Designing optimal controls by parameter optimization for a stance-control knee-ankle-foot orthosis

Inverse dynamics simulation is often used in robotic and mechatronic systems to track a desired trajectory by feed-forward control. Musculoskeletal multibody systems are highly overactuated and show a switching number of closed kinematical loops. The method of inverse dynamics is also successfully applied to overactuated systems by parameter optimization for two- and three-dimensional models of the human musculoskeletal system. The presented simulation approach is fully based on optimizationPostprint (published version

Lower-Limb Exosuits for Rehabilitation or Assistance of Human Movement: A Systematic Review

Background: The aim of this review is to provide a comprehensive overview of the technological state-of-the-art of exosuits and the clinical results obtained when applied to users with mobility impairment. Methods: Searches are carried out in the COCHRANE, PubMed, IEEE Xplore and MEDLINE databases. Titles, abstracts and full texts are screened for inclusion criteria. Technological and clinical data are extracted. The quality of the studies is evaluated via a study quality assessment tool. Results: 19 studies are identified as relevant. Active (47%) and passive exosuits (53%) are used. Most are used untethered (84%), accommodating the demand of mobility. No study reports power consumption, which is important for dimensioning power systems. Fields of applications are post-stroke (79%), osteoarthritis (16%) and post-trauma (5%). Mostly the ankle joint is addressed (57%), while less studies address multiple joints (21%). The outcomes of clinical evaluations of lower-limb exosuits with patients suffering from mobility impairments are positive in the correction of gait pattern and reducing metabolic energy consumption during hemiparetic walking. Conclusions: Lower-limb exosuits for clinical applications are still facing technological challenges. Fields of application are limited to stroke, osteoarthritis and trauma. While clinical outcomes are overall positive, improvements in the study protocols are suggested.Peer ReviewedObjectius de Desenvolupament Sostenible::3 - Salut i BenestarPostprint (published version

A review of lower-limb wearable exoskeletons for overground rehabilitation

Gait disorders are common among people with neuromuscular impairments –60% of the patients– and generally have a high impact on their quality of life . Lack of physical activity increases the risk of secondary health conditions such as respiratory and cardiovascular complications, bowel/bladder dysfunction, obesity, osteoporosis and ulcers; which can further diminish life expectancy. Therefore, walking recovery is one of the main rehabilitation priorities for patients with a neuromuscular impairment. Wearable exoskeletons are emerging as a revolutionary device for gait rehabilitation, mainly due to both the active participation required from the user promoting physical activity10 and the possibility to work as an assistive device in the community. In fact, the number of research studies during the past 10 years has shown a large increase following the general tendency of rehabilitation robotics . Although wearable exoskeletons are starting to be used in clinical practice, their efficacy is still not clear. This study provides a comprehensive overview on wearable powered exoskeletons for overground rehabilitation without body weight support in people with neuromuscular impairments.Peer ReviewedPostprint (published version

Some aspects of heel strike impact dynamics in the stability of bipedal locomotion

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Influence of the controller design on the accuracy of a forward dynamic simulation of human gait

The analysis of a captured motion can be addressed by means of forward or inverse dynamics approaches. For this purpose, a 12 segment 2D model with 14 degrees of freedom is developed and both methods are implemented using multibody dynamics techniques. The inverse dynamic analysis uses the experimentally captured motion to calculate the joint torques produced by the musculoskeletal system during the movement. This information is then used as input data for a forward dynamic analysis without any control design. This approach is able to reach the desired pattern within half cycle. In order to achieve the simulation of the complete gait cycle two different control strategies are implemented to stabilize all degrees of freedom: a proportional derivative (PD) control and a computed torque control (CTC). The selection of the control parameters is presented in this work: a kinematic perturbation is used for tuning PD gains, and pole placement techniques are used in order to determine the CTC parameters. A performance evaluation of the two controllers is done in order to quantify the accuracy of the simulated motion and the control torques needed when using one or the other control approach to track a known human walking pattern.Postprint (author's final draft

Performance evaluation of different control strategies for the forward dynamic simulation of human gait

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Analysis of muscle synergies and activation–deactivation patterns in subjects with anterior cruciate ligament deficiency during walking

The knowledge of muscle activation patterns when doing a certain task in subjects with anterior cruciate ligament deficiency could help to improve their rehabilitation treatment. The goal of this study is to identify differences in such patterns between anterior cruciate ligament–deficient and healthy subjects during walking. Methods Electromyographic data for eight muscles were measured in a sample of eighteen subjects with anterior cruciate ligament deficiency, in both injured (ipsilateral group) and non-injured (contralateral group) legs, and a sample of ten healthy subjects (control group). The analysis was carried out at two levels: activation-–deactivation patterns and muscle synergies. Muscle synergy components were calculated using a non-negative matrix factorization algorithm. Findings The results showed that there was a higher co-contraction in injured than in healthy subjects. Although all muscles were activated similarly since all subjects developed the same task (walking), some differences could be observed among the analyzed groups. Interpretation The observed differences in the synergy components of injured subjects suggested that those individuals alter muscle activation patterns to stabilize the knee joint. This analysis could provide valuable information for the physiotherapist to identify alterations in muscle activation patterns during the follow-up of the subject’s rehabilitation.Postprint (author's final draft

Analysis of friction coupling and the Painlevé paradox in multibody systems

Multibody models are useful to describe the macroscopic motion of the elements of physical systems. Modeling contact in such systems can be challenging, especially if friction at the contact interface is taken into account. Furthermore, the dynamics equations of multibody systems with contacts and Coulomb friction may become ill-posed due to friction coupling, as in the Painlevé paradox, where a solution for system dynamics may not be found. Here, the dynamics problem is considered following a general approach so that friction phenomena, such as dynamic jamming, can be analyzed. The effect of the contact forces on the velocity field of the system is the cornerstone of the proposed formulation, which is used to analyze friction coupling in multibody systems with a single contact. In addition, we introduce a new representation of the so-called generalized friction cone, a quadratic form defined in the contact velocity space. The geometry of this cone can be used to determine the critical cases where the solvability of the system dynamic equations can be compromised. Moreover, it allows for assessing friction coupling at the contact interface, and obtaining the values of the friction coefficient that can make the dynamics formulation inconsistent. Finally, the classical Painlevé example of a single rod and the multibody model of an articulated arm are used to illustrate how the proposed cone can detect the cases where the dynamic equations have no solution, or multiple solutions.Postprint (author's final draft

The discretized coulomb friction model in a non-singular complementarity formulation for multibody systems with contacts

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Simulación predictiva de la marcha asistida para la personalización de ortesis activas para lesionados medulares

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