The Experts below are selected from a list of 34647 Experts worldwide ranked by ideXlab platform
Massimo Sartori - One of the best experts on this subject based on the ideXlab platform.
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Voluntary control of wearable robotic Exoskeletons by patients with paresis via neuromechanical modeling
Journal of NeuroEngineering and Rehabilitation, 2019Co-Authors: Guillaume Durandau, Iris Dimbwadyo-terrer, Sergio Lerma-lara, Guillermo Asín-prieto, Juan C. M-moreno, Jose L Pons, Dario Farina, Massimo SartoriAbstract:BackgroundResearch efforts in neurorehabilitation technologies have been directed towards creating robotic Exoskeletons to restore motor function in impaired individuals. However, despite advances in mechatronics and bioelectrical signal processing, current robotic Exoskeletons have had only modest clinical impact. A major limitation is the inability to enable Exoskeleton voluntary control in neurologically impaired individuals. This hinders the possibility of optimally inducing the activity-driven neuroplastic changes that are required for recovery.MethodsWe have developed a patient-specific computational model of the human musculoskeletal system controlled via neural surrogates, i.e., electromyography-derived neural activations to muscles. The electromyography-driven musculoskeletal model was synthesized into a human-machine interface (HMI) that enabled poststroke and incomplete spinal cord injury patients to voluntarily control multiple joints in a multifunctional robotic Exoskeleton in real time.ResultsWe demonstrated patients’ control accuracy across a wide range of lower-extremity motor tasks. Remarkably, an increased level of Exoskeleton assistance always resulted in a reduction in both amplitude and variability in muscle activations as well as in the mechanical moments required to perform a motor task. Since small discrepancies in onset time between human limb movement and that of the parallel Exoskeleton would potentially increase human neuromuscular effort, these results demonstrate that the developed HMI precisely synchronizes the device actuation with residual voluntary muscle contraction capacity in neurologically impaired patients.ConclusionsContinuous voluntary control of robotic Exoskeletons (i.e. event-free and task-independent) has never been demonstrated before in populations with paretic and spastic-like muscle activity, such as those investigated in this study. Our proposed methodology may open new avenues for harnessing residual neuromuscular function in neurologically impaired individuals via symbiotic wearable robots.
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voluntary control of wearable robotic Exoskeletons by patients with paresis via neuromechanical modeling
Journal of Neuroengineering and Rehabilitation, 2019Co-Authors: Guillaume Durandau, Massimo Sartori, Jose L Pons, Dario Farina, Guillermo Asinprieto, Iris Dimbwadyoterrer, Sergio Lermalara, Juan MorenoAbstract:Research efforts in neurorehabilitation technologies have been directed towards creating robotic Exoskeletons to restore motor function in impaired individuals. However, despite advances in mechatronics and bioelectrical signal processing, current robotic Exoskeletons have had only modest clinical impact. A major limitation is the inability to enable Exoskeleton voluntary control in neurologically impaired individuals. This hinders the possibility of optimally inducing the activity-driven neuroplastic changes that are required for recovery. We have developed a patient-specific computational model of the human musculoskeletal system controlled via neural surrogates, i.e., electromyography-derived neural activations to muscles. The electromyography-driven musculoskeletal model was synthesized into a human-machine interface (HMI) that enabled poststroke and incomplete spinal cord injury patients to voluntarily control multiple joints in a multifunctional robotic Exoskeleton in real time. We demonstrated patients’ control accuracy across a wide range of lower-extremity motor tasks. Remarkably, an increased level of Exoskeleton assistance always resulted in a reduction in both amplitude and variability in muscle activations as well as in the mechanical moments required to perform a motor task. Since small discrepancies in onset time between human limb movement and that of the parallel Exoskeleton would potentially increase human neuromuscular effort, these results demonstrate that the developed HMI precisely synchronizes the device actuation with residual voluntary muscle contraction capacity in neurologically impaired patients. Continuous voluntary control of robotic Exoskeletons (i.e. event-free and task-independent) has never been demonstrated before in populations with paretic and spastic-like muscle activity, such as those investigated in this study. Our proposed methodology may open new avenues for harnessing residual neuromuscular function in neurologically impaired individuals via symbiotic wearable robots.
Dirk De Clercq - One of the best experts on this subject based on the ideXlab platform.
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Altering gait variability with an ankle Exoskeleton.
PloS one, 2018Co-Authors: Prokopios Antonellis, Dirk De Clercq, Samuel Galle, Philippe MalcolmAbstract:Exoskeletons can influence human gait. A healthy gait is characterized by a certain amount of variability compared to a non-healthy gait that has more inherent variability; however which Exoskeleton assistance parameters are necessary to avoid increasing gait variability or to potentially lower gait variability below that of unassisted walking are unknown. This study investigated the interaction effects of Exoskeleton timing and power on gait variability. Ten healthy participants walked on a treadmill with bilateral ankle-foot Exoskeletons under ten conditions with different timing (varied from 36% to 54% of the stride) and power (varied from 0.2 to 0.5 W∙kg-1) combinations. We used the largest Lyapunov exponent (LyE) and maximum Floquet multiplier (FM) to evaluate the stride-to-stride fluctuations of the kinematic time series. We found the lowest LyE at the ankle and a significant reduction versus powered-off with Exoskeleton power (summed for both legs) of 0.45 W∙kg-1 and actuation timing at 48% of the stride cycle. At the knee, a significant positive effect of power and a negative interaction effect of power and timing were found for LyE. We found significant positive interaction effects of the square of timing and power for LyE at the knee and hip joints. In contrast, the FM at the ankle increased with increasing power and later timing. We found a significant negative effect of power and a positive interaction effect of power and timing for FM at the knee and no significant effects of any of the Exoskeleton parameters for FM at the hip. The ability of the Exoskeleton to reduce the LyE at the ankle joint offers new possibilities in terms of altering gait variability, which could have applications for using Exoskeletons as rehabilitation devices. Further efforts could examine if it is possible to simultaneously reduce the LyE and FM at one or more lower limb joints.
