Adaptive swing-up and balancing control of acrobot systems

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2009.Cataloged from PDF version of thesis.Includes bibliographical references (p. 22).The field of underactuated robotics has become the core of agile mobile robotics research. Significant past effort has been put into understanding the swing-up control of the acrobot system. This thesis implements an online, adaptive swing-up and balancing controller with no previous knowledge of the system's mass or geometric parameters. A least squares method is used to identify the 5 parameters necessary to completely characterize acrobot dynamics. Swing up is accomplished using partial feedback linearization and a pump up strategy to add energy to the system. The controller then catches the swung up system in the basin of attraction of an LQR controller computed using the estimated parameter values generated from online system identification. These results are then simulated using a MATLAB simulation environment.by Luke B. Johnson.S.B

Decentralized task allocation for dynamic environments

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2012.Cataloged from PDF version of thesis.Includes bibliographical references (p. 93-98).This thesis presents an overview of the design process for creating greedy decentralized task allocation algorithms and outlines the main decisions that progressed the algorithm through three different forms. The first form was called the Sequential Greedy Algorithm (SGA). This algorithm, although fast, relied on a large number of iterations to converge, which slowed convergence in decentralized environments. The second form was called the Consensus Based Bundle Algorithm (CBBA). CBBA required significantly fewer iterations than SGA but it is noted that both still rely on global synchronization mechanisms. These synchronization mechanisms end up being difficult to enforce in decentralized environments. The main result of this thesis is the creation of the Asynchronous Consensus Based Bundle Algorithm (ACBBA). ACBBA broke the global synchronous assumptions of CBBA and SGA to allow each agent more autonomy and thus provided more robustness to the task allocation solutions in these decentralized environments.by Luke B. Johnson.S.M

China's iGeneration

Collection of essays on twenty-first century Chinese cinema and moving image culture. This innovative collection of essays on twenty-first century Chinese cinema and moving image culture features contributions from an international community of scholars, critics, and practitioners. Taken together, their perspectives make a compelling case that the past decade has witnessed a radical transformation of conventional notions of cinema. Following China's accession to the WTO in 2001, personal and collective experiences of changing social conditions have added new dimensions to the increasingly diverse Sinophone media landscape, and provided a novel complement to the existing edifice of blockbusters, documentaries, and auteur culture. The numerous 'iGeneration' productions and practices examined in this volume include 3D and IMAX films, experimental documentaries, animation, visual aides-mémoires, and works of pirated pastiche

Multi-UAV network control through dynamic task allocation: Ensuring data-rate and bit-error-rate support

A multi-UAV system relies on communications to operate. Failure to communicate remotely sensed mission data to the base may render the system ineffective, and the inability to exchange command and control messages can lead to system failures. This paper describes a unique method to control communications through distributed task allocation to engage under-utilized UAVs to serve as communication relays and to ensure that the network supports mission tasks. The distributed algorithm uses task assignment information, including task location and proposed execution time, to predict the network topology and plan support using relays. By explicitly coupling task assignment and relay creation processes the team is able to optimize the use of agents to address the needs of dynamic complex missions. The framework is designed to consider realistic network communication dynamics including path loss, stochastic fading, and information routing. The planning strategy is shown to ensure that agents support both datarate and interconnectivity bit-error-rate requirements during task execution. System performance is characterized through experiments both in simulation and in outdoor flight testing with a team of three UAVs.Aurora Flight Sciences Corp. (Fellowship Program

Allowing non-submodular score functions in distributed task allocation

Submodularity is a powerful property that can be exploited for provable performance and convergence guarantees in distributed task allocation algorithms. However, some mission scenarios cannot easily be approximated as submodular a priori. This paper introduces an algorithmic extension for distributed multi-agent multi-task assignment algorithms which provides guaranteed convergence using non-submodular score functions. This algorithm utilizes non-submodular ranking of tasks within each agent's internal decision making process, while externally enforcing that shared bids appear as if they were created using submodular score functions. Provided proofs demonstrate that all convergence and performance guarantees hold with respect to this apparent submodular score function. The algorithm allows significant improvements over heuristic approaches that approximate truly non-submodular score functions.United States. Air Force Office of Scientific Research (Grant FA9550-11-1-0134

