An experimental study of hierarchical control laws for grasping and manipulation using a two-fingered planar hand

Compares the performance of hierarchical and single-level controllers in a grasping context, and concludes that for rapid, planar grasping motions of heavy objects the performance of a hierarchical control structure is superior to that of the two single-level controllers tested. Although the theory discussed applies to grasping problems of arbitrary complexity, the focus is on planar, two-fingered grasping for the sake of clarity and to simplify implementation and experimental testing of the proposed control algorithms. The control algorithms have been implemented on a multifingered hand

Robust Strategies for Selecting Vision-Based Planar Grasps of Unknown Objects with a Three-Finger Hand

Supporting Informatio

Grasp Stability Analysis with Passive Reactions

Despite decades of research robotic manipulation systems outside of highly-structured industrial applications are still far from ubiquitous. Perhaps particularly curious is the fact that there appears to be a large divide between the theoretical grasp modeling literature and the practical manipulation community. Specifically, it appears that the most successful approaches to tasks such as pick-and-place or grasping in clutter are those that have opted for simple grippers or even suction systems instead of dexterous multi-fingered platforms. We argue that the reason for the success of these simple manipulation systemsis what we call passive stability: passive phenomena due to nonbackdrivable joints or underactuation allow for robust grasping without complex sensor feedback or controller design. While these effects are being leveraged to great effect, it appears the practical manipulation community lacks the tools to analyze them. In fact, we argue that the traditional grasp modeling theory assumes a complexity that most robotic hands do not possess and is therefore of limited applicability to the robotic hands commonly used today. We discuss these limitations of the existing grasp modeling literature and setout to develop our own tools for the analysis of passive effects in robotic grasping. We show that problems of this kind are difficult to solve due to the non-convexity of the Maximum Dissipation Principle (MDP), which is part of the Coulomb friction law. We show that for planar grasps the MDP can be decomposed into a number of piecewise convex problems, which can be solved for efficiently. Despite decades of research robotic manipulation systems outside of highlystructured industrial applications are still far from ubiquitous. Perhaps particularly curious is the fact that there appears to be a large divide between the theoretical grasp modeling literature and the practical manipulation community. Specifically, it appears that the most successful approaches to tasks such as pick-and-place or grasping in clutter are those that have opted for simple grippers or even suction systems instead of dexterous multi-fingered platforms. We argue that the reason for the success of these simple manipulation systemsis what we call passive stability: passive phenomena due to nonbackdrivable joints or underactuation allow for robust grasping without complex sensor feedback or controller design. While these effects are being leveraged to great effect, it appears the practical manipulation community lacks the tools to analyze them. In fact, we argue that the traditional grasp modeling theory assumes a complexity that most robotic hands do not possess and is therefore of limited applicability to the robotic hands commonly used today. We discuss these limitations of the existing grasp modeling literature and setout to develop our own tools for the analysis of passive effects in robotic grasping. We show that problems of this kind are difficult to solve due to the non-convexity of the Maximum Dissipation Principle (MDP), which is part of the Coulomb friction law. We show that for planar grasps the MDP can be decomposed into a number of piecewise convex problems, which can be solved for efficiently. We show that the number of these piecewise convex problems is quadratic in the number of contacts and develop a polynomial time algorithm for their enumeration. Thus, we present the first polynomial runtime algorithm for the determination of passive stability of planar grasps. For the spacial case we present the first grasp model that captures passive effects due to nonbackdrivable actuators and underactuation. Formulating the grasp model as a Mixed Integer Program we illustrate that a consequence of omitting the maximum dissipation principle from this formulation is the introduction of solutions that violate energy conservation laws and are thus unphysical. We propose a physically motivated iterative scheme to mitigate this effect and thus provide the first algorithm that allows for the determination of passive stability for spacial grasps with both fully actuated and underactuated robotic hands. We verify the accuracy of our predictions with experimental data and illustrate practical applications of our algorithm. We build upon this work and describe a convex relaxation of the Coulombfriction law and a successive hierarchical tightening approach that allows us to find solutions to the exact problem including the maximum dissipation principle. It is the first grasp stability method that allows for the efficient solution of the passive stability problem to arbitrary accuracy. The generality of our grasp model allows us to solve a wide variety of problems such as the computation of optimal actuator commands. This makes our framework a valuable tool for practical manipulation applications. Our work is relevant beyond robotic manipulation as it applies to the stability of any assembly of rigid bodies with frictional contacts, unilateral constraints and externally applied wrenches. Finally, we argue that with the advent of data-driven methods as well as theemergence of a new generation of highly sensorized hands there are opportunities for the application of the traditional grasp modeling theory to fields such as robotic in-hand manipulation through model-free reinforcement learning. We present a method that applies traditional grasp models to maintain quasi-static stability throughout a nominally model-free reinforcement learning task. We suggest that such methods can potentially reduce the sample complexity of reinforcement learning for in-hand manipulation.We show that the number of these piecewise convex problems is quadratic in the number of contacts and develop a polynomial time algorithm for their enumeration. Thus, we present the first polynomial runtime algorithm for the determination of passive stability of planar grasps

