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Hip exoskeleton with different actuators. (a) Motor with gear reducer (Shimada et al., 2009; Yasuhara et al., 2009; Buesing et al., 2015; Yang et al., 2021). (b) SEA (Giovacchini et al., 2015; Kang et al., 2018; Zhang et al., 2019a). (c) Pneumatic actuator (Young et al., 2017b; Thakur et al., 2018). (d) Motor with Bowden cable (Kim et al., 2019; Tricomi et al., 2022). (e) Passive (Zhou et al., 2021a,b).
Source publication
The aging population is now a global challenge, and impaired walking ability is a common feature in the elderly. In addition, some occupations such as military and relief workers require extra physical help to perform tasks efficiently. Robotic hip exoskeletons can support ambulatory functions in the elderly and augment human performance in healthy...
Citations
... In addition, due to the absence of force/torque sensors in the exoskeleton, we used the electrical current of the motors to control and estimate the assistance torques. Even though we improved the accuracy of our estimations by conducting benchtop calibration tests with external torque sensors rather than directly relying on the torque constant of the motors, errors in the applied and measured torques remain inevitable (Yang et al., 2022). Also, no information was available about other joint angles and therefore we could not study the effect of the assistance on the full kinematics of the leg. ...
Background: Efficient gait assistance by augmentative exoskeletons depends on reliable control strategies. While numerous control methods and their effects on the metabolic cost of walking have been explored in the literature, the use of different exoskeletons and dissimilar protocols limit direct comparisons. In this article, we present and compare two controllers for hip exoskeletons with different synchronization paradigms.
Methods: The implicit-synchronization-based approach, termed the Simple Reflex Controller (SRC), determines the assistance as a function of the relative loading of the feet, resulting in an emerging torque profile continuously assisting extension during stance and flexion during swing. On the other hand, the Hip-Phase-based Torque profile controller (HPT) uses explicit synchronization and estimates the gait cycle percentage based on the hip angle, applying a predefined torque profile consisting of two shorter bursts of assistance during stance and swing. We tested the controllers with 23 naïve healthy participants walking on a treadmill at 4 km ⋅ h⁻¹, without any substantial familiarization.
Results: Both controllers significantly reduced the metabolic rate compared to walking with the exoskeleton in passive mode, by 18.0% (SRC, p < 0.001) and 11.6% (HPT, p < 0.001). However, only the SRC led to a significant reduction compared to walking without the exoskeleton (8.8%, p = 0.004). The SRC also provided more mechanical power and led to bigger changes in the hip joint kinematics and walking cadence. Our analysis of mechanical powers based on a whole-body analysis suggested a reduce in ankle push-off under this controller. There was a strong correlation (Pearson’s r = 0.778, p < 0.001) between the metabolic savings achieved by each participant with the two controllers.
Conclusion: The extended assistance duration provided by the implicitly synchronized SRC enabled greater metabolic reductions compared to the more targeted assistance of the explicitly synchronized HPT. Despite the different assistance profiles and metabolic outcomes, the correlation between the metabolic reductions with the two controllers suggests a difference in individual responsiveness to assistance, prompting more investigations to explore the person-specific factors affecting assistance receptivity.
... Wearable devices, such as exoskeleton robots and exosuits, have garnered significant attention in fields such as rehabilitation [1], augmentation [2], and elderly care [3] owing to their potential to offer timely movement guidance or torque assistance to users [4]. Recent advancements in portable walking-assist exoskeletons demonstrate considerable potential in improving the wearers' mobility, for instance, by reducing metabolic costs [5][6][7][8] or muscular activity [9,10]. ...
