For mobile robots to navigate autonomously, one of the most important and challenging task is localisation. Localisation refers to the process whereby a robot locates itself within a map of a known environment or with respect to a known starting point within an unknown environment. Localisation of a robot in unknown environment is done by tracking the trajectory of a robot whilst knowing the initial pose. Trajectory estimation becomes challenging if the robot is operating in an unknown environment that has scarcity of landmarks, is GPS denied, is slippery and dark such as in underground mines. This dissertation addresses the problem of estimating a robot's trajectory in underground mining environments. In the past, this problem has been addressed by using a 3D laser scanner. 3D laser scanners are expensive and consume lot of power even though they have high measurements accuracy and wide eld of view. For this research work, trajectory estimation is accomplished by the fusion of an ego-motion provided by Time of Flight(ToF) camera and measurement data provided by a low cost Inertial Measurement Unit(IMU). The fusion is performed using Kalman lter algorithm on a mobile robot moving in a 2D planar surface. The results shows a signi cant improvement on the trajectory estimation. Trajectory estimation using ToF camera only is erroneous especially when the robot is rotating. The fused trajectory estimation algorithm is able to estimate accurate ego-motion even when the robot is rotating. / [Durban, South Africa] : University of KwaZulu-Natal, 2013.

Networks of cameras such as building security systems can be a source of localization information for a mobile robot assuming a map of camera locations as well as calibration information for each camera is available. This thesis describes an automated system to acquire such information. A fully automated camera calibration system uses fiducial markers and a mobile robot in order to drastically improve ease-of-use compared to standard techniques. A 6DOF EKF is used for mapping and is validated experimentally over a 50 m hallway environment. Motion planning strategies are considered both in front of a single camera to maximize calibration accuracy and globally between cameras in order to facilitate accurate measurements. For global motion planning, an adaptive exploration strategy based on heuristic search allows compromise between distance traveled and final map uncertainty which provides the system a level of autonomy which could not be obtained with previous techniques.

This thesis presents advances in the state-of-the-art in legged locomotion through the development of bounding and galloping gaits as well as new modes of hybrid wheeled-leg modes of locomotion. Two four-legged running robots, Scout II and PAW, are examined, the latter of which is distinguished by actuated wheels at the ends of its legs. / First, hybrid modes of locomotion are demonstrated which use legs to dynamically reposition wheels at specific locations with respect to the body. These modes improve the stability and tire-wear of turning and braking manoeuvres and allow pitch-controlled slope ascent and descent in a wheeled-leg vehicle such as the PAW robot. / Second, through hip actuation, passive leg compliance and controlled wheel action it is possible to make the same vehicle run using a dynamically stable legged gait called the bound. Experimental evidence of this is presented and compared to similar experiments on the same robot with mechanically blocked wheels, a 3D simulation of the same, as well as bounding on a completely different quadrupedal robot, Scout II. While a casual observer finds no difference in blocked-wheel and active wheel control modes, detailed examination of the gaits reveals lower speeds and efficiency as well as decreased repeatability when the wheels are actively controlled. / A new method of forward speed control is presented for the bounding gait using liftoff, as opposed to touchdown, leg angles. The liftoff angle method of speed control is shown to be particularly suited to fine-tuning of certain gait performance indices. / Third, the underactuated bounding gait is extended to demonstrate, for the first time, that robotic galloping is possible and that it can be achieved in two underactuated quad-rupedal robots and with varying levels of decoupled control. In the Scout II robot the front leg pair and rear leg pairs function independently; while in the PAW robot galloping is achieved with no controlled coupling between any of the four legs. The rotary gallop gait demonstrated by both robots is characterized by a significant yaw component and is compared to another bound-derived turning gait which uses liftoff angles to produce yaw. In particular, the correspondence of lead leg to yaw direction in both cases is found to match results from biology. In contrast, while it is thought that animals pivot about their lead leg to turn, the rotary gallop demonstrated by these robots shows that yaw occurs primarily in the leg behind the lead leg.

