集成几何约束与物性仿真技术的虚拟装配

针对传统装配定位导航中零部件位姿的突变问题,利用线性插值与四元数球形插值 的方法,求解零部件约束定位变换过程的渐变运动;同时利用导纳式力觉交互控制模式,解决了 约束定位变换后的控制信号分离问题;在装配运动导航阶段,将约束几何元素具象化为力觉约束 模型,以满足虚拟装配对力觉反馈的需求。针对虚拟装配对物性仿真的需求,将开源物理引擎 Bullet 集成到仿真系统中,提出几何约束与物性仿真技术相结合的装配流程,最后在自主研发的 虚拟装配原型系统中进行了应用实例验证。     

基于分布式系统的虚拟力感知与交互技术

针对现有人机交互系统中的力觉交互沉浸感不足的问题,提出了一种基于分布式系统的动态碰撞检测与虚拟力觉交互的控制策略。力觉交互系统采用分布式设计,主要包括:人机交互接口管理、空间位形解算和运动控制与碰撞检测等单元设计。在交互过程中,采用分层方式处理碰撞效果。根据模型所处虚拟空间的相对几何位置与碰撞后的运动状态构建虚拟力觉,并由交互管理单元映射至实体交互设备,实现操作者的力觉感知与交互。采用PHANTOM omni力反馈设备与Visual Studio 2010构建了动态碰撞检测的仿真实验系统,并进行了虚拟力觉交互实验。实验结果表明:操作者通过力反馈设备能够实现力觉感知与交互,有效解决了交互过程中的力觉效果不足的问题。     

约束切换与阻抗显示力反馈设备的稳定性研究

􀁽研究了虚拟现实力觉交互系统中基于阻抗显示原理的交互设备丧失稳定性的原因以及振荡抑制方法.通过分析单边约束的特点,将复杂虚拟物体形状的感知和交互过程归结为动态单边约束的接触问题.采用力反馈设备Phantom建立试验平台,通过分析不同类型的单边约束下虚拟力信号的时间和空间分布规律,发现了动态单边约束交互仿真中产生振荡的原因.给出了基于虚拟力信号空间梯度的消除振荡的方法.试验表明,该方法可以有效抑制振荡,实现稳定的力觉交互控制.     

基于实时点云建模虚拟夹具辅助力觉交互研究

为满足遥操作的精度和实时性要求,应对在操作过程中出现的目标工件形状发生变化或与机械臂末端间出现相对移动等状况,提出一种融合RGB与深度图像信息的点云建模方法。对未知的操作环境进行实时建模,在此基础上实时构建虚拟夹具,继而研究遥操作系统中的力觉交互环节。实验结果表明,基于实时点云建模的虚拟夹具能够有效辅助操作者操纵力反馈设备与点云进行力觉交互,力觉临场感效果良好,可用于规避固定或动态障碍物,完成相对精确的操作任务。     

基于虚拟3D视觉和力觉交互的SEM遥纳操作系统

为增强纳米操作的交互性,本文结合虚拟现实技术,借助力觉反馈设备搭建了基于虚拟3D视觉反馈与虚拟力觉反馈的遥纳操作平台.为确保虚拟环境能够正确反映真实的纳米操作环境,对虚拟模型的碰撞检测和力觉渲染进行了详细设计;同时在力觉反馈设备和虚拟环境之间引入虚拟匹配环节保证力觉交互接口的稳定,增强主端控制模块的协调性.为实现准确的纳米操作,采用基于兴趣区域的图像特征方法提取探针深度信息,快速建立图像模糊度与探针到基底的距离的关系,实现对探针的闭环控制.最后,利用所述的系统平台以及操作方法,完成了单根ZnO纳米线的转移实验.     

