Integrating Vehicle Slip and Yaw in Overarching Multi-Tiered Automated Vehicle Steering Control to Balance Path Following Accuracy, Gracefulness, and Safety

Balancing path following accuracy and error convergence with graceful motion in steering control is challenging due to the competing nature of these requirements, especially across a range of operating speeds and conditions. This paper demonstrates that an integrated multi-tiered steering controller considering the impact of slip on kinematic control, dynamic control, and steering actuator rate commands achieves accurate and graceful path following. This work is founded on multi-tiered sideslip and yaw-based models, which allow derivation of controllers considering error due to sideslip and the mapping between steering commands and graceful lateral motion. Observer based sideslip estimates are combined with heading error in the kinematic controller to provide feedforward slip compensation. Path following error is compensated by a continuous Variable Structure Controller (VSC) using speed-based path manifolds to balance graceful motion and error convergence. Resulting yaw rate commands are used by a backstepping dynamic controller to generate steering rate commands. A High Gain Observer (HGO) estimates sideslip and yaw rate for output feedback control. Stability analysis of the output feedback controller is provided, and peaking is resolved. The work focuses on lateral control alone so that the steering controller can be combined with other speed controllers. Field results provide comparisons to related approaches demonstrating gracefulness and accuracy in different complex scenarios with varied weather conditions and perturbations

Autonomous navigation of a wheeled mobile robot in farm settings

This research is mainly about autonomously navigation of an agricultural wheeled mobile robot in an unstructured outdoor setting. This project has four distinct phases defined as: (i) Navigation and control of a wheeled mobile robot for a point-to-point motion. (ii) Navigation and control of a wheeled mobile robot in following a given path (path following problem). (iii) Navigation and control of a mobile robot, keeping a constant proximity distance with the given paths or plant rows (proximity-following). (iv) Navigation of the mobile robot in rut following in farm fields. A rut is a long deep track formed by the repeated passage of wheeled vehicles in soft terrains such as mud, sand, and snow. To develop reliable navigation approaches to fulfill each part of this project, three main steps are accomplished: literature review, modeling and computer simulation of wheeled mobile robots, and actual experimental tests in outdoor settings. First, point-to-point motion planning of a mobile robot is studied; a fuzzy-logic based (FLB) approach is proposed for real-time autonomous path planning of the robot in unstructured environment. Simulation and experimental evaluations shows that FLB approach is able to cope with different dynamic and unforeseen situations by tuning a safety margin. Comparison of FLB results with vector field histogram (VFH) and preference-based fuzzy (PBF) approaches, reveals that FLB approach produces shorter and smoother paths toward the goal in almost all of the test cases examined. Then, a novel human-inspired method (HIM) is introduced. HIM is inspired by human behavior in navigation from one point to a specified goal point. A human-like reasoning ability about the situations to reach a predefined goal point while avoiding any static, moving and unforeseen obstacles are given to the robot by HIM. Comparison of HIM results with FLB suggests that HIM is more efficient and effective than FLB. Afterward, navigation strategies are built up for path following, rut following, and proximity-following control of a wheeled mobile robot in outdoor (farm) settings and off-road terrains. The proposed system is composed of different modules which are: sensor data analysis, obstacle detection, obstacle avoidance, goal seeking, and path tracking. The capabilities of the proposed navigation strategies are evaluated in variety of field experiments; the results show that the proposed approach is able to detect and follow rows of bushes robustly. This action is used for spraying plant rows in farm field. Finally, obstacle detection and obstacle avoidance modules are developed in navigation system. These modules enables the robot to detect holes or ground depressions (negative obstacles), that are inherent parts of farm settings, and also over ground level obstacles (positive obstacles) in real-time at a safe distance from the robot. Experimental tests are carried out on two mobile robots (PowerBot and Grizzly) in outdoor and real farm fields. Grizzly utilizes a 3D-laser range-finder to detect objects and perceive the environment, and a RTK-DGPS unit for localization. PowerBot uses sonar sensors and a laser range-finder for obstacle detection. The experiments demonstrate the capability of the proposed technique in successfully detecting and avoiding different types of obstacles both positive and negative in variety of scenarios

MS

thesisIn this research, a computerized motion planning and control system for multiple robots is presented. Medium scale wheeled mobile robot couriers move wireless antennas within a semicontrolled environment. The systems described in this work are integrated as components within Mobile Emulab, a wireless research testbed. This testbed is publicly available to users remotely via the Internet. Experimenters use a computer interface to specify desired paths and configurations for multiple robots. The robot control and coordination system autonomously creates complex movements and behaviors from high level instructions. Multiple trajectory types may be created by Mobile Emulab. Baseline paths are comprised of line segments connecting waypoints, which require robots to stop and pivot between each segment. Filleted circular arcs between line segments allow constant motion trajectories. To avoid curvature discontinuities inherent in line-arc segmented paths, higher order continuous polynomial spirals and splines are constructed in place of the constant radius arcs. Polar form nonlinear state feedback controllers executing on a computer system connected to the robots over a wireless network accomplish posture stabilization, path following and trajectory tracking control. State feedback is provided by an overhead camera based visual localization system integrated into the testbed. Kinematic control is used to generate velocity commands sent to wheel velocity servo loop controllers built into the robots. Obstacle avoidance in Mobile Emulab is accomplished through visibility graph methods. The Virtualized Phase Portrait Method is presented as an alternative. A virtual velocity field overlay is created from workspace obstacle zone data. Global stability to a single equilibrium point, with local instability in proximity to obstacle regions is designed into this system