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Reducing the metabolic cost of walking with an ankle Exoskeleton: interaction between actuation timing and power
Journal of neuroengineering and rehabilitation, 2017Co-Authors: Samuel Galle, Philippe Malcolm, Steven H. Collins, Dirk De ClercqAbstract:Powered ankle-foot Exoskeletons can reduce the metabolic cost of human walking to below normal levels, but optimal assistance properties remain unclear. The purpose of this study was to test the effects of different assistance timing and power characteristics in an experiment with a tethered ankle-foot Exoskeleton. Ten healthy female subjects walked on a treadmill with bilateral ankle-foot Exoskeletons in 10 different assistance conditions. Artificial pneumatic muscles assisted plantarflexion during ankle push-off using one of four actuation onset timings (36, 42, 48 and 54% of the stride) and three power levels (average positive Exoskeleton power over a stride, summed for both legs, of 0.2, 0.4 and 0.5 W∙kg−1). We compared metabolic rate, kinematics and electromyography (EMG) between conditions. Optimal assistance was achieved with an onset of 42% stride and average power of 0.4 W∙kg−1, leading to 21% reduction in metabolic cost compared to walking with the Exoskeleton deactivated and 12% reduction compared to normal walking without the Exoskeleton. With suboptimal timing or power, the Exoskeleton still reduced metabolic cost, but substantially less so. The relationship between timing, power and metabolic rate was well-characterized by a two-dimensional quadratic function. The assistive mechanisms leading to these improvements included reducing muscular activity in the ankle plantarflexors and assisting leg swing initiation. These results emphasize the importance of optimizing Exoskeleton actuation properties when assisting or augmenting human locomotion. Our optimal assistance onset timing and average power levels could be used for other Exoskeletons to improve assistance and resulting benefits.
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Exoskeleton plantarflexion assistance for elderly
Gait and Posture, 2017Co-Authors: Samuel Galle, Wim Derave, Philippe Malcolm, Frederick Bossuyt, Patrick Calders, Dirk De ClercqAbstract:Elderly are confronted with reduced physical capabilities and increased metabolic energy cost of walking. Exoskeletons that assist walking have the potential to restore walking capacity by reducing the metabolic cost of walking. However, it is unclear if current Exoskeletons can reduce energy cost in elderly. Our goal was to study the effect of an Exoskeleton that assists plantarflexion during push-off on the metabolic energy cost of walking in physically active and healthy elderly. Seven elderly (age 69.3 ± 3.5 y) walked on treadmill (1.11 m s2) with normal shoes and with the Exoskeleton both powered (with assistance) and powered-off (without assistance). After 20 min of habituation on a prior day and 5 min on the test day, subjects were able to walk with the Exoskeleton and assistance of the Exoskeleton resulted in a reduction in metabolic cost of 12% versus walking with the Exoskeleton powered-off. Walking with the Exoskeleton was perceived less fatiguing for the muscles compared to normal walking. Assistance resulted in a statistically nonsignificant reduction in metabolic cost of 4% versus walking with normal shoes, likely due to the penalty of wearing the Exoskeleton powered-off. Also, Exoskeleton mechanical power was relatively low compared to previously identified optimal assistance magnitude in young adults. Future Exoskeleton research should focus on further optimizing Exoskeleton assistance for specific populations and on considerate integration of Exoskeletons in rehabilitation or in daily life. As such, Exoskeletons should allow people to walk longer or faster than without assistance and could result in an increase in physical activity and resulting health benefits.
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Optimization of Exoskeleton assistance : timing of actuation and Exoskeleton power
2015Co-Authors: Jozefien Speeckaert, Philippe Malcolm, Samuel Galle, Dirk De ClercqAbstract:Introduction: Robotic devices, called Exoskeletons, are being developed to improve walking metabolic economy of an able-bodied wearer. These devices can assist plantar flexion during walking by means of pneumatic muscles. The timing of actuation and the amount of Exoskeleton power are key parameters for a maximum reduction in metabolic cost. A reduction below the cost of normal walking can be realised if timing of actuation occurs just before heel contact of opposite leg [1]. However, the effect of Exoskeleton power has not been studied for bilateral Exoskeleton walking. The goal of the present study was to optimize the actuation pattern of the Exoskeletons to reduce the cost of legged locomotion. Methods: 13 subjects walked in 12 powered conditions at 1.25 m.s -1 wearing a powered ankle foot Exoskeleton. The powered conditions varied in onset of actuation (31, 36, 41, 46% of stride cycle) and amount of Exoskeleton power (low, medium and high). Each condition lasted 3 minutes in a habituation session and 4 minutes in the actual data collection one week later. Also, one unpowered (=without pneumatic muscle actuation) and one shod condition was done. Full body kinematics, Exoskeleton kinetics, EMG, respiratory gas analysis and perception were measured.
