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.     

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.     

6DoF haptic rendering using distance maps over implicit representations

This paper presents a haptic rendering scheme based on distance maps over implicit surfaces. Using the successful concept of support planes and mappings, a support plane mapping formulation is used so as to generate a convex representation and efficiently perform collision detection. The proposed scheme enables, under specific assumptions, the analytical reconstruction of the rigid 3D object’s surface, using the equations of the support planes and their respective distance map. As a direct consequence, the problem of calculating the force feedback can be analytically solved using only information about the 3D object’s spatial transformation and position of the haptic interaction point. Moreover, several haptic effects are derived by the proposed mesh-free haptic rendering formulation. Experimental evaluation and computational complexity analysis demonstrates that the proposed approach can reduce significantly the computational cost when compared to existing methods.     

Haptic interaction with objects in a picture based on pose estimation

In pictures, every object is displayed in 2D space. Seeing the 2D image, people can perceptually reconstruct and understand information regarding the scene. To enable users to haptically interact with an object that appears in the image, the present study proposes a geometry-based haptic rendering method. More specifically, our approach is intended to estimate haptic information from the object’s structure contained in an image while preserving the two-dimensional visual information. Of the many types of objects that can be seen in everyday pictures, this paper mainly deals with polyhedron figures or objects composed of rectangular faces, some of which might be shown in a slanted configuration in the picture. To obtain the geometric layout of the object being viewed from the image plane, we first estimate homographic information that describes a mapping from the object coordinate to the target image coordinate. Then, we transform the surface normals of the object face using the extrinsic part of homography that locates the face of the object we are viewing. Because the transformed normals are utilized for calculating the force in the image space, we call this process normal vector perturbation in the 2D image space. To physically represent the estimated normal vector without distorting the visual information, we employed a lateral haptic rendering scheme in that it fits with our interaction styles on 2D images. The active force value at a given position on the slanted faces is calculated during the interaction phase. To evaluate our approach, we conducted an experiment with different stimulus conditions, in which it was found that participants could reliably estimate the geometric layout that appears in the picture. We conclude with explorations of applications and a discussion of future work.     

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．     

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).     

High-fidelity passive force-reflecting virtual environments

Passivity theory is applied to the creation of synthetic, complex multidimensional haptic environments. It can be shown that under appropriate conditions, sufficiently high rendering rates can guarantee the passivity of a simulation produced by a haptic device coupled to a discrete-time realization of a nominally passive environment. The creation of a passive, globally defined, virtual environment is either analytically complex or computationally costly. A method is described whereby a passive environment is created from transitions between locally defined force models that encode static conservative force fields. This is applied to the haptic rendering of tool contact with deformable bodies, in which sparse force-deflection responses are used to define local models. Passivity, continuity, and fidelity are provided by response-function interpolation rather than by interpolation of forces, as in previous methods. The work also includes an illustrative example.     

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.     

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.     

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.     

面向磁悬浮视触觉交互的多速率系统框架

非接触式磁悬浮视触觉交互克服了机械式交互的固有摩擦,具有广阔应用前景,但存在交互过程中虚拟工具穿透物体、图形渲染与触觉渲染速率不一致等问题.针对上述问题,提出面向磁悬浮视触觉交互的多速率系统框架,通过扩展三自由度(3-DOF)单射线触觉渲染方法,利用多射线对虚拟工具进行建模,避免工具穿透,实现六自由度(6-DOF)触觉...     

Layered rhombus-chain-connected model for real-time haptic rendering

The modeling and simulation of deformable objects is a challenging topic in the field of haptic rendering between human and virtual environment. In this paper, a novel and efficient layered rhombus-chain-connected haptic deformation model based on physics is proposed for an excellent haptic rendering. During the modeling, the accumulation of relative displacements in each chain structure unit in each layer is equal to the deformation on the virtual object surface, and the resultant force of corresponding springs is equivalent to the external force. The layered rhombus-chain-connected model is convenient and fast to calculate, and can satisfy real-time requirement due to its simplicity. Experimental study in both homogenous and non-homogenous virtual human liver and lungs based on the proposed model are conducted, and the results demonstrate that our model provides stable and realistic haptic feeling in real time. Meanwhile, the display result is vivid.     

