深空探测柔性太阳帆航天器动力学建模与姿态控制

太阳帆利用太阳辐射压力提供太空航行的必要动力,由于具有理论上的无限速度和无需消耗任何燃料等优势,被认为是完成未来深空探测任务的有效技术途径之一.柔性太阳帆航天器的动力学模型包括多体动力学、刚柔耦合动力学和太阳辐射光压模型,复杂的动力学特性导致其姿态控制设计具有很强的挑战性.针对带有控制杆的柔性太阳帆航天器,本文采用拉格朗日方程和有限元法,给出了面向控制的解析式动力学模型.所推导的刚柔耦合动力学模型,刻画了太阳帆航天器的本质动力学特性,即双框架控制杆的短周期运动,姿态与柔性太阳帆的耦合效应,以及在太阳光压恢复力矩下的姿态静稳定性和长周期运动.基于带控制杆的太阳帆航天器的双时间尺度特性,提出了双回路控制结构,用于实现航天器俯仰轴和偏航轴的姿态控制.将内回路设计为PD控制器,用于实现质心位置的调整.将外回路设计为PID控制器,用于阻尼姿态运动,并实现在平衡太阳光压力矩下的姿态保持.从而将柔性太阳帆航天器的复杂姿态控制问题转化为两个低阶子问题,实现了在不同频带上的控制设计.仿真结果验证了动力学建模和姿态控制设计方法的有效性.     

基于整形器的两轴柔性航天器自适应姿态控制

针对非线性柔性航天器大角度姿态机动问题,为了抑制在高速运动中产生的振动,提出了一种整形参考轨迹和自适应滑模姿态跟踪控制方法.跟踪过程中所使用的期望姿态角是由最优任意时延(Optimal Arbitrary Time-delay,OAT)输入整形器整形所得参考指令作用于参考模型得到,利用该期望姿态角能够得到更好地跟踪和抑制振动效果.针对非线性柔性航天器参数的未知时变特性和欠驱动特性,设计的自适应滑模控制器不仅能够完成期望的姿态角跟踪,同时还能够有效抑制姿态机动过程中的振动,并应用于单轴非线性柔性航天器的大角度姿态控制系统,并进行了仿真验证.结果表明,所提出的方法是可行而有效的.     

基于机械臂耦合力矩评估的组合航天器姿态协调控制

针对在轨服务任务中服务航天器和目标航天器对接后组合体的姿态稳定问题,提出一种基于机械臂耦合力矩评估的组合航天器姿态协调控制方法.首先,对空间机械臂和组合航天器进行了动力学建模与分析;其次,利用空间机械臂和组合体平台之间的强耦合特点,采用空间机械臂的运动来协调组合航天器平台的姿态运动,并给出了相应的协调规划方法;然后,考虑传统航天器燃料有限、反作用轮易饱和等因素,采用以空间机械臂为主、反作用轮为辅的方式对组合航天器进行姿态协调控制,并设计了基于机械臂耦合力矩评估的姿态协调控制器;最后利用仿真实验与传统航天器姿态控制方法进行了比较分析,结果表明:所提方法仅通过空间机械臂和反作用轮就能实现对组合航天器的姿态稳定控制,而不需要消耗昂贵的喷气燃料.     

接近非合作目标的部分状态反馈姿轨联合控制

飞行器在轨精度跟踪优化问题,根据在轨服务任务需求,针对非合作翻滚目标航天器的自主接近跟踪问题,首先从采用视线坐标系表示的轨道动力学方程和修正罗德里格斯参数表示的姿态动力学方程出发,建立了航天器六自由度类拉格朗日动力学方程;然后仅利用相对位置和相对姿态反馈信息并针对航天器惯性参数不确定性,采用自适应非线性输出反馈控制和神经网络逼近控制方法设计了姿轨联合控制器,并通过Lyapunov直接法证明了该闭环系统的全局渐进稳定性;最后通过仿真验证了采用的方法能够实现对非合作目标的精确跟踪.     

挠性航天器鲁棒后步滑模姿态跟踪及主动振动控制

针对挠性航天器姿态跟踪及振动抑制问题,提出一种双回路鲁棒控制方法.首先,采用滑模控制与后步法设,计了姿态跟踪控制器,基于Lyapunov方法分析系统的渐近稳定性,并从实际应用角度考虑了反作用飞轮的动态特性;其次,为抑制挠性结构的振动,采用压电智能材料作为敏感器和作动器,设计了应变速率反馈补偿器.仿真结果表明,所提方法在保证完成姿态跟踪任务的同时,能有效抑制挠性附件的振动.     

飞轮安装偏差的过驱动航天器有限时间姿态控制

针对反作用飞轮安装存在偏差的过驱动航天器姿态跟踪问题, 提出一种有限时间姿态补偿控制策略. 通过设计自适应滑模控制器保证实现对不确定性转动惯量与外部干扰的鲁棒控制, 同时实现对飞轮安装偏差的补偿控制, 并应用Lyapunov 稳定性理论证明了该控制器能够在有限时间内实现姿态跟踪控制. 最后, 将该控制器应用于某型航天器的姿态跟踪控制, 仿真结果验证了所提出方法的有效性.     