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Walking with a plantar flexion assisting ankle-foot Exoskeleton in an older population
2015Co-Authors: Samuel Galle, Philippe Malcolm, Dirk De ClercqAbstract:Introduction and Objectives: Walking is the most frequent way of locomotion in humans and the ability to walk has a strong influence on quality of life. With the contribution of biomechanists and physiologists in the field of robotics, assistive robotic legs (Exoskeletons) that can be attached to the legs are developed to restore walking ability for subjects with reduced walking capacity. Walking capacity diminishes while getting older and when walking becomes difficult, people are dependent on walking frames, wheelchairs or mobility scooters. These devices are often unpractical and dissociate us from our natural way of interacting with our environment. Reduced walking speed in the elderly is related to reduced ankle power and therefore an ankle-foot Exoskeletons that adds ankle power to the biological ankle joint seems a practical solution to improve their walking capacity. For such mobility assistance, reduction in human energy cost is the benchmark. On the other hand, the assisted walking has to remain a stable gait pattern. Previous research in 3 subjects [1] suggested that the elderly could walk with plantarflexion assistance which resulted in a reduction in metabolic cost but the number of subjects was insufficient to draw conclusions. The objective of this study was to test if a healthy older population (age 65 or more) could walk after a short habituation with a simple pneumatically actuated ankle-foot Exoskeleton with plantarflexion assistance [2], if this results in a reduced metabolic cost for powered Exoskeleton walking compared to walking with normal shoes and if walking stability is influenced. This study must be seen as a necessary step towards the assistance of an older population with walking impairments. Methods: Eight healthy subjects with no specific walking impairments and no experience with treadmill nor Exoskeleton walking participated in the experiment. One subject was not able to walk with the device comfortably because of deviating walking kinematics, which resulted in reduced Exoskeleton function. The seven remaining subjects (6 male and 1 female; age 69.3±3.5 years; body mass 73.1±6.9 kg; stature 170.4±6.2 cm; European shoe size 42.1±1.8) performed a 30 min habituation protocol on a first day. On a second day, subjects performed four 5-min walking intervals at 1.11 m·s-1 (normal shoes, unpowered Exoskeleton and 2 times powered Exoskeleton: Powered 1 and Powered 2). O2 consumption and CO2 production, subjects’ perception and Exoskeleton kinetics were measured for every condition on this second day. Results: Subjects did not perceive walking on the treadmill with their own shoes significantly more difficult than overground walking and perceived Exoskeleton walking during the second powered condition less difficult compared to unpowered Exoskeleton walking. The net metabolic cost during walking with the powered Exoskeleton was significantly reduced with 9.4±6.1% for the first powered condition and 12.0±6.9% in the second powered condition compared to unpowered walking (Fig.). This indicates that also an older population can benefit from plantarflexion assistance. However, no significant differences in net metabolic cost could be found between powered Exoskeleton walking and walking with normal shoes, which is mainly due to the 9.8±8.0% increase in metabolic cost in the powered condition due to the weight and the hindrance of the unpowered Exoskeleton. Recent improvements in Exoskeleton design and function have shown that this penalty could be reduced to 0 to 5%, which would result in a reduction in net metabolic cost for powered walking versus walking with normal shoes, also in an older population. Conclusion: Our findings support the introduction of (ankle-foot) Exoskeletons in the elderly as we found a reduction of more than 12% for powered Exoskeleton walking versus unpowered Exoskeleton walking. However, not all subjects were able to walk with our standard Exoskeleton with a fixed assistance algorithm and further data analysis needs to learn us how walking stability is influenced. Also, regardless of the prior habituation session there seemed to be a habituation effect during the data collection as both the reduction in metabolic cost and the perceived difficulty further reduced from the first to the second powered condition. This suggests that a more individual approach for actuation optimization and a longer habituation, together with improved Exoskeleton design and hardware, could lead to reductions in metabolic cost for powered Exoskeleton walking versus normal walking in the elderly and could ultimately lead to Exoskeletons that can assist elderly (with walking impairments) during daily life.
Philippe Malcolm - One of the best experts on this subject based on the ideXlab platform.
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Altering gait variability with an ankle Exoskeleton.
PloS one, 2018Co-Authors: Prokopios Antonellis, Dirk De Clercq, Samuel Galle, Philippe MalcolmAbstract:Exoskeletons can influence human gait. A healthy gait is characterized by a certain amount of variability compared to a non-healthy gait that has more inherent variability; however which Exoskeleton assistance parameters are necessary to avoid increasing gait variability or to potentially lower gait variability below that of unassisted walking are unknown. This study investigated the interaction effects of Exoskeleton timing and power on gait variability. Ten healthy participants walked on a treadmill with bilateral ankle-foot Exoskeletons under ten conditions with different timing (varied from 36% to 54% of the stride) and power (varied from 0.2 to 0.5 W∙kg-1) combinations. We used the largest Lyapunov exponent (LyE) and maximum Floquet multiplier (FM) to evaluate the stride-to-stride fluctuations of the kinematic time series. We found the lowest LyE at the ankle and a significant reduction versus powered-off with Exoskeleton power (summed for both legs) of 0.45 W∙kg-1 and actuation timing at 48% of the stride cycle. At the knee, a significant positive effect of power and a negative interaction effect of power and timing were found for LyE. We found significant positive interaction effects of the square of timing and power for LyE at the knee and hip joints. In contrast, the FM at the ankle increased with increasing power and later timing. We found a significant negative effect of power and a positive interaction effect of power and timing for FM at the knee and no significant effects of any of the Exoskeleton parameters for FM at the hip. The ability of the Exoskeleton to reduce the LyE at the ankle joint offers new possibilities in terms of altering gait variability, which could have applications for using Exoskeletons as rehabilitation devices. Further efforts could examine if it is possible to simultaneously reduce the LyE and FM at one or more lower limb joints.
