Textile Actuators Research Articles

Clutchable Fabric Actuator for Energy‐Efficient Wearable Robots

AbstractEnergy‐efficient yet energy‐dense soft actuators are essential for untethered wearable robots. This work reports a fabric‐like actuator, combining shape memory alloy (SMA) springs and electrostatic clutches (ESClutches). The SMA springs provide high force density, with only 18 g of materials generating 40 N of force at actuation strains of over 35%, but requiring 78 W of power to hold that strain. The ESClutches cannot generate motion on their own, but can maintain the force and contraction generated by SMAs consuming only a few mW, thus allowing the SMAs to be turned off. By combining SMAs and ESClutches, a soft wearable fabric actuator is developed with force and stroke suited for an upper‐limb soft exoskeleton, able to lock in any given position using negligible power. The design is scalable: the number and dimensions of the SMA springs and of the ESClutches can be chosen to meet size and actuator performance requirements. This work reports two wearable use cases, where the combined SMAs and ESClutches consume over 70% lower power than SMAs alone.

Synchronous Cation-Driven and Anion-Driven Polypyrrole-Based Yarns toward In-Air Linear Actuators.

Conducting polymers (CP) have shown great features in building textile actuators. To date, most of the yarn-based or CP-yarn actuators have been operated in liquid electrolytes in a three-electrode-cell configuration, comprising an external counter and a reference electrode. For integration in textiles, a two-electrode system is needed, where both electrodes are in a yarn format. This can be achieved by having two CP-yarns, where one acts as the anode and the other as the cathode. For these two CP-yarns to operate synchronically, they both need to expand (or contract) during opposite reactions. This can be achieved by doping one CP-yarn with mobile anions that will expand during oxidation, while the other CP-yarn should be doped with immobile anions expanding during reduction. As a result, the same movement is created upon opposite redox reactions, both collaborating with the actuation in the same direction without the need for an external passive electrode to close the electrical circuit, which could oppose or hinder the movement. Most of the studies on textile actuators are based on cation-driven CP-yarn actuators, while little is known about anion-driven systems in CP-yarn actuators. Here, we first present a study of the effect of the dopants, solvents, and polymer layer combinations on the mechanism and strain of CP-yarns. The CP-yarns are coated with two layers: an inner poly(3,4-ethylenedioxythiophene) (PEDOT) layer and the outer and active polypyrrole (PPy) layer. According to our results, the dopant of the inner PEDOT layer seems to affect the actuation mechanism of the outer PPy layer and, thereby, of the whole CP-yarn actuator, influencing the direction of the movement and enhancing or hindering the total strain of the actuator. We show that a CP-yarn coated with PEDOT(Tos)/PPy(ClO4) and actuated in LiClO4 aqueous solution showed a pure anion-driven actuation. Next, based on the latter results, we demonstrate for the first time the dual actuation of two CP-yarns, doped with two different dopants, ClO4 - and DBS-, actuating simultaneously driven by opposite redox reactions and exhibiting an average of 0.5% of strain, an important step toward in-air actuating yarns.

A Straightforward Approach of Wet‐Spinning Poly(3,4‐ethylenedioxythiophene):Polystyrene Sulfate Fibers for Use in All Conducting Polymer‐Based Textile Actuators

Poly(3,4‐ethylenedioxythiophene) (PEDOT), an inherently electrically conductive or conjugated polymer (CP), exhibits the potential to play a significant role in the development of innovative fiber materials for use in smart textiles, such as wearables. Furthermore, these fibers can function as artificial muscles in the emerging field of interactive fiber rubber composites. This study introduces a straightforward and efficient method for creating PEDOT‐based, biomimetic, fiber‐shaped, linearly contracting ionic electroactive polymer actuators. To achieve this, a wet‐spinning technique is presented, which enables a continuous production of PEDOT:polystyrene sulfate (PSS) fibers at high production rates of 34 m h−1, an additional fiber washing step and a sulfuric acid posttreatment step to increase the fibers conductivity. The fibers provide a high conductivity of 1028 S cm−1, maximum tensile strength reaching 182 MPa, and a maximum elongation of 24%. When utilized as CP actuators in an aqueous sodium dodecylbenzenesulfonate electrolyte medium, the fibers demonstrate a repeatable maximum isometric contractile force of 1.64 mN and repeatable linear contractile strain up to 0.56%. Furthermore, a high level of cyclic long‐term actuation stability can be demonstrated. Notably, these contractile strains are, to the best of knowledge, the highest reported values for pristine PEDOT:PSS fibers.

