VRML技术结合全方位运动轮椅的应用实践探索

协同虚拟现实技术具有广泛的应用背景,文中以全方位轮椅为应用对象,探讨虚拟现实技术的应用.结合Mecanum轮、连续切换轮、锥滚轮这三种全向轮的运动原理与排布方式,分析了轮椅的运动学关系.在轮椅三维Pro/E模型的基础上,利用虚拟现实建模语言（VRML）对全方位轮椅进行实时定制和仿真,通过操作定制控制台可以实现零件颜色的改变和轮椅部件的替换.运动仿真控制台可以实现轮椅的直走、横走、斜走以及原地打转等运动方式的仿真.这样用户能参与到轮椅的定制设计中,得到符合自己要求的轮椅,同时对全方位轮椅的特殊运动功能有了更加深刻和形象的认识.     

Riccati discrete time transfer matrix method for elastic beam undergoing large overall motion

An efficient method for dynamics simulation for elastic beam with large overall spatial motion and nonlinear deformation, namely, the Riccati discrete time transfer matrix method (Riccati-DT-TMM), is proposed in this investigation. With finite segments, continuous deformation field of a beam can be decomposed into many rigid bodies connected by rotational springs. Discrete time transfer matrices of rigid bodies and rotational springs are used to analyze the dynamic characteristic of the beam, and the Riccati transform is used to improve the numerical stability of discrete time transfer matrix method of multibody system dynamics. A predictor-corrector method is used to improve the numerical accuracy of the Riccati-DT-TMM. Using the Riccati-DT-TMM in dynamics analysis, the global dynamics equations of the system are not needed and the computation time required increases linearly with the system’s number of degrees of freedom. Three numerical examples are given to validate the method for the dynamic simulation of a geometric nonlinear beam undergoing large overall motion.     

Algorithm for identifying parameters of the dynamic system of an aircraft. II

The problem of identification of aerodynamic parameters of IL-96-300 aircraft by processing digital information on its longitudinal and lateral motion provided by on-board measurement complex according to real flight data (longitudinal motion) and results of mathematical simulation (lateral motion) is studied. The problem of algorithmic parameter identification for the nonlinear dynamic system, whose model corresponds to the control system of a modern maneuvering aircraft, is considered.     

Generation and Analyses of the Reinforced Wave Gait for a Mammal-Like Quadruped Robot

The statically stable gait control of a mammal-like quadruped robot that provides an adequate or stable manner of traversing over irregular terrain was addressed. The reinforced wave gait which integrates new parameters of the lateral offset and displacements of the center of gravity (COG) based on the profiles of standard wave gait was investigated. The continuous and discontinuous motion trajectory of a robot’s COG in the periodic reinforced wave gait could be realized. The longitudinal and lateral stability margins of a reinforced wave gait were formulated for the gait generation and control of a quadruped robot. Moreover, the effects of the lateral offset on the stability, velocity and the energy efficiency were studied in details. The reinforced wave gait with lateral sway motion adequately improved the stability, and two particular gait patterns that involve the lateral sway motion for a maximal velocity and maximum achievable stability were described. With consideration of a quadruped robot with asymmetric carrying loads on its body, a scheme that relates to the gait parameters of the displacement of a robot’s COG to avoid losing stability was proposed. The simulation and experimental results about the effects of lateral offset added in the reinforced wave gait on the minimum power consumption during a quadruped robot walking on a flat terrain indicated that the reinforced wave gait with a larger lateral offset would generate a better wave gait with a higher velocity and energy efficiency.     

