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Experimental Implementation of Underactuated Potential Energy Shaping on a Powered Ankle-Foot Orthosis.

ABSTRACT: Traditional control methodologies of rehabilitation orthoses/exoskeletons aim at replicating normal kinematics and thus fall into the category of kinematic control. This control paradigm depends on pre-defined reference trajectories, which can be difficult to adjust between different locomotor tasks and human subjects. An alternative control category, kinetic control, enforces kinetic goals (e.g., torques or energy) instead of kinematic trajectories, which could provide a flexible learning environment for the user while freeing up therapists to make corrections. We propose that the theory of underactuated potential energy shaping, which falls into the category of kinetic control, could be used to generate virtual body-weight support for stroke gait rehabilitation. After deriving the nonlinear control law and simulating it on a human-like biped model, we implemented this controller on a powered ankle-foot orthosis that was designed specifically for testing torque control strategies. Experimental results with an able-bodied human subject demonstrate the feasibility of the control approach for both positive and negative virtual body-weight augmentation.

SUBMITTER: Lv G

PROVIDER: S-EPMC4932867 | biostudies-literature | 2016 May

REPOSITORIES: biostudies-literature

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Experimental Implementation of Underactuated Potential Energy Shaping on a Powered Ankle-Foot Orthosis.

Lv Ge G Zhu Hanqi H Elery Toby T Li Luwei L Gregg Robert D RD

IEEE International Conference on Robotics and Automation : ICRA : [proceedings]. IEEE International Conference on Robotics and Automation 20160501

Traditional control methodologies of rehabilitation orthoses/exoskeletons aim at replicating normal kinematics and thus fall into the category of <i>kinematic control</i>. This control paradigm depends on pre-defined reference trajectories, which can be difficult to adjust between different locomotor tasks and human subjects. An alternative control category, <i>kinetic control</i>, enforces kinetic goals (e.g., torques or energy) instead of kinematic trajectories, which could provide a flexible ...[more]

PMID: 27390625

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Project description:ObjectiveTo explore the perceptions of wearing an ankle-foot orthosis (AFO) in patients with peripheral artery disease (PAD) who did and did not adopt the AFO intervention. This follows a clinical trial of the effectiveness of an AFO in improving walking distances for patients with PAD-related claudication.DesignA randomized crossover trial of standard of care and an AFO for 3 months. Semistructured interviews were conducted 1.5 months into the AFO intervention to understand acceptability, demand, implementation, and practicality. Data were analyzed using a summative content analysis approach.SettingVascular surgery clinic and biomechanics research laboratory.ParticipantsPatients (N=15; male, 100%; age, 71.9±.6.7y; body mass index [calculated as weight in kilograms divided by height in meters squared], 29.0±.5.5; ankle brachial index: AFO intervention withdrawal, 0.543; AFO intervention completion, 0.740) with claudication completed the study, and 6 withdrew prior to intervention completion.InterventionsA certified orthotist fit participants with an AFO that was worn for 3 months.Main outcome measuresQualitative analysis of the semistructured interviews.ResultsKey differences were reported between AFO intervention completion and AFO intervention withdrawal. Six of 14 of AFO intervention completion participants described their initial reactions to the AFO as negative vs 3 of 6 AFO intervention withdrawal participants. Only 5 of 15 AFO intervention completion participants reported minimal use of the AFO compared with 5 of 6 AFO intervention withdrawal participants. The AFO intervention withdrawal group reported higher levels of physical discomfort with the use of the AFO (4/6 vs 7/15) and preexisting health issues becoming a barrier to the use of the AFO (3/6 vs 5/15). Positive aspects reported included ease in standing and walking for AFO intervention withdrawal (4/6) and AFO intervention completion groups (13/15) as well as walking straighter and longer with less pain for AFO intervention withdrawal (3/6) and AFO intervention completion groups (9/15).ConclusionsPatients withdrawing prior to completion of AFO intervention tended to have more negative perceptions, more comorbidities, and more physical discomfort than those completing the intervention. Both groups reported positive aspects of the AFO. Implementation studies are needed to address barriers to AFO adoption.

Project description:BackgroundIn the last decades, several powered ankle-foot orthoses have been developed to assist the ankle joint of their users during walking. Recent studies have shown that the effects of the assistance provided by powered ankle-foot orthoses depend on the assistive profile. In compliant actuators, the stiffness level influences the actuator's performance. However, the effects of this parameter on the users has not been yet evaluated. The goal of this study is to assess the effects of the assistance provided by a variable stiffness ankle actuator on healthy young users. More specifically, the effect of different onset times of the push-off torque and different actuator's stiffness levels has been investigated.MethodsEight healthy subjects walked with a unilateral powered ankle-foot orthosis in several assisted walking trials. The powered orthosis was actuated in the sagittal plane by a variable stiffness actuator. During the assisted walking trials, three different onset times of the push-off assistance and three different actuator's stiffness levels were used. The metabolic cost of walking, lower limb muscles activation, joint kinematics, and gait parameters measured during different assisted walking trials were compared to the ones measured during normal walking and walking with the powered orthosis not providing assistance.ResultsThis study found trends for more compliant settings of the ankle actuator resulting in bigger reductions of the metabolic cost of walking and soleus muscle activation in the stance phase during assisted walking as compared to the unassisted walking trial. In addition to this, the study found that, among the tested onset times, the earlier ones showed a trend for bigger reductions of the activation of the soleus muscle during stance, while the later ones led to a bigger reduction in the metabolic cost of walking in the assisted walking trials as compared to the unassisted condition.ConclusionsThis study presents a first attempt to show that, together with the assistive torque profile, also the stiffness level of a compliant ankle actuator can influence the assistive performance of a powered ankle-foot orthosis.

