On performance evaluation in online approximation for control

This article analyzes the evaluation of approximation accuracy in online applications. In particular, it is first shown that the most commonly used approximation accuracy evaluation method (e.g., analysis of training or tracking error) is not in itself sufficient to demonstrate proper function approximation. In spite of this, many articles use tracking (training) errors as the means to demonstrate successful function approximation. This article presents two alternative methods for the evaluation of online performance. Related issues include probably approximately correct learning from statistics and persistence of excitation from adaptive control.     

一种基于CMAC的自学习控制器

现有的基于CMAC的自学习控制器能够有效地减小跟踪误差,但是在跟踪连续变化信号如正弦波时,由于累积误差的影响会产生过学习现象,进而导致系统的不稳定.为此,提出一种新的基于CMAC的自学习控制器,它以系统的动态误差作为CMAC的激励信号,从而避免了累积误差的影响.仿真结果表明,该控制器不仅是有效的,而且具有很强的鲁棒性.此外,它可以使用较高的学习速率,实时性强.     

大学生在线学习效果调查研究

疫情爆发以来,为响应中央"停课不停教、停课不停学"的指导意见,在线学习在大学生间真正普及。虽然现已基本的资源平台、通讯渠道、设备要求等等外部条件得到满足,但在内部真正影响大学生在线学习效果的因素仍然存在。本文将从大学生在线学习的效果、对在线学习的态度以及影响在线学习效果的各种因素进行分析,得到启示,并由此给相关方面的完善提供参考意见。     

基于改进霍夫森林框架的多目标跟踪算法

针对单目视觉对多个相似的目标跟踪因遮挡等因素影响而失效的问题,提出一种基于改进霍夫森林框架的多目标跟踪算法。在将多目标跟踪问题归结为基于目标检测的轨迹关联过程基础上,通过引入在线学习霍夫森林框架将轨迹关联计算转化为最大后验概率（MAP）问题。通过在线采集多目标样本、提取目标外观和运动特征构建霍夫森林,进行森林训练得到轨迹关联概率,从而关联多目标轨迹;而引入低秩逼近Hankel矩阵进行轨迹校验,修复了误匹配的轨迹,改进了在线更新训练样本算法的效能。实验表明,轨迹误匹配率显著改善,能有效提高单目摄像机对多个相似目标有遮挡情况下跟踪的准确性和鲁棒性。     

Instructor accents in online education and their effect on learning and attitudes

Reductions in perceptual fluency have been shown to negatively impact attitudes towards learning material, but not learning itself. The current study extends this work to spoken presentations and examines whether the presence of a foreign accent negatively affects learners' experience in an online learning environment. Results indicate that the presence of an instructor accent, consistent with prior work on perceptual fluency, does not impact learning, but does cause learners to rate the instructor as less effective. Further, for those who received accented presentations, changes in participants' attitudes towards both the content area and online instruction were not predicted by learning, but instead their attitude towards the instructor. This suggests that learners in online learning environments with accented narration are potentially miscalibrated, and these biases in judgement could be inappropriately linked to a specific instructor, rather than their success of learning in the field.     

A laguerre neural network-based ADP learning scheme with its application to tracking control in the Internet of Things

Sensory data have becoming widely available in large volume and variety due to the increasing presence and adoption of the Internet of Things. Such data can be tremendously useful if they are processed properly in a timely fashion. They could play a key role in the coordination of industrial production. It is thus desirable to explore an effective and efficient scheme to support data tracking and monitoring. This paper intends to propose a novel automatic learning scheme to improve the tracking efficiency while maintaining or improving the data tracking accuracy. A core strategy in the proposed scheme is the design of Laguerre neural network (LaNN)-based approximate dynamic programming (ADP). As a traditional optimal learning strategy, ADP is a popular approach for data processing. The action neural network (NN) and the critic NN as two important components in ADP have big impact on the performance of ADP. In this paper, a LaNN is employed as the implementation of the action NN in ADP considering Laguerre polynomials’ approximation capability. In addition, this LaNN-based ADP is integrated into an online parameter-tuning framework to optimize those parameters of characteristic model that is used to trace the data in the tracking control system. Meanwhile, this article provides an associated Lyapunov convergence analysis to guarantee a uniformly ultimately boundedness property for tracking errors in the proposed approach. Furthermore, the proposed LaNN-based ADP optimal online parameter-tuning scheme is validated using a temperature dynamic tracking control task. The simulation results demonstrate that the scheme has satisfactory learning performance over time.     

