Article

Elastomeric Origami: Programmable Paper-Elastomer Composites as Pneumatic Actuators

Wiley
Advanced Functional Materials
Authors:
To read the full-text of this research, you can request a copy directly from the authors.

Abstract

The development of soft pneumatic actuators based on composites consisting of elastomers with embedded sheet or fiber structures (e.g., paper or fabric) that are flexible but not extensible is described. On pneumatic inflation, these actuators move anisotropically, based on the motions accessible by their composite structures. They are inexpensive, simple to fabricate, light in weight, and easy to actuate. This class of structure is versatile: the same principles of design lead to actuators that respond to pressurization with a wide range of motions (bending, extension, contraction, twisting, and others). Paper, when used to introduce anisotropy into elastomers, can be readily folded into 3D structures following the principles of origami; these folded structures increase the stiffness and anisotropy of the elastomeric actuators, while being light in weight. These soft actuators can manipulate objects with moderate performance; for example, they can lift loads up to 120 times their weight. They can also be combined with other components, for example, electrical components, to increase their functionality.

No full-text available

Request Full-text Paper PDF

To read the full-text of this research,
you can request a copy directly from the authors.

... The main actuation technologies are pneumatic, shape memory materials, electroactive, magnetic, and chemical [2,4,6,7]. Pneumatic soft actuators, made of compliant materials, require complex geometries to transfer pressure into actuation and stiffening [8][9][10][11]. Actuators are often casted in complex procedures combining several components with multi-stage casting to create the required geometrical structures [8,10,[12][13][14][15][16][17][18]. ...
... Pneumatic soft actuators, made of compliant materials, require complex geometries to transfer pressure into actuation and stiffening [8][9][10][11]. Actuators are often casted in complex procedures combining several components with multi-stage casting to create the required geometrical structures [8,10,[12][13][14][15][16][17][18]. ...
... Additive manufacturing (AM) and fused filament fabrication (FFF) allows for the fabrication of components by extruding thermoplastic filament into a solidifying geometry [19][20][21]. Availability, simplicity, design flexibility, and affordability have made AM a common soft robotics mold fabrication method for elastomer casting [8,10,[12][13][14][16][17][18]. However, AM and FFF also introduces design freedom compared to casting processes, allowing for single-step fabrication with internal structures, thin walls, minimal volume 2 of 11 compartments, and complex geometries [3,5,22]. ...
Article
Full-text available
Additive manufacturing (AM) offers new possibilities in soft robotics as materials can easily be combined in multi-material designs. Proper sensing is essential for the soft actuators to interact with the surroundings successfully. By fabricating sensors through AM, sensors can be embedded directly into the components during manufacturing. This paper investigates NinjaTek Eels electrical resistance response to strain and the feasibility of using the material to create strain sensors. Strain sensors were 3D-printed out of NinjaTek Eel, a soft conductive TPU, and was tested during cyclic loading. A custom resistance-strain test rig was developed for measuring sensor behavior. The rig was calibrated for electric resistance, able to measure electric resistance as a function of strain. A parabolic response curve was observed during cyclic loading, which led to ambiguous readings. A 10-specimen validation test was conducted, evaluating the statistical variation for the first 100 loading cycles. The validation test showed that the sensor is capable of accurate and predictable readings during single load cases and cyclic loading, with the overall root mean square error being 66.9 Ω. Combining two sensors of different cross-sections gave promising results in terms of calibrating. By monitoring load cycles and strain rates, calibration can also be achieved by machine learning models by the microcontroller used to extract data. The presented work in this article explores the potential of using conductive TPUs as sensors embedded in products such as soft robotics, life monitoring of products with structural, and digital twins for live product to user feedback.
... This article presents research on developing and controlling the bending angle of a foldable soft actuator based on the origami principle without the need for a curvature sensor. Origami, the traditional Japanese art of folding paper, has been effectively used in several studies to fabricate pliable actuators [23][24][25]. Origami can provide enhanced strain capabilities for low-pressure actuation and lower strain energy when utilized in lightweight structures under certain arrangements. The use of several folds in a foldable structure enhances the mechanical flexibility of the mechanism. ...
... The thermodynamic process within the chamber was assumed to be adiabatic (q in −q out = 0); therefore, equation (25) can be expressed aṡ ...
Article
Full-text available
Soft actuators have recently attracted considerable attention owing to their inherent flexibility and adaptability. Nevertheless, for a soft robot to successfully engage with its surroundings and perform tasks with optimal effectiveness, it encounters a range of obstacles, including the need for precise and skillful movement, the capacity to perceive its own position and motion and the ability to effectively regulate its flexible structures. Researchers have developed techniques to integrate curvature sensors onto flexible devices, enabling them to detect and react to their positions. However, the integration of curvature sensors into flexible structures presents a substantial challenge in the structural manufacturing process. To address these concerns, this article presents a technique for designing, dynamic modeling and controlling the bending angle of foldable soft actuator without the need for curvature sensors. An optimal design for the geometric dimensions of the soft structure utilizing origami concepts to guarantee the requisite bending properties is suggested. A model-based control method that considers both the motion dynamic and the air dynamic is proposed for controlling the angular bending of the actuator. The motion dynamic was developed using the constant volume principle of the elastomer material and the neo-Hookean hyperelastic theory to establish the correlation between the applied pressure and bending angle. This dynamic model incorporates both the hyperelastic material characteristics of silicone rubber and the geometry of the actuator. Soft actuators have variations in the air chamber’s volume during operation and accurately measuring this variation is challenging. In order to tackle this problem, the fuzzy active disturbance rejection controller is used to predict these variations. The controller possesses exceptional position-tracking capability. This control strategy exhibited excellent responsiveness throughout the range of steady-state error values from approximately 1°–2°. Removing the curvature sensor increases the longevity of this soft actuator and promotes the efficiency of the manufacturing process, hence enhancing the practical application possibilities for the soft actuator made from super elastic material.
... [13] This structure is augmented by distributed magnetic actuation and a segmented design, which together significantly improve its controllability. The fluid-driven is the most commonly used actuation for origami robots, the origami pattern is usually incorporated with sealed chambers, and the actuation is achieved by pressurizing [14,15] or vacuuming [16,17] the chamber. The fabrication of complicated Origami patterns can be easily achieved by mold casting [14] with silicon or 3D printing. ...
... The fluid-driven is the most commonly used actuation for origami robots, the origami pattern is usually incorporated with sealed chambers, and the actuation is achieved by pressurizing [14,15] or vacuuming [16,17] the chamber. The fabrication of complicated Origami patterns can be easily achieved by mold casting [14] with silicon or 3D printing. [15] However, the source of the pressure is an obstacle to applying fluid-driven robots in many scenarios. ...
Article
Full-text available
Origami robots, inspired by an ancient form of paper folding art, are capable of achieving high displacement in a lightweight and compact design that conventional robots can hardly attain. It, however, remains a challenge to drive origami robots with in situ active materials that imply minimal added mass and complexity and can be easily controlled to achieve multiple actuation modalities. Herein, inspired by the Twisted Tower origami structure, dielectrophoretic liquid zipping actuation concept is employed to develop a modular architecture, capable of achieving complicated motions with multiple degrees of freedom (DoF). The experimental results show a maximum of 3.9 degrees tilting per layer toward any desired direction, a 56.1% contraction of the original length, and 5.4 degrees twisting per layer. Each layer can generate a maximum contractile force of 1.03 N with a maximum 64.7% power efficiency and 2.775 W kg⁻¹ power‐to‐weight ratio. A modified heterochiral arrangement of this modular actuator is proposed to enhance controllability across various movement modes. Its use in robotic‐wrist‐like actuation has been demonstrated, highlighting its significant potential for integration into soft robotic multi‐DoF structures, such as continuum arms.
... morphing a flat sheet into a conical shell). This paradigm of 'metric mechanics' is common in biology [1][2][3][4][5][6][7][8], but can also be realized artificially in gels [9][10][11][12][13][14][15] or inked polymers [16] encoded with patterns of isotropic (de)swelling, pneumatic fabrics or elastomers containing patterns of inflatable channels [17][18][19][20][21][22] or liquid-crystal elastomers/glasses (LCE/Gs) [23][24][25][26][27][28][29][30][31][32][33][34]. These systems hold huge promise for morphing machines and deployable structures, especially given the revolution of three-dimensional printing, and as a result, they have become a bustling research area, with potential applications in biomimetics, microfluidics, tissue engineering and soft robotics. ...
Article
Full-text available
Shape-programmed sheets morph from one surface into another upon activation by stimuli such as illumination, and have attracted much interest for their potential engineering applications, especially in soft robotics. Complex shape changes can be achieved by patterning a simple local active deformation (e.g. isotropic swelling), to generate differential growth. Usually the material itself is designed — for example by patterning a molecular director — such that a particular shape change occurs upon exposure to a spatially uniform stimulus. A limitation of this paradigm is that typically only one target geometry can be attained as the stimulus is adjusted. Here we show that this limitation can be overcome by patterning the stimulus itself, thereby exercising spatiotemporal control over local deformation magnitudes. Thus a single physical sample can be induced to traverse a continuous family of target geometries, opening the door to precise shape adjustments, new functionalities, and designable non-reciprocal loops in shape space. We illustrate these possibilities with examples including active parabolic reflectors, chiral flow guides, and bending channels. Finding the necessary patterns of activation involves solving families of metric inverse problems; we solve these by reduction to ODEs in an axisymmetric setting, then present a novel numerical scheme to solve them in generality.
