基于终态神经网络的冗余机械臂重复运动规划

为解决冗余机械臂在运动过程中出现的关节角漂移现象,提出了一种终态吸引优化指标,形成冗余机械臂重复运动规划的二次优化方法。采用具有有限值激活函数的终态神经网络来求解,在初值位置偏移目标位置的情形下,实现冗余机械臂有限时间收敛的重复运动规划任务。同时,分别以新型的终态神经网络(TNN)和其加速网络(ATNN)求解运动规划问题,该网络求解方法具有终态吸引特性,能够在有限的时间内得到有效解。相比具有渐近收敛动态特性的神经网络(ANN),终态神经网络方法不仅改变了收敛速度,而且提高了收敛的精度。基于冗余机械臂PUMA560的计算机仿真结果表明了所提方法的有效性和实时性。     

基于二次型规划的平面冗余机械臂的自运动

提出一种基于二次型性能指标的方法,用于规划平面冗余机械臂的自运动轨迹．鉴于实际的机械臂都存在关节物理约束,该自运动规划方案考虑了关节极限和关节速度极限的躲避．提出了基于线性变分不等式的原对偶神经网络,并将其作为所对应的二次型规划方案的实时求解器．仿真结果证实了该基于神经网络的自运动规划方案的有效性．     

有限值终态递归神经网络计算

通常的递归神经网络计算方法采用渐近收敛的网络模型,误差函数渐近收敛于零,理论上需经过无穷长的计算时间才能获得被求解问题的精确解。文中提出了一种终态递归神经网络模型,该网络形式新颖,具有有限时间收敛特性,用于解决时变矩阵计算问题时可使得计算过程快速收敛,且计算精度高。该网络的另一特点是动态方程右端函数值有限,易于实现。首先,分析渐近收敛网络模型在时变计算问题求解方面的缺陷,说明引入终态网络模型的必要性;然后,给出终态网络动态方程,推导出该网络收敛时间的具体表达式。对于时变矩阵逆和广义逆求解,定义一个误差函数,并依据误差函数构造终态递归神经网络进行求解,使计算过程在有限时间内收敛便能得到精确解。在将任意初始位置下的冗余机械臂轨迹规划任务转换为二次规划问题后,利用所提出的神经网络进行计算,得出的关节角轨迹导致末端执行器完成封闭轨迹跟踪,且关节角严格返回初始位置,以实现可重复运动。使用MATLAB/SIMULINK对时变矩阵计算问题和机器人轨迹规划任务分别进行仿真,通过比较分别采用渐近网络模型和终态网络模型时的计算过程与结果可以看出,使用终态网络模型的计算过程收敛快且显著提高了计算精度。对不同时变计算问题的求解体现了所提神经网络的应用背景。     

重复运动速度层和加速度层方案的等效性

探讨冗余机械臂之重复运动规划(Repetitive motion planning, RMP), 对应速度层重复运动规划方案, 提出了加速度层重复运动规划方案, 并进一步发现和探讨了速度层与加速度层RMP方案的等效性关系. 基于神经动力学方法的理论分析和基于PUMA560机械臂的计算机仿真结果均证实了本文所提出的加速度层RMP方案在冗余度解析问题上的有效性, 以及速度层和加速度层RMP方案的等效性.     

Sylvester时变矩阵方程求解的终态神经网络算法

为了更好地提高收敛的速度和精度,提出一种终态神经网络(TNN)及其加速形式(ATNN)的求解方法。该网络求解方法具有终态吸引特性,能够在有限的时间内得到时变矩阵的有效解。相比于具有渐近收敛动态特性的神经网络,该神经网络方法具有有限时间收敛性,不仅能够改变收敛速度,而且能达到较高的收敛精度。将3种不同的神经网络方法用于求解时变Sylvester动态方程;同时,以终态神经网络求解二次优化问题,实现冗余机械臂Katana6M180有限时间收敛的重复运动规划任务。仿真结果验证了终态神经网络方法的有效性。     

物理受限冗余机械臂逆运动学凸优化求解

针对冗余机械臂逆运动学求解结果极有可能超过机械臂物理限制的问题,提出一种基于凸优化的逆运动学求解方法使得逆解结果满足物理约束.首先分析了关节速度与力矩关系,采用机械臂动能及重复运动为优化指标,以关节速度、关节力矩为优化变量.然后将逆运动学求解问题转化为凸优化问题,进一步转化为二次规划问题,充分利用冗余特性,实现逆运动学求解时避免关节位置、关节速度、关节力矩极限.最后利用7自由度冗余机械臂KUKA LBR iiwa进行仿真,求解关节量结果符合物理极限及优化准则.结果表明本文提出的方法适用于物理受限冗余机械臂的逆运动学求解.     