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Reducing the metabolic cost of walking with an ankle Exoskeleton: interaction between actuation timing and power
Journal of neuroengineering and rehabilitation, 2017Co-Authors: Samuel Galle, Philippe Malcolm, Steven H. Collins, Dirk De ClercqAbstract:Powered ankle-foot Exoskeletons can reduce the metabolic cost of human walking to below normal levels, but optimal assistance properties remain unclear. The purpose of this study was to test the effects of different assistance timing and power characteristics in an experiment with a tethered ankle-foot Exoskeleton. Ten healthy female subjects walked on a treadmill with bilateral ankle-foot Exoskeletons in 10 different assistance conditions. Artificial pneumatic muscles assisted plantarflexion during ankle push-off using one of four actuation onset timings (36, 42, 48 and 54% of the stride) and three power levels (average positive Exoskeleton power over a stride, summed for both legs, of 0.2, 0.4 and 0.5 W∙kg−1). We compared metabolic rate, kinematics and electromyography (EMG) between conditions. Optimal assistance was achieved with an onset of 42% stride and average power of 0.4 W∙kg−1, leading to 21% reduction in metabolic cost compared to walking with the Exoskeleton deactivated and 12% reduction compared to normal walking without the Exoskeleton. With suboptimal timing or power, the Exoskeleton still reduced metabolic cost, but substantially less so. The relationship between timing, power and metabolic rate was well-characterized by a two-dimensional quadratic function. The assistive mechanisms leading to these improvements included reducing muscular activity in the ankle plantarflexors and assisting leg swing initiation. These results emphasize the importance of optimizing Exoskeleton actuation properties when assisting or augmenting human locomotion. Our optimal assistance onset timing and average power levels could be used for other Exoskeletons to improve assistance and resulting benefits.
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Exoskeleton plantarflexion assistance for elderly
Gait and Posture, 2017Co-Authors: Samuel Galle, Wim Derave, Philippe Malcolm, Frederick Bossuyt, Patrick Calders, Dirk De ClercqAbstract:Elderly are confronted with reduced physical capabilities and increased metabolic energy cost of walking. Exoskeletons that assist walking have the potential to restore walking capacity by reducing the metabolic cost of walking. However, it is unclear if current Exoskeletons can reduce energy cost in elderly. Our goal was to study the effect of an Exoskeleton that assists plantarflexion during push-off on the metabolic energy cost of walking in physically active and healthy elderly. Seven elderly (age 69.3 ± 3.5 y) walked on treadmill (1.11 m s2) with normal shoes and with the Exoskeleton both powered (with assistance) and powered-off (without assistance). After 20 min of habituation on a prior day and 5 min on the test day, subjects were able to walk with the Exoskeleton and assistance of the Exoskeleton resulted in a reduction in metabolic cost of 12% versus walking with the Exoskeleton powered-off. Walking with the Exoskeleton was perceived less fatiguing for the muscles compared to normal walking. Assistance resulted in a statistically nonsignificant reduction in metabolic cost of 4% versus walking with normal shoes, likely due to the penalty of wearing the Exoskeleton powered-off. Also, Exoskeleton mechanical power was relatively low compared to previously identified optimal assistance magnitude in young adults. Future Exoskeleton research should focus on further optimizing Exoskeleton assistance for specific populations and on considerate integration of Exoskeletons in rehabilitation or in daily life. As such, Exoskeletons should allow people to walk longer or faster than without assistance and could result in an increase in physical activity and resulting health benefits.
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Optimization of Exoskeleton assistance : timing of actuation and Exoskeleton power
2015Co-Authors: Jozefien Speeckaert, Philippe Malcolm, Samuel Galle, Dirk De ClercqAbstract:Introduction: Robotic devices, called Exoskeletons, are being developed to improve walking metabolic economy of an able-bodied wearer. These devices can assist plantar flexion during walking by means of pneumatic muscles. The timing of actuation and the amount of Exoskeleton power are key parameters for a maximum reduction in metabolic cost. A reduction below the cost of normal walking can be realised if timing of actuation occurs just before heel contact of opposite leg [1]. However, the effect of Exoskeleton power has not been studied for bilateral Exoskeleton walking. The goal of the present study was to optimize the actuation pattern of the Exoskeletons to reduce the cost of legged locomotion. Methods: 13 subjects walked in 12 powered conditions at 1.25 m.s -1 wearing a powered ankle foot Exoskeleton. The powered conditions varied in onset of actuation (31, 36, 41, 46% of stride cycle) and amount of Exoskeleton power (low, medium and high). Each condition lasted 3 minutes in a habituation session and 4 minutes in the actual data collection one week later. Also, one unpowered (=without pneumatic muscle actuation) and one shod condition was done. Full body kinematics, Exoskeleton kinetics, EMG, respiratory gas analysis and perception were measured.
