El dispositivo de accionamiento para ortesis activa comprende unos soportes proximal y distal (1, 2) previstos para ser fijados a unas partes proximal y distal de la ortesis, respectivamente. Los soportes proximal y distal (1, 2) están conectados entre sí por una articulación de soporte (3). En el soporte proximal (1) están instalados un husillo (5) conectado operativamente para ser girado por un motor eléctrico (4), una corredera (10) movible a lo largo de unas guías lineales (11) paralela al husillo (5), una tuerca (9) fijada a la corredera (10) y acoplada al husillo (5). Una biela (6) tiene un primer extremo conectado a la corredera (10) por una articulación proximal (7) y un segundo extremo conectado al soporte distal (2) por una articulación distal (8). La biela (6) convierte el movimiento de la corredera (10) en un giro del soporte distal (2) alrededor de la articulación de soporte (3).
Pàmies-Vilà, R.; Pätkau, O.; Doria-Cerezo, A.; Font-Llagunes, J.M. Mechanism and machine theory Vol. 107, p. 123-138 DOI: 10.1016/j.mechmachtheory.2016.09.002 Data de publicació: 2017-01 Article en revista
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.
Romero, F.; Alonso, F.J.; Gragera, C.; Lugrís, U.; Font-Llagunes, J.M. Journal of the Brazilian Society of Mechanical Sciences and Engineering Vol. 38, num. 8, p. 2213-2223 DOI: 10.1007/s40430-016-0575-x Data de publicació: 2016-12-01 Article en revista
The estimation of muscular forces is useful in several areas such as biomedical or rehabilitation engineering. As muscular forces cannot be measured in vivo non-invasively they must be estimated by using indirect measurements such as surface electromyography (sEMG) signals or by means of inverse dynamic (ID) analyses. This paper proposes an approach to estimate muscular forces based on both of them. The main idea is to tune a gain matrix so as to compute muscular forces from sEMG signals. To do so, a curve fitting process based on least-squares is carried out. The input is the sEMG signal filtered using singular spectrum analysis technique. The output corresponds to the muscular force estimated by the ID analysis of the recorded task, a dumbbell weightlifting. Once the model parameters are tuned, it is possible to obtain an estimation of muscular forces based on sEMG signal. This procedure might be used to predict muscular forces in vivo outside the space limitations of the gait analysis laboratory.
The evaluation of contact forces during an impact requires the use of continuous force-based methods. An accurate prediction of the impact force demands the identification of the contact parameters on a case-by-case basis. In this paper, the preimpact effective kinetic energy is put forward as an indicator of the intensity of the impact force along the contact normal direction. This represents a part of the total kinetic energy of the system that is associated with the subspace of constrained motion defined by the impact constraints at the moment of contact onset. Its value depends only on the mechanical parameters and the configuration of the system. We illustrate in this paper that this indicator can be used to characterize the impact force intensity. The suitability of this indicator is confirmed by numerical simulations and experiments.
The evaluation of contact forces during an impact requires the use of continuous force-based methods. An accurate prediction of the impact force demands the identification of the contact parameters on a case-by-case basis. In this paper, the preimpact effective kinetic energy (Formula presented.) is put forward as an indicator of the intensity of the impact force along the contact normal direction. This represents a part of the total kinetic energy of the system that is associated with the subspace of constrained motion defined by the impact constraints at the moment of contact onset. Its value depends only on the mechanical parameters and the configuration of the system. We illustrate in this paper that this indicator can be used to characterize the impact force intensity. The suitability of this indicator is confirmed by numerical simulations and experiments
Serrancoli, G.; Kinney, A.L.; Fregly, B.J.; Font-Llagunes, J.M. Journal of biomechanical engineering Vol. 138, num. 8, p. 081001-1-081001-11 DOI: 10.1115/1.4033673 Data de publicació: 2016-08-01 Article en revista
The study of inertial forces effects at high speeds in flexible parallel manipulators, which generate undesired deviations, is a challenging task due to the coupled and complicated equations of motion. A dynamic model of the Revolute Prismatic Revolute (RPR) planar manipulators (specifically 3-RPR, 2-RPR and 1-RPR) with flexible intermediate links is developed based on the assumed mode method. The flexible intermediate links are modeled as Euler-Bernoulli beams with fixed-free boundary conditions. Using the Lagrange multipliers, a generalized set of differential algebraic equations (DAEs) of motion is developed. In the simulations, the rigid body motion of the end-effector is constrained by some moving constraint equations while the vibrations of the flexible intermediate links cause deviations from the desired trajectory. From this analysis, the dynamic performance of the manipulators when tracking a desired trajectory is evaluated. A comparison of the results indicates that in some cases, adding each extra RPR chain in the n-RPR planar manipulators with flexible intermediate links reduces the stiffness and accuracy due to the inertial forces of the flexible links, which is opposite to what would be expected. The study provides insights to the design, control and suitable selection of the flexible manipulators.
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.
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.
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.
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.
The dynamic analysis and simulation of human gait using multibody dynamics techniques has been a major area of research in the last decades. Nevertheless, not much attention has been paid to the analysis and simulation of robotic-assisted gait. Simulation is a very powerful tool both for assisting the design stage of active rehabilitation robots and predicting the subject–orthoses cooperation and the resulting aesthetic gait. This paper presents a parameter optimization approach that allows simulating gait motion patterns in the particular case of a subject with incomplete spinal cord injury (SCI) wearing active knee–ankle–foot orthoses at both legs. The subject is modelled as a planar multibody system actuated through the main lower limb muscle groups. A muscle force-sharing problem is solved to obtain optimal muscle activation patterns. Furthermore, denervation of muscle groups caused by the SCI is parameterized to account for different injury severities. The active orthoses are modelled as external devices attached to the legs, and their dynamic and performance parameters are taken from a real prototype. Numerical results using energetic and aesthetic objective functions, and considering different SCI severities are obtained. Detailed discussions are given related to the different motion and actuation patterns both from muscles and orthoses. The proposed methodology opens new perspectives towards the prediction of human-assisted gait, which can be very helpful for the design of new rehabilitation robots.