冗余机械臂角偏差消去方案之原理分析

本文利用优化方法及递归神经网络实时求解器消除冗余机器手臂在运动过程中出现的角偏差问题.鉴于机器手臂都存在着关节物理约束,我们的优化方案也因此考虑关节极限和关节速度极限的躲避.更重要的是,本文详细分析了该成功解决关节角偏差问题的二次型性能指标的设计原理.仿真结果证实了该方法的可行性与有效性.     

基于Kinect的类人机械臂关节运动直接示教

针对人机自然交互技术研究中人臂与机械臂的关节映射问题,提出了一种7自由度类人机械臂关节运动直接示教方法.该方法利用Kinect获取笛卡儿空间内人臂特征点的空间位置坐标,研究了一种基于肘部约束的冗余7自由度人臂逆运动学解法,求解得到关节角度数据.为解决由于Kinect对人臂追踪性能限制所造成的机械臂抖动问题,提出了一种滤波方法来平滑处理机械臂的关节运动轨迹.最终,通过搭建基于Motoman类人机器人的实验平台并开展相应实验研究,验证了所提方案的可行性与有效性.     

基于伪逆的导轨机械臂关节速度纠偏运动规划方案

针对导轨机械臂在任务执行过程中出现的关节速度偏离期望值的问题,提出了一种基于伪逆算法的导轨机械臂关节速度纠偏运动规划方案。首先,根据机械臂的关节角状态和末端执行器的运动状态,运用伪逆算法对导轨机械臂在速度层上进行冗余度解析。然后,设计时变函数对关节速度进行约束调整,使偏离后的关节速度收敛于期望值。接着,针对末端执行器出现的位置误差设计了误差修正方法以保证轨迹跟踪任务的顺利执行。最后,将运动规划方案在Matlab软件上以基座直线移动和弧形移动的四连杆冗余度机械臂为例进行了仿真实验。仿真结果表明了该方案能纠正导轨机械臂在任务执行过程中偏离期望值的关节速度,且能使末端执行器的轨迹跟踪达到较高的精度。     

基于伪逆的导轨机械臂关节速度纠偏运动规划方案

针对导轨机械臂在任务执行过程中出现的关节速度偏离期望值的问题，提出了一种基于伪逆算法的导轨机械臂关节速度纠偏运动规划方案。首先，根据机械臂的关节角状态和末端执行器的运动状态，运用伪逆算法对导轨机械臂在速度层上进行冗余度解析。然后，设计时变函数对关节速度进行约束调整，使偏离后的关节速度收敛于期望值。接着，针对末端执行器出现的位置误差设计了误差修正方法以保证轨迹跟踪任务的顺利执行。最后，将运动规划方案在Matlab软件上以基座直线移动和弧形移动的四连杆冗余度机械臂为例进行了仿真实验。仿真结果表明了该方案能纠正导轨机械臂在任务执行过程中偏离期望值的关节速度，且能使末端执行器的轨迹跟踪达到较高的精度。     

European Community policy and the market

Abstract This paper starts with some reflections on the policy considerations and priorities which are shaping European Commission (EC) research programmes. Then it attempts to position the current projects which seek to capitalise on information and communications technologies for learning in relation to these priorities and the apparent realities of the marketplace. It concludes that while there are grounds to be optimistic about the contribution EC programmes can make to the efficiency and standard of education and training, they are still too technology driven.     

一种自适应子融合集成多分类器方法

融合集成方法已经广泛应用在模式识别领域,然而一些基分类器实时性能稳定性较差,导致多分类器融合性能差,针对上述问题本文提出了一种新的基于多分类器的子融合集成分类器系统。该方法考虑在度量层融合层次之上通过对各类基多分类器进行动态选择,票数最多的类别作为融合系统中对特征向量识别的类别,构成一种新的自适应子融合集成分类器方法。实验表明,该方法比传统的分类器以及分类融合方法识别准确率明显更高,具有更好的鲁棒性。     

Explanation and prediction: an architecture for default and abductive reasoning

Although there are many arguments that logic is an appropriate tool for artificial intelligence, there has been a perceived problem with the monotonicity of classical logic. This paper elaborates on the idea that reasoning should be viewed as theory formation where logic tells us the consequences of our assumptions. The two activities of predicting what is expected to be true and explaining observations are considered in a simple theory formation framework. Properties of each activity are discussed, along with a number of proposals as to what should be predicted or accepted as reasonable explanations. An architecture is proposed to combine explanation and prediction into one coherent framework. Algorithms used to implement the system as well as examples from a running implementation are given.     

Three Process Perspectives: Organizations, Teams, and People

This paper provides the author's personal views and perspectives on software process improvement. Starting with his first work on technology assessment in IBM over 20 years ago, Watts Humphrey describes the process improvement work he has been directly involved in. This includes the development of the early process assessment methods, the original design of the CMM, and the introduction of the Personal Software Process (PSP)^SM and Team Software Process (TSP){^SM}. In addition to describing the original motivation for this work, the author also reviews many of the problems he and his associates encountered and why they solved them the way they did. He also comments on the outstanding issues and likely directions for future work. Finally, this work has built on the experiences and contributions of many people. Mr. Humphrey only describes work that he was personally involved in and he names many of the key contributors. However, so many people have been involved in this work that a full list of the important participants would be impractical.     

