Soft Robotic Actuators Research Articles

3D Printing of a Photo-thermal Self-folding Actuator

The demand for rapid and accurate fabrication of light-weight, biocompatible, and soft actuators in soft robotics has perused researchers to design and fabricate such products by rapid manufacturing techniques. The self-folding origami structure is a type of soft actuator that has applications in micro electro mechanical systems, soft electronics, and biomedical devices. 3-dimentional (3D) printing is a current manufacturing process that can be used for fabrication of involute soft self-folding products by means of shape memory polymer materials. This paper presents, for the first time, a method for developing a photo thermal self-folding soft actuator using a 3D bioplotter. Easily accessible and inexpensive pre-strained polystyrene is opted for the backbone of actuator. The polystyrene film (PS) is then structured in a hand shape gripper. Chitosan hydrogel and carbon black ink were combined for printing active hinges on the hand gripper. Various active hinges with different widths and thicknesses were printed on the hand gripper using the 3D bioplotter. An infra-red (IR) heating lamp was placed at a reasonable distance to emit IR light uniformly on the hand gripper. The temperature distribution on the hand gripper was observed using a thermographic camera and the bending angles of the samples were recorded by a video camera. It was observed that the bending angles of the hand fingers depend on factors such as the intensity of the heat flux generated by the IR light intensity, distance, onset temperature, geometry of the fingers such as width and thickness, and area of the hinges.

Using Voice Coils to Actuate Modular Soft Robots: Wormbot, an Example.

In this study, we present a modular worm-like robot, which utilizes voice coils as a new paradigm in soft robot actuation. Drive electronics are incorporated into the actuators, providing a significant improvement in self-sufficiency when compared with existing soft robot actuation modes such as pneumatics or hydraulics. The body plan of this robot is inspired by the phylum Annelida and consists of three-dimensional printed voice coil actuators, which are connected by flexible silicone membranes. Each electromagnetic actuator engages with its neighbor to compress or extend the membrane of each segment, and the sequence in which they are actuated results in an earthworm-inspired peristaltic motion. We find that a minimum of three segments is required for locomotion, but due to our modular design, robots of any length can be quickly and easily assembled. In addition to actuation, voice coils provide audio input and output capabilities. We demonstrate transmission of data between segments by high-frequency carrier waves and, using a similar mechanism, we note that the passing of power between coupled coils in neighboring modules—or from an external power source—is also possible. Voice coils are a convenient multifunctional alternative to existing soft robot actuators. Their self-contained nature and ability to communicate with each other are ideal for modular robotics, and the additional functionality of sound input/output and power transfer will become increasingly useful as soft robots begin the transition from early proof-of-concept systems toward fully functional and highly integrated robotic systems.

What Is the Path Ahead for Soft Robotics?

Soft RoboticsVol. 3, No. 4 Special Issue: The Path AheadGuest Editors: Joshua Schultz, Yiğit Mengüç, Michael Tolley, Bram VanderborghtEditorialWhat Is the Path Ahead for Soft Robotics?Joshua Schultz, Yiğit Mengüç, Michael Tolley, and Bram VanderborghtJoshua SchultzDepartment of Mechanical Engineering, The University of Tulsa, Tulsa, Oklahoma.Search for more papers by this author, Yiğit MengüçSchool of Mechanical, Industrial, and Manufacturing Engineering, Oregon State University, Corvallis, Oregon.Search for more papers by this author, Michael TolleyDepartment of Mechanical and Aerospace Engineering, University of California San Diego, La Jolla, California.Search for more papers by this author, and Bram VanderborghtDepartment of Mechanical Engineering, Vrije Universiteit Brussel, Brussels, Belgium.Search for more papers by this authorPublished Online:1 Dec 2016https://doi.org/10.1089/soro.2016.29010.jscAboutSectionsView articleView Full TextPDF/EPUB Permissions & CitationsPermissionsDownload CitationsTrack CitationsAdd to favorites Back To Publication ShareShare onFacebookTwitterLinked InRedditEmail View article"What Is the Path Ahead for Soft Robotics?." Soft Robotics, 3(4), pp. 159–160FiguresReferencesRelatedDetailsCited byModeling the dynamics of soft robots by discs and threadsHard questions for soft roboticsScience Robotics, Vol. 6, No. 53BPActuators: Lightweight and Low-Cost Soft Actuators by Balloons and PlasticsInvestigating the Mechanics of Human-Centered Soft Robotic Actuators with Finite Element AnalysisSoft LEGO: Bottom-Up Design Platform for Soft RoboticsSoft robotics: Definition and research issues Volume 3Issue 4Dec 2016 InformationCopyright 2016, Mary Ann Liebert, Inc.To cite this article:Joshua Schultz, Yiğit Mengüç, Michael Tolley, and Bram Vanderborght.What Is the Path Ahead for Soft Robotics?.Soft Robotics.Dec 2016.159-160.http://doi.org/10.1089/soro.2016.29010.jscPublished in Volume: 3 Issue 4: December 1, 2016PDF download