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Walking with a plantar flexion assisting ankle-foot Exoskeleton in an older population
2015Co-Authors: Samuel Galle, Philippe Malcolm, Dirk De ClercqAbstract:Introduction and Objectives: Walking is the most frequent way of locomotion in humans and the ability to walk has a strong influence on quality of life. With the contribution of biomechanists and physiologists in the field of robotics, assistive robotic legs (Exoskeletons) that can be attached to the legs are developed to restore walking ability for subjects with reduced walking capacity. Walking capacity diminishes while getting older and when walking becomes difficult, people are dependent on walking frames, wheelchairs or mobility scooters. These devices are often unpractical and dissociate us from our natural way of interacting with our environment. Reduced walking speed in the elderly is related to reduced ankle power and therefore an ankle-foot Exoskeletons that adds ankle power to the biological ankle joint seems a practical solution to improve their walking capacity. For such mobility assistance, reduction in human energy cost is the benchmark. On the other hand, the assisted walking has to remain a stable gait pattern. Previous research in 3 subjects [1] suggested that the elderly could walk with plantarflexion assistance which resulted in a reduction in metabolic cost but the number of subjects was insufficient to draw conclusions. The objective of this study was to test if a healthy older population (age 65 or more) could walk after a short habituation with a simple pneumatically actuated ankle-foot Exoskeleton with plantarflexion assistance [2], if this results in a reduced metabolic cost for powered Exoskeleton walking compared to walking with normal shoes and if walking stability is influenced. This study must be seen as a necessary step towards the assistance of an older population with walking impairments. Methods: Eight healthy subjects with no specific walking impairments and no experience with treadmill nor Exoskeleton walking participated in the experiment. One subject was not able to walk with the device comfortably because of deviating walking kinematics, which resulted in reduced Exoskeleton function. The seven remaining subjects (6 male and 1 female; age 69.3±3.5 years; body mass 73.1±6.9 kg; stature 170.4±6.2 cm; European shoe size 42.1±1.8) performed a 30 min habituation protocol on a first day. On a second day, subjects performed four 5-min walking intervals at 1.11 m·s-1 (normal shoes, unpowered Exoskeleton and 2 times powered Exoskeleton: Powered 1 and Powered 2). O2 consumption and CO2 production, subjects’ perception and Exoskeleton kinetics were measured for every condition on this second day. Results: Subjects did not perceive walking on the treadmill with their own shoes significantly more difficult than overground walking and perceived Exoskeleton walking during the second powered condition less difficult compared to unpowered Exoskeleton walking. The net metabolic cost during walking with the powered Exoskeleton was significantly reduced with 9.4±6.1% for the first powered condition and 12.0±6.9% in the second powered condition compared to unpowered walking (Fig.). This indicates that also an older population can benefit from plantarflexion assistance. However, no significant differences in net metabolic cost could be found between powered Exoskeleton walking and walking with normal shoes, which is mainly due to the 9.8±8.0% increase in metabolic cost in the powered condition due to the weight and the hindrance of the unpowered Exoskeleton. Recent improvements in Exoskeleton design and function have shown that this penalty could be reduced to 0 to 5%, which would result in a reduction in net metabolic cost for powered walking versus walking with normal shoes, also in an older population. Conclusion: Our findings support the introduction of (ankle-foot) Exoskeletons in the elderly as we found a reduction of more than 12% for powered Exoskeleton walking versus unpowered Exoskeleton walking. However, not all subjects were able to walk with our standard Exoskeleton with a fixed assistance algorithm and further data analysis needs to learn us how walking stability is influenced. Also, regardless of the prior habituation session there seemed to be a habituation effect during the data collection as both the reduction in metabolic cost and the perceived difficulty further reduced from the first to the second powered condition. This suggests that a more individual approach for actuation optimization and a longer habituation, together with improved Exoskeleton design and hardware, could lead to reductions in metabolic cost for powered Exoskeleton walking versus normal walking in the elderly and could ultimately lead to Exoskeletons that can assist elderly (with walking impairments) during daily life.
Samuel Galle - One of the best experts on this subject based on the ideXlab platform.
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Altering gait variability with an ankle Exoskeleton.
PloS one, 2018Co-Authors: Prokopios Antonellis, Dirk De Clercq, Samuel Galle, Philippe MalcolmAbstract:Exoskeletons can influence human gait. A healthy gait is characterized by a certain amount of variability compared to a non-healthy gait that has more inherent variability; however which Exoskeleton assistance parameters are necessary to avoid increasing gait variability or to potentially lower gait variability below that of unassisted walking are unknown. This study investigated the interaction effects of Exoskeleton timing and power on gait variability. Ten healthy participants walked on a treadmill with bilateral ankle-foot Exoskeletons under ten conditions with different timing (varied from 36% to 54% of the stride) and power (varied from 0.2 to 0.5 W∙kg-1) combinations. We used the largest Lyapunov exponent (LyE) and maximum Floquet multiplier (FM) to evaluate the stride-to-stride fluctuations of the kinematic time series. We found the lowest LyE at the ankle and a significant reduction versus powered-off with Exoskeleton power (summed for both legs) of 0.45 W∙kg-1 and actuation timing at 48% of the stride cycle. At the knee, a significant positive effect of power and a negative interaction effect of power and timing were found for LyE. We found significant positive interaction effects of the square of timing and power for LyE at the knee and hip joints. In contrast, the FM at the ankle increased with increasing power and later timing. We found a significant negative effect of power and a positive interaction effect of power and timing for FM at the knee and no significant effects of any of the Exoskeleton parameters for FM at the hip. The ability of the Exoskeleton to reduce the LyE at the ankle joint offers new possibilities in terms of altering gait variability, which could have applications for using Exoskeletons as rehabilitation devices. Further efforts could examine if it is possible to simultaneously reduce the LyE and FM at one or more lower limb joints.
