Browsing by Subject "Control"

Now showing 1 - 20 of 38

A framework for whole body augmentative exoskeleton control
(2018-12-06) Campbell, Orion Hubert, IV; Sentis, Luis
In this thesis, I present two primary contributions towards more capable augmentative exoskeleton systems including (1) the design and implementation of a robot-agnostic, high-level control infrastructure for better real-time performance and (2) a cohesive framework for whole-body augmentative exoskeleton control in a high-degree-of-freedom (dof) exoskeleton system. Both contributions were part of a larger project, in which our team designed and built a form-fitting lower-body augmentative exoskeleton with the objective to enhance a pilot's load carrying ability without sacrificing speed or maneuverability. Modern high-level control systems require excellent timing and low communication latencies to ensure stable, robust, and high-performance multijoint control. Towards this end, I designed and implemented a nodelet-based high-level controller wrapper that abstracts away and optimizes many of the implementation details involved in building such a control infrastructure. My first iteration of improvements used ROS's (Robot Operating System) intraprocess communication protocol along with proper integration of our RT-preempt kernel to ensure reliable, low-jitter timing performance and low-latency communication. I then helped to design infrastructure improvements that further reduced round-trip times via full system synchronization. My high-level control infrastructure has enabled significant advances for a variety of projects in the Human-Centered Robotics Lab (HCRL), including the development of a controller for an augmentative exoskeleton and dynamic walking using the lab's point-foot bipedal robot, Mercury. The second major contribution in this thesis is an algorithm that I developed for whole-body augmentative exoskeleton control. It uses a model of the exoskeleton to cancel static, gravitational loads, and measured cuff forces to attenuate human-exo interaction forces, including inertial loads and those caused by disturbances from the environment. The key contribution of this control scheme relative to other exoskeleton transparency controllers is how this algorithm (1) handles contact switching given the corresponding discrete changes in the dynamics and (2) routes the needed reaction forces to the ground given the underactuated, floating-base dynamics with contact constraints. I formulate a Quadratic Programming (QP) optimization problem to solve for permissible reaction forces and actuator torques that come as close as possible to providing the desired dynamic attenuation behavior of the controller while also satisfying wrench-cone constraints for each of the exoskeleton's contacts. A relaxation variable, penalized in the cost function, ensures the solver can always find a feasible solution, and cost function weights penalizing contact point accelerations and reaction force magnitudes are smoothly interpolated to ensure continuous torque commands as the system switches between two discrete sets of contacts
A meta-analysis of teacher autonomy support and control
(2018-05-07) Hooper, Sophia Man Yang; Falbo, Toni; Patall, Erika A.; Yeager, David; Schallert, Diane; Pustejovsky, James
A meta-analysis of 184 correlational studies and 25 experimental studies examined the relationships between teacher autonomy support and student academic and psychosocial outcomes. The results indicated that 1) teacher autonomy support was positively associated with desirable student academic and psychological outcomes (e.g., autonomous motivation, autonomy, and academic performance), 2) teacher control was negatively associated with desirable student outcomes, and 3) teacher autonomy support interventions enhanced desirable student outcomes. Moderator tests revealed several factors that explained the variation in teacher autonomy support relationships for certain outcomes. 1) The relationships of teacher autonomy support with students’ optimal outcomes were stronger when teacher autonomy support included multiple dimensions than when it included a single dimension. 2) The relationships of teacher autonomy support with students’ optimal outcomes were stronger for middle school students than for high school and college students. 3) The relationships of teacher control with students’ optimal outcomes were also stronger for middle school students than for students from other grade levels. 4) The teacher autonomy support correlations with proximal outcomes (i.e., autonomy, competence, and relatedness) were stronger than those with distal outcomes (i.e., engagement and academic performance). Implications for theory and future research were discussed.
Analysis and order reduction of an autonomous lunar lander navigation system
(2009-08) Newman, Clark Patrick; Bishop, Robert H., 1957-; Akella, Maruthi R.
