Optimized hip-knee-ankle exoskeleton assistance at a range of walking speeds

Bryan, Gwendolyn M.; Franks, Patrick W.; Song, Seungmoon; Voloshina, Alexandra S.; Reyes, Ricárdo; O’Donovan, Meghan P.; Gregorczyk, Karen N.; Collins, Steven H.

doi:10.1101/2021.03.26.437212

Cited by 8 publications

(31 citation statements)

References 32 publications

(31 reference statements)

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“…We optimized hip-knee-ankle exoskeleton assistance while participants walked at 1.25 m/s with a light load (15% of body weight) and a heavy load (30% of body weight). We optimized exoskeleton assistance for a no load condition at the same speed in previous studies [18,20], and we re-validated the results for two participants in this study. We used human-in-the-loop optimization to minimize the metabolic cost of walking with each load.…”

Section: Methodsmentioning

confidence: 79%

“…2). The torque parameterization was successful in previous optimization studies with this device [18,20]. The profiles were generated with splines, and parameter ranges were limited for participant comfort (Supplementary).…”

Section: Exoskeleton Controlmentioning

confidence: 99%

“…We found this experimental order was easiest for participants as they transitioned between load conditions. The no load condition was optimized in previous studies [18,20]. For this study, we validated the no load condition for participants 1 and 2 again because the original validations occurred over 7 months earlier and before the implementation of Covid-19 masking protocols.…”

Section: Optimization Protocolmentioning

confidence: 99%

“…We used human-in-the-loop optimization to minimize the metabolic cost of walking. This strategy has been successful to reduce the metabolic cost of walking with exoskeleton assistance [9,18,20,[22][23][24]. We optimized assistance with the covariance matrix algorithm-evolutionary strategy (CMA-ES), which was successful in previous exoskeleton optimization studies [9,18,19,22,25,26].…”

Section: Optimization Algorithmmentioning

confidence: 99%

“…We hypothesized that exoskeleton assistance would reduce metabolic cost for all loaded conditions and that the optimized extension torques would increase with load. Three participants wore a hip-knee-ankle exoskeleton emulator [19] while we used human-in-the-loop optimization to reduce the metabolic cost of walking with no load [18,20], while carrying 15% of body weight, and while carrying 30% of body weight. The loads were applied with a weight vest with an attached waist strap such that the majority of the load was applied to the user's iliac crests.…”

Section: Introductionmentioning

confidence: 99%

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Optimized Hip-Knee-Ankle Exoskeleton Assistance Reduces the Metabolic Cost of Walking With Worn Loads

Bryan

Franks

Song

et al. 2021

Preprint

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BackgroundLoad carriage is a typical activity in a wide range of professions, but prolonged load carriage is associated with increased fatigue and overuse injuries. Exoskeletons could improve the quality of life of these professionals by reducing metabolic cost to combat fatigue and reducing muscle activity to prevent injuries. Current exoskeletons have reduced the metabolic cost of loaded walking by up to 23% when assisting one or two joints. Greater metabolic reductions may be possible with optimized assistance of the entire leg. MethodsWe used human-in the-loop optimization to optimize hip-knee-ankle exoskeleton assistance with no additional load, a light load (15% of body weight), and a heavy load (30% of body weight) for three participants. All loads were applied through a weight vest with an attached waist belt. We measured metabolic cost, exoskeleton assistance, kinematics, and muscle activity. We performed one-tailed paired t-tests to determine significant reductions for metabolic cost and muscle activity, and we performed an analysis of variance (ANOVA) to determine significant changes across load conditions for metabolic cost and applied power. ResultsExoskeleton assistance reduced the metabolic cost of walking relative to walking in the device without assistance for all tested conditions. Exoskeleton assistance reduced the metabolic cost of walking by 47% with no load (p = 0.02), 35% with the light load (p = 0.03), and 43% with the heavy load (p = 0.02). The smaller metabolic reduction with the light load may be due to insufficient participant training or lack of optimizer convergence. The total applied positive power was similar for all tested conditions, and the positive knee power decreased slightly as load increased. Optimized torque timing parameters were consistent across participants and load conditions while optimized magnitude parameters varied. ConclusionsWhole-leg exoskeleton assistance can reduce the metabolic cost of walking while carrying a range of loads. The consistent optimized timing parameters suggest that metabolic cost reductions are sensitive to torque timing. The variable torque magnitude parameters could imply that torque magnitude should be customized to the individual, or that there is a range of useful torque magnitudes. Future work should test whether applying the load to the exoskeleton rather than the person's torso results in larger benefits.