... Textiles play a central role as they offer flexibility and breathability, making them ideal for building robots that mimic human clothing and interact with thermal, electrical, and hygroscopic stimuli [13]. At the same time, techniques such as origami and kirigami are incorporated to enhance the anisotropy and kinematics of robots [14,15]. The research community recognizes the importance of including children in design, as they offer unique perspectives that enrich robot development and function [16]. ...
Conference Paper
Full-text available
Recent studies in child-robot interaction indicate a propensity for children to trust robots with humanoid characteristics, fostering social relationships that enhance interaction quality. Trust is fundamental in Human-Robot Interaction (HRI) and can be affected by parameters such as the robot's appearance, texture, or performed activity. In the current paper, we investigate whether children's trust in a SAR, specifically the Nao robot, increases after they design and dress it with handmade clothes using the felting technique. Children had the chance to interact with robots both naked and dressed in and without their creations and share a secret wish with one of them. Behavioral observations and wish content analysis provided insights into children's emotional engagement and trust preferences. Most children chose to confide in the robot wearing their crafted outfit, using wish statements that reflect aspirational desires, contrasting with immediate wants expressed to the 'naked' robot. This study underscores the role of co-design and initial interaction quality in fostering trust and emotional engagement between children and SARs, highlighting avenues for enhancing HRI outcomes.
... To overcome the challenges, we have employed origami technology, which has experienced remarkable growth within the realm of soft robotics, primarily due to its capacity for substantial deformation during deployment [30][31][32][33][34] . Emerging research indicates that elastomers reinforced with origami structures exhibit improved performance by reducing ineffective deformation while maintaining a broad range of motion 35,36 . By constraining facets, it becomes feasible to calculate the intricate deformation of a 3D structure based on a crease pattern designed in a 2D plane, adhering to origami principles. ...
Article
Full-text available
Prosthetic knees represent a prevalent solution for above-knee amputation rehabilitation. However, satisfying the ambulation requirements of users while achieving their comfort needs in terms of lightweight, bionic, shock-absorbing, and user-centric, remains out of reach. Soft materials seem to provide alternative solutions as their properties are conducive to the comfort aspect. Unfortunately, the pronounced flexibility restricts the application of soft robots on prosthetic knees regarding morphological computation and weight-bearing performance. Here, we innovate a soft prosthetic knee for transfemoral amputees, addressing current challenges through the integration of origami technology and bioinspired weight-bearing principle, achieving its lightweight, compactness, low cost, and simple fabrication. The soft knee can hold the weight of a human (more than 75 kg), perform biomimetic polycentric flexion, absorb impacts during walking (absorbing 11.5% to 17.3% more impact forces), and actively support amputees to walk across ramps, stairs, and obstacles. The efficacy of the proposed design has been corroborated through bench-top and ambulation experiments. The proposal might lead to a paradigm shift in the lower limb prosthetic design.
... In practice, bending (or unbending) of the beam can be actuated through shape memory polymers [27], dielectric elastomers [26,32], electroactive polymers [33], bimorph actuator [34][35][36][37], or pneumatic/fluid pressurization [5,11,38,39], etc., discussed in Section 5. In simulation, repetitive beam bending and unbending can be achieved, by applying an extension strain, ...
Preprint
In nature, a variety of limbless locomotion patterns flourish from the small or basic life form (Escherichia coli, the amoeba, etc.) to the large or intelligent creatures (e.g., slugs, starfishes, earthworms, octopuses, jellyfishes, and snakes). Many bioinspired soft robots based on locomotion have been developed in the past decades. In this work, based on the kinematics and dynamics of two representative locomotion modes (i.e., worm-like crawling and snake-like slithering), we propose a broad set of innovative designs for soft mobile robots through simple mechanical principles. Inspired by and go beyond existing biological systems, these designs include 1-D (dimensional), 2-D, and 3-D robotic locomotion patterns enabled by simple actuation of continuous beams. We report herein over 20 locomotion modes achieving various locomotion functions, including crawling, rising, running, creeping, squirming, slithering, swimming, jumping, turning, turning over, helix rolling, wheeling, etc. Some of them are able to reach high speed, high efficiency, and overcome obstacles. All these locomotion strategies and functions can be integrated into a simple beam model. The proposed simple and robust models are adaptive for severe and complex environments. These elegant designs for diverse robotic locomotion patterns are expected to underpin future deployments of soft robots and to inspire series of advanced designs.
... VEI received considerable attention over recent years due to its relevance to a wide spectrum of natural processes and applications. These include biological flows [2,3], geophysical and geological flows [4], suppression of viscous fingering instabilities [5][6][7][8][9][10], manufacturing of micro-electro-mechanical systems [11,12], development of flexible microfluidic valves [13], and soft robotics [14][15][16][17]. ...
Preprint
In a wide range of applications, microfluidic channels are implemented in soft substrates. In such configurations, where fluidic inertia and compressibility are negligible, the propagation of fluids in channels is governed by a balance between fluid viscosity and elasticity of the surrounding solid. The viscous-elastic interactions between elastic substrates and non-Newtonian fluids are particularly of interest due to the dependence of viscosity on the state of the system. In this work, we study the fluid-structure interaction dynamics between an incompressible non-Newtonian fluid and a slender linearly elastic cylinder under the creeping flow regime. Considering power-law fluids and applying the thin shell approximation for the elastic cylinder, we obtain a non-homogeneous p-Laplacian equation governing the viscous-elastic dynamics. We present exact solutions for the pressure and deformation fields for various initial and boundary conditions for both shear-thinning and shear-thickening fluids. We show that in contrast to Stokes' problem where a compactly supported front is obtained for shear-thickening fluids, here the role of viscosity is inversed and such fronts are obtained for shear-thinning fluids. Furthermore, we demonstrate that for the case of a step in inlet pressure, the propagation rate of the front has a tnn+1t^{\frac{n}{n+1}} dependence on time (t), suggesting the ability to indirectly measure the power-law index (n) of shear-thinning liquids through measurements of elastic deformation.
... On the other hand, the development of soft actuators using flexible materials has been advanced, which partially overcomes these weaknesses. Elastomeric Origami [8], Origami structures of various shapes [9], and 3D printed soft actuators [10], have been developed using elastomer materials with high stretchability and large deformability, but have the disadvantage of being difficult to perform contact operations and to be used for large muscles. HASEL actuator [11] and Peano-HASEL actuators [12] are electrohydraulic actuators using flexible materials, and have been applied to circular muscles [13], but it is difficult to use them for large threedimensional muscles. ...
Preprint
Muscles of the human body are composed of tiny actuators made up of myosin and actin filaments. They can exert force in various shapes such as curved or flat, under contact forces and deformations from the environment. On the other hand, muscles in musculoskeletal robots so far have faced challenges in generating force in such shapes and environments. To address this issue, we propose Patterned Structure Muscle (PSM), artificial muscles for musculoskeletal robots. PSM utilizes patterned structures with anisotropic characteristics, wire-driven mechanisms, and is made of flexible material Thermoplastic Polyurethane (TPU) using FDM 3D printing. This method enables the creation of various shapes of muscles, such as simple 1 degree-of-freedom (DOF) muscles, Multi-DOF wide area muscles, joint-covering muscles, and branched muscles. We created an upper arm structure using these muscles to demonstrate wide range of motion, lifting heavy objects, and movements through environmental contact. These experiments show that the proposed PSM is capable of operating in various shapes and environments, and is suitable for the muscles of musculoskeletal robots.
... Actuation mechanisms include manual actuation using cables [15], motor-driven mechanisms [23], pneumatic actuators that use air pressure to inflate, deflate, or deploy structures [24], [25], and hydraulic actuators that fold origami structures using liquid hydrogels [26] or microfluidic channels [27]. These methods utilize mechanical loads to actuate the origami structure. ...
Article
This article presents the first shape-changing phased array operating at 28 GHz as an alternative to traditional planar phased arrays. By combining electrical beamsteering with mechanical shape change, this design achieves high degrees of freedom, resulting in near-limitless radiation pattern reconfigurability and overcoming the tradeoff between gain and angular coverage. Utilizing the eggbox origami structure, a 4-D multifaceted foldable phased array is developed, and a modular tile-based (unit-cell) approach is employed to enable TX/RX selective activation and scalability to massive MIMO. This results in near 360360^{\circ} continuous beam steering in the azimuth plane with reconfigurable multibeam or quasi-isotropic radiation patterns. Additive manufacturing processes are employed to realize the first shape-changing phased array at a miniaturized millimeter scale. The eggbox phased array features highly integrated on-structure beamformer ICs and a flexible feeding network utilizing a uniquely designed foldable interconnect. As the first additively manufactured mm-wave hinge interconnects, the presented “arch” interconnect exhibits near-constant insertion loss of 0.02 dB/mm across various folding angles and cycles. In addition, a microservo-based actuation mechanism is designed to precisely control the origami folding action. Measurements demonstrate the phased array’s pattern reconfigurability, and its effectiveness is further validated in an orthogonal frequency division multiplexing (OFDM)-based communication testbed setup. Furthermore, this article provides a holistic multidisciplinary framework guiding the development of a new era of mm-wave shape-changing phased arrays, encompassing considerations in hardware realization, actuation, and 3-D beam shaping/calibration. Given its multitude of novel features, the eggbox phased array can enable a plethora of applications, ranging from multimode in-band full-duplex applications to multifunction multibeam use cases, extreme interference mitigation, and space-constrained deployments.
... In engineering, origami research is mainly divided into two categories: rigid foldable [19,29,36] and deformable [22,23,35]. Whereas rigid origami can be studied purely from a mechanism point of view, i.e., by solving the equations of motion of rigid bodies [30], deformable origami requires taking into account the storage of elastic energy to predict deployment. ...
