1,720,976 research outputs found
On the Benefits of Torque Vectoring for Automated Collision Avoidance at the Limits of Handling
Full text linkThis paper presents a novel approach integrating motion replanning, path tracking and vehicle stability for collision avoidance using nonlinear Model Predictive Contouring Control. Employing torque vectoring capabilities, the proposed controller is able to stabilise the vehicle in evasive manoeuvres at the limit of handling. A nonlinear double-track vehicle model, together with an extended Fiala tyre model, is used to capture the nonlinear coupled longitudinal and lateral dynamics. The optimised control inputs are the steering angle and the four longitudinal wheel forces to minimise the tracking error in safe situations and maximise the vehicle-to-obstacle distance in emergency manoeuvres. These optimised longitudinal forces generate an additional direct yaw moment, enhancing the vehicle's lateral agility and aiding in obstacle avoidance and stability maintenance. The longitudinal tyre forces are constrained using the tyre friction cycle. The proposed controller has been tested on rapid prototyping hardware to prove real-time capability. In a high-fidelity simulation environment validated with experimental data, our proposed approach successfully avoids obstacles and maintains vehicle stability. It outperforms two baseline controllers: one without torque vectoring and another one without collision avoidance prioritisation. Furthermore, we demonstrate the robustness of the proposed approach to vehicle parameter variations, road friction, perception, and localisation errors. The influence of each variation is statistically assessed to evaluate its impact on the performance, providing guidelines for future controller design
State Estimation for a Tractor Semi-trailer System using a Minimum-Energy Filter
Full text linkIn this article we apply a second-order minimum-energy filter based on Lie groups to the problem of parking a truck with a semi-trailer in a docking station. The use of the filter, that exploits the geometry of Lie groups to estimate the truck and trailer pose, is useful to improve the precision of the state and thus perform better controls. We consider two different types of measurements: the first consists of GPS-like devices that detect the positions of the front wheels of the truck and the rear wheels of the trailer, and the second improves the measurement of the rear wheels with the measurement of the pose of the trailer with a LIDAR sensor. The accuracy of the LIDAR is useful for having a better estimate when parking in reverse. We show two simulations with two different datasets
Longitudinal control for heterogeneous vehicle platooning with uncertain dynamics: Vehicle Platooning
No full textThe work presented in this report focuses on longitudinal control of heterogeneous platoon. Firstly, merging maneuver is looked upon, considering heterogeneity in the vehicles i.e. considering different dynamics for the vehicles involved. Then heterogeneity in platoon, arising from the difference in potential limits of the vehicles is taken into account, which the current literature fails to address. The uncertain/heterogeneous dynamics are addressed through the difference in the engine driveline constant, which differs for different vehicles and keeps on changing during operation. The heterogeneity is tackled by using Adaptive control, which adapts to the changing dynamics and estimates the uncertainty to act accordingly. Adaptive strategies for formation keeping in platoons of automated vehicles have been recently proposed; while these strategies are able to cope with uncertain vehicle parameters, they have the drawback of handling only acyclic graphs (e.g. look-ahead topology). This prevents from enhancing formation keeping protocols with more complex platooning maneuvers such as synchronized merging/splitting. This work proposes an adaptive strategy for performing synchronized merging maneuvers in the presence of uncertain vehicle parameters: during these maneuvers, a cyclic communication graph is instantiated, which must be handled in a suitable way. The strategy is framed as a synchronization protocol with a set of adaptive control laws, designed via Lyapunov stability theory. A benchmark scenario in which two platoons formed in different lanes are required to merge, (e.g. due to a lane closure because of roadworks) is presented to show the effectiveness of the proposed strategy. The approach is proven to be scalable to platoons with arbitrary number of vehicles. In later part of the work, a method is proposed which takes the limits of the vehicles into consideration, to make the platooning realistic. An adaptive platooning strategy is used so as the vehicles can adaptively synchronize to desired reference dynamics. In order to handle engine limits, a mechanism is proposed based on making the reference dynamics `not too demanding', by properly saturating their control action. Such saturation action will allow all vehicles in the platoon to remain in their engine potential limits throughout. Another problem that affects the stability of the platoon is that, any perturbations or disturbance in the platoon leaves the vehicle scattered if the vehicles are already running at their potential limits. This work proposes an adaptive platooning method with bi-directional interaction and a mechanism coping with engine constraints. The bi-directional interaction allows the vehicle to not only look at the error in spacing from the preceding vehicle (vehicle in front) but also the succeeding vehicle, this makes the vehicle's control action (acceleration) depend on both front and back errors, the vehicle can thus slow down for the following vehicle if it lags behind. The bi-directional strategy developed is then proved string stable, which the literature struggles to establish with the already developed bi-directional strategies. Simulations are then conducted to validate the theoretical analysis and show the effectiveness of the method in retaining cohesiveness of the platoon. The simulations include a merging maneuver to check the effectiveness of merging with synchronized cyclic communication. For the engine potential limits, the firstly state of the art algorithm's simulation is run which is then compared to the performance of the proposed algorithm. Finally, to check the effectiveness of bi-directional CACC strategy simulations for a specific case is run for both uni-directional and bi-directional strategies proposed in the thesis and are then compared, showing the advantage of using bi-directional CACC strategy over uni-directional