Crowdsourcing with online quantitative design analysis

Design is a balancing act between people’s competing concerns, design options and design performance. Recently collecting data on such concerns such as sustainability or aesthetics has become possible through online crowdsourcing, particularly in 3d. However, such systems rarely present more than a single design alternative or allow users to change the design and seldom provide quantitative design analysis to gauge design performance. This precludes a more participatory approach including a wider audience and their insight in the design process.To improve the design process we propose a system to assist the design team in exploring the balance of concerns, design options and their performance. We augment a 3d visualisation crowdsourcing environment with quantitative on-demand assessment of design variants run in the cloud. This enables crowdsourced exploration of the design space and its performance. Automated participant tracking and explicit submitted feedback on design options are collated and presented to aid the design team in balancing the demands of urban master planning. We report application of this system to an urban masterplan with Arup.     

在线特征选取的多示例学习目标跟踪

目的 传统的多示例学习跟踪在跟踪过程中使用了自学习过程,当目标跟踪失败时分类器很容易退化。针对这个问题,提出一种基于在线特征选取的多示例学习跟踪方法(MILOFS)。方法 首先,该文使用稀疏随机矩阵来简化视频跟踪中图像特征的构建,使用随机矩阵投影来自高维度的图像信息。然后,利用Fisher线性判别模型构建包模型的损失函数,依照示例响应值直接在示例水平构建分类器的判别模型。最后,从梯度下降角度看待在线增强模型,使用梯度增强法来构建分类器的选取模型。结果 对不同场景的图像序列进行对比实验,实验结果中在线自适应增强(OAB)、在线多实例学习跟踪(MILTrack)、加权多实例学习跟踪(WMIL)、在线特征选取多实例学习跟踪(MILOFS)的平均跟踪误差分别为36像素、23像素、24像素、13像素,本文算法在光照变化、发生遮挡,以及形变的情况下都能准确跟踪目标,且具有很高的实时性。结论 基于在线特征选取的多示例学习跟踪,跟踪过程使用梯度增强法并直接在示例水平构建包模型的判别模型,可以有效克服传统多示例学习中的分类器退化问题。     

Precise position control of tubular linear motors with neural networks and composite learning

This paper examines an adaptive control scheme for tubular linear motors with micro-metric positioning tolerances. Uncertainties such as friction and other electro-magnetic phenomena are approximated with a radial basis function neural network, which is trained online using a learning law based on Lyapunov design. Differently from related literature, the approximator is trained using a composite adaptation law combining the tracking error and the model prediction error. Stability analysis and bounds for both errors are established, and an extensive experimental investigation is performed to assess the practical advantages of the proposed scheme.     

基于ip-iq算法谐波检测的高压APF在煤矿电网中的应用

通过对煤矿电网的电能质量普查分析,发现了煤矿6kV主副井提升机谐波含量与6kV母线电压谐波总畸变率严重超标。经过有针埘性的分析、调查、研究和试验,确定了适合煤矿实际的补偿治理方案,并设计出了一套用于高压系统的基于ip-iq算法谐波检测的APF装置。该高压APF装置谐波电流检测方法采用瞬时无功功率理论（ip-iq算法）,电流跟踪采用三角载波比较方式。对直流侧电容电压控制采朋滑模变结构控制方法,该方法跟踪性能好、鲁棒性强,克服了传统PI调解超调量和静态响应误差大、响应速度慢、参数难调节等缺点。     

Multilayer neural-net robot controller with guaranteed trackingperformance

A multilayer neural-net (NN) controller for a general serial-link rigid robot arm is developed. The structure of the NN controller is derived using a filtered error/passivity approach. No off-line learning phase is needed for the proposed NN controller and the weights are easily initialized. The nonlinear nature of the NN, plus NN functional reconstruction inaccuracies and robot disturbances, mean that the standard delta rule using backpropagation tuning does not suffice for closed-loop dynamic control. Novel online weight tuning algorithms, including correction terms to the delta rule plus an added robust signal, guarantee bounded tracking errors as well as bounded NN weights. Specific bounds are determined, and the tracking error bound can be made arbitrarily small by increasing a certain feedback gain. The correction terms involve a second-order forward-propagated wave in the backpropagation network. New NN properties including the notions of a passive NN, a dissipative NN, and a robust NN are introduced.     