Studies on Development of Soft Robotic Bending Actuator using Natural Rubber

Objectives: This article investigates the usage of natural rubber in raw form as an alternative to commercial elastomeric for manufacturing the soft robotic actuator. Methods: Soft actuator is fabricated with pure latex as well as with formic acid as additive. The mold surface was coated with releasing agent and the latex is carefully poured into the mold. Curing was made at room temperature for 2 days and post curing is done at 80°C for two hours. Findings: The actuator made using natural latex without acid exhibited higher shrinkage. Whereas, the actuator treated with formic acid confirms the dimensional stability and comparatively lesser pores. Hence the natural latex with suitable additives can be used in the manufacture of soft actuators for robots. However, there is need of further investigation for establishing optimum combinations of the additives with natural rubber to obtain the desired properties in the actuator. Application: The developments in the proposed field of soft actuator reduce the cost of end effectors which find applications in medical as well as in engineering domain.

Methodology for designing and manufacturing complex biologically inspired soft robotic fluidic actuators: prosthetic hand case study

We present a novel methodology for the design and manufacture of complex biologically inspired soft robotic fluidic actuators. The methodology is applied to the design and manufacture of a prosthetic for the hand. Real human hands are scanned to produce a 3D model of a finger, and pneumatic networks are implemented within it to produce a biomimetic bending motion. The finger is then partitioned into material sections, and a genetic algorithm based optimization, using finite element analysis, is employed to discover the optimal material for each section. This is based on two biomimetic performance criteria. Two sets of optimizations using two material sets are performed. Promising optimized material arrangements are fabricated using two techniques to validate the optimization routine, and the fabricated and simulated results are compared. We find that the optimization is successful in producing biomimetic soft robotic fingers and that fabrication of the fingers is possible. Limitations and paths for development are discussed. This methodology can be applied for other fluidic soft robotic devices.

Understanding the Role of ECM Protein Composition and Geometric Micropatterning for Engineering Human Skeletal Muscle.

Skeletal muscle lost through trauma or disease has proven difficult to regenerate due to the challenge of differentiating human myoblasts into aligned, contractile tissue. To address this, we investigated microenvironmental cues that drive myoblast differentiation into aligned myotubes for potential applications in skeletal muscle repair, organ-on-chip disease models and actuators for soft robotics. We used a 2D in vitro system to systematically evaluate the role of extracellular matrix (ECM) protein composition and geometric patterning for controlling the formation of highly aligned myotubes. Specifically, we analyzed myotubes differentiated from murine C2C12 cells and human skeletal muscle derived cells (SkMDCs) on micropatterned lines of laminin compared to fibronectin, collagen type I, and collagen type IV. Results showed that laminin supported significantly greater myotube formation from both cells types, resulting in greater than twofold increase in myotube area on these surfaces compared to the other ECM proteins. Species specific differences revealed that human SkMDCs uniaxially aligned over a wide range of micropatterned line dimensions, while C2C12s required specific line widths and spacings to do the same. Future work will incorporate these results to engineer aligned human skeletal muscle tissue in 2D for in vitro applications in disease modeling, drug discovery and toxicity screening.