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Section: Methodsmentioning

confidence: 79%

Section: Exoskeleton Controlmentioning

confidence: 99%

Section: Optimization Protocolmentioning

confidence: 99%

Section: Optimization Algorithmmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Optimized Hip-Knee-Ankle Exoskeleton Assistance Reduces the Metabolic Cost of Walking With Worn Loads

Bryan

Franks

Song

et al. 2021

Preprint

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The Effects of Incline Level on Optimized Lower-Limb Exoskeleton Assistance

Franks

Bryan

Reyes

et al. 2021

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For exoskeletons to be successful in real-world settings, they will need to be effective across a variety of terrains, including on inclines. While some single-joint exoskeletons have assisted incline walking, recent successes in level-ground assistance suggest that greater improvements may be possible by optimizing assistance of the whole leg. To understand how exoskeleton assistance should change with incline, we used human-in-the-loop optimization to find whole-leg exoskeleton assistance torques that minimized metabolic cost on a range of grades. We optimized assistance for three expert, able-bodied participants on 5 degree, 10 degree and 15 degree inclines using a hip-knee-ankle exoskeleton emulator. For all assisted conditions, the cost of transport was reduced by at least 50% relative to walking in the device with no assistance, a large improvement to walking that is comparable to the benefits of whole-leg assistance on level-ground. This corresponds to large absolute reductions in metabolic cost, with the most strenuous conditions reduced by 4.9 W/kg, more than twice the entire energy cost of level walking. Optimized extension torque magnitudes and exoskeleton power increased with incline, with hip extension, knee extension and ankle plantarflexion often growing as large as allowed by comfort-based limits. Applied powers on steep inclines were double the powers applied during level-ground walking, indicating that larger exoskeleton power may be optimal in scenarios where biological powers and costs are higher. Future exoskeleton devices can be expected to deliver large improvements in walking performance across a range of inclines, if they have sufficient torque and power capabilities.

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Assisting walking balance using a bio-inspired exoskeleton controller

Afschrift

Asseldonk

Mierlo

et al. 2022

Preprint

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Balance control is important for mobility, yet exoskeleton research has mainly focused on improving metabolic energy efficiency. Here we present a biomimetic exoskeleton controller that supports walking balance and reduces muscle activity. Humans restore balance after a perturbation by adjusting activity of the muscles actuating the ankle in proportion to deviations from steady-state center of mass kinematics. We designed a controller that mimics the neural control of steady-state walking and the balance recovery responses to perturbations. This controller uses both feedback from ankle kinematics in accordance with an existing model and feedback from the center of mass velocity. Control parameters were estimated by fitting the experimental relation between kinematics and ankle moments observed in humans that were walking while being perturbed by push and pull perturbations. This identified model was implemented on a bilateral ankle exoskeleton. The exoskeleton provided 30% of the estimated ankle moment during steady-state and perturbed walking. Across twelve subjects, exoskeleton support reduced calf muscle activity in steady-state walking by 19 % with respect to a minimal impedance controller. Proportional feedback of the center of mass velocity improved balance support after perturbation. Muscle activity is reduced in response to push and pull perturbations by 10 and 16 % and center of mass deviations by 9 and 18% with respect to the same controller without center of mass feedback. Our control approach implemented on bilateral ankle exoskeletons can thus effectively support steady-state walking and balance control and therefore has the potential to improve mobility in balance-impaired individuals.

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Optimized hip-knee-ankle exoskeleton assistance at a range of walking speeds

Cited by 8 publications

References 32 publications

Optimized Hip-Knee-Ankle Exoskeleton Assistance Reduces the Metabolic Cost of Walking With Worn Loads

Optimized Hip-Knee-Ankle Exoskeleton Assistance Reduces the Metabolic Cost of Walking With Worn Loads

The Effects of Incline Level on Optimized Lower-Limb Exoskeleton Assistance

Assisting walking balance using a bio-inspired exoskeleton controller

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