基于LuGre 摩擦模型的机械臂模糊神经网络控制

针对未知摩擦非线性会使机械臂控制精度难以提高的缺陷,建立基于动态LuGre摩擦的机械臂模型.在系统参数未知和机械臂负载变化的情况下,设计一种自适应模糊神经网络控制器,采用基函数中心和宽度均自适应变化的模糊神经网络补偿器,实现对系统中包括LuGre摩擦在内的非线性环节的逼近,并利用滑模控制项减小逼近误差.通过Lyapunov方法证明了闭环系统的稳定性,并通过仿真结果验证了所提出控制方法的有效性.     

Periodic sampling: maximising the sampling period

The process of periodic sampling is investigated for a class of nonlinear systems. The objective is to achieve the longest sampling period that is compatible with a specified error bound. It is shown that there are robust optimal controllers that achieve this objective. It is also shown that the performance of such optimal controllers can be approximated by bang-bang controllers – controllers that are relatively easy to design and implement.     

An adaptive friction compensator for global tracking in robot manipulators

A novel adaptive friction compensator based on a dynamic model recently proposed in the literature is presented in this paper. The compensator ensures global position tracking when applied to an n degree of freedom robot manipulator perturbed by friction forces with only measurements of position and velocity, and all the system parameters (robot and friction model) unknown. Instrumental for the solution of the problem is the observation that friction compensation can be recasted as a disturbance rejection problem. The control signal is then designed in two steps, first a classical adaptive robot controller that (strictly) passifies the system, and then a relay-based outer-loop that rejects the disturbance.     

机器人转动关节的LuGre摩擦模型参数辨识

根据Lu Gre摩擦模型辨识理论,以伺服电机驱动轴与伺服电机内部的摩擦模拟机器人关节摩擦,建立Lu Gre摩擦模型。对伺服电机做基于固高卡的模拟量控制,通过C++编程,从编码器中读取角度、转速值、加速度值。正转速度和对应的驱动力矩,以及反转速度和对应的驱动力矩,分别构成静态参数辨识的两组数据。位移、速度、加速度和驱动力矩构成动态参数辨识数据。在MATLAB中编写粒子群算法辨识程序,对以上数据进行处理,最终得到Lu Gre模型的6个参数的辨识值。     

含有摩擦补偿的全方位移动机器人自抗扰控制

本文针对全方位移动机器人轨迹追踪中的摩擦补偿问题,提出了一种改进的非线性自抗扰控制器.首先建立了含有经典静态摩擦模型的全方位移动机器人动力学模型.其次,基于该模型设计非线性控制器和线性扩张状态观测器并给出了系统的稳定性分析.通过将模型已知项加入线性扩张状态观测器中得到摩擦力的估计值,并将估计值用于非线性控制器中摩擦补偿部分.为减小摩擦力对机器人低速运动轨迹追踪控制的影响,非线性控制器采用变增益控制器进行轨迹追踪控制.最后通过仿真结果验证本文提出控制器的有效性.     

Control of a three-link robot moving on the plane with friction

A three-link robot capable of moving on a plane rough surface by varying its configuration is considered. A method for controlling slow (quasi-static) motions of such a robot is suggested, and feasibility of such motion for certain parameters of the robot is proved.     

Investigations of the capillary effect for gripping silicon chips

Capillary forces in microsystems are very powerful. During wet etching they can cause sticking or even destruction of moving or underetched parts of the microstructure. But capillary forces can also be used in a controlled way for gripping and handling of micro objects. This paper shows that forces exerted on a silicon chip with dimensions of 4 × 4 mm² and a thickness of 600 m are approximately 200-times higher than the inertial force of the chip. The force exerted is dependent on the gap height and can be estimated for different drop sizes with simple estimation formulas or with solutions from differential equations. A numerical solution gives a better understanding of the non-linear behavior of a capillary liquid in a gap. The result of the investigation shows the behavior of the capillary effect in small gaps. For small gap widths and liquid volumes the force developed is overestimated by conventional formulas and calculations. Additionally the general behavior of liquids in microgaps are shown, which also can help to design other liquid based microsystems e.g. micro biological sensor systems.The author is thankful for the support given for this work by Prof. Dr.-Ing. L. Kiesewetter from the Technical University of Brandenburg/Germany.     

Model-free controller design for a single-link flexible smart materials robot

In this paper, controller design is investigated for a single-link flexible smart materials robot which combines the advantages of both flexible link robots and piezoelectric materials. To avoid the drawbacks resulting from model uncertainties and/or model truncations, model-free controllers (both decentralized and centralized) are proposed for tip regulation and residual vibration suppression. In contrast to traditional model-based methods, the controllers presented in the paper are derived from the basic energy-work relationship and can guarantee the asymptotic stability of the damped truncated system with arbitrarily any finite number of flexible modes. Furthermore, the controllers are easily implementable because all the signals can be chosen to be readily measurable. Simulations are carried out to show the effectiveness of the approach presented.     

