实时多组织虚拟手术的反馈力模拟

为了在虚拟下颌整形手术系统中提供实时和真实的触觉交互,分别构建了基于虚拟中介平面的推操作触觉模型、基于粘附力的拉操作触觉模型和基于非线性粘弹性的针刺触觉模型,以模拟皮肤拉钩、整形镊和针的典型手术操作;同时通过相邻组织间的动态触觉约束建立了多组织联合形变模型,以避免表面弹簧-质点模型形变过程中可能出现的表面间相互穿透的异常现象;并进一步将触觉交互模型和多组织形变模型集成于虚拟下颌手术系统,从而为医生提供一个手术训练的虚拟平台.触觉感知和交互效率的实验结果表明,通过触觉交互识别皮肤、肌肉和骨骼能够获得较高的识别正确率,并能提供实时的触觉和视觉交互体验.     

虚拟现实大空间下多虚拟目标被动触觉交互方法

针对虚拟现实（VR）大空间下为重定向行走的用户提供被动触觉时存在的虚实交互目标无法一一对应的问题,提出了一种用两个物理代理作为触觉代理为多个虚拟目标提供触觉反馈的方法,以在基于人工势场（APF）的重定向行走过程中,交替地满足用户被动触觉的需求。针对重定向行走算法本身以及标定不精确等原因造成的虚实不对齐的问题,对虚拟目标的位置及朝向进行设计并且在交互阶段引入触觉重定向。仿真实验表明对虚拟目标位置和朝向的设计可以大幅降低对齐误差;而用户实验结果证明触觉重定向的引入进一步提升了交互准确性,且能为用户带来更丰富、更具沉浸感的体验。     

带有振动触觉反馈的上肢康复系统

康复机器人在脑卒中患者的术后恢复治疗中起着重要作用。为了提高患者在康复训练过程中的主动性和专注度,提出了一种带有振动反馈的上肢康复训练系统。该系统利用多传感器获取人的上肢位姿信息,实现与虚拟场景的实时交互,并通过实时多层级振动反馈引导人的康复动作。通过心理物理学实验评估受试者对不同振动强度的感受,得出了人体感受区分明显的3个振动强度等级。构建了视触觉有效性实验,受试者需要在虚拟场景中完成特定的康复动作,实验结果表明,相较于无触觉反馈,受试者在振动触觉反馈的作用下可以更稳定高效地完成康复任务。     

实现牙体预备触觉交互仿真的图形显示

介绍了在牙科手术训练触觉交互系统的虚拟手术环境中,通过材料去除速率控制构成牙齿的网格变形实现牙齿被切削时材料去除过程的图形仿真.针对牙体预备操作和触觉交互装置输出力的特点,在交互系统的虚拟环境中,当工具与牙体模型发生接触时,所有进入工具空间范围的顶点都会沿着其外法线的反方向进行投射,投射量受控于材料去除速度,且网格变形速度不超过真实的牙齿材料去除速度,同时针对网格的变形位置绘制虚拟工具.通过限制网格变形可以动态的实现牙齿被切削过程的形状变化,图形显示逼真同时没有滞后.     

视触觉融合的增强现实三维注册方法

增强现实技术是近年来人机交互领域的研究热点。在增强现实环境下加入触觉感知,可使用户在真实场景中看到并感知到虚拟对象。为了实现增强现实环境下与虚拟对象之间更加自然的交互,提出一种视触觉融合的三维注册方法。基于图像视觉技术获得三维注册矩阵;借助空间转换关系求解出触觉空间与图像空间的转换关系;结合两者与摄像头空间的关系实现视触觉融合的增强现实交互场景。为验证该方法的有效性,设计了一个基于视触觉增强现实的组装机器人项目。用户可触摸并移动真实环境中的机器人零件,还能在触摸时感受到反馈力,使交互更具真实感。     