Preprint
Full-text available
Bistable mechanical systems exhibit two stable configurations where the elastic energy is locally minimized. To realize such systems, origami techniques have been proposed as a versatile platform to design deployable structures with both compact and functional stable states. Conceptually, a bistable origami motif is composed of two-dimensional surfaces connected by one-dimensional fold lines. This leads to stable configurations exhibiting zero-energy local minima. Physically, origami-inspired structures are three-dimensional, comprising facets and hinges fabricated in a distinct stable state where residual stresses are minimized. This leads to the dominance of one stable state over the other. To improve mechanical performance, one can solve the constrained optimization problem of maximizing the bistability of origami structures, defined as the amount of elastic energy required to switch between stable states, while ensuring materials used for the facets and hinges remain within their elastic regime. In this study, the Mesh Adaptive Direct Search (MADS) algorithm, a blackbox optimization technique, is used to solve the constrained optimization problem. The bistable waterbomb-base origami motif is selected as a case-study to present the methodology. The elastic energy of this origami pattern under deployment is calculated via Finite Element simulations which serve as the blackbox in the MADS optimization loop. To validate the results, optimized waterbomb-base geometries are built via Fused Filament Fabrication and their response under loading is characterized experimentally on a Uniaxial Test Machine. Ultimately, our method offers a general framework for optimizing bistability in mechanical systems, presenting opportunities for advancement across various engineering applications.
... However, early work in soft pneumatic actuators heavily relied on elastomeric architectures, which typically exhibit inflatable deformations in all directions upon air actuation. [13][14][15][16][17] As a result, their actuation strain, output force, and actuation efficiency are constrained by the inherent homogeneity of the elastic materials. 18 Recent advances in fiber-based actuators have improved the actuation strain and load capacity of pneumatic actuators via wrapping fibers around the exterior of the silicone material of the actuators to impart the directional strain 19,20 ; however, such a combination of fibers and silicone can introduce complexity into the preparation process, and the casting and molding fabrication of silicone membranes for programmed actuators is also time consuming and costly. ...
Article
Full-text available
Pneumatic soft robotics are highly desirable for interacting with humans and navigating uncertain environments. However, it remains a great challenge to simultaneously achieve high actuation efficiency, programmable deformations, real-time feedback, and robustness. Herein, a textile engineering approach is harnessed to integrate multifunctionality into woven actuators by tailoring yarn groupings using all-in-one industrial weaving technologies. The unique nearly zero Poisson’s ratio inflatable deformation of the actuators contributes to a large bending strain (2,250° m−1), a high output force (30 N MPa−1), and robust mechanical performance. Bilateral bending actuators with negative, zero, and positive curvatures are realized by hierarchical shape transformations of the woven layers. The embedded sensing yarns provide facile and effective methods to proprioceptively sense actuation deformation without compromising actuation performance. Moreover, this manufacturing method is cost efficient and highly scalable, which expands practical applications of soft actuators in healthcare and offers a new perspective on the structure design of customized soft actuators.
... In particular, the exploration of shape approximation through the versatile aesthetics of origami or kirigami tessellations, where sheets of paper are folded along strictly prescribed crease patterns, has attracted significant attention in computer graphics [Choi et al. 2019;Dudte et al. 2016;Jiang et al. 2020;Narumi et al. 2023]. Origami and kirigami are traditionally associated with flat sheets of paper and can potentially be extended to other sheet materials, such as cardboard and silicone rubber [Jin et al. 2020;Martinez et al. 2012]. The rigidity and inextensibility of the used materials pose a unique challenge for the inverse design problem with origami and kirigami: the fabrication constraints of the materials must be taken into account along with the goal of Authors' addresses: Aviv Segall, ETH Zurich, Switzerland, aviv.segall@inf.ethz.ch; ...
Article
Full-text available
We present a novel method for realizing freeform surfaces with pieces of flat fabric, where curvature is created by stitching together points on the fabric using a technique known as smocking. Smocking is renowned for producing intricate geometric textures with voluminous pleats. However, it has been mostly used to realize flat shapes or manually designed, limited classes of curved surfaces. Our method combines the computation of directional fields with continuous optimization of a Tangram graph in the plane, which together allow us to realize surfaces of arbitrary topology and curvature with smocking patterns of diverse symmetries. Given a target surface and the desired smocking pattern, our method outputs a corresponding 2D smocking pattern that can be fabricated by sewing specified points together. The resulting textile fabrication approximates the target shape and exhibits visually pleasing pleats. We validate our method through physical fabrication of various smocked examples.
... Pneumatic network actuators (pneu-nets) are one common design of soft actuators (20)(21)(22)(23)(24)(25). Various embodiments of pneu-nets-such as fiber-reinforced (26)(27)(28)(29)(30)(31), multimaterial (32)(33)(34), buckling (35,36), origami-inspired (37)(38)(39)(40), and fabric/textile (41)(42)(43) soft actuators-are noteworthy in this context. Pneu-nets consist of pneumatically actuating constructs primarily made of silicone rubbers (20). ...
Article
This paper introduces an approach to fabricating lightweight, untethered soft robots capable of diverse biomimetic locomotion. Untethering soft robotics from electrical or pneumatic power remains one of the prominent challenges within the field. The development of functional untethered soft robotic systems hinges heavily on mitigating their weight; however, the conventional weight of pneumatic network actuators (pneu-nets) in soft robots has hindered untethered operations. To address this challenge, we developed film-balloon (FiBa) modules that drastically reduced the weight of soft actuators. FiBa modules combine transversely curved polymer thin films and three-dimensionally printed pneumatic balloons to achieve varied locomotion modes. These lightweight FiBa modules serve as building blocks to create untethered soft robots mimicking natural movement strategies. These modules substantially reduce overall robot weight, allowing the integration of components such as pumps, valves, batteries, and control boards, thereby enabling untethered operation. FiBa modules integrated with electronic components demonstrated four bioinspired modes of locomotion, including turtle-inspired crawling, inchworm-inspired climbing, bat-inspired perching, and ladybug-inspired flying. Overall, our study offers an alternative tool for designing and customizing lightweight, untethered soft robots with advanced functionalities. The reduction of the weight of soft robots enabled by our approach opens doors to a wide range of applications, including disaster relief, space exploration, remote sensing, and search and rescue operations, where lightweight, untethered soft robotic systems are essential.
... Similar to common pneu-net actuators, [17] this LV-net actuator has an array of bellows on one side and a strain limiting layer on the other side. In addition to using LVCs in the molding process, we used flexible but inextensible polyester-woven fabric sheets as the strain limiting layer, similar to the flexible paper used by Martinez et al. [59] The casting process for the LV-net actuator uses an open-faced semi-bellow-shaped mold, a base connector in the exit channel to hold the LVC in place, and a cap to cover the exit's open face ( Figure S1E, Supporting Information). The mold, base connector, and cap are all made with a fused filament fabrication (FFF) 3D printer. ...
Article
Full-text available
This study introduces the low‐volume core (LVC) fabrication method, which enables the monolithic molding of compact, complex, versatile, and intelligent soft robotic systems. This method uses thin and flexible thermoplastic sheets to mold internal chambers in soft fluidic actuators, valves, and circuits. The LVC fabrication method creates low‐volume networks in soft actuators (LV‐net actuators) that can be made with compact and complex geometries, enabling both low actuation volume input and multi‐degree‐of‐freedom actuators. LVC fabrication can also be used for compact, completely soft, and monolithic logic components (valves with low‐volume core, also called as LV valves) to provide directional resistance as well as a switching mechanism that enables fluidic logic in soft systems. The compatibility of the fabrication methods for both soft actuators and valves facilitates the creation of compact, integrated, and versatile soft robotic systems with embodied intelligence. This study introduces two examples of such intelligent soft robotic systems that integrate both LV‐net actuators and LV valves to demonstrate capability for complex system fabrication.
... morphing a flat sheet into a conical shell). This paradigm of 'metric mechanics' is common in biology [1][2][3][4][5][6][7][8], but can also be realised artificially in gels [9][10][11][12][13][14][15][16] or inked polymers [17] encoded with patterns of isotropic (de)swelling, pneumatic fabrics or elastomers containing patterns of inflatable channels [18][19][20][21][22][23], or liquid-crystal elastomers/glasses (LCE/Gs) [24][25][26][27][28][29][30][31][32][33][34][35]. These systems hold huge promise for morphing machines and deployable structures, especially given the revolution of 3D printing, and as a result they have become a bustling research area, with potential applications in biomimetics, microfluidics, tissue engineering, and soft robotics. ...
Preprint
Full-text available
Shape-programmed sheets morph from one surface into another upon activation by stimuli such as illumination, and have attracted much interest for their potential engineering applications, especially in soft robotics. Complex shape changes can be achieved by patterning a simple local active deformation (e.g. isotropic swelling), to generate differential growth. Usually the material itself is designed — for example by patterning a molecular director — such that a particular shape change occurs upon exposure to a spatially uniform stimulus. A limitation of this paradigm is that typically only one target geometry can be attained as the stimulus is adjusted. Here we show that this limitation can be overcome by patterning the stimulus itself, thereby exercising spatiotemporal control over local deformation magnitudes. Thus a single physical sample can be induced to traverse a continuous family of target geometries, opening the door to precise shape adjustments, new functionalities, and designable non-reciprocal loops in shape space. We illustrate these possibilities with examples including active parabolic reflectors, chiral flow guides, and bending channels. Finding the necessary patterns of activation involves solving families of metric inverse problems; we solve these by reduction to ODEs in an axisymmetric setting, then present a novel numerical scheme to solve them in generality.
