Stable haptic rendering in interactive virtual control laboratory

Stable control of haptic interfaces is one of the most important challenges in haptic simulations, because any instability of a haptic interface can cause it to get far from the realistic sense. In this paper, the control strategies employed for a stable haptic rendering in an interactive virtual control laboratory are presented. In this interactive virtual laboratory, there are different scenarios to teach the control concepts, in which a haptic interface is used in the two cases of force control and position control. In this regard, two control strategies are employed to avoid instability. An energy-compensating controller is utilized to remove energy leakage. Besides, a fuzzy impedance control is used along with the energy-compensating controller for the position control scenarios. The results obtained indicate the proposed approaches practically guarantee the stability of the haptic interface for an educational application in practice.     

Physically accurate haptic rendering with dynamic effects

We focus on the realism/transparency aspect of haptic rendering. We introduce a novel approach that enables physically correct and accurate simulation of contact wrench W/sub c/ for general rigid objects in real time, taking into account not only friction and gravity but also dynamic effects. Our method for contact force and moment simulation builds on the real-time identification of geometrically valid contact states despite digital errors. Our approach applies to general rigid bodies including both polyhedral and nonpolyhedral objects. For nonpolyhedral, curved objects, we build our contact state representation and contact force/moment model directly on the smooth and accurate representation of the object surfaces. Our approach's key idea is to solve for the contact force and moment analytically based on not only the contact configuration, but also the real-time identification of the exact type of the corresponding contact state, the type of instantaneous motion of the held object prior to reaching the contact configuration.     

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.     

A practical and fast rendering algorithm for dynamic scenes using adaptive shadow fields

Recently, a precomputed shadow fields method was proposed for achieving fast rendering of dynamic scenes under environment illumination and local light sources. This method can render shadows fast by precomputing the occlusion information at many sample points arranged on concentric shells around each object and combining multiple precomputed occlusion information rapidly in the rendering step. However, this method uses the same number of sample points on all shells, and cannot achieve real-time rendering due to the rendering computation rely on CPU rather than graphics hardware. In this paper, we propose an algorithm for decreasing the data size of shadow fields by reducing the amount of sample points without degrading the image quality. We reduce the number of sample points adaptively by considering the differences of the occlusion information between adjacent sample points. Additionally, we also achieve fast rendering under low-frequency illuminations by implementing shadow fields on graphics hardware.     

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.     

Stable haptic interaction based on adaptive hierarchical shape matching

Computational Visual Media - In this paper, we present a framework allowing users to interact with geometrically complex 3D deformable objects using (multiple) haptic devices based on an extended...     

Stable iterative adaptive dynamic programming algorithm with approximation errors for discrete-time nonlinear systems

In this paper, a novel iterative adaptive dynamic programming (ADP) algorithm is developed to solve infinite horizon optimal control problems for discrete-time nonlinear systems. When the iterative control law and iterative performance index function in each iteration cannot be accurately obtained, it is shown that the iterative controls can make the performance index function converge to within a finite error bound of the optimal performance index function. Stability properties are presented to show that the system can be stabilized under the iterative control law which makes the present iterative ADP algorithm feasible for implementation both on-line and off-line. Neural networks are used to approximate the iterative performance index function and compute the iterative control policy, respectively, to implement the iterative ADP algorithm. Finally, two simulation examples are given to illustrate the performance of the present method.     

A Novel Six Degrees-of-Freedom Parallel Robot for MEMS Fabrication

This paper introduces a new architecture of a six degrees-of-freedom parallel robot suitable for microelectromechanical systems (MEMS) fabrication. The robot consists of only revolute joints for the passive joints, and linear actuators located at the base for the active ones, both of which are easier to manufacture in MEMS technology. The hybrid kinematic structure contains three single-loop submechanisms connected in parallel to the moving platform. The solutions of the inverse and direct kinematics problems are presented     

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.     

Stable multirate algorithm for robust adaptive control

A new multirate adaptive control algorithm for plants with unmodelled dynamics and bounded disturbances is presented. Different rates are employed for parameter estimation, controller design and controller implemeniation. A modified constant trace least-square algorithm with dead zone and pole placement are used for the algorithm, It is shown that the closed-loop system is globally stable and that set point tracking can be well achieved.     

并行绘制的动态负载平衡算法研究

负载平衡是影响并行绘制效率的关键问题。提出了动态负载平衡算法两阶段映射的模型,给出了负载平衡性能的一种度量方法;还提出了一种最佳的任务调度算法,对该算法的性能进行了分析,得出绘制时间的理论上限值,同时给出了多任务划分的方法。     

网格环境下地形绘制的任务调度算法研究

随着用户不断增多,导致服务器不能满足多用户实时绘制地形的需求.利用地形实时绘制技术,提出了一种在网格环境下的基于地形分块的T-MIN-MIN任务调度算法.该算法根据地形块相互独立和绘制时块中三角形数目按比例分布的特点进行调度,提高了地形块调度的效率.提出的地形块的代价估算计算方法使得地形块能够按照接近实际值参与调度.实验结果表明,网格环境中地形分块的任务调度方法具有较高的效率.     

