• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 27
  • 10
  • 3
  • 2
  • 1
  • 1
  • Tagged with
  • 46
  • 15
  • 12
  • 9
  • 6
  • 6
  • 6
  • 6
  • 5
  • 5
  • 5
  • 5
  • 4
  • 4
  • 4
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
41

Estimativa do estado de carga de baterias em robôs móveis autônomos / Battery state of charge estimation in autonomous mobile robots

Marcelo Manoel de Oliveira 19 April 2013 (has links)
Cada vez mais robôs móveis autônomos estão sendo utilizados em diversas tarefas e em ambientes com elevado risco para atividades humanas que a paralisação de suas atividades podem gerar outros riscos, perdas e elevados custos. Assim, o estado de carga (SOC) de sistemas de baterias em robôs móveis autônomos é um parâmetro importante na prevenção de uma falha primária nessa aplicação, a ausência de energia. Este trabalho apresenta os métodos existentes na literatura para a determinação do estado de carga de baterias e as tecnologias de baterias disponíveis utilizadas em robôs móveis autônomos ou veículos autônomos guiados. A partir desses estudos foi desenvolvido um modelo de medida, baseado no modelo combinado e foram realizados testes de bancadas para levantamento dos parâmetros e características de três modelos de células de baterias: Lítio Polímero (Li-PO), Níquel-Cádmio (NiCd) e Lítio-Ferro-Polímero (LiFePO4). Com esses parâmetros, aplicou-se o método de estimativa de carga baseado na técnica do Filtro de Kalman Estendido (EKF). Através dos testes, analisou-se comparativamente a resposta do método proposto e a resposta do método OCV e a capacidade de carga real. / Autonomous mobile robots have being increasingly used in various tasks, environments and activities of high risk to human that the stoppage of its activities may generate other risks, losses and high costs. Thus the state of charge (SOC) of battery systems in autonomous mobile robots, is an important parameter to prevent a primary failure in this application, the lack of energy. The paper presents the existing methods in the literature to determine the battery state of charge and battery commercial technologies available used in an autonomous mobile robot or autonomous guided vehicle, from these studies a measurement model based on combined model was developed and testing benches for three cells models on Lithium Polymer Battery (Li-PO), Nickel Cadmium (NiCd) and lithium-iron-Polymer (LiFePO4) batteries were performed for lifting the parameters and apply the battery state of charge method based on the Extended Kalman Filter (EKF) technique. The tests were analyzed in order to observe the comparatively response of the proposed method, the OCV method and Real charge capacity.
42

Exponering av luftföroreningar : -vid arbete i hamnmagasin / Occupational exposure to air pollution : -at port warehouse

