Zhong You

Foldable bar structures

A new, general type of two-dimensional foldable structures is presented, which extends and generalises the standard trellis-type foldable structure consisting of two sets of parallel straight rods connected by hinges. It is shown that any structure consisting of rigid, multi-angulated rods, i.e., straight rods with kinks at the hinge positions, can be folded if the rods form a tessellation of parallelograms. This discovery is exploited to investigate the structural layouts of flat and curved structures which can be folded along their perimeter.

Folding and deployment of curved tape springs

This paper presents a study of a special type of tape springs, that are both longitudinally and transversely curved, as required for the ribs of a novel deployable reflector. It is shown that, although curved tape springs have much in common with straight tape springs, there is an important difference for equal-sense folds with small rotation angles. Thus, it is shown that full deployment of the reflector cannot be guaranteed if equal-sense folds are used when packaging it.

Origami of thick panels

Expanding origami to thicker materials A vast array of origami patterns can be applied to the folding of any material of near-zero thickness, such as paper. However, the folding of thick materials requires adding material and offsets. Chen et al. develop a general model in which the standard spherical linkages (creases) are replaced with rigid panels connected via offset folds, so that the folding motion of both near-zero–thickness and thick objects is the same. Furthermore, the hinges are constrained to move in only one direction, which is important for applications such as unfolding solar panels in space or large engineering structures, where you want the folding to occur automatically. Science, this issue p. 396 A kinematic model enables application of origami patterns for zero-thickness sheets to panels made from thick materials. Origami patterns, including the rigid origami patterns in which flat inflexible sheets are joined by creases, are primarily created for zero-thickness sheets. In order to apply them to fold structures such as roofs, solar panels, and space mirrors, for which thickness cannot be disregarded, various methods have been suggested. However, they generally involve adding materials to or offsetting panels away from the idealized sheet without altering the kinematic model used to simulate folding. We develop a comprehensive kinematic synthesis for rigid origami of thick panels that differs from the existing kinematic model but is capable of reproducing motions identical to that of zero-thickness origami. The approach, proven to be effective for typical origami, can be readily applied to fold real engineering structures.

Cable-Stiffened Pantographic Deployable Structures Part 2: Mesh Reflector

The general concept of deployable structures based on pantographs that are deployed and stiffened by means of cables is applied to the design of the support structure for a large mesh reector. The two main components of this structure are a cable-stiffened pantographic ring that deploys and pretensions a cable network that, in turn, provides a series of stiff, geometrically accurate support points to which a reective wire mesh orexible membranewould beconnected.Thepantographicring isahighly redundantstructurewith an internalmechanism that permits synchronous deployment without any strain in the rods. The geometric conditions that have to be satis® ed in order for an n-sided ring to fold without any strain are investigated, including the effects of joint size. An experimental model has been designed and tested. In the folded con® guration, it has a diameter of 0.6 m and height of 1.2 m; in the deployed con® guration, it has a diameter of 3.5 m. Stiffness and deployment tests on this model have shown its behavior to be linear and the maximum shape error to be § 0.3 mm. HIS paper is the second in a series that deals with a new type of deployable structures where a foldable bar structure, which consists of pairs of straight bars connected by pivots and forming a pantograph, is deployed and stiffened by two sets of cables, known as active and passive cables. The passive cables are short cable elements connected to joints of the pantograph that get farther apart during deployment,and the length of each passive cable is such that it becomes taut when the pantograph is fully deployed. The active cables are longer elements that run over small pulleys and whose overall length is controlled by one or more electric motors. The layout of these cables is such that deployment of the pantograph can be activated by shortening the length of at least one of the active cables.Oncethepantographisdeployed,andhenceallofthepassive cables are taut, it is possible to set up an overall state of prestress in

Mobile assemblies based on the Bennett linkage

This paper presents a method of building large mobile assemblies using the Bennett linkage. The method is based on a basic single-layer layout consisting of overlapping 4R loops, each of which is a Bennett linkage. The assemblies created have a single degree of freedom, and are overconstrained and scaleable, allowing unlimited extension by repetition. In general, they deploy into a circular or non-circular cylindrical profile. The joints of the assemblies move spirally on the surface during deployment. Under some particular geometrical conditions, the profiles of the assemblies can become arch-like or flat. Moreover, the single-layer assemblies can be extended to form multi-layer mechanisms, even mobile masts. The paper shows the great versatility of the Bennett linkage and demonstrates that the century-old invention can play an important role in the construction of deployable structures.