Development of finger movement assistive gloves with pneumatic fabric actuators

We developed flexible, lightweight, and washable gloves with actuators to assist finger movements and improve ease of wearing. Performance and wearability were measured using standardized tests, triangulation of bending angles, electromyography (EMG), and grip strength. User satisfaction was measured using a survey. EMG sensors were attached to the flexor digitorum superficialis and extensor digitorum communis to capture movement data for grasping and releasing, lifting and putting down, and opening and closing an object with (a) gloves and an actuator, (b) gloves and no actuator, and (c) no gloves. The actuator-equipped glove weighed 31.4 g—lighter than in any earlier studies. In situation (a), the average EMG values for the four participants decreased, ranging from −2.06% to −44.1%, confirming the superior performance of the gloves. Survey results revealed high levels of user satisfaction. Our study offers insights into the development of rehabilitation robotic gloves that assist muscle movements and are easy to wear.

Woven Fabric Muscle for Soft Wearable Robotic Application Using Two-Dimensional Zigzag Shape Memory Alloy Actuator.

In this study, we propose a fabric muscle based on the Zigzag Shape Memory Alloy (ZSMA) actuator. Soft wearable robots have been gaining attention due to their flexibility and the ability to provide significant power support to the user without hindering their movement and mobility. There has been an increasing focus on the research and development of fabric muscles, which are crucial components of these robots. This article introduces a high-performance fabric muscle utilizing zigzag-shaped shape memory alloy (SMA), ZSMA, a new form of SMA actuator. Through modeling and experimentation of the ZSMA actuator, we identified an optimized actuator design and detailed the fabric muscle fabrication process. The proposed fabric actuator, weighing only 7.5 g, demonstrated the impressive capability to lift a weight of 2 kg with a contraction displacement of 40%. This significant achievement paves the way for future research possibilities in soft wearable robotics.

Shape Programmable and Multifunctional Soft Textile Muscles for Wearable and Soft Robotics

Textiles are promising candidates for use in soft robots and wearable devices due to their inherent compliance, high versatility, and skin comfort. Planar fluidic textile‐based actuators exhibit low profile and high conformability, and can seamlessly integrate additional components (e.g., soft sensors or variable stiffness structures [VSSs]) to create advanced, multifunctional smart textile actuators. In this article, a new class of programmable, fluidic soft textile muscles (STMs) that incorporate multilayered silicone sheets with embedded fluidic channels is introduced. The STMs are scalable and fabricated by apparel engineering techniques, offering a fabrication approach able to create large‐scaled multilayered structures that can be challenging for current microfluidic bonding methods. They are also highly automation compatible due to no manual insertion of elastic tubes/bladders into textile structures. Liquid metal is employed for creating fluidic channels. It is not only used for actuation but also used as channels for additional features such as soft piezoresistive sensors with enhanced sensitivity to STMs’ pressure‐induced elongation, or VSSs of either low‐melting‐point alloys or a new thermo‐responsive epoxy with low viscosity and transition temperature. The STMs hold promising prospects for soft robotic and wearable applications, which is demonstrated by an example of a textile‐based wearable 3D skin‐stretch haptic interface.

Design and Characterization of Soft Fabric Omnidirectional Bending Actuators

Soft robots, inspired by biological adaptability, can excel where rigid robots may falter and offer flexibility and safety for complex, unpredictable environments. In this paper, we present the Omnidirectional Bending Actuator (OBA), a soft robotic actuation module which is fabricated from off-the-shelf materials with easy scalability and consists of three pneumatic chambers. Distinguished by its streamlined manufacturing process, the OBA is capable of bending in all directions with a high force-to-weight ratio, potentially addressing a notable research gap in knit fabric actuators with multi-degree-of-freedom capabilities. We will present the design and fabrication of the OBA, examine its motion and force capabilities, and demonstrate its capability for stiffness modulation and its ability to maintain set configurations under loads. The mass of the entire actuation module is 278 g, with a range of omnidirectional bending up to 90.80°, a maximum tolerable pressure of 862 kPa, and a bending payload (block force) of 10.99 N, resulting in a force-to-weight ratio of 39.53 N/kg. The OBA’s cost-effective and simple fabrication, compact and lightweight structure, and capability to withstand high pressures present it as an attractive actuation primitive for applications demanding efficient and versatile soft robotic solutions.

Perception Threshold for Pressure by a Soft Textile Actuator.

