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Towards clearer paths: Addressing camera obstructions in autonomous vehicles through neural networksHarvel, Nicholas J. 10 May 2024 (has links) (PDF)
This study addresses the challenge of lens obfuscations in off-road autonomous vehicles, which compromise the essential visual inputs for safe navigation. Using a tiered approach, the research employs neural network architectures for preliminary image classification, semantic segmentation, and image-to-image translation to rectify obscured visual inputs. Initial classification using MobileNetV2 sets the stage for U-Net-driven semantic segmentation to identify obfuscated regions, followed by a modified Pix-to-Pix model for image restoration. The evaluation showcases promising results in improving visual clarity, marking a significant stride towards enhancing autonomous vehicle operational robustness in off-road environments. This work lays a foundation for future explorations into advanced neural network architectures for real-time implementations in off-road terrains.
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Real-time measurement of on-road fine particulate matter in AtlantaPapier, Mark Elliot 01 April 2008 (has links)
Particulate matter is increasingly linked to health effects not only for what was previously thought to be just a respiratory problem, but also for the cardiovascular system. Literature not only supports that high particulate matter over long periods of time is correlated to morbidity and mortality due to both cardiovascular and respiratory means, but that high levels of particulate matter, even in short bursts of high concentrations, may be the triggering mechanism for the onset of such problems. Due to automobiles being a prime source of particulate matter, roadway concentrations are often higher than those measured at off-road measurement sites run by various parts of the United States Government. Furthermore, the government run sites are averaged over timescales at a minimum of an hour and at a maximum of a running three-day twenty-four hour length. These are both so long that mesoscale information about the particulate matter, such as short duration high intensity bursts, would be completely removed from the dataset. This study utilizes a real-time portable instrumentation package, which can effectively measure particulate matter concentrations on the roadways of metro Atlanta. Measurements are taken both inside the cabin of a vehicle, which does have an in-cabin filtration system, and on a bicycle ridden along the streets without any form of filtration. These instruments, specifically calibrated handheld particle counters, did indeed find some spikes of particulates above the government s one-hour averages inside the cabin of a vehicle. Arguably more importantly, while riding a bicycle these handheld particle counters also found spikes of particulates approaching six times the amount monitored by the government sites, and several roadway averages that were higher than the off-road averages for the same time.
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Eyes on the Road! : Off-Road Glance Durations when Performing Tasks on In-Vehicle Systems while Driving in a SimulatorWahlberg, Linnea January 2013 (has links)
The 85th percentile off-road glances while performing three tasks on an in-vehicle system while driving in a simulator was investigated. The tasks were a radio task, a telephone task and a sound settings task which were performed at three occasions each. The distribution of 85th percentile off-road glance durations for each subject and task showed that durations differed between individuals rather than between tasks. It also turned out that durations longer than 2.00 seconds were not rare and 2 of 16 subjects had durations longer than 2.00 seconds in the radio task. Even though the distribution showed small differences between tasks on an individual level, differences on a group level were found between the tasks. A tendency of a learning effect was found, which implied a decrease in 85th percentile off-road glance durations as the tasks were performed at several occasions. A tendency of a floor effect in 85th percentile off-road glance durations, when the subjects are familiarized with tasks, was also found. Performance on a computerized trail-making test, measuring ability of visual search, motor speed and mental flexibility, was found not to be related with 85th percentile off-road glance durations.