Fuzzy rule generation for adaptive scheduling in a dynamic manufacturing environment

This paper proposes a fuzzy rule-based system for an adaptive scheduling, which dynamically selects and applies the most suitable strategy according to the current state of the scheduling environment. The adaptive scheduling problem is generally considered as a classification task since the performance of the adaptive scheduling system depends on the effectiveness of the mapping knowledge between system states and the best rules for the states. A rule base for this mapping is built and evolved by the proposed fuzzy dynamic learning classifier based on the training data cumulated by a simulation method. Distributed fuzzy sets approach, which uses multiple fuzzy numbers simultaneously, is adopted to recognize the system states. The developed fuzzy rules may readily be interpreted, adopted and, when necessary, modified by human experts. An application of the proposed method to a job-dispatching problem in a hypothetical flexible manufacturing system (FMS) shows that the method can develop more effective and robust rules than the traditional job-dispatching rules and a neural network approach.     

Learning-based multi-pass adaptive scheduling for a dynamic manufacturing cell environment

Because the essential attributes are uncertain in a dynamic manufacturing cell environment, to select a near-optimal subset of manufacturing attributes to enhance the generalization ability of knowledge bases remains a critical, unresolved issue for classical artificial neural network-based (ANN-based) multi-pass adaptive scheduling (MPAS). To resolve this problem, this study develops a hybrid genetic /artificial neural network (GA/ANN) approach for ANN-based MPAS systems. The hybrid GA/ANN approach is used to evolve an optimal subset of system attributes from a large set of candidate manufacturing system attributes and, simultaneously, to determine configuration and learning parameters of the ANN according to various performance measures. In the GA/ANN-based MPAS approach, for a given feature subset and the corresponding topology and learning parameters of an ANN decoded by a GA, an ANN was applied to evaluate the fitness in the GA process and to generate the MPAS knowledge base used for adaptive scheduling control mechanisms. The results demonstrate that the proposed GA/ANN-based MPAS approach has, according to various performance criteria, a better system performance over a long period of time than those obtained with classical machine learning-based MPAS approaches and the heuristic individual dispatching rules.     

High performance haptic device for force rendering in textile exploration

The HAPTEX system aims to develop a new multi-sensory environment for the immersive exploration of textiles. HAPTEX is based on a multi-layer/multi-thread architecture that optimizes the computational speed and integrates three different types of sensory feedback: vision, tactile and haptic. Such kind of environment is suitable for demanding VR applications such as the online marketing of novel textiles or garments, however it requires the design of a high performance multi-point haptic interface. The present work focuses on the haptic device design and describes how demanding requirements can be met by integrating on a high performance device a force sensor to achieve closed loop control. The methodology for the dimensioning of a motion based explicit force control on the basis of the dynamic parameters will be discussed and the specific implementation for the HAPTEX system presented.     

Synergistic visual/haptic rendering modes for scientific visualization

Our approach uses a visual/haptic interface to display scientific data both graphically and haptically. The haptic interface provides a natural means of interacting with the data through direct tactile sensing and manipulation of the data display. Our experience with this interface suggests that users understand the data more clearly when the haptic component acts as a synergistic companion to the visual display. That is, rather than replace the visual display of data or display disparate data haptically, the haptic component reinforces and clarifies visual information via compatible haptic data rendering.     

ROAM动态地形渲染算法的改进

三维真实感地形的生成一直是计算机图形学领域中的焦点课题,研究了基于层次细节的实时优化自适应网格动态地形渲染算法,采用了基于地形块包围盒的可见性投影剔除技术的实时优化策略,提出了嵌套包围球方法和屏幕空间误差法相结合的优化算法来改进误差判据,以提高地形绘制的快速性,给出了该层次细节模型在地形渲染中的实现方法。实验证明,通过对实时优化自适应网格算法的实现和优化,在保证一定的地形渲染效果的前提下,减少了开销同时提高了实时渲染速度。     

An efficient adaptive dynamic algorithm

An automatic time stepping scheme utilizing a modified Newton approach is discussed for the solution of nonlinear structural problems. Through the application of rather simple logic, the formation of costly stiffness matrices are minimized, while the time steps are maintained at a reasonable level to ensure an efficient analysis. The algorithm is applied to two simple but highly nonlinear transient problems. The results indicate a robust adaptive scheme that should be very cost-effective, especially for large sized problems in which stiffness formation and inversion is particularly costly.     

面向动态环境的视觉惯性SLAM算法

针对传统的同时定位与建图(SLAM)算法在动态环境中会降低自身运动估计的精确性以及系统鲁棒性的问题,提出一种适用于动态环境的视觉惯性SLAM算法——DVI-SLAM(dynamic visual inertial SLAM).根据对极几何约束检测并去掉动态特征,利用更加精确的静态特征进行状态估计;添加视觉信息自适应权重...     

Measurement-based modeling of contact forces and textures for haptic rendering

Haptic texture represents the fine-grained attributes of an object's surface and is related to physical characteristics such as roughness and stiffness. We introduce an interactive and mobile scanning system for the acquisition and synthesis of haptic textures that consists of a visually tracked handheld touch probe. The most novel aspect of our work is an estimation method for the contact stiffness of an object based solely on the acceleration and forces measured during stroking of its surface with the handheld probe. We establish an experimental relationship between the estimated stiffness and the contact stiffness observed during compression. We also measure the height-displacement profile of an object's surface enabling us to generate haptic textures. We show an example of mapping the textures on to a coarse surface mesh obtained with an image-based technique, but the textures may also be combined with coarse surface meshes obtained by manual modeling.