Passive dynamic turning in 3D biped locomotion: an extension to passive dynamic walking

Passive dynamic walking usually refers to a kind of walking where a biped walker is able to walk downhill, without any actuation or control, just due to the gravity. Although most of works done in this regard have concentrated on passive walking along a straight line, in this paper we extend this concept to a more general case of locomotion, i.e. turning or walking along curved path. We call the novel extension passive turning, and categorize it to two types of finite and infinite. We showed that the finite type is still applicable on a typical downhill or ramp, while the infinite type is only practical on a specific surface profile that we call it helical ramp. Furthermore, several stability and parameter analysis are also conducted to evaluate more aspects of this notion. We highlighted that surprisingly, the passive straight walking is actually a special case of passive turning, just with infinite radius of turn and less asymptotical stability. It should be noted that the present study is performed using a model of an arc-foot three-dimensional (3D) compass gait walker.     

A Java extension with support for dimensions

We present an extension to the Java language with support for physical dimensions and units of measurement. This should reduce programming errors in scientific and technological areas. We discuss various aspects of dimensions and units, and then design principles for support in programming languages. An overview of earlier work shows that some language extensions focused on units, whereas we argue that dimensions are a better starting point; units can then simply be treated as constants. Then we present the Java extension, and show how to define and use dimensions and units. The communication between the program and the outer world gets special attention. The programmer can still make dimensional errors there, but we claim the risk is reduced. It has been simple to build support for this extension into an existing Java compiler. We outline the applied technique. Copyright © 1999 John Wiley & Sons, Ltd.     

A novel compound biped locomotion algorithm for humanoid robots to realize biped walking

In this paper, a compound biped locomotion algorithm for a humanoid robot under development is presented. This paper is organized in two main parts. In the first part, it mainly focuses on the structural design for the humanoid. In the second part, the compound biped locomotion algorithm is presented based on the reference motion and reference Zero Moment Point （ZMP）. This novel algorithm includes calculation of the upper body motion and trajectory of the Center of Gravity （COG） of the robot. First, disturbances from the environment are eliminated by the compensational movement of the upper body; then based on the error between a reference ZMP and the real ZMP as well as the relation between ZMP and CoG, the CoG error is calculated, thus leading to the CoG trajectory. Then, the motion of the robot converges to its reference motion, generating stable biped walking. Because the calculation of upper body motion and trajectory of CoG both depend on the reference motion, they can work in parallel, thus providing double insurances against the robot＇s collapse. Finally, the algorithm is validated by different kinds of simulation experiments.     

Toward the enhancement of biped locomotion and control techniques: walking pattern classification

A new walking pattern classification method is proposed for a 5-link 7-DOF biped robot walking on an uneven floor. This method extracts the patterns in the current floor position of the stance foot and the transitioning floor conditions of the swing foot during locomotion. When a global path composed of stairs, obstacles, etc., and certain walking parameters, such as the speed of walking and the total walking time, are put into the system, the guidance controller unit determines the trajectory of the footsteps in terms of step patterns by using a genetic algorithm-based optimization technique while ensuring the biped’s stability criterion. A demonstration of the biped with different pattern classes was realized by a dynamic simulator.     

代价与样本相关的简约核支持向量机

针对机器学习领域中误分类代价与样本相关的情况,提出一种以最小化总代价为目标的样本相关代价敏感的简约核支持向量机sd2sSVM。首先,在GSVM框架下,将优化目标转换为无约束数学规划问题,再引入分段多项式平滑函数逼近正号函数,使用Newton-YUAN方法求无约束问题的唯一最优解,最后引入简约核提高解非线性问题的效率。实验结果表明,与传统的样本相关代价敏感支持向量机相比,sd2sSVM的分类精度、误分类代价相当,但训练时间、预测时间则更短。另外,讨论了参数C对sd2sSVM分类性能的影响。     