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Multi-objective optimization and performance evaluation of active, semi-active and passive suspensions for forestry machines / Flermålsoptimering och utvärdering av prestandan hos aktiva, semi-aktiva och passiva fjädringssystem för skogsmaskinerBaez, Federico January 2014 (has links)
The development of forestry machines is currently heading towards new solutions that reduce their impact on the environment and in particular on the soft forest soil in which the machines operate. The terrain conditions that forestry machines encounter in their regular duties can be very rough, and if the vehicle-ground interaction is not properly controlled cumulative damage can progressively aggravate these conditions and potentially render a route or a zone impracticable, apart from causing a detrimental effect in the forest environment. In addition, new machine solutions must be considerably less damaging, both physically and mentally, to operators. There are certain imposed limits to the whole body vibrations to which industrial workers are exposed daily, which are very hard to fulfil in the context of wood harvesting operations with the current technological state of the machines. Chassis-suspended solutions in the market of forestry vehicles are practically inexistent. Multiple wheeled tracks and/or bogies are current solutions that improve dynamic performance and ground contact area of forestry vehicles, but they do not include suspension elements. Cab and seat suspensions are also used to reduce whole body vibrations, but they are only effective up to a certain degree, due to their relatively short stroke length and directional limitations. The implementation of chassis suspensions in forestry machines is therefore a very interesting open area of research in forestry technology. In this context the XT28, a forwarder prototype with active pendulum arm suspension, is currently being developed by Extractor AB in collaboration with Skogforsk; the Forestry Research Institute of Sweden. The present project focuses in analysis and comparison of the performance that active, semi-active and passive suspension systems with pendulum arm architecture would present, by studying their application in the XT28 machine. These systems have the potential to significantly improve forestry vehicle performance in terms of terrain friendliness and whole body vibrations over an unsuspended system. The task is carried out with the help of Multi-Body Dynamics simulation software along with other simulation and computational tools. Additionally, a general method to optimize and analyse forestry vehicle suspension performance is proposed and applied to the case of the XT28, which provides a fair and standardized way to compare the performance of the different suspensions. Keywords: Forestry machine, suspension, multi-objective optimization, forwarder, pendulum arm, active, semi-active, passive, XT28, Multibody Dynamics, soil-friendly, off-road. / Utvecklingen av skogsmaskiner är för närvarande på väg mot nya lösningar som minskar deras påverkan på miljön och i synnerhet på mjuk skogsmark. Skogsmaskinerna verkar ofta i mycket oländig och ojämn terräng, och om interaktionen mellan fordon och mark är alltför okontrollerad, så kan interaktionen ge upphov till kumulativa markskador som gradvis förvärras efter flera passager och eventuellt göra en rutt eller en zon oframkomlig, bortsett från att de orsaka skador på skogsmiljön. Dessutom måste nya maskinlösningar vara skonsammare, både fysiskt och mentalt, för förarna. Det finns nya gränser för maximala helkroppsvibrationer och maximala dagliga vibrationsdoser, som är mycket svåra att uppfylla vid skogsavverkning med dagens skogsmaskinsteknik. Chassidämpade lösningar är praktiskt taget obefintliga på dagens skogsmaskiner. Band och/eller boggier är aktuella lösningar som i viss mån förbättrar maskinernas dynamisk interaktion med marken, men de innehåller inga dämpelement, utan det är enbart däckens flexibilitet som ger maskinen en dämpfunktion. Hytt-och stolsdämpning används också för att minska helkroppsvibrationer, men de är endast effektiva till en viss grad, på grund av deras relativt korta slaglängd och riktningsbegränsningar. Införande av chassidämpning för skogsmaskiner är därför ett mycket intressant skogstekniskt forskningsområde. För närvarande utvecklas en skotare med aktivt dämpade pendelarmar av Extractor AB i samarbete med Skogforsk. Maskinen går under beteckningen XT28. Detta projekt fokuserar på att analysera och jämföra prestandan hos aktivt, semi-aktivt och passivt dämpade pendelarmlösningar, genom att implementera dessa i XT28-maskinen. Dessa system har potential att avsevärt förbättra skogsmaskinernas framkomlighet i oländig terräng och att minska helkroppsvibrationerna, jämfört med ofjädrade system. Uppgiften genomförs med hjälp av dynamiksimuleringsprogram i kombination med andra simulerings- och beräkningsverktyg. Dessutom föreslås en generell metodik för att optimera och analysera prestandan hos chassidämpningslösningar för skogsmaskiner. Metodiken tillämpas sedan på en XT28, som då, i detta fall, får fungera som en demonstrator för att jämföra prestandan hos olika chassidämplösningar. Nyckelord: Skogsmaskin, fjädring, optimering, skotare, pendelarm, aktiv, semi-aktiv, passiv, XT28, flerkroppsdynamik, markvänlig, off-road.