Mismatch strain programmed shape transformation of curved bilayer-flexible support assembly

Shape transformation in three dimensional (3D) structures is of interest in the design of engineered systems capable of accomplishing particular tasks that are unachievable by two dimensional (2D) architectures or static 3D ones. One approach involves the incorporation of stimuli responsive materials into the structural assembly to induce such transformations. In this work, we investigate the transformation of a curved bilayer ribbon supported by a flexible assembly that belongs to a family of complex three dimensional architectures. Through finite element analysis, we identified key design parameters and their effects on the deformation behavior of the assembly when it is subjected to an external stimuli in the form of a mismatch strain. Our results show that the behavior of the curved bilayer in response to the stimuli could be tuned by controlling the structural properties of the assembly. Our calculations also reveal a diverse set of deformation mechanisms including gradual flipping, snapping and creasing of the curved bilayer under specific circumstances. The design principles established in this work could be used to engineer 3D sensors, actuators for traditional and soft robotics, electronic device components, metamaterials, energy storage and harvesting devices with on-demand functional capabilities enabled by 3D transformations.

On constitutive relations for a rod-based model of a pneu-net bending actuator

The recent surge of interest in soft robotics has led to interesting designs and fabrication of flexible actuators composed of soft matter. Modeling these actuators to obtain quantitative estimates of their dynamics is challenging. In the present paper, a rod-based model for a popular pneumatically activated soft robot arm is developed. The model is based on Euler’s theory of the elastica and is arguably the simplest possible model. Through a synthesis of experiment and theory, we find that the constitutive relations needed to accurately capture the deformation of the arm differ considerably from the simple classical relation that the bending moment is linearly proportional to a change in curvature. The present paper also provides a framework to evaluate whether future soft robot actuator designs can be captured using simple models.

Low-voltage electrically driven homeostatic hydrogel-based actuators for underwater soft robotics

We present the synthesis, fabrication and electro-mechanical characterization of a novel electro-responsive hydrogel based on Na-4-vinylbenzenesulfonate (Na-4-VBS) that can operate as a fast response bending actuator in a low voltage regime (0.2–5V), in NaCl aqueous solutions. The bending speed can reach values up to 22°/s at 3V and of 2.7°/s at 1V. The responsive behavior of the benders was observed in physiological environments as well, such as phosphate buffer solution (PBS) and Dulbecco’s Modified Eagle’s Medium (DMEM) and exhibited similar performance. The material is a co-polymer comprising also hydroxyethyl methacrylate (HEMA) and acrylonitrile (AN), to confer high hydrophilicity to the structure and to enhance its elastic properties. According to the swelling and electro-mechanical testing results, the electrically driven deformation of the hydrogels was interpreted as a dynamic osmotic equilibrium effect taking place at the interface between the polymer and the surrounding medium, induced by the free ionic species migration throughout the polymer. This material constitutes a promising solution for the design and production of highly performing soft underwater actuators and biomimetic smart systems that can be controllably operated at the macro and mesoscale in fluids of biological interest, with minimal power consumption and below the standard potential of water electrolysis.

Dielectric Elastomer Based "Grippers" for Soft Robotics.

The use of few stiff fibers to control the deformation of dielectric elastomer actuators, in particular to break the symmetry of equi-biaxial lateral strain in the absence of prestretch, is demonstrated. Actuators with patterned fibers are shown to evolve into unique shapes upon electrical actuation, enabling novel designs of gripping actuators for soft robotics.

Amplifying the response of soft actuators by harnessing snap-through instabilities

Soft, inflatable segments are the active elements responsible for the actuation of soft machines and robots. Although current designs of fluidic actuators achieve motion with large amplitudes, they require large amounts of supplied volume, limiting their speed and compactness. To circumvent these limitations, here we embrace instabilities and show that they can be exploited to amplify the response of the system. By combining experimental and numerical tools we design and construct fluidic actuators in which snap-through instabilities are harnessed to generate large motion, high forces, and fast actuation at constant volume. Our study opens avenues for the design of the next generation of soft actuators and robots in which small amounts of volume are sufficient to achieve significant ranges of motion.

Rigidity-tuning conductive elastomer

We introduce a conductive propylene-based elastomer (cPBE) that rapidly and reversibly changes its mechanical rigidity when powered with electrical current. The elastomer is rigid in its natural state, with an elastic (Young’s) modulus of 175.5 MPa, and softens when electrically activated. By embedding the cPBE in an electrically insulating sheet of polydimethylsiloxane (PDMS), we create a cPBE–PDMS composite that can reversibly change its tensile modulus between 37 and 1.5 MPa. The rigidity change takes ∼6 s and is initiated when a 100 V voltage drop is applied across the two ends of the cPBE film. This magnitude of change in elastic rigidity is similar to that observed in natural skeletal muscle and catch connective tissue. We characterize the tunable load-bearing capability of the cPBE–PDMS composite with a motorized tensile test and deadweight experiment. Lastly, we demonstrate the ability to control the routing of internal forces by embedding several cPBE–PDMS ‘active tendons’ into a soft robotic pneumatic bending actuator. Selectively activating the artificial tendons controls the neutral axis and direction of bending during inflation.