Image-based virtual exhibit and its extension to 3D

In this paper we introduce an image-based virtual exhibition system especially for clothing product.It can provide a powerful material substitution function,which is very useful for customization clothing-built.A novel color substitution algorithm and two texture morphing methods are designed to ensure realistic substitution result.To extend it to 3D,we need to do the model reconstruction based on photos.Thus we present an improved method for modeling human body.It deforms a generic model with shape details extracted from pictures to generate a new model.Our method begins with model image generation followed by silhouette extraction and segmentation.Then it builds a mapping between pixeis inside every pair of silhouette segments in the model image and in the picture.Our mapping algorithm is based on a slice space representation that conforms to the natural features of human body.     

Terrain evaluation and its application to path planning for walking machines

Motion planning of walking machines normally contains two aspects: gait planning and body trajectory planning. When generating an optimal body trajectory on natural terrain, the leg movement must be taken into account. Due to the large searching space resulting from the combination of leg movement and terrain conditions, it is quite time consuming to produce an optimal result of body trajectory planning. In this paper, an effective method of body trajectory planning is introduced by virtue of a terrain evaluation that links the terrain conditions with machine mobility. Based on the evaluation, a potential field is constructed for graph searching. Best first planning (BFP) is adopted to search the optimal path. The path generated with the proposed method could offer the best opportunity to place the machine feet moving with a certain gait over a rough terrain. The assumptions and shortages associated with the present work are also discussed.     

Applications of computational thermodynamics — the extension from phase equilibrium to phase transformations and other properties

Complex equilibria and phase transformations involving diffusion can now be calculated quickly and efficiently. Detailed examples are given for cases which involve varying degrees of non-equilibrium and therefore time-dependence. Despite very good agreement between such calculations and experimental results, many potential end-users are still not convinced that such techniques could be usefully applied to their own specific problems. Friendly graphic interface versions of calculating software are now generally available, so the authors conclude that the most likely source of the reluctance to use such tools lies in the formulation of relevant questions and the interpretation of the results. Although the potential impact of such tools was foreseen many years ago [M. Hillert, Calculation of phase equilibria, in: Conference on Phase Transformations, 1968], few changes in the relevant teaching curricula have taken into account the availability and power of such techniques.     

Exploiting perceptual limitations and illusions to support walking through virtual environments in confined physical spaces

Head-mounted displays (HMDs) allow users to immerse in a virtual environment (VE) in which the user’s viewpoint can be changed according to the tracked movements in real space. Because the size of the virtual world often differs from the size of the tracked lab space, a straightforward implementation of omni-directional and unlimited walking is not generally possible. In this article we review and discuss a set of techniques that use known perceptual limitations and illusions to support seemingly natural walking through a large virtual environment in a confined lab space. The concept behind these techniques is called redirected walking. With redirected walking, users are guided unnoticeably on a physical path that differs from the path the user perceives in the virtual world by manipulating the transformations from real to virtual movements. For example, virtually rotating the view in the HMD to one side with every step causes the user to unknowingly compensate by walking a circular arc in the opposite direction, while having the illusion of walking on a straight trajectory. We describe a number of perceptual illusions that exploit perceptual limitations of motion detectors to manipulate the user’s perception of the speed and direction of his motion. We describe how gains of locomotor speed, rotation, and curvature can gradually alter the physical trajectory without the users observing any discrepancy, and discuss studies that investigated perceptual thresholds for these manipulations. We discuss the potential of self-motion illusions to shift or widen the applicable ranges for gain manipulations and to compensate for over- or underestimations of speed or travel distance in VEs. Finally, we identify a number of key issues for future research on this topic.     

Acoustic OFDM system and its extension

This paper presents a method of aerial acoustic communication in which data is modulated using OFDM (Orthogonal Frequency Division Multiplexing) and embedded in regular audio material without significantly degrading the quality of the original sound. It replaces the high frequency band of the audio signal with OFDM carriers, each of which is power-controlled according to the spectrum envelope of the original audio signal. The implemented system enables the transmission of short text messages from loudspeakers to mobile handheld devices at a distance of around 3 m. This paper also provides the subjective assessment results and the transmission performances.

