Organizational Unit:
George W. Woodruff School of Mechanical Engineering
George W. Woodruff School of Mechanical Engineering
Permanent Link
Research Organization Registry ID
Description
Previous Names
Parent Organization
Parent Organization
Organizational Unit
Includes Organization(s)
Organizational Unit
Organizational Unit
Organizational Unit
Organizational Unit
Organizational Unit
ArchiveSpace Name Record
88 results
Publication Search Results
Now showing
1 - 10 of 88
-
ItemTransporting fabric: Decentralized multi-agent control through a distributed active environment(Georgia Institute of Technology, 2019-11-12) Motter, KyleThe garment manufacturing industry has largely not benefited from the rapid advances in robotics and automation due to the inherent difficulty in handling flexible materials. At present the vast majority of sewing operations and material handling is still performed by humans in low-wage conditions. However, the industry is undergoing a paradigm shift toward custom and on demand manufacturing, increasing the need for automated handling of cut fabric. This thesis presents a comprehensive system based on novel distributed actuators, called budgers, for fabric manipulation and control. Using these distributed actuators as a foundation, this thesis explores a system architecture to provide practical, factory-ready local fabric control and a scalable solution for routing material through a large-scale implementation. This is presented within the context of treating the fabric as an “unactuated robot” traversing through the “actuated environment” of a budger array. Examined holistically as applied research, the thesis focuses on the actuation, feedback, and control, necessary for robust fabric manipulation. The budger is physically redesigned for significant performance, manufacturability, and serviceability gains. A custom vision feedback algorithm is presented for real-time stable feedback on the state of the fabric, including position and wrinkle information even in the case of deformation or occlusion. And a system architecture for the unactuated robot provides a scalable solution to handling large numbers of fabric across a decentralized network of budger groups.
-
ItemCoordinated rate control user interface and task identification of an excavator(Georgia Institute of Technology, 2016-12-09) Domingue, Beau B.Excavators are ubiquitous machines used in construction and agriculture globally. Many fluid power machines, including excavators, are operated directly by humans. For this reason, the efficacy of the communication channels between the human and machine have a high impact on system performance. While current excavator controls have been mastered by experts in the field, novel methods of control can improve operator performance and accelerate the learning process for novice operators. The current state of the art in excavator control uses 2 dual degree of freedom joysticks to control the flow to each of the excavator joints. There is a steep learning curve associated with this interface due to the large cognitive load it places on the operator. A coordinated rate control scheme was developed to alleviate the need for the operator to mentally perform the inverse kinematics of the linkage, and implemented using the standard joysticks to ensure compatibility with current state of the art hardware. In a 20 person experiment, subjects using coordinated rate control consistently removed more soil/time and soil/fuel than subjects using the conventional control. A novel method of task identification was developed to determine which phase of a trenching cycle the excavator is in at each time step. A supervised Artificial Neural Network with eight inputs, the four joystick velocity inputs and four joint positions, is used to classify the data into one of the three phases of a trenching cycle: dig, unload, and return. The ability to segment data enabled further analysis of the controllers within each phase, and can potentially be used to change the hydraulic priorities real time or to augment the operator input to achieve an optimal command.
