基于开源场景图形的三维可视化与信息管理系统设计

对于产品虚拟装配的三维呈现过程中难以实现零件信息管理问题,结合电动车模型的拆装,提出三维可视化与信息管理技术融为一体的设计方案。首先,建立三维模型库,并根据电动车模型的拓扑结构和辅助信息,如零件的材质、型号等,建立信息库;其次,读取信息库中零件与子装配体间的父子关系信息建立目录树,根据子装配体与场景树均为“多叉树”组成结构的原理进行子装配体的三维呈现,再对子装配体的各个节点设置动画完成拆装呈现;最后,采用多线程方法将电动车配件信息管理与可视化有机结合,实现支持三维的拾取交互查询和检索定位查询等功能。系统以世纪鸟电动车进行验证,实现了三维可视化技术与信息系统相融合,能快速有效地为电动车的三维呈现和虚拟装配提供技术支持。实例验证表明,所设计系统可以有效地将零件的信息管理融入到虚拟装配的三维可视化中。     

基于薄膜蒸发器的远程三维设计技术研究

CAD技术的发展使得参数化设计由二维向三维转化,而Internet技术的逐步完善又为远程设计提供了保障.利用WebClass技术,开发了基于SolidWorks的薄膜蒸发器远程三维设计系统,包括零部件和装配图的三维参数化设计及其虚拟装配.系统的开发大大提高了设计效率,缩短了开发周期,为网络化制造和进一步优化分析奠定了基础.     

A Microassembled Low-Profile Three-Dimensional Microelectrode Array for Neural Prosthesis Applications

This paper describes the design and micro- assembly process of a low-profile 3-D microelectrode array for mapping the functional organization of targeted areas of the central nervous system and for possible application in neural prostheses. The array consists of multiple planar complimentary metal-oxide-semiconductor stimulating probes and 3-D assembly components. Parylene-encapsulated gold beams supported by etch-stopped silicon braces allow the backends of the probes to be folded over to reduce the height of the array above the cortical surface. A process permitting parylene to be used at wafer level with bulk-silicon wet release has been reported. Spacers are used to fix the microassembled probes in position and are equipped with interlocking structures to facilitate the assembly process and increase yield. Four-probe 256-site 3-D arrays operate from plusmn5 V with an average per-channel power dissipation of 97 muW at full range stimulation with pulse widths of 100 mus at 500-Hz frequency. Thirty-two sites can be stimulated simultaneously with maximum currents of plusmn127 muA and a current resolution of plusmn1 muA. The microassembly techniques allow a variety of 3-D microstructures to be created from planar components.     

Development and application of a three-dimensional artificial visual system

A three-dimensional artificial visual system has been developed to aid in the analysis of 3-D fluorescence images of smooth muscle cells. The system consists of three sets of 3-D spatial filters that decompose the image to enable a simple recombination algorithm to locate the discrete bodies of protein concentration in a cell, classify the concentration bodies as globular or oval, and determine the 3-D orientation of the oval bodies. A graphic model of the protein concentration is created from the data provided by the artificial visual system. Patterns of organization in the distribution of the protein bodies are investigated using an interactive graphics system.     

Fabrication and characterization of hydrogel-based microvalves

Several microvalves utilizing stimuli-responsive hydrogel materials have been developed. The hydrogel components are fabricated inside microchannels using a liquid phase polymerization process. In-channel processing greatly simplifies device construction, assembly, and operation since the functional components are fabricated in situ and can perform both sensing and actuation functions. Two in situ photopolymerization techniques, "laminar stream mode" and "mask mode," have been explored. Three two-dimensional (2-D) valves were fabricated and tested (response time, pressure drop, maximum differential pressure). In addition, a hydrogel/PDMS three-dimensional (3-D) hybrid valve that physically separates the sensing and regulated streams was demonstrated. Analytical modeling was performed on the 3-D valve. Hydrogel-based microvalves have a number of advantages over conventional microvalves, including relatively simple fabrication, no external power requirement, no integrated electronics, large displacement (185 μm), and large force generation (22 mN)     

