GA-tuning of nonlinear observers for sensorless control of automotive power steering IPMSMs

The paper considers two observer-based rotor position estimation schemes for sensorless control of interior permanent magnet synchronous motors (IPMSMs) for use in future automotive power steering systems. Specifically, emphasis is given to techniques based on feedback-linearisation followed by classical Luenberger observer design, and direct design of non-linear observers. Genetic algorithms (GAs), using the principles of evolution, natural selection and genetic mutation, are introduced to address difficulties in selecting correction gains for the observers, since no analytical tuning mechanisms yet exist. Experimental measurements from an automotive power steering test-facility are included, to demonstrate the enhanced performance attributes offered by tuning the proposed observer schemes, online, in this manner

Motion Coordination of Multiple Autonomous Vehicles in a Spatiotemporal Flowfield

The long-term goal of this research is to provide theoretically justified control strategies to operate autonomous vehicles in spatiotemporal flowfields. The specific objective of this dissertation is to use estimation and nonlinear control techniques to generate decentralized control algorithms that enable motion coordination for multiple autonomous vehicles while operating in a time-varying flowfield. A cooperating team of vehicles can benefit from sharing data and tasking responsibilities. Many existing control algorithms promote collaboration of autonomous vehicles. However, these algorithms often fail to account for the degradation of control performance caused by flowfields. This dissertation presents decentralized multivehicle coordination algorithms designed for operation in a spatially or temporally varying flowfield. Each vehicle is represented using a Newtonian particle traveling in a plane at constant speed relative to the flow and subject to a steering control. Initially, we assume the flowfield is known and describe algorithms that stabilize a circular formation in a time-varying spatially nonuniform flow of moderate intensity. These algorithms are extended by relaxing the assumption that the flow is known: the vehicles dynamically estimate the flow and use that estimate in the control. We propose a distributed estimation and control algorithm comprising a consensus filter to share information gleaned from noisy position measurements, and an information filter to reconstruct a spatially varying flowfield. The theoretical results are illustrated with numerical simulations of circular formation control and validated in outdoor unmanned aerial vehicle (UAV) flight tests

Neural Network-Based Output Feedback Controller for Lean Operation of Spark Ignition Engines

Spark ignition (SI) engines running at very lean conditions demonstrate significant nonlinear behavior by exhibiting cycle-to-cycle dispersion of heat release even though such operation can significantly reduce NOx emissions and improve fuel efficiency by as much as 5-10%. A suite of neural network (NN) controller without and with reinforcement learning employing output feedback has shown ability to reduce the nonlinear cyclic dispersion observed under lean operating conditions. The neural network controllers consists of three NN: a) A NN observer to estimate the states of the engine such as total fuel and air; b) a second NN for generating virtual input; and c) a third NN for generating actual control input. For reinforcement learning, an additional NN is used as the critic. The uniform ultimate boundedness of all closed-loop signals is demonstrated by using Lyapunov analysis without using the separation principle. Experimental results on a research engine at an equivalence ratio of 0.77 show a drop in NOx emissions by around 98% from stoichiometric levels. A 30% drop in unburned hydrocarbons from uncontrolled case is observed at this equivalence ratio

Collision-free motion of two robot arms in a common workspace

Collision-free motion of two robot arms in a common workspace is investigated. A collision-free motion is obtained by detecting collisions along the preplanned trajectories using a sphere model for the wrist of each robot and then modifying the paths and/or trajectories of one or both robots to avoid the collision. Detecting and avoiding collisions are based on the premise that: preplanned trajectories of the robots follow a straight line; collisions are restricted to between the wrists of the two robots (which corresponds to the upper three links of PUMA manipulators); and collisions never occur between the beginning points or end points on the straight line paths. The collision detection algorithm is described and some approaches to collision avoidance are discussed

