Outdoor navigation of mobile robots

AGVs in the manufacturing industry currently constitute the largest application area for mobile robots. Other applications have been gradually emerging, including various transporting tasks in demanding environments, such as mines or harbours. Most of the new potential applications require a free-ranging navigation system, which means that the path of a robot is no longer bound to follow a buried inductive cable. Moreover, changing the route of a robot or taking a new working area into use must be as effective as possible. These requirements set new challenges for the navigation systems of mobile robots. One of the basic methods of building a free ranging navigation system is to combine dead reckoning navigation with the detection of beacons at known locations. This approach is the backbone of the navigation systems in this study. The study describes research and development work in the area of mobile robotics including the applications in forestry, agriculture, mining, and transportation in a factory yard. The focus is on describing navigation sensors and methods for position and heading estimation by fusing dead reckoning and beacon detection information. A Kalman filter is typically used here for sensor fusion. Both cases of using either artificial or natural beacons have been covered. Artificial beacons used in the research and development projects include specially designed flat objects to be detected using a camera as the detection sensor, GPS satellite positioning system, and passive transponders buried in the ground along the route of a robot. The walls in a mine tunnel have been used as natural beacons. In this case, special attention has been paid to map building and using the map for positioning. The main contribution of the study is in describing the structure of a working navigation system, including positioning and position control. The navigation system for mining application, in particular, contains some unique features that provide an easy-to-use procedure for taking new production areas into use and making it possible to drive a heavy mining machine autonomously at speed comparable to an experienced human driver.reviewe

Design and Steering Control of a Center-Articulated Mobile Robot Module

This paper discusses the design and steering control for an autonomous modular mobile robot. The module is designed with a center-articulated steering joint to minimize the number of actuators used in the chain. We propose a feedback control law which allows steering between configurations in the plane and show its application as a parking control to dock modules together. The control law is designed by Lyapunov techniques and relies on the equations of the robot in polar coordinates. A set of experiments have been carried out to show the performance of the proposed approach. The design is intended to endow individual wheeled modules with the capability to merge and make a single snake-like robot to take advantage of the benefits of modular robotics