Matching 3-D Models to 2-D Images

We consider the problem of analytically characterizing the set of all 2-D images that a group of 3-D features may produce, and demonstrate that this is a useful thing to do. Our results apply for simple point features and point features with associated orientation vectors when we model projection as a 3-D to 2-D affine transformation. We show how to represent the set of images that a group of 3-D points produces with two lines (1-D subspaces), one in each of two orthogonal, high-dimensional spaces, where a single image group corresponds to one point in each space. The images of groups of oriented point features can be represented by a 2-D hyperbolic surface in a single high-dimensional space. The problem of matching an image to models is essentially reduced to the problem of matching a point to simple geometric structures. Moreover, we show that these are the simplest and lowest dimensional representations possible for these cases.We demonstrate the value of this way of approaching matching by applying our results to a variety of vision problems. In particular, we use this result to build a space-efficient indexing system that performs 3-D to 2-D matching by table lookup. This system is analytically built and accessed, accounts for the effects of sensing error, and is tested on real images. We also derive new results concerning the existence of invariants and non-accidental properties in this domain. Finally, we show that oriented points present unexpected difficulties: indexing requires fundamentally more space with oriented than with simple points, we must use more images in a motion sequence to determine the affine structure of oriented points, and the linear combinations result does not hold for oriented points.     

A novel approach to 3-D gaze tracking using stereo cameras

A novel approach to three-dimensional (3-D) gaze tracking using 3-D computer vision techniques is proposed in this paper. This method employs multiple cameras and multiple point light sources to estimate the optical axis of user's eye without using any user-dependent parameters. Thus, it renders the inconvenient system calibration process which may produce possible calibration errors unnecessary. A real-time 3-D gaze tracking system has been developed which can provide 30 gaze measurements per second. Moreover, a simple and accurate calibration method is proposed to calibrate the gaze tracking system. Before using the system, each user only has to stare at a target point for a few (2-3) seconds so that the constant angle between the 3-D line of sight and the optical axis can be estimated. The test results of six subjects showed that the gaze tracking system is very promising achieving an average estimation error of under 1 degrees.     

Intelligent approaches for generating assembly drawings from 3-D computer models of mechanical products

In order to reduce the time of mechanical product design and ensure the high quality of their assembly drawings, this paper develops an intelligent approach for generating assembly drawings automatically from three-dimensional (3-D) computer assembly models of mechanical products by simulating the experienced human designer's thinking mode with the aid of computer graphics and knowledge-based expert system. The key issues include the strategies and methods for selecting the necessary views in an assembly drawing, determining necessary sectional views in each view, eliminating the unreasonable projective overlap of the components in each view, and minimizing the numbers of both the views in an assembly drawing and the sectional views in each view. Based on the approach, corresponding software prototype was developed. Finally, it is demonstrated, from an example of the fixture in a modularized drilling machine, that its assembly drawing was generated successfully using this intelligent software prototype.     

COMPUTER GRAPHIC ASSEMBLY TECHNOLOGY FOR COMPOUND-BODY

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A Three-Dimensional Fuzzy Control Methodology for a Class of Distributed Parameter Systems

The traditional fuzzy set is two-dimensional (2-D) with one dimension for the universe of discourse of the variable and the other for its membership degree. This 2-D fuzzy set is not able to handle the spatial information. The traditional fuzzy logic controller (FLC) developed from this 2-D fuzzy set should not be able to control the distributed parameter system that has the tempo-spatial nature. A three-dimensional (3-D) fuzzy set is defined to be made of a traditional fuzzy set and an extra dimension for spatial information. Based on concept of the 3-D fuzzy set, a new fuzzy control methodology is proposed to control the distributed parameter system. Similar to the traditional FLC, it still consists of fuzzification, rule inference, and defuzzification operations. Different to the traditional FLC, it uses multiple sensors to provide 3-D fuzzy inputs and possesses the inference mechanism with 3-D nature that can fuse these inputs into a so called ldquospatial membership function.rdquo Thus, a simple 2-D rule base can still be used for two obvious advantages. One is that rules will not increase as sensors increase for the spatial measurement; the other is that computation of this 3-D fuzzy inference can be significantly reduced for real world applications. Using only a few more sensors, the proposed FLC is able to process the distributed parameter system with little complexity increased from the traditional FLC. The 3-D FLC is successfully applied to a catalytic packed-bed reactor and compared with the traditional FLC. The results demonstrate its effectiveness to the nonlinear unknown distributed parameter process and its potential to a wide range of engineering applications.     

