New Approaches to Multi-functional Soft Materials

Soft robotics is a relatively new, but fast-developing field of science and technology that utilizes soft materials such as polymers in their body structure. Despite significant progress in soft robotic devices, robots that can sense their environments are still very rare. Although some soft robots have exhibited sensing capabilities, they still have not demonstrated synergistic coupling of sensing and actuation. From our perspective, this type of coupling may take us one step closer to fabricate soft robots with autonomous feedback dynamics. In this work, we present new approaches to soft robotic devices, which are fabricated from responsive soft materials and are able to exhibit synergistic coupling of structural color-based sensing and actuation in response to environmental stimuli. Cephalopods, such as cuttlefish, are excellent models of coupled sensing and actuation. They demonstrate remarkable adaptability to the coloration and texture of their surroundings by modulating their skin color and surface morphology simultaneously and reversibly, for adaptive camouflage and signal communication. Inspired by this unique feature of cuttlefish skins, we present a general approach to remote-controlled, smart films that undergo simultaneous changes of surface color and morphology upon infrared (IR) actuation. The smart film has a reconfigurable laminated structure that comprises an IR-responsive nanocomposite actuator layer and a mechanochromic elastomeric photonic crystal layer. Upon global or localized IR irradiation, the actuator layer exhibits fast, large, and reversible strain in the irradiated region, which causes a synergistically coupled change in the shape of the laminated film and color of the mechanochromic elastomeric photonic crystal layer in the same region. Complex 3D shapes, such as bending and twisting deformations, can be created under IR irradiation, by modulating the strain direction in the actuator layer of the laminated film. Finally, the laminated film has been used in a remote-controlled inchworm walker that can directly couple a color-changing skin with the robotic movements. Such IR-actuated, reconfigurable films could enable new functions in soft robots and wearable devices. A crucial aspect of soft robotics is the sensing capabilities of the robot. Colorimetric sensing based on structural colors, mostly photonic crystals, has been explored. A major challenge is overcoming the problems of limited scalability and time-consuming fabrication process, which affect the real-world applications of photonic crystals. Herein, we have developed a new scalable and affordable platform technology for fabrication of stimuli-responsive, interference colored films. Our system is composed of a thin film of a transparent polymer deposited on a metal-coated substrate. The facile fabrication process allows us to create full spectrum of interference colors on both rigid and soft substrates by simply adjusting the thickness of the polymer layer. Furthermore, our films have been used as colorimetric sensors which undergo fast and reversible change of surface color upon changes in environmental humidity. Such polymer-based, responsive interference coloration could empower colorimetric sensing of various environmental stimuli (e.g. humidity, chemicals, heat, and mechanical forces), which could enable a wide range of applications

Large-Scale Surface Shape Sensing with Learning-Based Computational Mechanics

Proprioception, the ability to perceive one's own configuration and movement in space, enables organisms to safely and accurately interact with their environment and each other. The underlying sensory nerves that make this possible are highly dense and use sophisticated communication pathways to propagate signals from nerves in muscle, skin, and joints to the central nervous system wherein the organism can process and react to stimuli. In a step forward to realize robots with such perceptive capability, a flexible sensor framework that incorporates a novel modeling strategy, taking advantage of computational mechanics and machine learning, is proposed. The sensor framework on a large flexible sensor that transforms sparsely distributed strains into continuous surface is implemented. Finite element (FE) analysis is utilized to determine design parameters, while an FE model is built to enrich the morphological data used in the supervised training to achieve continuous surface reconstruction. A mapping between the local strain data and the enriched surface data is subsequently trained using ensemble learning. This hybrid approach enables real time, robust, and high‐order surface reconstruction. The sensing performance is evaluated in terms of accuracy, repeatability, and feasibility with numerous scenarios, which has not been demonstrated on such a large‐scale sensor before

Spring-IMU Fusion Based Proprioception for Feedback Control of Soft Manipulators

This paper presents a novel framework to realize proprioception and closed-loop control for soft manipulators. Deformations with large elongation and large bending can be precisely predicted using geometry-based sensor signals obtained from the inductive springs and the inertial measurement units (IMUs) with the help of machine learning techniques. Multiple geometric signals are fused into robust pose estimations, and a data-efficient training process is achieved after applying the strategy of sim-to-real transfer. As a result, we can achieve proprioception that is robust to the variation of external loading and has an average error of 0.7% across the workspace on a pneumatic-driven soft manipulator. The realized proprioception on soft manipulator is then contributed to building a sensor-space based algorithm for closed-loop control. A gradient descent solver is developed to drive the end-effector to achieve the required poses by iteratively computing a sequence of reference sensor signals. A conventional controller is employed in the inner loop of our algorithm to update actuators (i.e., the pressures in chambers) for approaching a reference signal in the sensor-space. The systematic function of closed-loop control has been demonstrated in tasks like path following and pick-and-place under different external loads

