Soft Exosuits

Y. Ding, M. Kim, S. Kuindersma, and C. J. Walsh, “Human-in-the-loop optimization of hip assistance with a soft exosuit during walking,” Science Robotics, vol. 3, no. 15, pp. eaar5438, 2018. Publisher's VersionAbstract
Wearable robotic devices have been shown to substantially reduce the energy expenditure of human walking. However, response variance between participants for fixed control strategies can be high, leading to the hypothesis that individualized controllers could further improve walking economy. Recent studies on human-in-the-loop (HIL) control optimization have elucidated several practical challenges, such as long experimental protocols and low signal-to-noise ratios. Here, we used Bayesian optimization—an algorithm well suited to optimizing noisy performance signals with very limited data—to identify the peak and offset timing of hip extension assistance that minimizes the energy expenditure of walking with a textile-based wearable device. Optimal peak and offset timing were found over an average of 21.4 ± 1.0 min and reduced metabolic cost by 17.4 ± 3.2% compared with walking without the device (mean ± SEM), which represents an improvement of more than 60% on metabolic reduction compared with state-of-the-art devices that only assist hip extension. In addition, our results provide evidence for participant-specific metabolic distributions with respect to peak and offset timing and metabolic landscapes, lending support to the hypothesis that individualized control strategies can offer substantial benefits over fixed control strategies. These results also suggest that this method could have practical impact on improving the performance of wearable robotic devices.
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L. Baker, et al., “Ankle Optimization with a Soft Exosuit Reduces Metabolic Cost of Loaded Walking,” International Symposium on Wearable Robotics (WeRob). 2017. PDF
D. Choe, J. Kim, G. Lee, N. Karavas, N. Menard, and C. Walsh, “Autonomous soft exosuit with hip extension assistance for overground walking and jogging,” International Symposium on Wearable Robotics (WeRob). 2017. PDF
F. A. Panizzolo, et al., “Lower limb biomechanical analysis during an unanticipated step on a bump reveals specific adaptations of walking on uneven terrains,” Journal of Experimental Biology, vol. 220, no. 22, pp. 4169–4176, 2017. Publisher's VersionAbstract
Although it is clear that walking over different irregular terrain is associated with altered biomechanics, there is little understanding of how we quickly adapt to unexpected variations in terrain. This study aims to investigate which adaptive strategies humans adopt when performing an unanticipated step on an irregular surface, specifically a small bump. Nine healthy male participants walked at their preferred walking speed along a straight walkway during five conditions: four involving unanticipated bumps of two different heights, and one level walking condition. Muscle activation of eight lower limb muscles and three-dimensional gait analysis were evaluated during these testing conditions. Two distinct adaptive strategies were found, which involved no significant change in total lower limb mechanical work or walking speed. An ankle-based strategy was adopted when stepping on a bump with the forefoot, whereas a hip-based strategy was preferred when stepping with the rearfoot. These strategies were driven by a higher activation of the plantarflexor muscles (6–51%), which generated a higher ankle joint moment during the forefoot conditions and by a higher activation of the quadriceps muscles (36–93%), which produced a higher knee joint moment and hip joint power during the rearfoot conditions. These findings provide insights into how humans quickly react to unexpected events and could be used to inform the design of adaptive controllers for wearable robots intended for use in unstructured environments that can provide optimal assistance to the different lower limb joints.
M. Kim, et al., “Human-in-the-loop Bayesian optimization of wearable device parameters,” PLOS ONE, vol. 12, no. 9, pp. 1-15, 2017. Publisher's VersionAbstract
The increasing capabilities of exoskeletons and powered prosthetics for walking assistance have paved the way for more sophisticated and individualized control strategies. In response to this opportunity, recent work on human-in-the-loop optimization has considered the problem of automatically tuning control parameters based on realtime physiological measurements. However, the common use of metabolic cost as a performance metric creates significant experimental challenges due to its long measurement times and low signal-to-noise ratio. We evaluate the use of Bayesian optimization—a family of sample-efficient, noise-tolerant, and global optimization methods—for quickly identifying near-optimal control parameters. To manage experimental complexity and provide comparisons against related work, we consider the task of minimizing metabolic cost by optimizing walking step frequencies in unaided human subjects. Compared to an existing approach based on gradient descent, Bayesian optimization identified a near-optimal step frequency with a faster time to convergence (12 minutes, p < 0.01), smaller inter-subject variability in convergence time (± 2 minutes, p < 0.01), and lower overall energy expenditure (p < 0.01).
J. Bae, et al., “Exosuit-induced improvements in walking after stroke: comprehensive analysis on gait energetics and biomechanics,” International Symposium on Wearable Robotics (WeRob). 2017. PDF
L. N. Awad, et al., “Soft Exosuits Increase Walking Speed and Distance after Stroke,” International Symposium on Wearable Robotics (WeRob). 2017. PDF
L. N. Awad, et al., “A soft robotic exosuit improves walking in patients after stroke,” Science Translational Medicine, vol. 9, no. 400, pp. eaai9084, 2017. Publisher's VersionAbstract

Passive assistance devices such as canes and braces are often used by people after stroke, but mobility remains limited for some patients. Awad et al. studied the effects of active assistance (delivery of supportive force) during walking in nine patients in the chronic phase of stroke recovery. A soft robotic exosuit worn on the partially paralyzed lower limb reduced interlimb propulsion asymmetry, increased ankle dorsiflexion, and reduced the energy required to walk when powered on during treadmill and overground walking tests. The exosuit could be adjusted to deliver supportive force during the early or late phase of the gait cycle depending on the patient’s needs. Although long-term therapeutic studies are necessary, the immediate improvement in walking performance observed using the powered exosuit makes this a promising approach for neurorehabilitation.

