Product modeling framework based on interaction feature pair

Designing products effectively and efficiently is of great significance. However, currently part models are usually created without knowing how they will interact with other parts, leading to gaps between part modeling and assembly modeling and between other applications, and to tedious and redundant labor. This paper proposes a novel product modeling framework to address the problems. The framework is different from current product modeling systems from two aspects. On the architecture level, a new module based on a concept of interaction feature pair (IFP) is developed. An IFP incorporates information of interaction type, related feature pairs and behavioral information that fulfill the interactions. The new module can model the structure of IFPs mathematically through operators and functions defined in a space spanned from six basic IFPs. It can also utilize the constituent elements of an IFP as state variables to form behavior models for the IFP. On the process level, the IFP-based framework can support both bottom-up and top-down approaches, and integrate part modeling and assembly modeling together by changing the workflows. Concretely, IFPs will be embedded into part models at part modeling stage to make them pre-interact with each other, and at assembly modeling stage, parts will be assembled by instantiating the embedded IFPs instead of specifying mating constraints, thus reducing the tedious and redundant labor. Incorporating knowledge of different domains, IFPs can also be developed to integrate more applications together. The implementation of the framework is demonstrated through a prototype system.     

基于双手交互的虚拟装配仿真技术研究

针对现存的虚拟装配系统交互的沉浸感和适应性不强等缺点,采用一对正交放置的光学摄像机,首先从二值图像中提取双手轮廓,自动跟踪双手的运动轨迹,同时利用手势轮廓的Hu矩特征进行手势识别,分离出左右手的移动向量,根据物体的轴向包围盒进行碰撞检测,实现了一个可以用双手与计算机进行交互的虚拟装配系统,验证了方法的可行性。     

A virtual environment for complex products collaborative assembly operation simulation

As complex products such as automobiles and ships are usually developed at geographically dispersed locations, it brings the difficulty for component model verification and assembly process evaluation. To cope with this challenge, a relatively comprehensive system scheme which supports complex product real-time collaborative interactive assembly is proposed. To get high performance, the technologies such as parallel rendering for complex scene based on pc-cluster, high-efficient collision detection method, the mechanism of event synchronization based on HLA/RTI (High level Architecture/Run-time Infrastructure) are applied. A prototype system named Distributed Parallel Virtual Assembly Environment (DPVAE) is developed. With DPVAE, users at different location can do assembly operation collaboratively by hand or by tool, to conduct the component model verification and assembly process evaluation at the same time. Through a case study of RA750 car assembly, the validity of system functions has been demonstrated successfully.     

虚拟人环境感知的仿真方法研究

针对目标驱动的追击问题,将视线升维为柱体的视线筒,提出了一种虚拟人环境感知的筒视线方法.根据虚拟人所处的环境和行进速度,以变频方式、周期性地向目标发射筒视线,根据该筒视线与环境中障碍物的各碰撞点的信息和预先设置的行动推理知识库,确定虚拟人的追逐行动;为不完全可知的、动态虚拟环境中的目标追击问题提供了一种新的解决方案.该方案抛开了基于传统视野范围的拟人方式,以通过性的感知为中心,形成虚拟世界的互动性感知标准,建立虚拟人自身的感知功能,取得了更加逼真的仿真效果.原型系统验证了该方法的可行性和有效性.     

Fatigue evaluation in maintenance and assembly operations by digital human simulation in virtual environment

Virtual human techniques have been used a lot in industrial design in order to consider human factors and ergonomics as early as possible, and it has been integrated into VR applications to complete ergonomic evaluation tasks. In order to generalize the evaluation task in VE, especially for physical fatigue evaluation, we integrated a new fatigue model into a virtual environment platform. Virtual Human Status is proposed in this paper in order to assess the difficulty of manual handling operations, especially from the physical perspective. The decrease of the physical capacity before and after an operation is used as an index to indicate the difficulty level. The reduction of physical strength is simulated in a theoretical approach on the basis of a fatigue model in which fatigue resistances of different muscle groups were regressed from 24 existing maximum endurance time models. A framework based on digital human modeling technique is established to realize the comparison of physical status. An assembly case in airplane assembly is simulated and analyzed under the framework in VRHIT experiment platform. The endurance time and the decrease of the joint moment strengths are simulated. The experimental result in simulated operations under laboratory conditions confirms the feasibility of the theoretical approach: integration of virtual human simulation into virtual reality for physical fatigue evaluation.     