Scalable Tactile Sensing for an Omni-adaptive Soft Robot Finger

Robotic fingers made of soft material and compliant structures usually lead to superior adaptation when interacting with the unstructured physical environment. In this paper, we present an embedded sensing solution using optical fibers for an omni-adaptive soft robotic finger with exceptional adaptation in all directions. In particular, we managed to insert a pair of optical fibers inside the finger's structural cavity without interfering with its adaptive performance. The resultant integration is scalable as a versatile, low-cost, and moisture-proof solution for physically safe human-robot interaction. In addition, we experimented with our finger design for an object sorting task and identified sectional diameters of 94\% objects within the $\pm$6mm error and measured 80\% of the structural strains within $\pm$0.1mm/mm error. The proposed sensor design opens many doors in future applications of soft robotics for scalable and adaptive physical interactions in the unstructured environment.Comment: 8 pages, 6 figures, full-length version of a submission to IEEE RoboSoft 202

Actionneurs en polymère cristallins liquides poreux

Les actionneurs en matériaux souples possèdent des caractéristiques distinctives qui les rendent utiles pour de nombreuses applications. Parmi les matériaux souples à des fins d'actionnement, les élastomères cristallins liquides (LCE - abréviation en anglais) sont particulièrement prometteurs en raison de leur grande déformation réversible, de leur im-portante force mécanique lors de l’actionnement, et de leurs mouvements diversifiés dé-clenchés par des stimuli. Dans ce domaine de recherche, la plupart des efforts ont été con-sacrés à la conception de nouvelles structures moléculaires de LCE, au contrôle de l'ali-gnement LC qui est crucial pour la déformation, et à l'ingénierie des structures ou archi-tectures d'actionneurs. Toutefois, tant pour la recherche fondamentale que pour les appli-cations, il est important de développer de nouvelles approches qui, sans changer les struc-tures du LCE et de l'actionneur et en utilisant le même alignement LC, peuvent donner lieu à de nouvelles fonctions d'actionnement. C’est le but de la présente thèse qui porte sur le développant d’un nouveau type d’actionneurs, à savoir, actionneurs poreux en LCE. Afin de fabriquer des actionneurs LCE poreux, nous avons développé une méthode simple et efficace qui consiste à, successivement, disperser des nanoparticules inorganiques (celles du CaCO3 et du MOF : metal-organic framework) dans un film LCE, préparer l'ac-tionneur par étirement mécanique pour l'alignement des mésogènes et irradiation à la lu-mière UV pour la réticulation du polymère, et enlever les nanoparticules inorganiques de la matrice LCE par voie de gravure chimique. Nos études sur les actionneurs LCE poreux résultants ont non seulement révélé de nouvelles fonctions ou fonctionnalités d'actionne-ment, mais aussi démontré leur potentiel pour des applications. Premièrement, bien que le LCE utilisé soit hydrophobe, son actionneur poreux est capable d’absorber une grande quantité d'eau et gonfler comme un hydrogel. L’étude montre que ce changement de propriété est probablement causé par des ions restants dans l'actionneur gravé, ce qui améliore l'affinité entre les surfaces des pores et les molécules d'eau. Malgré la présence d'eau, l'alignement des mésogènes peut être préservé en grande partie. Par con-séquent, l'actionneur LCE poreux gonflé peut présenter une déformation réversible par changement de volume lors de l'absorption et de la désorption d'eau (comme un hydrogel) ou par une transition de phase ordre-désordre des mésogènes induite thermiquement (une caractéristique de LCE). Des comportements en actionnement particuliers peuvent être obtenus en combinant ces deux mécanismes d'actionnement différents. Cette nouvelle fonctionnalité est abordée dans les chapitres 2 et 4. Deuxièmement, le gonflement important de l’actionneur poreux dans l'eau offre un moyen efficace pour introduire dans l'actionneur un additif dissous dans l’eau, et après séchage, l’additive ainsi encapsulé par les canaux de pores peut doter l’actionneur d'une fonction au-delà de l’actionnement. Nous avons démontré une nouvelle fonctionnalité dite « recon-figurabilité des fonctions » en chargeant, lavant et rechargeant trois différents additifs fonctionnels dans un même actionneur LCE poreux : un liquide ionique (IL) pour la con-ductivité ionique, un colorant photothermique pour le mouvement piloté par la lumière et un fluorophore pour l'émission de couleur. Cette nouvelle fonctionnalité est rapportée au chapitre 2. De plus, nous avons utilisé un actionneur LCE poreux contenant un liquide ionique (PLCE-IL) pour démontrer séparément la détection et l'actionnement qui sont normalement deux fonctions obtenues avec deux classes de matériaux : matériaux défor-mables pour détection par voir électrique et matériaux souples pour actionnement déclen-ché par des stimuli. D'une part, lors de la transition de phase ordre-désordre des méso-gènes alignés, le PLCE-IL se comporte comme un actionneur typique capable de changer sa forme de manière réversible et peut être utilisé pour assembler un robot souple alimenté par la lumière. D'autre part, à des températures en-dessous de la transition de phase, le PLCE-IL est un élastomère qui peut supporter et détecter de grandes déformations de di-vers modes ainsi que des changements de conditions environnementales en signalant la variation de résistance électrique correspondante. L'utilisation