Actuador linear para teste de teclas na indústria automóvel

As indústrias de componentes e acessórios automóveis são um elo fundamental no processo produtivo da indústria automóvel. Neste leque industrial encontra-se a Preh Portugal, Lda, como empresa fornecedora de componentes electrónicos, mais concretamente, painéis de controlo de climatização. Os painéis fornecidos pela Preh aos seus clientes encontram-se sujeitos a rigorosos testes de qualidade e funcionalidade. Neste sentido o teste funcional das teclas surge, relacionando o curso da tecla em função de uma força actuante. Esta relação está comprometida com uma curva característica padrão para o tipo de tecla. Para além destes compromissos, também é necessário que a tecla feche e abra o seu contacto eléctrico. Esta tese foca-se no desenvolvimento do teste de teclas, apresentando uma alteração ao sistema actual com a introdução de um sistema embebido, no intuito de flexibilizar o sistema de teste e reduzindo custos. O sistema embebido pretende dar capacidade de processamento ao teste e, desta forma, substituir o actual computador como elemento de processamento. A solução implementada consistiu numa mudança estrutural, através da inclusão do sistema embebido entre o computador e o sistema de deslocamento. Passando o foco central do processo de teste a residir no sistema embebido, este tem de estabelecer comunicações com os restantes elementos intervenientes no teste. Estabelece comunicações série RS-232 com o sistema de deslocamento (leitura do curso e força na tecla), Ethernet com o computador (comandos, parâmetros e resultados) e CAN com o painel de controlo de climatização (fecho/abertura do contacto eléctrico). A concretização deste projecto resultou numa nova estrutura e aplicação, a qual é facilmente integrada na linha de produção com as vantagens de ser menos onerosa e mais flexível, conforme o pretendido.

Controlador Boundary-Scan

A crescente complexidade dos sistemas electrónicos associada a um desenvolvimento nas tecnologias de encapsulamento levou à miniaturização dos circuitos integrados, provocando dificuldades e limitações no diagnóstico e detecção de falhas, diminuindo drasticamente a aplicabilidade dos equipamentos ICT. Como forma de lidar com este problema surgiu a infra-estrutura Boundary Scan descrita na norma IEEE1149.1 “Test Access Port and Boundary-Scan Architecture”, aprovada em 1990. Sendo esta solução tecnicamente viável e interessante economicamente para o diagnóstico de defeitos, efectua também outras aplicações. O SVF surgiu do desejo de incutir e fazer com que os fornecedores independentes incluíssem a norma IEEE 1149.1, é desenvolvido num formato ASCII, com o objectivo de enviar sinais, aguardar pela sua resposta, segundo a máscara de dados baseada na norma IEEE1149.1. Actualmente a incorporação do Boundary Scan nos circuitos integrados está em grande expansão e consequentemente usufrui de uma forte implementação no mercado. Neste contexto o objectivo da dissertação é o desenvolvimento de um controlador boundary scan que implemente uma interface com o PC e possibilite o controlo e monitorização da aplicação de teste ao PCB. A arquitectura do controlador desenvolvido contém um módulo de Memória de entrada, um Controlador TAP e uma Memória de saída. A implementação do controlador foi feita através da utilização de uma FPGA, é um dispositivo lógico reconfiguráveis constituído por blocos lógicos e por uma rede de interligações, ambos configuráveis, que permitem ao utilizador implementar as mais variadas funções digitais. A utilização de uma FPGA tem a vantagem de permitir a versatilidade do controlador, facilidade na alteração do seu código e possibilidade de inserir mais controladores dentro da FPGA. Foi desenvolvido o protocolo de comunicação e sincronização entre os vários módulos, permitindo o controlo e monitorização dos estímulos enviados e recebidos ao PCB, executados automaticamente através do software do Controlador TAP e de acordo com a norma IEEE 1149.1. A solução proposta foi validada por simulação utilizando o simulador da Xilinx. Foram analisados todos os sinais que constituem o controlador e verificado o correcto funcionamento de todos os seus módulos. Esta solução executa todas as sequências pretendidas e necessárias (envio de estímulos) à realização dos testes ao PCB. Recebe e armazena os dados obtidos, enviando-os posteriormente para a memória de saída. A execução do trabalho permitiu concluir que os projectos de componentes electrónicos tenderão a ser descritos num nível de abstracção mais elevado, recorrendo cada vez mais ao uso de linguagens de hardware, no qual o VHDL é uma excelente ferramenta de programação. O controlador desenvolvido será uma ferramenta bastante útil e versátil para o teste de PCBs e outras funcionalidades disponibilizadas pelas infra-estruturas BS.