... It is closely related to the fields of mathematics and mechanics. Its ability to convert 2D sheets into complex 3D shapes or reshape unfolded structures into compact folded states has received significant attention and development in different engineering fields and research areas, including aeronautical structures, [37,38] metamaterials, [39][40][41][42][43] robotics, [44][45][46][47] biomedical devices, [48,49] reconfigurable electronics, [50][51][52] and architecture. [53] Therefore, a different kind of spark is rubbed when mature origami art is applied to EM control. ...
Article
Full-text available
Miura origami's reconfigurable characteristic and structural asymmetry, combined with electromagnetic (EM) wave manipulation, crashed a unique spark. However, the complexity of the three‐dimensional (3D) origami structure after folding makes it challenging to study the phase regulation mechanism. Here, we propose a reconfigurable phase gradient metasurface based on Miura origami and derive the underlying mechanism of phase modulation in detail under linearly and circularly polarized (LP and CP) incidence. We adopt the one‐dimensional (1D) gradient design along the x direction to verify the idea. The phase calculation formulas are given under LP and CP incidence through the Jones matrix's derivation. The beam deflector angles corresponding to LP and CP waves are identical in the planar state. As the folding angle increases, the phase evolution rules corresponding to the LP and CP waves are discrepant, leading to differential beam steering. Finally, the origami sample is processed for verification, and the experimental data are consistent with the simulation and theoretically calculated values. We believe this work can help analyze the EM behavior of complex 3D origami structures and lay a foundation for designing a multifunctional EM origami metasurface.
... The SBPM, contingent upon specific chamber configurations or constraint structures, engenders deliberate and continuous deformations and propulsive forces upon the application of internal air pressure. Within this landscape, prevailing devices can be broadly classified into three principal categories: fiber-reinforced pneumatic actuators [28,29], elastic chamber actuators [30,31], and origamiinspired pneumatic actuators [32,33]. Notably, elastic chamber actuators, typically constructed from rubber-like materials, epitomize exceptional compliance and flexibility. ...
Article
Full-text available
Pneumatic actuators exhibit significant potential across various applications owing to their compliance, yet achieving precise motion control remains challenging due to rate-dependent and asymmetric hysteresis. While the Prandtl–Ishlinskii model adeptly captures intricate hysteresis traits, its practical control usage often necessitates intricate inversions, resulting in elevated computational burden and limited accommodation of system uncertainties and model inaccuracies. This study introduces an online, rate-dependent modified generalized Prandtl–Ishlinskii model derived via the gradient descent algorithm. This model is seamlessly amalgamated with a model predictive control strategy, addressing the inversion challenge inherent in the Prandtl–Ishlinskii model. Leveraging integration with a three-layer fuzzy neural network controller, the proposed approach achieves closed-loop trajectory tracking control for a soft bending pneumatic muscle. Convergence analysis, grounded in Lyapunov theory, underscores the efficacy of the proposed model. Comprehensive real-world comparative experiments affirm the approach’s effectiveness and reliability.
... Shuguang Li's team proposed a fluid-driven artificial muscle based on the folding structure, which can be used in wearable robotic exoskeletons, foldable space exploration structures, and many other fields [15]. Martinez et al. developed a driver consisting of a flexible composite material that uses the folding structure as an integral structure [16]. GE Healthcare collaborated with Brigham Young University to design an origami shield for the external extension arm of an X-ray machine used by doctors during surgery [17]. ...
Article
Full-text available
In this study an innovative parameterized water-bomb wheel modeling method based on recursive solving are introduced, significantly reducing the modeling workload compared to traditional methods. A multi-link supporting structure is designed upon the foundation of the water-bomb wheel model. The effectiveness of the supporting structure is verified through simulations and experiments. For robots equipped with this water-bomb wheel featuring the multi-link support, base on the kinematic model of multi-link structure, a mapping algorithm that incorporates parameterized kinematic solutions and IMU-fused parameterized odometry is proposed. Based on this algorithm, SLAM and autonomous navigation experiments are carried out in simulation environment and real environment respectively. Compared with the traditional algorithm, this algorithm the precision of SLAM is enhanced, achieving high-precision SLAM and autonomous navigation with a robot error rate below 5%.
Article
Full-text available
This article provides a comprehensive exploration of the current research landscape in the field of soft actuation technology applied to bio-inspired soft robots. In sharp contrast to their conventional rigid counterparts, bio-inspired soft robots are primarily constructed from flexible materials, conferring upon them remarkable adaptability and flexibility to execute a multitude of tasks in complex environments. However, the classification of their driving technology poses a significant challenge owing to the diverse array of employed driving mechanisms and materials. Here, we classify several common soft actuation methods from the perspectives of the sources of motion in bio-inspired soft robots and their bio-inspired objects, effectively filling the classification system of soft robots, especially bio-inspired soft robots. Then, we summarize the driving principles and structures of various common driving methods from the perspective of bionics, and discuss the latest developments in the field of soft robot actuation from the perspective of driving modalities and methodologies. We then discuss the application directions of bio-inspired soft robots and the latest developments in each direction. Finally, after an in-depth review of various soft bio-inspired robot driving technologies in recent years, we summarize the issues and challenges encountered in the advancement of soft robot actuation technology.
Article
Soft actuators have developed over the last decade for diverse applications including industrial machines and biomedical devices. Integration of chemical sensors with soft actuators would be beneficial in analyzing chemical...
Article
Although rigid exoskeletons can strengthen human capabilities or provide full assistance to patients with disabilities, their rigidity may constrain natural movement, developing tissue damage in long-term usage. Soft and semi-soft exoskeletons and exosuits exhibit both compliance and comfort, and offer the potential to provide practical and widely-adopted assistance. Soft pneumatic muscles have been explored as a means to drive wearable assist devices for over a decade; however, their softness leads to compromises in terms of power output and the precision by which forces can be applied to the human body. In this article, we introduce a novel soft extending pneumatic actuator, which combines a compliant scissor structure inspired by human cartilage and soft pneumatic muscles. The structure behaves as a compliant skeleton to the force generating pneumatic muscle, guiding its actuation behaviour and maintaining high force transmission through its body. Different designs and dimensions of the actuator and structure were investigated to observe the effect of compliance on key performance parameters. A soft single-module actuator can deliver extending force over 100 N and achieve a maximum strain of 178% when inflated at 50 kPa. A slightly thicker, but still compliant, continuum two-module actuator exhibits twice the extension compared to a single-module actuator with the same design under the same load up to 4 kg, a significant and suitable force for comfortable wearable devices. Last, a wearable prototype of this novel actuator is demonstrated, exhibiting both extension and bending actuation behaviours.
Article
Full-text available
The Yoshimura tubular origami mechanism possesses numerous advantageous properties and, when integrated with advanced material technologies, can be applied across various engineering disciplines. However, current research on Yoshimura origami predominantly focuses on centrally symmetric tubular origami mechanisms, which restricts the structural forms and motion patterns of these mechanisms. Drawing inspiration from the biological concept of “morphological variation,” we propose a novel tubular origami mechanism based on the Yoshimura pattern, which is the main contribution of this research. We analyze the Yoshimura planar crease elements and introduce both heterocellular and homocellular tubular origami mechanisms. Furthermore, we establish the origami topology matrices for the Yoshimura tubular origami mechanisms. This research also investigates complex motion forms that differ from traditional Yoshimura origami mechanisms, including macroscopic twisting and compound movements, thereby providing an intuitive design approach and extensive structural guidance for research in Yoshimura tubular origami engineering. Based on the tubular origami mechanism, we created an origami robot and investigate its motion characteristics.
Preprint
Manipulation of thin sheets by folding and cutting offers opportunity to engineer structures with novel mechanical properties, and to prescribe complex force-displacement relationships via material elasticity in combination with the trajectory imposed by the fold topology. We study the mechanics of cellular Kirigami that rotates upon compression, which we call Flexigami; the addition of diagonal cuts to an equivalent closed cell permits its reversible collapse without incurring significant tensile strains in its panels. Using finite-element modeling and experiment we show how the mechanics of flexigami is governed by the coupled rigidity of the panels and hinges and we design flexigami to achieve reversible force response ranging from smooth mono-stability to sharp bi-stability. We then demonstrate the use of flexigami to construct laminates with multi-stable behavior, a rotary-linear boom actuator, and self-deploying cells with activated hinges. Advanced digital fabrication methods can enable the practical use of flexigami and other metamaterials that share its underlying principles, for applications such as morphing structures, soft robotics and medical devices.
Article
The excellent flexibility and plasticity of a flexible robotic hand enable it to grip objects of various shapes and sizes. Currently, most of the flexible robotic hand fingers on the market use pneumatic drives. However, the unstable power of the pneumatic drive can cause the object gripped by the finger to slip. Additionally, the pneumatic pump can create noise pollution. To address these issues, a flexible end-effector is designed using an electromagnetic coil as the power source. The electromagnetic-driven end-effector has high precision and fast response, without the need for external devices. It only requires controlling the current to control the magnetic force of the electromagnet, thereby controlling the degree of end-effector bending. The finite element simulation is used to analyze the impact of the structural parameters of the end-effector on bending degree. And the optimal basic parameters of the end-effector are determined. Under the same intensity of the current, when the bottom layer thickness is 5 mm, end-effector knuckle spacing is 4 mm, the maximum angle of end-effector bending is reached.