改进可拓识别方法及其在突水水源判别中的应用

针对已有可拓识别方法用于矿井突水水源判别时易造成误判的问题,提出了一种改进的可拓识别方法。首先对已有方法中经典域、节域量值范围以及待判物元的量值进行了归一化处理,并优化了最优值的选取,然后提出了新的位值计算方法。实验结果表明,将改进后的可拓识别方法应用到煤矿突水水源判别,提高了待判物元正确归属于某个含水层的程度,从而提高了水源判别的准确率。     

A support vector machine classifier with automatic confidence and its application to gender classification

In this paper, we propose a support vector machine with automatic confidence (SVMAC) for pattern classification. The main contributions of this work to learning machines are twofold. One is that we develop an algorithm for calculating the label confidence value of each training sample. Thus, the label confidence values of all of the training samples can be considered in training support vector machines. The other one is that we propose a method for incorporating the label confidence value of each training sample into learning and derive the corresponding quadratic programming problems. To demonstrate the effectiveness of the proposed SVMACs, a series of experiments are performed on three benchmarking pattern classification problems and a challenging gender classification problem. Experimental results show that the generalization performance of our SVMACs is superior to that of traditional SVMs.     

Adaptive splitbelt treadmill walking of a biped robot using nonlinear oscillators with phase resetting

To investigate the adaptability of a biped robot controlled by nonlinear oscillators with phase resetting based on central pattern generators, we examined the walking behavior of a biped robot on a splitbelt treadmill that has two parallel belts controlled independently. In an experiment, we demonstrated the dynamic interactions among the robot mechanical system, the oscillator control system, and the environment. The robot produced stable walking on the splitbelt treadmill at various belt speeds without changing the control strategy and parameters, despite a large discrepancy between the belt speeds. This is due to modulation of the locomotor rhythm and its phase through the phase resetting mechanism, which induces the relative phase between leg movements to shift from antiphase, and causes the duty factors to be autonomously modulated depending on the speed discrepancy between the belts. Such shifts of the relative phase and modulations of the duty factors are observed during human splitbelt treadmill walking. Clarifying the mechanisms producing such adaptive splitbelt treadmill walking will lead to a better understanding of the phase resetting mechanism in the generation of adaptive locomotion in biological systems and consequently to a guiding principle for designing control systems for legged robots.     

Baker 映射的三维扩展及其在多媒体加密中的应用

对Baker映射进行三维扩展，提出一种基于三维混沌映射的混沌加密方案．与二维映射相比，扩展后的三维Baker映射具有更大的密钥空间、更快的混迭速度和更广的应用范围．这种三维Baker映射与扩散函数相结合，增加了密码强度，起到良好的加密作用．实验结果表明，与传统基于数论的DES加密算法相比，该算法具有更快的速度，更适合于多媒体数据的加密．     

Optimization-based analysis of push recovery during walking motions to support the design of rigid and compliant lower limb exoskeletons

Abstract

Lower limb exoskeletons provide a promising approach to allow disabled people to walk again in the future. Designing such exoskeletons and tuning the required actuators is challenging, since the full dynamics of the combined human-exoskeleton system have to be taken into account. In particular, it is important to not only consider nominal walking motions but also extreme situations such as the recovery from large perturbations. In this paper, we present an approach based on push recovery experiments while walking, multibody system models, and least-squares optimal control to analyze the required torques to be generated by the exoskeleton, assuming that the human provides no torque. We consider seven different trials with varying push locations and push magnitudes applied on the back of the subject. In a first study, we investigate the dependency of these total joint torques on the exoskeleton mass – and compare the torques required for a human without exoskeleton to the ones for the human with two different exoskeleton configurations. In a second study, we investigate how optimally chosen passive spring-damper elements can support the required torques in the exoskeleton joints. It can be shown that the active torques can be reduced significantly in the different joints and cases.     