虚拟骨科手术中触觉交互建模方法综述

虚拟骨科手术可以让骨科医生使用多种虚拟骨科手术器械在三维重建的骨性解剖结构模型上进行骨科手术操作和 训练。力触觉交互在骨科手术中起着不容忽视的作用,如何在骨科手术模拟中实现真实快速的触觉交互,已成为近年来 虚拟骨科手术研究的热点。文章主要对现有的骨科手术模拟系统中用到的触觉交互模型进行了研究、分类和总结,分析 了现有的一些模型的特点和不足,并展望了骨科手术系统中未来力触觉交互的发展。     

基于触觉交互界面的虚拟现实警务训练系统

虚拟现实凭借着其高沉浸感的体验,在警务仿真培训中有着广泛应用,由于商用虚拟现实系统多关注视觉反馈,难以使用标准的手控器为警务培训提供逼真的触觉交互体验。触觉交互界面基于多功能的离散单点触控交互系统,可实现虚拟现实中的道具操作直接交互,针对虚拟训练中的警务场景,该系统能够识别用户所选道具,并响应用户的交互动作,以提高虚拟现实系统的交互真实性。该系统使用HTC Vive 追踪器对用户进行运动捕捉,以生成人体骨架驱动虚拟代理。同时,使用单片机获取并处理用户的道具选择信息及用户与道具的交互信息,再通过蓝牙通信传输至上位机。硬件设计采用 STM32F103 系列中的 C8T6 最小系统板,相关功能通过软件 Keil5 编程实现。实验验证了系统的正确性和可行性,能够提供多样的物理触觉代理,增强了虚拟环境中的交互体验。该系统为虚拟现实交互技术提供了新的思路和方向,具有很好的应用前景。     

基于触觉反馈和运动约束的虚拟装配操作

该文将人对虚拟对象的抓取分为两个过程,然后分别对这两个过程的触觉反馈进行模拟,使用户产生真实的操作感觉。然后根据零件在装配过程中受到的约束,对零件的运动进行约束,同时提出基于虚拟工具的运动轴线与连接件的轴线对齐的方法对虚拟工具的运动进行约束,从而实现自然直观的交互手段。     

虚拟装配中基于导纳控制的力觉渲染技术

传统的力触觉渲染多采用阻抗控制,不能很好地满足虚拟装配的应用要求,相比之下导纳控制模式更适用这一领域.为此提出一种基于导纳控制的双线程力觉渲染构架,并给出相应的力觉渲染算法.首先建立用于导纳控制的动力学模型,并讨论了碰撞和约束这2个状态下的力觉渲染;为了使用力觉交互接口进行虚拟装配中的小间隙装配,提出物理约束与几何约束结合的力觉渲染方法;最后针对物理计算和力反馈循环2个线程刷新频率不匹配的问题,利用二次拉格朗日多项式进行数值插值,实现了力觉交互接口的平稳输出.通过力反馈设备与自主开发的虚拟装配原型系统VAPP的连接与应用,验证了所提出的算法满足虚拟装配系统中力觉交互的应用要求.     

一种高保真视-触觉增强现实系统的搭建

随着增强现实技术的发展,仅包含视觉的增强现实技术已经不能满足人们的需求,而加入触觉信息形成的视-触觉融合的增强现实系统却越来越受到关注。触觉设备是将真实环境和虚拟环境连接起来的纽带。然而,触觉设备在视场中的存在会带来两个问题,一方面触觉设备占据了很大的视觉空间,另一方面触觉设备的定位往往会出现较大的误差,导致了视-触觉增强现实的真实性下降。为了增加使用者的体验感,提出一种高保真视-触觉增强现实环境的搭建方法。首先基于改进的ORB(Oriented FAST and Rotated BRIEF)和KLT(Kanade-Lucas-Tomasi)增强现实跟踪注册算法搭建稳定的视觉增强现实环境。其次提出了一种能校准触笔位置和方向的方法,以提升交互体验。然后提出一种基于力反馈的触觉渲染算法,最后使用改进的全局泊松方程和Criminisi算法对触觉设备进行隐藏和修复,减小因触觉设备存在对用户沉浸感造成的影响。     

Stable adaptive algorithm for Six Degrees-of-Freedom haptic rendering in a dynamic environment

Recently, physically-based simulations with haptics interaction attracted many researchers. In this paper, we propose an adaptive Six Degrees-of-Freedom (6-DOF) haptic rendering algorithm based on virtual coupling, which can automatically adjust virtual coupling parameters according to mass values of the simulated virtual tools. The algorithm can overcome the virtual tool displacement problem caused by the large mass values of the virtual tool and can provide stable force/torque display. The force/torque magnitude is saturated to the maximum force/torque values of the haptic device automatically. The implemented algorithm is tested on the simple and complex standard benchmarks. The experimental results confirm that the proposed adaptive 6-DOF haptic rendering algorithm displays good stability and accuracy for haptic rendering of dynamic virtual objects with mass values.     

