In recent years, more and more research has begun to focus on the flexible and lightweight design of wearable robots. During this process, many novel concepts and achievements have been continuously made and shown to the public, while new problems have emerged at the same time, which need to be solved. In this paper, we give an overview of the development status of soft wearable robots for human movement assistance. On the basis of a clear definition, we perform a system classification according to the target assisted joint and attempt to describe the overall prototype design level in related fields. Additionally, it is necessary to sort out the latest research progress of key technologies such as structure, actuation, control and evaluation, thereby analyzing the design ideas and basic characteristics of them. Finally, we discuss the possible application fields, and propose the main challenges of this valuable research direction.

Exoskeletons can track the wearer’s movements in real time, thereby enhancing physical performance or restoring mobility for individuals with gait impairments. These wearable assistive devices have demonstrated significant potential in both rehabilitation and industrial applications. This review focuses on the major advancements in exoskeleton technology published since 2020, with particular emphasis on the development of structural designs for lower-limb exoskeletons employed in locomotion assistance. We employed a systematic literature review methodology, categorizing the included studies into three main types: rigid exoskeleton, soft exoskeleton, and tethered platform. The current development status of robotic exoskeletons is analyzed based on publication year, system weight, target assistive joints, and main effects. Furthermore, we examine the factors driving these advancements and their implications for the field. The key challenges and opportunities that may influence the future development of exoskeleton technologies are also highlighted in this review.

Human intention recognition belongs to the algorithm basis for exoskeleton robots to generate synergic movements and provide corresponding assistance. In this article, we acquire and analyze the mechanomyography (MMG) to estimate the current joint torque and apply this method to the rehabilitation training research of the upper extremity exosuit. In order to obtain relatively pure biological signals, a MMG processing method based on the Hilbert-Huang Transform (HHT) is proposed to eliminate the mixed noise and motion artifacts. After extracting features and forming the dataset, a random forest regression (RFR) model is designed to build the mapping relationship between MMG and human joint output through offline learning. In addition, an upper extremity exosuit is constructed for multi-joint assistance. Based on the above research, we develop a torque estimation-based control strategy and make it responsible for the intention understanding and motion servo of this customized system. Finally, an actual test verifies the accuracy and reliability of this recognition algorithm, and an efficiency evaluation experiment also proves the feasibility for power assistance.

Wearable assistive devices (WADs) show potential for future applications in industrial and medical fields. However, wearing discomfort, caused by factors such as additional weight penalties, inappropriate straps, and joint misalignment, may disrupt the natural balance of human motion, leading to increased metabolic expenditure, muscle fatigue, and even physical injury. These challenges severely restrict the practical application of WADs. To address these challenges, we have developed a reactionless, lightweight WAD that utilizes a single device attached to the shoe, eliminating the need for additional rigid links or straps on the shank or thigh. This design provides assistive torque directly to the target limbs during human locomotion. The proposed device weighs 0.67 kg and can provide an assistive torque of 12 N·m and mechanical power of 10 W. Furthermore, we introduced a human-in-the-loop multiobjective optimization approach considering the assistance effectiveness, power consumption, system size, service safety, and actuator constraints to achieve relative optimality in performance of the proposed device. Cardiopulmonary exercise test and surface electromyography test results from seven participants indicated that the device can reduce the average gross metabolic rate by 12.62%, and the muscle activation of the rectus femoris and soleus by 35.12% and 4.10%, respectively.

In the field of rehabilitation engineering, wearable robots for upper limbs tend to help powerless arms of patients smoothly complete daily activities. Compared with traditional rigid exoskeleton, soft exosuit takes the advantage of high movement flexibility and relatively compact structure so that it could be a more adaptive and compliant alternative for the elder and the disabled. In this study, a novel dual-arm exosuit is proposed to provide active assistance for multiple joints through bidirectional cable-driven modules. Several Bowden cables achieve power transmission from actuators mounted on the back to shoulders and elbows. The actuator is designed with reference to the principle of differential mechanism, in order to automatically preload both cables wrapped around it, generate assistive torque in two opposite rotation directions of a joint, and keep the human-robot interaction as safe as possible. This study adopts the constant torque control to assist in the pre-tightening process, and develop a model-based control strategy for bidirectional joint motion enhancement according to mathematical models of the human-robot system. The experimental results demonstrate that the prototype can impose pretension on each cable, and offer enough support on the joint according to the wearers’ demands.

Cable-driven exosuits have the advantages of being lightweight, compact, and well-adapted due to avoiding extensive usage of rigid structures to transmit power. However, applying too many flexible materials into the system will cause some problems such as insufficient stiffness, easy deformation, and non-negligible friction, thus increasing the difficulty of synergistic control between the human and cable-driven exosuit. In this letter, we attempt to control the exosuit effectively and reliably to provide assistance for the elbow, by analyzing the force and position relationship of connecting parts between the power source and the joint. The fundamental laws of Tendon-Sheath Mechanism (TSM) are deeply analyzed, which has obtained the corresponding mathematical description of force transmission and cable elongation. A spring-damping model is introduced between the tendon end and forearm to describe the character of textile-based interface, whose parameters could be identified by the least square method with the forgetting factor. Then, these theoretical analyses are incorporated into the human-in-the-loop modeling that can achieve appropriate motion generation from the desired joint torque to the actuator output. In the experiments, we have evaluated the output performance of the fabricated prototype and its efficacy on muscle activity based on the identification of spring coefficient and damping coefficient. The results demonstrate that the exosuit is able to respond appropriately to the changes of elbow position while realizing accurate tracking of the torque profile (the RMSE is 0.092 ± 0.011 Nm). In addition, it can effectively reduce the magnitude of muscle activation (29.52% reduction in biceps activation), thereby alleviating physical fatigue.