A navigation system for precision lunar descent and landing is presented and analyzed. The navigation algorithm is based upon the extended Kalman Filter and employs measurements from an inertial measurement unit to propagate the vehicle position, velocity, and attitude forward in time. External measurements from an altimeter, star camera, terrain camera, and velocimeter are utilized in state estimate updates. The navigation algorithm also attempts to estimate the values of uncertain parameters associated with the sensors. The navigation algorithm also estimates the map-tie angle of the landing site which is a measure of the misalignment of the actual landing site location on the surface of the Moon versus the estimated position of the landing site. The navigation algorithm is subject to a sensitivity analysis which investigates the contribution of each error source to the total estimation performance of the navigation system. Per the results of the sensitivity analysis, it is found that certain error sources need not be actively estimated to achieve similar estimation performance at a reduced computational burden. A new, reduced-order system is presented and tested through covariance analysis and a monte carlo analysis. The new system is shown to have comparable estimation performance at a fraction of the computer run-time, making it more suitable for a real-time implementation.
Analysis of the power grid: structure and secure operations
(2015-08) Deka, Deepjyoti; Vishwanath, Sriram; Baldick, Ross; Kwasinski, Alexis; Meyers, Lauren A.; Moorty, Sainath
Power Grids form one of the vital backbone-networks of our society providing electricity for daily socio-economic activities. Given its importance, there is a greater need to understand the structure and control of the power grid for fair power market computations and efficient delivery of electricity. This work studies two problems associated with different aspects of today's power grid network and combines techniques from network science, control theory and optimization to analyze them. The first problem relates to understanding the common structural features observed in several power grids across the world and developing a trackable modeling framework that incorporates these features. Such a framework can lead to insights on structural vulnerability of the grid and help design realistic test cases to study effects of structural and operational reinforcements as the grid evolves with time. We develop a generative model based on spatial point process theory that provably produces the distinct exponential degree distribution observed in several power grids. Further, critical graph parameters like diameter, eigen-spread, betweenness centralities and clustering coefficients are used to compare the performance of our framework in modeling the power grids in Western USA and under ERCOT in Texas. The second problem discussed here involves a detailed study of malicious data attacks on state estimation in the power grid. Such data attacks pose a serious threat to efforts related to implementing distributed control for efficient operations in the grid. We develop a graph-theoretic framework to analyze the design of optimal data attacks and study cost-optimal techniques to build resilience against them. The study involves attacks by a practical adversary capable of modifying meter readings as well as of jamming the flow of information from meters to the grid controller. We prove that the design of optimal `hidden' and `detectable' attacks can be formulated as constrained graph-cut problems that depend on the relative costs of adversarial techniques, and present algorithms for attack construction. Further, we design a new `topology' attack regime where an adversary changes beaker statuses of grid lines to affect state estimation in systems where all meter measurements are encrypted and hence secure from manipulation. We discuss bounds on the security requirements imposed by the developed attack models and design algorithms for determining the optimal protection strategy. This helps present an accurate characterization of grid vulnerability to general data attacks and eavesdroppers and motivates efforts to expand the presence of new secure meters to foil cyber attacks in the grid.
An attitude determination and control system for small satellites
(2015-05) Tam, Margaret Hoi Ting; Fowler, Wallace T.; Lightsey, E. Glenn
A flexible, robust attitude determination and control (ADC) system is presented for small satellite platforms. Using commercial-off-the-shelf sensors, reaction wheels, and magnetorquers which fit within the 3U CubeSat form factor, the system delivers arc-minute pointing precision. The ADC system includes a multiplicative extended Kalman filter for attitude determination and a slew rate controller that acquires a view of the Sun for navigation purposes. A pointing system is developed that includes a choice of two pointing controllers -- a proportional derivative controller and a nonlinear sliding mode controller. This system can reorient the spacecraft to satisfy a variety of mission objectives, but it does not enforce attitude constraints. A constrained attitude guidance system that can enforce an arbitrary set of attitude constraints is then proposed as an improvement upon the unconstrained pointing system. The momentum stored by the reaction wheels is managed using magnetorquers to prevent wheel saturation. The system was thoroughly tested in realistic software- and hardware-in-the-loop simulations that included environmental disturbances, parameter uncertainty, actuator dynamics, and sensor bias and noise.