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Navegação de veículos autônomos em ambientes externos não estruturados baseada em visão computacional / Autonomous vehicles navigation on external unstructured terrains based in computer visionKlaser, Rafael Luiz 06 June 2014 (has links)
Este trabalho apresenta um sistema de navegação autônoma para veículos terrestres com foco em ambientes não estruturados, tendo como principal meta aplicações em campos abertos com vegetação esparsa e em cenário agrícola. É aplicada visão computacional como sistema de percepção principal utilizando uma câmera estéreo em um veículo com modelo cinemático de Ackermann. A navegação é executada de forma deliberativa por um planejador baseado em malha de estados sobre um mapa de custos e localização por odometria e GPS. O mapa de custos é obtido através de um modelo de ocupação probabilístico desenvolvido fazendo uso de uma OctoMap. É descrito um modelo sensorial para atualizar esta OctoMap a partir da informação espacial proveniente de nuvens de pontos obtidas a partir do método de visão estéreo. Os pontos são segmentados e filtrados levando em consideração os ruídos inerentes da aquisição de imagens e do processo de cálculo de disparidade para obter a distância dos pontos. Os testes foram executados em ambiente de simulação, permitindo a replicação e repetição dos experimentos. A modelagem do veículo foi descrita para o simulador físico Gazebo de acordo com a plataforma real CaRINA I (veículo elétrico automatizado do LRM-ICMC/USP), levando-se em consideração o modelo cinemático e as limitações deste veículo. O desenvolvimento foi baseado no ROS (Robot Operating System) sendo utilizada a arquitetura básica de navegação deste framework a partir da customização dos seus componentes. Foi executada a validação do sistema no ambiente real em cenários com terreno irregular e obstáculos diversos. O sistema apresentou um desempenho satisfatório tendo em vista a utilização de uma abordagem baseada em apenas uma câmera estéreo. Nesta dissertação são apresentados os principais componentes de um sistema de navegação autônoma e as etapas necessárias para a sua concepção, assim como resultados de experimentos simulados e com o uso de um veículo autônomo real / This work presents a system for autonomous vehicle navigation focusing on unstructured environments, with the primary goal applications in open fields with sparse vegetation, unstructured environments and agricultural scenario. Computer vision is applied as the main perception system using a stereo camera in a car-like vehicle with Ackermann kinematic model. Navigation is performed deliberatively using a path planner based on a lattice state space over a cost map with localization by odometry and GPS. The cost map is obtained through a probabilistic occupation model developed making use of an OctoMap. It is described a sensor model to update the spatial occupancy information of the OctoMap from a point cloud obtained by stereo vision. The points are segmented and filtered taking into account the noise inherent in the image acquisition and calculation of disparity to obtain the distance from points. Tests are performed in simulation, allowing replication and repetition of experiments. The modeling of the vehicle is described to be used in the Gazebo physics simulator in accordance with the real platform CaRINA I (LRM-ICMC/USP automated electrical vehicle) taking into account the kinematic model and the limitations of this vehicle. The development is based on ROS (Robot Operating System) and its basic navigation architecture is customized. System validation is performed on real environment in scenarios with different obstacles and uneven terrain. The system shows satisfactory performance considering a simple configuration and an approach based on only one stereo camera. This dissertation presents the main components of an autonomous navigation system and the necessary steps for its conception as well as results of experiments in simulated and using a real autonomous vehicle
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Flexible multibody dynamics approach for tire dynamics simulationYamashita, Hiroki 01 December 2016 (has links)
The objective of this study is to develop a high-fidelity physics-based flexible tire model that can be fully integrated into multibody dynamics computer algorithms for use in on-road and off-road vehicle dynamics simulation without ad-hoc co-simulation techniques. Despite the fact detailed finite element tire models using explicit finite element software have been widely utilized for structural design of tires by tire manufactures, it is recognized in the tire industry that existing state-of-the-art explicit finite element tire models are not capable of predicting the transient tire force characteristics accurately under severe vehicle maneuvering conditions due to the numerical instability that is essentially inevitable for explicit finite element procedures for severe loading scenarios and the lack of transient (dynamic) tire friction model suited for FE tire models. Furthermore, to integrate the deformable tire models into multibody full vehicle simulation, co-simulation technique could be an option for commercial software. However, there exist various challenges in co-simulation for the transient vehicle maneuvering simulation in terms of numerical stability and computational efficiency. The transient tire dynamics involves rapid changes in contact forces due to the abrupt braking and steering input, thus use of co-simulation requires very small step size to ensure the numerical stability and energy balance between two separate simulation using different solvers.
