Wearable Soft Robotics Research Articles

Evaluation of Gait-Assistive Soft Wearable Robot Designs for Wear Comfort, Focusing on Electroencephalogram and Satisfaction

Evaluation of Gait-Assistive Soft Wearable Robot Designs for Wear Comfort, Focusing on Electroencephalogram and Satisfaction

Soft Upper‐Limb Wearable Robotic Devices: Technology and Applications

One of the practical applications in the field of soft robotics involves the development of soft robotic wearable devices. These devices make use of their intrinsically compliant structures to interact safely and harmoniously with the human body. While soft wearable robots demonstrate their utility in lower‐limb applications for locomotion, the upper‐limb domain offers significant prospects in a wide range of applications that soft robotic technology can address. In this review, the current state of technology in the field of soft wearable upper limbs is systematically analyzed and categorized. Categorizations are made based on their applications in rehabilitation, activities of daily living support, and human augmentation. Furthermore, in this study, also contemporary technological aspects, encompassing sensing technology and control systems, are explored. Despite exciting potential in this domain, several limitations from existing devices inherently impede widespread adoption and thus hinder further progress in the field. In this study, also an overview of the different facets of the domain is provided and key considerations for the advancement of soft wearable robotic devices intended for upper‐limb applications are prescribed.

Advancements in Soft Wearable Robots: A Systematic Review of Actuation Mechanisms and Physical Interfaces

Advancements in Soft Wearable Robots: A Systematic Review of Actuation Mechanisms and Physical Interfaces

A portable inflatable soft wearable robot to assist the shoulder during industrial work.

Repetitive overhead tasks during factory work can cause shoulder injuries resulting in impaired health and productivity loss. Soft wearable upper extremity robots have the potential to be effective injury prevention tools with minimal restrictions using soft materials and active controls. We present the design and evaluation of a portable inflatable shoulder wearable robot for assisting industrial workers during shoulder-elevated tasks. The robot is worn like a shirt with integrated textile pneumatic actuators, inertial measurement units, and a portable actuation unit. It can provide up to 6.6 newton-meters of torque to support the shoulder and cycle assistance on and off at six times per minute. From human participant evaluations during simulated industrial tasks, the robot reduced agonist muscle activities (anterior, middle, and posterior deltoids and biceps brachii) by up to 40% with slight changes in joint angles of less than 7% range of motion while not increasing antagonistic muscle activity (latissimus dorsi) in current sample size. Comparison of controller parameters further highlighted that higher assistance magnitude and earlier assistance timing resulted in statistically significant muscle activity reductions. During a task circuit with dynamic transitions among the tasks, the kinematics-based controller of the robot showed robustness to misinflations (96% true negative rate and 91% true positive rate), indicating minimal disturbances to the user when assistance was not required. A preliminary evaluation of a pressure modulation profile also highlighted a trade-off between user perception and hardware demands. Finally, five automotive factory workers used the robot in a pilot manufacturing area and provided feedback.

Paediatric ankle rehabilitation system based on twisted and coiled polymer actuators

Rehabilitation is crucial for children with physical disabilities arising from various conditions. Traditional exoskeletons, reliant on electric motors and rigid components, making them cumbersome, heavy, and unsuitable for use outside clinical facilities. To overcome these, researchers are turning to soft wearable rehabilitation robots (SWRRs) with artificial muscles based on smart materials like twisted and coiled polymer actuators (TCPs). TCPs offer enhanced compliance, adaptability, comfort, safety, and reduced weight—critical for paediatric use. Despite facing challenges like low operating frequencies and high temperatures, TCPs are explored as potential artificial muscles for SWRRs, due to their advantages on the force they can generate, the strain and a linear behaviour. This study details a proof of concept for a paediatric rehabilitation system for ankles based on TCPs, including the actuator characterization, mechanical design, control strategy, and human-computer-interface (HCI). The resulting device achieved a 1.4 Nm torque, a 10° range of motion in dorsiflexion within 5 s, and integrated electromyographic HCI. This research marks a promising step towards innovative, soft wearable rehabilitation solutions for children with physical disabilities.

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.

