Defense Advanced Research Projects Agency

La Defense Advanced Research Projects Agency (DARPA) (« Agence pour les projets de recherche avancée de défense ») est une agence du département de la Défense des États-Unis chargée de la recherche et développement des nouvelles technologies destinées à un usage militaire. Jusqu'à aujourd'hui, la DARPA a été à l'origine du développement de nombreuses technologies qui ont eu des conséquences considérables dans le monde entier dont les réseaux informatiques (notamment l'ARPANET qui a fini par devenir Internet) et le NLS (sigle représentant, en anglais, l'expression « oN-Line System », en français, littéralement, « système en ligne ») qui a été à la fois le premier système hypertexte et un précurseur important des interfaces graphiques devenues omniprésentes de nos jours. Mission accomplie parallèlement
Actuellement, l'énoncé de la mission de la DARPA est de . Histoire Les origines historiques d'un tel service remontent à la mise en place à partir de 1940 du Nat

Design optimization and dynamic analysis of a tensegrity-based footbridge

Nizar Bel Hadj Ali, Alberto Pascual Albi, Landolf-Giosef-Anastasios Rhode-Barbarigos, Ian Smith

Tensegrity structures are spatial structural systems composed of struts and cables with pin-jointed connections. Their stability is provided by the self-stress state in tensioned and compressed members. Although much progress has been made in advancing research into the tensegrity concept, a rapid survey of current activities in engineering practice shows that much of its potential has yet to be accomplished. A design optimization study for a tensegrity-based footbridge is presented in order to further advance the tensegrity concept in modern structural engineering. In the absence of specific design guidelines, design requirements for a tensegrity footbridge are stated. A genetic algorithm based optimization scheme is used to find a cost-effective design solution. The dynamic performance of the tensegrity footbridge is studied through parametric studies. Design results illustrate that the proposed tensegrity-based footbridge meets typical static and dynamic design criteria.

Elsevier2010

An Active Deployable Tensegrity Structure

Landolf-Giosef-Anastasios Rhode-Barbarigos

Tensegrity structures are spatial reticulated structures composed of cables and struts. Their stability is provided by a self-stress state among tensioned and compressed members. Although much progress has been made in advancing research into the tensegrity concept, the concept is not yet part of mainstream structural design. A design study for an active deployable tensegrity footbridge composed of pentagonal tensegrity-ring modules is presented in this thesis to further advance the tensegrity concept in modern structural engineering. Tensegrity-ring modules are deployable circuit-pattern modules that when combined form a "hollow rope". In the absence of specific design guidelines, a design procedure is proposed. Deployment is also included as a consideration for sizing. Deployment is usually not a critical design case for sizing members of deployable structures. However, for tensegrity systems, deployment may become critical due to the actuation required. The influence of continuous cables and spring elements in statics, dynamics as well as in deployment is investigated. A stochastic search algorithm is used to find cost-effective design solutions. The deployment of the tensegrity "hollow-rope" system requires employing active cables to simultaneously adjust several degrees of freedom. Therefore, actuation schemes with individually actuated cables, continuous actuated cables and spring elements are investigated. The geometric study of the deployment for a single module identifies the contact-free deployment-path space and the path with the minimum number of actuators required. The number of actuators is further reduced by employing continuous cables and spring elements. The structural response during deployment is studied numerically using a dynamic relaxation algorithm. Active elements can also be used to enhance performance during deployment and service. Although deployment is found to be feasible with a single actuation step for all actuated cables, obtaining a desired shape involves independent actuation in several cables. Independent actuation steps are successfully found with the combination of the dynamic relaxation algorithm and a stochastic search algorithm. Experimental studies conducted on physical models validate the feasibility of the active deployable tensegrity footbridge. Although results on the near-full-scale physical model are mitigated by eccentricities in the joints, unwanted joint movements and friction, they reveal the potential of the active deployable tensegrity system. Conclusions are as follows: Design results illustrate that the tensegrity "hollow-rope" concept is a viable system for a footbridge meeting typical static and dynamic design criteria. For the "hollow-rope" tensegrity footbridge, deployment is a critical design case when spring elements and continuous cables are employed in the system. The proposed actuation schemes successfully direct deployment and correct midspan displacements under service, but are less efficient regarding shape corrections during deployment. Future work involves studies aiming to improve the control of the structure and to employ actuated cables for damage compensation during deployment.

EPFL2012

Agency in Walking Humans Sensorimotor & [and] Cognitive Contributions to Bodily Self-Consciousness

Oliver Alan Kannape

Acting in our environment and experiencing ourselves as conscious agents are fundamental aspects of human selfhood. While large advances have been made with respect to understanding human sensorimotor control from an engineering approach, knowledge about its interaction with cognition and the conscious experience of movement, i.e. the sense of agency, is still speculative. In this thesis I have investigated these relationships by implementing a Virtual Reality platform, which allowed me to adapt agency paradigms previously limited to movements of individual body-parts to continuous full-body movements, i.e. locomotion. In a series of behavioural studies I investigated how a) spatial and b) temporal sensorimotor mismatches between participants' veridical gait-movements and their life-size visual feedback affected agency and gait. Our results illustrate that humans monitor the details of their movements and their location in space with surprisingly low accuracy. Participants did not become aware of sensorimotor mismatches below 15° and temporal mismatches of 210 ms, even though they automatically adapted their movements. These data confirm that gait and gait agency are distinct brain processes, that these can further be separated by taxing cognitive resources in dual task paradigms, and that they are comparable to agency mechanisms that have been described for upper limb movements. Together, these studies help to investigate sensorimotor components of selfhood that are of scientific, clinical, and legal relevance.

EPFL2012

An Active Deployable Tensegrity Structure

Landolf-Giosef-Anastasios Rhode-Barbarigos

EPFL2012