Nordgren, Susanne January 2015 (has links)
Syftet med examensarbetet var att översiktligt undersöka vilka hälsofarliga luftföroreningarsom medarbetarna vid hamnmagasinen eventuellt exponeras föroch huruvida något hygieniskt gränsvärde riskerade att överskridas samt att seom de skyddsåtgärder som vidtagits kan förbättras. Resultatet från studien visaratt det finns vissa exponeringsrisker för de som arbetar vid hamnen både frångods, dieselavgaser samt rester av gasbehandlingsmedel i containrar.Arbetsmomenten där truckföraren befinner sig inne i trucken bedöms somrelativt skyddat både från partiklar och gaser, men det finns andra arbetsuppgifterdär arbetaren inte är lika skyddad. Mätningarna av kvävedioxid visadeatt exponeringen av dieselavgaser för den medarbetare som öppnadecontainrarna inte översteg några hygieniska gränsvärden, under de dagar sommätningarna genomfördes, men var något högre än för truckföraren som satt ihytten. Huruvida exponeringen av damm från gods riskerar att utvecklas tillhälsoproblem är omöjligt att avgöra utan en grundlig riskbedömning, därdammätningar kan ge en fingervisning om hur riskfylld situationen är för desom eventuellt exponeras.Organisationen bör implementera säkrare rutiner och genomföra åtgärder sommotiverar medarbetarna att använda befintlig skyddsutrustning. Det gäller intebara för exponering av dieselavgaser och damm från lossning och lastning avgods utan även vid öppnandet av containrar där rester av gasbehandlingsmedelkan finnas kvar i containern och där några ämnen misstänkts varacancerframkallande.Slutsatser: Genomföra en grundlig riskbedömning och kartlägga möjliga hälsoriskerkring luftföroreningar. Upprätta skriftliga arbetsbeskrivningar där eventuella risker föreligger. Installera ventilation i magasinen som styrs av halten kvävedioxid för attsäkerställa att höga halter av dieselavgaser inte uppstår. Behov av motivationshöjande insatser kring säkerhetskultur ochanvändningen av skyddsutrustning. Implementera fungerande rutiner som följer lagstiftningen förhanteringen av damm och gaser som gäller för cancerframkallandeämnen. / The purpose of this thesis was to examine the risk of hazardous air pollutantsthat employees at the harbor may be exposed to and assess whether anyexposure limits might be exceeded, and to review if the security measures taken,can be improved. The results of the study show that there is some risk ofexposure for those working in the harbor from both the cargo, diesel exhaustand residues from fumigants in the containers. The operations when the truckdriver is inside the forklift is considered relatively protected from both particlesand gases, but there are other tasks where the worker is not as protected.Measurements of nitrogen dioxide showed that exposure to diesel exhaust forthe employee who opened the containers during the days that the measurementswere performed did not exceed some critical values, but was slightly higherthan for the driver who was sitting in the forklift. Whether the exposure to dust,from the cargo, constitutes a risk for health effects is impossible to determinewithout a thorough risk assessment, where measurements of dust can give anindication of how risky the situation is for the exposed workers.The organization should implement safer practices and implementing measuresthat motivates employees to use existing protective equipment. This applies notonly for exposure to diesel exhaust and dust from loading and unloading ofgoods, but also at the opening the doors on the containers in which residues offumigants, in which some are suspected to be carcinogenic, can remain in thecontainer.Conclusions: Conduct a thorough risk assessment and identify potential health riskswith air pollution. Establish written work instructions where potential hazards exist. Install ventilation in the warehouses, which is controlled by the levels ofnitrogen dioxide, to ensure that high levels of diesel exhaust does notoccur. Need to increase motivation for safety and the use of protectiveequipment. Implement procedures to comply with the legislation for the managementof dust and gases that applies to carcinogens substances.
43

Development of Methodology for Finite Element Simulation of Overhead Guard Impact Test / Utveckling av metodik för finita elementsimulering av skyddstak utsatt för fallprov

Hallén, Axel, Hjorth, Jacob January 2022 (has links)
Forklifts that are capable of lifting heavy loads and reaching high lift heights are required by stan-dards to have an overhead guard to protect the operator from falling objects. The same standardsspecify a standardized procedure for testing the strength of these overhead guards. The test in-volves dropping ten 45 kg wooden cubes and a heavy timber load onto the overhead guard. Thesedestructive tests are time-consuming and expensive, and it is the purpose of this master’s thesis todevelop a methodology for simulating this kind of test using the finite element method with a largedisplacements, explicit scheme using the solver RADIOSS by Altair. This was achieved by firstdesigning, constructing, and testing a physical prototype of an overhead guard to use as a referencefor a finite element methodology to be validated against. The work has also included tensile testingof the overhead guard material, and this was done both to obtain material data from the sametype of material as the prototype, and to get Johnson-Cook material parameters, which are hardto come by in the literature. Next, a basic finite element model was created which showed a verylarge discrepancy compared to the physical test results. An extensive investigation into aspectssurrounding finite element modeling and material modeling was undertaken, and resulted in a fi-nal model which overestimated the displacements by about 40 % only. The remaining inaccuracyis believed to mostly stem from inadequate strain-rate sensitivity data, caused by limitations inavailable resources for material testing.
44

Vätgasdrivna arbetsmaskiners tekniska mognad : Dagens etableringsmöjligheter och potentiella tillämpningar i Gävleborgs framtida vätgassamhälle

