Bioinspired Soft Robotics: state of the art, challenges, and future directions

Purpose of Review: This review provides an overview of the state of the art in bioinspired soft robotics with by examining advancements in actuation, functionality, modeling, and control. Recent Findings: Recent research into actuation methods, such as artificial muscles, have expanded the functionality and potential use of bioinspired soft robots. Additionally, the application of finite dimensional models has improved computational efficiency for modeling soft continuum systems, and garnered interest as a basis for controller formulation. Summary: Bioinspiration in the field of soft robotics has led to diverse approaches to problems in a range of task spaces. In particular, new capabilities in system simplification, miniaturization, and untethering have each contributed to the field's growth. There is still significant room for improvement in the streamlining of design and manufacturing for these systems, as well as in their control

Bio-Inspired Robotics Based on Liquid Crystalline Elastomers(LCEs) and Flexible Stimulators

Soft robotics are most inspired from animals harnessing soft structures to move on ground or even harsh topological surface. Soft materials are the primary composition of soft robotics. Although they are not as durable and strong as ceramics and metals, soft materials stand out for their reversibility of deformation, response to stimuli and bio-compatibility. In this dissertation, liquid crystalline elastomer(LCE) combined with patterned flexible electronics and liquid metal have been used as soft robotics that simulating different kinds of worm-like movement. Besides, the impressive bendability of LCE finds itself a lot of potential in nature-camouflage area.First of all, the conception of soft robotics was deeply dug out through references about smart materials, for example, shape memory alloy(SMA), shape memory polymer(SMP), liquid crystalline elastomer(LCE) and etc. In this dissertation, LCE, as an advanced smart material, is used to fabricate soft robots, simulating inchworm movement. Another key point is the designation of actuator, in the research, flexible electronics were integrated onto LCE strip, when voltage was applied, the electronics increased temperature of specific part on one side of strip. Temperature difference between top and bottom surface induced LCE bending to approach anticipated location. Several cycles of inchworm movement were achieved, change in actuation sequence induces an inverse movement direction.Secondly, an improvement was carried out for crawling robots with combination of liquid metal(LM). Different from flexible electronics which are actually solid, “liquid electronics” suits more in the term “flexible”. Liquid metal was introduced into the research due to elevated requirement of bending curvature for its freely and reversibly transition between solid and liquid. New attachment approach was carried out using passive PDMS layer embedding to solidify contact between liquid metal and LCE. As consequence, the soft robotics could grasp a stick and move itself towards bi-direction. Repeatability test was conducted for the composite bending, twisting and shrinking.Last but not the least, the LCE/LM system patterned in different shape could easily camouflage itself as black agaric, seaweed and origami pentagram, in another word, the potential application in camouflage of this structure was developed. In specific parts of passive eco-flex layer, LCE segments were embedded and connected by liquid metal channels. For example, to simulate black agaric, four or five spots of the system were expected to bend, when external input was applied, LM in these areas generate and conduct heat around causing bending and maintaining the system at a specific shape, also, black paints were cast onto composite in advance. Repeatability test was conducted and reported

Optically controlled grasping-slipping robot moving on tubular surfaces

Stimuli-responsive polymers provide unmatched opportunities for remotely controlled soft robots navigating in complex environments. Many of the responsive-material-based soft robots can walk on open surfaces, with movement directionality dictated by the friction anisotropy at the robot-substrate interface. Translocation in one-dimensional space such as on a tubular surface is much more challenging due to the lack of efficient friction control strategies. Such strategies could in long term provide novel application prospects in, e.g. overhaul at high altitudes and robotic operation within confined environments. In this work, we realize a liquid-crystal-elastomer-based soft robot that can move on a tubular surface through optical control over the grasping force exerted on the surface. Photoactuation allows for remotely switched gripping and friction control which, together with cyclic body deformation, enables light-fueled climbing on tubular surfaces of glass, wood, metal, and plastic with various cross-sections. We demonstrate vertical climbing, moving obstacles along the path, and load-carrying ability (at least 3 × body weight). We believe our design offer new prospects for wirelessly driven soft micro-robotics in confined spacing.publishedVersionPeer reviewe