In order to address these essential and challenging issues on the high-fidelity flexible tire model suited for multibody vehicle dynamics simulation, a physics-based tire model using the flexible multibody dynamics approach is proposed in this study. To this end, a continuum mechanics based shear deformable laminated composite shell element is developed based on the finite element absolute nodal coordinate formulation for modeling the complex fiber reinforced rubber tire structure. The assumed natural strain (ANS) and enhanced assumed strain (EAS) approaches are introduced for alleviating element lockings exhibited in the element. Use of the concept of the absolute nodal coordinate formulation leads to various advantages for tire dynamics simulation in that (1) constant mass matrix can be obtained for fully nonlinear dynamics simulation; (2) exact modeling of rigid body motion is ensured when strains are zero; and (3) non-incremental solution procedure utilized in the general multibody dynamics computer algorithm can be directly applied without specialized updating schemes for finite rotations. Using the proposed shear deformable laminated composite shell element, a physics-based flexible tire model is developed. To account for the transient tire friction characteristics including the friction-induced hysteresis that appears in severe maneuvering conditions, the distributed parameter LuGre tire friction model is integrated into the flexible tire model. To this end, the contact patch predicted by the structural tire model is discretized into small strips across the tire width, and then each strip is further discretized into small elements to convert the partial differential equations of the LuGre tire friction model to the set of first-order ordinary differential equations. By doing so, the structural deformation of the flexible tire model and the LuGre tire friction force model are dynamically coupled in the final form of the equations, and these equations are integrated simultaneously forward in time at every time step.
Furthermore, a systematic and automated procedure for parameter identification of LuGre tire friction model is developed. Since several fitting parameters are introduced to account for the nonlinear friction characteristics, the correlation of the model parameters with physical quantities are not clear, making the parameter identification of the LuGre tire friction model difficult. In the procedure developed in this study, friction parameters in terms of slip-dependent friction characteristics and adhesion parameter are estimated separately, and then all the parameters are identified using the nonlinear least squares fitting. Furthermore, the modified friction characteristic curve function is proposed for wet road conditions, in which the linear decay in friction is exhibited in the large slip velocity range. It is shown that use of the proposed numerical procedure leads to an accurate prediction of the LuGre model parameters for measured tire force characteristics under various loading and speed conditions. Furthermore, the fundamental tire properties including the load-deflection curve, the contact patch lengths, contact pressure distributions, and natural frequencies are validated against the test data. Several numerical examples for hard braking and cornering simulation are presented to demonstrate capabilities of the physics-based flexible tire model developed in this study.
Finally, the physics-based flexible tire model is further extended for application to off-road mobility simulation. To this end, a locking-free 9-node brick element with the curvature coordinates at the center node is developed and justified for use in modeling a continuum soil with the capped Drucker-Prager failure criterion. Multiplicative finite strain plasticity theory is utilized to consider the large soil deformation exhibited in the tire/soil interaction simulation. In order to identify soil parameters including cohesion and friction angle, the triaxial soil test is conducted. Using the soil parameters identified including the plastic hardening parameters by the compression soil test, the continuum soil model developed is validated against the test data. Use of the high-fidelity physics-based tire/soil simulation model in off-road mobility simulation, however, leads to a very large computational model to consider a wide area of terrains. Thus, the computational cost dramatically increases as the size of the soil model increases. To address this issue, the component soil model is proposed such that soil elements far behind the tire can be removed from the equations of motion sequentially, and then new soil elements are added to the portion that the tire is heading to. That is, the soil behavior only in the vicinity of the rolling tire is solved in order to reduce the overall model dimensionality associated with the finite element soil model. It is shown that use of the component soil model leads to a significant reduction in computational time while ensuring the accuracy, making the use of the physics-based deformable tire/soil simulation capability feasible in off-road mobility simulation.