A six degree-of-freedom god-object method for haptic display of rigid bodies with surface properties

This paper describes a generalization of the god-object method for haptic interaction between rigid bodies. Our approach separates the computation of the motion of the six degree-of-freedom god-object from the computation of the force applied to the user. The motion of the god-object is computed using continuous collision detection and constraint-based quasi-statics, which enables high-quality haptic interaction between contacting rigid bodies. The force applied to the user is computed using a novel constraint-based quasi-static approach, which allows us to suppress force artifacts typically found in previous methods. The constraint-based force applied to the user, which handles any number of simultaneous contact points, is computed within a few microseconds, while the update of the configuration of the rigid god-object is performed within a few milliseconds for rigid bodies containing up to tens of thousands of triangles. Our approach has been successfully tested on complex benchmarks. Our results show that the separation into asynchronous processes allows us to satisfy the different update rates required by the haptic and visual displays. Force shading and textures can be added and enlarge the range of haptic perception of a virtual environment. This paper is an extension of M. Ortega et al., [2006]     

Six degree-of-freedom haptic rendering using spatialized normal cone search

This paper describes a haptic rendering algorithm for arbitrary polygonal models using a six degree-of-freedom haptic interface. The algorithm supports activities such as virtual prototyping of complex polygonal models and adding haptic interaction to virtual environments. The underlying collision system computes local extrema in distance between the model controlled by the haptic device and the rest of the scene. The haptic rendering computes forces and torques on the moving model based on these local extrema. The system is demonstrated on models with tens of thousands of triangles and developed in an accessibility application for finding collision-free paths.     

Adaptive haptic rendering for time‐varying haptic and video frame rates in multi‐modal interactions

In multi‐modal interactions including haptics, problems such as input sensor noise, temporal mismatch between graphics and haptics, and non‐constant refresh rates may cause non‐smooth force/torque display. This paper proposes temporal smoothing technique for haptic interaction using a sensing glove in multi‐modal applications. The proposed technique employs two processes: (1) a noise reduction method is applied to reduce jitter noise at the sensors in the sensing glove and (2) an adaptive force extrapolation is applied for time‐varying haptic and video frame rates. To demonstrate the performance of the proposed method, we developed a test platform to assess a simple box model and relatively complex models such as gamephone, portable media player (PMP). It was subsequently demonstrated that the proposed method can support smooth haptic interactions in multi‐modal applications where a haptic device and a sensing glove are used. Copyright © 2009 John Wiley & Sons, Ltd.     

Biological cell injection visual and haptic interface

This paper presents a new three-dimensional (3-D) biomicromanipulation system for biological objects such as embryos, cells or oocytes. As the cell is very small, kept in liquid and observed through a microscope, 2-D visual feedback makes accurate manipulation in the 3-D world difficult. To improve the manipulation work, we proposed an intelligent human–machine interface. The 3-D visual information is provided to the operator through a 3-D reconstruction method using vision-based tracking deformations of the cell embryo. In order to perform stable microinjection tasks, the operator needs force feedback and haptic assistance during penetration of the cell envelop — the chorion. Thus, realistic haptic rendering techniques have been implemented to validate stable insertion of a micropipette in a living cell. The proposed human–machine user's interface allows real-time realistic visual and haptic control strategies for constrained motion in image coordinates, virtual haptic rendering to constrain the path of insertion and removal in the 3-D scene or to avoid cell destruction by adequately controlling position, velocity and force parameters. Experiments showed that the virtualized reality interface acts as a tool for total guidance and assistance during microinjection tasks.     