装配序列约束下的飞机虚拟维修过程建模仿真

针对当前飞机虚拟维修过程模型固化,对维修复杂行为关系缺乏考虑,无法满足学员多样性实训需求的现状,充分考虑了飞机系统的复杂度、学员操作的不规范性和随机性等因素,依据各维修装配序列间的优先约束关系,构建了优先约束矩阵,进而定义了优先约束时间有色Petri网模型。在系统梳理维修实体及其维修操作行为的基础上,提出了虚拟维修实体操作元模型和元模型融合下的过程建模,阐述了基于优先约束时间有色Petri网的动态虚拟维修过程实现方法。最后,以A320飞机加油活门的某一个随机拆卸过程为例,进行建模仿真,验证了模型的有效性。     

Visual simulation for granular rocks crush in virtual environment based on fractal geometry

In this paper, a new method is proposed for the simulation of rock crushing in virtual environment. The method can be described as a combination of a physical behavioral model with a phenomenological rock generator. The main modules of the solution consist of a Virtual Reality system, fractal geometric modeling, and physical control models. Virtual Reality and geometric modeling compose the phenomenological rock generator, which simulates the process; while the physical behavioral model controls or affects the results of the simulation, We present the key algorithms of the visual simulation solution, such as the rapid modeling algorithm for rock with complex topology, distributed parallel rendering for large scale and complex rock objects. To evaluate the system, a virtual simulation for rocks crushed in cone crusher is introduced.     

基于网格的分布式虚拟环境仿真

针对传统分布式虚拟环境仿真的不足,将网格计算技术引入到分布式虚拟环境仿真中。提出了基于网格的分布式虚拟环境仿真分层体系结构。该体系结构自底向上依次为网格节点、高性能通信系统、数据存储系统、计算系统、资源管理系统、仿真应用系统,并通过网格门户提供统一的仿真应用系统入口。建立了一个基于该体系结构的原型系统并进行了仿真测试。仿真结果表明所提出的体系结构设计满足虚拟环境仿真实时性、稳定性和可靠性的要求。     

Motion navigation for arc welding robots based on feature mapping in a simulation environment

The efficiency of the off-line programming for the arc welding robots depends on the complexity of the workpieces and the welding experience of the technician. When the workpieces or fixtures are redesigned or the robot workstation layout is changed, the result of prior off-line programming cannot be reused. With the thought of CAD/CAPP/CAM integration, this paper presents a feature mapping algorithm, which converts the design features of the workpieces to the machining features of the seams. Then a motion navigation method based on feature mapping in a simulation environment is proposed. This method comprises initial position guiding and seam tracking. For initial position guiding, a motion path with the least energy consumption is generated based on the weighted optimal control; then the path is revised for avoiding obstacles by setting the path tags dynamically. For seam tracking, the seam is dispersed into discrete welding points; then the welding gun moves through each point according to the welding sequence. The method is implemented in the development of an off-line programming simulation system. Industrial cases of the welding robot workcell layout for automobile door frames show the method can make the off-line programming much more effective.     

Quadruped virtual robot simulation in a virtual environment obeying physical laws

In the development of a robot, the validation of that robot with the use of real machinery takes a considerable amount of time and money. In particular, it is difficult to validate a robot’s behavior in an unsafe place. The developers also have to pay attention to virtual debugging. Using a program validated in VR space makes the verification of a real machine’s behavior more efficient. In this research, we make a virtual robot walk on a road autonomously by using a program where the virtual robot tracks a line in a virtual environment.     

Creation and evaluation of a multi-sensory virtual assembly environment

The multi-modal information presentation, integrated into the virtual environment （VE）, has potential for stimulating different senses, improving the user＇s impression of immersion, and increasing the amount of information that is accepted and processed by the user＇s perception system. The increase of the useful feedback information may reduce the user＇s cognitive load, thus enhancing the user＇s efficiency and performance while interacting with VEs. This paper presents our creation of a multi-sensory virtual assembly environment （VAE） and the evaluation of the effects of multi-sensory feedback on the usability. The VAE brings together complex technologies such as constraint-based assembly simulation, optical motion tracking technology, and real-time 3D sound generation technology around a virtual reality workbench and a common software platform. The usability evaluation is in terms of its three attributes： efficiency of use, user satisfaction, and reliability. These are addressed by using task completion times （TCTs）, questionnaires, and human performance error rates （HPERs）, respectively. Two assembly tasks have been used to perform the experiments, using sixteen participants. The outcomes showed that the multi-sensory feedback could improve the usability. They also indicated that the integrated feedback offered better usability than either feedback used in isolation. Most participants preferred the integrated feedback to either feedback （visual or auditory） or no feedback. The participants＇ comments demonstrated that nonrealistic or inappropriate feedback had negative effects on the usability, and easily made them feel frustrated. The possible reasons behind the outcomes are also analysed by using a unifying human computer interaction framework. The implications, concluded from the outcomes of this work, can serve as useful guidelines for improving VE system design and implementation.     

