从序列图象获取运动刚体的三维信息

从序列图象获取运动刚体的三维信息是计算机视觉学中一项很有意义的工作。本文提出了在两种运动分解形式下的刚体运动方程,论述了刚体运动参数和三维坐标的求解问题,建立了一种求解旋转矩阵R的新算法,该算法是线性的。因而与已有的算法相比,它的计算简单、计算量小,便于实时处理。所附算例证明了本算法稳定性优于已有算法,计算精度有所提高。     

轴测投影的原形及刚体运动参数的计算

由投影恢复其原形是投影理论的基本问题之一,也是计算机视觉的基本问题。本文首先研究了在斜投影下刚体复原的问题,提出恢复原形的充要条件。在此基础上利用刚体在同一时刻的两个投影而恢复其空间位置及结构,进而计算刚体在两位置之间的运动参数。     

基于特征光流的角点匹配快速算法

为了解决视频序列点匹配过程中的实时性和误匹配问题,本文提出了一种基于特征光流技术的快速角点匹配方法。该方法通过多分辨率策略,求出特征光流场概略运动矢量,然后依据匹配准则做相应特征点匹配处理,得到的精确运动矢量用作下一步的光流场计算。这样,既消除了误匹配点,又克服了光流计算的迭代负担。实验结果表明,算法正确匹配率达到98%以上,平均处理帧率24,能够满足系统实时性要求。     

双自由度离心振动系统的动力耦合分析

本文揭示了刚体转动对由质量和弹簧组成的双自由度振动系统的频率、模态和动力响应造成的影响,可为一般弹性体和结构的离心振动耦合动力学分析提供重要指导。离心振动系统存在两阶动频,随刚体转速的增加,第一阶动频线性减小而第二阶动频线性增加。质点的动力响应表现为质点运动轨迹的动态演化,决定于振动初始条件、刚体转速、初始偏心位置、振动刚度等四个因素。质点的运动轨迹由非偏心振动和偏心振动两部分构成,非偏心振动依赖于振动初始条件和刚体转速以及振动刚度,偏心振动取决于初始偏心位置和刚体转速以及振动刚度但与振动初始条件无关。根据对动频和质点运动的分析,提出了双自由度离心振动系统的最大刚体转速和临界转速。     

弹体落水过程中附加质量变化影响研究

基于势流理论,建立弹体边界元模型,研究了弹体刚体运动、弹性振动引起的附加质量随弹体浸湿长度的变化规律,以及砰击力的变化。并在结构多自由度系统运动方程中计及附加质量的变化影响,得到附加质量变化不仅引起系统质量阵变化,还将影响阻尼系数阵。     

质量静矩和惯性矩对水翼流致振动及噪声影响的数值研究

采用URANS方法数值计算了具有两个自由度三维刚性水翼的流致振动和声辐射问题,三维刚性水翼的振动是通过解刚性体的运动方程的方式实现,流场在Fluent里用k-ω SST湍流模型计算。进行了网格无关性验证和时间步长的验证,并和相关的试验结果以及Theodorsen非定常理论的结果进行了对比,计算结果具有较高的吻合度;重点计算了质量静矩和质量惯性矩对振动以及振动临界状态的影响,并且计算了不同振动状态下的声辐射问题。计算结果表明,质量静矩和质量惯性矩对水翼的振动有较大的影响,而水翼的振动会使噪声大幅增加。     

弹体落水过程中附加质量变化影响研究

基于势流理论,建立弹体边界元模型,研究了弹体刚体运动、弹性振动引起的附加质量随弹体浸湿长度的变化规律,以及砰击力的变化.并在结构多自由度系统运动方程中计及附加质量的变化影响,得到附加质量变化不仅引起系统质量阵变化,还将影响阻尼系数阵.     

两自由度系统气弹响应特性研究

基于计算流体动力学(Computational Fluid Dynamics,CFD)离散时间气动模型,计算了有无结构阻尼的薄平板在均匀流中分别受单自由度或两自由度(同时)初始位移激励下的系统气弹响应,分析了气弹位移及气动力时程特征及相互关系。研究表明:任意一个自由度的激励将激发起系统两个自由度方向的振动;低折算风速下,气动耦合项作用很小,气动力能对气弹系统产生气动正阻尼作用,且产生的竖弯气动阻尼大于扭转气动阻尼。研究还表明:系统任意一个自由度方向的气弹位移响应,以及升力或扭矩时程均有系统两个振动模态参与。气弹系统以某一系统频率发生的振动,是一个自由度方向的主运动和另一个自由度方向的耦合运动以一定的参与程度组合形成的牵连运动。     

舰船设备冲击隔离系统优化设计计算

本文首先把舰船设备冲击隔离系统简化为一个具有六自由度的单刚体冲击隔离系统。其运动微分方程采用状态空间法来描述，刚体的动态响应则采用直接积分法——龙格一库格法进行计算。最后提出并采用有约束非线性规划方法进行冲击隔离系统的优化设计计算。     