交互式乐器演奏的六自由度力觉渲染方法

目的在进行虚拟乐器交互演奏时,需要模拟触力觉-视觉-听觉多通道同步反馈,其中触力觉反馈的难点在于模拟人手操作乐器的六自由度(6-Do F)力觉交互过程。方法提出一种基于混合模型和单边约束优化的六自由度力觉合成方法,实现了虚拟人手和琴弦的多点多区域接触力觉模拟。虚拟人手采用层次化球树模型表达,古琴采用混合模型表达,其中琴体和琴弦分别采用层次化球树模型和直线解析模型。提出了基于混合模型的离散碰撞检测算法,实时检测虚拟手和琴弦是否产生碰撞;基于发生碰撞的几何元素对建立单边不可穿透约束方程,通过Active Set方法求解约束优化后方程,获得6维位姿变量保证图形显示场景中的虚拟手不会和琴弦产生穿透。为模拟琴弦变形,提出变直径的圆柱体模型来模拟琴弦在不同振动幅度下的动力学响应;提出交互状态敏感的力计算模型以刻画人手在弹奏不同状态琴弦(静态、振动态)的力觉感受差异。结果基于力觉交互设备Phantom Premium 3.0建立了实验平台,实验结果表明,本文算法可以模拟单点、多点等不同接触状态,并能模拟6维力和力矩,操作者可以感受到琴弦振动时的细腻力感觉,力觉交互过程稳定,算法计算效率在1 k Hz以上。结论算法可模拟针对琴弦一类的超薄形状物体的多点接触力觉交互过程,算法计算效率高,包含碰撞检测、约束优化、琴弦变形仿真等计算回路的更新频率也能达到要求,该混合模型能为后续复杂形状物体的碰撞响应研究提供思路。     

面向牙科手术培训的力觉合成技术

虚拟现实系统的沉浸感和交互性是高性能系统的重要特征,对于医学应用的虚拟现实尤其如此.文中针对牙科手术培训中训练医生触力觉感受的需求,重点研究基于三角面片网格模型的真实感触力觉合成技术,包括基于多更新率的力觉渲染体系架构、基于均匀空间划分和时间连续性的实时碰撞检测算法、基于虚拟代理的接触碰撞响应算法、基于等效接触模型的切削力计算模型,以及滑动速度驱动的大规模数据多层次力觉渲染算法等.建立了力觉-视觉融合的牙科操作培训系统的原型物理样机,实现了龋齿探查、牙齿纵截面物理属性感知、牙体钻削制备等典型牙科手术操作模拟.文中的触力觉合成技术是构建虚拟现实培训系统的共性问题,不但适用于牙科手术操作领域,也可用于其他外科手术培训系统.     

虚拟手抓持力觉生成算法真实性的评价

目的 虽然许多学者研发了多种虚拟手交互触力觉生成算法,但是如何评价虚拟手交互触力觉生成算法的真实性是一个富有挑战性的新问题,值得深入研究.方法 构建手指抓持力测量平台,设计3种抓持姿态下指尖静力抓持球体实验内容,测得各指尖作用力的实测值;通过虚拟手静力抓持力觉生成算法,求得这3种抓持姿态下各手指作用力的理论值;对实测值进行统计和分析,并与理论值进行对比和讨论;结果 日常抓持经验和实测值是完全相符的,实测值和理论值很接近且偏差均在可接受范围之内.单个手指作用力或多个手指合力的实测值与理论值的偏差均在1%6%.结论 本文实现了一种基于物理的实验方法,评价和分析了虚拟手静力抓持力觉生成算法的真实性,证实此算法可以逼真地生成虚拟手抓持力,可应用于具有力反馈的自然的虚拟手交互.     

虚拟手术中表面网格模型的力反馈算法与仿真

提出一个带力反馈的虚拟腹部外科手术系统,并重点研究及实现了基于表面网格模型的力反馈算法。为了提高系统的稳定性,使用基于线段与表面三角网格的碰撞检测方法;基于四阶Runge-Kutta方法的表面网格mass-spring模型进行变形仿真;基于力的广度优先传播来解决变形仿真的局部性。通过仿真实验验证了该原型系统可以实现与可变形的三维模型的实时力觉交互。最后,把该方法应用到虚拟腹部外科手术系统中,并实现带力反馈的手术仿真操作。     

支持嵌入式Web服务器的多层级力觉交互仿真

针对传统力觉交互操作过程复杂、模拟物理场景不真实的问题,提出支持嵌入式Web服务器的多层级力觉交互仿真研究方法.在嵌入式Web服务器的基础上添加离散LOD模型,计算相对交互速度,获得目标多层级的序列号进行碰撞计算,构建速度驱动模型.将碰撞检验离散速度驱动模型与SCP层级映射算法相结合,判定映射约束线段、映射约束包围盒单元,运用GHOST SDK计算二者的正交函数,确认满足模型的限制速度阈值条件,从而获得模型的速度参数值以及切换速度,完成力觉交互研究.仿真结果证明,所提方法可以有效解决力觉交互过程中出现的振动现象,提升场景真实感,并且计算简便,具有较高的稳定性与适用性.     

