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

2021 ◽  
Author(s):  
Gwendolyn M Bryan ◽  
Patrick Franks ◽  
Seungmoon Song ◽  
Ricardo Reyes ◽  
Meghan O’Donovan ◽  
...  
Keyword(s):  
Body Weight ◽  
Muscle Activity ◽  
Metabolic Cost ◽  
Load Carriage ◽  
Heavy Load ◽  
Human In The Loop ◽  
Light Load ◽  
Wide Range ◽  
Ankle Exoskeleton ◽  
Load Conditions

Abstract 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.

scholarly journals Optimized hip-knee-ankle exoskeleton assistance reduces the metabolic cost of walking with worn loads

2021 ◽  
Vol 18 (1) ◽  
Author(s):  
Gwendolyn M. Bryan ◽  
Patrick W. Franks ◽  
Seungmoon Song ◽  
Ricardo Reyes ◽  
Meghan P. O’Donovan ◽  
...  
Keyword(s):  
Body Weight ◽  
Muscle Activity ◽  
Metabolic Cost ◽  
Load Carriage ◽  
Heavy Load ◽  
Human In The Loop ◽  
Light Load ◽  
Wide Range ◽  
Ankle Exoskeleton ◽  
The Individual

Abstract Background Load carriage is common 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 22% relative to walking in the device with no assistance when assisting one or two joints. Greater metabolic reductions may be possible with optimized assistance of the entire leg. Methods We 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 Friedman’s tests to analyze trends across worn loads and paired t-tests to determine whether changes from the unassisted conditions to the assisted conditions were significant. Results Exoskeleton 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 48% with no load (p = 0.05), 41% with the light load (p = 0.01), and 43% with the heavy load (p = 0.04). 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. Conclusions Whole-leg exoskeleton assistance can reduce the metabolic cost of walking while carrying a range of loads. The consistent optimized timing parameters across participants and conditions 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.

scholarly journals An Electromyographic Study of the Hip Abductor Muscles as Subjects With a Hip Prosthesis Walked With Different Methods of Using a Cane and Carrying a Load

1999 ◽  
Vol 79 (12) ◽  
pp. 1163-1173 ◽  
Author(s):  
Donald A Neumann
Keyword(s):  
Body Weight ◽  
Muscle Activity ◽  
Hip Prosthesis ◽  
Load Condition ◽  
Surface Emg ◽  
Emg Activity ◽  
Emg Signal ◽  
Hip Abductor ◽  
Load Conditions

Abstract Background and Purpose. Certain methods of carrying handheld loads or using a cane can reduce the demands placed on the hip abductor (HA) muscles and the loads on the underlying prosthetic hip. In certain conditions, unusually large forces from the HA muscles may contribute to premature loosening of a prosthetic hip. The purpose of this study was to examine HA use by measuring the amplitude of the electromyographic (EMG) signal from the HA muscles as subjects carried a load and simultaneously used a cane. Subjects. Twenty-four active subjects (mean age=63.3 years, SD=10.7, range=40–86) with a unilateral prosthetic hip were tested. Methods. The HA muscle surface EMG activity was analyzed as subjects carried loads weighing 5%, 10%, or 15% of body weight held by either their contralateral or ipsilateral arm relative to their prosthetic hip. They simultaneously used a cane with their free hand. Results. The contralateral cane and ipsilateral load conditions produced HA muscle EMG activity that was approximately 40% less than the EMG activity produced while walking without carrying a load or using a cane. Conclusion and Discussion. People who are in danger of premature loosening of their prosthetic hip should, if possible, avoid carrying loads. If a load must be carried, however, then the contralateral cane and ipsilateral load condition appears to minimize the loads placed on the prosthetic hip due to HA muscle activity.

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

2021 ◽  
Author(s):  
Gwendolyn M Bryan ◽  
Patrick W. Franks ◽  
Seungmoon Song ◽  
Alexandra S Voloshina ◽  
Ricardo Reyes ◽  
...  
Keyword(s):  
Muscle Activity ◽  
Metabolic Cost ◽  
Positive Power ◽  
Fast Walking ◽  
Know How ◽  
Ankle Torque ◽  
Slow Walking ◽  
Limited Success ◽  
Ankle Exoskeleton ◽  
Walking Speeds