Lärkfors, Selinn, Svedlund, Carolina January 2021 (has links)
Förbränning av fossila bränslen är den största orsaken till ökade växthusgasutsläpp i atmosfären som i sin tur ligger till grund för klimatförändringarna. Europeiska Unionen uttrycker klimatförändringarna som ett existentiellt hot och har som mål att Europa ska bli en klimatneutral kontinent till år 2050. Arbetsmaskiner, som vanligtvis drivs på diesel, är ett energikrävande fordonsslag vid användning som år 2016 stod för 6 % av Sveriges totala växthusgasutsläpp. Vätgas kan vara ett alternativt drivmedel till diesel eller andra fossila drivmedel för att minska de utsläpp som arbetsmaskiner ger upphov till. Syftet med studien är att uppmärksamma arbetsmaskiners roll i en omställning till vätgasdrift samt sprida kunskap om vad en omställning skulle innebära för dagens användare av arbetsmaskiner. Detta görs genom att belysa möjlig etablering i nutid av fem utvalda vätgasdrivna arbetsmaskiner samt gestalta dem i ett framtida vätgassamhälle. De arbetsmaskiner som inkluderas i studien är hjullastare, pistmaskin, sopmaskin, traktor och motviktstruck. Metoden består av en förenklad litteraturöversyn i kombination med personlig kommunikation samt en anpassning av verktyget Technology Readiness Level (TRL) i syfte att bedöma den tekniska mognaden. Resultatet visar att det i dagsläget finns etableringsmöjligheter i olika former för samtliga arbetsmaskiner i regionen baserat på TRL. Vätgasdrivna motviktstruckar och sopmaskiner är båda tillräckligt mogna tekniker för att etableras direkt på marknaden genom inköp. Vätgasdrivna hjullastare, traktorer och pistmaskiner är fortfarande under utveckling och kan därför etableras i regionen genom forskning och ytterligare utveckling eller först efter produktlansering på marknaden. De utvalda vätgasdrivna arbetsmaskinerna kan verka i ett framtida vätgassamhälle på liknande vis som motsvarande fossildrivna arbetsmaskiner gör idag med fördelar som mindre miljöpåverkan, vibrationer och buller som i sin tur medför mindre underhållsbehov med tillhörande kostnader. Resultatet visar att det finns möjligheter redan idag att påskynda en förändring, inte bara i Gävleborg utan i hela Sverige. De utvalda arbetsmaskinerna är verksamma inom branscher som motsvarar stora delar av det svenska näringslivet, en omställning till vätgasdrift kan därför ha en stor betydelse för en nationell reducering av växthusgasutsläpp. Det finns stor potential, särskilt för aktörer inom industrin, att upprätta egen vätgasproduktion och därmed bli självförsörjande på vätgas som drivmedel till arbetsmaskiner. Detta kan bli en av de radikala förändringar som enligt EU behövs för att uppnå målet om att åstadkomma klimatneutralitet år 2050. / Burning of fossil fuels is the biggest cause of increased greenhouse gas (GHG) emissions into the atmosphere, which in turn leads to climate change. The European Union expresses climate change as an existential threat and aims to make Europe a climate-neutral continent by 2050. Non-road machinery vehicles (NMV), which are usually powered by diesel, are an energy-intensive type of vehicle during usage that in 2016 accounted for 6% of Sweden's total GHG emissions. Hydrogen can be an alternative fuel to diesel or other fossil fuels in order to reduce the emissions that originate from NMVs. The aim of this study is to draw attention to the role of NMVs in a conversion to hydrogen operation and to spread knowledge about what a conversion would mean for today's users of work machines. This is done by highlighting possible establishment in the present of five selected hydrogen powered NMVs and illustrate them in a future hydrogen society. The NMVs included in the study are wheel loaders, snow groomers, street sweepers, tractors and counterbalanced forklifts. The method consists of a simplified literature review in combination with personal communication and an adaptation of the tool Technology Readiness Level (TRL) in order to assess technical maturity. The results show that there are establishment opportunities in the present in various forms for all NMVs in Gävleborg based on TRL. Hydrogen powered counterbalanced forklifts and street sweepers are both sufficiently mature technologies to be established directly in the market through purchasing. Hydrogen powered wheel loaders, tractors and snow groomers are still under development and can therefore be established in the region through research and further development or after product launch. The selected hydrogen powered NMVs can operate in a future hydrogen society similarly to fossil-fueled NMVs but with benefits such as less environmental impact, vibrations and noise which in turn entails less maintenance needs with associated costs. There are opportunities already today to accelerate a change, not only in Gävleborg but throughout Sweden. The selected NMVs are active in industries that correspond to large parts of the Swedish business community, a transition to hydrogen operation can therefore be of great importance for a national reduction of GHG emissions. There is great potential, especially for players in the industry, to establish their own hydrogen production and thereby become self-sufficient in hydrogen intended for NMVs. This could be one of the radical changes that, according to the EU, are needed to achieve the goal of accomplishing climate-neutrality by 2050.
45