Independent joint control: Estimation and compensation of coupling and friction effects in robot position control

The method of independent joint control has been widely used in the position control of industrial robots. In order to improve the control performance of this type of controllers, the concept of nonlinearity-estimation and-compensation is introduced. With this extended method comparable results can be obtained as with the method of exact linearization. Especially by the treatment of unmodeled or inaccurate effects, e.g., friction, load variation or parameter inaccuracy, the presented control concept shows great advantages.     

The MATS robot: service climbing robot for personal assistance

The human care and service field requires an innovative robotic solution to make the daily care of elderly and disabled people in both home and workplace environments easier. The European Union (EU) project MATS (flexible mechatronic assistive technology system) has developed a new concept of a climbing robot for this type of service application. The climbing process is performed by moving the robot between very simple docking stations (DSs) placed in the environment. The MATS climbing robot is a symmetrical, five degrees of freedom (5 DOF), self-containing manipulator that includes all the control and communication systems on board. To fulfil the climbing movements successfully, the developed robot is lightweight, about 11 kg for a 1.3 m reach. This article presents real experiments conducted with the robot during its climbing movements and assistance tasks for disabled persons.     

Searching for clues: Diagnosing IC failures

Reviewed in this issue Data Mining and Diagnosing IC Fails, by Leendert M. Huisman (Springer, 2005, ISBN 0-387-24993-1, 250 pp., $129). As ICs grow in size, finding a failure's cause has become more and more difficult. This book describes how statistical methods can help uncover the source of a problem using data provided by IC test. It discusses failures during IC manufacture, rather than at the board or assembly level or in the field. Even though the title does not indicate it, much of this book is devoted to yield enhancement, which makes it far more interesting than if it were completely devoted to traditional diagnosis.     

Simulation of the motion of a five-link crawling robot with controlled friction on a surface having obstacles

We consider the motion of a five-link crawling robot in an environment with obstacles located discretely. The robot is fitted with special controlled friction elements for the periodic fixation of links on the surface and has a possibility of the spatial configuration change due to a detachment of the end links from the surface. One of the possible crawling modes is analyzed as the end links are detached from the surface and the adjacent links rotate by a given angle in the plane of motion without interaction with obstacles. As the result of simulating by the numerical method, we establish the dependence between the average velocity of the plant (and its maneuverability between obstacles) and control values.     

Service robot for the elderly

In recent years, service robots have received a lot of attention from both industry and academia. They are individually designed to performtasks in an unstructured environment for working with or assisting humans [1], [2]. Such robots thus have to be able to actively interact with potential users in their surroundings and to appropriately offer their services. Until now, a number of service robots have been introduced such as vacuum cleaning robots, home security robots, entertainment robots, and guide robots [2]?[4]. In particular, robots that are able to assist the elderly are becoming very important with a dramatic increase in the aging population and costs of elderly care [1], [2], [5]. Several projects have been initiated in some developed countries to develop service robots, especially robotic aid systems [2], [5].     

A new methodology for measuring the vibration transmission from handle to finger whilst gripping

The transmission of vibration from hand-held tools via work gloves and into the operators' hands can be affected by several factors such as glove material properties, tool vibration conditions, grip force, and temperature. The primary aim of this study is to develop a new methodology to measure and evaluate vibration transmissibility for a human finger in contact with different materials, whilst measuring and controlling the grip force. The study presented here used a new bespoke lab-based apparatus for assessing vibration transmissibility that includes a generic handle instrumented for vibration and grip force measurements. The handle is freely suspended and can be excited at a range of real-world vibration conditions whilst being gripped by a human subject. The study conducted a frequency response function (FRF) of the handle using an instrumented hammer to ensure that the handle system was resonance free at the important frequency range for glove research, as outlined in ISO 10819: 1996: 2013, and also investigated how glove material properties and design affect the tool vibration transmission into the index finger (Almagirby et al. 2015). The FRF results obtained at each of six positions shows that the dynamic system of the handle has three resonance frequencies in the low frequency range (2, 11 and 17 Hz) and indicated that no resonances were displayed up to a frequency of about 550 Hz. No significant vibration attenuation was shown at frequencies lower than 150 Hz. The two materials cut from the gloves that were labelled as anti-vibration gloves (AV) indicated resonance at frequencies of 150 and 160 Hz. However, the non-glove material that did not meet the requirements for AV gloves showed resonance at 250 Hz. The attenuation for the three materials was found at frequencies of 315 Hz and 400 Hz. The level and position of the true resonance frequencies were found to vary between samples and individual subjects.     

