虚拟拆卸环境中工具的操作技术

在虚拟拆卸环境中借助工具拆除紧固零件，能够使虚拟环境下的拆卸活动更加真实，有利于获得符合工程实际的拆卸序列．提出工具定位约束的概念，对虚拟拆卸环境中工具的操作技术进行了深入研究．首先分析工具的拆卸操作过程；然后对常用工具的工具定位约束进行研究，并论述了虚拟环境中工具精确定位的实现方式；最后以Bell-roller产品装配体模型为例，在沉浸式虚拟环境中基于工具定位约束、操作螺钉起子和扳手完成紧固零件的拆除。     

虚拟环境中基于约束动态解除的产品拆卸技术研究

虚拟拆卸是验证产品可拆卸性与可维护性、确定产品装配序列的有效手段．提出虚拟拆卸过程中配合约束的自动解除方法．随着拆卸过程的递进，根据设计者的交互意图，适时取消零件所受的配合约束．实现了虚拟拆卸过程中零件的约束运动，将运动传感器检测到的设计者手的实际运动映射到虚拟环境中零件的可自由运动空间，以有效地支持虚拟环境中交互拆卸的完成．相关方法在虚拟设计与装配原型系统的研究与开发中得到实现．     

基于物理模型的虚拟装配技术研究

虚拟装配是虚拟现实技术在产品设计领域的一个重要应用 .为了从运动学与动力学的角度来考察虚拟装配过程中零件的运动 ,以便更真实地反映虚拟环境中零件装配运动的本质规律 ,提出了一种虚拟装配环境中用于将装配几何约束自动映射为运动副约束的基于运动自由度分析的物理约束生成方法 ,同时 ,提出了基于变刚度弹簧模型的装配力交互输入方法 ,并实现了位移输入与装配力输入的映射 .另外 ,还给出了基于物理模型的虚拟装配的基本过程 .该方法在虚拟设计与装配原型系统的研究与开发中已得到实现 .     

三维虚拟机器人运动仿真系统设计

通过对三维虚拟机器人运动仿真系统的发展进行介绍和分析, 描述了基于零件拼装的三维虚拟机器人运动仿真的有效方法。针对三维虚拟机器人零件结构特点和拼装功能, 对虚拟机器人零件的图形建模方法、虚拟机器人运动及传感器功能仿真进行了分析设计, 重点分析了运动仿真过程的设计方法。实验结果表明, 系统能够很好地遵循物理特性实现虚拟机器人的运动仿真, 且性能较优。     

协同虚拟维修中的零件特征模型

协同维修中大型装备零件多、关系复杂。针对协同虚拟维修中零件信息如 何组织和共享等问题,文章分析协同维修过程所需的信息,采用面向对象的建模思想,构建 了包含拆装序列、拆装运动约束、人员角色和维修工具等特征信息的零件特征模型,并将其 映射成关系数据类型,存储在数据库中。最后,实例验证了模型能够把零件中有关维修的信 息很好的组织起来,解决了零件信息异地用户共享问题。     

循序渐进学Pro/ENGINEER 第四课 Pro/ENGINEER的装配

一、装配的常用约束1．匹配匹配就是贴合，它可以使两个平面面对面的贴合在一起。图1所示的就是上面零件的底面和下面零件的顶面采用匹配约束的效果。图1 匹配约束2．匹配偏距和“匹配”的形式类似，只是可以通过输入偏距值来控制两个平面间的距离。图2所示的就是上面零件的底面和下面零件的顶面采用匹配偏距约束的效果。图2 匹配偏距约束3．对齐用“对齐”约束可使两个平面共面，即平面重合并且同方向。也可以用来约束两条轴线同轴、两条边重合或两个点重合。可以对齐旋转曲面。图3所示的是两个零件的顶面采用对齐约束的效果。图3 对齐约束…     

基于装配约束动态管理的虚拟拆卸

装配约束是虚拟拆卸环境下必须考虑的装配体的重要信息，提出虚拟拆卸过程中装配约束的动态管理机制，并实现了基于装配约束导航的虚拟拆卸。装配约束的动态管理包括虚拟环境下装配约束的获取、表达以及拆卸过程中装配约束的动态维护，即装配约束的动态解除和产生，文中用装配约束图表达零件间的装配约束，提出装配约束的间接解除方法，并实现了基于装配约束推理的零件可拆卸方向的推导。最后，通过一个简单装配体的拆卸实例，对文中方法进行了验证。     

飞机复杂机构虚拟培训场景运动建模方法

针对含有飞机复杂机构的虚拟培训场景建模过程复杂、生成的场景帧率低、交互性差等问题,提出一种虚拟场景建模方法。首先,对原动件在其运动范围内进行运动状态采样;然后利用机构仿真平台进行运动学建模与解算,获取所有零件的运动状态作为机构的运动状态库,并对运动状态库进行压缩;最后,在虚拟现实引擎中将库文件与经过材质编辑的网格模型融合,采用索引、插值替代实时解算,以获取零件的位置姿态数据,生成虚拟场景。使用起落架收放机构与后缘襟翼收放机构进行实验,结果表明,该方法可以实现真实感强、交互性好的飞机复杂机构虚拟培训场景运动建模。     