Haptic force control based on impedance/admittance control aided by visual feedback

This paper demonstrates a haptic device for interaction with a virtual environment. The force control is added by visual feedback that makes the system more responsive and accurate. There are two popular control methods widely used in haptic controller design. First, is impedance control when user motion input is measured, and then, the reaction force is fed back to the operator. The alternative method is admittance control, when forces exerted by user are measured and motion is fed back to the user. Both, impedance and admittance control are also basic ways for interacting with a virtual environment. In this paper, several experiments were performed to evaluate the suitability of force-impedance control for haptic interface development. The difference between conventional application of impedance control in robot motion control and its application in haptic interface development is investigated. Open loop impedance control methodology is implemented for static case and a general-purpose robot under open loop impedance control was developed as a haptic device, while a closed loop model based impedance control was used for haptic controller design in both static and dynamic case. The factors that could affect to the performance of a haptic interface are also investigated experimentally using parametric studies. Experimental results for 1 DOF rotational motion and 2 DOF planar translational motion systems are presented. The results show that the impedance control aided by visual feedback broaden the applicability of the haptic device and makes the system more responsive and accurate.

A Survey of Haptic Rendering Techniques

Computer Graphics technologies have developed considerably over the past decades. Realistic virtual environments can be produced incorporating complex geometry for graphical objects and utilising hardware acceleration for per pixel effects. To enhance these environments, in terms of the immersive experience perceived by users, the human's sense of touch, or haptic system, can be exploited. To this end haptic feedback devices capable of exerting forces on the user are incorporated. The process of determining a reaction force for a given position of the haptic device is known as haptic rendering. For over a decade users have been able to interact with a virtual environment with a haptic device. This paper focuses on the haptic rendering algorithms which have been developed to compute forces as users manipulate the haptic device in the virtual environment.     

A Fundamental Tradeoff Between Performance and Sensitivity Within Haptic Rendering

In this paper, we show that for haptic rendering using position feedback, the structure of the feedback loop imposes a fundamental tradeoff between accurate rendering of virtual environments and sensitivity of closed-loop responses to hardware variations and uncertainty. Due to this tradeoff, any feedback design that achieves high-fidelity rendering incurs a quantifiable cost in terms of sensitivity. Analysis of the tradeoff reveals certain combinations of virtual environment and haptic device dynamics for which performance is achieved only by accepting very poor sensitivity. This analysis may be used to show that certain design specifications are infeasible and may guide the choice of hardware to mitigate the tradeoff severity. We illustrate the predicted consequences of the tradeoff with an experimental study.     

Rendering stiffer walls: a hybrid haptic system using continuous and discrete time feedback

Instability in conventional haptic rendering destroys the perception of rigid objects in virtual environments. Inherent limitations in the conventional haptic loop restrict the maximum stiffness that can be rendered. In this paper we present a method to render virtual walls that are much stiffer than those achieved by conventional techniques. By removing the conventional digital haptic loop and replacing it with a part-continuous and part-discrete time hybrid haptic loop, we were able to render stiffer walls. The control loop is implemented as a combinational logic circuit on an field-programmable gate array. We compared the performance of the conventional haptic loop and our hybrid haptic loop on the same haptic device, and present mathematical analysis to show the limit of stability of our device. Our hybrid method removes the computer-intensive haptic loop from the CPU—this can free a significant amount of resources that can be used for other purposes such as graphical rendering and physics modeling. It is our hope that, in the future, similar designs will lead to a haptics processing unit (HPU).     