Frictional Effects on the Diagnostics of Helical Gear Tooth Defects

Tooth Defect is a common failure mode that frequently occurs in gears. To develop successful diagnostic techniques, this study examines the capability of helical gear dynamic responses with the inclusion of different time-varying friction models, i.e. friction-free, Coulomb and elasto-hydrodynamic lubrication (EHL) models. The gear system is a 10-DOF (degree-of-freedom) vibration system, which incorporates the effects of gear pair, supporting bearings, driving motor and loading system. Moreover, it couples the transverse and torsional motions resulting from time-varying friction forces, time varying mesh stiffness excitations and different tooth breakage severities. To explore the vibration response, spectral peaks at characteristic mesh frequency and its harmonics along with their sidebands are considered in the light of the impulsive sources from tooth damages and different frictional excitation models. It has found that the sidebands exhibit significant difference between different friction models and mesh components for tooth defects. It is concluded that the frictional effect should be taken into account if it is to be an accurate method for the detection and diagnostic different tooth surface defects

Active vibration control of flexible bodied railway vehicles via smart structures

Future railway vehicles are going to be designed lighter in order to achieve higher speed. Suppressing the flexible modes becomes a crucial issue for improving the ride quality of the light-weight high speed railway vehicles. The concept of smart structure brings structural damping to flexible structures by integrating smart actuators and sensors onto the structure. Smart structure eliminates the need for extensive heavy mechanical actuation systems and achieves higher performance levels through their functionality for suppressing the flexible modes. Active secondary suspension is the effective conventional approach for vibration control of the railway vehicle to improve the ride quality. But its ability in suppressing the flexible modes is limited. So it is motivated to combine active structural damping for suppressing the flexible modes and the vibration control through active secondary suspension which has an effect on both rigid and flexible modes. The side-view model of the flexible-bodied railway vehicle integrated with piezoelectric actuators and sensors is derived. The procedure for selection of placement configurations of the piezoelectric actuators and sensors using structural norms is presented. Initial control studies show that the flexibility of the vehicle body will cause a considerable degradation in ride quality if it is neglected in the design model. Centralized and decentralized control strategies with various control approaches (e.g. modal control with skyhook damping, LQG/H2 control, H_infinity control and model predictive control (MPC))are applied for the combined control of active structural damping and active suspension control. The active structural damping effectively suppresses the flexible modes as a complement to the work of the active suspension control

"It's time to kick a** and chew bubble gum" :an ideological critique of narrative in action games

PhD ThesisIf videogames are carriers of ideological frameworks which work in favour of certain groups in society, how are such meanings divulged? Despite the achievement of important landmarks the academic field of game studies is still rife with gaps which need to be addressed. Hence, this study aims to provide for this general lack of tools by offering for scrutiny the means to carry out a systematic and analytical narrative analysis of games. What is proposed here is a comprehensive set of theoretical as well as methodological tools to deal more effectively and empirically with the kind of narratives emerging in games. In order to identify and study these narratives, two tools have been selected, each one to be used for a specific objective. The tools in question are narrative and content analysis. Whilst the former is used to address the narrative dimension of the games in question, the latter is used to identify and define their ideological nuances. In this thesis it will be argued that this content is mostly dispersed through narrative. Though it has been argued many times that videogame narratives are infantile and poor reflections of film and novel forms of storytelling, they nonetheless contain within them the same capacity of the older forms to dispense or insinuate ideological content. As such videogames are both influenced by ideological principles as well as cultural distributors of the latter. By being recruited by the forces of ‘good’ to defeat the forces of ‘evil’, the player is given an important role to play in an ideologically saturated fantasy. Nonetheless the nature of heroism present in these games is not of the conventional kind but has Nietzschian characteristics to it, in that it is bound to the idea of empowerment. The player is invited to partake in a fantasy where everything is possible and there are no barriers which cannot be overcome. The action component, or rather the acts of shooting and killing, so commonly associated with the action genre, become the primary source through which a sense of empowerment is channelled. At their core, action games are primarily about the illusion of control over the self, non- Western countries, cultures, ideologies, women etc. As a consequence of this, these games have become an important colonizing tool, which consolidates the hegemony of Western white men. This is also particularly evident in the way female characters are 2 represented. While male figures are portrayed as heroic, virile and empowered, female characters are objectified, sexualized and deemed of secondary importance. By exploring the ideological nature of action games, this project seeks to reaffirm the importance of studying popular culture artefacts, not solely in terms of their constituting elements but also in the wider context of their origin and point of consumption.Malta Government Scholarship Scheme for partially funding this research wor