仿真软件Vega中的路径与导航器模块

在虚拟仿真环境中经常要事先设置虚拟对象的运动路径，并且需要在仿真过程中动态的、有规律的进行一系列运动路径的变化，专业仿真软件Vega提供的路径和导航器模块很好地解决了这一问题。首先讨论了基于仿真软件Vega的路径和导航器基本原理及其API接口函数，详细阐述了如何应用这两个模块在Lynx中创建路径和导航对象，以及怎样通过Path Tool路径工具设鬣路径控制点和导航参数，然后介绍了路径和导航器在VC编程中的应用，最后基于实践应用探讨了仿真环境中虚拟对象运动路径的精确定位、速度的设定、张力因子选取以及运动方向的调整方法。     

3D视觉结合图像检测与导纳控制的圆轴孔零件机器人装配

面向机器人柔顺装配圆轴与圆孔零件,建立基于3D、单目视觉与导纳控制的机器人自动装配系统,提出基于三维点云的轴线位姿估计算法、图像深度学习目标检测、导纳控制结合的圆轴孔零件的装配策略.针对3D视觉估计圆孔零件位姿问题,重点研究基于三维点云的轴线位姿估计算法.首先,介绍三维点云关键点选取方法;然后,以点云表面法线与轴线的几何约束为基础,提出并分析轴线粗估计的算法;最后,在轴线粗估计的基础上,提出并分析基于迭代鲁棒最小二乘的轴线位姿优化的算法.实验结果表明:轴线位姿估计的角度均方根误差为0.248°,位置均方根误差为0.463 mm,与现有流行的轴线估计方法相比,所提方法的精度更高,使装配策略很好地满足了机器人圆形轴孔零件装配的精度高、稳定可靠的要求.     

Direct 3D Manipulation Techniques for Interactive Constraint-based Solid Modelling

This paper presents a novel constraint-based 3D manipulation approach to interactive constraint-based solid modelling. This approach employs a constraint recognition process to automatically recognise assembly relationships and geometric constraints between entities from 3D manipulation. A technique referred to as allowable motion is used to achieve accurate 3D positioning of a solid model by automatically constraining its 3D manipulation without menu interaction. A set of virtual design tools, which can be used to construct constraint-based solid models within a virtual environment, are also supported. These tools have been implemented as functional 3D objects associated with several pre-defined modelling functions to simulate physical tools such as a drilling tool and T-square. They can be directly manipulated by the user, and precisely positioned relative to other solid models through the constraint-based 3D manipulation approach. Their modelling functions can be automatically triggered, depending upon their associated constraints and the user's manipulation manner. A prototype system has been implemented to demonstrate the feasibility of these techniques for model construction and assembly operations.     

Application of hidden Markov model to acquisition of manipulation skills from haptic rendered virtual environment

This paper explores the feasibility of reconstructing human manipulation skills in complex constrained motion by tracing and learning the manipulation performed by the operator. The peg-in-hole insertion problem is used as a case study, which represents a typical constrained motion force sensitive manufacturing task with the attendant issues of jamming, tight clearance and the need for quick assembly times. In the developed system, position and contact force and torque as well as orientation data generated in the haptic rendered virtual environment combined with a priori knowledge about the task are used to identify and learn the skills in the newly demonstrated task. The recorded training data is classified into contact states, which are identified with hidden Markov model (HMM) as human skills. The HMM parameters are obtained from the training data. By evaluating the controller's performance in each contact state from haptic rendered virtual environment, the robot develops the best trajectories to imitate the human behaviour. In this paper the significance of this research project is highlighted and the developed approach and the progress made so far on this project are reported.     

On performance enhancement of parallel kinematic machine

This paper proposes a spatial three degrees of freedom (DOF) parallel kinematic machine enhanced by a passive leg and a web-based remote control system. First, the geometric model of the parallel kinematic machine is addressed. In the mechanism, a fourth kinematic link—a passive link connecting the base center to the moving platform center—is introduced. Each of the three parallel limbs is actuated by one prismatic joint, respectively. The additional link has three passive DOF, namely two rotations around x and y axes and one translation along z axis. With the existence of this link, the unwanted motion of the tool (located in the moving platform) is constrained. The fourth link also enhances the global stiffness of the structure and distributes the torque from machining. With the kinematic model, a web-based remote control approach is applied. The concept of the web-based remote manipulation approach is introduced and the principles behind the method are explored in detail. Finally, a remote manipulation is demonstrated to the proposed structure using web-based remote control concept.     