Background: Effective autonomous exoskeletons will need to be useful at a variety of walking speeds, but we do not know how optimal exoskeleton assistance should change with speed. Optimal exoskeleton assistance may increase with speed similar to biological torque changes or a well-tuned assistance profile may be effective at a variety of speeds. Methods: We optimized hip-knee-ankle exoskeleton assistance to reduce metabolic cost for three participants walking at 1.0 m/s, 1.25 m/s and 1.5 m/s. We measured metabolic cost, muscle activity, exoskeleton assistance and kinematics. We performed two tailed paired t-tests to determine significance. Results: Exoskeleton assistance reduced the metabolic cost of walking compared to wearing the exoskeleton with no torque applied by 26%, 47% and 50% at 1.0, 1.25 and 1.5 m/s, respectively. For all three participants, optimized exoskeleton ankle torque was the smallest for slow walking, while hip and knee torque changed slightly with speed in ways that varied across participants. Total applied positive power increased with speed for all three participants, largely due to increased joint velocities, which consistently increased with speed. Conclusions: Exoskeleton assistance is effective at a range of speeds and is most effective at medium and fast walking speeds. Exoskeleton assistance was less effective for slow walking, which may explain the limited success in reducing metabolic cost for patient populations through exoskeleton assistance. Exoskeleton designers may have more success when targeting activities and groups with faster walking speeds. Speed-related changes in optimized exoskeleton assistance varied by participant, indicating either the benefit of participant-specific tuning or that a wide variety of torque profiles are similarly effective.

scholarly journals Comparing optimized exoskeleton assistance of the hip, knee, and ankle in single and multi-joint configurations

2021 ◽  
Vol 2 ◽  
Author(s):  
Patrick W. Franks ◽  
Gwendolyn M. Bryan ◽  
Russell M. Martin ◽  
Ricardo Reyes ◽  
Ava C. Lakmazaheri ◽  
...  
Keyword(s):  
Human Mobility ◽  
Metabolic Cost ◽  
Metabolic Energy ◽  
Maximum Effect ◽  
Loop Optimization ◽  
Human In The Loop ◽  
Ankle Joints ◽  
Individual Effects ◽  
Single Well ◽  
Ankle Exoskeleton

Abstract Exoskeletons that assist the hip, knee, and ankle joints have begun to improve human mobility, particularly by reducing the metabolic cost of walking. However, direct comparisons of optimal assistance of these joints, or their combinations, have not yet been possible. Assisting multiple joints may be more beneficial than the sum of individual effects, because muscles often span multiple joints, or less effective, because single-joint assistance can indirectly aid other joints. In this study, we used a hip–knee–ankle exoskeleton emulator paired with human-in-the-loop optimization to find single-joint, two-joint, and whole-leg assistance that maximally reduced the metabolic cost of walking. Hip-only and ankle-only assistance reduced the metabolic cost of walking by 26 and 30% relative to walking in the device unassisted, confirming that both joints are good targets for assistance (N = 3). Knee-only assistance reduced the metabolic cost of walking by 13%, demonstrating that effective knee assistance is possible (N = 3). Two-joint assistance reduced the metabolic cost of walking by between 33 and 42%, with the largest improvements coming from hip-ankle assistance (N = 3). Assisting all three joints reduced the metabolic cost of walking by 50%, showing that at least half of the metabolic energy expended during walking can be saved through exoskeleton assistance (N = 4). Changes in kinematics and muscle activity indicate that single-joint assistance indirectly assisted muscles at other joints, such that the improvement from whole-leg assistance was smaller than the sum of its single-joint parts. Exoskeletons can assist the entire limb for maximum effect, but a single well-chosen joint can be more efficient when considering additional factors such as weight and cost.

Tribological Behavior and Mechanisms of the Deloro60 Alloy Coatings by Electro Spark Deposition under Dry Sliding Friction Conditions

2014 ◽  
Vol 692 ◽  
pp. 428-432
Author(s):  
Xiao Long Wang ◽  
Ting Xu ◽  
Ye Fa Tan ◽  
Li Zhou An ◽  
Lu Lu Wang ◽  
...  
Keyword(s):  
High Speed ◽  
Sliding Friction ◽  
Base Alloy ◽  
Dry Sliding ◽  
Heavy Load ◽  
Micro Cutting ◽  
Light Load ◽  
Rational Combination ◽  
Dry Sliding Friction ◽  
Load Conditions

The Ni-base alloy coatings of Derolo60 were prepared on the surface of carbon steel by electro spark deposition. The tribological properties of the coatings were investigated in a tribometer under dry sliding friction conditions. The results show that the coatings exhibit excellent properties of wear resistance because of their unique microstructure with a rational combination of hard phases and tough matrix. With the increase of the normal loads and sliding speeds, the friction coefficients of the coatings decrease, while the wear losses increase. The main wear mechanisms of the coatings are micro-cutting wear and multi-plastic deformation wear at low speed and light load conditions, and then gradually change into micro-cutting wear and adhesive wear as well as fatigue fracture accompanied by some oxidation wear at high speed and heavy load conditions.