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Reducing the metabolic cost of walking with an ankle Exoskeleton: interaction between actuation timing and power
Journal of neuroengineering and rehabilitation, 2017Co-Authors: Samuel Galle, Philippe Malcolm, Steven H. Collins, Dirk De ClercqAbstract:Powered ankle-foot Exoskeletons can reduce the metabolic cost of human walking to below normal levels, but optimal assistance properties remain unclear. The purpose of this study was to test the effects of different assistance timing and power characteristics in an experiment with a tethered ankle-foot Exoskeleton. Ten healthy female subjects walked on a treadmill with bilateral ankle-foot Exoskeletons in 10 different assistance conditions. Artificial pneumatic muscles assisted plantarflexion during ankle push-off using one of four actuation onset timings (36, 42, 48 and 54% of the stride) and three power levels (average positive Exoskeleton power over a stride, summed for both legs, of 0.2, 0.4 and 0.5 W∙kg−1). We compared metabolic rate, kinematics and electromyography (EMG) between conditions. Optimal assistance was achieved with an onset of 42% stride and average power of 0.4 W∙kg−1, leading to 21% reduction in metabolic cost compared to walking with the Exoskeleton deactivated and 12% reduction compared to normal walking without the Exoskeleton. With suboptimal timing or power, the Exoskeleton still reduced metabolic cost, but substantially less so. The relationship between timing, power and metabolic rate was well-characterized by a two-dimensional quadratic function. The assistive mechanisms leading to these improvements included reducing muscular activity in the ankle plantarflexors and assisting leg swing initiation. These results emphasize the importance of optimizing Exoskeleton actuation properties when assisting or augmenting human locomotion. Our optimal assistance onset timing and average power levels could be used for other Exoskeletons to improve assistance and resulting benefits.
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Exoskeleton plantarflexion assistance for elderly
Gait and Posture, 2017Co-Authors: Samuel Galle, Wim Derave, Philippe Malcolm, Frederick Bossuyt, Patrick Calders, Dirk De ClercqAbstract:Elderly are confronted with reduced physical capabilities and increased metabolic energy cost of walking. Exoskeletons that assist walking have the potential to restore walking capacity by reducing the metabolic cost of walking. However, it is unclear if current Exoskeletons can reduce energy cost in elderly. Our goal was to study the effect of an Exoskeleton that assists plantarflexion during push-off on the metabolic energy cost of walking in physically active and healthy elderly. Seven elderly (age 69.3 ± 3.5 y) walked on treadmill (1.11 m s2) with normal shoes and with the Exoskeleton both powered (with assistance) and powered-off (without assistance). After 20 min of habituation on a prior day and 5 min on the test day, subjects were able to walk with the Exoskeleton and assistance of the Exoskeleton resulted in a reduction in metabolic cost of 12% versus walking with the Exoskeleton powered-off. Walking with the Exoskeleton was perceived less fatiguing for the muscles compared to normal walking. Assistance resulted in a statistically nonsignificant reduction in metabolic cost of 4% versus walking with normal shoes, likely due to the penalty of wearing the Exoskeleton powered-off. Also, Exoskeleton mechanical power was relatively low compared to previously identified optimal assistance magnitude in young adults. Future Exoskeleton research should focus on further optimizing Exoskeleton assistance for specific populations and on considerate integration of Exoskeletons in rehabilitation or in daily life. As such, Exoskeletons should allow people to walk longer or faster than without assistance and could result in an increase in physical activity and resulting health benefits.
-
Optimization of Exoskeleton assistance : timing of actuation and Exoskeleton power
2015Co-Authors: Jozefien Speeckaert, Philippe Malcolm, Samuel Galle, Dirk De ClercqAbstract:Introduction: Robotic devices, called Exoskeletons, are being developed to improve walking metabolic economy of an able-bodied wearer. These devices can assist plantar flexion during walking by means of pneumatic muscles. The timing of actuation and the amount of Exoskeleton power are key parameters for a maximum reduction in metabolic cost. A reduction below the cost of normal walking can be realised if timing of actuation occurs just before heel contact of opposite leg [1]. However, the effect of Exoskeleton power has not been studied for bilateral Exoskeleton walking. The goal of the present study was to optimize the actuation pattern of the Exoskeletons to reduce the cost of legged locomotion. Methods: 13 subjects walked in 12 powered conditions at 1.25 m.s -1 wearing a powered ankle foot Exoskeleton. The powered conditions varied in onset of actuation (31, 36, 41, 46% of stride cycle) and amount of Exoskeleton power (low, medium and high). Each condition lasted 3 minutes in a habituation session and 4 minutes in the actual data collection one week later. Also, one unpowered (=without pneumatic muscle actuation) and one shod condition was done. Full body kinematics, Exoskeleton kinetics, EMG, respiratory gas analysis and perception were measured.
