Hongbin Fang

Recoverable and Programmable Collapse from Folding Pressurized Origami Cellular Solids.

We report a unique collapse mechanism by exploiting the negative stiffness observed in the folding of an origami solid, which consists of pressurized cells made by stacking origami sheets. Such a collapse mechanism is recoverable, since it only involves rigid folding of the origami sheets and it is programmable by pressure control and the custom design of the crease pattern. The collapse mechanism features many attractive characteristics for applications such as energy absorption. The reported results also suggest a new branch of origami study focused on its nonlinear mechanics associated with folding.

Dynamics of a bistable Miura-origami structure

Origami-inspired structures and materials have shown extraordinary properties and performances originating from the intricate geometries of folding. However, current state of the art studies have mostly focused on static and quasistatic characteristics. This research performs a comprehensive experimental and analytical study on the dynamics of origami folding through investigating a stacked Miura-Ori (SMO) structure with intrinsic bistability. We fabricate and experimentally investigated a bistable SMO prototype with rigid facets and flexible crease lines. Under harmonic base excitation, the SMO exhibits both intrawell and interwell oscillations. Spectrum analyses reveal that the dominant nonlinearities of SMO are quadratic and cubic, which generate rich dynamics including subharmonic and chaotic oscillations. The identified nonlinearities indicate that a third-order polynomial can be employed to approximate the measured force-displacement relationship. Such an approximation is validated via numerical study by qualitatively reproducing the phenomena observed in the experiments. The dynamic characteristics of the bistable SMO resemble those of a Helmholtz-Duffing oscillator (HDO); this suggests the possibility of applying the established tools and insights of HDO to predict origami dynamics. We also show that the bistability of SMO can be programmed within a large design space via tailoring the crease stiffness and initial stress-free configurations. The results of this research offer a wealth of fundamental insights into the dynamics of origami folding, and provide a solid foundation for developing foldable and deployable structures and materials with embedded dynamic functionalities.

Self-locking degree-4 vertex origami structures

A generic degree-4 vertex (4-vertex) origami possesses one continuous degree-of-freedom for rigid folding, and this folding process can be stopped when two of its facets bind together. Such facet-binding will induce self-locking so that the overall structure stays at a pre-specified configuration without additional locking elements or actuators. Self-locking offers many promising properties, such as programmable deformation ranges and piecewise stiffness jumps, that could significantly advance many adaptive structural systems. However, despite its excellent potential, the origami self-locking features have not been well studied, understood, and used. To advance the state of the art, this research conducts a comprehensive investigation on the principles of achieving and harnessing self-locking in 4-vertex origami structures. Especially, for the first time, this study expands the 4-vertex structure construction from single-component to dual-component designs and investigates their self-locking behaviours. By exploiting various tessellation designs, this research discovers that the dual-component designs offer the origami structures with extraordinary attributes that the single-component structures do not have, which include the existence of flat-folded locking planes, programmable locking points and deformability. Finally, proof-of-concept experiments investigate how self-locking can effectively induce piecewise stiffness jumps. The results of this research provide new scientific knowledge and a systematic framework for the design, analysis and utilization of self-locking origami structures for many potential engineering applications.

Phase coordination and phase–velocity relationship in metameric robot locomotion

This research proposes a new approach for the control of metameric robot locomotion via phase coordination. Unlike previous studies where global wave-like rules were pre-specified to construct the actuation sequence of segments, this phase coordination method generates robot locomotion by assigning the actuation phase differences between adjacent segments without any global prerequisite rules. To effectively coordinate the phase differences, different symmetry properties are introduced. Optimization is then carried out on various symmetrically coordinated phase-difference patterns to maximize the average steady-state velocity of the robot. It is shown that the maximum average velocity is always achieved when the reflectional symmetry is included in the phase-difference pattern, and the identical-phase-difference (IPD) pattern is preferred for implementation because it reduces the number of independent phase variables to only one without significant loss in locomotion performance. Extensive analytical investigations on the IPD pattern reveal the relationship between the average locomotion velocity and some important parameters. Theoretical findings on the relationship between the average velocity and the phase difference in the IPD pattern are verified via experimental investigations on an 8-segment earthworm-like metameric robot prototype. Finally, this paper reveals an interesting result that the optimized phase-difference pattern can naturally generate peristalsis waves in metameric robot locomotion without global prerequisite wave-like rules.

Design and experimental gait analysis of a multi-segment in-pipe robot inspired by earthworm's peristaltic locomotion

This paper reports the experimental progress towards developing a multi-segment in-pipe robot inspired by earthworm’s body structure and locomotion mechanism. To mimic the alternating contraction and elongation of a single earthworm’s segment, a robust, servomotor based actuation mechanism is developed. In each robot segment, servomotor-driven cords and spring steel belts are utilized to imitate the earthworm’s longitudinal and circular muscles, respectively. It is shown that the designed segment can contract and relax just like an earthworm’s body segment. The axial and radial deformation of a single segment is measured experimentally, which agrees with the theoretical predictions. Then a multisegment earthworm-like robot is fabricated by assembling eight identical segments in series. The locomotion performance of this robot prototype is then extensively tested in order to investigate the correlation between gait design and dynamic locomotion characteristics. Based on the principle of retrograde peristalsis wave, a gait generator is developed for the multi-segment earthworm-like robot, following which gaits of the robot can be constructed. Employing the generated gaits, the 8-segment earthworm-like robot can successfully perform both horizontal locomotion and vertical climb in pipes. By changing gait parameters, i.e., with different gaits, locomotion characteristics including average speed and anchor slippage can be significantly tailored. The proposed actuation method and prototype of the multi-segment in-pipe robot as well as the gait generator provide a bionic realization of earthworm’s locomotion with promising potentials in various applications such as pipeline inspection and cleaning.

