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Research in the area of autonomous mobile robots has increased over the last several years. Autonomous mobile robots are now being used in a wide variety of applications, including nuclear plant maintenance, interplanetary exploration, military missions and smart highway systems. This thesis is a survey of recent publications, 1990-1996, of wheeled autonomous mobile robots for harsh environments. Various sensing, navigation, and motion control strategies commonly used on autonomous mobile robots are compared. The integration of all three systems in a system architecture is also presented. Following a general discussion of autonomous mobile robot technology, vehicles that have entered the Unmanned Ground Robotics Competition are presented as a focused study of the application of this broad field of research. / Master of Science

Biological systems offer novel and efficient solutions to many engineering applications, including marine propulsion. It is of interest to determine how fish interact with the water around them, and how best to utilize the potential their methods offer. A stingray-like fin was chosen for analysis due to the maneuverability and versatility of stingrays. The stingray fin was modeled in 2D as a sinusoidal wave with an amplitude increasing from zero at the leading edge to a maximum at the trailing edge. Using this model, a parametric study was performed to examine the effects of the fin on surrounding water in computational fluid dynamics (CFD) simulations. The results were analyzed both qualitatively, in terms of the pressure contours on the fin and vorticity in the trailing wake, and quantitatively, in terms of the resultant forces and the mechanical power requirements to actuate the desired fin motion. The average thrust was shown to depend primarily on the relationship between the swimming speed and the frequency and wavelength (which both are directly proportional to the wavespeed of the fin), although amplitude can be used to augment thrust production as well. However, acceleration was shown to significantly correlate with a large variation in lift and moment, as well as with greater power losses. Using results from the parametric study, the potential for power regeneration was also examined. Relationships between frequency, velocity, drag, and power input were determined using nonlinear regression that explained more than 99.8% of the data. The actuator for a fin was modeled as a single DC motor-shaft system, allowing the combination of the energetic effects of the motor with the fin-fluid system. When combined, even a non-ideal fin model was able to regenerate more power at a given flow speed than was required to swim at the same speed. Even in a more realistic setting, this high proportion of regenerative power suggests that regeneration and energy harvesting could be both feasible and useful in a mission setting. / Master of Science / Animals interact with the world much differently than engineered systems, and can offer new and efficient ways to solve engineering problems, including underwater vehicles. To learn how to move an underwater vehicle in an environmentally conscious way, it is useful to study how a fish’s movements affect the manner in which it moves through the water. Through careful study, the principles involved can be implemented for an efficient, low-disturbance underwater vehicle. The particular fish chosen for in-depth study was the stingray, due to its maneuverability and ability to travel close to the seafloor without disturbing the sediment and creatures around it. In this work, computational analysis was performed on a model of a single stingray fin to determine how the motion of the fin affects the water around it, and how the water affects the fin in turn. The results were analyzed both in terms of the wake behind the fin and in terms of how much power was required to make the fin move in a particular way. The speed of the fin motion was found to have the strongest effect in controlling swimming speed, although the lateral motion of the fin also helped with accelerating faster. Additionally, the potential for a robotic stingray fin to harness power from the water around it was examined. Based on results from simulations of the fin, a mathematical model was formulated to relate energy harvesting with the flow speed past the fin. This model was used to determine how worthwhile it was to use energy harvesting. Analysis of the model showed that harvesting energy from the water was quite efficient, and would likely be a worthwhile investment for an exploration mission.