collective de ces deux fonc-tions intégrées dans un dispositif a également été montrée. Ce travail est discuté au cha-pitre 3. Finalement, rapporté au chapitre 4, nous avons fait une découverte inattendue en étudiant les actionneurs LCE chargés de MOF (LCE-MOF). Après gravure chimique pour le retrait des cristaux MIL-88A, l'actionneur poreux devient magnétiquement sensible, réagissant à un aimant proche. L’analyse suggère la formation in situ de nanoparticules magnétiques de Fe3O4 due à la gravure chimique et à l'irradiation par la lumière UV. En plus des fonc-tionnalités susmentionnées, un actionneur poreux magnétique peut être dirigé par un ai-mant d’entreprendre des mouvements multidirectionnels à la surface de l'eau. En plus, la présence des nanoparticules de Fe3O4 donne un important effet photothermique qui peut être mis à profit pour obtenir un mouvement efficace de l'actionneur poreux alimenté par la lumière.Abstract: Soft materials-based actuators possess distinctive characteristics making them useful for applications in many fields. Among the soft materials for actuation, liquid crystalline elas-tomers (LCEs) stand out owing to their unique actuation features including large shape deformation, high mechanical forces, and diversiform movements driven by variety of stimuli. In terms of material research in the field of LCE actuators, understandably, most effort has been dedicated to designing new molecular structures of LCE, controlling LC alignment, and engineering actuator structures or architectures. However, it is of funda-mental interest to develop new approaches that, without changing the LCE and actuator structures and using the same LC alignment, can give rise to new actuation functions. The purpose of the present thesis is to address this important issue by developing porous LCE actuators. To fabricate porous LCE actuators, we developed a simple and efficient direct templating method that consists in dispersing inorganic nanoparticles, like CaCO3 and MIL-88A (metal-organic framework, MOF) in LCE film, preparing the actuator through mechanical stretching for alignment of mesogens and UV light irradiation for polymer chain crosslink-ing, and subsequently removing inorganic nanoparticles from the LCE matrix by means of chemical etching. Our studies of porous LCE actuators not only revealed a number of new actuation functions but also demonstrated the potential for applications. First, although the LCE used is hydrophobic, porous LCE actuators can absorb large amounts of water and swell like hydrogel, which is likely due to ions remained in the etched actuator leading to improved affinity between pore surfaces and water molecules. Despite the presence of water, the alignment of mesogens can be preserved to a great extent. Con-sequently, swollen porous LCE actuator can exhibit reversible deformation through either volume change upon water absorption and desorption (like hydrogel) or thermally induced order-disorder phase transition of the mesogens (characteristic of LCE). Unusual actuation behaviors can be obtained by combining these two different actuation mechanisms. This new feature is discussed in Chapters 2 and 4. Secondly, by dissolving a given active additive in water, the large swelling of porous LCE actuator in water provides an effective means to introduce this additive in the actuator and thus endow it with a beyond-actuation function enabled by the additive embedded in pore channels after drying. We demonstrated the new feature of function reconfigurability by loading, washing out and reloading different functional additives in a same porous LCE actuator: an ionic liquid (IL) for ionic conductivity, a photothermal dye for light-driven movement and a fluorophore for color emission. This new feature is reported in Chapter 2. Furthermore, we went on to use porous LCE actuator containing ionic liquid (PLCE-IL) for separate sensing and actuation that are normally two functions obtained with two clas-ses of materials: electrically responsive and deformable materials for sensing and soft ac-tive materials for stimuli-triggered actuation. On one hand, upon the order–disorder phase transition of aligned mesogens, PLCE-IL behaves like a typical actuator capable of reversi-ble shape change and can be used to assemble light-fueled soft robot. On the other hand, at temperatures below the phase transition, PLCE-IL is an elastomer that can sustain and sense large deformations of various modes as well as environmental condition changes by reporting the corresponding electrical resistance variation. The collective use of the two functions integrated in one device was also shown. This work, discussed in Chapter 3, shows that electrically responsive porous LCEs are a potential materials platform that of-fers possibilities for merging deformable electronic and actuation applications. Finally, reported in Chapter 4, we made an unexpected finding in studying MOF-loaded LCE actuators (LCE-MOF). After chemical etching for removal of MIL-88A crystals, the porous LCE-MOF actuator becomes magnetically responsive. The characterization results suggest the in-situ formation of magnetic Fe3O4 nanoparticles due to acid etching and UV light irradiation. In addition to the aforementioned features of porous LCE actuators, with a magnetic LCE actuator, a magnet can be used to drive its multi-directional movement on water surface, and the enhanced photothermal effect due to light absorption of Fe3O4 na-noparticles can be taken advantage to achieve efficient light-driven locomotion of the po-rous actuator