Skins and Sleeves for Soft Robotics: Inspiration from Nature and Architecture

This paper is on the design, fabrication, and testing of skins and sleeves for soft robotics with the focus on the mechanical features of the microstructure of these skins, drawing inspiration from nature and architecture. Biological inspirations drawn from animals are used for designing skin membranes or skin structures for soft robotic actuators, in particular pneumatic actuators that protect, guide, and contribute to the development of the actuated shape. The results presented in this paper will be a new step toward advancing the state‐of‐the‐art of biologically inspired soft robots for minimally invasive surgery. Inspirations from architecture are of particular interest in the areas of formability of design and continuous flow. The report presents a trade‐off study using various skin and sleeve technologies of innovative fiber structures and combinations of different materials in different innovative designs, surrounding a pneumatically actuated, soft robot of variable stiffness.

Simulations of Two Patterns Fiber Weaves Reinforced in Rubber Actuator

Over recent years, studies on soft mechanism are rapidly being paid to attention especially in pneumatic actuator field. Good actuator should be able to provide sufficient force and flexibility in movement, hence bending motion is vital criteria needed in soft robotic actuation. In this paper, a solution to soft bending pneumatic actuator is proposed in which several patterns fiber weave designs are introduced. The objectives of the simulations is to investigate which weave patterns combination of fiber reinforced actuator models yields the best bending characteristics and its relation to the contraction or extension characteristics shown by single weave pattern actuator models. From the results, when two patterns of fiber weave are attached together to form a sleeve, significant bending were obtained from most of the models simulated. Large bending resulted from combined two patterns fiber weave models are achieved when maximum contraction and extension characteristics exhibit by both fiber weave patterns.

Biologically Inspired Soft Robot for Thumb Rehabilitation1

More than 130,000 people have strokes each year in the United States [1]. Of these victims, 76% are left with disabilities that cost the nation over $54 billion in lost work and medical fees. One prominent disability is upper extremity hemiplegia, which occurs among approximately 50% of stroke sufferers [2]. Robotic technology has the potential to provide an automated platform for controlled rehabilitation and assisted, task-oriented therapy. Several systems have been designed to assist in patient articulation of an impaired hand using rigid robotic components. While these products have been successful in articulating the pure bending motions of the four fingers, the limited capabilities of rigid technologies fail to reproduce the complicated motion path [5] of the thumb during opposition grasp (see Figure 1). This is the most important articulation for normal hand function and specifically for picking up everyday objects. To date, robotic systems for thumb rehabilitation have not been widely investigated [3] apart from some recent work [4] that used a multi-joint rigid robot.

Pneumatic Networks for Soft Robotics that Actuate Rapidly

Soft robots actuated by inflation of a pneumatic network (a “pneu‐net”) of small channels in elastomeric materials are appealing for producing sophisticated motions with simple controls. Although current designs of pneu‐nets achieve motion with large amplitudes, they do so relatively slowly (over seconds). This paper describes a new design for pneu‐nets that reduces the amount of gas needed for inflation of the pneu‐net, and thus increases its speed of actuation. A simple actuator can bend from a linear to a quasi‐circular shape in 50 ms when pressurized at ΔP = 345 kPa. At high rates of pressurization, the path along which the actuator bends depends on this rate. When inflated fully, the chambers of this new design experience only one‐tenth the change in volume of that required for the previous design. This small change in volume requires comparably low levels of strain in the material at maximum amplitudes of actuation, and commensurately low rates of fatigue and failure. This actuator can operate over a million cycles without significant degradation of performance. This design for soft robotic actuators combines high rates of actuation with high reliability of the actuator, and opens new areas of application for them.