scholarly journals A Wide Load Current and Voltage Range Switched Capacitor DC–DC Converter with Load Dependent Configurability for Dynamic Voltage Implementation in Miniature Sensors

Energies ◽  
2018 ◽  
Vol 11 (11) ◽  
pp. 3092 ◽  
Author(s):  
Hassan Saif ◽  
Yongmin Lee ◽  
Hyeonji Lee ◽  
Minsun Kim ◽  
Muhammad Khan ◽  
...  
Keyword(s):  
Switched Capacitor ◽  
Peak Efficiency ◽  
Load Range ◽  
Heavy Load ◽  
Load Current ◽  
Voltage Range ◽  
Light Load ◽  
Wide Range ◽  
Dynamic Voltage ◽  
Voltage Swing

Advancements in low power circuits and batteries have enabled the design of miniature sensors with tiny batteries. In such systems, implementing dynamic voltage scaling (DVS) is crucial for maximizing system lifetime. In this paper, a new switched capacitor (SC) converter that is capable of handling a wide range of load currents and output voltages is presented for on-chip DVS implementation. The proposed converter consists of multi-ratio multi-leaf SC stages and reconfigurable interconnect, enabling fine voltage resolution. The stage interconnect scheme enables cascaded or parallel connection of stages. The multi-leaf structure allows load-dependent switch size selection, offering a better trade-off between losses over a wide load range. A limited-voltage-swing switch-driving scheme allows efficient down-conversion from high battery voltage input. A prototype was fabricated in a 180 nm process, providing an output voltage with effective resolution of 16 mV over a load current range of 300 nA to 300 μA (1000×) from a 4 V battery. Efficiency greater than 62% and a peak efficiency of 77% are achieved under a light load (500 nA) over a voltage range of 400 mV to 1.6 V. Efficiency greater than 64% and a peak efficiency of 72% are achieved under a heavy load (200 μA) over a voltage range of 700 mV to 1.6 V.

scholarly journals The effects of ankle stiffness on mechanics and energetics of walking with added loads: a prosthetic emulator study

2019 ◽  
Vol 16 (1) ◽  
Author(s):  
Erica A. Hedrick ◽  
Philippe Malcolm ◽  
Jason M. Wilken ◽  
Kota Z. Takahashi
Keyword(s):  
Energy Cost ◽  
Load Condition ◽  
Metabolic Cost ◽  
Load Carriage ◽  
Metabolic Energy ◽  
Additional Load ◽  
Ankle Stiffness ◽  
Human Ankle ◽  
Positive Work ◽  
Load Conditions

Abstract Background The human ankle joint has an influential role in the regulation of the mechanics and energetics of gait. The human ankle can modulate its joint ‘quasi-stiffness’ (ratio of plantarflexion moment to dorsiflexion displacement) in response to various locomotor tasks (e.g., load carriage). However, the direct effect of ankle stiffness on metabolic energy cost during various tasks is not fully understood. The purpose of this study was to determine how net metabolic energy cost was affected by ankle stiffness while walking under different force demands (i.e., with and without additional load). Methods Individuals simulated an amputation by using an immobilizer boot with a robotic ankle-foot prosthesis emulator. The prosthetic emulator was controlled to follow five ankle stiffness conditions, based on literature values of human ankle quasi-stiffness. Individuals walked with these five ankle stiffness settings, with and without carrying additional load of approximately 30% of body mass (i.e., ten total trials). Results Within the range of stiffness we tested, the highest stiffness minimized metabolic cost for both load conditions, including a ~ 3% decrease in metabolic cost for an increase in stiffness of about 0.0480 Nm/deg/kg during normal (no load) walking. Furthermore, the highest stiffness produced the least amount of prosthetic ankle-foot positive work, with a difference of ~ 0.04 J/kg from the highest to lowest stiffness condition. Ipsilateral hip positive work did not significantly change across the no load condition but was minimized at the highest stiffness for the additional load conditions. For the additional load conditions, the hip work followed a similar trend as the metabolic cost, suggesting that reducing positive hip work can lower metabolic cost. Conclusion While ankle stiffness affected the metabolic cost for both load conditions, we found no significant interaction effect between stiffness and load. This may suggest that the importance of the human ankle’s ability to change stiffness during different load carrying tasks may not be driven to minimize metabolic cost. A prosthetic design that can modulate ankle stiffness when transitioning from one locomotor task to another could be valuable, but its importance likely involves factors beyond optimizing metabolic cost.

scholarly journals Comparing optimized exoskeleton assistance of the hip, knee, and ankle in single and multi-joint configurations