-
ItemCaregiver-machine collaborative manipulation with an advanced hydraulically actuated patient transfer assist device(Georgia Institute of Technology, 2016-11-07) Humphreys, HeatherA significant need has been identified for an improved device to assist in transferring mobility limited patients, particularly those who are heavier or bariatric. Typical transfers include moving between a bed, wheelchair, chair/couch, toileting chair or toilet, car, or the floor. Currently, clinicians suffer more disabling workplace injuries than construction workers or firefighters, many of which are attributable to moving patients. A new, cost effective, hydraulically actuated prototype patient transfer assist device has been developed and fabricated; hydraulic actuation has advantages in terms of force density over electrical actuators that are typically used at this power scale. More generally, improved methods have been developed for control of machines that work collaboratively with humans, sharing a task and a workspace. Furthermore, this work investigates how hydraulic power, specifically electro-hydraulic pump controlled actuation, can be utilized in the human power scale. It also aims to overcome some of the control challenges with these actuation systems in this type of application, such as non-ideal characteristics of the low-cost actuation systems and management of a machine with large force capability operating in a home or clinical environment with humans in its workspace. A needs assessment has been performed, and the results indicate several needed improvements over current market patient lifts. A new prototype mobile patient transfer assist device (PTAD) has been designed and fabricated, with four actuated degrees of freedom (DOFs) fully functional. Each DOF is actuated by an electro-hydraulic pump control system. A simple, intuitive caregiver interface has been implemented, which provides coordinated rate control using an operator input from a force sensing handle mounted near the patient. This machine enables the exploration of controls and operator interfaces that have potential to transform healthcare. With a powerful machine working in a relatively delicate environment, it is necessary for the controller to manage any external interaction forces, to keep them in a safe range, in addition to smoothly controlling motion. A significant challenge lies in implementation of interaction control with these electro-hydraulic pump controlled actuators, which are intrinsically stiff, have slow dynamics, and have many nonlinear or non-ideal features. An impedance control framework has been formulated and implemented, using redundant sensing of obstacles, with feedback of both external interaction forces and proximity. Operator experiments were performed, using a mannequin representing the patient, including transfer operations between various locations in a simulated home/clinical environment. Some transfer experiments included obstacles to evaluate the control performance in unwanted collisions. Results indicate improvements over current market lifts in terms of operator ratings, even with this first generation prototype, and they show that comparable stages of the transfer operations can be performed considerably faster with a single operator using the PTAD than with the current market patient lift. Operator control experiment results show that the interaction control results in statistically significant reductions in collision forces by an average of 53%, and greater reductions in cases where the machine is moving faster. Similar software input experiments testing interaction control performance show reductions in collision forces of 87%. Overall, the results demonstrate that the new features of the patient transfer assist device make it easier, more efficient and safer to use, as compared with current market patient lifts. Beyond the patient transfer application, this project aims to make steps toward improving control in the broader application set of machines that work collaboratively with humans, sharing a task and a workspace; for example, in construction, manufacturing, or distribution.
-
ItemConstrained model predictive control for compliant position tracking of pneumatic systems(Georgia Institute of Technology, 2016-05-20) Daepp, Hannes GorkinPneumatic actuation is frequently applied to situations that warrant inherent compliance, such as prostheses, orthoses or walking robots, i.e., natural motions and applications in which interaction with humans/the environment are anticipated. However, compliance, as well as friction, lead to position control challenges that are commonly countered using aggressive controllers like sliding mode (SMC) or high-gain PID control, resulting in stiff system dynamics. Even hybrid force-position controller dynamics are ultimately subject to a clear trade-off of compliance and accuracy. In this thesis, this challenge is addressed via a constrained Model Predictive Controller that treats compliance as a bound rather than a target to achieve compliant tracking. A comprehensive literature review explores the state-of-the-art and defines performance targets, and a set of 1 degree of freedom (DoF) tests is established to compare controllers and convert qualitative controller goals into quantitative design specifications. Four benchmark controllers that span the stiffness-accuracy spectrum -- SMC, Linear Quadratic Regulation/Tracking, PID, and Impedance Control -- are implemented in simulation and on hardware, and are used to produce baseline results and verify performance targets. The predictive controller is implemented with admittance and impedance constraints and compared to benchmarks on the 1-DoF system. Additionally, new friction compensation methods are introduced that leverage the predictive structure to improve friction compensation for slow systems, and are compared to additive compensation methods. Results show that constrained MPC enforces impedance bounds on a tracked system, and achieve results with accuracy comparable to the best benchmark performance at a given compliance bound. Additionally, because compliance is enforced as a bound rather than a target, the highest tracking accuracy achieved with MPCs ultimately happens at the minimum necessitated impedance, without a-priori knowledge of that impedance bound. Results are shown to extend to a multi-DoF system using a planar robotic arm with simultaneously actuated joints and subject to unexpected disturbances.