This study discusses the design of a force control strategy for reducing force disturbances in the Virginia Tech – Federal Railroad Administration (VT-FRA) Roller Rig. The VT-FRA Roller Rig is a state-of-the-art roller Rig for studying contact mechanics. It consists of a 0.2m diameter wheel and a 1m diameter roller in vertical configuration, which replicates the wheel-rail contact in a 1/4th scale. The Rig has two 19.4 kW servo motors for powering the rotational bodies and six heavy-duty servo linear actuators that control other boundary conditions. The Rig was operationalized successfully with all degrees of freedom working in the default position feedback control. During the Rig's commissioning, this approach was found to result in vertical force fluctuations that are larger than desired. Since the vertical force affects the longitudinal and lateral traction between the wheel and roller, keeping the fluctuations to a minimum provides a better test condition. Testing and data analysis revealed the issue to be in the control method. The relative position of the wheel and roller was being controlled instead of controlling the forces between them. The latter is a far more challenging control setup because it requires a faster dynamic response and full knowledge of forces at the interface. Additionally, force control could result in dynamic instability more readily than position control. Multiple methods for force control are explored and documented. The most satisfactory solution is found in a cascaded loop force/position controller. The closed loop system is tested for stability and performance at various load, speed, and creepage conditions. The results indicate that the controller is able to reduce the standard deviation of vertical force fluctuations at the wheel-rail contact by a factor of four. In terms of power of the vertical force fluctuations, this corresponds to a 12 dB reduction with the force control when compared with the previous control method. This study also explores the possibility of automating the tests in order to enable running a larger number of tests in a shorter period of time. A multi-thread software is developed in C++ for executing a user-defined position, velocity, or force vs. time trajectory, and for recording the data automatically. The software also provides continuous monitoring, and performs a safe shutdown if a fault is detected. An intuitive GUI is provided for constant data polling and ease of user operation. The code is modular in order to accommodate future modifications and additions for various testing needs. The engineering upgrades included in this study, together with the baseline testing, complete the commissioning of the VT-FRA Roller Rig. With unparalleled parameter control and testing repeatability, the VT-FRA Roller Rig holds the promise of being used successfully for various contact mechanics needs that may arise in the railroad industry. / MS / Roller Rigs have seen widespread use around the world for research and development of railway vehicles. These test rigs are specialized machinery that provide the means to test a particular aspect of railroading in a controlled environment, allowing for thorough parametric analyses which aid in the design and development of railroad vehicles. One such test rig is the Virginia Tech – Federal Railroad Administration (VT-FRA) Roller Rig, located at the Railway Technologies Laboratory in Blacksburg, Virginia. It is a state-of-the-art test rig which is developed with the objective of providing a controlled test environment for studying railway contact mechanics. A good understanding of the wheel/rail contact is critical to railroad engineering, and this problem has been the subject of research for about a century now. Several compelling mathematical models have been proposed, but the experimental verification of those theories has proven to be difficult. Traditionally, field testing data has been utilized for comparison with prediction from the models. However, field tests are plagued by a low level of noise control and the inability to carry out sophisticated parametric analyses. VT-FRA Roller Rig holds the promise to fill this gap with its sophisticated electro-mechanical design and high precision instrumentation. The VT-FRA Roller Rig replicates the wheel-rail contact in a 1 /4 th scale by utilizing the INRETS scaling strategy. The locomotive wheel is replicated by a 0.2m diameter wheel and the tangent track is replicated by a 1m diameter roller. The relative size difference ensures that the contact distortion effects from the use of roller are kept to a minimum. The wheel and the roller are arranged in a vertical configuration, and are independently powered by two 19.4 kW servo motors. This enables the VT-FRA Roller Rig to achieve a precise creepage control of up to 0.1%. VT-FRA Roller Rig also has six heavy-duty servo linear actuators which are responsible for controlling four boundary conditions: cant angle, angle of attack, lateral displacement and vertical load. A sophisticated six-axis contact force-moment measurement system allows for precise measurements with a high dynamic bandwidth. The Rig was operationalized successfully with all degrees of freedom working in the default position feedback control. During the Rig’s commissioning, this approach was found to result in force fluctuations that were larger than desired. Since the vertical