3D printed pneumatic soft actuators and sensors: their modeling, performance quantification, control and applications in soft robotic systems

Continued technological progress in robotic systems has led to more applications where robots and humans operate in close proximity and even physical contact in some cases. Soft robots, which are primarily made of highly compliant and deformable materials, provide inherently safe features, unlike conventional robots that are made of stiff and rigid components. These robots are ideal for interacting safely with humans and operating in highly dynamic environments. Soft robotics is a rapidly developing field exploiting biomimetic design principles, novel sensor and actuation concepts, and advanced manufacturing techniques. This work presents novel soft pneumatic actuators and sensors that are directly 3D printed in one manufacturing step without requiring postprocessing and support materials using low-cost and open-source fused deposition modeling (FDM) 3D printers that employ an off-the-shelf commercially available soft thermoplastic poly(urethane) (TPU). The performance of the soft actuators and sensors developed is optimized and predicted using finite element modeling (FEM) analytical models in some cases. A hyperelastic material model is developed for the TPU based on its experimental stress-strain data for use in FEM analysis. The novel soft vacuum bending (SOVA) and linear (LSOVA) actuators reported can be used in diverse robotic applications including locomotion robots, adaptive grippers, parallel manipulators, artificial muscles, modular robots, prosthetic hands, and prosthetic fingers. Also, the novel soft pneumatic sensing chambers (SPSC) developed can be used in diverse interactive human-machine interfaces including wearable gloves for virtual reality applications and controllers for soft adaptive grippers, soft push buttons for science, technology, engineering, and mathematics (STEM) education platforms, haptic feedback devices for rehabilitation, game controllers and throttle controllers for gaming and bending sensors for soft prosthetic hands. These SPSCs are directly 3D printed and embedded in a monolithic soft robotic finger as position and touch sensors for real-time position and force control. One of the aims of soft robotics is to design and fabricate robotic systems with a monolithic topology embedded with its actuators and sensors such that they can safely interact with their immediate physical environment. The results and conclusions of this thesis have significantly contributed to the realization of this aim

Control-based 4D printing: adaptive 4D-printed systems

Building on the recent progress of four-dimensional (4D) printing to produce dynamic structures, this study aimed to bring this technology to the next level by introducing control-based 4D printing to develop adaptive 4D-printed systems with highly versatile multi-disciplinary applications, including medicine, in the form of assisted soft robots, smart textiles as wearable electronics and other industries such as agriculture and microfluidics. This study introduced and analysed adaptive 4D-printed systems with an advanced manufacturing approach for developing stimuli-responsive constructs that organically adapted to environmental dynamic situations and uncertainties as nature does. The adaptive 4D-printed systems incorporated synergic integration of three-dimensional (3D)-printed sensors into 4D-printing and control units, which could be assembled and programmed to transform their shapes based on the assigned tasks and environmental stimuli. This paper demonstrates the adaptivity of these systems via a combination of proprioceptive sensory feedback, modeling and controllers, as well as the challenges and future opportunities they present

Toward Intrinsic Force Sensing and Control in Parallel Soft Robots

With soft robotics being increasingly employed in settings demanding high and controlled contact forces, recent research has demonstrated the use of soft robots to estimate or intrinsically sense forces without requiring external sensing mechanisms. While this has mainly been shown in tendon-based continuum manipulators or deformable robots comprising of push–pull rod actuation, fluid drives still pose great challenges due to high actuation variability and nonlinear mechanical system responses. In this work, we investigate the capabilities of a hydraulic, parallel soft robot to intrinsically sense and subsequently control contact forces. A comprehensive algorithm is derived for static, quasi-static, and dynamic force sensing, which relies on fluid volume and pressure information of the system. The algorithm is validated for a single degree-of-freedom soft fluidic actuator. Results indicate that axial forces acting on a single actuator can be estimated with mean error of 0.56 ± 0.66 N within the validated range of 0–6 N in a quasi-static configuration. The force sensing methodology is applied to force control in a single actuator as well as the coupled parallel robot. It can be seen that forces are controllable for both systems, with the capability of controlling directional contact forces in case of the multidegree-of-freedom parallel soft robot