University of Technology, Sydney. Faculty of Engineering. / The thesis focuses on issues of vehicle modelling incorporating wheel-terrain interaction and low-level control design taking into account uncertainties and input time delay. Addressing these issues is of significant importance in achieving persistent autonomy for outdoor UGVs, especially when navigating on unprepared terrains. The test-bed vehicle used for this research is retrofitted from an all-terrain 20-hp, 0.5-tonne vehicle. Its driveline system consists of an internal combustion engine, continuous variable transmission (CVT), gearbox, differential, chains, and eight wheels. The vehicle is driven in the skid-steering mode, which is popular for many off-road land-vehicle platforms. In this thesis, a comprehensive approach is proposed for modelling the driveline. The approach considers the difference in speed between two outputs of the differential and the turning mechanism of the vehicle. It describes dynamics of all components in the vehicle driveline in an integrated manner with the vehicle motion. Given a pattern of the throttle position, left and right braking efforts as the inputs, the dynamic behaviour of the wheels and other components of the UGV can be predicted. For controlling the vehicle at the low level, PID controllers are firstly used for all actuators. As many components of the vehicle exhibit nonlinearities and time delay, the large overshoots encountered in the outputs can lead to undesirable vehicle behaviours. To alleviate the problem, a novel control approach is proposed for suppression of overshoots resulting from PID control. Sliding mode control (SMC) is employed, for this, with time delay compensated by using an output predictor. As a result, the proposed approach can improve significantly system robustness and reduce substantially step response overshoot. Notably, the design is generic in that it can be applied for many dynamic processes. Knowledge of the interaction between the UGV and the terrain plays an important role in increasing its autonomy and securing the safety for off-road locomotion. In this regard, vehicle kinematic equations are combined with the theory of terramechanics for dynamic modelling of the interaction between the vehicle wheels and a variety of terrain types. Also, a fast algorithm is developed to enable online implementation. The novel interaction model takes into account the relationship between normal stresses, shear stresses, and shear displacement of the terrain that is in contact with the wheels in deriving the three-dimensional reaction forces. Finally, all modelling and control algorithms are integrated into a unique simulator for emulating the vehicle mobility characteristics. In particular, the wheel’s slip and rolling resistance can also be derived to provide useful information for closed-loop control when the UGV is navigating in an unknown environment. The simulator, as a tool for analysing the vehicle mobility, is helpful for further research on relevant topics such as traction control, safe and effective locomotion.

The first part of this thesis documents experimental investigation into the use of vision for wheeled robot navigation problems. Specifically, using a video camera as a source of feedback to control a wheeled robot toward a static and a moving object in an environment in real-time. The wheeled robot control algorithms are dependent on information from a vision system and an estimator. The vision system design consists of a pan video camera and a visual gaze algorithm which attempts to search and continuously maintain an object of interest within limited camera field of view. Several vision-based algorithms are presented to recognize simple objects of interest in an environment and to calculate relevant parameters required by the control algorithms. An estimator is designed for state estimation of the motion of an object using visual measurements. The estimator uses noisy measurements of relative bearing to an object and object's size on an image plane formed by perspective projection. These measurements can be obtained from the vision system. A set of algorithms have been designed and experimentally investigated using a pan video camera and two wheeled robots in real-time in a laboratory setting. Experimental results and discussion are presented on the performance of the vision-based control algorithms where a wheeled robot successfully approached an object in various motions. The second part of this thesis investigates the coordination problem of flocking in multi-robot system using concepts from graph theory. New control laws are presented for flocking motion of groups of mobile robots based on several leaders. Simulation results are provided to illustrate the control laws and its applications.

Thesis (M.S.)--University of Missouri--Rolla, 2007. / Vita. The entire thesis text is included in file. Title from title screen of thesis/dissertation PDF file (viewed November 28, 2007) Includes bibliographical references.

Thesis (Ph.D.)--University of Wollongong, 2003. / Typescript. Bibliographical references: leaf 461-470.

Thesis (M.S.)--Rochester Institute of Technology, 2008. / Typescript. Includes bibliographical references (leaves 84-87).

Thesis (Ph. D.)--Carnegie Mellon University, 1995. / "September 29, 1995." Includes bibliographical references and index.

Thesis (Ph. D.)--University of Washington, 2004. / Vita. Includes bibliographical references (p. 188-204).