Modelling and control of an articulated underground mining vehicle

The automation of the tramming or load, haul and dump (LHD) procedure, performed by a LHD vehicle, holds the potential to improve productivity, efficiency and safety in the mining environment. Productivity is mainly increased by longer working hours; efficiency is improved by repetitive, faultless and predictable work; and safety is improved by removing the human operator from the harsh environment. However, before the automation of the process can be addressed, a thorough understanding of the process and its duty in the overall mining method is required. Therefore, the current applicable mining methods and their areas of potential automation are given. Since the automation of the LHD vehicle is at the core of this project, its implementation in the tramming process is also justified. Also, the current underground navigation methods are given and their shortcomings are named. It is concluded that infrastructure-free navigation is the only viable solution in the ever-changing mining environment. With that in mind, the feasibility of various navigation sensors is discussed and conclusions are drawn. Both kinematic and dynamic modelling of LHD vehicles are introduced. Various forms of kinematic models are given and their underlying modelling assumptions are named. The most prominent assumptions concern the vehicle’s half-length and the inclusion of a wheel-slip factor. Dynamic modelling techniques, with a strong emphasis on tyre modelling, are also stated. In order to evaluate the modelling techniques, field tests are performed on the articulated vehicles, namely the Wright 365 LHD and the Bell 1706C loader. The test on the Wright 365 LHD gives a good impression of the harsh ergonomics under which the operator has to work. A more thorough test is performed on the Bell 1706C articulated loader. The test results are then compared to simulation results obtained from the kinematic models. Also, the above-named assumptions are tested, evaluated and discussed. A dynamic model is also simulated and discussed. Lastly, two localization and control methods are given and evaluated. The first method is an open-loop nonlinear optimal control strategy with periodic position resetting and the second method is a pathtracking controller. AFRIKAANS : Automatisering van die laai-, vervoer- en dompel- (LVD) prosedure het die potensiaal om die produktiwiteit, effektiwiteit en veiligheid van die mynbedryf te verbeter. Produktiwiteit word hoofsaaklik deur langer werksure verhoog, effektiwiteit word deur herhalende, foutlose en voorspelbare werk verbeter en veiligheid word verbeter omdat menslike operateurs uit die gevaarlike ondergrondse omgewing verwyder word. Voordat aandag aan die automatisering van die prosedure geskenk kan word, moet die prosedure en die algemene mynbedrywighede rakende die prosedure deeglik bestudeer en verstaan word. As gevolg hiervan word die huidige, toepaslike mynboumetodes hier gedokumenteer. Die implementering van ʼn gekoppelde LVD-voertuig in die LVD-prosesword ook geregverdig. Verder word die huidige metodes van ondergrondse navigasie genoem en hulle tekortkominge aangedui. Die gevolgtrekking dat infrastruktuur-vrye navigasie die enigste lewensvatbare navigasiemetode in die immer veranderende ondergrondsemynbouomgewing is, word ook gemaak. In die lig daarvan word ʼn verskeidenheid sensors genoem en bespreek. Kinematiese en dinamiese modellering van ʼn LVD-voertuig word bekendgestel. Verskeie kinematiese modelle en hulle onderliggende aannames word genoem. Die mees prominente aannames is die lengte van die gekoppelde voertuig se hoofdele en die insluiting van ʼn wielglipfaktor. Die tegnieke van dinamiese modellering, met die klem op bandmodellering, word ook gegee. Praktyktoetse op gekoppelde voertuie is ook gedoen om die verskillende modelle te evalueer. Die toets op die Wright 365-LVD bied goeie insig in die strawwe ergonomiese toestande waaronder die operateurs moet werk. ʼn Deeglike toets is op ʼn BELL 1706C- gekoppelde laaier, wat kinematies identies aan ʼn LVD-voertuig is, uitgevoer. Die bevindinge van die toets word met bogenoemde modelsimulasies vergelyk en gevolgtrekkings word gemaak. Laastens word lokalisiering en beheer van ʼn LVDvoertuig behandel. Twee beheermetodes, opelus- nie-lineêre optimale beheer met periodieke herstel en padvolgingbeheer word geëvalueer en bespreek. CopyrightDissertation (MEng)--University of Pretoria, 2012.Electrical, Electronic and Computer Engineeringunrestricte

High-Speed Obstacle Avoidance at the Dynamic Limits for Autonomous Ground Vehicles

Enabling autonomy of passenger-size and larger vehicles is becoming increasingly important in both military and commercial applications. For large autonomous ground vehicles (AGVs), the vehicle dynamics are critical to consider to ensure vehicle safety during obstacle avoidance maneuvers especially at high speeds. This research is concerned with large-size high-speed AGVs with high center of gravity that operate in unstructured environments. The term `unstructured' in this context denotes that there are no lanes or traffic rules to follow. No map of the environment is available a priori. The environment is perceived through a planar light detection and ranging sensor. The mission of the AGV is to move from its initial position to a given target position safely and as fast as possible. In this dissertation, a model predictive control (MPC)-based obstacle avoidance algorithm is developed to achieve the objectives through an iterative simultaneous optimization of the path and the corresponding control commands. MPC is chosen because it offers a rigorous and systematic approach for taking vehicle dynamics and safety constraints into account. Firstly, this thesis investigates the level of model fidelity needed for an MPC-based obstacle avoidance algorithm to be able to safely and quickly avoid obstacles even when the vehicle is close to its dynamic limits. Five different representations of vehicle dynamics models are considered. It is concluded that the two Degrees-of-Freedom (DoF) representation that accounts for tire nonlinearities and longitudinal load transfer is necessary for the MPC-based obstacle avoidance algorithm to operate the vehicle at its limits within an environment that includes large obstacles. Secondly, existing MPC formulations for passenger vehicles in structured environments do not readily apply to this context. Thus, a novel nonlinear MPC formulation is developed. First, a new cost function formulation is used that aims to find the shortest path to the target position. Second, a region partitioning approach is used in conjunction with a multi-phase optimal control formulation to accommodate the complicated forms of obstacle-free regions from an unstructured environment. Third, the no-wheel-lift-off condition is established offline using a fourteen DoF vehicle dynamics model and is included in the MPC formulation. The formulation can simultaneous optimize both steering angle and reference longitudinal speed commands. Simulation results show that the proposed algorithm is capable of safely exploiting the dynamic limits of the vehicle while navigating the vehicle through sensed obstacles of different size and number. Thirdly, in the algorithm, a model of the vehicle is used explicitly to predict and optimize future actions, but in practice, the model parameter values are not exactly known. It is demonstrated that using nominal parameter values in the algorithm leads to safety issues in about one fourth of the evaluated scenarios with the considered parametric uncertainty distributions. To improve the robustness of the algorithm, a novel double-worst-case formulation is developed. Results from simulations with stratified random scenarios and worst-case scenarios show that the double-worst-case formulation considering both the most likely and less likely worst-case scenarios renders the algorithm robust to all uncertainty realizations tested. The trade-off between the robustness and the task completion performance of the algorithm is also quantified. Finally, in addition to simulation-based validation, preliminary experimental validation is also performed. These results demonstrate that the developed algorithm is promising in terms of its capability of avoiding obstacles. Limitations and potential improvements of the algorithm are discussed.PHDMechanical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/135770/1/ljch_1.pd