Dynamic Grasp Adaptation:From Humans To Robots

The human hand is an amazing tool, demonstrated by its incredible motor capability and remarkable sense of touch. To enable robots to work in a human-centric environment, it is desirable to endow robotic hands with human-like capabilities for grasping and object manipulation. However, due to its inherent complexity and inevitable model uncertainty, robotic grasping and manipulation remains a challenge. This thesis focuses on grasp adaptation in the face of model and sensing uncertainties: Given an object whose properties are not known with certainty (e.g., shape, weight and external perturbation), and a multifingered robotic hand, we aim at determining where to put the fingers and how the fingers should adaptively interact with the object using tactile sensing, in order to achieve either a stable grasp or a desired dynamic behaviour. A central idea in this thesis is the object-centric dynamics: namely, that we express all control constraints into an object-centric representation. This simplifies computa- tion and makes the control versatile to the type of hands. This is an essential feature that distinguishes our work from other robust grasping work in the literature, where generating a static stable grasp for a given hand is usually the primary goal. In this thesis, grasp adaptation is a dynamic process that flexibly adapts the grasp to fit some purpose from the objectâs perspective, in the presence of a variety of uncertainties and/or perturbations. When building a grasp adaptation for a given situation, there are two key problems that must be addressed: 1) the problem of choosing an initial grasp that is suitable for future adaptation, and more importantly 2) the problem of design- ing an adaptation strategy that can react adequately to achieve desired behaviour of the grasped object. To address challenge 1 (planning a grasp under shape uncertainty), we propose an approach to parameterizing the uncertainty in object shape using Gaussian Processes (GPs) and incorporate it as a constraint into contact-level grasp planning. To realize the planned contacts using different hands interchangeably, we further develop a prob- abilistic model to predict the feasible hand configurations, including hand pose and finger joints, given the desired contact points only. The model is built using the con- cept of Virtual Frame(VF), and it is independent from the choice of hand frame and object frame. The performance of the proposed approach is validated on two differ- ent robotic hands, an industrial gripper (4 DOF Barrett hand) and a humanoid hand (16 DOF Allegro hand) to manipulate objects of daily use with complex geometry and various texture (a spray bottle, a tea caddy, a jug and a bunny toy). In the second part of this thesis, we propose an approach to the design of adapta- tion strategy to ensure grasp stability in the presence of physical uncertainties of objects(object weight, friction at contacts and external perturbation). Based on an object-level impedance controller, we first design a grasp stability estimator in the object frame using the grasp experience and tactile sensing. Once a grasp is predicted to be unstable during online execution, the grasp adaptation strategy is triggered to improve the grasp stability, by either changing the stiffness at finger level or relocating the position of one fingertip to a better area

A Predictive Fuzzy-Neural Autopilot for the Guidance of Small Motorised Marine Craft

This thesis investigates the design and evaluation of a control system, that is able to adapt quickly to changes in environment and steering characteristics. This type of controller is particularly suited for applications with wide-ranging working conditions such as those experienced by small motorised craft. A small motorised craft is assumed to be highly agile and prone to disturbances, being thrown off-course very easily when travelling at high speed 'but rather heavy and sluggish at low speeds. Unlike large vessels, the steering characteristics of the craft will change tremendously with a change in forward speed. Any new design of autopilot needs to be to compensate for these changes in dynamic characteristics to maintain near optimal levels of performance. This study identities the problems that need to be overcome and the variables involved. A self-organising fuzzy logic controller is developed and tested in simulation. This type of controller learns on-line but has certain performance limitations. The major original contribution of this research investigation is the development of an improved self-adaptive and predictive control concept, the Predictive Self-organising Fuzzy Logic Controller (PSoFLC). The novel feature of the control algorithm is that is uses a neural network as a predictive simulator of the boat's future response and this network is then incorporated into the control loop to improve the course changing, as well as course keeping capabilities of the autopilot investigated. The autopilot is tested in simulation to validate the working principle of the concept and to demonstrate the self-tuning of the control parameters. Further work is required to establish the suitability of the proposed novel concept to other control

Aerospace medicine and biology: A continuing bibliography with indexes (supplement 344)

This bibliography lists 125 reports, articles and other documents introduced into the NASA Scientific and Technical Information System during January, 1989. Subject coverage includes: aerospace medicine and psychology, life support systems and controlled environments, safety equipment, exobiology and extraterrestrial life, and flight crew behavior and performance