Azharite Clerics in Egypt : protection of their professional role in a changing religious and political environment, 1805-1968
(2015-05) Cumming, Willis Winfield; Di-Capua, Yoav, 1970-; Moin, Azfar A
This study seeks to investigate the relationship of the religious seminary, Azhar, in Egypt between the years of Muhammad Ali's reign (1805-1849), and the 1960s under Gamal Abdel Nasser (1918-1970). It pays special attention to the relationship that developed as a result of the "Development of Azhar Law" that Nasser promulgated in 1961. While the change in politics and popular religious culture during the late nineteenth and early twentieth century initially created difficulties for the institution’s religious scholars in preserving their professional role in Egyptian society, Azhar gained a new political importance as a center for producing works of apology in favor of Nasser's post-colonial regime. This new relationship proved auspicious not only for the state who could rely on Azhar's support against written attacks against it by Islamists, but also for the institution itself which gained the security of state financial support and a vested interest of the state in keeping the seminary graduates employed and active in social and political life. This transformation, although giving the institution a new political relevance, compromised its independence from state control to the point where it incorporated pro-state propaganda into its religious message. Consideration of these historical phenomena lead us to wonder about resulting legacy of Azhar's religious message and the implications it has for popular religion and politics in Egypt.
Closed-loop control of shock location to prevent hypersonic inlet unstart
(2014-08) Ashley, Jonathan Michael; Akella, Maruthi Ram, 1972-
Hypersonic inlet unstart remains a major technical obstacle in the successful implementation of hypersonic air-breathing propulsion systems such as ramjets and scramjets. Unstart occurs when combustor-induced pressure fluctuations lead to rapid expulsion of the shock system from the isolator, and is associated with loss of thrust. The research presented here attempts to mitigate this behavior through the design and implementation of a closed-loop control scheme that regulates shock location within a Mach 1.8 wind tunnel isolator test section. To localize the position of the shock within the isolator, a set of high frequency Kulite pressure transducers are used to measure the static pressure at various points along the wind tunnel test section. A novel Kalman filter based approach is utilized, which fuses the estimates from two distinct shock localization algorithms running at 250 Hz to determine the location of the shock in real time. The primary shock localization algorithm is a geometrical shock detection scheme that can estimate the position of the shock system even when it is located between pressure transducers. The second algorithm utilizes a sum-of-pressures technique that can be calibrated by the geometrical algorithm in real time. The closed-loop controller generates commands every 100 ms to actuate a motorized flap downstream of the test section in an effort to regulate the shock to the desired location. The closed-loop control implementation utilized a simple logic-based controller as well as a Proportional-Integral (PI) and a Proportional-Derivative (PD) Controller. In addition to the implementation of control algorithms, the importance of various design criteria necessary to achieve satisfactory control performance is explored including parameters such as pressure transducer spacing, shock localization speed, flap-motor actuation speed and actuator resolution. Experimental results are presented for various test scenarios such as regulation of the shock location in the presence of stagnation pressure disturbances as well as tracking of time-varying step inputs. Performance and robustness properties of the tested control implementations are discussed. Further areas of improvement for the closed-loop control system in both hardware and software are discussed, and the need for reduced-order dynamics-based controllers is presented.
A compliant control law for industrial, dual-arm manipulators
(2013-05) Zelenak, Andrew J; Landsberger, Sheldon; Pryor, Mitchell Wayne
Many of the first robots ever built, decades even before the first industrial robots, were humanoids. It seems like researchers have always sought to imitate the human form with their robots, and with good reason. Humans are incredibly flexible; they can perform a huge variety of tasks, from locomotion over rough terrain, to delicate assembly, to heavy lifting. A human’s second arm allows him to lift twice as much weight. His workspace is approximately doubled, and he can perform a broader variety of tasks as items are passed back and forth between hands. We sought to impart some of that same functionality to a strong, rigid, dual-arm robot. Specifically, we developed a control law that allows two robot arms to lift and manipulate an object in cooperation. As opposed to the prior art, our control law is tailored for industrial robots. These robots do not usually allow torque control and their control frequency is generally 60 Hz. Through the use of fuzzy logic, the control law is quite robust at 60 Hz control rates. Its simple structure reduces the computational cost of the algorithm by approximately 75% over Jacobian-based methods. Stability is proven and the controller parameters can be adjusted to handle perturbances of arbitrary magnitude. Since the robots behave as an admittance, torque control is not required. Several experiments were conducted to benchmark and validate the performance of this control law. The controller is able to maintain a clamp force within ± 4N despite a wide variation in trajectory and control frequency. This fine level of force control makes the controller suitable for delicate tasks. The conclusion suggests several extensions that would make this control law more useful. For example, adaptive control would improve the performance. A position feedback controller should be cascaded so that the robot arms’ tracking accuracy is improved. Many tasks (such as co-robotics) require external compliance, and we show how external compliance could easily be incorporated.