Navigation semi-autonome d'un fauteuil roulant motorisé en environnements restreints

RÉSUMÉ Ce travail introduit un système de navigation semi-autonome pour fauteuil roulant motorisé (FRM) visant à assister les personnes à mobilité réduite dans leurs déplacements quotidiens. Différentes fonctionnalités d’assistance à la navigation sont offertes, telles que l’assistance d’évitement de collision et de déblocage lors d’impasses, puis l’exécution de manoeuvres automatiques : de mouvements rectilignes, de suivi de murs, de suivi de personnes, de traversée de passages étroits et de stationnement. Élaboré avec l’appui de professionnels en réadaptation et d’usagers de FRM, le système de navigation proposé se distingue par sa facilité d’appropriation attribuable à des fonctionnalités simples à maîtriser, par sa navigation intuitive, confortable et sécuritaire, puis par ses aptitudes à opérer en environnements restreints, variés et inconnus. Le système est validé à l’aide du WST (Wheelchair Skills Test) en collaboration avec des professionnels en réadaptation du centre Lucie-Bruneau de Montréal. Huit usagers sains et neuf usagers handicapés ont exécuté le test. Les 8.8 kilomètres parcourus sur vingt-cinq heures d’expérimentation ont démontré l’efficacité et la fiabilité de la solution proposée. Les commentaires positifs des usagers confirment l’intérêt des différentes facettes du système. Les expériences ont, en outre, démontré une aptitude exceptionnelle à la réalisation automatique de manoeuvres en environnements restreints, comme lors de passage de portes standards (moins de 90 cm de large) et de stationnement. Ces performances sont rendues possibles en redéfinissant comment une plate-forme mobile doit se mouvoir dans l’espace, réagir aux obstacles, gérer l’incertitude des mesures, compenser l’erreur d’exécution, établir des stratégies valides dans la plupart des contextes liés aux fonctionnalités et, enfin, organiser l’ensemble des fonctionnalités sous une architecture de contrôle facilitant leur développement. Ce travail contribue ainsi à la robotique mobile par l’apport d’approches de suivi de séquence de points (et de trajectoires), d’évitement stratégique de collisions et d’impasses, de stationnement parallèle, de traversée de passages étroits, d’autolocalisation en environnement partiellement inconnu et par une architecture de contrôle sous laquelle opère l’ensemble des fonctionnalités. Ces méthodes se distinguent par leur capacité à s’adapter à des contextes variés et restreints, puis par leur simplicité d’utilisation. Chaque approche est étudiée individuellement, puis conjointement dans l’application de fauteuil roulant semi-autonome.----------ABSTRACT This work presents a semi-autonomous navigation system for powered wheelchairs which provides assistance to people with mobility impairments during their activities of daily living. The system has various functionalities such as collision assistance, anti-deadlock assistance, automatic maneuvers including moving on a distance, following a wall, following a person, passing through a narrow passage and parking in restrained areas. Built in regard to the advices of clinicians and wheelchair users, the proposed navigation system is especially easy to run due to a set of easy to- understand functions providing an intuitive, comfortable and secure navigation. It is capable to operate in various restrained and unknown environments. The system has been validated using the Wheelchair Skills Test (WST) by clinicians from the Lucie-Bruneau rehabilitation center in Montreal. Eight healty users and nine impaired users have done the test. The 8.8 kilometers covered in 25 hours of experimentation have shown the efficiency and the reliability of the proposed solution. The positive user comments point out the relevance of the different system features. Specifically, the experiments have demonstrated the system’s exceptional skills in carrying out automatic maneuvers in restrained environments, such as passing standard doors (width less than 90 cm) and parking. The special system’s efficiency to perform in various restrained environments is made possible by redefining how a mobile platform should move, react to obstacles, deal with measurement uncertainties, compensate for execution errors, set up strategies that are applicable in most operation contexts and organize the overall functionalities into an efficient control architecture. The work resulting from this investigation contributes to the mobile robotic field by proposing novel approaches for the problems of waypoint-following (and path-following), collision assistance, deadlock avoidance, parallel parking, narrow passages and self-localization, as well as for a special control architecture that underlies all functionalities. All these approaches differ from previous ones in their adaptability to varied and restrained contexts, and for their simplicity of use. The approaches are first studied separately, next jointly in the semi-autonomous navigation system