Do the most productive firms become exporters? Application of a test for the case of Portugal

Using a longitudinal database (1996-2003) at the plant level, this article aims to shed light on the proposition that most productive domestic firms self-select to export markets. Self-selection and learning by exporting are two non-mutually-exclusive theses that attempt to explain the high correlation between firms’ international trade involvement and their superior performance relative to domestic firms. In general, we find evidence of a self-selection to exports. However, there is significant heterogeneity of sales destinations, firm import status before exporting,and the specificities of the sectors firms belong to.

Cu2ZnSnS4 solar cells prepared with sulphurized dc-sputtered stacked metallic precursors

In the present work we report the details of the preparation and characterization results of Cu2ZnSnS4 (CZTS) based solar cells. The CZTS absorber was obtained by sulphurization of dc magnetron sputtered Zn/Sn/Cu precursor layers. The morphology, composition and structure of the absorber layer were studied by scanning electron microscopy, energy dispersive spectroscopy, X-ray diffraction and Raman scattering. The majority carrier type was identified via a hot point probe analysis. The hole density, space charge region width and band gap energy were estimated from the external quantum efficiency measurements. A MoS2 layer that formed during the sulphurization process was also identified and analyzed in this work. The solar cells had the following structure: soda lime glass/Mo/CZTS/CdS/i-ZnO/ZnO:Al/Al grid. The best solar cell showed an opencircuit voltage of 345 mV, a short-circuit current density of 4.42 mA/cm2, a fill factor of 44.29% and an efficiency of 0.68% under illumination in simulated standard test conditions: AM 1.5 and 100 mW/cm2.

Supporting real-time distributed computer-controlled systems with multi-hop P-NET networks

Fieldbus communication networks aim to interconnect sensors, actuators and controllers within process control applications. Therefore, they constitute the foundation upon which real-time distributed computer-controlled systems can be implemented. P-NET is a fieldbus communication standard, which uses a virtual token-passing medium-access-control mechanism. In this paper pre-run-time schedulability conditions for supporting real-time traffic with P-NET networks are established. Essentially, formulae to evaluate the upper bound of the end-to-end communication delay in P-NET messages are provided. Using this upper bound, a feasibility test is then provided to check the timing requirements for accessing remote process variables. This paper also shows how P-NET network segmentation can significantly reduce the end-to-end communication delays for messages with stringent timing requirements.

EMMON: a system architecture for large- scale, dense and real-time WSNs

In spite of the significant amount of scientific work in Wireless Sensor Networks (WSNs), there is a clear lack of effective, feasible and usable WSN system architectures that address both functional and non-functional requirements in an integrated fashion. This poster abstract outlines the EMMON system architecture for large-scale, dense, real-time embedded monitoring. EMMON relies on a hierarchical network architecture together with integrated middleware and command&control mechanisms. It has been designed to use standard commercially– available technologies, while maintaining as much flexibility as possible to meet specific applications’ requirements. The EMMON WSN architecture has been validated through extensive simulation and experimental evaluation, including through a 300+ node test-bed, the largest WSN test-bed in Europe to date

EMMON: a WSN system architecture for large scale and dense real-time embedded monitoring

Wireless sensor networks (WSNs) have attracted growing interest in the last decade as an infrastructure to support a diversity of ubiquitous computing and cyber-physical systems. However, most research work has focused on protocols or on specific applications. As a result, there remains a clear lack of effective, feasible and usable system architectures that address both functional and non-functional requirements in an integrated fashion. In this paper, we outline the EMMON system architecture for large-scale, dense, real-time embedded monitoring. EMMON provides a hierarchical communication architecture together with integrated middleware and command and control software. It has been designed to use standard commercially-available technologies, while maintaining as much flexibility as possible to meet specific applications requirements. The EMMON architecture has been validated through extensive simulation and experimental evaluation, including a 300+ node test-bed, which is, to the best of our knowledge, the largest single-site WSN test-bed in Europe to date.

