An Active Deployable Tensegrity Structure

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.

A transformable tensegrity-footbridge system

Nizar Bel Hadj Ali, René Motro, Landolf-Giosef-Anastasios Rhode-Barbarigos, Ian Smith, Nicolas Willy Veuve

Tensegrity structures are self-stressed pin-jointed structures composed of cables and struts. They are advantageous systems for transformable applications since structural elements and active elements can be combined. A transformable “hollow-rope” tensegrity system that has been found viable for a deployable footbridge application is explored in this paper. Its deployment requires employing active cables to simultaneously adjust several degrees of freedom. However, 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 requires independent cable actuation. Actuation steps are thus identified with the combination of the dynamic relaxation algorithm and a stochastic search algorithm. Moreover, an experimental study was conducted on a near-full-scale physical model to validate the feasibility of the transformable tensegrity system. The scale was motivated by studying a model representative of a real civil structure having practical challenges that are similar to full-scale issues such as actuation-device constraints, joint eccentricities and friction. Although the numerical studies with dynamic relaxation reflect correctly the behavior of the idealized model, transformation of the near-full-scale transformable tensegrity model is limited by eccentricities in the joints, unwanted joint movements and friction. These results highlight the potential of this system and underline the importance of combining analytical models with large-scale physical models in the development of novel transformable structures.

EDITORIAL STARBOOKS2013

A Novel 4-DOF Origami Grasper With an SMA-Actuation System for Minimally Invasive Surgery

Marco Salerno

Minimally invasive surgery (MIS) is one of the most challenging techniques for robot designers due to the limited size of access points, the high miniaturization level, and the dexterity needed for performing surgical tasks. Conversely, only a few microfabrication technologies are currently available for developing such small-sized systems, which allow safe operations in human bodies. In order to match these challenges in MIS, both design and integration of actuation systems should proceed in parallel with an identification of most effective transmission mechanisms and kinematics. In this paper, an origami parallel module that generates two rotations and one translation is integrated with a twisting module and a compliant gripper to form a novel four-degree-offreedom grasper. The rotational motion leads to the pitch and yaw motion of the gripper, while the translational motion is converted to a roll motion of the gripper via the twisting module that is stacked on top of the parallel module. In light of plane-symmetric properties of the origami structure in the parallel module, both inverse and forward kinematics are resolved with a geometric approach, revealing a unique joint space and a kinematic mapping of the parallel module, leading to the design of two sets of on-board actuation systems. During the analysis, bending motion of a central spring and static properties of the compliant gripper are modeled using finite-element methods. The structure of the twisting module for motion transmission of the grasper is designed and fabricated using origami folding techniques. Gripping forces of the compliant gripper are evaluated in experimental tests. Further analyses of the system performance are addressed in accordance with the scaling ratio of miniaturization and the scalability of the system is demonstrated by a millimeter-sized origami parallel module produced by the smart composite microstructure fabrication process.

Ieee-Inst Electrical Electronics Engineers Inc2016

Experimental and numerical study on structural behavior of a single timber textile module

Markus Hudert, Laurent Humbert, Meisam Sistaninia, Yves Weinand

The present work investigates an innovative class of timber structure with potential applications in roofing, facade and bridge construction, called Timberfabric. The development of Timberfabric structures originates from the approach of harnessing the structural, modular and qualities of textiles in timber construction (Weinand and Hudert, 2010) [9]. Timberfabric structures are comprised of repetitive arrangements of one or more structural unit cells called Textile Modules. When properly designed, one obtains a modular and lightweight structure with interesting and unusual geometrical and structural qualities.This paper focuses on the single timber Textile Module. Based on the finite element (FE) method, a reliable procedure is proposed for modeling the overall assembly process of the Textile Module. For comparison, Textile Module prototypes are constructed at two different scales (large and intermediate scales) with different assembly conditions. The proposed geometrically nonlinear FE model allows evaluation of the stresses that are induced during the construction process and which may affect the structural integrity of the module. In particular, the risk of failure during assembly is identified using the anisotropic Tsai-Hill criterion. The structural behavior of the timber Textile Module is then investigated through bending tests using the constructed prototypes. During the loading procedure, the vertical deflections are measured at different locations on the prototype surface by means of external displacement transducers. Using the FE model, the corresponding deformed shapes are simulated by applying the bending loads on the prestressed Textile Module. Experimental displacements and FE predictions are thus compared and found to be in good agreement.

Elsevier2013

A Novel 4-DOF Origami Grasper With an SMA-Actuation System for Minimally Invasive Surgery

Marco Salerno

Ieee-Inst Electrical Electronics Engineers Inc2016