基于路径规划的挠性航天器姿态自适应控制

针对挠性航天器存在动力学参数不确定性以及三轴非线性强耦合的特点,提出了一种基于余弦函数路径规划的姿态自适应控制方法。首先,分析挠性航天器动力学模型,给出了其姿态控制系统的总体结构;然后,为有效抑制挠性附件振动对控制性能的影响,设计了一种余弦角加速度姿态路径规划方法对指令信号进行柔化,以减少指令信号中的高频成分;最后,将柔化指令信号作为控制系统的期望输入信号,并采用基于多输入多输出特征建模理论,设计了姿态自适应跟踪控制器。通过MATLAB/Simulink仿真,验证了所提姿态控制策略的有效性。     

基于模糊PD控制的柔性航天器振动抑制研究

研究柔性结构振动与航天器姿态运动的刚柔耦合的控制问题,采用非约束模态法对柔性航天器构建适合控制器设计的状态空间模型.针对柔性航天器姿态机动控制问题,根据期望姿态角度与实际姿态角度给出的姿态信息得出姿态误差信号,以此信号设计了一种PD控制律.考虑到柔性航天器初始阶段姿态角速度过大的情况,在原有的PD控制基础上,加入了模糊...     

姿态变化一致有界的姿态稳定控制器设计

针对航天器姿态稳定控制问题, 设计一种迭代学习姿态控制器. 将连续非周期运动的姿态跟踪过程分解为队列重复运动, 采用前一周期的姿态跟踪误差修正后一周期的控制输入, 分别对未知参数和干扰构建有界迭代学习律, 给出航天器姿态稳定控制器, 并从理论上分析了闭环系统的渐近稳定性和姿态跟踪误差的一致有界性. 通过在轨捕获非合作目标过程中航天器姿态跟踪控制问题的数值仿真, 验证了迭代学习控制器的鲁棒性和强抗干扰性.

     

基于物联网及ADRC的航天器在轨姿态监测系统设计

在特殊航天环境中,由于电磁波等干扰条件的存在,容易导致航天器设备偏离预设的轨迹路径,为解决此问题,设计基于物联网及ADRC的航天器的在轨姿态监测系统;分析物联网监测体系中的位姿控制需求,分层次连接主动振动控制器与航天器姿态控制器,借助FBG应变传感器,建立主机结构与航天器元件之间的监测感应连接,实现在轨姿态监测系统的硬件应用结构设计;在此基础上,对应变传感器进行标定处理,通过计算姿态传递系数的方式,确定航天器的横向在轨应变效应,再通过ADRC原理,提取航天器在轨姿态感知参量的最佳行进状态信号,完善航天器的在轨姿态监测控制律,实现基于物联网及航天器的在轨姿态监测系统设计;对比实验结果显示,与光纤传感型监测系统相比,物联网监测系统能够有效屏蔽电磁波干扰,确保航天器在特殊航天环境中不会出现偏离预设轨迹路径的行进行为.     

Only connect: teaching, technology and telesis

Abstract This paper describes an approach to the design of interactive multimedia materials being developed in a European Community project. The developmental process is seen as a dialogue between technologists and teachers. This dialogue is often problematic because of the differences in training, experience and culture between them. Conditions needed for fruitful dialogue are described and the generic model for learning design used in the project is explained.     

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。     

Avoiding semantic and temporal gaps in developing software intensive systems

Development of software intensive systems (systems) in practice involves a series of self-contained phases for the lifecycle of a system. Semantic and temporal gaps, which occur among phases and among developer disciplines within and across phases, hinder the ongoing development of a system because of the interdependencies among phases and among disciplines. Such gaps are magnified among systems that are developed at different times by different development teams, which may limit reuse of artifacts of systems development and interoperability among the systems. This article discusses such gaps and a systems development process for avoiding them.     

Designing economic np control charts: A programmed simulation approach

This paper presents control charts models and the necessary simulation software for the location of economic values of the control parameters. The simulation program is written in FORTRAN, requires only 10K of main storage, and can run on most mini and micro computers. Two models are presented - one describes the process when it is operating at full capacity and the other when the process is operating under capacity. The models allow the product quality to deteriorate to a further level before an existing out-of-control state is detected, and they can also be used in situations where no prior knowledge exists of the out-of-control causes and the resulting proportion defectives.     

The development of robot art

Going through a few examples of robot artists who are recognized worldwide, we try to analyze the deepest meaning of what is called “robot art” and the related art field definition. We also try to highlight its well-marked borders, such as kinetic sculptures, kinetic art, cyber art, and cyberpunk. A brief excursion into the importance of the context, the message, and its semiotics is also provided, case by case, together with a few hints on the history of this discipline in the light of an artistic perspective. Therefore, the aim of this article is to try to summarize the main characteristics that might classify robot art as a unique and innovative discipline, and to track down some of the principles by which a robotic artifact can or cannot be considered an art piece in terms of social, cultural, and strictly artistic interest. This work was presented in part at the 13th International Symposium on Artificial Life and Robotics, Oita, Japan, January 31–February 2, 2008     

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.