Fast augmentation algorithms for maximising the output flow in repairable flow networks after edge failures

The article discuses a number of fundamental results related to determining the maximum output flow in a network after edge failures. On the basis of four theorems, we propose very efficient augmentation algorithms for restoring the maximum possible output flow in a repairable flow network, after an edge failure. In many cases, the running time of the proposed algorithm is independent of the size of the network or varies linearly with the size of the network. The high computational speed of the proposed algorithms makes them suitable for optimising the performance of repairable flow networks in real time and for decongesting overloaded branches in networks. We show that the correct algorithm for maximising the flow in a static flow network, with edges fully saturated with flow, is a special case of the proposed reoptimisation algorithm, after transforming the network into a network with balanced nodes. An efficient two-stage augmentation algorithm has also been proposed for maximising the output flow in a network with empty edges. The algorithm is faster than the classical flow augmentation algorithms. The article also presents a study on the link between performance, topology and size of repairable flow networks by using a specially developed software tool. The topology of repairable flow networks has a significant impact on their performance. Two networks built with identical type and number of components can have very different performance levels because of slight differences in their topology.     

Fabrication of polymer-based micro devices: Formulation and study of the paste

We investigate in the present work the fabrication of polymer-based micro-fluidic and micro-mechanical devices using sacrificial, resistive/conductive pastes, through a screen-printing process. An organic sacrificial paste is first screen-printed onto a substrate, building the future empty space (channels, cavities…) where it lies. Then, a resistive paste based on thermosetting polymer resin and graphite is deposited onto the previous layer. Finally, the sacrificial paste is removed at 150 °C by sublimation through the composite, thus yielding the desired pattern. For such applications, the key is naturally the formulation of the pastes. In a previous work, we already proposed a potential formulation for the organic sacrificial paste, based on polyols [1]. In the present paper, we will focus on the formulation of the cover paste, which must be adapted rheologically for the screen-printing process, but also chemically due to strong potential interactions between the sacrificial layer and the over-layer. Finally, micro-devices such as simple fluidic channels and suspended structures were produced and shown to be operational, demonstrating the high potential of our process.     

Searching the Web for conflicting topics: Page and user factors

Web users tend to search only the pages displayed at the top of the search engine results page (the ‘top link’ heuristic). Although it might be reasonable to use this heuristic to navigate simple and unambiguous facts, it might be risky when searching for conflicting socio-scientific topics, such as potential measures to reduce greenhouse gas emissions. In the present study, we explored the extent to which students consider other Web page characteristics, such as topic relevance and trustworthiness, when searching and bookmarking pages concerning a conflicting topic. We also examined the extent to which prior background knowledge moderates students’ behavior. The results revealed that while the study participants actually used a ‘top link’ heuristic to navigate the results, they engaged in more systematic processes to bookmark pages for further study. Furthermore, the students’ background knowledge was related to the assessment of Web page trustworthiness. We discuss these results from the perspective of a dual-processing model.     

Searching for the two sigma advantage: Evaluating algebra intelligent tutors

This study evaluated 2 off-the-shelf, computer-based, mathematics intelligent-tutoring systems that provide instruction in algebra during a remedial mathematics summer program. The majority of the enrolled high school students failed to pass algebra in the previous semester. Students were randomly assigned in approximately equal proportions to work with the Carnegie Learning Algebra Cognitive Tutor or the ALEKS Algebra Course. Using the tutoring system exclusively, the students completed a 4-h-a-day, 14-day summer school high school algebra class for credit. The results revealed that both tutoring systems produced statistically and practically meaningful learning gains on measures of arithmetic and algebra knowledge.     

Searching for Software on the EGEE Infrastructure

Several large-scale Grid infrastructures are currently in operation around the world, federating an impressive collection of computational resources, a wide variety of application software, and hundreds of user communities. To better serve the current and prospective users of Grid infrastructures, it is important to develop advanced software retrieval services that could help users locate software components suitable to their needs. In this paper, we present the design and implementation of Minersoft, a distributed, multi-threaded harvester for application software located in large-scale Grid infrastructures. Minersoft crawls the sites of a Grid infrastructure, discovers installed software resources, annotates them with keyword-rich metadata, and creates inverted indexes that can be used to support full-text software retrieval. We present insights derived from the implementation and deployment of Minersoft on EGEE, one of the largest Grid production services currently in operation. Experimental results show that Minersoft achieves a high performance in crawling EGEE sites and discovering software-related files, and a high efficiency in supporting software retrieval.     

Searching for Anne Frank on the Internet

ABSTRACT

Teaching the subject of the Holocaust is difficult enough for educators; identifying useful, topical, and appropriate Internet sites is most complicated given the plethora of sites on this subject. This article is a result of visiting and evaluating hundreds of Web sites to highlight those sites that are the most effective for students, teachers, scholars, and librarians.