force affects the longitudinal and lateral traction between the wheel and roller, keeping the fluctuations to a minimum provides a better test condition. Testing and data analysis revealed the issue to be in the control method. The relative position of the wheel and roller was being controlled instead of controlling the forces between them. This study documents the development process of a reliable force control methodology for the VTFRA Roller Rig. Force control is a far more challenging control problem when compared to position control because it requires a faster dynamic response and full knowledge of forces at the interface. Additionally, force control could result in dynamic instability more readily than position control. Multiple methods for force control were implemented on the VT-FRA Roller Rig. Satisfactory solution is achieved with the complicated cascaded loop force/position controller, and the stability and performance of the control system is ensured by a slew of tests at various operating conditions. This study also explores the possibility of automating the tests in order to enable running a larger number of tests in a shorter period of time. A multi-thread software is developed in C++ for executing a user-defined position, velocity, or force vs. time trajectory, and for recording the data automatically. The software also provides continuous monitoring, and performs a safe shutdown if a fault is detected. An intuitive GUI is provided for constant data polling and ease of user operation. The code is modular in order to accommodate future modifications and additions for various testing needs. The engineering upgrades included in this study, together with the baseline testing, complete the commissioning of the VT-FRA Roller Rig. With unparalleled parameter control and testing repeatability, the VT-FRA Roller Rig holds the promise of being used successfully for various contact mechanics needs that may arise in the railroad industry.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2006. / This thesis is about the dynamic control of a permanent magnet assisted reluctance synchronous machine (PMA RSM). The PMA RSM in this thesis is a 110 kW traction machine and is ideal for the use in electrical rail vehicles. An application of the dynamic control of the PMA RSM in electrical rail vehicles is to reduce wheel slip. The mathematical model of the PMA RSM is derived and explained in physical terms. Two methods of current control for the PMA RSM are investigated, namely constant field current control (CFCC) and constant current angle control (CCAC). It is shown that CCAC is more appropriate for the PMA RSM. A current controller for the PMA RSM that guarantees stability is derived and given as an analytic formula. This current controller can be used for any method of current control, i.e. CFCC or CCAC. An accurate simulation model for the PMA RSM is obtained using results from finite element analysis (FEA). The accurate model is used in a simulation to verify CCAC. A normal proportional integral speed controller for the PMA RSM is designed and the design is also verified by simulation. Practical implementation of the current and speed controllers is considered along with a general description of the entire drive system. The operation of the resolver (for position measurement) is given in detail. Important safety measures and the design of the electronic circuitry to give protection are shown. Practical results concerning current and speed control are then shown. To improve the dynamic performance of the PMA RSM, a load torque observer with compensation current feedback is investigated. Two observer structures are considered, namely the reduced state observer and the full state observer. The derivation of the full state observer and the detail designs of the observer elements are given. The accurate simulation model of the PMA RSM is used to verify the operation of the observer structures and to evaluate the dynamic performance. Both observer structures are implemented practically and practical results are shown. One method of position sensorless control, namely the high frequency voltage injection method, is discussed in terms of the PMA RSM. This work is additional to the thesis but it is shown, because it raises some interesting questions regarding the dynamic control of the PMA RSM.

A motion compensated ADV system was evaluated to determine its ability to make measurements necessary for characterizing the variability of the ambient current in the Gulf Stream. The impact of IMU error relative to predicted turbulence spectra was quantified, as well as and the ability of the motion compensation approach to remove sensor motion from the ADV measurements. The presented data processing techniques are shown to allow the evaluated ADV to be effectively utilized for quantifying ambient current fluctuations from 0.02 to 1 Hz (50 to 1 seconds) for dissipation rates as low as 3x10-7. This measurement range is limited on the low frequency end by IMU error, primarily by the calculated transformation matrix, and on the high end by Doppler noise. Inshore testing has revealed a 0.37 Hz oscillation inherent in the towfish designed and manufactured as part of this project, which can nearly be removed using the IMU. / Includes bibliography. / Thesis (M.S.)--Florida Atlantic University, 2014. / FAU Electronic Theses and Dissertations Collection