Decentralized Task Allocation with Coupled Constraints in Complex Missions

This paper presents a decentralized algorithm that creates feasible assignments for a network of autonomous agents in the presence of coupled constraints. The coupled constraints address complex mission characteristics that include assignment relationships, where the value of a task is conditioned on whether or not another task has been assigned, and temporal relationships, where the value of a task is conditioned on when it is performed relative to other tasks. The new algorithm is developed as an extension to the Consensus-Based Bundle Algorithm (CBBA), introducing the notion of pessimistic or optimistic bidding strategies and the relative timing constraints between tasks. This extension, called Coupled-Constraint CBBA (CCBBA), is compared to the baseline in a complex mission simulation and is found to outperform the baseline, particularly for task-rich scenarios.United States. Air Force Office of Scientific Research (Grant FA9550-08-1-0086)United States. Air Force Office of Scientific Research. Multidisciplinary University Research Initiative (Grant FA9550-08-1-0356

China's iGeneration

Collection of essays on twenty-first century Chinese cinema and moving image culture. This innovative collection of essays on twenty-first century Chinese cinema and moving image culture features contributions from an international community of scholars, critics, and practitioners. Taken together, their perspectives make a compelling case that the past decade has witnessed a radical transformation of conventional notions of cinema. Following China's accession to the WTO in 2001, personal and collective experiences of changing social conditions have added new dimensions to the increasingly diverse Sinophone media landscape, and provided a novel complement to the existing edifice of blockbusters, documentaries, and auteur culture. The numerous 'iGeneration' productions and practices examined in this volume include 3D and IMAX films, experimental documentaries, animation, visual aides-mémoires, and works of pirated pastiche

Ensuring Network Connectivity for Decentralized Planning in Dynamic Environments

This work addresses the issue of network connectivity for a team of heterogeneous agents operating in a dynamic environment. The Consensus-Based Bundle Algorithm (CBBA), a distributed task allocation framework previously developed by the authors and their colleagues, is introduced as a methodology for complex mission planning, and extensions are proposed to address limited communication environments. In particular, CBBA with Relays leverages information available through already existing consensus phases to predict the network topology at select times and creates relay tasks to strengthen the connectivity of the network. By employing underutilized resources, the presented approach improves network connectivity without limiting the scope of the active agents, thus improving mission performance.United States. Air Force Office of Scientific Research (Grant FA9550-08-1-0086)United States. Air Force Office of Scientific Research. Multidisciplinary University Research Initiative (FA9550-08-1-0356

Understanding decision making in a food-caching predator using hidden Markov models

Financial support was provided by the People’s Trust for Endangered Species (PTES), Zoologische Gesellschaft für Arten- und Populationsschutz (ZGAP), Quagga Conservation Fund and IdeaWild.Background Tackling behavioural questions often requires identifying points in space and time where animals make decisions and linking these to environmental variables. State-space modeling is useful for analysing movement trajectories, particularly with hidden Markov models (HMM). Yet importantly, the ontogeny of underlying (unobservable) behavioural states revealed by the HMMs has rarely been verified in the field. Methods Using hidden Markov models of individual movement from animal location, biotelemetry, and environmental data, we explored multistate behaviour and the effect of associated intrinsic and extrinsic drivers across life stages. We also decomposed the activity budgets of different movement states at two general and caching phases. The latter - defined as the period following a kill which likely involves the caching of uneaten prey - was subsequently confirmed by field inspections. We applied this method to GPS relocation data of a caching predator, Persian leopard Panthera pardus saxicolor in northeastern Iran. Results Multistate modeling provided strong evidence for an effect of life stage on the behavioural states and their associated time budget. Although environmental covariates (ambient temperature and diel period) and ecological outcomes (predation) affected behavioural states in non-resident leopards, the response in resident leopards was not clear, except that temporal patterns were consistent with a crepuscular and nocturnal movement pattern. Resident leopards adopt an energetically more costly mobile behaviour for most of their time while non-residents shift their behavioural states from high energetic expenditure states to energetically less costly encamped behaviour for most of their time, which is likely to be a risk avoidance strategy against conspecifics or humans. Conclusions This study demonstrates that plasticity in predator behaviour depending on life stage may tackle a trade-off between successful predation and avoiding the risks associated with conspecifics, human presence and maintaining home range. Range residency in territorial predators is energetically demanding and can outweigh the predator’s response to intrinsic and extrinsic variables such as thermoregulation or foraging needs. Our approach provides an insight into spatial behavior and decision making of leopards, and other large felids in rugged landscapes through the application of the HMMs in movement ecology.Publisher PDFPeer reviewe