Modelling rigid origami with quaternions and dual quaternions

This paper examines the mathematical modelling of rigid origami, a type of origami where all the panels are rigid and can only rotate about crease lines. The rotating vector model is proposed, which establishes the loop-closure conditions among a group of characteristic vectors. By building up an explicit relationship between the single-vertex origami and the spherical linkage mechanism, the rotating vector model can conveniently and directly describe arbitrary three-dimensional configurations and can detect some self-intersection. Quaternion and dual quaternion are then employed to represent the origami model, based on which two numerical methods have been developed. Through examples, it has been shown that the first method can effectively track the entire rigid-folding procedure of an initially flat or a non-flat pattern with a single vertex or multiple vertices, and thereby provide judgment for its rigid foldability and flat foldability. Furthermore, its ability to rule out some self-intersecting configurations during folding is illustrated in detail, leading to its ability of checking rigid foldability in a more or less sufficient way. The second method is especially for analysing the multi-vertex origami. It can also effectively track the trajectories of multiple vertices during folding.

Miura-Base Rigid Origami: Parameterizations of First-Level Derivative and Piecewise Geometries

Miura and Miura-derivative rigid origami patterns are increasingly used for engineering and architectural applications. However, geometric modelling approaches used in existing studies are generally haphazard, with pattern identifications and parameterizations varying widely. Consequently, relationships between Miura-derivative patterns are poorly understood, and widespread application of rigid patterns to the design of folded plate structures is hindered. This paper explores the relationship between the Miura pattern, selected because it is a commonly used rigid origami pattern, and first-level derivative patterns, generated by altering a single characteristic of the Miura pattern. Five alterable characteristics are identified in this paper: crease orientation, crease alignment, developability, flat-foldability, and rectilinearity. A consistent parameterization is presented for five derivative patterns created by modifying each characteristic, with physical prototypes constructed for geometry validation. It is also shown how the consistent parameterization allows first-level derivative geometries to be combined into complex piecewise geometries. All parameterizations presented in this paper have been compiled into a matlab Toolbox freely available for research purposes.

Polymeric coating of surface modified nitinol stent with POSS-nanocomposite polymer

Stent angioplasty is a successful treatment for arterial occlusion, particularly in coronary artery disease. The clinical communities were enthusiastic about the use of drug-eluting stents; however, these stents have a tendency to be a contributory factor towards late stage thrombosis, leading to mortality in a significant number of patients per year. This work presents an innovative approach in self-expanding coronary stents preparation. We developed a new nanocomposite polymer based on polyhedral oligomeric silsesquioxanes (POSS) and poly(carbonate-urea)urethane (PCU), which is an antithrombogenic and a non-biodegradable polymer with in situ endothelialization properties. The aim of this work is to coat a NiTi stent alloy with POSS-PCU. In prolonged applications in the human body, the corrosion of the NiTi alloy can result in the release of deleterious ions which leads to unwanted biological reactions. Coating the nitinol (NiTi) surface with POSS-PCU can enhance surface resistance and improve biocompatibility. Electrohydrodynamic spraying was used as the polymer deposition process and thus a few experiments were carried out to compare this process with casting. Prior to deposition the NiTi has been surface modified. The peel strength of the deposit was studied before and after degradation of the coating. It is shown that the surface modification enhances the peel strength by 300%. It is also indicated how the adhesion strength of the POSS-PCU coating changes post-exposure to physiological solutions comprised of hydrolytic, oxidative, peroxidative and biological media. This part of the study shows that the modified NiTi presents far greater resistance to decay in peel strength compared to the non-modified NiTi.

On mobile assemblies of Bennett linkages

This paper deals with deployable structures formed by interconnected Bennett linkages. A total of eight cases that allow mobile assemblies of Bennett linkages being built have been found by considering the links that may contain sections with negative length. Among the eight assemblies, four are distinct ones, including the one that we reported previously, and the remaining can be obtained by modifying the four cases. All these assemblies consist of a grid of nested Bennett linkages. The layout of the assemblies can be repeated to form a large deployable structure. When the Bennett linkages are equilateral, the assemblies expand to form arches. For a non-equilateral case, the assemblies deploy into a helical shape with a cylindrical profile. They are geometrically overconstrained with a single degree of mobility. The newly found assemblies provide more choices in the design of deployable structures.

Active and Passive Cable Elements in Deployable/Retractable Masts

This paper describes a new type of deployable masts for use in Space, based on the following elements. A deployable backbone, consisting of rods and/or plates, which can be folded or deployed freely. One or more active cable, following specially chosen routes along the mast, and running over small pulleys. The overall length of an active cable can vary between two extremes: a maximum length when the mast is fully folded; a minimum length when the mast is fully deployed. A set of passive cables joining pairs of points on the backbone. The passive cables are all slack when the backbone is partially folded and become taut when it is fully extended. A final, essential ingredient is structural prestress in the deployed state, so that all of the cables are in a state of pretension and therefore are able to carry any tensile or compressive force changes induced by external loads. An additional effect of this state of prestress is to remove backlash at the joints. Three deployable masts based on this approach are presented in the paper.