Enhancing wearability: designing wearable suit platforms for industrial workers

PurposeThe objective of this study was to develop wearable suit platforms with various anchoring structure designs with the intention of improving wearability and enhancing user satisfaction.Design/methodology/approachThis study selected fabrics and materials for the suit platform through material performance tests. Two anchoring structure designs, 11-type and X-type are compared with regular clothing under control conditions. To evaluate the comfort level of the wearable suit platform, a satisfaction survey and electroencephalogram (EEG) measurements are conducted to triangulate the findings.FindingsThe 11-type exhibited higher values in comfort indicators such as α, θ, α/High-β and lower values in concentration or stress indicators such as β, ϒ, sensorimotor rhythm (SMR)+Mid-β/θ, and a spectral edge frequency of 95% compared to the X-type while walking. The 11-type offers greater comfort and satisfaction compared to the X-type when lifting based on the EEG measurements and the participants survey.Originality/valueIt is recommended to implement the 11-type when designing wearable suit platforms. These findings offer essential data on wearability, which can guide the development of soft wearable robots.

Muscle-inspired stiffness-tunable flexible fiber jamming structure for wearable robots *

Soft robotics have found their tremendous application prospects in wearable robots due to the inherent compliance of soft materials when interacting with human bodies. However, the limited load-bearing and output capabilities impeded their application in real world. Variable stiffness design contributes to tackling this problem by enhancing the overall structural rigidity. Nevertheless, most of current jamming-based variable stiffness structures realize their stiffness enhancement by squeezing discrete rigid elements, resulting in the loss of structural compliance in the high stiffness state, which could significantly reduce the deformability and even injure the individuals when utilized in wearable robots. In this paper, we propose a muscle-inspired stiffness-continuously-adjustable flexible fiber jamming (FFJ) structure for soft wearable robots. The FFJ structure can achieve continuous stiffness-variation by controlling the fiber overlapping length, which maintains stretchability even in the high stiffness state. We provide a theoretical model to analyze the mechanical performance of the proposed FFJ structure with different design parameters, and verify the model experimentally. The preliminary results show that we achieved 9 times of stiffness enhancement of the proposed FFJ structure by controlling the vacuum pressure, and the maximum tensile stiffness is 4.1 N mm−1. We further demonstrated the effectiveness of the proposed FFJ structure on wearable robots in three different working scenarios: active finger rehabilitation, active elbow rehabilitation, and passive trunk support. The results show that the FFJ structure was able to provide controllable impedance force for active finger/elbow rehabilitation, and help support the human body during long-term labor. This work broadens the frontiers of soft wearable robots and leads a way to the future design of soft and strong robots and devices.

Design and fabrication of a soft wearable robot using a novel pleated fabric pneumatic artificial muscle (pfPAM) to assist walking

Defects in walking can substantially impact individuals' quality of life. Utilizing wearable robots is one of the known methods to improve this daily activity for individuals with disabilities or limited mobility. In recent years, one of the challenges confronting researchers has been improving these devices' comfort and efficacy. This research aims to provide a lower-limb exosuit that aids in walking while being more comfortable and efficient than previous models in some certain respects. One factor that reduces the usability of these active wearables is the heavy and rigid structure of the force interaction mechanism and their inflexible actuators. This study's wearable robot benefits from a new Pneumatic Artificial Muscle (PAM) and a skeletal-free force mechanism, which, due to their innovative design and garment-like structure, when combined with a sensor network, weigh only 536 g. Also, the compressed air system is designed so that the user can quickly wear or remove it. The developed exosuit considerably improves the wearer's walking ability while remaining lightweight and comfortable. This claim has been checked and validated through numerous tests. The final results reveal that the user's posterior thigh muscles had an activity reduction of 7.4% in each complete gate cycle and 22.7% at peak time when using the exosuit compared with walking without the exosuit. Additionally, compared with the state where the exosuit was worn but inactive, the reduction was 16.2% overall and 63.9% at peak time. The motion cycle analysis also indicated that the system caused the user to take longer and more frequent steps than when walking without the exosuit. One of the reasons that has caused the performance of wearable robots to drop significantly as they become softer is the weakness of their actuators. In pursuit of this study's primary objective, a functional PAM was devised, which may have some of the most suitable features for such wearable robots. A contraction of up to 40%, a force-to-weight ratio of one thousand (with a weight of 44 g), a fabric-based structure for use alongside the body, low-cost production, contractibility at low pressures, and high controllability compared to its peer actuators are some of the soft contractile actuator features developed in this research.