基于2-RPS/UPRS并联机构的自动分拣机运动分析

目的 针对目前物流行业大都采用人工分拣,耗费了大量人力成本的问题,提出一种新型2-RPS/UPRS并联机构来解决这一问题.方法 首先进行机构的自由度分析和工作空间仿真,以验证2-RPS/UPRS并联机构是否具有较大的工作空间.基于螺旋理论进行空间并联机构自由度分析,在三维软件中建模,添加合适的驱动验证其自由度.通过闭环矢量法和运动支链参数D-H矩阵表示法求解机构动平台的位置逆解.最后在Matlab程序中进行工作空间的仿真分析.结果 2-RPS/UPRS并联机构末端执行器在空间中具有2个转动自由度,2个方向的移动自由度.工作空间形状规则,无奇异位型.结论 基于2-RPS/UPRS并联机构的分拣装置结构简单,可以在生产线上实现精准控制.该并联机构两转两移的运动特性能适应不同倾斜角斜面的分拣任务.     

基于序列图像中二次曲线对应的纯旋转运动参数估计算法

采用特征对应的视觉运动分析方法，建立了基于二次曲线的刚体纯旋转运动方程，提出了求解刚体纯旋转运动参数的算法。在刚体纯旋转运动分析中，最少利用前后两幅图像中7对匹配二次曲线，就可用线性方程组求解刚体旋转运动参数，线性算法的提出使旋转运动参数的求解精度得到很大提高。最后利用合成数据和真实图像对纯旋转运动估计算法的精度和有效性进行了验证，表明该算法能准确、可靠地估计旋转运动参数。     

运动背景中结合特征位移矢量场模糊分割与 OTSU法的运动检测

运动背景中的运动检测难度较大,背景运动补偿后差分以及分割光流场可实现动目标和背景的分离,差分前需进行鲁棒的背景估计,且差分后易出现空洞,而光流估计在噪声以及目标运动速度较大时并不准确,尤其在光照变化时,两种方法均易失效。本文提出一种特征点位移矢量场模糊分割与图像自适应阈值化相结合的运动检测方法,实现在无任何关于运动目标或者运动背景先验信息条件下的动目标检测。通过改进的 SIFT匹配方法生成鲁棒的特征位移矢量场,采用模糊 C均值聚类算法对 SIFT位移矢量场进行无监督分类,实现动目标与背景特征的自适应分离。 OTSU法和形态学操作实现图像的自适应分割,用以修正特征点凸包,最终分割出动目标区域。与鲁棒的背景运动补偿后差分以及光流估计的对比实验表明,在目标运动速度较大、光照变化以及噪声情况下,本文方法均能够检测出运动目标,且在光照变化下的优势明显。     

Towards Eliminating the Displacement Bias Due to Out‐Of‐Plane Motion in 2D Inverse Problems: A Case of General Rigid‐Body Motion

This article reports an important development related to the inverse characterization of material constitutive parameters using 2D optical displacement field measurements. The out‐of‐plane motion of the specimen, which has traditionally been considered detrimental to the accuracy of these experiments, is generally of two types: (a) a global out‐of‐plane rigid‐body motion of the specimen relative to the camera and (b) out‐of‐plane deformations resulting from material heterogeneity or out‐of‐plane loads. In an earlier article, we proposed to partially relax the condition of no out‐of‐plane motion by allowing for (b) in 2D inverse procedures, in the context of finite element update method, and introduced a compensation strategy by redefining the cost function on the object plane of the acquisition system. The experimental errors due to (a) were assumed negligible. Here, we propose that the global rigid‐body motion (a) may also be recovered within the inverse procedures, hence completely waiving the condition of strictly in‐plane displacements for inverse problems. The recovery is achieved by identifying and including the possible modes of global rigid‐body motion within the cost function together with careful selection of test configuration. The effects of individual rigid‐body modes on the computed displacement fields are studied in detail and utilized as a guideline for selection of test configuration. The approach is fully demonstrated and validated by simulated as well as real experiments for determining elastic constants of isotropic and orthotropic materials using different experimental setups. Effects of improving the optimization routine, for cost function minimization, and experimental noise are also presented.     

基于子空间约束的面部特征点跟踪算法

为克服纹理不丰富和非刚性形变等因素引起的面部特征点跟踪困难,提出了一种基于子空间约束的面部特征点跟踪算法。针对人脸运动特点,将面部特征点分为具有复杂运动模式和简单运动模式的特征点集。用通过样例学习得到的特定描述模型准确刻画了具有复杂运动模式的特征点集的变化,保证了子空间约束的有效性。对运动模式简单的特征点集的跟踪则采用基于光流的算法,以提高算法的效率,也为基于特定描述模型的跟踪算法提供了更准确的起始搜索位置。对跟踪结果进一步应用子空间约束解决跟踪中的开孔问题和消除跟踪误差。实验结果表明,在存在较大验部变形和部分特征点纹理不丰富的情况下,该方法可以有效地跟踪较密集的面部特征点。     

An overview of optical flow-based approaches for motion segmentation

The goal of motion segmentation is to segregate a visual scene into independently moving objects. It is an indispensable pre-processing step for various tasks in computer vision and has evolved as an active and flourishing research area in the last few decades. In the sequences captured using a monocular camera, motion segmentation is typically performed by analyzing apparent motion of pixels in the image plane, i.e. the optical flow. Optical flow is generally contemplated as an appropriate representation of image motion. Numerous techniques for reliable flow estimation and subsequent advancements in their framework have been proposed in the last couple of decades and are outlined briefly in this work. The paper attempts to give a summary of diverse optical flow-based approaches used for robust segmentation of static or dynamic scenes containing rigidly moving objects and discusses in brief the shortcomings associated with them.     