Computationally efficient algorithms for spacecraft relative navigation and rendezvous
(2023-08-02) Kaki, Siddarth Bhargava; Akella, Maruthi Ram, 1972-; Jones, Brandon; Zanetti, Renato; Russell, Ryan; D’Souza, Christopher
There is tremendous interest in the development of spacecraft guidance, navigation, and control technologies that enable on-orbit servicing, assembly, and manufacturing missions with limited human supervisory support. These applications provide strong motivations for the design of computationally lightweight algorithms that enable autonomous operations, especially for missions constrained by size, weight, power, and cost (SWaP-C) such as cubesats. However, the more democratic access to space has also further contributed to the space debris problem, with worryingly many defunct and derelict spacecraft crowding up precious space. Dealing with such noncooperative objects poses significant challenges, with large uncertainties in mass properties and applied forces by the environment. This dissertation addresses such problems related to SWaP-C constraints and also noncooperative targets within the fields of relative spacecraft navigation and rendezvous. The first topic addresses relative angular velocity and associated uncertainty estimation from a geometrical perspective via batch processes. The second topic addresses real-time relative pose estimation and tracking using monocular imagery for cubesat applications. The third topic addresses analytical guidance solutions for radial-thrust-based far-field rendezvous and orbit rotations. Finally, the fourth topic addresses semi-analytical techniques to achieve circular orbit changes with radial and velocity-normal thrust.
Control, learning, and innovation : a syncretic approach
(2010-05) Romo de Vivar y Sandoval, Carmen Alejandra; Browning, Larry D.
This research focuses on understanding the processes involved in successful innovation---a topic that has appeared in a large body of research, but no conclusive trend has emerged about it. For this reason, I chose a different lens in order to gain a more panoramic view of the events leading up to an innovation. In particular, this research utilized a methodology and ontology that set it apart from previous work. In previous research control/exploitation and learning/exploration are either presented as two categorically separate concepts or as continuum that runs between them. This research supports the idea that innovation operates on a continuum but does not support the idea that it only occurs when the pendulum settles toward the learning/exploration side. Instead, the data shows that innovation could indeed occur at any point along the learning/exploration side of the continuum and even at the central point where learning/exploration and control/exploitation weigh evenly. To conceptualize this middle point, I term this a "syncretism" of two normally opposing forces to account for a significant portion of the interview data.
Controlling trace impurities in a dividing wall distillation column
(2018-12) Donahue, Melissa Mary; Baldea, Michael; Eldridge, R. Bruce; Downs, Jim J; Edgar, Thomas; Rochelle, Gary
Dividing wall distillation columns (DWCs) separate a feed mixture into three pure product streams using one column shell. Though attractive due to capital and operational savings, DWCs have yet to gain widespread industrial acceptance. One notable concern is controllability. The research within this document examines a four component feed mixture to evaluate the operational flexibility of a fixed-design DWC through experimental and simulation-based studies. A pilot DWC was successfully controlled at multiple operating points, and a dynamic model was developed to reflect the pilot dividing wall column. As a form of process intensification, DWCs have a higher risk for controller interaction making conventional PID control potentially inadequate. This work successfully used two PID temperature controllers to maintain the column at steady state, transition the column between steady states, and reject feed disturbances without controller interaction. These controller pairings were determined using conventional controller design techniques. Therefore, for this chemical system and column design, traditional approaches to distillation control are sufficient to handle the intensified nature of DWCs. Because more components are present in DWCs in larger amounts, there is concern that temperature control will no longer imply composition control. Temperature control proved successful in this study. Controlling two temperatures maintained column operation against feed disturbances. In addition, prefractionator temperature correlated well with reboiler duty for multiple feed qualities therefore serving as a promising control variable though more disturbances such as feed composition should be examined. The minimum energy controller was not tested experimentally. A steady state model with heat transfer matching the pilot data was scaled to the size of an industrial tower and used to generate a minimum energy response surface for different vapor and liquid split values. In summary, this research investigated the operational flexibility of a fixed-design DWC using a four component mixture, tested the ability of conventional distillation control design techniques to determine control structures for a DWC, and created a minimum energy operating surface that could be used to examine control structures. A technique to determine the overall heat transfer coefficients was developed, and the model closely matched experimental steady state data.