Control of a Scaled Vehicle in and Beyond Stable Limit Handling
No full textIn this research a controller is developed that can control path-tracking both within and beyond stable limit handling. A controller is developed, based on the equations of motion of the nonlinear bicycle model. The performance of the controller is evaluated in both simulation and on a 1/10 scale radio controlled car. The controller is able to track a path in typical cornering conditions and let the vehicle enter and maintain a drift while remaining close to the desired path.Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Cognitive Robotic
Modelling and Control of a Scaled Car In and Beyond Stable Limit Handling
No full textOver the past century, cars have become the most important means of transportation. With the increasing number of vehicles on the road, safety has become an important topic. The introduction of driver assistance systems, like Electronic Stability Control, has led to a significant decrease in fatal accidents. By preventing the vehicle from entering unstable behaviour, it remains controllable for the average driver. In rally racing, though, unstable manoeuvres, like drifting, are widely used for improved agility on low friction surfaces and in sharp corners. The average driver, however, is unable to perform such a manoeuvre safely.With the development of autonomous driving systems, steps are taken to increase driver safety by removing the effects of human error. By taking over full control of the vehicle, these systems do not need to consider the driving skills of the average driver. Furthermore, the driving skills of the autonomous driving system are a result of its design. The autonomous driving system could, therefore, be designed to use advanced driver techniques, like drifting, to increase the safety of the passengers and other road users.The objective of this research is to develop a vehicle controller that is capable of path-tracking within and beyond the limits of stable handling. To reduce the costs of testing, the controller is developed for an experimental platform in the form of a 1/10 scale radio controlled car. A nonlinear vehicle model of the scaled vehicle is developed and analysed regarding unstable vehicle behaviour. Since the behaviour and actuation of a vehicle differ in typical cornering and limit handling conditions, two separate controllers are used. In typical cornering conditions, a steering controller is used for path-tracking. Beyond stable limit handling, the lateral motion is actuated by both the steering angle and throttle input. A drift controller is used to determine the appropriate actuator inputs to sustain the drift, based on the yaw rate and direction of motion. The main contribution of this research is an extension of that controller to add path-tracking capabilities. Simulation analysis shows the controller can enter and sustain a drift, while successfully tracking the given path. Implementation of the controller in the scaled car shows great path-tracking performance in typical cornering conditions. Furthermore, the controller is able to, on command, make the vehicle enter sustain a drift
Lyapunov Stable Path Planning and Control for Autonomous Vehicles
No full textIn modern society cars are one of the most important means of transportation. Unfortunately, many people die in car accidents around the world. Research shows that the number of fatal casualties in car accidents has been increasing for the past decade and that the largest cause of these accidents is the human driver. For this reason, research on fully autonomous vehicles has gained a lot of attention. However, currently autonomous driving is only implemented to reduce the errors of human drivers. More research is necessary in order for fully autonomous vehicles to be implemented and to remove the human driver completely. A robust navigation algorithm which is able to run in real time is one of the challenges in development of fully autonomous vehicles. Important topics in navigation of autonomous vehicles include the path planner and the motion controller. The path planner finds a path for the vehicle from its current location to the target location. At the same time the path planner avoids obstacles and fulfills the non-holonomic constraints of the autonomous vehicle. The motion controller tries to follow the path the path planner made as close as possible by controlling the vehicle. These two topics influence each other and are therefore dependent. In literature little research is done on integrated algorithms that combine path planning and motion control. Therefore, this thesis will research navigation of autonomous vehicles by using an integrated algorithm that includes both path planning and motion control. The objective of this thesis is to develop a Lyapunov stable control algorithm that is capable of planning a path for all possible vehicle maneuvers. Besides path planning the proposed algorithm must be capable of controlling the vehicle along this path. Furthermore, the algorithm needs to include obstacles and the non-holonomic dynamics of an autonomous vehicle. The main contribution of this thesis is an integrated path planner and motion controller for navigation of autonomous vehicles. The stability of the proposed algorithm is proven by using the Lyapunov method. Simulation results prove that the algorithm is capable of planning the path and the motion of the autonomous vehicle with non-holonomic constraints and with the presence of obstacles.Mechanical Engineering | Systems and Contro
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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