3D-printed passive bellow actuator for portable soft wearable robots

The compliance of soft wearable robots driven by fluids is high, but their portability and controllability are limited due to complex fluidic systems. On the other hand, tendon-driven soft wearable robots are compact and easy to control, but they have lower compliance when actively interacting with unknown environments. To address this trade-off between compliance and controllability, we propose a novel actuator design for soft wearable robots, named the passive bellow actuator (PBA). The PBA is 3D-printed using elastic materials, which enables it to be easily customized into various shapes and sizes. When tendons running through the PBA are pulled, it contracts and preserves elastic potential energy. When the tendons are released, the PBA extends like a spring and exerts the stored elastic energy to drive the human body. Additionally, programmable deformation can be easily achieved by adjusting the thickness of the PBA chamber. By utilizing these effects, the PBA can be used to assist human flexion and extension movements. We developed a portable soft robotic glove to demonstrate the feasibility of the PBA. The glove is light weight, power safe, and is inherently compliant when grasping irregular objects. Theoretical modeling and experimental tests were conducted to characterize the PBA, and experimental tests were conducted to demonstrate the performance of the soft robotic gloves.

A soft wearable exoglove for rehabilitation assistance: a novel application of knitted shape-memory alloy as a flexible actuator

We developed the knitted shape-memory alloy (SMA) as a flexible actuator and applied it to a soft wearable exoglove for rehabilitation assistance. Based on user needs and anthropometric data, we custom-designed the exoglove for three hemiplegic patients using the knitted-SMA actuator and evaluated its bending performance, gripping force and wearability under the four simulation conditions (S1–S4). To address the specific needs, both SMA plain- and double-knit modules were applied to the exoglove based on the patients’ finger joint range of motion (ROMs). The joint ROMs of all fingers increased by 13.71% and the skin temperature increased by 2.21 °C after actuating the glove (p = 0.006). The gripping force increased as much as 55.01%, when compared to the baseline. All patients were able to don and doff the developed glove independently, and positively evaluated their subjective satisfaction and thermal perception. The findings suggested the potential of the knitted SMA for the future development of soft wearable robots.

Review: Application of 3D Printing Technology in Soft Robots.

Soft robots, inspired by living organisms in nature, are primarily made of soft materials, and can be used to perform delicate tasks due to their high flexibility, such as grasping and locomotion. However, it is a challenge to efficiently manufacture soft robots with complex functions. In recent years, 3D printing technology has greatly improved the efficiency and flexibility of manufacturing soft robots. Unlike traditional subtractive manufacturing technologies, 3D printing, as an additive manufacturing method, can directly produce parts of high quality and complex geometry for soft robots without manual errors or costly post-processing. In this review, we investigate the basic concepts and working principles of current 3D printing technologies, including stereolithography, selective laser sintering, material extrusion, and material jetting. The advantages and disadvantages of fabricating soft robots are discussed. Various 3D printing materials for soft robots are introduced, including elastomers, shape memory polymers, hydrogels, composites, and other materials. Their functions and limitations in soft robots are illustrated. The existing 3D-printed soft robots, including soft grippers, soft locomotion robots, and wearable soft robots, are demonstrated. Their application in industrial, manufacturing, service, and assistive medical fields is discussed. We summarize the challenges of 3D printing at the technical level, material level, and application level. The prospects of 3D printing technology in the field of soft robots are explored.

Soft Artificial Muscle Based on Pre-Detwinned Shape Memory Alloy Spring Actuator Achieving High Passive Assistive Torque for Wearable Robot.

