Soft Exosuits

2017
Assistance magnitude versus metabolic cost reductions for a tethered multiarticular soft exosuit
B. T. Quinlivan, et al., “Assistance magnitude versus metabolic cost reductions for a tethered multiarticular soft exosuit,” Science Robotics, vol. 2, no. 2, 2017. Publisher's VersionAbstract

When defining requirements for any wearable robot for walking assistance, it is important to maximize the user’s metabolic benefit resulting from the exosuit assistance while limiting the metabolic penalty of carrying the system’s mass. Thus, the aim of this study was to isolate and characterize the relationship between assistance magnitude and the metabolic cost of walking while also examining changes to the wearer’s underlying gait mechanics. The study was performed with a tethered multiarticular soft exosuit during normal walking, where assistance was directly applied at the ankle joint and indirectly at the hip due to a textile architecture. The exosuit controller was designed such that the delivered torque profile at the ankle joint approximated that of the biological torque during normal walking. Seven participants walked on a treadmill at 1.5 meters per second under one unpowered and four powered conditions, where the peak moment applied at the ankle joint was varied from about 10 to 38% of biological ankle moment (equivalent to an applied force of 18.7 to 75.0% of body weight). Results showed that, with increasing exosuit assistance, net metabolic rate continually decreased within the tested range. When maximum assistance was applied, the metabolic rate of walking was reduced by 22.83 ± 3.17% relative to the powered-off condition (mean ± SEM).

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2016
Y. Ding, et al., “Effect of timing of hip extension assistance during loaded walking with a soft exosuit,” Journal of NeuroEngineering and Rehabilitation, vol. 2016, no. 13, pp. 87, 2016. Publisher's VersionAbstract

 

Background
Recent advances in wearable robotic devices have demonstrated the ability to reduce the metabolic cost of walking by assisting the ankle joint. To achieve greater gains in the future it will be important to determine optimal actuation parameters and explore the effect of assisting other joints. The aim of the present work is to investigate how the timing of hip extension assistance affects the positive mechanical power delivered by an exosuit and its effect on biological joint power and metabolic cost during loaded walking. In this study, we evaluated 4 different hip assistive profiles with different actuation timings: early-start-early-peak (ESEP), early-start-late-peak (ESLP), late-start-early-peak (LSEP), late-start-late-peak (LSLP).

Methods
Eight healthy participants walked on a treadmill at a constant speed of 1.5 m · s-1 while carrying a 23 kg backpack load. We tested five different conditions: four with the assistive profiles described above and one unpowered condition where no assistance was provided. We evaluated participants’ lower limb kinetics, kinematics, metabolic cost and muscle activation.

Results
The variation of timing in the hip extension assistance resulted in a different amount of mechanical power delivered to the wearer across conditions; with the ESLP condition providing a significantly higher amount of positive mechanical power (0.219 ± 0.006 W · kg-1) with respect to the other powered conditions. Biological joint power was significantly reduced at the hip (ESEP and ESLP) and at the knee (ESEP, ESLP and LSEP) with respect to the unpowered condition. Further, all assistive profiles significantly reduced the metabolic cost of walking compared to the unpowered condition by 5.7 ± 1.5 %, 8.5 ± 0.9 %, 6.3 ± 1.4 % and 7.1 ± 1.9 % (mean ± SE for ESEP, ESLP, LSEP, LSLP, respectively).

Conclusions
The highest positive mechanical power delivered by the soft exosuit was reported in the ESLP condition, which showed also a significant reduction in both biological hip and knee joint power. Further, the ESLP condition had the highest average metabolic reduction among the powered conditions. Future work on autonomous hip exoskeletons may incorporate these considerations when designing effective control strategies.

 

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N. Karavas, et al., “Autonomous Soft Exosuit for Hip Extension Assistance,” in International Symposium on Wearable Robotics (WeRob) 2016, La Granja, Spain, 2016.
T. Miyatake, et al., “Biomechanical analysis and inertial sensing of ankle joint while stepping on an unanticipated bump,” in International Symposium on Wearable Robotics (WeRob) 2016, La Granja, Spain, 2016.
M. Grimmer, et al., “Comparison of Ankle Moment Inspired And Ankle Positive Power Inspired Controllers for a Multi-articular Soft Exosuit for Walking Assistance,” in International Symposium on Wearable Robotics (WeRob) 2016, La Granja, Spain, 2016.
H. Su, et al., “Evaluation of Force Tracking Controller with Soft Exosuit for Hip Extension Assistance,” in International Symposium on Wearable Robotics (WeRob) 2016, La Granja, Spain, 2016.
O. Araromi, C. J. Walsh, and R. J. Wood, “Fabrication of Stretchable Composites with Anisotropic Electrical Conductivity for Compliant Pressure Transducers,” in IEEE Sensors Conference 2016, Orlando, Florida, 2016. Publisher's VersionAbstract

We present a simple fabrication approach for anisotropically conductive stretchable composites, towards novel flexible pressure transducers. Flexible electronic systems have gained great interest in recent years, and within this space, anisotropic conducting materials have been explored for enhanced sensing performance. However, current methods for producing these materials are complex or are limited to small fabrication areas. Our method uses film applicator coating to render commercially available conductive RTVs anisotropically conductive. A ratio of in-plane surface resistance to through-thickness resistance of 1010 was achieved using our method. Furthermore, we show that when a normal pressure is applied to such films, the in-plane resistance can be reduced by seven orders of magnitude for an applied pressure of 10 kPa. Hence these materials show great promise for the development of novel, robust pressure transducers.