Ciphertext-policy attribute-based encryption supporting access policy update and its extension with preserved attributes

Attribute-based encryption (ABE) allows one-to-many encryption with static access control. In many occasions, the access control policy must be updated, but the original encryptor might be unavailable to re-encrypt the message, which makes it impractical. Unfortunately, to date the work in ABE does not consider this issue yet, and hence this hinders the adoption of ABE in practice. In this work, we consider how to update access policies in ciphertext-policy attribute-based encryption (CP-ABE) systems efficiently without encrypting each ciphertext with new access policies. We introduce a new notion of CP-ABE supporting access policy update that captures the functionalities of attribute addition and revocation to access policies. We formalize the security requirements for this notion and subsequently construct two provably secure CP-ABE schemes supporting AND-gate access policy with constant-size ciphertext for user decryption. The security of our schemes are proved under the augmented multi-sequences of exponents decisional Diffie–Hellman assumption. We also present a different construction in which certain attributes in an access policy can be preserved by the original encryptor, while other attributes can be revoked efficiently so that the ability of attribute revocation can be appropriately restrained.     

粗SVM方法及其在发动机故障诊断中的应用

支持向量机是一种具有完备统计学习理论基础和出色学习性能的新型机器学习方法,它能够较好地克服过学习和泛化能力低等缺陷.但是在利用支持向量机的分类算法处理实际问题时,该算法的计算速度较慢、处理问题效率较低.文中介绍了一种新的学习算法粗SVM分类方法,就是将粗糙集和支持向量机相结合,利用粗糙集对支持向量机的训练样本进行预处理,通过属性约简方法以减少属性个数,且在属性约简过程中选出几组合适的属性集组成新的属性集,使模型具有一定的抗信息丢失能力,同时充分利用SCM的良好推广性能,从而缩短样本的训练时间,实现快速故障诊断.对航空发动机故障诊断的实验结果表明了该方法的优越性. 型机器学习方法,它能够较好地克服过学习和泛化能力低等缺陷.但是在利用支持向量机的分类算法处理实际问题时,该算法的计算速度较慢、处理问题效率较低.文中介绍了一种新的学习算法粗SVM分类方法,就是将粗糙集和支持向量机相结合,利用粗糙集对支持向量机的训练样本进行预处理,通过属性约简方法以减少属性个数,且在属性约筒过程中选出几组合适的属性集组成新的属性集,使模型具有一定的抗信息丢失能力,同时充分利用SCM的良好推广性能,从而缩短样本的训练时间,实现快速故障诊 .对航空发动机故障诊断的实验结果表明了该方法的优越性. 型机器学习方法     

粗SVM 分类方法及其在污水处理过程中的应用

提出一种基于粗糙集理论和支持向量机理论的粗SVM分类方法，该方法采用粗糙集属性约筒方法以减少属性个数，且在属性约筒过程中选出几组合适的属性集组成新的属性集，使模型具有一定的抗信息丢失能力，同时充分利用SVM的良好推广性能，提高了预测分类精度，对城市污水处理厂运行状态的实验结果表明了该方法的优越性。     

A modified support vector machine and its application to image segmentation

Recently, researchers are focusing more on the study of support vector machine (SVM) due to its useful applications in a number of areas, such as pattern recognition, multimedia, image processing and bioinformatics. One of the main research issues is how to improve the efficiency of the original SVM model, while preventing any deterioration of the classification performance of the model. In this paper, we propose a modified SVM based on the properties of support vectors and a pruning strategy to preserve support vectors, while eliminating redundant training vectors at the same time. The experiments on real images show that (1) our proposed approach can reduce the number of input training vectors, while preserving the support vectors, which leads to a significant reduction in the computational cost while attaining similar levels of accuracy. (2)The approach also works well when applied to image segmentation.