A critical evaluation of modern low-thrust, feedback-driven spacecraft control laws
(2012-12) Hatten, Noble Ariel; Ocampo, Cesar; Akella, Maruthi
Low-thrust spacecraft trajectory optimization is often a difficult and time-consuming process. One alternative is to instead use a closed-loop, feedback-driven control law, which calculates the control using knowledge of only the current state and target state, and does not require the solution of a nonlinear optimization problem or system of nonlinear equations. Though generally suboptimal, such control laws are attractive because of the ease and speed with which they may be implemented and used to calculate feasible low-thrust maneuvers. This thesis presents the theoretical foundations for seven modern low-thrust control laws based on control law "blending" and Lyapunov control theory for a particle spacecraft operating in an inverse-square gravitational field. The control laws are evaluated critically to determine those that present the best combinations of thoroughness of method and minimization of user input required. The three control laws judged to exhibit the most favorable characteristics are then compared quantitatively through three numerical simulations. The simulations demonstrate the effectiveness of feedback-driven control laws, but also reveal several situations in which the control laws may perform poorly or break down altogether due to either theoretical shortcomings or numerical difficulties. The causes and effects of these issues are explained, and methods of handling them are proposed, implemented, and evaluated. Various opportunities for further work in the area are also described.
Data-driven modeling and optimization of sequential batch-continuous process
(2016-05) Park, Jungup; Edgar, Thomas F.; Baldea, Michael; Djurdjanovic, Dragan; Rochelle, Gary T; Truskett, Thomas M
Driven by the need to lower capital expenditures and operating costs, as well as by competitive pressure to increase product quality and consistency, modern chemical processes have become increasingly complex. These trends are manifest, on the one hand, in complex equipment configurations and, on the other hand, in a broad array of sensors (and control systems), which generate large quantities of operating data. Of particular interest is the combination of two traditional routes of chemical processing: batch and continuous. Batch to continuous processes (B2C), which constitute the topic of this dissertation, comprise of a batch section, which is responsible for preparing the materials that are then processed in the continuous section. In addition to merging the modeling, control and optimization approaches related to the batch and continuous operating paradigms --which are radically different in many aspects-- challenges related to analyzing the operation of such processes arise from the multi-phase flow. In particular, we will be considering the case where a particulate solid is suspended in a liquid ``carrier'', in the batch stage, and the two-phase mixture is conveyed through the continuous stage. Our explicit goal is to provide a complete operating solution for such processes, starting with the development of meaningful and computationally efficient mathematical models, continuing with a control and fault detection solution, and finally, a production scheduling concept. Owing to process complexity, we reject out of hand the use of first-principles models, which are inevitably high dimensional and computationally expensive, and focus on data-driven approaches instead. Raw data obtained from chemical industry are subject to noise, equipment malfunction and communication failures and, as such, data recorded in process historian databases may contain outliers and measurement noise. Without proper pretreatment, the accuracy and performance of a model derived from such data may be inadequate. In the next chapter of this dissertation, we address this issue, and evaluate several data outlier removal techniques and filtering methods using actual production data from an industrial B2C system. We also address a specific challenge of B2C systems, that is, synchronizing the timing of the batch data need with the data collected from the continuous section of the process. Variable-wise unfolded data (a typical approach for batch processes) exhibit measurement gaps between the batches; however, this type of behavior cannot be found in the subsequent