Article
Full-text available
Biological structures combine passive shape‐changing with force generation through intricate composite architectures. Natural fibers, with their tubular‐like structures and responsive components, have inspired the design of pneumatic tubular soft composite actuators. However, no development of passive structural actuation is available despite the recent rise of 4D printing. In this study, a biomimicry approach is proposed with inspiration from natural fiber architecture to create a novel concept of thermally active 4D printed tubular metacomposites. These metacomposites exhibit high mechanical performance and 3D‐to‐3D shape‐changing ability triggered by changes in temperature. A rotative printer is proposed for winding a continuous carbon fibers reinforced PolyAmide 6.I composite on a PolyAmide 6.6 polymer mandrel in a similar manner to the structure of cellulose microfibrils within the polysaccharide matrix of natural fiber cell‐walls. The resulting 4D printed tubular metacomposites exhibit programmable rotation and torque in response to thermal variations thanks to the control of their mesostructure and the overall geometry. Energy density values representing a trade‐off between the rotation and the torque are comparable to shape memory alloys when normalized by stiffness. Finally, a proof of concept for an autonomous solar tracker is presented, showcasing its potential for designing autonomous assemblies for structure morphing.
Article
Soft actuators producing bending motions have gained significant attention for their advantages in mimicking the properties and movements of human muscles. However, the research on soft rotary actuators has yet to keep pace with other soft actuators. This paper makes two key contributions to the design and modeling of these actuators. First, we introduce a novel design for a soft rotary pneumatic actuator. This design outperforms existing cylindrical shaped soft actuators, especially in terms of torque. Second, we present an analytical model based on finite deformation. This model accurately describes the relationship between rotational movement and corresponding torque. The accuracy of this model is validated through Finite Element Method (FEM) simulations and corresponding tests. By providing a mechanically efficient design and a highly accurate analytical model, this work offers a comprehensive solution for the development of new soft pneumatic actuators.
Article
In this work, a large-scale, high-viscosity vat photopolymerization additive manufacturing system is designed and fabricated to print 3D structures as large as 370 × 300 × 370 mm3 out of high-viscosity, low-reactivity elastomeric resins. A detailed overview is presented of the printer's design and capabilities, including a resin processing sub-system that stores and spreads high-viscosity resin; a roll-to-roll variable tensioning system to mitigate the separation forces after printing each layer; and a light patterning system that generates high-intensity light patterns across an area of 370 × 300 mm2 with a resolution of 3840 × 4320 pixels. The ability to print with both high-viscosity and low-reactivity resins enables additive manufacturing of new classes of materials that could not be printed previously using vat photopolymerization techniques. These materials include highly reinforced silica nanoparticle composites, high-molecular-weight polymers such as silicones and acrylate or methacrylate resins, and low-reactivity resins such as photocurable platinum-catalyzed liquid silicone rubber.
Article
Variable stiffness materials have shown considerable application in soft robotics. However, previously reported materials often struggle to reconcile high stiffness, stretchability, toughness, and self‐healing ability, because of the inherently conflicting requisite of these properties in molecular design. Herein, we propose a novel strategy that involves incorporating acid‐base ionic pairs capable of from strong crosslinking sites into a dense and robust hydrogen‐bonding network to construct rigid self‐healing polymers with tunable stiffness and excellent toughness. To demonstrate these distinct features, the polymer was employed to serve as the strain‐regulation layers within a fiber‐reinforced pneumatic actuator (FPA). The exceptional synergy between the configuration versatility of FPA and the dynamic molecular behavior of the supramolecular polymers equips the actuator with simultaneous improvement in motion dexterity, multimodality, loading capacity, robustness, and durability. Additionally, the concept of integrating high dexterity at both macro‐ and micro‐scale is prospective to inspire the design of intelligent yet robust devices across various domains.
Article
Full-text available
Variable stiffness materials have shown considerable application in soft robotics. However, previously reported materials often struggle to reconcile high stiffness, stretchability, toughness, and self‐healing ability, because of the inherently conflicting requisite of these properties in molecular design. Herein, we propose a novel strategy that involves incorporating acid‐base ionic pairs capable of from strong crosslinking sites into a dense and robust hydrogen‐bonding network to construct rigid self‐healing polymers with tunable stiffness and excellent toughness. To demonstrate these distinct features, the polymer was employed to serve as the strain‐regulation layers within a fiber‐reinforced pneumatic actuator (FPA). The exceptional synergy between the configuration versatility of FPA and the dynamic molecular behavior of the supramolecular polymers equips the actuator with simultaneous improvement in motion dexterity, multimodality, loading capacity, robustness, and durability. Additionally, the concept of integrating high dexterity at both macro‐ and micro‐scale is prospective to inspire the design of intelligent yet robust devices across various domains.
Article
The existing soft crawling robots usually have single-motion mode, which results in poor motion adaptability and significantly restricts the application field of the soft crawling robots. To further increase the motion adaptability of the soft crawling robots and expand their application space, in this work, inspired by the movement mechanism of the snake scales, we present a pneumatic soft crawling robot with multi-modal locomotion based on a deployable and foldable (D-F) mechanism. The robot adopts a four-chamber bellows actuator to further enhance the robot's movement adaptability in motion space. The head and tail parts of the robot are provided with a D-F mechanism imitating snake scales, which can be opened and closed through the extension and contraction of the bellows actuator. By adopting different actuation strategies and utilizing the anisotropy of friction and the alteration of the center of gravity, the robot can achieve multi-modal locomotion such as straight walking, steering, rolling and obstacle crossing to satisfy the requirements of varied surroundings. An open-loop control system of the robot is developed to assess its motion performance. The mathematical model of the robot is established using cosserat-rod theory to clarify the relationship between actuating pressure and robot's motion variables under various motion strategy combinations. The experimental results show that the soft crawling robot designed in this study can efficiently adapt to moving surfaces with different material properties and achieve diverse motion modes under different actuation strategies. Additionally, it can adapt to exploratory tasks in unstructured environment.
Article
Full-text available
Liquid crystal elastomer (LCE) has large and reversible deformation under stimulation, making it an ideal material for artificial muscles. Currently, multi‐stimulus responsive LCE actually responds to each stimulus independently rather than responding to several stimuli simultaneously. Achieving an enhanced effect from concurrent stimuli is still a challenge, which requires a new stimulus‐response mechanism. This work develops a novel and facile solvent evaporation‐assisted template method to prepare LCE hollow fiber (LCEHF) with axial alignment. Taking advantage of the enhanced effect of heat‐induced phase transition and mechanical force‐induced orientation transition of mesogens, the LCEHF under both heat and pressure can produce a large contraction ratio of ≈50%, which is higher than 42% of thermal stimulation or 27% of pneumatic stimulation. It can also enhance the respective response and recovery speed of LCEHF to 300 and 3700 times of pneumatic actuation. Additionally, the enhanced effect lowers the actuation temperature much below the phase transition temperature, imparting LCEHF with high mechanical performance during actuation. Furthermore, the dual thermal‐pneumatic responsive LCEHF can mimic human biceps and cause large and rapid bending of an artificial arm reversibly. This new actuation methodology sheds new light on improving LCE actuation performance and broadens its application scenarios.
Preprint
This work introduces a concept of origami electronic membranes that leverages the design and fabrication of flexible electronics and the mechanical behavior of engineering origami to achieve unique multifunctional, shape-reconfigurable, and adaptive membranes for mechanical and environmental sensing in benign and harsh conditions. This paper presents the materials, design, and fabrication methods for realizing six origami electronic membranes capable of reconfiguring planar or three-dimensional shapes based on the modified flasher, Kresling, Miura-ori, circular, letter, and Tachi-Miura origami patterns. These origami-based, thin-film flexible electronics can obtain both expansion and folding of their shapes, as well as transformation between different geometries. The origami electronic membranes can achieve mechanical and environmental sensing functions such as measuring motions, mechanical strains, temperatures, UV light, and humidity. The results reported here demonstrate the promise of combining engineering origami with flexible electronics to advance the state-of-the-art in multifunctional foldable and deployable electronics and systems.
Article
Full-text available
Origami, the art of paper folding, has emerged as a versatile technique for crafting intricate 3D structures from 2D sheets. Combined with the magnetic actuation, origami paper becomes the building blocks for cost‐effective, wirelessly controllable magnetic robots. Herein, a biodegradable magnetic paper with excellent formability and recyclability is developed, facilitating its convenient utilization and disposal. The programable magnetic paper, fabricated with specific magnetization and crease patterns, enables the transformation of 2D sheets into predetermined 3D structures. Leveraging the lightweight and pliable nature of paper‐based materials, exceptional control of origami robots with fast response is demonstrated, enabling a wide range of locomotion. Furthermore, the paper‐based approach enables the incorporation of electronic functionality into magnetic actuators. By introducing conductive nanoparticles into magnetic paper, an electrically conductive substance is created. Constructing electronic circuits and integrating electronic components onto the paper‐based printed circuit board platform enables the repairing of broken circuits inside complicated equipment and optical sensing of surrounding environments in conjunction with locomotive robots. The origami robots have a huge potential to be facilitated in diverse fields with various functions, demonstrating complex locomotion, and integrating chemical, optical, thermal, and mechanical sensors for monitoring environmental conditions in hard‐to‐reach locations. The array of possibilities holds significant promise for the widespread application of these origami magnetic robots across a diverse spectrum of research fields in soft robotics.
Article
The soft actuators of smart materials have attracted significant attention in recent years due to their unique functions and distinctive characteristics. The actuators are composed of smart materials that can demonstrate substantial alterations in their dimensions, shape, or mechanical characteristics when subjected to external stimuli, including but not limited to temperature, light, electricity, or magnetic fields. These aforementioned characteristics render them highly advantageous for various applications, including tissue engineering, prosthetics, surgical robots, drug delivery, and soft robotics. A deeper understanding of the principles of the actuators is crucial for their development and application expansion. This article provides a comprehensive analysis of soft actuators made from smart materials, explaining their underlying concepts, operational mechanisms, material composition, production techniques, and the diverse range of applications across various fields, including tissue engineering, prosthetics, surgical robotics, drug delivery systems, and the emerging field of soft robotics. This review further highlights the current challenges and prospects to address these problems to enable their ability to revolutionize into a variety of different technical fields.