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S. Lee, F. Panizzolo, T. Miyatake, D. M. Rossi, C. Siviy, and C. J. Walsh, “Lower limb biomechanical analysis of unanticipated step on a bump,” in Dynamic Walking, Holly, Michigan, USA, 2016.
J. Bae, et al., “Assisting paretic ankle motion with a soft exosuit can reduce whole-body compensatory gait patterns and improve walking efficiency for patients after stroke,” in Dynamic Walking, Holly, Michigan, USA, 2016.
F. A. Panizzolo, et al., “A biologically-inspired multi-joint soft exosuit that can reduce the energy cost of loaded walking,” Journal of NeuroEngineering and Rehabilitation, vol. 13, no. 1, pp. 1-14, 2016. Publisher's VersionAbstract

Carrying load alters normal walking, imposes additional stress to the musculoskeletal system, and results in an increase in energy consumption and a consequent earlier onset of fatigue. This phenomenon is largely due to increased work requirements in lower extremity joints, in turn requiring higher muscle activation. The aim of this work was to assess the biomechanical and physiological effects of a multi-joint soft exosuit that applies assistive torques to the biological hip and ankle joints during loaded walking.

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S. Lee, S. Crea, P. Malcolm, I. B. Galiana, A. T. Asbeck, and C. J. Walsh, “Controlling Negative and Positive Power at the Ankle with a Soft Exosuit,” in IEEE International Conference on Robotics and Automation (ICRA), Stockholm, Sweden, 2016. PDF
B. Quinlivan, et al., “Multi-articular soft exosuit continually reduces the metabolic cost of unloaded walking with increased assistance magnitude,” in Dynamic Walking, Holly, Michigan, USA, 2016.
C. Siviy, et al., “Optimization of soft exosuit peak force with ramp and step sweep protocol,” in Dynamic Walking, Holly, Michigan, USA, 2016.
L. N. Awad, et al., “A soft exosuit for assisting poststroke walking,” in 9th World Congress of Neurorehabilitation, Philadelphia, PA, USA, 2016.
L. N. Awad, et al., “Soft Wearable Robots Can Reduce the Energy Cost of Poststroke Walking: A Proof-of-Concept Study,” in Combined Sessions Meeting of the American Physical Therapy Association, Anaheim, CA, 2016.
P. Malcolm, et al., “Study of the contribution of negative work assistance at the ankle with a multi-articular soft exosuit during loaded walking,” in Dynamic Walking, Holly, Michigan, USA, 2016.
M. B. Yandell, D. Popov, B. Quinlivan, C. J. Walsh, and K. E. Zelik, “Systematic evaluation of human-exosuit physical interfaces,” in Dynamic Walking, Holly, Michigan, USA, 2016.
Y. Ding, et al., “Biomechanical and Physiological Evaluation of Multi-joint Assistance with Soft Exosuits,” IEEE Transactions on Neural Systems and Rehabilitation Engineering, vol. PP, no. 99, pp. 1, 2016. Publisher's VersionAbstract

To understand the effects of soft exosuits on human loaded walking, we developed a reconfigurable multi-joint actuation platform that can provide synchronized forces to the ankle and hip joints. Two different assistive strategies were evaluated on eight subjects walking on a treadmill at a speed of 1.25 m/s with a 23.8 kg backpack: 1) hip extension assistance and 2) multi-joint assistance (hip extension, ankle plantarflexion and hip flexion). Results show that the exosuit introduces minimum changes to kinematics and reduces biological joint moments. A reduction trend in muscular activity was observed for both conditions. On average, the exosuit reduced the metabolic cost of walking by 0.21 ± 0.04 W/kg and 0.67 ± 0.09 W/kg for hip extension assistance and multi-joint assistance respectively, which is equivalent to an average metabolic reduction of 4.6% and 14.6% demonstrating that soft exosuits can effectively improve human walking efficiency during load carriage without affecting natural walking gait. Moreover, it indicates that actuating multiple joints with soft exosuits provides a significant benefit to muscular activity and metabolic cost compared to actuating single joint.

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Y. Ding, I. Galiana, C. Siviy, F. A. Panizzolo, and C. J. Walsh, “IMU-based Iterative Control for Hip Extension Assistance with a Soft Exosuit,” in IEEE International Conference on Robotics and Automation (ICRA), Stockholm, Sweden, 2016.Abstract

In this paper we describe an IMU-based iterative controller for hip extension assistance where the onset timing of assistance is based on an estimate of the maximum hip flexion angle. The controller was implemented on a mono-articular soft exosuit coupled to a lab-based multi-joint actuation platform that enables rapid reconfiguration of different sensors and control strategy implementation. The controller design is motivated by a model of the suit-human interface and utilizes an iterative control methodology that includes gait detection and step-by-step actuator position profile generation to control the onset timing, peak timing, and peak magnitude of the delivered force. This controller was evaluated on eight subjects walking on a treadmill at a speed of 1.5 m/s while carrying a load of 23 kg. Results showed that assistance could be delivered reliably across subjects. Specifically, for a given profile, the average delivered force started concurrently with the timing of the maximum hip flexion angle and reached its peak timing 22.7 ± 0.63% later in the gait cycle (desired 23%) with a peak magnitude of 198.2 ± 1.6 N (desired 200 N), equivalent to an average peak torque of 30.5 ± 4.7 Nm. This control approach was used to assess the metabolic effect of four different assistive profiles. Metabolic reductions ranging from 5.7% to 8.5% were found when comparing the powered conditions with the unpowered condition. This work enables studies to assess the biomechanical and physiological responses to different assistive profiles to determine the optimal hip extension assistance during walking.

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2015
F. A. Panizzolo, et al., “Evaluation of a multi-joint soft exosuit for gait assistance,” in 7th International Symposium on Adaptive Motion of Animals and Machines (AMAM), Cambridge, MA, USA, 2015.

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