Exoskeleton robots hold promising prospects for rehabilitation training in individuals with weakened muscular conditions. However, achieving improved human–machine interaction and delivering customized assistance remains a challenging task. This paper introduces a muscle synergy-based human-in-the-loop (HIL) optimization framework for hip exoskeletons to offer more personalized torque assistance. Initially, we propose a muscle synergy similarity index to quantify the similarity of synergy while walking with and without the assistance of an exoskeleton. By integrating surface electromyography (sEMG) signals to calculate metrics evaluating muscle synergy and iteratively optimizing assistance parameters in real time, a muscle synergy-based HIL optimized torque configuration is presented and tested on a portable hip exoskeleton. Iterative optimization explores the optimal and suboptimal assistance torque profiles for six healthy volunteers, simultaneously testing zero torque and predefined assistance configurations, and verified the corresponding muscle synergy similarity indices through experimental testing. In our validation experiments, the assistance parameters generated through HIL optimization significantly enhance muscle synergy similarity during walking with exoskeletal assistance, with an optimal average of 0.80 ± 0.04 (mean ± std), marking a 6.3% improvement over prior assistive studies and achieving 96.4% similarity compared with free walking. This demonstrates that the proposed muscle synergy-based HIL optimization can ensure robotic exoskeleton-assisted walking as “natural” as possible.
... Today, the exoskeletons' technology progress have been studied and reviewed comprehensively [21][22][23]. Regarding powered hip robots, there are some reviews in terms of design and control [22,24]. However, we found no comprehensive review in terms of clinical gait outcomes with powered single hip joint exoskeletons (PSHJE). ...
... Today, the exoskeletons' technology progress have been studied and reviewed comprehensively [21][22][23]. Regarding powered hip robots, there are some reviews in terms of design and control [22,24]. However, we found no comprehensive review in terms of clinical gait outcomes with powered single hip joint exoskeletons (PSHJE). ...
Background
Gait disorders and as a consequence, robotic rehabilitation techniques are becoming increasingly prevalent as the population ages. In the area of rehabilitation robotics, using lightweight single hip joint exoskeletons are of significance. Considering no prior systematic review article on clinical outcomes, we aim to systematically review powered hip exoskeletons in terms of gait parameters and metabolic expenditure effects.
Methods
Three databases of PubMed, Scopus, and Web of science were searched for clinical articles comparing outcomes of gait rehabilitation using hip motorized exoskeleton with conventional methods, on patients with gait disorder or healthy individuals. Of total number of 37 reviewed articles, 14 trials were quantitatively analyzed. Analyses performed in terms of gait spatiotemporal parameters like speed (self-speed and maximum speed), step length, stride length, cadence, and oxygen consumption.
Results
Improved clinical outcomes of gait spatiotemporal parameters with hip joint exoskeletons are what our review’s findings show. In terms of gait values, meta-analysis indicates that rehabilitation with single hip joint exoskeleton enhanced parameters of maximum speed by 0.13 m/s (0.10–0.17) and step length by 0.06 m (0.05–0.07). For the remaining investigated gait parameters, no statistically significant difference was observed. Regarding metabolic parameters, oxygen consumption was lower in individuals treated with hip exoskeleton (− 1.23 ml/min/kg; range − 2.13 to − 0.32).
Conclusion
Although the analysis demonstrated improvement with just specific gait measures utilizing powered hip exoskeletons, the lack of improvement in all parameters is likely caused by the high patient condition heterogeneity among the evaluated articles. We also noted in patients who rehabilitated with the hip exoskeleton, the oxygen cost was lower. More randomized controlled trials are needed to verify both the short- and long-term clinical outcomes, including patient-reported measures.
Level of evidence
Level I (systematic review and meta-analysis).
... Wearable exoskeletons have great potential in enhancing human locomotion and walking efficiency by providing additional assistive forces required by the human body [1]. For a healthy user, portable and lightweight hip joint assistive devices are desirable and effective in reducing energy expenditure during human walking [2]. ...