Convective and Absolute Instability in the Incompressible Boundary Layer on a Rotating Disk in the Presence of a Uniform Magnetic Field

The stability of a conducting fluid flow over a rotating disk with a uniform magnetic field applied normal to the disk, is investigated. It is assumed that the magnetic field is unaffected by the motion of the fluid. The mean flow and linear stability equations are solved for a range of magnetic field-strength parameters and the absolute/convective nature of the stability is investigated. It is found that increasing the magnetic field parameter is in general stabilizing.     

振动条件下的尼龙拉链厚度尺寸视觉在线测量算法

针对尼龙拉链厚度尺寸的视觉在线测量过程中,振动对测量结果影响较大的问题,通过对拉链振动的机理分析,建立并求解出被测拉链横向振动模型的运动方程,再结合LK(Lucas Kanade)光流法测量原理,求取出某一时刻的拉链全局振动信息。在此基础上,提出了一种振动条件下的尼龙拉链厚度尺寸的视觉在线测量算法。首先提取出待补偿图像中被测拉链的边缘点坐标,其次根据运动补偿算法修正边缘点坐标,接着利用最小二乘法将边缘点坐标拟合成平行直线并求出其间距,最后根据像素当量转换为拉链厚度的实际尺寸。实验结果表明:该算法测量结果的不确定度为0.00051mm,远优于无运动补偿的视觉测量方法测量结果,能有效地抑制拉链振动对测量结果的影响。     

Pose estimation for autonomous grasping with a robotic arm system

A robust and accurate method for estimating the 3-D pose of a planar rigid object is presented. This article demonstrates that 3-D pose estimation becomes feasible by using the 2-D tracking points on an object of scale-invariant feature transform (SIFT) and 3-D point cloud detected by stereo vision on an object, assuming that a 3-D geometric model of an object is known a priori. The roll and pitch angles of an object are estimated by the normal vector of approximate plane of 3-D point cloud on an object and the yaw angle is estimated by 2-D tracking point on an object of SIFT. Accurate object detection and localization in the camera coordinate system is crucial for grasping. In the motion planning, the bidirectional rapidly exploring random tree algorithm is used to search for a valid path for efficient grasping. Our robot arm can robustly and autonomously grasp a randomly rotative rigid object detected by SIFT in 3-D space. We have realized a grasping scenario with a dexterous arm (ADAM) such that an object in front of ADAM can be grasped. This demonstration shows how the proposed components build a dexterous and robust system integrating object detection, pose estimation, and motion planning.     

Vortex motion in the early stages of unsteady flow around a circular cylinder

In this paper, processes in the early stages of vortex motion and the development of flow structure behind an impulsively-started circular cylinder at high Reynolds number are investigated by combining the discrete vortex model with boundary layer theory, considering the separation of incoming flow boundary layer and rear shear layer in the recirculating flow region. The development of flow structure and vortex motion, particularly the formation and development of secondary vortex and a pair of secondary vortices and their effect on the flow field are calculated. The results clearly show that the flow structure and vortices motion went through a series of complicated processes before the symmetric main vortices change into asymmetric: development of main vortices induces secondary vortices; growth of the secondary vortices causes the main vortex sheets to break off and causes the symmetric main vortices to become “free” vortices, while a pair of secondary vortices is formed; then the vortex sheets, after breaking off, gradually extend downstream and the structure of a pair of secondary vortices becomes relaxed. These features of vortex motion look very much like the observed features in some available flow field visualizations. The action of the secondary vortices causes the main vortex sheets to break off and converts the main vortices into free vortices. This should be the immediate cause leading to the instability of the motion of the symmetric main vortices. The flow field structure such as the separation position of boundary layer and rear shear layer, the unsteady pressure distributions and the drag coefficient are calculated. Comparison with other results or experiments is also made. This work was presented at the First Asian Congress of Fluid Mechanics, Bangalore in December 1980.     

Optimum rigid motion with one perspective view

One of the central problems in dynamic computer vision is the determination of motion from correspondence of points on the visible surface of a moving object obtained at two different times. In the problem we consider, the initial position of several feature points on some object is assumed to be known. Then at some later time instant the corresponding perspective projection of those points is given. The moving body may be nonrigid or the measurements may be corrupted with noise. In either case, we determine the multiplicity of possible solution for the best-fitting rigid motion. We show that whenever at least three point correspondences are given, there are at most two possible solutions for the best-fitting rigid motion if the object space is two-dimensional, while there are at most forty possible solutions if the object space is three-dimensional. In the latter case the number of possible solutions drops to four if three point correspondence are known, the body is rigid, and the measurements are noise-free. Several examples are worked out to illustrate our results.©1994 John Wiley & Sons Inc