Three-dimensional neuron–muscle constructs with neuromuscular junctions

This paper describes a fabrication method of muscle tissue constructs driven by neurotransmitters released from activated motor neurons. The constructs consist of three-dimensional (3D) free-standing skeletal muscle fibers co-cultured with motor neurons. We differentiated mouse neural stem cells (mNSCs) cultured on the skeletal muscle fibers into neurons that extend their processes into the muscle fibers. We found that acetylcholine receptors (AChRs) were formed at the connection between the muscle fibers and the neurons. The neuron–muscle constructs consist of highly aligned, long and matured muscle fibers that facilitate wide contractions of muscle fibers in a single direction. The contractions of the neuron–muscle construct were observed after glutamic acid activation of the neurons. The contraction was stopped by treatment with curare, an neuromuscular junction (NMJ) antagonist. These results indicate that our method succeeded in the formation of NMJs in the neuron–muscle constructs. The neuron–muscle construct system can potentially be used in pharmacokinetic assays related to NMJ disease therapies and in soft-robotic actuators.

1A2-H08 多自由度イオン導電性高分子アクチュエータの開発 : 微細加工技術を応用した電極のパターニング(MEMSとナノテクノロジー)

Polymer actuators are attracting considerable interest due to their special characteristics, including high flexibility and low weight. Ionic polymer-metal composite (IPMC) are polymer actuators that exhibit remarkable bending at driving voltages lower than 2 or 3 V. They have the potential to be used as soft robotic actuators. IPMC consists of a thin ion-exchange membrane with noble metal electrodes formed on both surfaces. Highly durable IPMCs will be fabricated using an electroless chemical plating technique to form metal electrodes. In this research, we have been developed a fabrication method of IPMC with patterned electrode which will be capable of a peristaltic movement. In this paper, we describe a fabrication method for patterning electrodes by the electroless chemical plating technique with SF_6 plasma treatment and the results of performance evaluation of IPMC with SF_6 plasma treatment.

Investigation on thermo-mechanical behaviors of artificial muscle films

IntroductionA recently presented model by de Gennes et al. [1]described the underlying principle of electro-thermo-dynamics in ionic polymers based on internal transportphenomena and electrophoresis. Ionic polymer metalcomposites (IPMCs) show a great potential as soft roboticactuators, artificial muscles, and dynamic sensors in themicro-to-macro scale [2]. Its performance is expected togreatly exceed the conventional actuators such as shapememory alloys and piezoelectrics. However, practical gelactuators have not been developed yet primarily becausemost of hydrogels matrix stiffness is quite weak [3] andtheir shape or volume change sensitivity to applied voltageis so low. Although a polyvinyl alcohol gel swollen withdimethyl sulfoxide has a relatively stiff matrix and exhibitsa fast shape changing upon applied voltage, the improve-ment of its matrix stiffness is still necessary and highervoltage bearing-capacity than several hundred volts is alsorequired [4]. Nafion, which has a relatively stiff matrix,was found to exhibit a fast self-bending upon a smallapplied voltage around 1 V or less. Investigations havebeen performed to develop practical actuators made bysuch ionic polymer-metal composite [5, 6]. Extensiveworks have been done on Nafion-based IPMC, includingoptimization of its mechanical properties and workingstability [7, 8], some excellent results on modeling ofIPMC with water have also been reported [9–12]. How-ever, few works have been done on another importantapplication such as an artificial muscle or artificial skin aswell as biosensor etc. In this work, the precise measuredmechanical properties and coefficients of thermal expan-sion (CTEs) for two typical films, matrix-Nafion117 filmand [Pt(NH

Formation of Patterned Electrode on Solid Polymer Electrolyte using Photolithography Technique

An Ionic Polymer-Metal Composite (IPMC) consists of a thin ionomeric membrane with noble metal electrodes formed on both surfaces. IPMCs have a potential as soft robotic actuators and artificial muscles with several advantages such as flexibility, light weight, and low driving voltages. Highly durable IPMCs will be fabricated using an electroless chemical plating technique to form metal electrodes. In this study, a fabrication method for patterning electrodes with a size of several micrometers has been developed to realize IPMCs, which will be capable of a peristaltic movement. A selective electroless gold plating and an epoxy-resin based photoresist are applied for patterning electrodes. By using a photomask with a pattern-size of 50 μm, patterned electrodes are formed on an ionomer (Nafion) membrane, resulting in the size of 65 μm. This pattern size is much smaller than that in conventional patterning methods using a selective electroless plating technique and masking tapes or stencil masks. The sheet resistance of the fabricated electrodes is lower than 30 Ω/□, which is almost same order of magnitude as that of electrodes formed by the conventional electroless plating without photolithography.