Integrated Dynamics Control and Energy Efficiency Optimization for Overactuated Electric Vehicles

A large number of studies have been conducted on the dynamics control of electric vehicles or on the optimization of their energy efficiency but few studies have looked at both of these together. In this study, an integrated dynamics control and energy efficiency optimization strategy is proposed for overactuated electric vehicles, where the control of both longitudinal and lateral dynamics is dealt with while the energy efficiency is optimized. First, considering the trade‐off between control performance and energy efficiency, criteria are defined to categorize the vehicle motion status as linear pure longitudinal motion and non‐linear motion or turning motion. Then different optimization targets are developed for different motion status. For the pure linear longitudinal motion and cornering motion, the energy efficiency and vehicle dynamics performance are equally important and a trade‐off control performance between them needs to be achieved. For the non‐linear turning motion, vehicle handling and stability performance are the primary concerns, and energy efficiency is a secondary target. Based on the defined targets, the desired longitudinal and lateral tyre forces and yaw moment are then optimally distributed to the wheel driving and steering torques. Finally numerical simulations are used to verify the effectiveness of the proposed strategies. The simulation results show that the proposed strategies can provide good dynamics control performance with less energy consumption.     

Image Sequence Stabilization in Real Time

This paper describes a method ofstabilizingimage sequences obtained by a camera carried by a ground vehicle. The motion of the vehicle can usually be regarded as consisting of a desired smooth motion combined with an undesired non-smooth motion that includes impulsive or high-frequency components. The goal of the stabilization process is to correct the images so that they are approximately the same as the images that would have been obtained if the motion of the vehicle had been smooth.We analyse the smooth and non-smooth motions of a ground vehicle and show that only the rotational components of the non-smooth motion have significant perturbing effects on the images. We show how to identify image points at which rotational image flow is dominant, and how to use such points to estimate the vehicle's rotation. Finally, we describe an algorithm that fits smooth (ideally, piecewise constant) rotational motions to these estimates; the residual rotational motion can then be used to correct the images. We have obtained good results for several image sequences obtained from a camera carried by a ground vehicle moving across bumpy terrain.     

位平面匹配的电子稳像算法的改进

针对位平面匹配算法很难对视频图像中存在的旋转运动进行估计的缺陷,提出了一种改进的电子稳像算法。该算法采用钻石搜索策略的位平面法来估计并补偿视频图像序列间的平移运动,对参考帧图像进行拉普拉斯变换,在靠近图像边缘处选取若干个特征小块与当前帧进行块匹配,进一步计算并补偿其可能存在的旋转运动。通过理论分析和实验仿真表明：在处理存在旋转运动的视频图像时,改进后的算法在满足实时性的同时提高了稳像精度。     

Fuzzy motion control strategy for cooperation of multiple automated vehicles with passengers comfort

This paper considers motion control for a cooperative system of automated passenger vehicles. It develops a cooperative scheme based on a decentralized planning algorithm which considers the vehicles in an initial open chain configuration. In this scheme the trajectories are intersections-free, and each trajectory is planned independently of the others. To ensure the stabilization of each vehicle in the planned trajectory, a fuzzy closed loop motion control is presented, where, based on the properties of the Fuzzy maps, the Lyapunov’s stability of the motion errors is demonstrated for all the vehicles. Based on the ISO 2631-1 standard, the saturation property of the Fuzzy maps guarantees low values of longitudinal and lateral accelerations, to ensure comfort of the human body during the motion. The validity of this control algorithm is supported by simulation experiments.     

Sparse Localized Decomposition of Deformation Gradients

Sparse localized decomposition is a useful technique to extract meaningful deformation components out of a training set of mesh data. However, existing methods cannot capture large rotational motion in the given mesh dataset. In this paper we present a new decomposition technique based on deformation gradients. Given a mesh dataset, the deformation gradient field is extracted, and decomposed into two groups: rotation field and stretching field, through polar decomposition. These two groups of deformation information are further processed through the sparse localized decomposition into the desired components. These sparse localized components can be linearly combined to form a meaningful deformation gradient field, and can be used to reconstruct the mesh through a least squares optimization step. Our experiments show that the proposed method addresses the rotation problem associated with traditional deformation decomposition techniques, making it suitable to handle not only stretched deformations, but also articulated motions that involve large rotations.     