Sensation-preserving haptic rendering

Most human-computer interactive systems focus primarily on the graphical rendering of visual information and, to a lesser extent, on the display of auditory information. Haptic interfaces have the potential to increase the quality of human-computer interaction by accommodating the sense of touch. They provide an attractive augmentation to visual display and enhance the level of understanding of complex data sets. A haptic rendering system generates contact or restoring forces to prevent penetration into the virtual objects and create a sense of touch. The system computes contact forces by first detecting if a collision or penetration has occurred. Then, the system determines the (projected) contact points on the model surface. Finally, it computes restoring forces based on the amount of penetration. Researchers have recently investigated the problem of rendering the contact forces and torques between 3D virtual objects. This problem is known as six-degrees-of-freedom (6-DOF) haptic rendering, as the computed output includes both 3-DOF forces and 3-DOF torques. This article presents an overview of our work in this area. We suggest different approximation methods based on the principle of preserving the dominant perceptual factors in haptic exploration.     

Function-based approach to mixed haptic effects rendering

Commonly, surface and solid haptic effects are defined in such a way that they hardly can be rendered together. We propose a method for defining mixed haptic effects including surface, solid, and force fields. These haptic effects can be applied to virtual scenes containing various objects, including polygon meshes, point clouds, impostors, and layered textures, voxel models as well as function-based shapes. Accordingly, we propose a way how to identify location of the haptic tool in such virtual scenes as well as consistently and seamlessly determine haptic effects when the haptic tool moves in the scenes with objects having different sizes, locations, and mutual penetrations. To provide for an efficient and flexible rendering of haptic effects, we propose to concurrently use explicit, implicit and parametric functions, and algorithmic procedures.     

Five-axis pencil-cut planning and virtual prototyping with 5-DOF haptic interface

In this paper, techniques of 5-axis pencil-cut machining planning with a 5-DOF (degree of freedom) output haptic interface are presented. Detailed techniques of haptic rendering and tool interference avoidance are discussed for haptic-aided 5-axis pencil-cut tool path generation. Five-axis tool path planning has attracted great attention in CAD/CAM and NC machining. For efficient machining of complex surfaces, pencil-cut uses relatively smaller tools to remove the remaining material at corners or highly curved regions that are inaccessible with larger tools. As a critical problem for 5-axis pencil-cut tool path planning, the tasks of tool orientation determination and tool collision avoidance are achieved with a developed 5-DOF haptic interface. A Two-phase rendering approach is proposed for haptic rendering and force-torque feedback calculation with haptic interface. A Dexel-based volume modeling method is developed for global tool interference avoidance with surrounding components in a 5-axis machining environment. Hardware and software implementation of the haptic pencil-cut system with practical examples are also presented in this paper. The presented technique can be used for CAD/CAM, 5-axis machining planning and virtual prototyping.     

用于实时柔性触觉再现的平行菱形链连接模型

精度高且实时性好的柔性触觉变形模型是实现触觉再现系统的关键。提出了一种新的基于物理意义的平行菱形链连接触觉变形模型,系统中各个链结构单元相对位移的叠加对外等效为物体表面的变形,与之相连的弹簧弹性力的合力等效为物体表面的接触力。使用Delta 6-DOF手控器,建立了触觉再现实验系统,对柔性体的接触变形和实时虚拟触觉反馈进行仿真, 实验结果表明所提出的模型不仅计算简单,而且能够保证触觉接触力和形变计算具有较高精度,满足虚拟现实系统对精细作业和实时性的要求。     

Effects of device obtrusion and tool-hand misalignment on user performance and stiffness perception in visuo-haptic mixed reality