一种提高基于线绳的力反馈设备显示阻抗范围的方法

提出一种通过动态调整线绳预紧力提高基于线绳的力反馈设备显示阻抗范围的方法．介绍了基于线绳的力反馈设备的基本结构, 从能量耗散的角度分析了线绳张力对设备显示高刚度虚拟物体时稳定性的影响,并分析线绳预紧力与力觉交互透明性之间的关系． 为同时满足稳定性和透明性的要求,根据设备操作末端与虚拟物体的接触状态,对线绳的预紧力进行动态调整．实验结果表明, 该方法能够在保持设备透明性的同时,有效提高其稳定性,从而提高设备显示的阻抗范围．     

Robot-enabled tangible virtual assembly with coordinated midair object placement

The assembly in Virtual Reality (VR) enables users to fit virtual parts into existing 3D models immersively. However, users cannot physically feel the haptic feedback when connecting the parts with the virtual model. This work presents a robot-enabled tangible interface that dynamically moves a physical structure with a robotic arm to provide physical feedback for holding a handheld proxy in VR. This enables the system to provide force feedback during virtual assembly. The cooperation between the physical support and the handheld proxy produces realistic physical force feedback, providing a tangible experience for various virtual parts in virtual assembly scenarios. We developed a prototype system that allowed the operator to place a virtual part onto other models in VR by placing the proxy onto the matched structure attached to a robotic arm. We conducted a user evaluation to explore user performance and system usability in a virtual assembly task. The results indicated that the robot-enabled tangible support increased the task completion time but significantly improved the system usability and sense of presence with a more realistic haptic experience.     

A haptic-rendering technique based on hybrid surface representation

A novel haptic rendering technique using a hybrid surface representation addresses conventional limitations in haptic displays. A haptic interface lets the user touch, explore, paint, and manipulate virtual 3D models in a natural way using a haptic display device. A haptic rendering algorithm must generate a force field to simulate the presence of these virtual objects and their surface properties (such as friction and texture), or to guide the user along a specific trajectory. We can roughly classify haptic rendering algorithms according to the surface representation they use: geometric haptic algorithms for surface data, and volumetric haptic algorithms based on volumetric data including implicit surface representation. Our algorithm is based on a hybrid surface representation - a combination of geometric (B-rep) and implicit (V-rep) surface representations for a given 3D object, which takes advantage of both surface representations.     

Toward realistic haptic rendering of surface textures

New sophisticated haptic-rendering algorithms let users experience virtual objects through touch. We systematically investigate the unrealistic behavior of virtual haptic textures. The emerging science of haptic rendering consists of delivering properties of physical objects through the sense of touch. Owing to the recent development of sophisticated haptic-rendering algorithms, users can now experience virtual objects through touch in many exciting applications, including surgical simulations, virtual prototyping, and data perceptualization. Haptics holds great promise to enrich the sensory attributes of virtual objects that these systems can produce. One area that has received increasing attention in the haptics community is haptic texture rendering, the goal of which is to introduce micro-geometry-scale features on object surfaces. Haptic objects rendered without textures usually feel smooth, and sometimes slippery. Appropriate haptic textures superimposed on haptic objects enhance an object's realism.     

Virtual prototyping of a car turn-signal switch using haptic feedback

The present work describes the virtual prototyping procedure of car turn-signal switches using a dedicated haptic feedback system. Although turn-signal switches have mechanisms with simple geometry, simulating the “feeling” during its operation is still a challenge. In order to allow ergonomics designers to directly assess the comfort of operation, a dedicated haptic system was developed for reproducing the force feedback that would characterize a real turn-signal switch. For the accurate haptic feedback generation and rendering purpose, a detailed computer-aided design model of the switch was developed together with a multibody simulation. For the design purpose a novel method for the synthesis of the cam mechanism was also developed, starting from an imposed force profile that was previously validated on the haptic device, for which the cam geometry is determined. Thus, the proposed approach enables the designer to also design the “feel” of the switch, and directly manufacture a good model, simplifying the usual iterative process necessary to implement the desired force profile. Finally, an example of virtual prototyping of a turn-signal switch is presented demonstrating the usability of the proposed method and the haptic system.