Locking mechanisms in degree-4 vertex origami structures

Origami has emerged as a potential tool for the design of mechanical metamaterials and metastructures whose novel properties originate from their crease patterns. Most of the attention in origami engineering has focused on the wellknown Miura-Ori, a folded tessellation that is flat-foldable for folded sheet and stacked blocks. This study advances the state of the art and expands the research field to investigate generic degree-4 vertex (4-vertex) origami, with a focus on facet-binding. In order to understand how facet-binding attributes to the mechanical properties of 4-vertex origami structures, geometries of the 4-vertex origami cells are analyzed and analytically expressed. Through repeating and stacking 4-vertex cells, origami sheets and stacked origami blocks can be constructed. Geometry analyses discover four mechanisms that will lead to the self-locking of 4-vertex origami cells, sheets, and stacked blocks: in-cell facet-binding, inlayer facet-binding, inter-layer facet binding, and in-layer and inter-layer facet-bindings. These mechanisms and the predicted self-locking phenomena are verified through 3D simulations and prototype experiments. Finally, this paper briefly introduces the unusual mechanical properties caused by the locking of 4-vertex origami structures. The research reported in this paper could foster a new breed of self-locking structures with various engineering applications.

Phase Control of a Bio-Inspired Meta-Structural Locomotion Robot

This research investigates the rectilinear locomotion of a meta-structural robot inspired by the earthworm. First of all, an equivalent multi-segment model of the meta-structural locomotion robot is derived. By the method of averaging, the robot’s average steady-state velocity is obtained, which is a function of the phase differences among segments. Then a novel locomotion control scheme of adjusting actuation phases is proposed for the robot. It is shown that such control of the phase differences among actuators can significantly tailor not only the magnitude but also the direction of the robot’s average steady-state velocity. Locomotion tests with equal phase difference among segments are carried out on the robot prototype in a horizontal pipe. The predicted phase-velocity relationship is verified, and it is shown that the proposed control is more effective than the more traditional peristaltic locomotion gaits. The presented earthworm-like robot belongs to the general class of metastructures, the concept of synthesizing adaptive structures via modular element design and integration. This study lays the foundation for understanding and advancing the properties of such meta-structural locomotion robots.Copyright

Locomotion Gait Design of an Earthworm-Like Robot Based on Multi-Segment Fluidic Flexible Matrix Composite Structures

In this research, a concept of earthworm-like robot with fluidic flexible matrix composite (F2MC) segments as its actuators is investigated. It explores a novel application of F2MC in the bionics field. Firstly, a general kinematics model of robot with earthworm-like locomotion is developed. Based on this model, the locomotion mechanism is analyzed in order to determine the actuation performance requirement for the F2MC segment. Then an analytical model of the F2MC segment is adopted to estimate the finite deformation under internal pressurization. By doing so, the optimal configuration of the F2MC segment that meets the requirements as an actuator is determined. A conceptual design of the earthworm-like robot based on F2MC segment is presented. After that, robotic gaits are constructed based on the kinematic locomotion mechanism with some necessary physical assumptions. Directed locomotion can be achieved based on the constructed gaits. Aiming at increasing the average velocity and motion efficiency of the robot, locomotion gaits are optimized. Optimal gaits corresponding to the maximal velocity and maximal locomotion efficiency are obtained, respectively.Copyright

An earthworm-like robot using origami-ball structures

Earthworms possess extraordinary on-ground and underground mobility, which inspired researchers to mimic their morphology characteristics and locomotion mechanisms to develop crawling robots. One of the bottlenecks that constrain the development and wide-spread application of earthworm-like robots is the process of design, fabrication and assembly of the robot frameworks. Here we present a new earthworm-like robot design and prototype by exploring and utilizing origami ball structures. The origami ball is able to antagonistically output both axial and radial deformations, similar as an earthworm’s body segment. The origami folding techniques also introduce many advantages to the robot development, including precise and low cost fabrication and high customizability. Starting from a flat polymer film, we adopt laser machining technique to engrave the crease pattern and manually fold the patterned flat film into an origami ball. Coupling the ball with a servomotor-driven linkage yields a robot segment. Connecting six segments in series, we obtain an earthworm-like origami robot prototype. The prototype is tested in a tube to evaluate its locomotion performance. It shows that the robot could crawl effectively in the tube, manifesting the feasibility of the origami-based design. In addition, test results indicate that the robot’s locomotion could be tailored by employing different peristalsis-wave based gaits. The robot design and prototype reported in this paper could foster a new breed of crawling robots with simply design, fabrication, and assemble processes, and improved locomotion performance.