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Evaluation of Roadside Collisions with Utility Poles and Trees at Intersection LocationsMattox, Todd Berry 15 November 2007 (has links)
The United States averages 40,000 traffic fatalities annually. The American Association of State Highway and Transportation Officials (AASHTO) Roadside Design Guide cites run-off-the-road crashes as contributing greatly to this statistic, with about one-third of all traffic deaths [1]. This number has remained relatively constant over the past four decades, and despite a major increase in vehicle miles traveled (VMT), the rate of fatalities per 100 million vehicle miles traveled has declined. However, this relatively large number of run-off-the-road crashes should remain a major concern in all roadway design.
The Highway Safety Act of 1966 marks a defining moment in the history of roadside safety [ ]. Before this point, roadways were only designed for motorists who remained on the roadway, with no regard for driver error. As there was no legislation or guidelines concerning roadside design, roadways constructed prior to 1966 are littered with fixed objects directly off of the edge of pavement. Fortunately, many of these roads have reached their thirty year design lives and have become candidates for improvement.
The following report examines roadside crashes on nine Atlanta urban arterial roadways. Accident type, severity, and location for all crashes on these were evaluated. It is found roadside collisions with utility poles and trees were more prone to occur at intersection locations than midblock locations. Also for the studied roadway corridors, on average, roadside collisions were more likely to result in serious injury or fatality. Based on these findings initial recommendations are offer for improving clear zone requirements.
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Styrning och nödbroms av ModuLithAttervall, Sebastian, Gustafsson, Nichlas January 2008 (has links)
<p>The purpose of this project is to get a fully functional, automatic steering system and a variable breaking system with an emergency breaking function to an off road vehicle. This off road vehicle is supposed to work as an aid in military situations. A team of two, Sebastian Attervall and Nichlas Gustafsson, got an order from Jonas Nyårds and the PreeRunners Project to construct a steering system that could manoeuvre an off road vehicle without any human involvement. To make this possible the vehicle would be guided by onboard sensors, cameras and computers. The team where also assigned to construct an automatic breaking system, there also no human would be involved. The breaking system should as well contain an emergency stop function to prevent any accidents. The team has solved the problems assigned by using theories by David G. Ullman. The system that was eventually chosen was a steering system containing a 48V, 250W DC motor. A planetary gear where chosen to increase the torque from the engine. To translate the torque from the planetary gear to the steering bar a chain with chainwheel where chosen, this because the chain and chainwheel could withstand the immense forces acting on the chain. Between the planetary gear and the chainwheel a skid clutch is placed to prevent destruction on the planetary gear due to overload. The whole steering system is monitored by two rotary encoders, one placed on the engine and one placed on the steering bar. The breaking system eventually chosen where a system build on the existing drum brakes, placed in the front. To make the system independent from any human interference a system containing a linear motor, an electromagnet and a spring where chosen. The system works by letting the spring act on the wire from the existing drum breaks. The spring is always compressed so a force will always act on the wire when the system is at rest. By compressing the spring further the force acting on the wire will decrease and by compressing it enough the breaks will be released. The force compressing the spring will come from the linear motor. And to make the system failsafe in case of an emergency an electromagnet will be placed between the linear motor and the spring. When the power is cut to the electromagnet the compressed spring will be released and the drum breaks will break. The breaking system as well will be supervised by encoders and in this case linear encoders.