Stroke-induced hemiparetic gait is characteristically slow and metabolically expensive. Passive assistive devices such as ankle-foot orthoses are often prescribed to increase function and independence after stroke; however, walking remains highly impaired despite—and perhaps because of—their use. We sought to determine whether a soft wearable robot (exosuit) designed to supplement the paretic limb’s residual ability to generate both forward propulsion and ground clearance could facilitate more normal walking after stroke. Exosuits transmit mechanical power generated by actuators to a wearer through the interaction of garment-like, functional textile anchors and cable-based transmissions. We evaluated the immediate effects of an exosuit actively assisting the paretic limb of individuals in the chronic phase of stroke recovery during treadmill and overground walking. Using controlled, treadmill-based biomechanical investigation, we demonstrate that exosuits can function in synchrony with a wearer’s paretic limb to facilitate an immediate 5.33 ± 0.91° increase in the paretic ankle’s swing phase dorsiflexion and 11 ± 3% increase in the paretic limb’s generation of forward propulsion (P < 0.05). These improvements in paretic limb function contributed to a 20 ± 4% reduction in forward propulsion interlimb asymmetry and a 10 ± 3% reduction in the energy cost of walking, which is equivalent to a 32 ± 9% reduction in the metabolic burden associated with poststroke walking. Relatively low assistance ( 12% of biological torques) delivered with a lightweight and nonrestrictive exosuit was sufficient to facilitate more normal walking in ambulatory individuals after stroke. Future work will focus on understanding how exosuit-induced improvements in walking performance may be leveraged to improve mobility after stroke.

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L. N. Awad, et al., “Reducing Circumduction and Hip Hiking During Hemiparetic Walking Through Targeted Assistance of the Paretic Limb Using a Soft Robotic Exosuit.American Journal of Physical Medicine & Rehabilitation, 2017. Publisher's VersionAbstract

The aim of the study was to evaluate the effects on common poststroke gait compensations of a soft wearable robot (exosuit) designed to assist the paretic limb during hemiparetic walking.

A single-session study of eight individuals in the chronic phase of stroke recovery was conducted. Two testing conditions were compared: walking with the exosuit powered versus walking with the exosuit unpowered. Each condition was 8 minutes in duration.

Compared with walking with the exosuit unpowered, walking with the exosuit powered resulted in reductions in hip hiking (27 [6%], P = 0.004) and circumduction (20 [5%], P = 0.004). A relationship between changes in knee flexion and changes in hip hiking was observed (Pearson r = −0.913, P < 0.001). Similarly, multivariate regression revealed that changes in knee flexion (β = −0.912, P = 0.007), but not ankle dorsiflexion (β = −0.194, P = 0.341), independently predicted changes in hip hiking (R2= 0.87, F(2, 4) = 13.48, P = 0.017).

Exosuit assistance of the paretic limb during walking produces immediate changes in the kinematic strategy used to advance the paretic limb. Future work is necessary to determine how exosuit-induced reductions in paretic hip hiking and circumduction during gait training could be leveraged to facilitate more normal walking behavior during unassisted walking.

P. Malcolm, et al., “Continuous sweep versus discrete step protocols for studying effects of wearable robot assistance magnitude,” Journal of NeuroEngineering and Rehabilitation, vol. 14, no. 1, pp. 72, 2017. Publisher's VersionAbstract

Different groups developed wearable robots for walking assistance, but there is still a need for methods to quickly tune actuation parameters for each robot and population or sometimes even for individual users. Protocols where parameters are held constant for multiple minutes have traditionally been used for evaluating responses to parameter changes such as metabolic rate or walking symmetry. However, these discrete protocols are time-consuming. Recently, protocols have been proposed where a parameter is changed in a continuous way. The aim of the present study was to compare effects of continuously varying assistance magnitude with a soft exosuit against discrete step conditions.

Seven participants walked on a treadmill wearing a soft exosuit that assists plantarflexion and hip flexion. In Continuous-up, peak exosuit ankle moment linearly increased from approximately 0 to 38% of biological moment over 10 min. Continuous-down was the opposite. In Discrete, participants underwent five periods of 5 min with steady peak moment levels distributed over the same range as Continuous-up and Continuous-down. We calculated metabolic rate for the entire Continuous-up and Continuous-down conditions and the last 2 min of each Discrete force level. We compared kinematics, kinetics and metabolic rate between conditions by curve fitting versus peak moment.