continuous section. These data gaps have an impact on data analysis and, in order to address this issue, we provide a method for filling in the missing values. The batch characteristic values are assigned in the gaps to match the data length with the continuous process, a procedure that preserves meaningful process correlations. Data-driven modeling techniques such as principal component analysis (PCA) and partial least squares (PLS) regression are well-established for modeling batch or continuous processes. In this thesis, we consider them from the perspective of the B2C systems under consideration. Specific challenges that arise during modeling of these systems are related to nonlinearity, which, in turn, is due to multiple operating modes associated with different product types/product grades. In order to deal with this, we propose partitioning the gap-filled data set into subsets using k-means clustering. Using the clustering method, a large data set that reflects multiple operating modes and the associated nonlinearity can be broken down into subsets in which the system exhibits a potentially linear behavior. Also, in order to further increase the model accuracy, the inputs to the model need to be refined. Unrelated variables may corrupt the resulting model by introducing unnecessary noise and irrelevant information. By properly eliminating any uninformative variables, the model performance can be improved along with the interpretability. We use variable selection methods to investigate the model coefficients or variable importance in projection (VIP) values to determine the variables to retain in the model. Developing a model to estimate the final product quality poses different challenges. Measuring and quantifying the final product quality online can be limited due to physical and economic constraints. Physically, there are some quantities that cannot be measured due to sensor sizes or surrounding environments. Economically, the offline ``lab'' measurements may lead to destroying the sample used for the testing. These constraints lead to multiple sampling rates. The process measurements are stored and available continuously in real-time, but the quality measurements have much lower sampling rate. In order to account for this discrepancy, the online process measurements are down-sampled to match the sampling frequency of the lab measurements, and subsequently, soft sensors are can be developed to estimated the final product quality. With the soft sensor in place, the process needs to be optimized to maximize the plant efficiency. Using the real-time optimization, the optimal sequence of manipulated inputs that minimizes the off-spec products are calculated. In addition, the optimal sequences of setpoints can be calculated by carrying out the scheduling calculation with the process model. Traditionally, the scheduling calculation is carried out without taking the process dynamics into account, which could result in off-spec products if a disturbance is introduced. Incorporating the process dynamics into the scheduling layer poses many different challenges numerically. The proposed time scale bridging model (SBM) is able to capture the input-output behavior of the process while greatly reducing the computational complexity and time.
Design of a CubeSat guidance, navigation, and control module
(2011-08) Kjellberg, Henri Christian; Lightsey, E. Glenn.; Fowler, Wallace T.
A guidance, navigation, and control (GN&C) module is being designed and fabricated as part of a series of CubeSats being built by the Satellite Design Laboratory at the University of Texas. A spacecraft attitude control simulation environment called StarBox was created in order to perform trade studies and conduct performance analysis for the GN&C module. Navigation and control algorithms were tested using StarBox and then implemented onto an embedded flight computer. These algorithms were then tested in a hardware-in-the-loop simulation. In addition, the feasibility of utilizing advanced constrained attitude control algorithms was investigated by focusing on implementation in flight software. A mechanical and electrical design for the GN&C module was completed. A prototype system was set up on a bench-top for integrated testing. The analysis indicates that the system will satisfy the requirements of several CubeSat missions, including the current missions at the University of Texas known as Bevo2 and ARMADILLO.