基于Plib的飞艇飞行视景仿真设计

由于飞艇体积大、密度小,受附加惯性力显著,其动力学特性与常规飞行器有较大不同。所以。为了直观全面地了解飞艇的飞行特点,对飞艇进行飞行视景仿真是必要的。为此首先介绍了视景仿真开发工具Plib和仿真系统总体框架,然后,应用机理分析方法建立了飞艇运动模型。在此基础上,调用Plib的类方法创建三维仿真环境,重点研究了天空海洋绘制、模型导入、视点变换、图形用户界面资源及键盘鼠标响应控制等关键技术。最后应用该系统对飞艇纵侧向扰动运动进行了仿真,展现了飞艇受扰后的飞行状态和各种运动模态的变化过程,结果表明该仿真系统真实感强,实时性好,可以为飞艇的后续研制工作提供参考和帮助。     

基于六自由度模型的飞机刹车仿真研究

针对飞机着陆刹车三自由度仿真模型存在的不足,研究了六自由度飞机对象建模的基本方法和原理,并给出了飞机机体的空间运动方程.考虑了飞机纵横向之间的耦合作用和决定飞机刹车性能的因素,没有对刚体运动模型做简化处理,直接根据牛顿第二定律推导出机体全量非线性方程,结合飞机起落架的纵横向刚度模型和传统液压刹车系统模型.建立了六自由度飞机刹车系统整体模型,并且基于maflab/simulink对其数学模型进行了转化,建立了可在计算机上实现的数学仿真模型,给出了湿跑道下仿真结果.结果表明,所建立的六自由度飞机刹车系统模型能够充分表征飞机着陆刹车的实际运行特性,为飞机刹车性能的改善和视景系统更多参数的体现提供了基础和前提.     

基于ROS的蛇形机器人基本仿生运动与自主爬台阶控制

设计了一种带正交关节和主动轮组合的蛇形机器人。该机器人不仅能够实现基本的蜿蜒运动、纵向行波运动、横向翻滚运动和横向行波运动,且针对台阶式障碍物提出了一种自主爬越台阶的控制策略。机器人通过激光测距传感器与头部关节的仰角得到台阶高度,抬起相应高度的关节将头关节搭在台阶上,控制主动轮的推进速度与关节抬起的角速度相结合的方式达到上台阶的目的,并且在运动过程中将头部俯仰关节舵机的负载反馈作为判别下台阶的条件。基于ROS （robot operating system）构建了蛇形机器人仿真模型,并通过仿真与实验验证了机器人的基本运动控制和自主爬台阶控制策略的有效性。     

Rigid-flexible coupling dynamics of three-dimensional hub-beams system

In the previous research of the coupling dynamics of a hub-beam system, coupling between the rotational motion of hub and the torsion deformation of beam is not taken into account since the system undergoes planar motion. Due to the small longitudinal deformation, coupling between the rotational motion of hub and the longitudinal deformation of beam is also neglected. In this paper, rigid-flexible coupling dynamics is extended to a hub-beams system with three-dimensional large overall motion. Not only coupling between the large overall motion and the bending deformation, but also coupling between the large overall motion and the torsional deformation are taken into account. In case of temperature increase, the longitudinal deformation caused by the thermal expansion is significant, such that coupling between the large overall motion and the longitudinal deformation is also investigated. Combining the characteristics of the hybrid coordinate formulation and the absolute nodal coordinate formulation, the system generalized coordinates include the relative nodal displacement and the slope of each beam element with respect to the body-fixed frame of the hub, and the variables related to the spatial large overall motion of the hub and beams. Based on precise strain-displacement relation, the geometric stiffening effect is taken into account, and the rigid-flexible coupling dynamic equations are derived using velocity variational principle. Finite element method is employed for discretization. Simulation of a hub-beams system is used to show the coupling effect between the large overall motion and the torsional deformation as well as the longitudinal deformation. Furthermore, conservation of energy in case of free motion is shown to verify the formulation.     

