Theses and Dissertations from UMD
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New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a give thesis/dissertation in DRUM
More information is available at Theses and Dissertations at University of Maryland Libraries.
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Item MECHANICAL DESIGN OF DEXTEROUS MANIPULATOR LINKS(2018) Carlsen, Christopher James; Akin, David L; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This paper explores the challenges of dense structure-electronics packaging, specifically for a structural and electronics upgrade to the Ranger Tele-robotic Shuttle Experiment (RTSX) manipulators at the University of Maryland (UMD). Long serial-link manipulators are popular in the space industry, where the need for a long reach and high manipulability outweighs the need for high tip stiffness. For larger systems with co-located electronics, such as those used to berth vehicles on orbit, electronics packaging is not inhibited by the diameter of the link body. As link diameter decreases, co-locating electronics in the manipulator becomes diffcult without adding external extensions to house them. In such densely packed bodies, the control electronics are so integrated with structure that electronics maintenance requires disassembly of primary structure.Item A Self-Sealing Suction Technology for Versatile Grasping(2018) Kessens, Chad; Desai, Jaydev P; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This thesis describes the design, development, and evaluation of a novel "self-sealing" suction technology for grasping. As humans desire robots capable of handling an increasingly diverse set of tasks, end effectors that are able to grasp the widest possible range of object shapes and sizes will be needed to achieve the desired versatility. Technologies enabling the exertion of local pulling contact forces (e.g. suction) can be extraordinarily useful toward this end by handling objects that do not have features smaller than the grasper, a challenge for traditional grippers. However, simple operation and cost effectiveness are also highly desirable. To achieve these goals, we have developed a self-sealing suction technology for grasping. A small valve inside each suction cup nominally seals the suction port to maintain a vacuum within the system. Through the reaction forces of object contact, a lever action passively lifts the valve to engage suction on the object. Any cups not contacting the object remain sealed. In this way, a system with a large number of cups may effectively operate using any subset of its cups, even just one, to grasp an object. All cups may be connected to a central vacuum source without the need for local sensors or powered actuators for operation, forming a simple, compact, cost effective system. This thesis begins with the detailed design and analysis of the self-sealing suction technology. An extensive evaluation of the technology's robustness and performance demonstrates its features and limits. This includes self-seal quality and leakage, object seal and reseal, cycle performance, and normal and shear force-displacement, among other characterizations. It then describes the development of several devices utilizing the technology. The potential impact of the technology is highlighted through applications of human-controlled, robotic, and aerial grasping and perching. Finally, mathematical tools are developed to analyze potential grasps developed using the technology.Item Active Attention for Target Detection and Recognition in Robot Vision(2017) Luan, Wentao; Baras, John S; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)In this thesis, we address problems in building an efficient and reliable target detection and recognition system for robot applications, where the vision module is only one component of the overall system executing the task. The different modules interact with each other to achieve the goal. In this interaction, the role of vision is not only to recognize but also to select what and where to process. In other words, attention is an essential process for efficient task execution. We introduce attention mechanisms into the recognition system that serve the overall system at different levels of the integration and formulate four problems as below. At the most basic level of integration, attention interacts with vision only. We consider the problem of detecting a target in an input image using a trained binary classifier of the target and formulate the target detection problem as a sampling process. The goal is to localize the windows containing targets in the image, and attention controls which part of the image to process next. We observe that detectors’ response scores of sampling windows fade gradually from the peak response window in the detection area and approximate this scoring pattern with an exponential de- cay function. Exploiting this property, we propose an active sampling procedure to efficiently detect the target while avoiding an exhaustive and expensive search of all the possible window locations. With more knowledge about the target, we describe the target as template graphs over segmented surfaces. Constraint functions are also defined to find the node and edge’s matching between an input scene graph and target’s template graph. We propose to introduce the recognition early into the traditional candidate proposal process to achieve fast and reliable detection performance. The target