Article
This paper focuses on soft actuators that utilize fluid power to drive soft robots and describes their features and applications. First, it discusses how soft actuators function as elemental technology in robots. This is followed by an introduction to the driving principle and features of fluid-driven soft actuators. It also classifies these soft actuators based on the fluid power source and the active mode of operation. Furthermore, an overview is provided on the materials employed in soft actuators and the control and evaluation methods for them. Finally, currently reported applications of these soft actuators, such as wearable devices, grippers, and bio-inspired robots, are presented.
Article
Elastomers with hyperelastic deformation bring prosperity to soft robotics, especially in constituting fluidic actuators, largely due to the merit of large deformation and airtightness. However, the large (typically 0.5-1.5 strain) in-plane stretching of such materials concurrent to motion generation inevitably causes energy loss, hinders force output and accuracy. Particularly, the high nonlinearity of the low-durometer (typically 10A to 30A Shore) hyperelastic elastomers makes the modeling and control of actuators a well-known challenge. In this work, we proposed an alternative approach of using semi-rigid elastomer of significantly larger durometer (70A to 100A) to create the typical fluidic soft actuator with axial translation, by utilizing small-strain folding to generate motion. Deformation constraints and property programming are combined into a single-piece body, enabling easy fabrication by Selective Laser Sintering 3D-printing and post-treatment for origami patterned structure. Systematic analyses on the principles, modeling and design are presented. The long lifespan (over 1 million cycles), superior output linearity, high energy efficiency (more than 60% increase), and drastically improved force output (more than 98% increase) were validated experimentally, showing high potentials in enabling high-performance soft actuators that are easy to design, fabricate and drive, strong to use, and accurate to control, towards even wider applications.
Article
Full-text available
Robot-assisted rehabilitation of gait still faces many challenges, one of which is improving physical human-robot interaction. The use of pleated pneumatic artificial muscles to power a step rehabilitation robot has the potential to meet this challenge. This paper reports on the development of a gait rehabilitation exoskeleton with a knee joint powered by pleated pneumatic artificial muscles. It is intended as a platform for the evaluation of design and control concepts in view of improved physical human-robot interaction. The design was focused on the optimal dimensioning of the actuator configuration. Safety being the most important prerequisite, a proxy-based sliding mode controller PSMC was implemented as it combines accurate tracking during normal operation with a smooth, slow and safe recovery from large position errors. Treadmill walking experiments of a healthy subject wearing the powered exoskeleton show the potential of PSMC as a safe robot-in-charge control strategy for robot-assisted gait training.
Article
Full-text available
Based on the sulfonated poly (styrene-b-ethylene-co-butylene-b-styrene) ionic membrane, a novel electro-active polymer, which can be used as sensors and actuators, was developed through the electroless plating procedure. The surface and cross-sectional morphologies of the SSEBS actuator were disclosed by using scanning electron microscope and transmission electron microscopy. The electromechanical results of the SSEBS actuators show high-speed bending actuation under constant voltages and also give excellent harmonic responses under sinusoidal excitation. In the voltage–current test, the electrical current is almost synchronous with the applied voltages, while the mechanical displacement shows high phase shift from the voltage signals. The SSEBS-based ionic polymer-metal composite can be a promising smart material and may possibly be used to implement biomimetic motion.
Article
Full-text available
The increasing demand for physical interaction between humans and robots has led to the development of robots that guarantee safe behavior when human contact occurs. However, attaining established levels of performance while ensuring safety poses formidable challenges in mechanical design, actuation, sens-ing and control. To achieve safety without compromising performance, the human-friendly robotic arm has been developed using the concept of hybrid actuation. The new design employs inherently-safe pneumatic artificial muscles augmented with small electrical actuators, human-bone-inspired robotic links, and newly designed distributed compact pressure regulators with proportional valves. The experimental results show that significant performance improvement that can be achieved with hybrid actuation over a system with pneumatic artificial muscles alone. The pa-per evaluates the safety of the new robot arm and demonstrates that the safety characteristics surpass those of previous human-friendly robots.
Article
Full-text available
Traditional robots have rigid underlying structures that limit their ability to interact with their environment. For example, conventional robot manipulators have rigid links and can manipulate objects using only their specialised end effectors. These robots often encounter difficulties operating in unstructured and highly congested environments. A variety of animals and plants exhibit complex movement with soft structures devoid of rigid components. Muscular hydrostats (e.g. octopus arms and elephant trunks) are almost entirely composed of muscle and connective tissue and plant cells can change shape when pressurised by osmosis. Researchers have been inspired by biology to design and build soft robots. With a soft structure and redundant degrees of freedom, these robots can be used for delicate tasks in cluttered and/or unstructured environments. This paper discusses the novel capabilities of soft robots, describes examples from nature that provide biological inspiration, surveys the state of the art and outlines existing challenges in soft robot design, modelling, fabrication and control.
Article
Full-text available
Continuum robotics has rapidly become a rich and diverse area of research, with many designs and applications demonstrated. Despite this diversity in form and purpose, there exists remarkable similarity in the fundamental simplified kinematic models that have been applied to continuum robots. However, this can easily be obscured, especially to a newcomer to the field, by the different applications, coordinate frame choices, and analytical formalisms employed. In this paper we review several modeling approaches in a common frame and notational convention, illustrating that for piecewise constant curvature, they produce identical results. This discussion elucidates what has been articulated in different ways by a number of researchers in the past several years, namely that constant-curvature kinematics can be considered as consisting of two separate submappings: one that is general and applies to all continuum robots, and another that is robot-specific. These mappings are then developed both for the single-section and for the multi-section case. Similarly, we discuss the decomposition of differential kinematics (the robot’s Jacobian) into robot-specific and robot-independent portions. The paper concludes with a perspective on several of the themes of current research that are shaping the future of continuum robotics.
Article
Full-text available
Airborne chemical sensing with mobile robots has been an active research areasince the beginning of the 1990s. This article presents a review of research work in this field,including gas distribution mapping, trail guidance, and the different subtasks of gas sourcelocalisation. Due to the difficulty of modelling gas distribution in a real world environmentwith currently available simulation techniques, we focus largely on experimental work and donot consider publications that are purely based on simulations.
Article
Full-text available
Bolted-down robots labor in our factories, performing the same task over and over again. Where are the robots that run and jump? Equaling human performance is very difficult for many reasons, including the basic challenge of demonstrating motors and transmissions that efficiently match the power per unit mass of muscle. In order to exceed animal agility, new actuators are needed. Materials that change dimension in response to applied voltage, so-called artificial muscle technologies, outperform muscle in most respects and so provide a promising means of improving robots. In the longer term, robots powered by atomically perfect fibers will outrun us all.
Article
Full-text available
This paper presents an introduction to ionic polymer-metal composites and some mathematical modeling pertaining to them. It further discusses a number of recent findings in connection with ion-exchange polymer-metal composites (IPMCS) as biomimetic sensors and actuators. Strips of these composites can undergo large bending and flapping displacement if an electric field is imposed across their thickness. Thus, in this sense they are large motion actuators. Conversely by bending the composite strip, either quasi-statically or dynamically, a voltage is produced across the thickness of the strip. Thus, they are also large motion sensors. The output voltage can be calibrated for a standard size sensor and correlated to the applied loads or stresses. They can be manufactured and cut in any size and shape. In this paper first the sensing capability of these materials is reported. The preliminary results show the existence of a linear relationship between the output voltage and the imposed displacement for almost all cases. Furthermore, the ability of these IPMCs as large motion actuators and robotic manipulators is presented. Several muscle configurations are constructed to demonstrate the capabilities of these IPMC actuators. This paper further identifies key parameters involving the vibrational and resonance characteristics of sensors and actuators made with IPMCS. When the applied signal frequency varies, so does the displacement up to a critical frequency called the resonant frequency where maximum deformation is observed, beyond which the actuator response is diminished. A data acquisition system was used to measure the parameters involved and record the results in real time basis. Also the load characterizations of the IPMCs were measured and it was shown that these actuators exhibit good force to weight characteristics in the presence of low applied voltages. Finally reported are the cryogenic properties of these muscles for potential utilization in an outer space environment of a few Torrs and temperatures of the order of - 140 degrees Celsius. These muscles are shown to work quite well in such harsh cryogenic environments and thus present a great potential as sensors and actuators that can operate at cryogenic temperatures.
Article
By integrating a number of different disciplines, rapid prototyping and manufacturing technology (RPM) is capable of forming parts with complicated structures and non-homogeneous materials. RPM techniques are mainly used as prototypes in such product invention process as stereo lithography, 3D printing, laminated object manufacturing and fused deposition modeling. So far, many new RPM techniques emerged out and have been already applied in such fields as rapid tooling/moulding, direct formed usable part, nano-/micro-RPM and biomanufacturing. The flexible digital manufacturing method will have a bright prospect.
Book
<<<Please do not ask me for the full text to this book! The book is under copyright to the publishers and I cannot give out the full text!!>>> Are you tired of picking up a book that claims to be on "practical" finite element analysis only to find that it is full of the same old theory rehashed and contains no advice to help you plan your analysis? If so then this book is for you! The emphasis of this book is on doing FEA, not writing a FE code. A method is provided to help you plan your analysis and a chapter is devoted to each choice you have to make when building your model giving you clear and specific advice. Finally nine case studies are provided which illustrate the points made in the main text and take you slowly through your first finite element analyses. The book is written in such a way that it is not specific to any particular FE software so it doesn't matter which FE software you use, this book can help you! The 2nd Edition of this very popular finite element analysis guide: 1)Emphasises practical finite element analysis with commercially available finite element software packages 2)Is written in a generic way so it is not specific to any particular software but clearly shows the methodology required for successful FEA 3)Is focused entirely on structural stress analysis 4)Offers specific advice on which element types to use, which material model to pick, which type of analysis to use and which type of results to look for 5)Provides specific, no nonsense advice on how to fix problems in the analysis 6)Contains over 300 illustrations 7)Provides nine detailed case studies which specifically show you how to perform various types of analysis 8)Does not weigh you down with unnecessary theory, but provides you with the minimum theory needed to understand the methods 9)Is an invaluable guide and reference for engineering students and practising engineers.