The Visuo-Haptic Mixed Reality (VHMR) is a branch of the Mixed Reality (MR) that is acquiring more and more interest in the recent years. Its success is due to the ability of merging visual and tactile perceptions of both virtual and real objects with a collocated approach. Like any emerging technology, the development of the VHMR systems is accompanied by challenges that, in this case, deals with the efforts to enhance the multi-modal human perception with the user-computer interface and interaction devices at the moment available.This paper deals with two of the typical problems related to VHMR systems, that are device obtrusion and tool–hand misalignment, and suggests solutions whose effectiveness has been tested by means of user studies.First, the paper analyzes the obtrusion problem and the benefits that users may gain performing task in a mixed environment with unobstructed haptic feedback, performed by means of a novel technique. Secondly, it investigates the effects of tool–hand misalignment on user perception and verifies the efficacy of a proposed misalignment correction technique by means of a comparative user test.Experimental results show that users would benefit from using the proposed unobstructed visuo-haptic approach and the misalignment compensation technique. These enhancements demonstrate the efficacy of the proposed solutions and at the same time get stronger the awareness that obtrusion and misalignment problems are fundamental issues to take into account for producing a realistic perception of a visuo-haptic mixed environment.     

速度驱动的复杂场景多层级力觉交互算法

触/力觉交互技术应用环境的复杂化,对复杂触/力觉场景的研究提出了新的挑战.文中以虚拟现实牙科手术训练系统为背景,研究基于速度驱动的复杂场景多层级力觉交互算法.文中采用CATIA对下牙列大量数据进行网格简化,建立了下牙列场景的层次细节(Levels Of Detail,LOD)模型;基于人类触觉感知的精度随交互速度的变化规律,设计了速度驱动的LOD模型触发机制;提出了虚拟工具化身SCP(Surface Contact Point)层级映射算法,保证了力觉交互设备的稳定性,并发现了映射约束线段的长度是保证力觉逼真性及实时性协调的关键变量;最后,设计了针对一般儿何体和复杂曲面的实验,量化评价文中算法的逼真性及实时性,证明了将人手运动速度作为场景模型复杂度切换驱动条件的有效性.     

A modular haptic rendering algorithm for stable and transparent 6-DOF manipulation

This paper presents a modular algorithm for six-degree-of-freedom (6-DOF) haptic rendering. The algorithm is aimed to provide transparent manipulation of rigid models with a high polygon count. On the one hand, enabling a stable display is simplified by exploiting the concept of virtual coupling and employing passive implicit integration methods for the simulation of the virtual tool. On the other hand, transparency is enhanced by maximizing the update rate of the simulation of the virtual tool, and thereby the coupling impedance, and allowing for stable simulation with small mass values. The combination of a linearized contact model that frees the simulation from the computational bottleneck of collision detection, with penalty-based collision response well suited for fixed time-stepping, guarantees that the motion of the virtual tool is simulated at the same high rate as the synthesis of feedback force and torque. Moreover, sensation-preserving multiresolution collision detection ensures a fast update of the linearized contact model in complex contact scenarios, and a novel contact clustering technique alleviates possible instability problems induced by penalty-based collision response.     

Touch-enabled haptic modeling of deformable multi-resolution surfaces

Currently, interactive data exploration in virtual environments is mainly focused on vision-based and non-contact sensory channels such as visual/auditory displays. The lack of tactile sensation in virtual environments removes an important source of information to be delivered to the users. In this paper, we propose the touch-enabled haptic modeling of deformable multi-resolution surfaces in real time. The 6-DOF haptic manipulation is based on a dynamic model of Loop surfaces, where the dynamic parameters are computed easily without subdividing the control mesh recursively. A local deforming scheme is developed to approximate the solution of the dynamics equations, thus the order of the linear equations is reduced greatly. During each of the haptic interaction loop, the contact point is traced and reflected to the rendering of updated graphics and haptics. The sense of touch against the deforming surface is calculated according to the surface properties and the damping-spring force profile. Our haptic system supports the dynamic modeling of deformable Loop surfaces intuitively through the touch-enabled interactive manipulation.