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Walking with a plantar flexion assisting ankle-foot Exoskeleton in an older population
2015Co-Authors: Samuel Galle, Philippe Malcolm, Dirk De ClercqAbstract:Introduction and Objectives: Walking is the most frequent way of locomotion in humans and the ability to walk has a strong influence on quality of life. With the contribution of biomechanists and physiologists in the field of robotics, assistive robotic legs (Exoskeletons) that can be attached to the legs are developed to restore walking ability for subjects with reduced walking capacity. Walking capacity diminishes while getting older and when walking becomes difficult, people are dependent on walking frames, wheelchairs or mobility scooters. These devices are often unpractical and dissociate us from our natural way of interacting with our environment. Reduced walking speed in the elderly is related to reduced ankle power and therefore an ankle-foot Exoskeletons that adds ankle power to the biological ankle joint seems a practical solution to improve their walking capacity. For such mobility assistance, reduction in human energy cost is the benchmark. On the other hand, the assisted walking has to remain a stable gait pattern. Previous research in 3 subjects [1] suggested that the elderly could walk with plantarflexion assistance which resulted in a reduction in metabolic cost but the number of subjects was insufficient to draw conclusions. The objective of this study was to test if a healthy older population (age 65 or more) could walk after a short habituation with a simple pneumatically actuated ankle-foot Exoskeleton with plantarflexion assistance [2], if this results in a reduced metabolic cost for powered Exoskeleton walking compared to walking with normal shoes and if walking stability is influenced. This study must be seen as a necessary step towards the assistance of an older population with walking impairments. Methods: Eight healthy subjects with no specific walking impairments and no experience with treadmill nor Exoskeleton walking participated in the experiment. One subject was not able to walk with the device comfortably because of deviating walking kinematics, which resulted in reduced Exoskeleton function. The seven remaining subjects (6 male and 1 female; age 69.3±3.5 years; body mass 73.1±6.9 kg; stature 170.4±6.2 cm; European shoe size 42.1±1.8) performed a 30 min habituation protocol on a first day. On a second day, subjects performed four 5-min walking intervals at 1.11 m·s-1 (normal shoes, unpowered Exoskeleton and 2 times powered Exoskeleton: Powered 1 and Powered 2). O2 consumption and CO2 production, subjects’ perception and Exoskeleton kinetics were measured for every condition on this second day. Results: Subjects did not perceive walking on the treadmill with their own shoes significantly more difficult than overground walking and perceived Exoskeleton walking during the second powered condition less difficult compared to unpowered Exoskeleton walking. The net metabolic cost during walking with the powered Exoskeleton was significantly reduced with 9.4±6.1% for the first powered condition and 12.0±6.9% in the second powered condition compared to unpowered walking (Fig.). This indicates that also an older population can benefit from plantarflexion assistance. However, no significant differences in net metabolic cost could be found between powered Exoskeleton walking and walking with normal shoes, which is mainly due to the 9.8±8.0% increase in metabolic cost in the powered condition due to the weight and the hindrance of the unpowered Exoskeleton. Recent improvements in Exoskeleton design and function have shown that this penalty could be reduced to 0 to 5%, which would result in a reduction in net metabolic cost for powered walking versus walking with normal shoes, also in an older population. Conclusion: Our findings support the introduction of (ankle-foot) Exoskeletons in the elderly as we found a reduction of more than 12% for powered Exoskeleton walking versus unpowered Exoskeleton walking. However, not all subjects were able to walk with our standard Exoskeleton with a fixed assistance algorithm and further data analysis needs to learn us how walking stability is influenced. Also, regardless of the prior habituation session there seemed to be a habituation effect during the data collection as both the reduction in metabolic cost and the perceived difficulty further reduced from the first to the second powered condition. This suggests that a more individual approach for actuation optimization and a longer habituation, together with improved Exoskeleton design and hardware, could lead to reductions in metabolic cost for powered Exoskeleton walking versus normal walking in the elderly and could ultimately lead to Exoskeletons that can assist elderly (with walking impairments) during daily life.
Hugh M Herr - One of the best experts on this subject based on the ideXlab platform.
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ICRA - An Autonomous Exoskeleton for Ankle Plantarflexion Assistance
2019 International Conference on Robotics and Automation (ICRA), 2019Co-Authors: Xingbang Yang, Hugh M Herr, Jiun-yih KuanAbstract:Lower-limb Exoskeletons are of great interest in the robotics community because of their various applications in enhancement and rehabilitation. In this paper we present an autonomous Exoskeleton platform for ankle plantarflexion assistance. The untethered Exoskeleton has a high efficiency transmission system with reduction ratio of 27.4:1. This allows relocating the actuator to the wearer’s hip, which reduces device inertia. A feed-forward controller based on field oriented control was implemented to control the brushless DC motor on the Exoskeleton. Through various performance tests, the Exoskeleton was shown to provide a torque control bandwidth of 17.5Hz and can effectively track biological torque profiles. The augmentation factor (AF) of the Exoskeleton is 64.7W, implying potential to reduce walking metabolic cost. This Exoskeleton establishes an autonomous platform for experiments involving ankle assistance.