3-D curve matching using splines

A machine vision algorithm to find the longest common subcurve of two 3-D curves is presented. The curves are represented by splines fitted through sequences of sample points extracted from dense range data. The approximated 3-D curves are transformed into 1-D numerical strings of rotation and translation invariant shape signatures, based on a multiresolution representation of the curvature and torsion values of the space curves. The shape signature strings are matched using an efficient hashing technique that finds longest matching substrings. The results of the string matching stage are later verified by a robust, least-squares, 3-D curve matching technique, which also recovers the Euclidean transformation between the curves being matched. This algorithm is of average complexity O(n) where n is the number of the sample points on the two curves. The algorithm has applications in assembly and object recognition tasks. Results of assembly experiments are included.     

一个简单的机器人视觉引导装配实验系统

本文对视觉控制下的一个简单实验室装配系统作了介绍,讨论了系统组成、机器人控制、二维图象特征的提取、对物体自动识别、定位定向、系统标定、实现垒积木装配工作.本实验系统用的是我所研制的国内第一台示教再现机器人.     

Evaluating part designs for automatic feeding in robotic assembly systems: A geometric analysis of the nesting of polyhedral objects

One of the problems encountered by automatic feeding devices, such as vibratory bowl feeders, in robotic assembly systems is nesting which leads to inseparability of parts and jamming. In this paper, we describe a design evaluation procedure to determine whether a part is prone to nesting and to quantify the degree of nesting. The proposed methodology reduces the 3-D protrusion-hole polyhedral containment problem of nesting to a 2-D polygon containment problem by employing a loop-based feature recognition scheme. Subsequently, the 3-D containment configuration is reconstructed from that of the 2-D by using a strategy calleddrop, pull and push. In this context, we introduce the notion of axis as a characteristic direction of a feature that facilitates the analysis of generalized 3-D polyhedral containment. The algorithms are applicable to generic B-Rep CAD data, and their time and space complexities are polynomial.     

利用 WebGL 技术实现机房动态虚拟装配设计的可视化

本文设计并实现了一个面向机房的动态虚拟装配系统.该系统将传统的三维虚拟装配分解为二维装配和三维可视化两部分.在二维装配阶段,用户只需简单的交互操作就可完成机房的装配,配置结果记录在系统动态生成的配置文件中;在三维可视化阶段,系统根据配置文件可视化装配结果,实现虚拟装配.这种动态虚拟装配的架构有效提高了装配的效率,使装配更简捷、修改更容易.此外,该系统采用 WebGL 技术实现可视化,使得该系统的操作可全部在浏览器端完成,系统的发布和使用更加便捷.     

Error Resilient 3-D Mesh Compression

An error resilient three-dimensional (3-D) mesh coding system is proposed in this paper. The encoder uses a shape adaptive data partitioning scheme to alleviate the effect of error propagation. An input mesh surface is coarsely divided into smooth and detailed regions, and each region is further divided into partitions of similar sizes. Then, those partitions are progressively compressed and their joint boundaries are compressed using the boundary edge collapse rule. At the decoder, the boundary edge collapse rule facilitates the seamless assembly of the partitions. When no data is available for a partition due to transmission errors, we employ a concealment scheme based on the projection onto convex sets (POCS) theory. Simulation results demonstrate that the proposed algorithm reconstructs 3-D mesh surfaces faithfully even in severe error prone environments.     