The effects of control and uncertainty on children's supernatural beliefs
(2015-05) Cornelius, Chelsea Ann; Woolley, Jacqueline D.; Bigler, Rebecca; Markman, Arthur; Reeves, Lauretta; Whitson, Jennifer
Most people believe that the world is orderly and predictable, and one mechanism by which this belief is maintained is a sense of personal control, or the belief that one can predict and steer outcomes. Research indicates that when adults perceive a threat to their personal control, they will compensate for this threat by seeking other sources of control. However, it is unclear whether children also feel threatened by a lack of personal control or whether they seek similar sources of compensatory control as adults. The proposed studies investigated the process of compensatory control in children. A novel game primed children to feel either high personal control or low personal control in order to evaluate the extent to which children seek compensatory control via 1) the detection of visual patterns in random noise, 2) endorsement of superstitious explanations for events, and 3) explicit belief in supernatural sources of control. Children also completed a questionnaire designed to measure their intolerance of uncertainty. It was predicted that both the manipulation of control and individual differences in children’s willingness to tolerate uncertainty would affect compensatory control seeking behaviors. Results indicated that manipulation of personal control did not affect children’s pattern detection; however, the manipulation did affect children’s endorsement of karma-like explanations, such that children in the low-control condition were significantly more likely to endorse such explanations compared to children in the high-control condition. Regarding individual differences, results indicated a positive relationship between children’s intolerance of uncertainty and their explicit belief in God. These results are interpreted with regard to existing research with adults, and the implications for situational and dispositional motivations for control are discussed.
Embedding dynamics and control considerations in operational optimization of process and energy systems
(2016-05) Touretzky, Cara Rose; Baldea, Michael; Edgar, Thomas F; Truskett, Thomas M; Bonnecaze, Roger T; Novpselac, Atila
Embedding dynamics and control considerations within operational optimization decisions can result in improved performance of processes and energy systems. These efforts are motivated by modern sustainability initiatives, in particular demand response and demand management strategies for improving the efficiency of the electric grid. In these scenarios residential, commercial, and industrial electricity consumers are provided with a financial incentive to shift their demand such that the total load on the grid can be satisfied using efficient generation technologies and renewable energy sources. The financial incentive is typically a time-dependent price structure, where rates reflect the demand level and stress on the grid. Reacting to such fast-changing energy markets requires that process and energy systems be highly flexible, which is a significant departure from traditional steady state operation under fixed market conditions. In this context, flexibility means the ability to make frequent changes to the system operation (e.g., production setpoints, constraint levels, etc.) while still maintaining stability and satisfying operating constraints at all times. This necessitates the development of advanced control and decision making strategies which are aware of system dynamics. Accounting for dynamics by incorporating detailed, first-principles models of a system into optimization-based controllers or scheduling calculations would provide ample dynamic information. However, the resulting dynamic optimization formulations would be plagued by a large problem size, numerical difficulties associated with stiff equations and multiple time scales, and the presence of integer decisions. In this dissertation, we address these challenges through hierarchical controller designs and novel scheduling (and rescheduling) formulations including low-order models of relevant system dynamics, which are identified through an appropriate model reduction or system identification procedure. Case studies involving the built environment and chemical processes are used to demonstrate the proposed methods.
Energy-based periodic control of underactuated dissipative systems
(2021-05-07) Maweu, John Musembi; Longoria, Raul G.; Li, Wei
The variable length pendulum (VLP) is used as a platform to demonstrate that Lyapunov stabilizing control is achievable for underactuated systems in the presence of energy dissipation. The necessary background to describe the system is developed from elementary assumptions and Lagrangian mechanics. Phase portraits and limit cycles, whose discussion is essential to the development of the controller and to the presentation of results, are introduced. An existing Lyapunov control is adapted from the literature and extended to dissipative models and a discrete control. Nondimensionalization as described may be used for front-end engineering of model realizations. Results for control of both the VLP and the closely related skateboard model are then presented in a way that simplifies qualitative interpretations of the interactions of state variables.
Exploring the Relationships Between Childhood Externalizing Behaviors and Parenting Domains
(2023-05) Ecklund, Madison C.; Harden, K. Paige
Decades of previous research has found childhood externalizing behaviors and parenting practices to be significantly associated. Both genetics and environment have been investigated as potential influences of child and parent behavior. Results maintain that both mechanisms influence parent and child behavior within the context of the family system. The directionality of influence between child and parent behavior is not well understood, as different studies find conflicting results. Using longitudinal data from a sample of school-aged participants from the Texas Twin Project, the study in this thesis hypothesized a reciprocal causal relationship between childhood externalizing behavior, made up of rule-breaking and aggressive behavior, and the parenting domains of warmth and control. Through structural equation modeling, correlation plots and cross-lagged panel models were made in an effort to understand and explain the patterns of correlation and covariation among the variables of interest. This study found that childhood externalizing behaviors, parental warmth, and parental control are all significantly correlated with each other. It also found that each of those variables remain stable across time. This study found significant inverse covariation between parental control and parental warmth. Increased maternal control at Time 1, led to a decrease in maternal warmth at Time 2. Similarly, increased paternal control at Time 1, led to a decrease in paternal warmth at Time 2. The study did not detect any other significant causal relationships between the child and parent variables, and thus was unable to determine the direction of influence. While clearly associated, the nature of parent-child relationships in the context of the family unit remains ambiguous.
