Haptics-based dynamic implicit solid modeling

We systematically present a novel, interactive solid modeling framework, haptics-based dynamic implicit solid modeling, which is founded upon volumetric implicit functions and powerful physics-based modeling. In particular, we augment our modeling framework with a haptic mechanism in order to take advantage of additional realism associated with a 3D haptic interface. Our dynamic implicit solids are semialgebraic sets of volumetric implicit functions and are governed by the principles of dynamics, hence responding to sculpting forces in a natural and predictable manner. In order to directly manipulate existing volumetric data sets as well as point clouds, we develop a hierarchical fitting algorithm to reconstruct and represent discrete data sets using our continuous implicit functions, which permit users to further design and edit those existing 3D models in real-time using a large variety of haptic and geometric toolkits, and visualize their interactive deformation at arbitrary resolution. The additional geometric and physical constraints afford more sophisticated control of the dynamic implicit solids. The versatility of our dynamic implicit modeling enables the user to easily modify both the geometry and the topology of modeled objects, while the inherent physical properties can offer an intuitive haptic interface for direct manipulation with force feedback.     

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.     

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。     

Fitted BVH for Fast Raytracing of Metaballs

Raytracing metaballs is a problem that has numerous applications in the rendering of dynamic soft objects such as fluids. However, current techniques are either limited in the visual effects that they can render or their performance drops as the number of metaballs and their density increase. We present a new acceleration structure based on BVH and kd‐tree for efficient raytracing of a large number of metaballs. This structure is built from an adapted SAH using a fast greedy algorithm and allows the visualization of several hundreds of thousands metaballs at interactive‐to‐real‐time framerates. Our method can handle arbitrary rays to simulate any complex secondary effects such as reflections or soft shadows, and is robust with respect to the density of metaballs. We achieve this performance thanks to a balanced CPU‐GPU (using CUDA) implementation of the animation, structure creation, and rendering.     

虚拟体空间中的触觉雕刻

目前，在虚拟环境中大多数的信息获取是通过视觉、听觉等非接触感觉获得的。然而缺乏触觉反馈的信息减少了很大一部分的信息源。在看和听之外，能够触摸、感觉和操纵物体，在很大程度上提高了虚拟环境的真实性。该文研究了触觉绘制的基本模型，提出了采用虚平面作为中介实现体数据的实时触觉绘制。并在此基础上探讨了体的局部变形及结合触觉反馈模型，实现了具有触觉反馈的虚拟雕刻交互系统。该系统可应用于融化、燃烧、印记、构造和着色实时交互操作。     

Predictive haptic guidance: intelligent user assistance for the control of dynamic tasks

Intelligent systems are increasingly able to offer real-time information relevant to a user's manual control of an interactive system, such as dynamic system control space constraints for animation control and driving. However, it is difficult to present this information in a usable manner and other approaches which have employed haptic cues for manual control in "slow" systems often lead to instabilities in highly dynamic tasks. We present a predictive haptic guidance method based on a look-ahead algorithm, along with a user evaluation which compares it with other approaches (no guidance and a standard potential-field method) in a 1-DoF steered path-following scenario. Look-ahead guidance outperformed the other methods in both quantitative performance and subjective preference across a range of path complexity and visibility and a force analysis demonstrated that it applied smaller and fewer forces to users. These results (which appear to derive from the predictive guidance's supporting users in taking earlier and more subtle corrective action) suggest the potential of predictive methods in aiding manual control of dynamic interactive tasks where intelligent support is available.     

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.     

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.     

基于广义元球的一般约束变形

在计算机动画和形状设计中，变形是一个非常重要的工具.基于广义元球所具有的特殊势函数分布，提出了一个新的包含点、线、面和体约束的一般变形模型.用户定义一系列约束、每个约束的影响半径和偏移量，变形模型根据每个约束和其影响半径产生该约束的广义元球.广义元球确定了一个以约束点集为中心的势函数，该势函数在约束点集处为1，在影响半径处渐变为0.模型直接对整个空间进行变形，而与物体的表示无关，并且变形可由偏移量和广义元球的参数来细微调整.实验表明，该一般约束变形模型不仅有效，而且使传统方法难以做到的线、面、体约束变形成     

Modelling and design of an augmented reality differential drive mobility aid in an enabled environment

In this paper the authors discuss the modelling and design of an augmented reality platform for disabled wheeled mobility studies. This design consists of a virtual environment with two degrees of freedom motion platform and integrated ground contact force feedback. Differential drive mobility users continue to be in touch with reality on their own mobility aid while interacting with virtual objects. The major domain related to the differential drive mobility of the disabled members of society which coincides with the use of manual wheelchairs, electric wheelchairs and mobility scooters. In order to account for environmental and dynamic effects, the wheeled mobility user needs to map the intended trajectory into the virtual world. Motion and inertia force feedback produced on the augmented simulator give the users a haptic sensory stimulus input regarding spatial movement and ground contact forces. The main objective is to model and design an augmented reality platform with real world kinematic and dynamic properties to place a wheeled mobility user closer to real world encounters. The use of the designed augmented reality platform will be beneficial to disabled wheeled mobility users in need of occupational therapist training and evaluation.     