Interaction styles in tools for developing virtual environments

This article discusses and compares interaction styles in development tools for virtual environments (VE). The comparison relies on a qualitative empirical study of two development processes where a command language and a direct manipulation based tool were used to develop the same virtual environment application. The command language tool proved very flexible and facilitated an even distribution of effort and progress over time, but debugging and identification of errors was very difficult. Contrasting this, the direct manipulation tool enabled faster implementation of a first prototype but did not facilitate a shorter implementation process as a whole. On the basis of these findings, the strength and weaknesses of direct manipulation for developing virtual environment applications are explored further through a comparison with a successful direct manipulation tool for developing interactive multimedia applications. The comparisons are used to identify and emphasize key requirements for virtual environment development tool interface design.     

Eliminating constraint drift in the numerical simulation of constrained dynamical systems

By means of the Udwadia–Kalaba approach we propose an explicit equation of constrained motion developed to simulate constrained dynamical systems without error accumulation due to constraint drift. The basic idea is to embed a small virtual force and a small virtual impulse to the equation of motion, in order to avoid the drift typically experienced in constrained multibody simulations. The embedded correction terms are selected to minimally alter the dynamics in an acceleration and kinetic energy norm sense. The formulation allows one to use a standard ODE solver, avoiding the need for iterative constraint stabilization. The equation is based on the pseudoinverse of a constraint matrix such that it can be used under redundant constraints and kinematic singularities. The proposed method takes into account the finite word-length of the computational environment, and also accommodates possibly inconsistent initial conditions.     

直线伺服6 位置环虚拟轴机床的运动学解耦

使用直线电机驱动虚拟轴机床 ,可满足高速时动态响应和提高精度的要求。如何解决 6位置环虚拟轴机床的强耦合 ,一直是虚拟轴机床伺服控制中的一个难题。为此 ,将局部结构化方法与解耦理论相结合 ,提出一种新的解耦算法 ,从理论上实现了对 6位置环虚拟轴机床的平动和转动之间的解耦     

Virtual factory as a useful tool for improving production processes

Virtual production in the virtual factory is a modern approach to support the production process and offers a possibility to achieve continuous progress at the logistical level of the organization of the production process.The first part of the paper presents an innovative approach of a virtual factory for use in SMEs with one off production. In the following, a virtual factory created on this basis and on real example of a tool shop is explained. With simple settings, the simulation of the defined production plans can be carried out quickly and the simulation results can be used to identify potential bottlenecks and thus to create an optimal production plan. In the third part, the built-in indicators are explained, which clearly characterized the state of the production process in the virtual factory. It is possible to identify the progress of each operation on a time axis. It is also possible to identify the expected utilization of production capacities depending on the various set of production parameters and the utilization of production processes by production capacity. And as the next option it is easy to determine the free production capacities for the selected period.     

虚拟轴数控机床刀具运动状态的实时规划

提出了虚拟轴数控机床的递阶控制方法, 并着 重介绍了递阶控制的第一级——刀具运动状态实时规划所涉及的切削路径生成、刀具运动路 径计算和刀具运动姿态规划三个关键问题的求解过程, 为虚拟轴机床数控系统的研究开发奠 定了必要的理论与技术基础．     

Multiple homographies with omnidirectional vision for robot homing

Two relevant issues in vision-based navigation are the field-of-view constraints of conventional cameras and the model and structure dependency of standard approaches. A good solution of these problems is the use of the homography model with omnidirectional vision. However, a plane of the scene will cover only a small part of the omnidirectional image, missing relevant information across the wide range field of view, which is the main advantage of omnidirectional sensors. The interest of this paper is in a new approach for computing multiple homographies from virtual planes using omnidirectional images and its application in an omnidirectional vision-based homing control scheme. The multiple homographies are robustly computed, from a set of point matches across two omnidirectional views, using a method that relies on virtual planes independently of the structure of the scene. The method takes advantage of the planar motion constraint of the platform and computes virtual vertical planes from the scene. The family of homographies is also constrained to be embedded in a three-dimensional linear subspace to improve numerical consistency. Simulations and real experiments are provided to evaluate our approach.     

Biological cell injection visual and haptic interface

This paper presents a new three-dimensional (3-D) biomicromanipulation system for biological objects such as embryos, cells or oocytes. As the cell is very small, kept in liquid and observed through a microscope, 2-D visual feedback makes accurate manipulation in the 3-D world difficult. To improve the manipulation work, we proposed an intelligent human–machine interface. The 3-D visual information is provided to the operator through a 3-D reconstruction method using vision-based tracking deformations of the cell embryo. In order to perform stable microinjection tasks, the operator needs force feedback and haptic assistance during penetration of the cell envelop — the chorion. Thus, realistic haptic rendering techniques have been implemented to validate stable insertion of a micropipette in a living cell. The proposed human–machine user's interface allows real-time realistic visual and haptic control strategies for constrained motion in image coordinates, virtual haptic rendering to constrain the path of insertion and removal in the 3-D scene or to avoid cell destruction by adequately controlling position, velocity and force parameters. Experiments showed that the virtualized reality interface acts as a tool for total guidance and assistance during microinjection tasks.