-
ItemRobust state estimation for the control of flexible robotic manipulators(Georgia Institute of Technology, 2013-07-16) Post, Brian KarlIn this thesis, a novel robust estimation strategy for observing the system state variables of robotic manipulators with distributed flexibility is established. Motivation for the derived approach stems from the observation that lightweight, high speed, and large workspace robotic manipulators often suffer performance degradation because of inherent structural compliance. This flexibility often results in persistent residual vibration, which must be damped before useful work can resume. Inherent flexibility in robotic manipulators, then, increases cycle times and shortens the operational lives of the robots. Traditional compensation techniques, those which are commonly used for the control of rigid manipulators, can only approach a fraction of the open-loop system bandwidth without inducing significant excitation of the resonant dynamics. To improve the performance of these systems, the structural flexibility cannot simply be ignored, as it is when the links are significantly stiff and approximate rigid bodies. One thus needs a model to design a suitable compensator for the vibration, but any model developed to correct this problem will contain parametric error. And in the case of very lightly damped systems, like flexible robotic manipulators, this error can lead to instability of the control system for even small errors in system parameters. This work presents a systematic solution for the problem of robust state estimation for flexible manipulators in the presence of parametric modeling error. The solution includes: 1) a modeling strategy, 2) sensor selection and placement, and 3) a novel, multiple model estimator. Modeling of the FLASHMan flexible gantry manipulator is accomplished using a developed hybrid transfer matrix / assumed modes method (TMM/AMM) approach to determine an accurate low-order state space representation of the system dynamics. This model is utilized in a genetic algorithm optimization in determining the placement of MEMs accelerometers for robust estimation and observability of the system’s flexible state variables. The initial estimation method applied to the task of determining robust state estimates under conditions of parametric modeling error was of a sliding mode observer type. Evaluation of the method through analysis, simulations and experiments showed that the state estimates produced were inadequate. This led to the development of a novel, multiple model adaptive estimator. This estimator utilizes a bank of similarly designed sub-estimators and a selection algorithm to choose the true value from a given set of possible system parameter values as well as the correct state vector estimate. Simulation and experimental results are presented which demonstrate the applicability and effectiveness of the derived method for the task of state variable estimation for flexible robotic manipulators.
-
ItemMatching feedback with operator intent for efficient human-machine interface(Georgia Institute of Technology, 2012-11-09) Elton, Mark DavidVarious roles for operators in human-machine systems have been proposed. This thesis shows that all of these views have in common the fact that operators perform best when given feedback that matches their intent. Past studies have shown that position control is superior to rate control except when operating large-workspace and/or dynamically slow manipulators and for exact tracking tasks. Operators of large-workspace and/or dynamically slow manipulators do not receive immediate position feedback. To remedy this lack of position feedback, a ghost arm overlay was displayed to operators of a dynamically slow manipulator, giving feedback that matches their intent. Operators performed several simple one- and two-dimensional tasks (point-to-point motion, tracking, path following) with three different controllers (position control with and without a ghost, rate control) to indicate how task conditions influence operator intent. Giving the operator position feedback via the ghost significantly increased performance with the position controller and made it comparable to performance with the rate control. These results were further validated by testing coordinated position control with and without a ghost arm and coordinated rate control on an excavator simulator. The results show that position control with the ghost arm is comparable, but not superior to rate control for the dynamics of our excavator example. Unlike previous work, this research compared the fuel efficiencies of different HMIs, as well as the time efficiencies. This work not only provides the design law of matching the feedback to the operator intent, but also gives a guideline for when to choose position or rate control based on the speed of the system.
-
ItemSimultaneous control of coupled actuators using singular value decomposition and semi-nonnegative matrix factorization(Georgia Institute of Technology, 2012-11-08) Winck, Ryder ChristianThis thesis considers the application of singular value decomposition (SVD) and semi-nonnegative matrix factorization (SNMF) within feedback control systems, called the SVD System and SNMF System, to control numerous subsystems with a reduced number of control inputs. The subsystems are coupled using a row-column structure to allow mn subsystems to be controlled using m+n inputs. Past techniques for controlling systems in this row-column structure have focused on scheduling procedures that offer limited performance. The SVD and SNMF Systems permit simultaneous control of every subsystem, which increases the convergence rate by an order of magnitude compared with previous methods. In addition to closed loop control, open loop procedures using the SVD and SNMF are compared with previous scheduling procedures, demonstrating significant performance improvements. This thesis presents theoretical results for the controllability of systems using the row-column structure and for the stability and performance of the SVD and SNMF Systems. Practical challenges to the implementation of the SVD and SNMF Systems are also examined. Numerous simulation examples are provided, in particular, a dynamic simulation of a pin array device, called Digital Clay, and two physical demonstrations are used to assess the feasibility of the SVD and SNMF Systems for specific applications.