Project description:Background Impairments of trunk movements in gait of stroke are often reported. Ankle foot orthosis (AFO) is commonly used to improve gait of stroke; however, the effect of different types of AFOs on the pelvic and thoracic movements during gait in stroke has not been clarified. Methods Thirty-four patients with stroke were randomly allocated to undergo 2 weeks of gait training by physiotherapists while wearing a rigid AFO (RAFO) with a fixed ankle or an AFO with an oil damper (AFO-OD) that provides plantarflexion resistance and free dorsiflexion. A motion capture system was used for measurements of shod gait without AFO at baseline and with and without AFO after gait training. Two-way repeated ANOVA, Wilcoxon signed-rank test, and Mann–Whitney U test were performed for the data after the gait training to know the effect of different kinds of AFOs. Results Twenty-nine patients completed the study (AFO-OD group: 14, RAFO group: 15). Interactions were found in pelvic rotation angle, change of shank-to-vertical angle (SVA) in the stance, and paretic to non-paretic step length, which increased in AFO-OD group with AFOs (p < 0.05), while the SVA decreased in RAFO group with AFOs (p < 0.05). The main effects were found in pelvic rotation at the contralateral foot off, and thoracic tilt at foot off when an AFO was worn. The change of SVA in stance was positively correlated with the pelvic rotation in the AFO-OD group (r = 0.558). At initial contact, pelvic rotation was positively correlated with thoracic rotation in both groups. Conclusions The findings in 29 patients with stroke showed that pelvic and thoracic movements especially the rotation were affected by the type of AFOs. Pelvic rotation and lower limb kinematics exhibited significant improvements with AFO-OD, reflecting more desirable gait performance. On the other hand, the increase in thoracic in-phase rotation might expose the effect of insufficient trunk control and dissociation movement. Trial registration UMIN000038694, Registered 21 November 2019, https://center6.umin.ac.jp/cgi-open-bin/ctr_e/ctr_his_list.cgi?recptno=R000044048. Supplementary Information The online version contains supplementary material available at 10.1186/s12938-023-01068-0.

Project description:BackgroundThe stiffness of a dorsal leaf AFO that minimizes walking energy cost in people with plantarflexor weakness varies between individuals. Using predictive simulations, we studied the effects of plantarflexor weakness, passive plantarflexor stiffness, body mass, and walking speed on the optimal AFO stiffness for energy cost reduction.MethodsWe employed a planar, nine degrees-of-freedom musculoskeletal model, in which for validation maximal strength of the plantar flexors was reduced by 80%. Walking simulations, driven by minimizing a comprehensive cost function of which energy cost was the main contributor, were generated using a reflex-based controller. Simulations of walking without and with an AFO with stiffnesses between 0.9 and 8.7 Nm/degree were generated. After validation against experimental data of 11 people with plantarflexor weakness using the Root-mean-square error (RMSE), we systematically changed plantarflexor weakness (range 40-90% weakness), passive plantarflexor stiffness (range: 20-200% of normal), body mass (+ 30%) and walking speed (range: 0.8-1.2 m/s) in our baseline model to evaluate their effect on the optimal AFO stiffness for energy cost minimization.ResultsOur simulations had a RMSE < 2 for all lower limb joint kinetics and kinematics except the knee and hip power for walking without AFO. When systematically varying model parameters, more severe plantarflexor weakness, lower passive plantarflexor stiffness, higher body mass and walking speed increased the optimal AFO stiffness for energy cost minimization, with the largest effects for severity of plantarflexor weakness.ConclusionsOur forward simulations demonstrate that in individuals with bilateral plantarflexor the necessary AFO stiffness for walking energy cost minimization is largely affected by severity of plantarflexor weakness, while variation in walking speed, passive muscle stiffness and body mass influence the optimal stiffness to a lesser extent. That gait deviations without AFO are overestimated may have exaggerated the required support of the AFO to minimize walking energy cost. Future research should focus on improving predictive simulations in order to implement personalized predictions in usual care. Trial Registration Nederlands Trial Register 5170. Registration date: May 7th 2015. http://www.trialregister.nl/trialreg/admin/rctview.asp?TC=5170.

Dataset Information

Experimental Implementation of Underactuated Potential Energy Shaping on a Powered Ankle-Foot Orthosis.

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Experimental Implementation of Underactuated Potential Energy Shaping on a Powered Ankle-Foot Orthosis.

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