Real-time haptic interaction with RGBD video streams

Video interaction is a common way of communication in cyberspace. It can become more immersive by incorporating haptic modality. Using commonly available depth sensing controllers like Microsoft Kinect, information about the depth of a scene can be captured in real-time together with the video. In this paper, we present a method for real-time haptic interaction with videos containing depth data. Forces are computed based on the depth information. Spatial and temporal filtering of the depth stream is used to provide stability of force feedback delivered to the haptic device. Fast collision detection ensures the proposed approach to be used in real-time. We present an analysis of various factors that affect algorithm performance. The usefulness of the approach is illustrated by highlighting possible application scenarios.     

Haptic rendering for dental training system

Immersion and interaction are two key features of virtual reality systems, which are especially important for medical applications. Based on the requirement of motor skill training in dental surgery, haptic rendering method based on triangle model is investigated in this paper. Multi-rate haptic rendering architecture is proposed to solve the contradiction between fidelity and efficiency requirements. Realtime collision detection algorithm based on spatial partition and time coherence is utilized to enable fast contact determination. Proxy-based collision response algorithm is proposed to compute surface contact point. Cutting force model based on piecewise contact transition model is proposed for dental drilling simulation during tooth preparation. Velocity-driven levels of detail haptic rendering algorithm is proposed to maintain high update rate for complex scenes with a large number of triangles. Hapticvisual collocated dental training prototype is established using half-mirror solution. Typical dental operations have been realized including dental caries exploration, detection of boundary within dental cross-section plane, and dental drilling during tooth preparation. The haptic rendering method is a fundamental technology to improve immersion and interaction of virtual reality training systems, which is useful not only in dental training, but also in other surgical training systems. Supported by National Natural Science Foundation of China (Grant Nos. 60605027, 50575011), National High-Tech Research & Development Program of China (Grant No. 2007AA01Z310)     

Real-time area-based haptic rendering and the augmented tactile display device for a palpation simulator

Although people usually contact a surface with some area rather than a point, most haptic devices allow a user to interact with a virtual object at one point at a time and likewise most haptic rendering algorithms deal with such situations only. In a palpation procedure, medical doctors push and rub the organ's surface, and are provided the sensation of distributed pressure and contact force (reflecting force) for discerning doubtable areas of the organ. In this paper, we suggest real-time area-based haptic rendering to describe distributed pressure and contact force simultaneously, and present a haptic interface system to generate surface properties in accordance with the haptic rendering algorithm. We represent the haptic model using the shape-retaining chain link (S-chain) framework for a fast and stable computation of the contact force and distributed pressure from a volumetric virtual object. In addition, we developed a compact pin-array-type tactile display unit and attached it to the PHANToM^TM haptic device to complement each other. For the evaluation, experiments were conducted with non-homogenous volumetric cubic objects consisting of approximately 500 000 volume elements. The experimental results show that compared to the point contact, the area contact provides the user with more precise perception of the shape and softness of the object's composition, and that our proposed system satisfies the real-time and realism constraints to be useful for a virtual reality application.     

Priority-based haptic event filtering for transmission and error control in networked virtual environments

A data filtering scheme is proposed for transmission and error control of haptic events in haptic-based network virtual environments; this scheme is called as priority-based haptic event filtering. Because a high update rate of approximately 1 kHz is required for haptic rendering, sophisticated transmission rate control and reduction schemes are necessary for the haptic events. Although existing schemes can reduce the transmission rate without any perception impairment, they are very sensitive to packet losses. In this paper, we prioritize the haptic events according to the delay and loss effects. Utilizing the proposed haptic event prioritization, the proposed filtering scheme adapts the transmission rate and updates the predicted loss rate according to the current network state. Our simulation and experiment results confirm that the proposed scheme can effectively select important haptic events and guarantee an improved haptic interaction quality over a bandwidth-limited lossy network than existing transmission schemes tailored for networked haptics.