detection thence becomes finding subgraphs from the segmented input scene graph that match the template graphs. In this problem, attention provides the order of constraints in checking the graph matching, and a reasonable sequence can help filter out negatives early, thus reducing computational time. We put forward a sub-optimal checking order, and prove that it has bounded time cost compared to the optimal checking sequence, which is not obtainable in polynomial time. Experiments on rigid and non-rigid object detection validate our pipeline. With more freedom in control, we allow the robot to actively choose another viewpoint if the current view cannot deliver a reliable detection and recognition result. We develop a practical viewpoint control system and apply it to two human-robot interaction applications, where the detection task becomes more challenging with the additional randomness from the human. Attention represents an active process of deciding the location of the camera. Our viewpoint selection module not only considers the viewing condition constraints for vision algorithms but also incorporates the low-level robot kinematics to guarantee the reachability of the desired viewpoint. By selecting viewpoints fast using a linear time cost score function, the system can deliver smooth user interaction experience. Additionally, we provide a learning from human demonstration method to obtain the score function parameters that better serves the task’s preference. Finally, when recognition results from multiple sources under different environmental factor are available, attention means how to fuse the observations to get reliable output. We consider the problem of object recognition in 3D using an ensemble of attribute-based classifiers. We propose two new concepts to improve classification in practical situations, and show their implementation in an approach implemented for recognition from point-cloud data. First, we study the impact of the distance between the camera and the object and propose an approach to classifier’s accuracy performance, which incorporates distance into the decision making. Second, to avoid the difficulties arising from lack of representative training examples in learning the optimal threshold, we set in our attribute classifier two threshold values to distinguish a positive, a negative and an uncertainty class, instead of just one threshold value. We prove the theoretical correctness of this approach for an active agent who can observe the object multiple times.Item CONCURRENT LOCALIZATION AND MAPPING WITH SONAR SENSORS AND CONSIDERATION OF VEHICLE MOTION(2016) Ismail, Hesham; Balachandran, Balakumar; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Simultaneous Localization and Mapping (SLAM) is a procedure used to determine the location of a mobile vehicle in an unknown environment, while constructing a map of the unknown environment at the same time. Mobile platforms, which make use of SLAM algorithms, have industrial applications in autonomous maintenance, such as the inspection of flaws and defects in oil pipelines and storage tanks. A typical SLAM consists of four main components, namely, experimental setup (data gathering), vehicle pose estimation, feature extraction, and filtering. Feature extraction is the process of realizing significant features from the unknown environment such as corners, edges, walls, and interior features. In this work, an original feature extraction algorithm specific to distance measurements obtained through SONAR sensor data is presented. This algorithm has been constructed by combining the SONAR Salient Feature Extraction Algorithm and the Triangulation Hough Based Fusion with point-in-polygon detection. The reconstructed maps obtained through simulations and experimental data with the fusion algorithm are compared to the maps obtained with existing feature extraction algorithms. Based on the results obtained, it is suggested that the proposed algorithm can be employed as an option for data obtained from SONAR sensors in environment, where other forms of sensing are not viable. The algorithm fusion for feature extraction requires the vehicle pose estimation as an input, which is obtained from a vehicle pose estimation model. For the vehicle pose estimation, the author uses sensor integration to estimate the pose of the mobile vehicle. Different combinations of these sensors are studied (e.g., encoder, gyroscope, or encoder and gyroscope). The different sensor fusion techniques for the pose estimation are experimentally studied and compared. The vehicle pose estimation model, which produces the least amount of error, is used to generate inputs for the feature extraction algorithm fusion. In the experimental studies, two different environmental configurations are used, one without interior features and another one with two interior features. Numerical and experimental findings are discussed. Finally, the SLAM algorithm is implemented along with the algorithms for feature extraction and vehicle pose estimation. Three different cases are experimentally studied, with the floor of the environment intentionally altered to induce slipping. Results obtained for implementations with and without SLAM are compared and discussed. The present work represents a step towards the realization of autonomous inspection platforms for performing concurrent localization and mapping in harsh environments.Item HUMAN FACTORS EVALUATION OF OPERATOR INTERFACES FOR TELEOPERATION OF A