2021 ◽  
Author(s):  
Patrick W. Franks ◽  
Gwendolyn M. Bryan ◽  
Russell M. Martin ◽  
Ricardo Reyes ◽  
Steven H. Collins
Keyword(s):  
Human Mobility ◽  
Metabolic Cost ◽  
Metabolic Energy ◽  
Maximum Effect ◽  
Loop Optimization ◽  
Human In The Loop ◽  
Ankle Joints ◽  
Individual Effects ◽  
Single Well ◽  
Ankle Exoskeleton

Exoskeletons that assist the hip, knee, and ankle joints have begun to improve human mobility, particularly by reducing the metabolic cost of walking. However, direct comparisons of optimal assistance of these joints, or their combinations, have not yet been possible. Assisting multiple joints may be more beneficial than the sum of individual effects, because muscles often span multiple joints, or less effective, because single-joint assistance can indirectly aid other joints. In this study, we used a hip-knee-ankle exoskeleton emulator paired with human-in-the-loop optimization to find single-joint, two-joint, and whole-leg assistance that maximally reduced the metabolic cost of walking for three participants. Hip-only and ankle-only assistance reduced the metabolic cost of walking by 26% and 30% relative to walking in the device unassisted, confirming that both joints are good targets for assistance. Knee-only assistance reduced the metabolic cost of walking by 13%, demonstrating that effective knee assistance is possible. Two-joint assistance reduced the metabolic cost of walking by between 34% and 42%, with the largest improvements coming from hip-ankle assistance. Assisting all three joints reduced the metabolic cost of walking by 50%, showing that at least half of the metabolic energy expended during walking can be saved through exoskeleton assistance. Changes in kinematics and muscle activity indicate that single-joint assistance indirectly assisted muscles at other joints, such that the improvement from whole-leg assistance was smaller than the sum of its single-joint parts. Exoskeletons can assist the entire limb for maximum effect, but a single well-chosen joint can be more efficient when considering additional factors such as weight and cost.

scholarly journals Triceps surae torque-length relationships relevant for walking activity levels with and without an ankle exoskeleton

2019 ◽  
Author(s):  
Anthony L. Hessel ◽  
Brent J. Raiteri ◽  
Michael J. Marsh ◽  
Daniel Hahn
Keyword(s):  
Muscle Activity ◽  
Metabolic Cost ◽  
Activity Levels ◽  
Plantar Flexor ◽  
Plantar Flexors ◽  
Flexor Muscle ◽  
Fascicle Length ◽  
Lateral Gastrocnemius ◽  
Work Requirements ◽  
Ankle Exoskeleton

AbstractAnkle exoskeletons have been developed to assist walking by offloading the plantar flexors work requirements, which reduces muscle activity level. However, reduced muscle activity alters plantar flexor muscle-tendon unit dynamics in a way that is poorly understood. We therefore evaluated torque-fascicle length properties of the soleus and lateral gastrocnemius during voluntary contractions at simulated activity levels typical during late stance with and without an ankle exoskeleton. Soleus activity levels (100, 30, and 22% maximal voluntary activity) were produced by participants via visual electromyography feedback at ankle angles ranging from −10° plantar flexion to 35° dorsiflexion. Using dynamometry and ultrasound imaging, torque-fascicle length data of the soleus and lateral gastrocnemius were produced. The results indicate that muscle activity reductions observed with an exoskeleton shift the torque-angle and torque-fascicle length curves to more dorsiflexed ankle angles and longer fascicle lengths where no descending limb is physiologically possible. This shift is in line with previous simulations that predicted a similar increase in the operating fascicle range when wearing an exoskeleton. These data suggest that a small reduction in muscle activity causes changes to torque-fascicle length properties, which has implications for the design and testing of future ankle exoskeletons for assisted walking.Significance StatementAssistive lower-limb exoskeletons reduce the metabolic cost of walking by reducing the positive work requirements of the plantar flexor muscles. However, if the exoskeleton reduces plantar flexor muscle activity too much, then the metabolic benefit is lost. The biological reasons for this are unclear and hinder further exoskeleton development. This research study is the first to directly evaluate if a reduction in plantar flexor muscle activity similar to that caused by wearing an exoskeleton affects muscle function. We found that reduced muscle activity changes the torque-length properties of two plantar flexors, which could explain why reducing muscle activity too much can increase metabolic cost.

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

2021 ◽  
Author(s):  
Patrick W. Franks ◽  
Gwendolyn M. Bryan ◽  
Ricardo Reyes ◽  
Meghan P. O'Donovan ◽  
Karen N. Gregorczyk ◽  
...  
Keyword(s):  
Metabolic Cost ◽  
Knee Extension ◽  
Cost Of Transport ◽  
Loop Optimization ◽  
Human In The Loop ◽  
Lower Limb Exoskeleton ◽  
Walking Performance ◽  
Ankle Exoskeleton ◽  
The Cost ◽  
Hip Extension

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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