Contamination Level Detection of Hydraulic Pressure Filters in Forklifts : using only pump motor currents and load pressure measurements

Sehlstedt, Robert, Sellén, Erik January 2022 (has links)
With the advent of Industry 4.0 and the Internet of Things, collecting data on Cyber-Physical systems has become the norm practice in large scale industries. By collectingrelevant data, it is possible to monitor the health status of whole systems or specificcomponents within them. Such practices allow for historical maintenance strategies suchas reactive maintenance or preventive maintenance to be phased out.In this thesis two separate algorithms are presented, both designed to identify contaminationlevels in the hydraulic pressure filters of forklifts. Furthermore, in contrast torelevant literature for similar applications only sensory data from the hydraulic pump’smotor current and hydraulic fluid pressure at the load was used. More specifically, theproposed algorithms are based on trends observed in the relationship between the measurementsand how it changes over time. The algorithms were evaluated on data fromfour forklifts used in Toyota’s factory. The forklifts had been collecting data while usedin production for over a year.The results indicate strong evidence that both algorithms can be used to detect degradationin the hydraulic system. This is especially true for one forklift where it was knownthat the damage at the time of replacement was substantial. However, it cannot be trulyestablished without further testing whether the algorithms detect degradation in the filteror pump.
46

A deep learning based anomaly detection pipeline for battery fleets

Khongbantabam, Nabakumar Singh January 2021 (has links)
This thesis proposes a deep learning anomaly detection pipeline to detect possible anomalies during the operation of a fleet of batteries and presents its development and evaluation. The pipeline employs sensors that connect to each battery in the fleet to remotely collect real-time measurements of their operating characteristics, such as voltage, current, and temperature. The deep learning based time-series anomaly detection model was developed using Variational Autoencoder (VAE) architecture that utilizes either Long Short-Term Memory (LSTM) or, its cousin, Gated Recurrent Unit (GRU) as the encoder and the decoder networks (LSTMVAE and GRUVAE). Both variants were evaluated against three well-known conventional anomaly detection algorithms Isolation Nearest Neighbour (iNNE), Isolation Forest (iForest), and kth Nearest Neighbour (k-NN) algorithms. All five models were trained using two variations in the training dataset (full-year dataset and partial recent dataset), producing a total of 10 different model variants. The models were trained using the unsupervised method and the results were evaluated using a test dataset consisting of a few known anomaly days in the past operation of the customer’s battery fleet. The results demonstrated that k-NN and GRUVAE performed close to each other, outperforming the rest of the models with a notable margin. LSTMVAE and iForest performed moderately, while the iNNE and iForest variant trained with the full dataset, performed the worst in the evaluation. A general observation also reveals that limiting the training dataset to only a recent period produces better results nearly consistently across all models. / Detta examensarbete föreslår en pipeline för djupinlärning av avvikelser för att upptäcka möjliga anomalier under driften av en flotta av batterier och presenterar dess utveckling och utvärdering. Rörledningen använder sensorer som ansluter till varje batteri i flottan för att på distans samla in realtidsmätningar av deras driftsegenskaper, såsom spänning, ström och temperatur. Den djupinlärningsbaserade tidsserieanomalidetekteringsmodellen utvecklades med VAE-arkitektur som använder antingen LSTM eller, dess kusin, GRU som kodare och avkodarnätverk (LSTMVAE och GRU) VAE). Båda varianterna utvärderades mot tre välkända konventionella anomalidetekteringsalgoritmer -iNNE, iForest och k-NN algoritmer. Alla fem modellerna tränades med hjälp av två varianter av träningsdatauppsättningen (helårsdatauppsättning och delvis färsk datauppsättning), vilket producerade totalt 10 olika modellvarianter. Modellerna tränades med den oövervakade metoden och resultaten utvärderades med hjälp av en testdatauppsättning bestående av några kända anomalidagar under tidigare drift av kundens batteriflotta. Resultaten visade att k-NN och GRUVAE presterade nära varandra och överträffade resten av modellerna med en anmärkningsvärd marginal. LSTMVAE och iForest presterade måttligt, medan varianten iNNE och iForest tränade med hela datasetet presterade sämst i utvärderingen. En allmän observation avslöjar också att en begränsning av träningsdatauppsättningen till endast en ny period ger bättre resultat nästan konsekvent över alla modeller.

Page generated in 0.0474 seconds