Soft exosuit is widely researched to assist walking. Lacking of physical compliance in hip exosuits restricts wearing comfort of the system. This paper presents design and control of an underactuated hip exosuit with soft series elastic actuator (SSEA) that exhibits customized physical compliance. The actuation module is mounted on the backpack, and each motor is responsible for hip flexion and extension of one side. In high level control, a phase oscillator model was used for assistive force generation. In low level control, PID controllers were applied for flexion and extension forces tracking, respectively. Experimental results indicate the proposed hip exosuit can assist walking with physical compaliance and provide suitable force at the accurate timing. This work enables studies of exosuits with underactuated mechanism and actuator with physical compliance to pave the way for application of wearable robots in real-world.
... According to the action, the developments have three subcategories: passive [43], semiactive, and active [44]. The category of active exoskeletons refers to systems that employ actuators driven with additional energy, such as pneumatic and hydraulic actuators [45,46]. ...
... A fourth category of those that have presented more current developments corresponds to actuators based on muscles formed by multifilaments driven According to the action, the developments have three subcategories: passive [42], semi-active, and active [43]. The category of active exoskeletons refers to systems that employ actuators driven with additional energy, such as pneumatic and hydraulic actuators [44,45]. The semi-active exoskeletons provide energy to support the user's natural movement, allowing the recovery of the natural positions of the worker's limbs using mechanisms based on springs and the elastic recovery properties of materials. ...
... Concerning RQ1, various models, technologies, and types of exoskeletons have been identified that have been categorized by their type of assistance in exoskeletons for the knee, walking, posture, the lumbar area, and the arms [20,25,[34][35][36]. Classifications have been proposed according to the action performed by exoskeletons [39][40][41][42], structure types [43,44], and actuator technologies used to provide assistance and support to the user [45]. ...
This review aims to characterize the current landscape of exoskeletons designed to promote medical care and occupational safety in industrial settings. Extensive exploration of scientific databases spanning industries, health, and medicine informs the classification of exoskeletons according to their distinctive attributes and specific footholds on the human physique. Within the scope of this review, a comprehensive analysis is presented, contextualizing the integration of exoskeletons based on different work activities. The reviewers extracted the most relevant articles published between 2008 and 2023 from IEEE, Proquest, PubMed, Science Direct, Scopus, Web of Science, and other databases. In this review, the PRISMA-ScR checklist was used, and a Cohen's kappa coefficient of 0.642 was applied, implying moderate agreement among the reviewers; 75 primary studies were extracted from a total of 344. The future of exoskeletons in contributing to occupational health and safety will depend on continued collaboration between researchers, designers, healthcare professionals , and industries. With the continued development of technologies and an increasing understanding of how these devices interact with the human body, exoskeletons will likely remain valuable for improving working conditions and safety in various work environments.
... Wearable devices such as exoskeletons and exosuits have attracted attention in the fields of rehabilitation [1,2], augmentation [3], and elderly care [4] since these types of devices can provide correct motion or torque to users at the correct timing [5]. Recent advances in portable walking assist exoskeletons have demonstrated great potential to improve the locomotion performance of the wearers, such as reduction of metabolic cost [6][7][8][9] or muscle activity [10,11]. ...
Exoskeletons are promising devices used for walking training in patients with weak muscle strength. However, it is currently challenging to provide personalized assist profiles for better human-exoskeleton interaction. Human in-the-loop (HIL) optimization has been used by many studies to optimize assist torque by minimizing energy expenditure, but there are currently no studies on HIL optimization using muscle synergy as an evaluation index. In this paper, a muscle synergy-based HIL optimization framework is proposed for the hip exoskeleton to provide personalized torque assistance and reduce the effort of walking at the same time. Firstly, we put forward a muscle synergy similarity index to quantify the similarity of synergies during walking with and without exoskeleton assistance. In addition, by introducing sEMG signals to calculate the evaluation index of muscle synergy and iteratively optimizing the assist parameters in real time, muscle synergy-based HIL optimization of assist torque profile was proposed and tested on a portable hip exoskeleton. The optimal and sub-optimal torque profiles were explored through 35 iterations. The muscle synergy similarity index and the degree of muscle activation under 4 different assist profiles were tested by the validation experiment. The muscle synergy similarity during walking with exoskeleton assistance can be improved as much as possible by using the assist parameters generated by HIL optimizing, which reached 0.7113 in our experiment. This method can also reduce muscle activations of vastus medialis, gluteus maximus, tibialis anterior, soleus muscle, which proves that the HIL optimization based on muscle synergy proposed can reduce the effort of walking and ensure a "natural" walking as much as possible.