Article
Dynamic effects are very important in improving the design and study of the micro-robot. In the paper, our preliminary work in using ICPF to develop a novel tortoise-like flexible micro-robot with four legs and one tail is reported, which can crawl and swim underwater. ICPF is the abbreviation of Ionic Conducting Polymer gel Film which is a kind of smart film and can give large and fast bending displacement in the presence of a low applied voltage in wet condition. For controlling and analyzing easily the robot, we establish the micro-robot's tail dynamic model by applying Pseudo-Rigid-Body-Dynamic-Model (PRBDM). The model is established by considering the dynamic effect of the robot's tail, which is based on statics and kinematics. Then, the frequency analysis of a micro-robot based on PRBDM is investigated. Based on the PRBDM, the relation between the robot's tail angle displacement and the electrical voltage's frequency omega is theoretically derived and the simulation result for the tail's angle displacement is performed.
Article
Small and lightweight actuators that generate high force and high energy are strongly required for realizing powerful robots and tools. By applying ultra-high-strength p-phenylene-2,6-benzobisoxazole fiber sleeves to McKibben artificial muscles, new hydraulic artificial muscles have been developed. While conventional McKibben muscles are driven by a maximum pneumatic pressure of 0.7 MPa, the newly developed muscles are driven by a maximum water hydraulic of pressure of 4 MPa, resulting in very high force capability. This paper presents the materials and structure of the new artificial muscle and the experimental results. The developed muscles are evaluated by four parameters — force density per volume (FDV), force density per mass (FDM), energy density per volume (EDV) and energy density per mass (EDM) — for comparisons with other conventional linear actuators. The prototype artificial muscle, which is 40 mm in diameter and 700 mm in length, can achieve a maximum contracting force of 28 kN, FDV of 32.3 × 10 N/mm, FDM of 9.44 × 10 N/kg, EDV of 2600 × 10 J/mm and EDM of 762 × 10 J/kg. These values are 1.7 to 33 times larger than those of the typical conventional actuators. As the result, a high force artificial muscle of 40 mm in diameter that generates 28-kN contracting force has been developed successfully.
Article
An artificial muscle is one of the key technologies for soft robots. This paper describes design, fabrication, and characterization of an artificial muscle cell using an electro-conjugate fluid (ECF) and integration of the cells. The ECF is a kind of dielectric and functional fluid, which generates a powerful jet flow or ECF jet under an electrostatic field applied with an electrode pair. It is experimentally clarified that the smaller electrodes generate a more powerful ECF jet with constant voltage applied. The authors propose in this study a new type of micro artificial muscle cell using electro-conjugate fluid (ECF micro artificial muscle cell). This soft actuator having a power source inside is compact enough for integration. By integrating a large number of cells, we can realize a macro-sized artificial muscle. In this paper, we fabricate a prototype of ECF micro artificial muscle cell (Ø 12.5 mm × 13 mm), and integrate four cells into a 2 × 2 ECF artificial muscle actuator showing larger stroke and force. The maximum stroke and force are 1.56 mm and 320.5 mN with a single cell, and they are increased to be 2.8 mm and 504.1 mN with the 2 × 2 ECF artificial muscle actuator.
Article
Table of Contents Introduction Building Blocks Elephant Design Traditional Bases Folding Instructions Stealth Fighter. Snail. Valentine. Ruby-Throated Hummingbird. Baby. Splitting Points Folding Instructions Pteranodon. Goatfish. Grafting Folding Instructions Songbird 1. KNL Dragon. Lizard. Tree Frog. Dancing Crane. Pattern Grafting Folding Instructions Turtle. Western Pond Turtle. Koi. Tiling Folding Instructions Pegasus Circle Packing Folding Instructions Emu. Songbird 2. Molecules Folding Instructions Orchid Blossom. Silverfish. Tree Theory Folding Instructions Alamo Stallion. Roosevelt Elk. Box Pleating Folding Instructions Organist. Black Forest Cuckoo Clock. Uniaxial Box Pleating Folding Instructions Bull Moose Polygon Packing Crease Patterns Flying Walking Stick. Salt Creek Tiger Beetle. Longhorn Beetle. Camel Spider. Water Strider. Scarab Beetle. Cicada Nymph. Scarab HP. Cyclomatus metallifer. Scorpion HP. Euthysanius Beetle. Spur-Legged Dung Beetle. Hybrid Bases Folding Instructions African Elephant References Glossary of Terms Index
Article
Many 4-DOF exoskeleton type robot devices have been widely developed for the gait rehabilitation of post-stroke patients. However, most systems run with purely position control not allowing voluntary active movements of the subject. The lack of intelligent control strategies for variable gait patterns has been a clinical concern of such kind exoskeleton man–machine systems. In this work, we establish a 5-link model for the usual 4-DOF gait rehabilitation exoskeleton type man–machine system and propose a gait trajectory adaption control strategy. A 4-DOF gait rehabilitation exoskeleton prototype is developed as a platform for the evaluation of design concepts and control strategies in the view of improved physical human–robot interaction. The experimental results with eight healthy volunteers and three stroke patients are encouraging.
Article
A novel transducer concept based on an organic electrochemical transistor is described. Its function as an integral part of an air humidity sensor, in which the proton conductor Nafion acts as sensitivity layer has been realised. The resulting electrochemical sensor–transistor, based on the conducting polymer PEDOT:PSS, operates at low voltages, on the order of 1 V. The sensor response, measured as the drain–source current of the electrochemical transistor, versus air humidity, has a close to exponential behaviour. The sensor can be realised using exclusively printing and coating fabrication techniques. Here, we demonstrate devices realised on plastic foils and on ordinary coated fine paper substrates. This organic electrochemical transducer promise future applications such as all-integrated low-cost sensor tags for single-use chemical sensors.
Book
Did you know that any straight-line drawing on paper can be folded so that the complete drawing can be cut out with one straight scissors cut? That there is a planar linkage that can trace out any algebraic curve, or even ‘sign your name’? Or that a ‘Latin cross’ unfolding of a cube can be refolded to 23 different convex polyhedra? Over the past decade, there has been a surge of interest in such problems, with applications ranging from robotics to protein folding. With an emphasis on algorithmic or computational aspects, this treatment gives hundreds of results and over 60 unsolved ‘open problems’ to inspire further research. The authors cover one-dimensional (1D) objects (linkages), 2D objects (paper), and 3D objects (polyhedra). Aimed at advanced undergraduate and graduate students in mathematics or computer science, this lavishly illustrated book will fascinate a broad audience, from school students to researchers.
Article
This paper discusses a method for controlling a hyper-redundant arm to manipulate an object on a plane. The hyper-redundant arm can perform simple whole-arm manipulation by coiling or wrapping around the object and then pulling the object toward the goal position. The process of object manipulation can be separated into two steps: encircling the object and transporting the object. In the process of encircling the object, the arm is controlled by a set of virtual constraints that guide the arm to reach around the object and encircle it, keeping the arm within a specified bound to ensure the circular shape around the object. In the process of transporting the object, a simplified desired shape is generated from a Bézier curve according to a given goal position and the arm geometry. Then, the gradient descent method is used to update the joint angles of the arm at each step to move the arm toward the desired shape until the object reaches its target position. The proposed method has been tested in both simulation and real experiments.
Article
This paper presents a three-dimensional (3-D) dynamic model for a self-propelled, multilink dolphin-like robot to predict the dynamic behaviors of the bio-inspired artificial dolphin system within the framework of multibody dynamics. The propulsive structure mimicking dorsoventral motion includes a multilink tail and a flexibly oscillating fluke moving in coordination, as well as a pair of mechanical flippers performing flapping movements. This configuration can practically be simplified as an open-chain, tree-like multibody with a mobile base. The Schiehlen method is then employed to formulate the equations of motion based on the well-integrated kinematic and dynamic analyses of propulsive elements. Several locomotor behaviors, via coordinated control of the propulsors, can be principally replicated and numerically evaluated. Comparative results between simulations and experiments on forward swimming and combined motions are shown to demonstrate the effectiveness of the created model and locomotion control methods for dolphin-like swimming.
Article
An electro-conjugate fluid (ECF) is a type of dielectric and functional fluid that generates a powerful jet flow when subjected to high DC voltage. Although a high voltage is needed to generate the jet flow, the current is quite low at several microamperes, resulting in a total power consumption of several milliwatts. Using this smart fluid, we can develop micro fluid-driven mechanical components without any bulky pumps. Also, it is clarified that the power density of the ECF jet is higher when the electrode pair is miniaturized; therefore, it is suitable for micro actuators. Here, we propose and fabricate three types of soft actuators with an antagonistic configuration: (i) micro artificial muscle cells, (ii) a McKibben-type micro artificial muscle actuator using the ECF effect and (iii) a micro finger actuator with two chambers to bend. The actuators basically consist of a silicone rubber tube covered with a fiber sleeve and a micro pressure source using the ECF effect. Next, we apply and integrate these actuators into a micro robot hand, driven with ECF jets. The driving characteristics of the micro artificial muscle actuator and the integrated micro ECF hand with ECF fingers were fabricated and experimentally investigated. The experimental results show that this ECF jet actuation is effective for driving soft micro hands.