Reduction in metabolic rate compared to Powered-off was smaller in Continuous-up than in Continuous-down at most peak moment levels, due to physiological dynamics causing metabolic measurements in Continuous-up and Continuous-down to lag behind the values expected during steady-state testing. When evaluating the average slope of metabolic reduction over the entire peak moment range there was no significant difference between Continuous-down and Discrete. Attempting to correct the lag in metabolics by taking the average of Continuous-up and Continuous-down removed all significant differences versus Discrete. For kinematic and kinetic parameters, there were no differences between all conditions.

The finding that there were no differences in biomechanical parameters between all conditions suggests that biomechanical parameters can be recorded with the shortest protocol condition (i.e. single Continuous directions). The shorter time and higher resolution data of continuous sweep protocols hold promise for the future study of human interaction with wearable robots.

A. Atalay, et al., “Batch Fabrication of Customizable Silicone-Textile Composite Capacitive Strain Sensors for Human Motion Tracking,” Advanced Materials Technologies, 2017. Publisher's VersionAbstract
This paper presents design and batch manufacturing of a highly stretchable textile-silicone capacitive sensor to be used in human articulation detection, soft robotics, and exoskeletons. The proposed sensor is made of conductive knit fabric as electrode and silicone elastomer as dielectric. The batch manufacturing technology enables production of large sensor mat and arbitrary shaping of sensors, which is precisely achieved via laser cutting of the sensor mat. Individual capacitive sensors exhibit high linearity, low hysteresis, and a gauge factor of 1.23. Compliant, low-profile, and robust electrical connections are established by fusing filaments of micro coaxial cable to conductive fabric electrodes of the sensor with thermoplastic film. The capacitive sensors are integrated on a reconstructed glove for monitoring finger motions.
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L. N. Awad, et al., “Soft Wearable Robots Can Increase Walking Speed and Distance After Stroke: Proof of Concept,” Combined Sections Meeting of the American Physical Therapy Association (APTA CSM). 2017. PDF
P. Malcolm, et al., “Varying negative work assistance at the ankle with a soft exosuit during loaded walking,” Journal of NeuroEngineering and Rehabilitation, vol. 14, no. 1, pp. 62, 2017. Publisher's VersionAbstract

Only very recently, studies have shown that it is possible to reduce the metabolic rate of unloaded and loaded walking using robotic ankle exoskeletons. Some studies obtained this result by means of high positive work assistance while others combined negative and positive work assistance. There is no consensus about the isolated contribution of negative work assistance. Therefore, the aim of the present study is to examine the effect of varying negative work assistance at the ankle joint while maintaining a fixed level of positive work assistance with a multi-articular soft exosuit.

We tested eight participants during walking at 1.5 ms−1 with a 23-kg backpack. Participants wore a version of the exosuit that assisted plantarflexion via Bowden cables tethered to an off-board actuation platform. In four active conditions we provided different rates of exosuit bilateral ankle negative work assistance ranging from 0.015 to 0.037 W kg−1 and a fixed rate of positive work assistance of 0.19 W kg−1.

All active conditions significantly reduced metabolic rate by 11 to 15% compared to a reference condition, where the participants wore the exosuit but no assistance was provided. We found no significant effect of negative work assistance. However, there was a trend (p = .08) toward greater reduction in metabolic rate with increasing negative work assistance, which could be explained by observed reductions in biological ankle and hip joint power and moment.

The non-significant trend of increasing negative work assistance with increasing reductions in metabolic rate motivates the value in further studies on the relative effects of negative and positive work assistance. There may be benefit in varying negative work over a greater range or in isolation from positive work assistance.

O. Araromi, C. J. Walsh, and R. J. Wood, “Hybrid carbon fiber-textile compliant force sensors for high-load sensing in soft exosuits,” in IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS), Vancouver, BC, Canada, September 24-28, 2017. PDF
G. Lee, Y. Ding, I. B. Galiana, N. Karavas, Y. M. Zhou, and C. J. Walsh, “Improved assistive profile tracking for walking and jogging soft exosuits with off-board actuation,” in IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS), Vancouver, BC, Canada, September 24-28, 2017. PDF
M. B. Yandell, B. T. Quinlivan, D. Popov, C. J. Walsh, and K. E. Zelik, “Human-Exosuit Interfaces Absorb and Return Energy, Reshaping Exosuit to Human Power Flow,” 41st Annual Meeting of the American Society of Biomechanics (ASB). 2017. Abstract Poster
P. Malcolm, et al., “Effect of slope and speed on kinetics of jogging with a backpack,” 41st Annual Meeting of the American Society of Biomechanics (ASB). 2017. PDF
W. Bowers, et al., “Effect of powered exosuit training on impulse during gait,” 41st Annual Meeting of the American Society of Biomechanics (ASB). 2017. PDF
L. Sloot, et al., “Unilateral ankle assisting soft robotic exosuit can improve post-stroke gait during overground walking,” 41st Annual Meeting of the American Society of Biomechanics (ASB). 2017. PDF
P. Kudzia, et al., “A uni-lateral soft exosuit for the paretic ankle can reduce gait compensations in patients post-stroke,” 41st Annual Meeting of the American Society of Biomechanics (ASB). 2017. Abstract Poster