H-NAMe: specifying, implementing and testing a hidden-node avoidance mechanism for wireless sensor networks

The hidden-node problem has been shown to be a major source of Quality-of-Service (QoS) degradation in Wireless Sensor Networks (WSNs) due to factors such as the limited communication range of sensor nodes, link asymmetry and the characteristics of the physical environment. In wireless contention-based Medium Access Control protocols, if two nodes that are not visible to each other transmit to a third node that is visible to the formers, there will be a collision – usually called hidden-node or blind collision. This problem greatly affects network throughput, energy-efficiency and message transfer delays, which might be particularly dramatic in large-scale WSNs. This technical report tackles the hidden-node problem in WSNs and proposes HNAMe, a simple yet efficient distributed mechanism to overcome it. H-NAMe relies on a grouping strategy that splits each cluster of a WSN into disjoint groups of non-hidden nodes and then scales to multiple clusters via a cluster grouping strategy that guarantees no transmission interference between overlapping clusters. We also show that the H-NAMe mechanism can be easily applied to the IEEE 802.15.4/ZigBee protocols with only minor add-ons and ensuring backward compatibility with the standard specifications. We demonstrate the feasibility of H-NAMe via an experimental test-bed, showing that it increases network throughput and transmission success probability up to twice the values obtained without H-NAMe. We believe that the results in this technical report will be quite useful in efficiently enabling IEEE 802.15.4/ZigBee as a WSN protocol.

A time division beacon scheduling mechanism for IEEE 802.15.4/Zigbee cluster-tree wireless sensor networks

While the IEEE 802.15.4/Zigbee protocol stack is being considered as a promising technology for low-cost low-power Wireless Sensor Networks (WSNs), several issues in the standard specifications are still open. One of those ambiguous issues is how to build a synchronized multi-hop cluster-tree network, which is quite suitable for ensuring QoS support in WSNs. In fact, the current IEEE 802.15.4/Zigbee specifications restrict the synchronization in the beacon-enabled mode (by the generation of periodic beacon frames) to star-based networks, while it supports multi-hop networking using the peer-to-peer mesh topology, but with no synchronization. Even though both specifications mention the possible use of cluster-tree topologies, which combine multihop and synchronization features, the description on how to effectively construct such a network topology is missing. This paper tackles this problem, unveils the ambiguities regarding the use of the cluster-tree topology and proposes a synchronization mechanism based on Time Division Beacon Scheduling to construct cluster-tree WSNs. We also propose a methodology for an efficient duty cycle management in each router (cluster-head) of a cluster-tree WSN that ensures the fairest use of bandwidth resources. The feasibility of the proposal is clearly demonstrated through an experimental test bed based on our own implementation of the IEEE 802.15.4/Zigbee protocol.

H-NAMe: a hidden-node avoidance mechanism for wireless sensor networks

The hidden-node problem has been shown to be a major source of Quality-of-Service (QoS) degradation in Wireless Sensor Networks (WSNs) due to factors such as the limited communication range of sensor nodes, link asymmetry and the characteristics of the physical environment. In wireless contention-based Medium Access Control protocols, if two nodes that are not visible to each other transmit to a third node that is visible to the formers, there will be a collision – usually called hidden-node or blind collision. This problem greatly affects network throughput, energy-efficiency and message transfer delays, which might be particularly dramatic in large-scale WSNs. This paper tackles the hiddennode problem in WSNs and proposes H-NAMe, a simple yet efficient distributed mechanism to overcome it. H-NAMe relies on a grouping strategy that splits each cluster of a WSN into disjoint groups of non-hidden nodes and then scales to multiple clusters via a cluster grouping strategy that guarantees no transmission interference between overlapping clusters. We also show that the H-NAMe mechanism can be easily applied to the IEEE 802.15.4/ZigBee protocols with only minor add-ons and ensuring backward compatibility with the standard specifications. We demonstrate the feasibility of H-NAMe via an experimental test-bed, showing that it increases network throughput and transmission success probability up to twice the values obtained without H-NAMe. We believe that the results in this paper will be quite useful in efficiently enabling IEEE 802.15.4/ZigBee as a WSN protocol

An IEEE 802.15.4 protocol implementation (in nesC/TinyOS): reference guide v1.0

This technical report is to provide a reference guide to the implementation of the IEEE 802.15.4 protocol in nesC/TinyOS for the MICAz motes. The implementation is provided as a tool that can be used to implement, test and evaluate the current functionalities defined in the protocol standard as well as to enable the development of functionalities not yet implemented and new add-ons to the protocol.