... Flexible exoskeletons and human-robot interactions have become one of the most challenging and hot topics in the fields of active rehabilitation and walking assistance [1], [2]. As a consequence, soft stretch sensors are receiving growing attention [3] and have become more and more popular in the application of flexible exoskeleton [4], threatening the status of inertial measurement units (IMU). Soft stretch sensors, which are used to detect displacement, can be divided into two classifications according to the transduction principles: the resistive sensors and the capacitive sensors. ...
Soft stretch sensors are increasingly used in wear-able devices and flexible exoskeleton. This paper presents a novel sensing-actuation integrated unit for elastic tension transmission and force estimation. The unit consists of a capacitive sensor, four elastic bands, which can provide enough stiffness, and two stretchable paper-cut fabric shielding layers, which can greatly shield the external interference. The mechanical and electrical properties of the unit were tested on a universal material testing machine and then a simulation test platform was designed to generate the sine curve with different travels and stretch rates. A great amount of data with a total of 35 cases were collected to train our models. Results demonstrated mean square error (MSE) less than 0.21 N 2 , normalized root mean square error (NRMSE) less than 1.7% for the selected calibration model, and MSE less than 0.28 N 2 , NRMSE less than 2.0% for the selected prediction model. Our unit together with its calibration and prediction methods in this paper holds great promise in applications such as lightweight flexible exoskeletons.
... Lower limb exoskeletons are promising solutions to enhance human locomotion performance and assist walking rehabilitation [1][2][3]. Recent advances in the newest-generation robotic exoskeletons [4][5][6][7] have demonstrated great potential to reduce metabolic expenditure [4,6,[8][9][10] and muscle activity [11,12] and concerned user preference within the control loop [13,14] as well. However, some specific issues still need to solve for better daily life human-exoskeleton interaction [15], for example, the gait phase estimation of walking-to-stop transition gaits during multimodal locomotion scenarios. ...
To be successfully used in daily life situations, exoskeletons should be effective across multimodal scenarios, including walking on various terrains, and transitions between locomotion modes such as walking-to-stop. Correct continuous gait phase estimation is essential for high-level walking assistance control. Despite the impressive advances in gait phase estimation for a variety of locomotion modes, transition gait phase estimation is rarely researched, leading to the jittering of exoskeletons during walking-to-stop transitions. We propose an optimized phase oscillator (PO-opt) that estimates the gait phase correctly during transition gaits in multimodal locomotion, which is beneficial to eliminating the jittering. In the phase plane, a lateral axis extreme difference (LAED) is adopted to classify transition gaits. The threshold of LAED for transition gaits in multimodal locomotion was preliminarily determined by simulation, which was then applied and validated in experiments. Simulation results indicated that a threshold of 15.0 was suitable for transition gaits classification during treadmill walking, free walking, and ramp ascent/descent, while results of the experiment showed that a threshold between 6.5 and 10.5 was applicable for treadmill walking, free walking, and stair ascent/descent. In particular, the jittering elimination rates for 3, 4, and 5 km/h treadmill walking were improved from 29%, 21%, and 4% (PO model) to 100%, respectively, when the threshold of LAED was set at 15.0 in PO-opt model. The results indicated a significant increase in the rate of jittering elimination when the PO-opt model was applied. The model holds great promise in real-world applications for prostheses and other types of exoskeletons.