</p> / <p>Syftet med detta projekt är att få ett fungerande automatiskt styrsystem och en variabel broms med nödbromsfunktion till en fyrhjuling som ska bli ett hjälpmedel i militära situationer. En projektgrupp bestående av Sebastian Attervall och Nichlas Gustafsson fick i uppgift av beställare Jonas Nygårds att ta fram ett system som ska kunna manövrera en fyrhjuling utan att en människa är inblandad. På detta vis ska den fungera helt automatiskt med hjälp av sensorer, kameror och datorer. Projektgruppen fick även i uppgift att ta fram en broms som ska kunna fungera utan inblandning av en människa. Den ska även kunna fungera som en nödbroms om systemet skulle strejka. Projektgruppen har löst de uppgifter som de har blivit tilldelade med hjälp av David G. Ullmans konstruktionsmetodik. Det system som tillslut valdes åt styrenheten blev ett system där momentet som vrider styrstången skapas med hjälp av en DC motor på 48 V och 250 W. Efter motorn sätts en planetväxel för att öka momentet. Som överföring av momentet från planetväxeln till styrstången används kedjedrift, detta på grund av att kedjan klarar av att ta upp de krafter som uppstår. En slirkoppling finns även med mellan planetväxeln och kedjedriften för att inte motorn och planetväxeln ska ta stryk vid överbelastning. Hela detta system övervakas med rotationsgivare vid motorn och styrstången så att inget fel uppstår. Konstruktionen för bromsen blev tillslut en lösning där de befintliga trumbromsarna på framhjulen används. För att bromsen ska kunna fungera utan inblandning av en människa har projektgruppen valt ett system bestående av ett linjärt ställdon, en elektromagnet och en fjäder. Systemet fungerar på så sätt att fjädern trycks ihop och en kraft uppstår. Denna kraft kommer att spänna bromsvajern så trumbromsen låser sig. Men för att inte trumbromsen ska ligga i hela tiden valde projektgruppen att använda sig av ett ställdon för att trycka ihop fjädern ytterligare så att vajern slaknar och bromskraften försvinner. För att nödbromsfunktionen ska fungera sattes en elektromagnet mellan ställdonet och fjädern. Om fyrhjulingen skulle bli strömlös släpper elektromagneten och fjädern drar åt bromsvajern. Även detta system kommer att övervakas av givare och i detta fall av en linjärgivare.</p>
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Modeling Roadside Safety Hazards to Predict Annual Crash Cost to Encroaching Vehicles in Rural Road NetworksDelgado, Isidro 01 January 2011 (has links)
Roadside crashes account for a large portion of total fatal crashes that occur annually in the United States. About 30% of those fatalities are the result of single vehicle run-off-road crashes. A large proportion of these fatal crashes occur in rural roads when vehicles depart from the travel lane and collide with trees or other roadside safety hazards. Many of these run-off-road accidents occur in local roads that carry traffic volumes between 1,000 and 20,000 vehicles per day. Many of these roads are part of the jurisdiction of county authorities faced with the dilemma of having too many "potentially dangerous" sites and lacking a methodology for assessing their risk to rank them accordingly; and to apply the limited resources to the ones that will bring the greatest benefit to society. This situation describes the case in Hillsborough County, Florida, in 2004 when they contracted a study with the Transportation Program of the Department of Civil and Environmental Engineering of the University of South Florida. The initial scope was to develop a methodology to assess the potential risk for each of 19 sites in a given list to prioritize further studies. The project was sponsored by the Engineering Division, Public Works Department, of Hillsborough County. The methodology developed considered the roadside safety hazards at each location and it was based on the use of the Road Safety Analysis Program (RSAP) software distributed as part of the 2002 AASHTO's Roadside Design Guide. This dissertation presents a further development of this approach: it continues to use the probabilistic approach built into RSAP to calculate the annual crash cost of each roadside safety hazard at 45 study segments. It then obtains regression models to predict that annual crash cost, as computed by RSAP, based on
roadway and traffic characteristics as well as on the nature, location and physical dimensions of the roadside safety hazard. For each study segment, the annual crash cost of each feature (as estimated with the models developed) is added for a final comparison with the RSAP Annual Crash Cost. A coefficient of determination (R2) of 0.80 was obtained. The models developed were finally used to replicate the original 2005 study for Hillsborough County. Although there were minor variations on the risk index originally computed, the ranking of the 19 study sites remained basically the same with a clear cut indication of the sites that should be considered for further engineering studies.