DEVELOPMENT OF A NANOCOMPOSITE SENSOR AND ELECTRONIC SYSTEM FOR MONITORING OF LOCOMOTION OF A SOFT EARTHWORM ROBOT

The ability to detect external stimuli and perceive the surrounding areas represents a key feature of modern soft robotic systems, used for exploration of harsh environments. Although people have developed various types of biomimetic soft robots, no integratedsensor system is available to provide feedback locomotion. Here, a stretchable nanocomposite strain sensor with integrated wireless electronics to provide a feedbackloop locomotion of a soft robotic earthworm is presented. The ultrathin and soft strain sensor based on a carbon nanomaterial and a low-modulus silicone elastomer allows for a seamless integration with the body of the soft robot, accommodating large strains derived from bending, stretching, and physical interactions with obstacles. A scalable, costeffective, screen-printing method manufactures an array of strain sensors that are conductive and stretchable over 100% with a gauge factor over 38. An array of stretchable nanomembrane interconnectors enables a reliable connection between soft strain sensors and wireless electronics, while tolerating the robot’s multi-modal movements. A set of computational and experimental studies of soft materials, stretchable mechanics, and hybrid packaging provides key design factors for a reliable, nanocomposite sensor system. The miniaturized wireless circuit, embedded in the robot joint, offers a real-time monitoring of strain changes on the earthworm skin. Collectively, the soft sensor system shows a great potential to be integrated with other flexible, stretchable electronics for applications in soft robotics, wearable devices, and human-machine interfaces.M.S

Analysis of actuation and instabilities in dielectric elastomer devices

Dielectric elastomer (DE) devices have gained significant interest in fields such as soft robotics, mechanical engineering, biomedical technology, and energy engineering due to their lightweight and fast actuation capabilities. However, these devices have several shortcomings that this thesis aims to address through the analysis of instabilities and actuation in various configurations. The electroelasticity theory is presented, defining the general kinematics and constitutive equations for these hyperelastic materials. Using this theory as a foundation, various configurations are introduced and analysed, with a focus on the novel ‘floating’ device as both a slab and tubular elastomer. These configurations are examined under different boundary conditions, and the deformation paths are analysed as geometrical parameters are varied. The onset of electro-mechanical instability is shown, as well as the introduction of the expansion limit. The theory of incremental deformations is specialised to investigate surface instabilities in three previously introduced elastomer slab configurations. It is shown that the instability is more sensitive to pre-stress in the ‘floating’ configuration, while the configuration deformed by sprayed charges is more stable against surface instabilities compared to the same configuration actuated by voltage. The effects of stiff electrodes on surface instabilities are also studied using surface-coating models, and it is demonstrated that the stability domain is significantly reduced when the device contracts. New bifurcation modes come into play and each one has been studied and characterised. Laminated composite elastomers are then considered, which are of particular interest due to their ability to enhance actuation characteristics. Using a small strain model and various boundary conditions, it is shown how, with specific parameters, an inverse mode of actuation can be achieved in both rank-1 and rank-2 laminated composites. The rank-2 laminate is demonstrated to enhance the rank-1 inverse actuation mode, and a guideline for optimizing composite parameters is provided. Existing materials are also analysed to show how current technology requires a rank-2 laminate to obtain the inverse mode of actuation

Soft pneumatic actuators: a review of design, fabrication, modeling, sensing, control and applications

