Multi-legged Structures Research Articles

Multilegged Underwater Running With Articulated Legs

Drawing inspiration from the locomotion modalities of animals, legged robots demonstrated the potential to traverse irregular and unstructured environments. Successful approaches exploited single-leg templates, like the spring-loaded inverted pendulum (SLIP), as a reference for the control of multilegged machines. Nevertheless, the anchoring between the low-order model and the actual multilegged structure is still an open challenge. This article proposes a novel strategy to derive actuation inputs for a multilegged robot by expressing the control requirements in terms of jump height and forward speed (derived from the limit cycle). We found that these requirements could be associated with a specific maximum force, successively split on an arbitrary number of legs and their relative actuation sets. The proposed approach has been validated in multibody simulation and real-world experiments by employing the underwater hexapod robot SILVER2. Results show that locomotion performances of the low-order model are reflected by the simulated and actual robot, showing that the articulated-USLIP (a-USLIP) model can faithfully explain the multilegged behavior under the imposed control inputs once hydrodynamic parameters have been tuned. More importantly, the proposed controller can be translated to the terrestrial case with minimal modifications and extended with additional layers to obtain more complex behaviors.

Peristaltic Wave Locomotion and Shape Morphing with a Millipede Inspired System

We present the mechanical model of a bio-inspired deformable system, modeled as a Timoshenko beam, which is coupled to a substrate by a system of distributed elements. The locomotion action is inspired by the coordinated motion of coupling elements that mimic the legs of millipedes and centipedes, whose leg-to-ground contact can be described as a peristaltic displacement wave. The multi-legged structure is crucial in providing redundancy and robustness in the interaction with unstructured environments and terrains. A Lagrangian approach is used to derive the governing equations of the system that couple locomotion and shape morphing. Features and limitations of the model are illustrated with numerical simulations.

Spin-orbit coupling, electron transport and pairing instabilities in two-dimensional square structures

Rashba spin-orbit effects and electron correlations in the two-dimensional cylindrical lattices of square geometries are assessed using mesoscopic two-, three- and four-leg ladder structures. Here the electron transport properties are systematically calculated by including the spin-orbit coupling in tight binding and Hubbard models threaded by a magnetic flux. These results highlight important aspects of possible symmetry breaking mechanisms in square ladder geometries driven by the combined effect of a magnetic gauge field spin-orbit interaction and temperature. The observed persistent current, spin and charge polarizations in the presence of spin-orbit coupling are driven by separation of electron and hole charges and opposite spins in real-space. The modeled spin-flip processes on the pairing mechanism induced by the spin-orbit coupling in assembled nanostructures (as arrays of clusters) engineered in various two-dimensional multi-leg structures provide an ideal playground for understanding spatial charge and spin density inhomogeneities leading to electron pairing and spontaneous phase separation instabilities in unconventional superconductors. Such studies also fall under the scope of current challenging problems in superconductivity and magnetism, topological insulators and spin dependent transport associated with numerous interfaces and heterostructures.

Heterogeneous nucleation for synthesis of sub-20 nm ZnO nanopods and their application to optical humidity sensing

We present a novel method for colloidal synthesis of one-dimensional ZnO nanopods by heterogeneous nucleation on zero-dimensional ZnO nanoparticle ‘seeds’. Ultra-small ZnO nanopods, multi-legged structures with sub-20nm individual leg diameters, can be synthesized by hydrolysis of a Zn2+ precursor growth solution in presence of ∼4nm ZnO seeds under hydrothermal conditions via microwave-assisted heating in as little as 20min of reaction time. One-dimensional ZnO nanorods are initially generated in the reaction mixture by heterogeneous nucleation and growth along the [0001] direction of the ZnO crystal. Growth of one-dimensional nanorods subsequently yields to an ‘attachment’ and size-focusing phase where individual nanorods fuse together to form multi-legged nanopods having diameters ∼15nm. ZnO nanopods exhibit broad orange-red defect-related photoluminescence in addition to a near-band edge emission at 373nm when excited above the band-gap at 350nm. The defect-related photoluminescence of the ZnO nanopods has been applied towards reversible optical humidity sensing at room temperature. The sensors demonstrated a linear response between 22% and 70% relative humidity with a 0.4% increase in optical intensity per % change in relative humidity. Due to their ultra-small dimensions, ZnO nanopods exhibit a large dynamic range and enhanced sensitivity to changes in ambient humidity, thus showcasing their ability as a platform for optical environmental sensing.

Model tests of four-legged jacket platforms in ice: Part 1. Model tests and results

Two series of model tests were performed to investigate the dynamic ice loads on two types of four-legged jacket platforms and the consequently structural responses. The first test series was carried out with cylindrical models and the second test series with conical models at the water level. To simulate the ice induce vibrations on multi-legged structures, a new series of test equipments was designed. The ice load on each model leg, structural displacements in three directions, and foundation reactions in two directions were measured during the tests. Different ice failure modes and structural responses were observed for different ice conditions and structural stiffness values. This paper provides a description of the test techniques and the experimental results. The important test phenomena are also discussed in this paper.

Redundant Parallel Mechanism for Haptic Applications

With haptic devices becoming increasingly common in both industrial field and consumer use, parallel mechanisms have been widely introduced for their high rigidity, output, accuracy and high backdrivability due to their multi-legged structure and fixed base actuators. In general parallel mechanism, redundancy enlarges the working area and avoids singularity. The redundant parallel mechanism we present introduces these advantages into haptic applications. Introducing this mechanism into a multiple degrees-of-freedom (DOF) structure realizes a wide range of working areas in rotation. The redundant parallel mechanism implemented in translational force display device, and multi-DOF force display device demonstrate the advantages of the redundant parallel mechanism in haptic applications. Following an overview, we introduce the prototype implementation and evaluation of these devices and discuss the effectiveness of the redundant parallel mechanism in haptic applications.

Dynamic Control of a Large Scale of Pneumatic Multichain Systems

AbstractThe aim of this paper is to propose a general principle able to manage the supervision, coordination, and control problems of a large scale of multichain structures in dynamic and interacting tasks. The main originality lays in its modular feature. The number of chains and of joint per chain are indeed not restricted. The only assumption is that all the chains are linked to a principal element from which the dynamic stability will be computed. This is for example the case for multi‐finger and multi‐legged structures for which respectively the palm and the trunk represent the principal element. The principle consists in controlling the stability of this element and distributing the effort on the other chains to maintain the stability of the whole. To increase the compliant feature, we consider that each joint is pneumatically actuated. Each joint is then dynamically controlled to ensure the asymptotic stability of the local chain it belongs to. A global architecture is presented where each part is detailed. An example is then displayed showing the performances of a two‐legged robot in the standing posture under external perturbation effects. © 2004 Wiley Periodicals, Inc.

Total Ice Forces on Multi-legged Structures

Total Ice Forces on Multi-legged Structures