Floating-bending tensile-integrity structures

This is a conceptual work about the form-finding of a hybrid tensegrity structure. The structure was obtained from the combination of arch-supported membrane systems and diamond-type tensegrity systems. By combining these two types of structures, the resulting system features the “tensile-integrity” property of cables and membrane together with what we call “floating-bending” of the arches, a term which is intended to recall the words “floating-compression” introduced by Kenneth Snelson, the father of tensegrities. Two approaches in the form-finding calculations were followed, the Matlab implementation of a simple model comprising standard constant-stress membrane/cable elements together with the so-called stick-and-spring elements for the arches, and the analysis with the commercial software WinTess, used in conjunction with Rhino and Grasshopper. The case study of a T3 floating-bending tensile-integrity structure was explored, a structure that features a much larger enclosed volume in comparison to conventional tensegrity prisms. The structural design of an outdoor pavilion of 6 m in height was carried out considering ultimate and service limit states. This study shows that floating-bending structures are feasible, opening the way to the introduction of suitable analysis and optimization procedures for this type of structures.

3D-printed programmable tensegrity for soft robotics

Tensegrity structures provide both structural integrity and flexibility through the combination of stiff struts and a network of flexible tendons. These structures exhibit useful properties: high stiffness-to-mass ratio, controllability, reliability, structural flexibility, and large deployment. The integration of smart materials into tensegrity structures would provide additional functionality and may improve existing properties. However, manufacturing approaches that generate multimaterial parts with intricate three-dimensional (3D) shapes suitable for such tensegrities are rare. Furthermore, the structural complexity of tensegrity systems fabricated through conventional means is generally limited because these systems often require manual assembly. Here, we report a simple approach to fabricate tensegrity structures made of smart materials using 3D printing combined with sacrificial molding. Tensegrity structures consisting of monolithic tendon networks based on smart materials supported by struts could be realized without an additional post-assembly process using our approach. By printing tensegrity with coordinated soft and stiff elements, we could use design parameters (such as geometry, topology, density, coordination number, and complexity) to program system-level mechanics in a soft structure. Last, we demonstrated a tensegrity robot capable of walking in any direction and several tensegrity actuators by leveraging smart tendons with magnetic functionality and the programmed mechanics of tensegrity structures. The physical realization of complex tensegrity metamaterials with programmable mechanical components can pave the way toward more algorithmic designs of 3D soft machines.

Topology Optimization of Cable-Actuated, Shape-Changing, Tensegrity Systems for Path Generation

This paper presents a topology optimization methodology to synthesize cable-actuated, shape-changing, tensegrity systems specified through path generation requirements. Estabished tensegrity topology optimization procedures exist for static structures. For active tensegrity systems, motion characteristics are typically explored after the structural topology is determined. The work presented in this paper extends the established procedure to introduce prescribed motion into the topology optimization. A ground structure approach is used in conjunction with the design space. The topology optimization problem is formulated into a mixed integer linear programming problem. Desired motion is prescribed by identifying trace points in the design space and corresponding paths. The result of this methodology is the creation of a tensegrity system that can achieve shape-change as specified with prescribed paths.

A Vector Approach for Analytical Dynamics of a System of Rigid Bars

An analytical mechanics approach to derive equations of motion from vector kinematic description of rigid bar assemblies is developed. It is shown that various holonomic constraints governing multibody mechanical systems can be modeled using vector kinematics without using trigonometric/transcendental functions. The principle of virtual work is utilized to derive a map between the generalized coordinates associated with the vector approach and the angular velocity vector associated with the rigid bars. The utility of the vector approach is demonstrated by deriving the dynamics of tensegrity systems and a carpal wrist joint.