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.     

Retargeting 3D Objects and Scenes with a General Framework

In this paper, we introduce an interactive method suitable for retargeting both 3D objects and scenes. Initially, the input object or scene is decomposed into a collection of constituent components enclosed by corresponding control bounding volumes which capture the intra‐structures of the object or semantic grouping of objects in the 3D scene. The overall retargeting is accomplished through a constrained optimization by manipulating the control bounding volumes. Without inferring the intricate dependencies between the components, we define a minimal set of constraints that maintain the spatial arrangement and connectivity between the components to regularize the valid retargeting results. The default retargeting behavior can then be easily altered by additional semantic constraints imposed by users. This strategy makes the proposed method highly flexible to process a wide variety of 3D objects and scenes under an unified framework. In addition, the proposed method achieved more general structure‐preserving pattern synthesis in both object and scene levels. We demonstrate the effectiveness of our method by applying it to several complicated 3D objects and scenes.     

The moderating role of sensation seeking tendency in robotic haptic interfaces

This study examined the interaction effects between haptic force feedback and users’ sensation seeking tendency (i.e. need for sensations) on users’ feelings of presence (i.e. the state in which users experience virtual objects and virtual environments as if they were actual) in robotic haptic interfaces. Users with low sensation seeking tendency felt stronger physical presence and spatial presence in response to force feedback haptic stimuli (versus no force feedback), whereas users with high sensation seeking tendency did not show any difference between the two conditions, thus confirming the moderating role of the users’ sensation seeking tendency in the robotic haptic interface. Theoretical implications for human–computer interaction (HCI) research and managerial implications for the interactive media market are discussed.     

Efficient analysis of pattern-based constraint specifications

Precision and consistency are important prerequisites for class models to conform to their intended domain semantics. Precision can be achieved by augmenting models with design constraints and consistency can be achieved by avoiding contradictory constraints. However, there are different views of what constitutes a contradiction for design constraints. Moreover, state-of-the-art analysis approaches for proving constrained models consistent either scale poorly or require the use of interactive theorem proving. In this paper, we present a heuristic approach for efficiently analyzing constraint specifications built from constraint patterns. This analysis is based on precise notions of consistency for constrained class models and exploits the semantic properties of constraint patterns, thereby enabling syntax-based consistency checking in polynomial-time. We introduce a consistency checker implementing these ideas and we report on case studies in applying our approach to analyze industrial-scale models. These studies show that pattern-based constraint development supports the creation of concise specifications and provides immediate feedback on model consistency.     

Robust adaptive control for a class of semi‐strict feedback systems with state and input constraints

This paper proposes a dynamic surface control (DSC)–based robust adaptive control scheme for a class of semi‐strict feedback systems with full‐state and input constraints. In the control scheme, a constraint transformation method is employed to prevent the transgression of the full‐state constraints. Specifically, the state constraints are firstly represented as the surface error constraints, then, an error transformation is introduced to convert the constrained surface errors into new equivalent variables without constraints. By ensuring the boundedness of the transformed variables, the violation of the state constraints can be prevented. Moreover, in order to obtain magnitude limited virtual control signal for the recursive design, the saturations are incorporated into the control law. The auxiliary design systems are constructed to analyze the effects of the introduced saturations and the input constraints. Rigorous theoretical analysis demonstrates that the proposed control law can guarantee all the closed‐loop signals are uniformly ultimately bounded, the tracking error converges to a small neighborhood of origin, and the full‐state constraints are not violated. Compared with the existing results, the key advantages of the proposed control scheme include: (i) the utilization of the constraint transformation can handle both time‐varying symmetric and asymmetric state constraints and static ones in a unified framework; (ii) the incorporation of the saturations permits the removal of a feasibility analysis step and avoids solving the constrained optimization problem; and (iii) the “explosion of complexity” in traditional backstepping design is avoided by using the DSC technique. Simulations are finally given to confirm the effectiveness of the proposed approach.     