Fingertip position and force control for dexterous manipulation through accurate modeling of hand-exoskeleton-environment
(2019-05-10) Esmatloo, Paria; Deshpande, Ashish D.
Despite mechanical advancements in the design of hand exoskeleton devices to help people with hand disabilities regain partial hand function, their manipulation performance has remained far inferior compared to the human hand. State-of-the-art control strategies implemented on exoskeletons are mainly focused on robot joint-level position control, although accurate control of fingertip positions and forces is a requirement for reaching human-like dexterity and manipulation. The relationships between inputs (motor commands) and outputs (fingertip positions and forces) are highly nonlinear due to the inherent limitations in actuation structure of multiple degree of freedom (DOF) exoskeletons. Moreover, the simplified coupled models of finger joint movements do not hold when humans interact with external objects and exert forces at their fingertips. Therefore achieving dexterous manipulation will require accurate models of interaction between the fingers, hand exoskeleton system, and fingertip environment. In this thesis we accomplish, for the first time, fingertip position and force control with an assistive multi-DOF hand exoskeleton through accurate modeling of the hand-exoskeleton-environment. First, we provide kinematic and kinetic models for the human fingers, robot structure, and the Bowden cable power transmission for a fully actuated hand exoskeleton design. Next, we validate the models in simulation and demonstrate the successful control of fingertip position and forces in everyday drawing tasks. Finally, we utilize an experimental setup with a finger exoskeleton unit with two actuated DOF attached to an instrumented testbed finger to demonstrate successful tracking of fingertip position and forces within human accuracy levels through model-based control.
A first-principles directional drilling simulator for control design
(2014-12) Leonard, Rebecca Leigh; Oort, Eric van; Pryor, Mitchell Wayne
A directional drilling simulator was constructed using a re-formulation of first-principles classical mechanics in order to serve as a platform for advanced control design. Dedicated focus was placed on building a modular solution that would interface with an existing Supervisory Control And Data Acquisition (SCADA) architecture. Model complexity was restricted to include only the features required to make an immediate step change in tool face control performance through more accurate determination of torsional dead time and time constant values. Development of this simulator advanced the art of drilling automation by building a foundation upon which developers may design novel control schemes using big data gathered in the modern oilfield. This first-principles model is supported by theoretical formulation of equations of motion that capture fundamental behavior of the drill string during both rotary and slide drilling operations. Wellbore trajectory was interpolated between survey points using the Minimum Curvature Method, and a semi-soft-string drill string model was assumed. Equations of motion were derived using energy methods captured in both Hamiltonian and Lagrangian mechanics and solved using the finite-element method. Transient dynamic solutions were obtained using Newmark integration methods. A sensitivity analysis was conducted to determine which parameters played the most influential roles in dynamic drill string behavior for various operational scenarios and to what extent those parameters influenced torsional dead time and time constant calculations. The torsional time constant was chosen as a measure of correlation between case studies, due to the significant role this value plays in state-of-the-art tool face control algorithms. Simulation results were validated using field data collected from rigs using a SCADA system to operate in various shale plays in North America. Results from field tests were used to compare torsional time constant values calculated using manually-determined, simulation-based, and analytical methods and investigate directional drilling performance over a range of operational scenarios. Simulation-based time constant calculation results were consistently more accurate than analytically-determined values when compared to manually-tuned values. The first-principles directional drilling simulator developed for this study will be adopted by the existing SCADA system in order to standardize and improve slide drilling performance.