Electroactive textile (EAT) has the potential to apply pressure stimuli to the skin, e.g. in the form of a squeeze on the arm. To present a perceivable haptic sensation we need to know the perception threshold for such stimuli. We designed a set-up based on motorized ribbons around the arm with five different widths (range 3 - 49 mm) for psychophysical studies. We investigated the perception threshold of force pressure and ribbon reduction in two studies, using two methods (PSI and 1up/3down staircase), comparing sex, the left and right arm, the lower and upper arm, and stimulated surface area with a total of 57 participants. We found that larger stimulation surfaces require less pressure to reach the perception threshold (0.151 N per cm 2 for 3 mm width, 0.00972 N per cm 2 for 49 mm width on the lower arm). This indicates a spatial summation effect for these pressure stimuli. We did not find significant differences in perception threshold for the left and right arm and, the upper and lower arm. Between male and female participants we found significant differences for two conditions (10 mm and 25 mm) in Experiment 1, but we could not reproduce this in Experiment 2.

Electropolymerization of a Conjugated Polymer on Top of a Different Conjugated Polymer for Yarn Actuators

Electropolymerization of conjugated polymers is usually performed on highly conductive metallic electrodes. However, for applications such as textile actuators this is not possible. There, the electropolymerization is performed on a different, previously deposited conjugated polymer. This resulted on some new electrochemical phenomena not present when the electropolymerization is done on a metallic substrate. Processes as the oxidation and overoxidation of the underlying conjugated polymer need to be taken into account. In this work we have investigated the best conditions for electropolymerization of polypyrrole on top of poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) coated textile yarns, when the electropolymerization was performed by either cyclic voltammetry, chronoamperometry or chronopotentiometry in order to achieve the best electroactive and actuating conjugated polymer.

Textile Actuators Comprising Reduced Graphene Oxide as the Current Collector

AbstractElectronic textiles (E‐textiles) are made using various materials including carbon nanotubes, graphene, and graphene oxide. Among the materials here, e‐textiles are fabricated with reduced graphene oxide (rGO) coating on commercial textiles. rGO‐based yarns are prepared for e‐textiles by a simple dip coating method with subsequent non‐toxic reduction. To enhance the conductivity, the rGO yarns are coated with poly(3,4‐ethylene dioxythiophene): poly(styrenesulfonic acid) (PEDOT) followed by electrochemical polymerization of polypyrrole (PPy) as the electromechanically active layer, resulting in textile actuators. The rGO‐based yarn actuators are characterized in terms of both isotonic displacement and isometric developed forces, as well as electron microscopy and resistance measurements. Furthermore, it is demonstrated that both viscose rotor spun (VR) and viscose multifilament (VM) yarns can be used for yarn actuators. The resulting VM‐based yarn actuators exhibit high strain (0.58%) in NaDBS electrolytes. These conducting yarns can also be integrated into textiles and fabrics of various forms to create smart e‐textiles and wearable devices.

Systematic Evaluation of Research Progress in the Textile Field over the Past 10 Years: Bibliometric Study on Smart Textiles and Clothing

Intelligent textile clothing is one of the most popular topics in the field. In recent decades, rapid advances have been made in the area of intelligent textile clothing research, and the intellectual structure pertaining to this domain has significantly evolved. We used CiteSpace 6.2.R4, VOSviewer 1.6.19, to evaluate and visualize the results, analyzing articles, countries, regions, institutions, authors, journals, citations, and keywords. Both a macroscopic sketch and a microscopic characterization of the entire knowledge domain were realized. The aim of this paper is to utilize bibliometric and knowledge mapping theories to identify relevant research papers on the subject of smart textiles and clothing that have been published by the China Knowledge Network Web of Science (WOS) within the last decade. It is concluded that the main topics of smart textile and garment research can be divided into nine categories: wearable electronics, smart textiles, flexible antennas, energy storage, textile actuators, mechanical properties, asymmetric supercapacitors, carbon nanotubes, and fiber extrusion. In addition to the latter analysis, emerging trends and future research foci were predicted. This review will help scientists discern the dynamic evolution of intelligent textile clothing research as well as highlight areas for future research.

Reconstructed Hierarchically-Structured Keratin Fibers with Shape-Memory Features Based on Reversible Secondary Structure Transformation.