Haptic sculpting of multi-resolution B-spline surfaces with shaped tools

In this paper, we first propose an implicit surface to B-spline surface haptic interface, which provides both force and torque feedback. We then present a new haptic sculpting system for B-spline surfaces with shaped tools of implicit surface. In the physical world, people touch or sculpt with their fingers or tools, instead of just manipulating points. Shaped virtual sculpting tools help users to relate the virtual modeling process to physical-world experience. Various novel haptic sculpting operations are developed to make the sculpting of B-spline surfaces more intuitive. Wavelet-based multi-resolution tools are provided to let modelers adjust the resolution of sculpture surfaces and thus the scale of deformation can be easily controlled. Moreover, sweep editing and 3D texture have been implemented by taking advantage of both the wavelet technique and haptic sculpting tools.     

A virtual environment simulator for mechanical system dynamics with online interactive control

Virtual prototyping is an effective tool in the development of mechanical product. Physically accurate simulation of multi-body mechanical system enables designers to investigate, explore, and experience the performance and behavior of an evolving product and thus reduce the number of physical prototypes needed. For the sake of better support for designers to manipulate the simulation, we have developed a dynamic simulation package of mechanical system, which provides an interactive control during the simulation process. The package incorporates physical behaviors and dynamic interactions by dynamics based modeling approach in multi-body mechanical system. In the package, user’s actions (e.g., loading a model, picking and dragging objects, steering objects during simulation process, etc.) are based on an ATN task management, and a multi-modal interface is provided which supports 2D desktop devices and 3D VR devices. The main contribution of the simulator is providing supports that allow users’ interactive manipulation in the simulation loop. During the simulation process, users can modify the constraints between components, apply force/torque to interested components and change the parameters of forces/torques. The simulator automatically updates the dynamic model of the mechanical system in real time, and then continuously simulates the behavior of the model under the current condition in the loop. An example of dynamic simulation of a vehicle is implemented and the simulation result is compared to that of ADAMS to verify the correctness and accuracy of the simulator. With the real-time interaction, solution and visualization of simulation model, the package affords better support for designers to participate in the simulation interactively and effectively.     

Checking consistency in multimedia synchronization constraints

Constraint-based design is often used to correctly author a multimedia scenario due to its flexibility and efficiency. However, such a system must provide a mechanism with which users can easily manipulate the underlying structures to meet the application requirements. This paper proposes a novel method for analyzing multimedia synchronization constraints based on the constraint graph and classification, which is essential in developing efficient system support tools for constraint-based authoring systems. We specify temporal and spatial relations between multimedia objects, and use a directed graph to represent the constraints among the objects in a multimedia scenario. Moreover, we develop a method for analyzing temporal and spatial synchronization constraints based on graph theory, solving the problems of completeness checking, consistency checking, constraints relaxation and automatic spatio-temporal layout generation in a unified theoretical framework. We also discuss the effects of user interactive authoring. Compared with other methods, the proposed approach is simpler, more efficient, and easier to implement.     

Phantom-based haptic interaction with virtual objects

In 1993, haptic interaction with computers took a significant step forward with the development of the Phantom haptic interface. This simple device has spawned a new field analogous to computer graphics-computer haptics-defined as the discipline concerned with the techniques and processes associated with generating and displaying synthesized haptic stimuli to the human user. Inspired by the authors' previous work in interpreting robot touch sensor information and study of human touch perception, the Phantom interface permits users to feel the forces of interaction they would encounter while touching objects with the end of a stylus or the tip of their finger. The resulting sensations prove startling, and many first-time users are quite surprised at the compelling sense of physical presence they encounter when touching virtual objects. To appreciate why the Phantom system succeeded where others failed, you need to understand the nature and functioning of the human haptic system.     

Networked multiplayer cooperative interaction using decoupled motion control method in a shared virtual environment with haptic,visual and movement feedback

This paper focuses on multiplayer cooperative interaction in a shared haptic environment based on a local area network. Decoupled motion control, which allows one user to manipulate a haptic interface to control only one‐dimensional movement of an avatar, is presented as a new type haptic‐based cooperation among multiple users. Users respectively move an avatar along one coordinate axis so that the motion of the avatar is the synthesis of movements along all axes. It is different from previous haptic cooperation where all users can apply forces on an avatar along any direction to move it, the motion of which completely depends on the resultant force. A novel concept of movement feedback is put forward where one user can sense other users’ hand motions through his or her own haptic interface. The concept can also be explained wherein one person who is required to move a virtual object along only one axis can also feel the motions of the virtual object along other axes. Movement feedback, which is a feeling of motion, differs from force feedback, such as gravity, collision force and resistance. A spring‐damper force model is proposed for the computation of motion feedback to implement movement transmission among users through haptic devices. Experimental results validate that movement feedback is beneficial for performance enhancement of such kind of haptic‐based cooperation, and the effect of movement feedback in performance improvement is also evaluated by all subjects.Copyright © 2012 John Wiley & Sons, Ltd.