将其嵌入标准卡尔曼滤波算法中实现自适应交互多模型卡尔曼滤波。针对车辆不同运动状态及动态行驶环境对车辆定位估计精度的影响,构建自适应交互多模型卡尔曼滤波器与多基站信息融合算法进行车辆位置实时估计,考虑不同车速与不同基站数等行驶工况下车辆定位精度的变化趋势,实现车辆实时位置的准确估计。利用PreScan-Simulink联合仿真平台进行虚拟仿真验证和实车试验验证。结果表明,基于交互多模型卡尔曼滤波与到达方向角的融合算法相对标准的卡尔曼滤波估计精度高,较好地改善了传统单一模型的卡尔曼滤波算法在进行车辆实时运动状态估计过程中精准定位问题,实车试验验证了提出算法对车辆定位精度较传统卡尔曼滤波算法的精度提高了一个数量级,实现了更精确的车辆位置估计。     

虚拟装配中的虚拟手交互技术

针对目前虚拟装配系统中操作者与虚拟对象交互的问题,本文的研究以数据手套作为虚拟装配操作的交互工具定义装配过程中虚拟手与零／部件的作用规则,建立虚拟手对零／部件的抓取,移动和释放的装配操作逻辑,成功地实现了虚拟装配环境中对零／部件合理而自然的装配操作。该操作方法已应用于集成虚拟装配系统(IVAE)。     

BRIEF算法在基于增强现实的产品装配引导中的应用研究

面向增强现实环境下采用零件自然特征的装配引导应用,提出一种基于BRIEF算法的虚实装配场景注册融合方法。利用BRIEF算法进行装配零件图像自然特征的提取,建立零件图像的特征描述符。通过海明距离进行装配引导过程中零件图像特征描述符的匹配,实现虚实装配零件的注册;同时将虚拟装配信息在真实装配场景中叠加,用于引导用户完成装配作业过程。实验结果表明:利用该算法进行虚实注册具有较好的鲁棒性和实时性,能够较好地应用于增强现实环境下的产品装配引导过程中。     

RESEARCH OF MOVEMENT NAVIGATION BASED ON ASSEMBLY CONSTRAINT RECOGNITION

0 INTRODUCTIONThe traditional assembly design stresses the final result of assembly modeling, but pays little attention to the process of assembly simulation. Nonetheless, the procedure of assembly is a cardinal element that determines the quality of assembly modeling. These drawbacks hinder the advancement of the speed and quality of assembly design. Moreover, in the traditional mode of product development, designers make prototypes to evaluate the function and appearances of products. P…     

飞机柔性件铆装中的接触力建模与偏差分析

基于线弹性小变形假设,分析飞机柔性板件装配过程中的相互接触作用。提出了基于三角网格模型几何干涉分析的接触状态检测,采用部分析因设计方法（FractorialFactorialDesign）建立了接触力与接触节点间隙的线性关系,并在此基础上设计了接触平衡位置求解算法。通过与实验对比,验证了基于接触力模型的装配偏差分析模型预测柔性板件装配偏差的准确性。     

Note: A novel integrated microforce measurement system for plane-plane contact research

The evaluation of plane-plane contact force has become a big issue in micro-/nano research, for example in microassembly. However with the lack of effective experimental equipments, the research on plane-plane contact has been limited to theoretical formulations or virtual simulation. In this paper, a microforce sensor and precision parallel robot integrated system is proposed for the microforce measurement of plane-plane contact. In the proposed system, the two objects are fixed on the parallel robot end-platform and the microforce sensor probe tip, respectively, and the high precision robot system is employed to provide six degree-of-freedom motions between both objects. So it is convenient for the microforce measurement between the planar objects with different orientations. As a significant application, the proposed system is utilized for measurements of pull-off force between planar objects, in which the validation of the system is demonstrated in practice. The proposed microforce measurement system is generic, which can be extended to a variety of microforce measurements in plane-plane contact.     

基于凸多面体边界元的接触状态判断

机器人装配操作状态可用装配对象间的接触状态描述。根据凸多面体几何模型边界元给出了三种基本接触对在运动(平移或转动)方向上的最小位移计算方法,首次详细分析了基本接触对在旋转情况下的最小角度生成方法,并得出了计算公式。此方法可用来判断下一运动时刻产生的接触状态关系对。最后以三维三轴孔装配状态仿真为例,验证了该方法的可行性。