Biocompatible and biodegradable shape-memory polymers have gained popularity as smart materials, offering a wide range of applications and environmental benefits. Herein, we investigate the possibility of fabricating regenerated water-triggered shape-memory keratin fibers from wool and cellulose in a more effective and environmentally friendly manner. The regenerated keratin fibers exhibit comparable shape-memory performance to other hydration-responsive materials, with a shape fixity ratio of 94.8 ± 2.15% and a shape recovery rate of 81.4 ± 3.84%. Owing to their well-preserved secondary structure and crosslinking network, keratin fibers exhibit outstanding water-stability and wet stretchability, with a maximum tensile strain of 362 ± 15.9%. In this system, we investigate the reconfiguration of the protein secondary structure between α-helix and β-sheet as the fundamental actuation mechanism in response to hydration. This responsiveness is studied under force loading and unloading along the fiber axis. Hydrogen bonds act as the "switches" clicked by water molecules to trigger the shape-memory effect, while disulfide bonds and cellulose nanocrystals play the role of "net-points" to maintain the permanent shape of the material. Water-triggered shape-memory keratin fibers are manipulable and exhibit potential in the fabrication of textile actuators, which may be applied in smart apparel and programmable biomedical devices. This article is protected by copyright. All rights reserved.

Recovery system-based textile actuators

This paper presents a medical recovery system based on electrical stimuli transmitted through textile electrodes based on copper microparticles. The textile electrodes are connected to an electronic device capable of generating transcutaneous electrical nerve stimulation (TENS) using low-frequency (0–100 Hz) (diadynamic or interference) electrical currents. To evaluate the system, the current intensity, frequency and supply voltage were measured using different multimeters (Agilent Technologies U3606A and portable digital multimeter), and the signal was analysed. Depending on the intensity of the transcutaneous electrostimulation program, obtained by varying the electrical parameters, such as electrical voltage (U, mV), current intensity (I, mA) and frequency (f, Hz), it is possible that the patient feels pinches or vibration.

Design and Evaluation of Smart Textile Actuator with Chain Structure.

Textiles composed of fibers can have their mechanical properties adjusted by changing the arrangement of the fibers, such as strength and flexibility. Particularly, in the case of smart textiles incorporating active materials, various deformations could be created based on fiber patterns that determine the directivity of active materials. In this study, we design a smart fiber-based textile actuator with a chain structure and evaluate its actuation characteristics. Smart fiber composed of shape memory alloy (SMA) generates deformation when the electric current is applied, causing the phase transformation of SMA. We fabricated the smart chain column and evaluated its actuating mechanism based on the size of the chain and the number of rows. In addition, a crochet textile actuator was designed using interlooping smart chains and developed into a soft gripper that can grab objects. With experimental verifications, this study provides an investigation of the relationship between the chain actuator's deformation, actuating force, actuator temperature, and strain. The results of this study are expected to be relevant to textile applications, wearable devices, and other technical fields that require coordination with the human body. Additionally, it is expected that it can be utilized to configure a system capable of flexible operation by combining rigid elements such as batteries and sensors with textiles.

Effect of Core Yarn on Linear Actuation of Electroactive Polymer Coated Yarn Actuators

AbstractSmart textiles combine the features of conventional textiles with promising properties of smart materials such as electromechanically active polymers, resulting in textile actuators. Textile actuators comprise of individual yarn actuators, so understanding their electro‐chemo‐mechanical behavior is of great importance. Herein, this study investigates the effect of inherent structural and mechanical properties of commercial yarns, that form the core of the yarn actuators, on the linear actuation of the conducting‐polymer‐based yarn actuators. Commercial yarns were coated with poly(3,4‐ethylenedioxythiophene)‐poly(styrenesulfonate) (PEDOT:PSS) to make them conductive. Then polypyrrole (PPy) that provides the electromechanical actuation is electropolymerized on the yarn surface under controlled conditions. The linear actuation of the yarn actuators is investigated in aqueous electrolyte under isotonic and isometric conditions. The yarn actuators generated an isotonic strain up to 0.99% and isometric force of 95 mN. The isometric strain achieved in this work is more than tenfold and threefold greater than the previously reported yarn actuators. The isometric actuation force shows an increase of nearly 11‐fold over our previous results. Finally, a qualitative mechanical model is introduced to describe the actuation behavior of yarn actuators. The strain and force created by the yarn actuators make them promising candidates for wearable actuator technologies.