Robust visual tracking via online semi-supervised co-boosting

This paper proposes a novel visual tracking algorithm via online semi-supervised co-boosting, which investigates the benefits of co-boosting (i.e., the integration of co-training and boosting) and semi-supervised learning in the online tracking process. Existing discriminative tracking algorithms often use the classification results to update the classifier itself. However, the classification errors are easily accumulated during the self-training process. In this paper, we employ an effective online semi-supervised co-boosting framework to update the weak classifiers built on two different feature views. In this framework, the pseudo-label and importance of an unlabeled sample are estimated based on the additive logistic regression for an integration of a prior model and an online classifier learned on one feature view, and then used to update the weak classifiers built on the other feature view. The proposed algorithm has a good ability to recover from drifting by incorporating prior knowledge of the object while being adaptive to appearance changes by effectively combining the complementary strengths of different feature views. Experimental results on a series of challenging video sequences demonstrate the superior performance of our algorithm compared to state-of-the-art tracking algorithms.     

Indirect robot model learning for tracking control

Learning task-space tracking control on redundant robot manipulators is an important but difficult problem. A main difficulty is the non-uniqueness of the solution: a task-space trajectory has multiple joint-space trajectories associated, therefore averaging over non-convex solution space needs to be done if treated as a regression problem. A second class of difficulties arise for those robots when the physical model is either too complex or even not available. In this situation machine learning methods may be a suitable alternative to classical approaches. We propose a learning framework for tracking control that is applicable for underactuated or non-rigid robots where an analytical physical model of the robot is unavailable. The proposed framework builds on the insight that tracking problems are well defined in the joint task- and joint-space coordinates and consequently predictions can be obtained via local optimization. Physical experiments show that state-of-the art accuracy can be achieved in both online and offline tracking control learning. Furthermore, we show that the presented method is capable of controlling underactuated robot architectures as well.     

Data-Driven Learning Control Algorithms for Unachievable Tracking Problems

For unachievable tracking problems, where the system output cannot precisely track a given reference, achieving the best possible approximation for the reference trajectory becomes the objective. This study aims to investigate solutions using the P-type learning control scheme. Initially, we demonstrate the necessity of gradient information for achieving the best approximation. Subsequently, we propose an input-output-driven learning gain design to handle the imprecise gradients of a class of uncertain systems. However, it is discovered that the desired performance may not be attainable when faced with incomplete information. To address this issue, an extended iterative learning control scheme is introduced. In this scheme, the tracking errors are modified through output data sampling, which incorporates low-memory footprints and offers flexibility in learning gain design. The input sequence is shown to converge towards the desired input, resulting in an output that is closest to the given reference in the least square sense. Numerical simulations are provided to validate the theoretical findings.     

基于参数自学习的无人车越野环境跟踪控制方法

针对无人车在越野环境下难以高速、高精度地跟踪复杂路况的问题,设计了一种参数自学习的前馈补偿控制器,与模型预测控制方法构成前馈-反馈的控制结构。在该控制结构中,前馈控制根据实时状态的跟踪误差在线更新学习系数,有效考虑车辆高速运动过程中无法精确建模的非线性动力学特性以及复杂路况不断变化的曲率和路面条件等的影响,在保证稳定性的同时快速减小跟踪误差。在越野场景进行了高速的S型与直角弯路径跟踪实车实验来验证参数自学习控制器的有效性,结果表明,所设计的参数自学习控制器相比传统的模型预测控制器跟踪误差和横摆都较小,在跟踪精度和车辆稳定性上都有较大改善。     

Meaningful posts and online learning in Blackboard across four cohorts of adult learners

In the present study, meaningful posts were tracked in Blackboard in a longitudinal study of a graduate statistics course in order to predict online learning. In previous research by the present author, digital immigrants from a baby-boomer cohort fare better than digital natives due to social reliance and meaningful posts. Meaningful posts include discussion comments that reflect meaning-based engagement with the course material. Students with optimal patterns and types of discussion participation do better than those students who just follow a point system of quantity-based engagement. Students were given three behavioral assessments and then monitored for meaningful posts and successful online behavior using the tracking features within Blackboard. Results were analyzed using a multiple regression and showed that a significant percentage of online learning is predicted by meaningful posts and homework performance while total online activity does not uniquely predict learning outcomes. Students with more meaningful posts show more engagement with the online materials and better learning than those with less meaningful posts.     