In-Field Observations of Heavy Mining Vehicle Wheels and Analyses of Proposed Solutions to Enhance Safety

This research strives to enhance the safety of multi-piece wheel assemblies as injuries and fatalities are associated with their failure, yet information on this topic is limited. Experiments were performed to determine mechanical performance and planar deformation characteristics of several tires to aid in numerical model development. For a 29.5-29 tire, observations included determining vertical versus lateral deflection relationships (0.310 mm/mm), and vertical (2.59 kN/mm) and lateral (6.29 kN/mm) stiffness. A database capable of tracking wheel maintenance trends based on historical data was developed, allowing maintenance schedules to be estimated. A safety shield system was proposed. Effectiveness of the design was examined through numerical simulation of the ISO 7141 impact test, a tire blowout, and a rotational side impact. Depending on the test condition, observations comparing shield-equipped versus standard wheels show reductions in von Mises stress between 15% and 55% and reductions in effective plastic strains between 20.3% and 92%

A tool for defining models of generic mobile machines

Tässä työssä esitellään mielivaltaisten liikkuvien työkoneiden nopeaan ja helppoon määrittelyyn tarkoitettu ohjelmisto. Käyttäjä määrittelee työkoneen yksinkertaisen, intuitiivisen 3D-käyttöliittymän avulla. Työkoneen määritelmän perusteella generoidaan sen kinemaattinen malli. Kinemaattisissa laskuissa käytetään uusimpia tutkimustuloksia erilaisten ajoneuvojen kinematiikasta. Generoiduilla kinemaattisilla malleilla voidaan simuloida mielivaltaisia konekonfiguraatioita erillisessä simulaattorimoduulissa, joka luotiin osana tätä työtä. Simulaattori tukee yleisimpiä teollisuudessa käytettyjä liikkuvia konetyyppejä, kuten automaisia, telaketjullisia, runkonivellettyjä tai passiivisesti yhdistettyjä koneita. Simuloidut ajoneuvot voivat myös yhdistellä eri konetyyppejä. Ohjelmistolla generoiduilla kinemaattisilla malleilla simuloidaan erilaisia tosimaailman ajoneuvokonfiguraatioita. Simulaatiotuloksia verrataan oikeista koneista saatuun dataan. Mallien havaitaan olevan tarkkoja ja sopivia erilaisiin tarkoituksiin, jotka vaativat ajoneuvon kinemaattisen mallin.In this thesis work, a software tool for quickly and easily defining a mobile vehicle is presented. Vehicles are defined through a simple, intuitive 3D graphical user interface. Based on the vehicle definition, a kinematic model is generated for the vehicle. The kinematics calculations use state-of-the-art knowledge on the kinematics of different vehicle types. The generated kinematic models can be used in a separate simulator module, also created for this thesis work, to simulate arbitrary vehicle configurations. Supported vehicle types include the most common mobile industrial vehicles, such as car-like, tracked, center-articulated or passively linked vehicles. Simulated vehicles can also be combinations of these types. Kinematic models generated with this software are tested against data sets gained from different real-world vehicle configurations. The models are found to be accurate and suitable for various purposes requiring a kinematic model of a vehicle