转子-轴承系统中滚动球轴承的非线性动力学相似特性研究

针对转子—轴承系统中滚动球轴承的动力学相似问题,提出一种考虑非线性振动特性的轴承系统相似模型建立方法.首先,建立滚动球轴承整体的非线性振动微分方程,运用积分模拟法推导了轴承整体的非线性振动特性相似关系,并结合滚动球轴承的动力学相似关系得到滚动球轴承系统的相似设计准则;其次,应用所得的相似准则,以深沟球轴承C204JUT为原型、6208为模型进行数值仿真实例计算,通过采用Newmark-β算法计算得到的分叉图分析了转速ω、径向载荷F_r、阻尼C及径向游隙γ大小对原型和模型轴承系统振动位移或速度响应的影响;最后,通过对比原型和模型的各参数(ω、F_r、C、γ)分叉图中分叉区间、趋于稳定运动参数值大小以及进入稳定周期运动时的稳态响应值大小验证相似准则的准确性和有效性.通过分析得到以下结论:1滚动球轴承非线性振动特性参数(如振动响应、结构阻尼等)相似关系可由轴承结构参数相似关系确定;2原型与模型非线性运动的分叉图形状一致,且模型能够很好的预测原型稳态振动响应,因此可将模型轴承用来预测原型轴承的非线性振动行为.     

基于Gaussian-Hermite矩的旋转运动模糊不变量

目的 模糊图像的分析与识别是图像分析与识别领域的重要方向。有些图像形成过程中成像系统与物体之间存在相对旋转运动,如因导弹高速自旋转造成的制导图像的旋转运动模糊。大多数对于这类图像的识别都需要先对模糊图像进行“去模糊”的预处理,且该类方法存在计算时间复杂度较高及不适定的问题。对此,提出一种直接提取旋转运动模糊图像中的不变特征,用于旋转运动模糊图像目标检索和识别。方法 本文以旋转运动模糊的退化模型为出发点,提出了旋转运动模糊Gaussian-Hermite(GH)矩,构造了一组由5个对旋转变换和旋转运动模糊保持不变性的GH矩不变量组成的特征向量(rotational motion blur Gaussian-Hermite moment invariants, RMB＿GHMI-5),可从旋转变换和旋转运动模糊的图像中直接进行目标检索和识别,无需前置复杂的“去模糊”预处理过程。结果 在USC-SIPI(University of Southern California—Signal and Image Processing Institute)数据集上进行不变性实验,对原图进行不同程度的旋...     

Rotational motion and lateral migration of an elliptical magnetic particle in a microchannel under a uniform magnetic field

We have numerically investigated the motion of an elliptical magnetic particle in a microfluidic channel subjected to an external uniform magnetic field. By using the direct numerical simulation method and an arbitrary Lagrangian–Eulerian technique, the involved particle–fluid-magnetic field problem can be solved in a fully coupled manner. The numerical predictions of the particle trajectory and orientation with and without a uniform magnetic field are in qualitative agreement with the existing experimental results, and numerical results have revealed the impacts of key parameters such as inlet flow velocity, magnetic field direction, and particle shape on the rotational motion and lateral migration of the elliptical particle. Meanwhile, the shape-based particle separation in a low Reynolds number flow with the aid of an applied uniform magnetic field has also been numerically demonstrated.     

Combined Inverse Kinematic and Static Analysis and Optimal Design of a Cable-Driven Mechanism with a Spring Spine

Abstract

A special humanoid neck with low motion noise requirements yields a cable-driven parallel mechanism to imitate the rotational motion of a human neck. The fixed base and moving platform of the mechanism are connected by four cables and a column compression spring. The four cables are actuated separately, while the spring can support weight on the moving platform. Although similar mechanisms exist in the literature, the analysis of them is scarce because a flexible spring instead of a rigid kinematic chain is used as the spine. With the spring’s lateral buckling motion, a new approach must be adopted to solve the kinematics. In this paper, we propose a method that combines the kinematics with the statics to solve them simultaneously. The configuration of the moving platform is parameterized with four parameters, one of which is considered as parasitic motion. Using the spring’s lateral buckling equation, we can obtain the parasitic motion and solve the inverse position problem. The optimal design for cable placements is then performed to minimize the actuation force. The method in this paper provides a novel way to analyze parallel mechanisms with a spring spine and it can be applied to other mechanisms with flexible spines.     