On the use of the ZigBee protocol for wireless sensor networks

This project was developed within the ART-WiSe framework of the IPP-HURRAY group (http://www.hurray.isep.ipp.pt), at the Polytechnic Institute of Porto (http://www.ipp.pt). The ART-WiSe – Architecture for Real-Time communications in Wireless Sensor networks – framework (http://www.hurray.isep.ipp.pt/art-wise) aims at providing new communication architectures and mechanisms to improve the timing performance of Wireless Sensor Networks (WSNs). The architecture is based on a two-tiered protocol structure, relying on existing standard communication protocols, namely IEEE 802.15.4 (Physical and Data Link Layers) and ZigBee (Network and Application Layers) for Tier 1 and IEEE 802.11 for Tier 2, which serves as a high-speed backbone for Tier 1 without energy consumption restrictions. Within this trend, an application test-bed is being developed with the objectives of implementing, assessing and validating the ART-WiSe architecture. Particularly for the ZigBee protocol case; even though there is a strong commercial lobby from the ZigBee Alliance (http://www.zigbee.org), there is neither an open source available to the community for this moment nor publications on its adequateness for larger-scale WSN applications. This project aims at fulfilling these gaps by providing: a deep analysis of the ZigBee Specification, mainly addressing the Network Layer and particularly its routing mechanisms; an identification of the ambiguities and open issues existent in the ZigBee protocol standard; the proposal of solutions to the previously referred problems; an implementation of a subset of the ZigBee Network Layer, namely the association procedure and the tree routing on our technological platform (MICAz motes, TinyOS operating system and nesC programming language) and an experimental evaluation of that routing mechanism for WSNs.

On a test-bed application for the ART-WiSe framework

This report describes the development of a Test-bed Application for the ART-WiSe Framework with the aim of providing a means of access, validate and demonstrate that architecture. The chosen application is a kind of pursuit-evasion game where a remote controlled robot, navigating through an area covered by wireless sensor network (WSN), is detected and continuously tracked by the WSN. Then a centralized control station takes the appropriate actions for a pursuit robot to chase and “capture” the intruder one. This kind of application imposes stringent timing requirements to the underlying communication infrastructure. It also involves interesting research problems in WSNs like tracking, localization, cooperation between nodes, energy concerns and mobility. Additionally, it can be easily ported into a real-world application. Surveillance or search and rescue operations are two examples where this kind of functionality can be applied. This is still a first approach on the test-bed application and this development effort will be continuously pushed forward until all the envisaged objectives for the Art-WiSe architecture become accomplished.

Mechanical and tribological characterization of TiB2 thin films

Titanium Diboride (TiB2) presents high mechanical and physical properties. Some wear studies were also carried out in order to evaluate its tribological properties. One of the most popular wear tests for thin films is the ball-cratering configuration. This work was focused on the study of the tribological properties of TiB2 thin films using micro-abrasion tests and following the BS EN 1071-6: 2007 standard. Due to high hardness usually patented by these films, diamond was selected as abrasive on micro-abrasion tests. Micro-abrasion wear tests were performed under five different durations, using the same normal load, speed rotation and ball. Films were deposited by unbalanced magnetron sputtering Physical Vapour Deposition (PVD) technique using TiB2 targets. TiB2 films were characterized using different methods as Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDS), Atomic Force Microscopy (AFM), X-ray Diffraction (XRD), Electron Probe Micro-Analyser (EPMA), Ultra Micro Hardness and Scratch-test Analysis, allowing to confirm that TiB2 presents adequate mechanical and physical properties. Ratio between hardness (coating and abrasive particles), wear resistance and wear coefficient were studied, showing that TiB2 films shows excellent properties for tribological applications.

Low-loss austempered ductile iron gears: experimental evaluation comparing materials and lubricants

An experimental study to evaluate the power dissipation of gears was performed. Three low-loss gear models were manufactured using standard 20° pressure angle tools. Austempered ductile iron (ADI) and 20MnCr5 carburized steel gears were tested in an FZG gear test machine using mineral, ester and polyalphaolephine (PAO)-based oils. The results compare power dissipation, the influence of different tooth flank geometries, materials and lubricants. This work concludes that conventional power-transmission gears can be replaced by these improved and more efficient low–loss models, which can be produced using common tools and that steel gears can be successfully replaced by austempered ductile iron gears.