For designing the assistive wearable rehabilitation robots, it is challenging to design the robot as energy efficient because the actuators have to be capable of overcoming human loads such as gravity of the body and spastic torque continuously during the assistance. To address these challenges, we propose a novel design of soft artificial muscle that utilizes shape memory alloy (SMA) spring actuators with pre-detwinning process. The SMA spring was fabricated through a process called pre-detwinning, which enhances the linearity of the SMA spring in martensite phase and unpowered restoring force, which is called passive force. The fabricated SMA spring can contract >60%. Finally, the soft wearable robot that can assist not only the gravitational torque exerted on the elbow by passive force, but also the elbow movements with active force was designed with a soft artificial muscle. A soft artificial muscle consists of the bundles of pre-detwinned SMA springs integrated with the stretchable coolant vessel. The stiffness of the muscle was measured as 1125 N/m in martensite phase and 1732 N/m in austenite phase. In addition, the muscle showed great actuation frequency performances, the bandwidth of which was measured as 0.5 Hz. The proposed wearable mechanism can fully compensate the gravitational torque for all the angles in passive mode. In addition, the proposed mechanism can produce high torque up to 3.5 Nm and movements in active mode.

Multiparameter Remote Contact Force Sensor With Embedded Bend Sensing for Tendon-Driven Hand Robots

Integrating multiple sensors without increasing the structural complexity and their original form factor is a major concern in robotic applications, particularly in tendon-driven systems. This study proposes a multiparameter contact force sensor with bend sensing by utilizing an improved Bowden cable design. The proposed sensor consists of an end tip with an elastomer membrane, a Bowden cable consisting of a sheath and dual inner wires, and a remotely separated sensing component. The electrical wirings are decoupled from the mechanical Bowden cable system. The displacement difference between the force-sensing and bend-sensing wires is transmitted through the sheath, indicating the contact force on the end tip. The modeling and experiments verify that the contact force applied on the end tip is linearly related to the sensor output signal and is reliable after repeated measurements. The proposed sensor, utilizing the flexible Bowden cable as its sensing modality, can be integrated into a diverse range of tendon-driven robotic applications. These applications include a robotic hand with tactile and angle sensing capabilities, as well as a soft wearable robot for the hand (Exo-glove Poly II). The compact form factor of the proposed sensor enables geometric sensing without increasing structural complexity for multiparameter sensing in robotic applications.

Evaluation and modeling of diaphragm displacement using ultrasound imaging for wearable respiratory assistive robot.

Assessing the influence of respiratory assistive devices on the diaphragm mobility is essential for advancing patient care and improving treatment outcomes. Existing respiratory assistive robots have not yet effectively assessed their impact on diaphragm mobility. In this study, we introduce for the first time a non-invasive, real-time clinically feasible ultrasound method to evaluate the impact of soft wearable robots on diaphragm displacement. We measured and compared diaphragm displacement and lung volume in eight participants during both spontaneous and robotic-assisted respiration. Building on these measurements, we proposed a human-robot coupled two-compartment respiratory mechanics model that elucidates the underlying mechanism by which our extracorporeal wearable robots augments respiration. Specifically, the soft robot applies external compression to the abdominal wall muscles, inducing their inward movement, which consequently pushes the diaphragm upward and enhances respiratory function. Finally, we investigated the level and shape of various robotic assistive forces on diaphragm motion. This robotic intervention leads to a significant increase in average diaphragm displacement by 1.95 times and in lung volume by 2.14 times compared to spontaneous respiration. Furthermore, the accuracy of the proposed respiratory mechanics model is confirmed by the experimental results, with less than 7% error in measurements of both diaphragm displacement and lung volume. Finally, the magnitude of robotic assistive forces positively correlates with diaphragm movement, while the shape of the forces shows no significant relationship with diaphragm activity. Our experimental findings validate the effective assistance mechanism of the proposed robot, which enhances diaphragm mobility and assists in ventilation through extracorporeal robotic intervention. This robotic system can assist with ventilation while increasing diaphragm mobility, potentially resolving the issue of diaphragm atrophy. Additionally, this work paves the way for improved robotic designs and personalized assistance, tailored to the dynamics of the diaphragm in respiratory rehabilitation.