DEXTEROUS MANIPULATOR(2014) Davis, Kevin Patrick; Akin, David L; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Ground teleoperation of a satellite servicing spacecraft is a challenging task for a human operator, especially when there is significant communications delay between the control station and spacecraft. On-orbit operations are further complicated by a communications time delay between the ground and spacecraft. Operator performance can be improved with the use of a graphical simulation of the robot. By displaying the robot's commanded position, graphical simulation can also mitigate some effects of time delay. This work implemented a visualization tool and commanded display to assist operation of a remote dexterous manipulator. A Fitts' Law experiment was designed to determine the effectiveness of the commanded display in reducing the impact of time delay. The experiment was conducted with a six degree of freedom manipulator over a range of time delays, from 0.0 to 6.0 seconds. The experimental results were analyzed to assess the reduction of task completion time and operator workload.Item Design of Compliance Assisted Gaits for a Quadrupedal Amphibious Robot(2013) Vogel, Andrew Richard; Gupta, Satyandra K.; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The goal of this thesis was to develop an amphibious legged quadrupedal robot and associated gaits. Gaits of interest included walking, swimming, and smoothly transitioning between the two. Compliance was employed in the robot's legs to achieve swimming. Various types and configurations of compliant legs were evaluated using physical experiments and simulation. Three primary, two secondary, and two transition gaits were developed. An algorithm was developed to determine the appropriate course of action based on the current gait performance and the desired performance. The robot developed in this thesis met the goals of the design and demonstrated the technical feasibility of using compliance in amphibious legged robots.Item DEVELOPMENT AND EVALUATION OF A FLEXIBLE DISTRIBUTED ROBOT CONTROL ARCHITECTURE(2010) Ellsberry, Andrew John; Akin, David; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The communications and electronic systems that comprise a distributed control architecture for a robotic manipulator tie the high level control and motion planning to the electromechanical components. Custom solutions to this problem can be expensive in terms of time, cost, and maintenance. The integration of commercial off the shelf (COTS) motion controllers, combined with a robust communication standard, offers the potential to reduce the costs and development times for new robots. This thesis demonstrates an implementation of this architecture using commercial controllers and the CANopen communications bus on two existing dexterous robots. Testing is conducted to quantify the single joint performance of these modules. Additionally, the implementation of the system on a second robot arm was conducted in order to test the flexibility of the system for use with different actuators and feedback.Item Towards the Use of Dielectric Elastomer Actuators as Locomotive Devices for Millimeter-Scale Robots(2012) Pearse, Justin Daminabo; Smela, Elisabeth; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Dielectric elastomer actuators (DEAs) are electromechanical transducers that are promising for small scale applications. The work presented in this thesis seeks to develop DEAs as an actuation technology that would serve the purpose of ambulating millimeter-scale robots in a robust and predictable manner. To begin, the "planar" DEA configuration was characterized and the performances of various elastomers were investigated. Then, based on the requirements of a proposed robot walking gait, two principles were examined as means of converting in-plane actuation strain to bending actuation. Bending DEAs were fabricated and tested, and a maximum end displacement of 1.5 mm was achieved for a 10 mm long sample. Bending actuator design was optimized by maximizing both speed and payload capabilities. Finally, some challenges facing the design of robots ambulated by DEAs were outlined; of particular note is the DEAs' electrostatic interaction with each other and their surroundings.Item Development of a Quadruped Robot and Parameterized Stair-Climbing Behavior(2011) Brewer, Thomas; Gupta, Satyandra K; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Stair-climbing is a difficult task for mobile robots to accomplish, particularly for legged robots. While quadruped robots have previously demonstrated the ability to climb stairs, none have so far been capable of climbing stairs of variable height while carrying all required sensors, controllers, and power sources on-board. The goal of this thesis was the development of a self-contained quadruped robot capable of detecting, classifying, and climbing stairs of any height within a specified range. The design process for this robot is described, including the development of the joint, leg, and body configuration, the design and selection of components, and both dynamic and finite element analyses performed to verify the design. A parameterized stair-climbing gait is then developed, which is adaptable to any stair height of known width and height. This behavior is then implemented on the previously discussed quadruped robot, which then demonstrates the capability to climb three different stair variations with no configuration change.