Composite adaptive dynamic surface control using online recorded data

This paper presents an online recorded data‐based design of composite adaptive dynamic surface control for a class of uncertain parameter strict‐feedback nonlinear systems, where both tracking errors and prediction errors are applied to update parametric estimates. Differing from the traditional composite adaptation that utilizes identification models and linear filters to generate filtered modeling errors as prediction errors, the proposed composite adaptation integrates closed‐loop tracking error equations in a moving time window to generate modified modeling errors as prediction errors. The time‐interval integral operation takes full advantage of online recorded data to improve parameter convergence such that the application of both identification models and linear filters is not necessary. Semiglobal practical asymptotic stability of the closed‐loop system is rigorously established by the time‐scales separation and Lyapunov synthesis. The major contribution of this study is that composite adaptation based on online recorded data is achieved at the presence of mismatched uncertainties. Simulation results have been provided to verify the effectiveness and superiority of this approach. Copyright © 2016 John Wiley & Sons, Ltd.     

Understanding the roles of online meetings in a net-based course

Abstract It is argued elsewhere that online learning environments constitute new conditions for carrying out collaborative learning activities. This article explores the roles of a series of online meetings in such an environment. The online meetings are arranged as part of a net-based course on object-oriented programming, and constitute a recurring shared experience for the participants throughout the semester. Through an activity theoretical analysis, we find that the meetings mediate the learners' actions towards the construction and maintenance of a community of practice. Our finding has implications for the standardization of digital learning resources. This is an issue that will challenge designers of research-oriented learning environments, should they attempt to move their systems into wider adoption. We suggest that an awareness of the internal systemic connections among the components of the course design we studied is of importance when considering redesign, with respect to the reuse and standardization of learning resources.     

Initial condition issues on iterative learning control for non-linear systems with time delay

Most of the available results on iterative learning control address trajectory tracking problem for systems without time delay. The role of the initial function in tracking performance of iterative learning control for systems with time delay is not yet fully understood. In this paper, asymptotic properties of a conventional learning algorithm are examined for a class of non-linear systems with time delay in the presence of initial function errors. It is shown that a non-zero initial function deviation can cause a lasting tracking error on the entire operation. Impulsive action is one method to eliminate such lasting tracking error but it is not a practical approach. As an alternative, an initial rectifying action is introduced in the learning algorithm. The initial rectifying action is finite and used over a specified interval. It is shown to be effective in the improvement of tracking performance, in particular robustness and uniform convergence. The results are further extended to systems with multiple time delays. An example is given and computer simulations are presented to demonstrate the performance of the proposed approach.     

LD-identify: 基于无源RFID的网络学习状态识别

在线教育中,学生实时动作能够准确反映学生当前的学习状态,在不影响学习注意力和保证个人隐私信息安全的情况下,准确识别学习动作是监测在线教育质量的关键要素.对此,提出一种基于无源RFID的网络学习动作识别系统LD-identify.LD-identify仅通过射频信号完成学生动作识别,所以识别系统可以很好地保护个人的隐私信息,且避免设备昂贵等一系列问题.通过提取相位和信号强度的有效特征和深度学习算法,LD-identify能够获得很好的识别准确率的性能.实验表明,LD-identify只需要在帽子的背面粘贴两个射频标签,就能很好地识别出抬头低头、左右摇头、前倾后倾3种动作.为了进一步验证系统性能,研究6名志愿者在不同的场景中的动作识别的准确率,实验结果显示LD-identify能够在不同的场景下很好地识别所有用户的3种动作,利用卷积神经网络构建分类模型来识别动作可以取得很好的识别率,识别准确率达到95.5%以上.