Soft robotics is a rapidly evolving field where robots are fabricated using highly deformable materials and usually follow a bioinspired design. Their high dexterity and safety make them ideal for applications such as gripping, locomotion, and biomedical devices, where the environment is highly dynamic and sensitive to physical interaction. Pneumatic actuation remains the dominant technology in soft robotics due to its low cost and mass, fast response time, and easy implementation. Given the significant number of publications in soft robotics over recent years, newcomers and even established researchers may have difficulty assessing the state of the art. To address this issue, this article summarizes the development of soft pneumatic actuators and robots up until the date of publication. The scope of this article includes the design, modeling, fabrication, actuation, characterization, sensing, control, and applications of soft robotic devices. In addition to a historical overview, there is a special emphasis on recent advances such as novel designs, differential simulators, analytical and numerical modeling methods, topology optimization, data-driven modeling and control methods, hardware control boards, and nonlinear estimation and control techniques. Finally, the capabilities and limitations of soft pneumatic actuators and robots are discussed and directions for future research are identified

Advanced Bionic Attachment Equipment Inspired by the Attachment Performance of Aquatic Organisms: A Review

In nature, aquatic organisms have evolved various attachment systems, and their attachment ability has become a specific and mysterious survival skill for them. Therefore, it is significant to study and use their unique attachment surfaces and outstanding attachment characteristics for reference and develop new attachment equipment with excellent performance. Based on this, in this review, the unique non-smooth surface morphologies of their suction cups are classified and the key roles of these special surface morphologies in the attachment process are introduced in detail. The recent research on the attachment capacity of aquatic suction cups and other related attachment studies are described. Emphatically, the research progress of advanced bionic attachment equipment and technology in recent years, including attachment robots, flexible grasping manipulators, suction cup accessories, micro-suction cup patches, etc., is summarized. Finally, the existing problems and challenges in the field of biomimetic attachment are analyzed, and the focus and direction of biomimetic attachment research in the future are pointed out

Modeling Active Anisotropic Materials Undergoing Finite Deformations

Biological and synthetic active materials have attracted a large amount of research attention over the last decade. This thesis is focuses on the development of constitutive models and computational frameworks for describing the behavior of active anisotropic materials. Active anisotropic materials are defined as consisting of an isotropic matrix embedded with fibers or oriented particles that are active. In this dissertation, new constitutive formulations for active anisotropic materials undergoing finite deformations are proposed and analyzed within a generalized continuum mechanics framework. The constitutive equations have been developed for two material classes: i) natural biological muscle tissue and ii) synthetic electroactive polymers. The proposed constitutive models are successfully implemented into a finite element environment to study a range of initial boundary value problems. In the first material class, a structure-based continuum model is proposed to capture the viscoelastic behavior due to smooth muscle tissue contractility. We employed a thick-walled model for healthy and diseased arteries to investigate the effect of active viscoelasticity on the mechanical response of the artery wall. The work focuses on the artery being overstretched on long time scales (around 1 minute), for example, during surgical events such as balloon angioplasty and stent implantation. Model results show an over fourfold increase in circumferential stresses and twofold increase in radial stresses when active viscoelasticity is considered. This suggests that active viscoelasticity has a non-negligible effect on the artery wall stresses when longer timescales are considered. In the second material class, a novel dielectric elastomer composite consisting of an isotropic matrix and embedded contractile fibers is proposed. Two activation modes are realized: through thickness actuation of the matrix and fiber actuation in the plane. A constitutive model is proposed to model the active anisotropic material behavior. A new user subroutine was developed for the proposed constitutive model and implemented into the commercial finite element software ABAQUS. A series of computational simulations to highlight novel deformation modes of the proposed dielectric elastomer composite are presented. The proposed composite significantly extends the actuation performance space for dielectric elastomers. Several new spatial architectures are proposed and the simulations demonstrate coordinated surface morphing through spatial activation and as a function of fiber orientation. Finally, we calculate the actuation response for complex 3D geometries, which opens the design space even further. The developed computational framework is demonstrated to be a very convenient and efficient numerical tool to study complex materials.PHDAerospace EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/138722/1/yalili_1.pd