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Styrning och nödbroms av ModuLithAttervall, Sebastian, Gustafsson, Nichlas January 2008 (has links)
The purpose of this project is to get a fully functional, automatic steering system and a variable breaking system with an emergency breaking function to an off road vehicle. This off road vehicle is supposed to work as an aid in military situations. A team of two, Sebastian Attervall and Nichlas Gustafsson, got an order from Jonas Nyårds and the PreeRunners Project to construct a steering system that could manoeuvre an off road vehicle without any human involvement. To make this possible the vehicle would be guided by onboard sensors, cameras and computers. The team where also assigned to construct an automatic breaking system, there also no human would be involved. The breaking system should as well contain an emergency stop function to prevent any accidents. The team has solved the problems assigned by using theories by David G. Ullman. The system that was eventually chosen was a steering system containing a 48V, 250W DC motor. A planetary gear where chosen to increase the torque from the engine. To translate the torque from the planetary gear to the steering bar a chain with chainwheel where chosen, this because the chain and chainwheel could withstand the immense forces acting on the chain. Between the planetary gear and the chainwheel a skid clutch is placed to prevent destruction on the planetary gear due to overload. The whole steering system is monitored by two rotary encoders, one placed on the engine and one placed on the steering bar. The breaking system eventually chosen where a system build on the existing drum brakes, placed in the front. To make the system independent from any human interference a system containing a linear motor, an electromagnet and a spring where chosen. The system works by letting the spring act on the wire from the existing drum breaks. The spring is always compressed so a force will always act on the wire when the system is at rest. By compressing the spring further the force acting on the wire will decrease and by compressing it enough the breaks will be released. The force compressing the spring will come from the linear motor. And to make the system failsafe in case of an emergency an electromagnet will be placed between the linear motor and the spring. When the power is cut to the electromagnet the compressed spring will be released and the drum breaks will break. The breaking system as well will be supervised by encoders and in this case linear encoders. / Syftet med detta projekt är att få ett fungerande automatiskt styrsystem och en variabel broms med nödbromsfunktion till en fyrhjuling som ska bli ett hjälpmedel i militära situationer. En projektgrupp bestående av Sebastian Attervall och Nichlas Gustafsson fick i uppgift av beställare Jonas Nygårds att ta fram ett system som ska kunna manövrera en fyrhjuling utan att en människa är inblandad. På detta vis ska den fungera helt automatiskt med hjälp av sensorer, kameror och datorer. Projektgruppen fick även i uppgift att ta fram en broms som ska kunna fungera utan inblandning av en människa. Den ska även kunna fungera som en nödbroms om systemet skulle strejka. Projektgruppen har löst de uppgifter som de har blivit tilldelade med hjälp av David G. Ullmans konstruktionsmetodik. Det system som tillslut valdes åt styrenheten blev ett system där momentet som vrider styrstången skapas med hjälp av en DC motor på 48 V och 250 W. Efter motorn sätts en planetväxel för att öka momentet. Som överföring av momentet från planetväxeln till styrstången används kedjedrift, detta på grund av att kedjan klarar av att ta upp de krafter som uppstår. En slirkoppling finns även med mellan planetväxeln och kedjedriften för att inte motorn och planetväxeln ska ta stryk vid överbelastning. Hela detta system övervakas med rotationsgivare vid motorn och styrstången så att inget fel uppstår. Konstruktionen för bromsen blev tillslut en lösning där de befintliga trumbromsarna på framhjulen används. För att bromsen ska kunna fungera utan inblandning av en människa har projektgruppen valt ett system bestående av ett linjärt ställdon, en elektromagnet och en fjäder. Systemet fungerar på så sätt att fjädern trycks ihop och en kraft uppstår. Denna kraft kommer att spänna bromsvajern så trumbromsen låser sig. Men för att inte trumbromsen ska ligga i hela tiden valde projektgruppen att använda sig av ett ställdon för att trycka ihop fjädern ytterligare så att vajern slaknar och bromskraften försvinner. För att nödbromsfunktionen ska fungera sattes en elektromagnet mellan ställdonet och fjädern. Om fyrhjulingen skulle bli strömlös släpper elektromagneten och fjädern drar åt bromsvajern. Även detta system kommer att övervakas av givare och i detta fall av en linjärgivare.
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