Article
Abstract Human muscular skeleton structure plays an important role for adaptive locomotion. Understanding of its mechanism is expected to be used for realizing adaptive locomotion of a humanoid robot as well. In this paper, a jumping robot driven by pneumatic artificial muscles is designed to duplicate human leg structure and function. It has three joints and nine muscles, three of them are biarticular muscles. For controlling such a redundant robot, we take biomechanical findings into account: biarticular muscles mainly contribute to joint coordination whereas monoarticular muscles contribute to provide power. Through experiments, we find (1) the biarticular muscles realize coordinated movement of joints when knee and/or hip is extended, (2) the extension of the ankle does not lead to coordinated movement, and (3) we can superpose extension of the knee with that of the hip without losing the joint coordination. The obtained knowledge can be used not only for robots, but may also contribute to understanding of adaptive human mechanism.
Article
This paper proposes a method to generate novel motions of mollusk-type deformable robots made of electro-active polymer gel. Simulation and experimental results show that large transformations can be obtained with multiple electrodes in a planar configuration. We have designed a starfish-shaped gel robot that can turn over using spatially varying electric fields.
Article
This paper describes the development of MEMS force sensors constructed using paper as the structural material. The working principle on which these paper-based sensors are based is the piezoresistive effect generated by conductive materials patterned on a paper substrate. The device is inexpensive (∼$0.04 per device for materials), simple to fabricate, lightweight, and disposable. Paper can be readily folded into three-dimensional structures to increase the stiffness of the sensor while keeping it light in weight. The entire fabrication process can be completed within one hour without expensive cleanroom facilities using simple tools (e.g., a paper cutter and a painting knife). We demonstrated that the paper-based sensor can measure forces with moderate performance (i.e., resolution: 120 μN, measurement range: ±16 mN, and sensitivity: 0.84 mV mN(-1)). We applied this sensor to characterizing the mechanical properties of a soft material. Leveraging the same sensing concept, we also developed a paper-based balance with a measurement range of 15 g, and a resolution of 0.39 g.
Article
Soft robots: A methodology based on embedded pneumatic networks (PneuNets) is described that enables large-amplitude actuations in soft elastomers by pressurizing embedded channels. Examples include a structure that can change its curvature from convex to concave, and devices that act as compliant grippers for handling fragile objects (e.g., a chicken egg).
Article
This protocol provides an introduction to soft lithography--a collection of techniques based on printing, molding and embossing with an elastomeric stamp. Soft lithography provides access to three-dimensional and curved structures, tolerates a wide variety of materials, generates well-defined and controllable surface chemistries, and is generally compatible with biological applications. It is also low in cost, experimentally convenient and has emerged as a technology useful for a number of applications that include cell biology, microfluidics, lab-on-a-chip, microelectromechanical systems and flexible electronics/photonics. As examples, here we focus on three of the commonly used soft lithographic techniques: (i) microcontact printing of alkanethiols and proteins on gold-coated and glass substrates; (ii) replica molding for fabrication of microfluidic devices in poly(dimethyl siloxane), and of nanostructures in polyurethane or epoxy; and (iii) solvent-assisted micromolding of nanostructures in poly(methyl methacrylate).
Article
This paper presents an innovative wormlike robot controlled by cellular neural networks (CNNs) and made of an ionic polymer-metal composite (IPMC) self-actuated skeleton. The IPMC actuators, from which it is made of, are new materials that behave similarly to biological muscles. The idea that inspired the work is the possibility of using IPMCs to design autonomous moving structures. CNNs have already demonstrated their powerfulness as new structures for bio-inspired locomotion generation and control. The control scheme for the proposed IPMC moving structure is based on CNNs. The wormlike robot is totally made of IPMCs, and each actuator has to carry its own weight. All the actuators are connected together without using any other additional part, thereby constituting the robot structure itself. Worm locomotion is performed by bending the actuators sequentially from "tail" to "head," imitating the traveling wave observed in real-world undulatory locomotion. The activation signals are generated by a CNN. In the authors' opinion, the proposed strategy represents a promising solution in the field of autonomous and light structures that are capable of reconfiguring and moving in line with spatial-temporal dynamics generated by CNNs.
Article
A biological paradigm of versatile locomotion and effective motion control is provided by the polychaete annelid worms, whose motion adapts to a large variety of unstructured environmental conditions (sand, mud, sediment, water, etc.), and could thus be of interest to replicate by robotic analogs. Their locomotion is characterized by the combination of a unique form of tail-to-head body undulations (opposite to snakes and eels), with the rowing-like action of numerous lateral appendages distributed along their long segmented body. Focusing on the former aspect of polychaete locomotion, computational models of crawling and swimming by such tail-to-head body undulations have been developed in this paper. These are based on the Lagrangian dynamics of the system and on resistive models of its interaction with the environment, and are used for simulation studies demonstrating the generation of undulatory gaits. Several biomimetic robotic prototypes have been developed, whose undulatory actuation achieves propulsion on sand and other granular unstructured environments. Extensive experimental studies demonstrate the feasibility of robot propulsion by tail-to-head body undulations in such environments, as well as the agreement of its qualitative and quantitative characteristics to the predictions of the corresponding computational models.
  • D J Shin
  • I Sardellitti
  • Y L Park
  • O Khatib
  • M Cutkosky
D. J. Shin, I. Sardellitti, Y. L. Park, O. Khatib, M. Cutkosky, Int. J. Rob. Res. 2010, 29, 571.
  • C P Santos
  • V Matos
C. P. Santos, V. Matos, Rob. Auton. Syst. 2011, 59, 620.
  • X Liu
  • M Mwangi
  • X Li
  • M O'brien
  • G M Whitesides
X. Liu, M. Mwangi, X. Li, M. O'Brien, G. M. Whitesides, Lab Chip 2011, 11, 2189.
  • R J Lang
  • T C Hull
R. J. Lang, T. C. Hull, Math Intell 2005, 27, 92.
  • P Arena
  • C Bonomo
  • L Fortuna
  • M Frasca
  • S Graziani
P. Arena, C. Bonomo, L. Fortuna, M. Frasca, S. Graziani, IEEE Trans. Syst. Man Cybernetics B 2006, 36, 1044.
  • D Trivedi
  • C Rahn
  • W Kier
  • I Walker
D. Trivedi, C. Rahn, W. Kier, I. Walker, Appl. Bionics Biomech. 2008, 5, 99.
  • K Takemura
  • F Yajima
  • S Yokota
  • K Edamura
K. Takemura, F. Yajima, S. Yokota, K. Edamura, Sens. Actuators A 2008, 144, 348.
  • D Qin
  • Y Xia
  • G Whitesides
D. Qin, Y. Xia, G. Whitesides, Nat. Protoc. 2010, 5, 491.
  • F Ilievski
  • A D Mazzeo
  • R F Shepherd
  • X Chen
  • G M Whitesides
F. Ilievski, A. D. Mazzeo, R. F. Shepherd, X. Chen, G. M. Whitesides, Angew. Chem. Int. Ed. 2011, 123, 1930.
  • P Beyl
  • M Van Damme
  • R Van Ham
  • B Vanderborght
  • D Lefeber
P. Beyl, M. Van Damme, R. Van Ham, B. Vanderborght, D. Lefeber, Appl. Bionics Biomech. 2009, 6, 229.
  • C D Onal
  • X Chen
  • G M Whitesides
  • D Rus
C. D. Onal, X. Chen, G. M. Whitesides, D. Rus, Int. Symp. Rob. Res. 2011, http://www.isrr-2011.org/ISRR-2011/Program_fi les/Papers/ Onal-ISRR-2011.pdf, 2011.
  • G La Spina
  • M Sfakiotakis
  • D P Tsakiris
  • A Menciassi
  • P Dario
G. La Spina, M. Sfakiotakis, D. P. Tsakiris, A. Menciassi, P. Dario, IEEE Trans. Rob. Autom. 2007, 23, 1200.
  • M Otake
  • Y Kagami
  • M Inaba
  • H Inoue
M. Otake, Y. Kagami, M. Inaba, H. Inoue, Rob. Auton. Syst. 2002, 40, 185. [ 20 ] Y. Bar-Cohen, Structure 2001.
  • L Cowan
  • I Walker
L. Cowan, I. Walker, Artif. Life 2008, 11, 126.
  • J Madden
J. Madden, Science 2007, 318, 1094.
  • R J Webster
  • B A Jones
R. J. Webster, B. A. Jones, J. Rob. Res. 2010, 29, 1661.
  • J Yu
  • Y F Li
  • Y Hu
  • L Wang
J. Yu, Y. F. Li, Y. Hu, L. Wang, Adv. Rob. 2009, 23, 1299.
  • M Mori
  • K Suzumori
  • M Takahashi
  • T Hosoya
M. Mori, K. Suzumori, M. Takahashi, T. Hosoya, Adv. Rob. 2010, 1, 233.
  • S Yokota
  • F Yajima
  • K Takemura
  • K Edamura
S. Yokota, F. Yajima, K. Takemura, K. Edamura, Adv. Rob. 2010, 24, 1929.
  • X L Wang
  • I K Oh
  • J Lu
  • J Ju
  • S Lee
X. L. Wang, I. K. Oh, J. Lu, J. Ju, S. Lee, Mater. Lett. 2007, 61, 5117.
  • M Otake
  • Y Kagami
  • M Inaba
  • H Inoue
M. Otake, Y. Kagami, M. Inaba, H. Inoue, Rob. Auton. Syst. 2002, 40, 185.
  • Y Bar-Cohen
Y. Bar-Cohen, Structure 2001.