Path Following and Motion Control for Articulated Frame Steering Mobile Working Machine Using ROS2

Autonomous vehicles (AVs) have been studied and researched at least since the middle of 19s century, and the interest in these vehicles has grown in the last decade. There are many vehicle types with different steering techniques. Each is designed and manufactured depending on the need to perform specific tasks (for example, transporting passengers, transporting goods, and doing heavy duties like cutting trees, digging earth, and harvesting crops). This thesis highlights the autonomous articulated frame steering (AFS) heavy-duty mobile working machines and aims to address the problems of autonomizing the AFS machine with basic autonomy requirements, which makes the machine move without the need for human direct and indirect control. The working environment (like mines, forests, and construction sites), where heavy-duty machines are used to perform some tasks, requires an expert machine operator to drive it and control its manipulator, which increases the operator’s workload. However, due to the working environment’s limited area, the machine mostly has repetitive tasks that include following the same paths; therefore, we proposed implementing a path-following control system that could be used to help the operator by reducing the work amount. The proposed path following is based on controlling the vehicle’s position and orientation to match the desired positions and orientation on a specified path where the position’s lateral error and orientation error are minimized to zero while the vehicle follows the given path. The implemented control system is divided into many subsystems; each is responsible for a specific task, and to communicate between them we used the Robot Operating System ROS2. In this thesis, we are focusing on two of these subsystems. The first subsystem, called path following that, generates linear and angular velocities needed to make the machine follow the path. The other subsystem, called motion control, is responsible for converting the linear and angular velocities to machine commands (gear, steering, gas) and controls the machine’s acceleration and steering angle. The implemented path-following control system required understanding the machine’s kinematics and modeling the steering system. The implemented system is tested first using an AFS robot in a simulation environment, then tested on a real AFS heavy-duty machine owned by Tampere university. Moreover, the tests repeated for another path following based on the modified pure pursuit technique provided by ROS2 navigation for compression and evaluation purposes

Autonomiset työkoneet ja autonomian vaikutus koneturvallisuuteen

Autonomous machines and vehicles are an increasing part of everyday life and industrial operations. These machines and vehicles have enjoyed rapid technological advancements in recent years, which has led to increasingly sophisticated functions and functionalities. The advancements in autonomous technologies have, however, given rise to questions and concerns relating to the safety of these machines and vehicles, and on how an adequate level of safety can be ensured when no dedicated operator or driver is present. This thesis looks at the main areas that affect the overall safety of autonomous industrial machines and civilian road vehicles, and presents the most prominent challenges faced in ensuring the safety of autonomous applications. The goal of the thesis is to give the reader an overview of the safety-related aspects of autonomy and to show what has to be considered when ensuring an adequate level of safety for autonomous machines or vehicles. This is achieved by an extensive literature review on autonomous applications in both industrial and automotive fields, and on the safety-related aspects of autonomy. Additionally, mining is used in the thesis as an example of autonomous machines in practice and on the challenges autonomy can face in industrial operations. Based on the research carried out, it can be said that the overall safety of machine autonomy is currently hindered by two main aspects: the lack of applicable standards, legislation and guidelines regarding the autonomy of machines and vehicles, and the paradox that arises from balancing the desired level of autonomy with the needed level of safety. This has led to a situation where, in theory, highly complex and sophisticated autonomous machines are possible from a technical standpoint, but they lack a common and thorough method for ensuring an adequate level of safety