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autonomous Exoskeleton reduces metabolic cost of human walking
Journal of Neuroengineering and Rehabilitation, 2014Co-Authors: Luke M. Mooney, Elliott J. Rouse, Hugh M HerrAbstract:Passive Exoskeletons that assist with human locomotion are often lightweight and compact, but are unable to provide net mechanical power to the exoskeletal wearer. In contrast, powered Exoskeletons often provide biologically appropriate levels of mechanical power, but the size and mass of their actuator/power source designs often lead to heavy and unwieldy devices. In this study, we extend the design and evaluation of a lightweight and powerful autonomous Exoskeleton evaluated for loaded walking in (J Neuroeng Rehab 11:80, 2014) to the case of unloaded walking conditions. The metabolic energy consumption of seven study participants (85 ± 12 kg body mass) was measured while walking on a level treadmill at 1.4 m/s. Testing conditions included not wearing the Exoskeleton and wearing the Exoskeleton, in both powered and unpowered modes. When averaged across the gait cycle, the autonomous Exoskeleton applied a mean positive mechanical power of 26 ± 1 W (13 W per ankle) with 2.12 kg of added exoskeletal foot-shank mass (1.06 kg per leg). Use of the leg Exoskeleton significantly reduced the metabolic cost of walking by 35 ± 13 W, which was an improvement of 10 ± 3% (p = 0.023) relative to the control condition of not wearing the Exoskeleton. The results of this study highlight the advantages of developing lightweight and powerful Exoskeletons that can comfortably assist the body during walking.
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Autonomous Exoskeleton reduces metabolic cost of human walking during load carriage
Journal of NeuroEngineering and Rehabilitation, 2014Co-Authors: Luke M. Mooney, Elliott J. Rouse, Hugh M HerrAbstract:Many soldiers are expected to carry heavy loads over extended distances, often resulting in physical and mental fatigue. In this study, the design and testing of an autonomous leg Exoskeleton is presented. The aim of the device is to reduce the energetic cost of loaded walking. In addition, we present the Augmentation Factor, a general framework of exoskeletal performance that unifies our results with the varying abilities of previously developed Exoskeletons. We developed an autonomous battery powered Exoskeleton that is capable of providing substantial levels of positive mechanical power to the ankle during the push-off region of stance phase. We measured the metabolic energy consumption of seven subjects walking on a level treadmill at 1.5 m/s, while wearing a 23 kg vest. During the push-off portion of the stance phase, the Exoskeleton applied positive mechanical power with an average across the gait cycle equal to 23 ± 2 W (11.5 W per ankle). Use of the autonomous leg Exoskeleton significantly reduced the metabolic cost of walking by 36 ± 12 W, which was an improvement of 8 ± 3% (p = 0.025) relative to the control condition of not wearing the Exoskeleton. In the design of leg Exoskeletons, the results of this study highlight the importance of minimizing exoskeletal power dissipation and added limb mass, while providing substantial positive power during the walking gait cycle.
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A QUASI-PASSIVE LEG Exoskeleton FOR LOAD-CARRYING AUGMENTATION
International Journal of Humanoid Robotics, 2007Co-Authors: Conor James Walsh, Ken Endo, Hugh M HerrAbstract:A quasi-passive leg Exoskeleton is presented for load-carrying augmentation during walk- ing. The Exoskeleton has no actuators, only ankle and hip springs and a knee variable- damper. Without a payload, the Exoskeleton weighs 11.7kg and requires only 2 Watts of electrical power during loaded walking. For a 36 kg payload, we demonstrate that the quasi-passive Exoskeleton transfers on average 80% of the load to the ground during the single support phase of walking. By measuring the rate of oxygen consumption on a study participant walking at a self-selected speed, we find that the Exoskeleton slightly increases the walking metabolic cost of transport (COT) as compared to a standard loaded backpack (10% increase). However, a similar Exoskeleton without joint springs or damping control (zero-impedance Exoskeleton) is found to increase COT by 23% com- pared to the loaded backpack, highlighting the benefits of passive and quasi-passive joint mechanisms in the design of efficient, low-mass leg Exoskeletons.
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Development of a lightweight, underactuated Exoskeleton for load-carrying augmentation
Proceedings - IEEE International Conference on Robotics and Automation, 2006Co-Authors: Conor James Walsh, William Grand, Daniel Paluska, Andrew Valiente, Kenneth Pasch, Hugh M HerrAbstract:Metabolic studies have shown that there is a metabolic cost associated with carrying load. Several leg Exoskeletons have been developed by various groups in an attempt to augment the load carrying capability of the human. Previous research efforts have not fully exploited the passive dynamics of walking and have largely focused on fully actuated Exoskeletons that are heavy with large energy requirements. In this paper, a lightweight, underactuated Exoskeleton design is presented that runs in parallel to the human and supports the weight of a payload. Two Exoskeleton architectures are pursued based on examining human walking data. A first architecture consists of springs at the hip, a variable impedance device at the knee, and springs at the ankle. A second architecture replaces the springs at the hip with a non-conservative actuator to examine the effect of adding power at desired instances throughout the gait cycle. Preliminary studies show that an efficient, underactuated leg Exoskeleton can effectively transmit payload forces to the ground during the walking cycle