Feasibility of a Wearable Soft Robot Triggered by Brain-Computer Interface for Stroke Upper Extremity Rehabilitation

Abstract Conventional robot designs have been applied as feedback stages in brain-computer interfaces (BCI) for stroke upper limb neurorehabilitation, showing promising results. Soft -robotic devices can be simpler and less expensive to manufacture, and provide ergonomic advantages over traditional designs, allowing to increase the efficacy and availableness of BCI systems for stroke neurorehabilitation. However, patients' degrees of control, neurophysiological activity, and system's usability with a BCI, using a soft robotic device as feedback, have not been assessed in stroke. For these reasons, a BCI system with a soft robotic feedback device was assessed in stroke patients. Fifty trials were acquired to setup the system, and another fifty trials were performed for evaluating patients' BCI control and cortical activity during movement intention (MI) and robotic feedback. User experience with the BCI was also assessed. Classification accuracy was in the range of 71.3% to 97.5%. Significant decrease in alpha power was observed during both motor intention and robotic feedback, but significant decrease in beta power was only observed during motor intention. BCI performance was high and in the range of reported BCI stroke interventions that used traditional robotics as feedback. Power decrease observed predominantly in alpha during soft robotic feedback was likely due to the eliciting of motor-related mechanisms. Quantification of user experience with the BCI implied that the system complexity is adequate for stroke patients. Therefore, a BCI system aimed at stroke neurorehabilitation can incorporate a soft robotic design as feedback and has potential for upper extremity interventions.

Personalized Medical Devices Connect Monitoring and Assistance: Emerging Wearable Soft Robotics.

As wearable health devices have the ability of intelligent monitoring, they are becoming cutting-edge technology in medical and health fields. However, the simplification of functions limits their further development. In addition, soft robotics with actuation functions can achieve therapeutic effects by doing external work, but their monitoring function is not sufficiently developed. The efficient integration of the two can guide future development. The functional integration of actuation and sensing can not only monitor the human body and surrounding environment but also realize actuation and assistance. Recent evidence shows that emerging wearable soft robotics can become the future of personalized medical treatment. In this Perspective, the comprehensive development in the field of actuators for simple structure soft robotics and the field of wearable application sensors are introduced, as well as their manufacturing processes and various potential medical applications. Furthermore, the challenges faced in this field are discussed, and future development directions are proposed.

In-Situ Measurement of Multi-Axis Torques Applied by Wearable Soft Robots for Shoulder Assistance

While a number of wearable soft robotic devices have been proposed to assist the shoulder, limited efforts have been made to quantify the amount of torque they apply to the body. Most work to-date has assessed soft actuator performance with simple benchtop experiments that may not be representative of the boundary conditions on the human body. We propose a new methodology to measure torques directly in-situ on the body and then use this technique to make a detailed comparison of two versions of a soft wearable shoulder assistance robot. The impact of a number of factors are considered, such as actuator design, garment anchoring, material hysteresis, arm pose, and inflation pressure. Many of these factors are not present on the benchtop and are found to significantly affect torque production. We compare results obtained on a simple benchtop test fixture with two on-body settings: an idealized mannequin and actual human subjects. The mannequin and human results were similar, but differed significantly from the benchtop, further motivating the need for on-body testing. Moving forward, we believe that the ability to directly quantify device performance in-situ will be critical to develop new design, modeling, and control strategies for wearable robots.

Design and Control of the Compact Cable-driven Series Elastic Actuator Module in Soft Wearable Robot for Ankle Assistance

Design and Control of the Compact Cable-driven Series Elastic Actuator Module in Soft Wearable Robot for Ankle Assistance

Soft Wearable Rehabilitation Robots with Artificial Muscles based on Smart Materials: A Review

Wearables robots have gained attention for the rehabilitation of people with physical disabilities. However, the current technology relies on heavy and bulky actuation components, making it hard to use outside clinical settings. Artificial muscles based on smart materials are trending for soft wearable rehabilitation robots as they present advantages of compliance, are lightweight, and do not require external components. Nevertheless, they present challenges that remain unresolved, preventing widespread adoption. This work reviews the current state of soft wearable rehabilitation robots with artificial muscles based on smart materials (AMSMs). A literature search is conducted utilizing Web of Science and Scopus. Based on the inclusion–exclusion criteria, 15 devices are found using four different smart materials. This study attempts to provide an insight into the distinct biomechanical requirements, the use of smart materials, their limitations, their designs, and possible future research directions, which can provide helpful guidance on the implementation and development of advanced soft wearable rehabilitation robots with AMSMs.