Electrochemical Considerations for the Electropolymerization of PPy on PEDOT:PSS for Yarn Actuator Applications

AbstractElectrochemical devices as conducting polymer‐based actuators or textile actuators often use layers of different conducting polymers. Although research has been performed on such devices, it is still not very clear how the different layers affect each other. Here we attempt to clarify such influence on yarn actuators using electrochemical methods. Different electrochemical methods as cyclic voltammetry, chronoamperometry or chronopotentiometry were used to electropolymerize polypyrrole on top of a poly(3,4‐ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) coated textile yarns by using different applied electrochemical conditions (potentials/currents). Thus, we found that selecting suitable conditions (as an applied potential of +0.8 V) for such electropolymerization is key to obtain a polypyrrole of high quality. Besides, we show that the underlying layer of PEDOT:PSS has an influence on such electropolymerization conditions and can be subjected to parallel redox reactions as oxidation or electrochemical degradation that influence the electropolymerized polypyrrole.

High-Performance Fasciated Yarn Artificial Muscles Prepared by Hierarchical Structuring and Sheath–Core Coupling for Versatile Textile Actuators

High-Performance Fasciated Yarn Artificial Muscles Prepared by Hierarchical Structuring and Sheath–Core Coupling for Versatile Textile Actuators

Improved heating method for shape-memory alloy using carbon nanotube and silver paste

Shape memory alloys (SMAs) have a special ability to remember their initial shape and return from operating temperature. For this special ability, there are many studies in the field of smart wearables to replace rigid, heavy, and large electric actuators with SMAs that can be a fabrication. The usual operating method of the SMA is heating the SMA by direct Joule heating with electricity. Although direct Joule heating is fast and easy, there is overshooting, unstable, and high-power consumption. For these issues to use the SMA as textile actuators, this research suggested a heating method with silver paste required lower power consumption and coating the basic fabric with carbon nanotubes (CNTs) to support heating stability and heat uniformity. The heating method evaluated the efficiency of heat by comparing direct heating and silver layer heating and the uniformity of heat with the infrared images of whether CNTs coated or not. In this research, we reached higher temperatures with lower power than direct Joule heating using wearable heaters manufactured using silver paste. In addition, we confirmed that coating the basic fabric with carbon nanotubes reduce the temperature imbalance, and improved the heating stability. This research is expected that SMA will be used as a wearable actuator to help develop wearable devices that can move.

Soft and lightweight fabric enables powerful and high-range pneumatic actuation.

Soft structures and actuation allow robots, conventionally consisting of rigid components, to perform more compliant, adaptive interactions similar to living creatures. Although numerous functions of these types of actuators have been demonstrated in the literature, their hyperelastic designs generally suffer from limited workspaces and load-carrying capabilities primarily due to their structural stretchability factor. Here, we describe a series of pneumatic actuators based on soft but less stretchable fabric that can simultaneously perform tunable workspace and bear a high payload. The motion mode of the actuator is programmable, combinable, and predictable and is informed by rapid response to low input pressure. A robotic gripper using three fabric actuators is also presented. The gripper demonstrates a grasping force of over 150 N and a grasping range from 70 to 350millimeters. The design concept and comprehensive guidelines presented would provide design and analysis foundations for applying less stretchable yet soft materials in soft robots to further enhance their practicality.

Exploiting a Simple Asymmetric Pleating Method to Realize a Textile Based Bending Actuator

This work presents the design, modeling and control of an asymmetrically pleated textile actuator (APTA). The presented actuator utilizes a simple inflatable beam which is constrained asymmetrically using a pleat that is fixed only to a single side. Due to the difference in length between the constrained side and the unconstrained side, a bend at the pleat is generated upon inflation. This method utilizes sewing and/or heat sealing to create bending, making it easy to manufacture compared to many soft actuators and further allows for the creation of complex 3D structures in conjunction with methods presented in literature due to the in-plane bending generated by the presented pleating method. The design, fabrication and modeling of the APTA are presented and the actuator characterization in the form of bending angle, quasi-static torque and hysteresis tests are performed. A maximum normalized output torque of 400 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\text{Nm/kPa.m}^{3}$</tex-math></inline-formula> was demonstrated by the presented APTA. An empirical model for the APTA using the collected data was derived to predict torque output throughout the actuator range of motion. A controller using the empirical model was designed to track desired torque profiles. Single and Multiple step response experiments were conducted to evaluate the efficacy of the controller for burst-like actuation which could have implications in physical assistance for biological systems and in shape forming deployable structures. Further, we present several potential applications to this actuator in the form of 3D inflatable structures, a continuum module segment, and a wearable elbow device.