Stability analysis and design for aircraft gust alleviation control

This paper is concerned with the stability analysis and the development of an on-line two-level gust alleviation control system for a high-speed aircraft operating in an unknown environment. As is well known, such an aircraft experiences dynamic instability in its lateral motion when subjected to the longitudinal and lateral gusts. This is due to the phenomenon of lateral-longitudinal aerodynamic cross-coupling.In the first part of this paper the instability behaviour, in the presence of a longitudinal gust, of two typical high-speed aircraft is analyzed. From theoretical and simulation studies it is shown that for a sinusoidal gust, and for a given configuration, the instability region is a function of both the amplitude and frequency of the gust disturbance.In the second part of the paper, an on-line gust alleviation control system is synthesized for such an aircraft operating over a wide range of unknown environmental conditions. This control system employs a two-level control structure. The controller, however, does not require an explicit knowledge of the aircraft parameters or the environment. Typical simulation results are presented which verify the theoretical predictions.     

Structure and dynamics of the GH loop of the foot-and-mouth disease virus capsid

The GH loop of VP1 of the foot-and-mouth disease virus capsid is important because it is a major antigenic site and an integrin recognition site. The GH loop is disordered in all X-ray structures of the capsid except for serotype O under reduced conditions in which the loop lies on the capsid surface. Although the structure of the capsid–integrin complex has not yet been determined, the GH loop is known to protrude from the capsid surface when the capsid is bound with an antigen-binding fragment (Fab). To clarify the structure and dynamics of the GH loop under natural unreduced conditions before binding to integrins or Fab fragments, we performed molecular dynamics simulation of 16.3 ns long under rotational symmetry boundary conditions for the capsid of serotype O using the X-ray structure of the reduced capsid for the initial coordinates. When the disulfide bond at the base of the GH loop was formed by the molecular mutation method, the loop protruded into the surrounding water, as reported for Fab–capsid complexes, and fluctuated like a tentacle. After equilibration, the GH loop overlapped the surface of the capsid but continued to fluctuate, being directed toward a 2-fold axis. The conformational change of the GH loop after formation of the disulfide bond was explained by a model of elastic tube. The side chains of arginine and aspartic acid of the integrin recognition residues (RGD tripeptide) extended in opposite directions, and the residues on the C-terminal side of the RGD tripeptide formed a hydrophobic cluster in close proximity of the arginine residue of the tripeptide.     

Vibration analysis of rotating rods based on the nonlocal elasticity theory and coupled displacement field

Free longitudinal vibration analysis of a rotating rod based on the Eringen’s nonlocal elasticity is studied in this paper. Rod is supposed to rotate around a fixed axis with a constant angular velocity. To capture the effect of the rotational motion into analysis of the continuous system, a linear proportional relation is introduced between axial and angular velocities. For the first time the mentioned relation is presented based on the internal motions of the infinitesimal element. This novelty makes the rotational displacement as a dependent function of axial displacement playing a significant role through the analysis. Variational approach is adopted to derive the equations of motion for clamped–clamped and clamped-free boundary conditions. For verification of the results obtained from the Galerkin approach, comparison with technical literature is reported. Finally current results illustrate the dependency of the dynamic-vibration analysis of the presented system on the nonlocality and the rotational velocity parameter. This dependency shows the decrement of the frequency with increment in both the angular velocity and the nonlocal parameter. As a result, the mentioned parameters are key factors in the design and analysis of such systems.