复杂三维曲面覆盖算法研究

针对无线传感器网络中三维空间曲面覆盖问题进行研究,建立传感器节点的三维感知模型,考虑到曲面的不规则性,曲面凸点会成为节点感知过程中的障碍物,形成三维空间中特有的三维感知盲区。首先从理论上对简单曲面进行分析,计算出实现有限曲面全覆盖所需的最少节点数,在对三维曲面进行网格划分以及根据三维感知盲区改进适应度函数后,引入差分进化（DE）算法对随机部署在三维空间中的传感器节点的位置坐标进行优化,通过大量仿真实验得出实现目标曲面全覆盖所需的最少的节点数,引入误差率,通过提出的测试准则验证了引用DE算法解决简单三维曲面覆盖问题的有效性。最后将DE算法运用到解决复杂三维曲面覆盖问题中,取得了良好的效果。     

Identifying Noncooperative Subjects at a Distance Using Face Images and Inferred Three-Dimensional Face Models

We present an approach to identify noncooperative individuals at a distance from a sequence of images, using 3-D face models. Most biometric features (such as fingerprints, hand shape, iris, or retinal scans) require cooperative subjects in close proximity to the biometric system. We process images acquired with an ultrahigh-resolution video camera, infer the location of the subjects' head, use this information to crop the region of interest, build a 3-D face model, and use this 3-D model to perform biometric identification. To build the 3-D model, we use an image sequence, as natural head and body motion provides enough viewpoint variation to perform stereomotion for 3-D face reconstruction. We have conducted experiments on a 2-D and 3-D databases collected in our laboratory. First, we found that metric 3-D face models can be used for recognition by using simple scaling method even though there is no exact scale in the 3-D reconstruction. Second, experiments using a commercial 3-D matching engine suggest the feasibility of the proposed approach for recognition against 3-D galleries at a distance (3, 6, and 9 m). Moreover, we show initial 3-D face modeling results on various factors including head motion, outdoor lighting conditions, and glasses. The evaluation results suggest that video data alone, at a distance of 3 to 9 meters, can provide a 3-D face shape that supports successful face recognition. The performance of 3-D–3-D recognition with the currently generated models does not quite match that of 2-D–2-D. We attribute this to the quality of the inferred models, and this suggests a clear path for future research.      

A dual-representation strategy for the virtual assembly of thin deformable objects

The two main objectives of virtual assembly are: (1) to train assembly-operators through virtual assembly models, and (2) to simultaneously evaluate products for ease-of-assembly. The focus of this paper is on developing computational techniques for virtual assembly of thin deformable beam and plate-like objects. To meet the objectives of virtual assembly, the underlying computational technique must: (1) be carried out at a high frame-rate (>20 frames/second), (2) be accurate (<5% error in deformation and force estimation), (3) be conducive to collision detection, and (4) support rapid design evaluations. We argue in this paper that popular computational techniques such as 3-D finite element analysis, boundary element analysis and classic beam/plate/shell analysis fail to meet these requirements. We therefore propose a new class of dual representation techniques for virtual assembly of thin solids, where the geometry is retained in its full 3-D form, while the underlying physics is dimensionally reduced, delivering: (1) high computational efficiency and accuracy (over 20 frames per second with <1% deformation error), and (2) direct CAD model processing, i.e., the CAD model is not geometrically simplified, and 3-D finite element mesh is not generated. In particular, a small-size stiffness matrix with about 300 degrees of freedom per deformable object is generated directly from a coarse surface triangulation, and its LU-decomposition is then exploited during real-time simulation. The accuracy and efficiency of the proposed method is established through numerical experiments and a case study.     

三维成像雷达高度计成像模拟研究

根据三维成像雷达高度计系统（CIALT,China Imaging Altimeter)的成像基本原理建立了一个模拟系统,用来获得原始数据并进行成像处理。在该模拟系统基础上,给出了对各种目标的模拟成像结果,并针对系统参数选择、窗函数选择以及聚焦深度和距离弯曲等因素对成像的影响进行了深入的讨论。最后,介绍了三维成像的初步结果。