Lot streaming for product assembly in job shop environment

Assembly job shop scheduling problem (AJSP) is an extension of classical job shop scheduling problem (JSP). AJSP starts with JSP and appends an assembly stage to the completed jobs. Lot streaming (LS) technique is a process of splitting jobs into smaller sub-jobs such that successive operations can be overlapped. This paper combines, for the first time, LS and AJSP, extending LS applicability to both machining and assembly. To solve this complex problem, an efficient algorithm is proposed using genetic algorithms and simple dispatching rules. Experimental results suggest that equal size LS outperforms varied size LS with respect to the objective function.     

基于最大信息系数的ReliefF和支持向量机交互的自动特征选择算法

为解决特征选择ReliefF算法在利用欧氏距离选取近邻样本过程中,算法稳定性差以及选取的特征子集分类准确率低的问题,提出了一种利用最大信息系数（MIC）作为近邻样本选择标准的MICReliefF算法;同时,以支持向量机（SVM）模型的分类准确率作为评价指标,并多次寻优,以自动确定其最优特征子集,从而实现MICReliefF算法与分类模型的交互优化,即MICReliefF-SVM自动特征选择算法。在多个UCI公开数据集上对MICReliefF-SVM算法的性能进行了验证。实验结果表明,MICReliefF-SVM自动特征选择算法不仅可以筛除更多的冗余特征,而且可以选择出具有良好稳定性和泛化能力的特征子集。与随机森林（RF）、最大相关最小冗余（mRMR）、相关性特征选择（CFS）等经典的特征选择算法相比,MICReliefF-SVM算法具有更高的分类准确率。     

Human-systems interaction for virtual environment team training

Virtual environments are increasingly used to support collaborative activities and distance learning. However, few are designed to support students, instructors and simulations in multi-participant team training. This paper describes the Training Studio, a system for authoring, delivering and evaluating multi-participant team training in an immersed virtual environment. The Training Studio focuses on human-systems interaction, allowing multiple students to learn and perform team tasks. The Training Studio supports collaborative learning for either single or multi-participant activity. This is accomplished through the use of agents which are assigned to students to act as personal mentors or missing team members. Conducting team training within a virtual environment introduces complexities and issues unique to team training and multiple-participant virtual environments. This paper describes our approach to virtual environment team training, discussing issues confronted and resulting design considerations and implementations.     

Real-time fluid simulation in a dynamic virtual environment

Simulating physically realistic complex fluid behaviors in a distributed interactive simulation (DIS) presents a challenging problem for computer graphics researchers. The authors consider how solving the 2D Navier-Stokes equations via a computational fluid dynamics method lets us map surfaces into 3D and achieves realistic real-time fluid surface behaviours     

基于区域特征的图像自动配准方法

通过分析比较不同配准方法的原理及优缺点,提出了一种基于图像区域特征的配准方法.算法首先对待配准图像进行自适应阈值分割,然后利用数学形态学方法进行区域轮廓提取优化,接着计算各区域的特征描述,最后以各特征向量距离最近区域的重心作为控制点集对图像进行配准.实验结果表明,该算法能够对图像进行快速准确的配准,而且具有纠正一定几何畸变的能力,是一种有效的自动配准方法.     

基于特征区域的图像自动配准

为了解决基于特征的图像配准中的特征点的定义和提取问题,提出了一种以特征区域替代特征点的定义和提取方法。该方法应用Moravec算子选择候选特征区域,使用具有旋转不变性的Zernike矩表征该区域的特性;采用二级匹配策略进行特征区域的匹配,即基于自组织映射神经网络的初始匹配及精细匹配;建立图像的配准框架并实现图像的配准。实验结果表明,该方法能有效地提取图像的特征点并能准确地进行特征点的匹配,整个配准过程完全自动进行。     

Natural and hybrid bimanual interaction for virtual assembly tasks

This paper focuses on the simulation of bimanual assembly/disassembly operations for training or product design applications. Most assembly applications have been limited to simulate only unimanual tasks or bimanual tasks with one hand. However, recent research has introduced the use of two haptic devices for bimanual assembly. We propose a more natural and low-cost bimanual interaction than existing ones based on Markerless motion capture (Mocap) systems. Specifically, this paper presents two interactions based on a Markerless Mocap technology and one interaction based on combining Markerless Mocap technology with haptic technology. A set of experiments following a within-subjects design have been implemented to test the usability of the proposed interfaces. The Markerless Mocap-based interactions were validated with respect to two-haptic-based interactions, as the latter has been successfully integrated into bimanual assembly simulators. The pure Markerless Mocap interaction proved to be either the most or least efficient depending on the configuration (with 2D or 3D tracking, respectively). Usability results among the proposed interactions and the two-haptic based interaction showed no significant differences. These results suggest that Markerless Mocap or hybrid interactions are valid solutions for simulating bimanual assembly tasks when the precision of the motion is not critical. The decision on which technology to use should depend on the trade-off between the precision requested to simulate the task, the cost, and inner features of the technology.