Time and subjectivity in contemporary short fiction

The aesthetics of contemporary short fiction have been shaped by its ability to engage with time as a boundless process of becoming. Historically and philosophically, the emergence of the short story as a specific genre may be related to modernist concepts of time and subjectivity. 'Real' time, as it is experienced by the subject, is a flux, in which past and present co-mingle. In Bergsonian terms, an unquantifiable 'duration' 1S contrasted with Newtonian concepts of absolute time as a succession of discrete units. As Hanson has argued, narrative in the short story 1S structured by a seemingly random association of 1mages rather than linear causality. I contextualize the short story genre, historically and culturally, examining texts by George Egerton and Katherine Mansfield before moving on to the main focus of my thesis, which is texts by Alice Munro and Grace Paley. These also present a dynamic reality, within time as a continuum. However, while utilizing modernist techniques, they also subvert them, problematizing concepts of transcendence. The blurring of the boundaries between autobiographical discourse, orality and fiction is used to destabilize notions of a unified subjectivity and of fixed truth. My analysis applies Bakhtinian theories on language and subject formation to investigate this presentation of time as endless self-renewal. I also draw on Genette's narrative theory and introduce Kristevan theory to investigate the speaking subject from a psychoanalytical viewpoint, with particular reference to the gendered subject. The Bakhtinian concept of the chronotope enables the theorization of the space-time nexus as the foundation of generic specificity; I offer a generic chronotope for the short story, which is grounded in the present moment. An examination of the fiction-making process, through a discussion of my own short stories, concludes this discussion of the short story as a form of contact with undefinable reality

Proceedings of the NASA Conference on Space Telerobotics, volume 3

The theme of the Conference was man-machine collaboration in space. The Conference provided a forum for researchers and engineers to exchange ideas on the research and development required for application of telerobotics technology to the space systems planned for the 1990s and beyond. The Conference: (1) provided a view of current NASA telerobotic research and development; (2) stimulated technical exchange on man-machine systems, manipulator control, machine sensing, machine intelligence, concurrent computation, and system architectures; and (3) identified important unsolved problems of current interest which can be dealt with by future research

Beyond the antisyzygy : Bakhtin and some modern Scottish writers

This dissertation shows how beneficial the ideas of the Russian literary theorist Mikhail Bakhtin are when used to investigate both classical and more recent Scottish writing. An exploration of how a desire for a Scottish literary identity early in this century became inextricably bound up with a sense of historical necessity and psychological division, known as the Caledonian Antisyzygy, forms the basis for the first section of this work. The limitations of this mode of thinking and its failure as a 'theory' are then exposed and compared with the greater benefits of Bakhtinian thought. Succeeding chapters lead the reader from the vision of an historically centered and 'fixed' perception of Scottish literature that dominated the early decades of this century, to one which offers the possibility of endless interpretation. Close analysis of works by Robert Burns, James Hogg, Robert Louis Stevenson, and Hugh MacDiarmid investigate how useful Bakhtin's theories are for reinterpreting classic Scottish texts. The remaining chapters analyze works by a selection of contemporary Scottish poets and novelists (Alasdair Gray, James Kelman, Tom Leonard, Edwin Morgan, Liz Lochhead, and Muriel Spark) in an effort to display both the continuity of a literary tradition and the applicability of Bakhtin's ideas of dialogic interaction and carnival response to recent fiction and poetry that is concerned with the preservation of unique yet pluralistic community identities. It will be shown how Bakhtin's work lends itself to the project of freeing cultural identity from the bonds of a linguistic, historical, and geographical determination that is based on sterile oppositional constructs

The Activity of Becoming a Second-Career Teacher

This is a study of three second-career teachers’ experiences of self transformation and the processes of socialization and identity formation each undergoes during his or her first three to five years as a full-time teacher. Each narrative offers a means through which to explore how liminal identity is at play during the transition to a new career—an experience that reshapes the experiences and self-understandings of individuals in the process of becoming teachers. The narratives that emerge from in-depth interviews showcase individuals with multi-faceted lives who have engaged in a multitude of personal and professional activities throughout their life course and find themselves between worlds occupying a liminal identity during the transition to a new culture. Exploring personal and professional histories provides an appreciation of the motivations, the transitional experiences, and the transformations of self that individuals experience as they seek to situate themselves within the new culture in and out of the classroom and formulate a life that includes teaching. The multiple cultural activities, and the selves constituted therein, allow second-career teachers to bring rich learning experiences to students not merely as experts in their professional field but as experienced and caring adults with complex lives to share. The presentation of co-constructed case histories and analysis of the narratives seeks to add to the literature stories that engender an appreciation of the complex transformations involved in becoming a second-career teacher. Implications for teacher education programs serving and retention of second-career teachers are discussed