... However, this review's scope could be extended to include a deeper understanding of human-robot coordination control at different levels incorporating recent impedance/admittance and servo control schemes. In another recent review by Wang et al. [87] the focus was on developing robotic hip exoskeletons and their potential to both support walking in the elderly and enhance human performance in healthy individuals. However, the study was limited to covering the design, actuation, and control aspects of hip exoskeletons only, and did not delve into the impact of subject-cooperative control schemes in a hierarchical manner. ...
Over the last decade, lower limb exoskeletons have seen significant development, with a particular focus on improving the interaction between the subject and the exoskeleton. This has been achieved by implementing advanced control strategies that enable the safe and efficient use of the exoskeleton. In this work, the control strategies for lower limb exoskeletons are divided into upper-level control (supervisory and high-level control) and lower-level control (the servo layer). Before discussing these control strategies, a brief introduction to lower limb exoskeletons and their control schemes is provided. The control hierarchy for lower limb exoskeletons is then systematically reviewed along with an overview of the techniques used. A Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) statement is used to highlight the systematic process of identifying relevant articles with inclusion and exclusion criteria. The details of supervisory control, high-level control, and servo control strategies are presented by citing relevant state-of-the-art studies, particularly from the past five years. The targeted lower limb joint, training mode, and development stage for different control strategies are highlighted in a tabulated form to articulate the overall hierarchy level. Finally, the potential opportunities and limitations of subject-cooperative control are discussed. Overall, this work aims to provide an in-depth understanding of the control strategies used in lower limb exoskeletons, focusing on subject cooperation. This knowledge can be used to improve the safety and efficacy of lower limb exoskeletons, ultimately benefiting individuals with mobility impairments.
... Thus, hip exo physical designs, and their controllers, can benefit from incorporating knowledge of such responses by the wearer with respect to quasi-stiffness at the hip joint during walking. A reasonable starting point is with understanding the actual influence of wearing added mass that is representative of hip exos and then extending this to increased walking speeds, as that is a common goal of exo assistance [20,25]. ...
... For both algorithms and many others like them, estimates of what profiles the wearer would naturally impose for their movement is critical to their tuning. For example, two active hip exos [38,39] presented in a recent exo review paper [25] exerted net mechanical energy only during hip flexion and/or extension phases of the gait cycle. To further tune such active control algorithms or even passive hip exo designs, knowledge of the quasi-stiffness during these phases would allow for better cooperative control. ...
... To emulate hip exos with different mass amounts and mass distributions, various amounts of added mass were attached to the participants' lower body (pelvis and both thighs). Specifically, the total added mass, 0 to~10 kg, was representative of the mass range of most recent exos with hip joint actuation [20,25]. The sagittal plane hip joint mechanical work generated during the two phases was also evaluated to observe whether any relationships could be described between quasi-stiffness and the mechanical energy consumption, or generation, at the hip joint. ...
Joint quasi-stiffness has been often used to inform exoskeleton design. Further understanding of hip quasi-stiffness is needed to design hip exoskeletons. Of interest are wearer responses to walking speed changes with added mass of the exoskeleton. This study analyzed hip quasi-stiffness at 3 walking speed levels and 9 added mass distributions among 13 young and 16 middle-aged adults during mid-stance hip extension and late-stance hip flexion. Compared to young adults, middle-aged adults maintained a higher quasi-stiffness with a smaller range. For a faster walking speed, both age groups increased extension and flexion quasi-stiffness. With mass evenly distributed on the pelvis and thighs or biased to the pelvis, both groups maintained or increased extension quasi-stiffness. With mass biased to the thighs, middle-aged adults maintained or decreased extension quasi-stiffness while young adults increased it. Young adults decreased flexion quasi-stiffness with added mass but not in any generalizable pattern with mass amounts or distributions. Conversely, middle-aged adults maintained or decreased flexion quasi-stiffness with even distribution on the pelvis and thighs or biased to the pelvis, while no change occurred if biased to the thighs. In conclusion, these results can guide the design of a hip exoskeleton’s size and mass distribution according to the intended user’s age.