-
ItemHuman-in-the-loop control for cooperative human-robot tasks(Georgia Institute of Technology, 2012-03-29) Chipalkatty, RahulEven with the advance of autonomous robotics and automation, many automated tasks still require human intervention or guidance to mediate uncertainties in the environment or to execute the complexities of a task that autonomous robots are not yet equipped to handle. As such, robot controllers are needed that utilize the strengths of both autonomous agents, adept at handling lower level control tasks, and humans, superior at handling higher-level cognitive tasks. To address this need, we develop a control theoretic framework that seeks to incorporate user commands such that user intention is preserved while an automated task is carried out by the controller. This is a novel approach in that system theoretic tools allow for analytic guarantees of feasibility and convergence to goal states which naturally lead to varying levels of autonomy. We develop a model predictive controller that takes human input, infers human intent, then applies a control that minimizes deviations from the intended human control while ensuring that the lower-level automated task is being completed. This control framework is then evaluated in a human operator study involving a shared control task with human guidance of a mobile robot for navigation. These theoretical and experimental results lay the foundation for applying this control method for human-robot cooperative control to actual human-robot tasks. Specifically, the control is applied to a Urban Search and Rescue robot task where the shared control of a quadruped rescue robot is needed to ensure static stability during human-guided leg placements in uneven terrain. This control framework is also extended to a multiple user and multiple agent system where the human operators control multiple agents such that the agents maintain a formation while allowing the human operators to manipulate the shape of the formation. User studies are also conducted to evaluate the control in multiple operator scenarios.
-
ItemDevelopment of a multi-platform simulation for a pneumatically-actuated quadruped robot(Georgia Institute of Technology, 2011-11-18) Daepp, Hannes GorkinSuccessful development of mechatronic systems requires a combination of targeted hardware and software design. The compact rescue robot (CRR), a quadruped pneumatically-actuated walking robot that seeks to use the benefits garnered from pneumatic power, is a prime example of such a system. This thesis discusses the development and testing of a simulation that will aid in further design and development of the CRR by enabling users to examine the impacts of pneumatic actuation on a walking robot. However, development of an entirely new dynamic simulation specific to the system is not practical. Instead, the simulation combines a MATLAB/Simulink actuator simulation with a readily available C++ dynamics library. This multi-platform approach results in additional incurred challenges due to the transfer of data between the platforms. As a result, the system developed here is designed in the fashion that provides the best balance of realistic behavior, model integrity, and practicality. An analytically derived actuator model is developed using classical fluid circuit modeling together with nonlinear area and pressure curves to model the valve and a Stribeck-Tanh model to characterize the effects of friction on the cylinder. The valve model is designed in Simulink and validated on a single degree-of-freedom test rig. This actuator model is then interfaced with SrLib, a dynamics library that computes dynamics of the robot and interactions with the environment, and validated through comparisons with a CRR prototype. Conclusions are focused on the final composition of the simulation, its performance and limitations, and the benefits it offers to the system as a whole.
-
ItemAdaptive control of variable displacement pumps(Georgia Institute of Technology, 2011-04-01) Wang, LongkeFluid power technology has been widely used in industrial practice; however, its energy efficiency became a big concern in the recent years. Much progress has been made to improve fluid power energy efficiency from many aspects. Among these approaches, using a valve-less system to replace a traditional valve-controlled system showed eminent energy reduction. This thesis studies the valve-less solution-pump displacement controlled actuators- from the view of controls background. Singular perturbations have been applied to the fluid power to account for fluid stiffness; and a novel hydraulic circuit for single rod cylinder has been presented to increase the hydraulic circuit stabilities. Recursive Least Squares has been applied to account for measurement noise thus the parameters have fast convergence rate, square root algorithm has further applied to increase the controller's numerical stability and efficiency. It was showed that this technique is consistent with other techniques to increase controller's robustness. The developed algorithm is further extended to a hybrid adaptive control scheme to achieve desired trajectory tracking for general cases. A hardware test-bed using the invented hydraulic circuit was built up. The experimental results are presents and validated the proposed algorithms and the circuit itself. The end goal of this project is to develop control algorithms and hydraulic circuit suitable for industrial practice.