基于复小波噪声方差显著修正的SAR图像去噪

提出了一种基于复小波域统计建模与噪声方差估计显著性修正相结合的合成孔径雷达(Synthetic Aperture Radar,SAR)图像斑点噪声滤波方法。该方法首先通过对数变换将乘性噪声模型转化为加性噪声模型,然后对变换后的图像进行双树复小波变换(Dualtree Complex Wavelet Transform,DCWT),并对复数小波系数的统计分布进行建模。在此先验分布的基础上,通过运用贝叶斯估计方法从含噪系数中恢复原始系数,达到滤除噪声的目的。实验结果表明该方法在去除噪声的同时保留了图像的细节信息,取得了很好的降噪效果。     

How do children do mathematics with LOGO?

Abstract  This paper considers some results of a study designed to investigate the kinds of mathematical activity undertaken by children (aged between 8 and 11) as they learned to program in LOGO. A model of learning modes is proposed, which attempts to describe the ways in which children used and acquired understanding of the programming/mathematical concepts involved. The remainder of the paper is concerned with discussing the validity and limitations of the model, and its implications for further research and curriculum development.     

Editorial: Special issue on recent advances in hybrid control theory and applications

正The demands of a rapidly advancing technology for faster and more accurate controllers have always had a strong influence on the progress of automatic control theory.In recent years control problems have been arising with increasing frequency in widely different areas,which cannot be addressed using conventional control techniques.The principal reason for this is the fact that a highly competitive economy is forcing systems to operate in regimes where     

Information for Authors

正Aim The Journals of Zhejiang University-SCIENCE(A/B/C)areedited by the international board of distinguished Chinese andforeign scientists,and are aimed to present the latest devel-opments and achievements in scientific research in China andoverseas to the world’s scientific circles,especially to stimulateand promote academic exchange between Chinese and for-eign scientists everywhere.     

Enhancing a leaf radiative transfer model to estimate concentrations and in vivo specific absorption coefficients of total carotenoids and chlorophylls a and b from single-needle reflectance and transmittance

The relative concentrations of different pigments within a leaf have significant physiological and spectral consequences. Photosynthesis, light use efficiency, mass and energy exchange, and stress response are dependent on relationships among an ensemble of pigments. This ensemble also determines the visible characteristics of a leaf, which can be measured remotely and used to quantify leaf biochemistry and structure. But current remote sensing approaches are limited in their ability to resolve individual pigments. This paper focuses on the incorporation of three pigments—chlorophyll a, chlorophyll b, and total carotenoids—into the LIBERTY leaf radiative transfer model to better understand relationships between leaf biochemical, biophysical, and spectral properties.Pinus ponderosa and Pinus jeffreyi needles were collected from three sites in the California Sierra Nevada. Hemispheric single-leaf visible reflectance and transmittance and concentrations of chlorophylls a and b and total carotenoids of fresh needles were measured. These data were input to the enhanced LIBERTY model to estimate optical and biochemical properties of pine needles. The enhanced model successfully estimated reflectance (RMSE = 0.0255, BIAS = 0.00477, RMS%E = 16.7%), had variable success estimating transmittance (RMSE = 0.0442, BIAS = 0.0294, RMS%E = 181%), and generated very good estimates of carotenoid concentrations (RMSE = 2.48 µg/cm², BIAS = 0.143 µg/cm², RMS%E = 20.4%), good estimates of chlorophyll a concentrations (RMSE = 10.7 µg/cm², BIAS = − 0.992 µg/cm², RMS%E = 21.1%), and fair estimates of chlorophyll b concentrations (RMSE = 7.49 µg/cm², BIAS = − 2.12 µg/cm², RMS%E = 43.7%). Overall root mean squared errors of reflectance, transmittance, and pigment concentration estimates were lower for the three-pigment model than for the single-pigment model. The algorithm to estimate three in vivo specific absorption coefficients is robust, although estimated values are distorted by inconsistencies in model biophysics. The capacity to invert the model from single-leaf reflectance and transmittance was added to the model so it could be coupled with vegetation canopy models to estimate canopy biochemistry from remotely sensed data.     

Mr. Twinn’s bombes

This article discusses the history and design of the special versions of the bombe key-finding machines used by Britain’s Government Code & Cypher School (GC&CS) during World War II to attack the Enigma traffic of the Abwehr (the German military intelligence service). These special bombes were based on the design of their more numerous counterparts used against the traffic of the German armed services, but differed from them in important ways that highlight the adaptability of the British bombe design, and the power and flexibility of the diagonal board. Also discussed are the changes in the Abwehr indicating system that drove the development of these machines, the ingenious ways in which they were used, and some related developments involving the bombes used by the U.S. Navy’s cryptanalytic unit (OP-20-G).