Romero, F.; Pàmies-Vilà, R.; Lugrís, U.; Alonso, F.J.; Font-Llagunes, J.M.; Cuadrado, J. Reunión del Capítulo Español de la Sociedad Europea de Biomecánica p. 6- Data de presentació: 2015-11-20 Presentació treball a congrés
Tassani, S.; Peiret, A.; Bosch, E.; Serrancoli, G.; Noailly, J.; Font-Llagunes, J.M. Reunión del Capítulo Español de la Sociedad Europea de Biomecánica p. 30 Data de presentació: 2015-11-20 Presentació treball a congrés
This article proposes a linear-by-part approach for elastoplastic 3D multiple-point smooth impacts in multibody systems with perfect constraints. The model is an extension of a previous version, restricted to the perfectly elastic case, able to account for the high sensitivity to initial conditions and for redundancy without assuming any particular collision sequence (Barjau et al., Multibody Syst. Dyn. 31:497–517, 2014). Energy losses associated with compression and expansion in percussive analysis is a matter as complex as the physical phenomena involved, at the nanoscale level, for different materials. Simplified models can be developed for specific purposes, which can retain the most relevant trends of internal damping and at the same time be suitable for a particular analytical approach of impact mechanics. In the context of this article, energy dissipation due to material deformation is introduced through a linear-by-part elastoplastic model consisting on two elementary sets of springs and dry-friction dampers. The first set accounts for inelastic behavior (energy loss without permanent indentation), whereas the second one introduces plasticity (that is, permanent indentation). In inelastic and plastic collisions, instantaneous unilateral constraints may appear, thus reducing the number of degrees of freedom (DOF) of the system. The calculation of the corresponding normal contact force at the constrained points is then necessary in order to detect whether the constraint holds or disappears (either because a new compression or an expansion phase starts, or because contact is lost). Different simulated application examples are presented and thoroughly discussed.
Based on the impulsive-dynamics formulation, this article presents the analysis of different strategies to regulate the energy dissipation at the heel-strike event in the context of human locomotion. For this purpose, a seven-link 2D human-like multibody model based on anthropometric data is used. The model captures the most relevant dynamic and energetic aspects of the heel-strike event in the sagittal plane. The pre-impact mechanical state of the system, around which the analysis of the heel impact contribution to energy dissipation is performed, is defined based on published data. In the context of the proposed impulsive-dynamics framework, different realistic strategies that the subject can apply to modify the impact dynamics are proposed and analyzed, namely, the trailing ankle push-off, the torso configuration and the degree of joint blocking in the colliding leg. Detailed numerical analysis and discussions are presented to quantify the effects of the mentioned strategies.
Gholami, F.; Pàmies-Vilà, R.; Koevecses, J.; Font-Llagunes, J.M. Mechanism and machine theory Vol. 93, p. 175-184 DOI: 10.1016/j.mechmachtheory.2015.07.003 Data de publicació: 2015-11-01 Article en revista
In this study, effects of some of the foot modelling assumptions on the ankle kinematics and dynamics are investigated based on the experimental data. For the kinematics analysis, the appropriateness of the stationary axis of rotation of the human ankle flexion is examined. Moreover, an interpolated function which is capable of predicting the directional changes of this axis is proposed. For the dynamics analysis, two main modelling assumptions of the number of the foot segments and the dimension of the foot model are the subject of the study. To this end, the ankle joint torque and power are selected as the comparison indicators and inverse dynamics analyses are carried out. The analyses show that the number of segments of the foot model does not have a considerable effect on the calculated ankle joint torque. On the other hand, the calculated ankle power is highly affected by both of the segmentation and the dimension of the foot model.
Tassani, S.; Peiret, A.; Bosch, E.; Serrancoli, G.; Noailly, J.; Font-Llagunes, J.M. Congress of the European Society of Biomechanics p. 483-484 Data de presentació: 2015-07-06 Presentació treball a congrés
Neuromusculoskeletal models used to predict muscle and joint contact forces for a specific individual require specification of muscle-tendon, skeletal geometry, and neural control model parameter values. Though these parameter values should ideally be calibrated using in vivo data collected from the subject, they are often taken from generic models. This study explored the influence of three model calibration methods on predicted lower limb muscle and knee contact forces during walking. The calibrated model from each approach was used in a static optimization that predicted knee contact forces for six walking trials. The predictions were evaluated using knee contact forces measured in vivo from a subject implanted with a force-measuring knee replacement. The first calibration approach used muscle-tendon model parameter values (i.e., optimal muscle fiber lengths and tendon slack lengths) taken directly from the literature. The second approach calibrated muscle-tendon model parameter values such that each muscle operated within a physiological range on the ascending region of its normalized force-length curve. The third approach used a novel two-level optimization that exploited knowledge of the knee contact force measurements to calibrate muscle-tendon, moment arm, and neural control model parameter values such that the calibrated model would predict the in vivo contact forces as closely as possible. For the third approach, three walking trials were used to calibrate the model and the remaining three to test the calibrated model. Overall, calibration method had a large affect on predicted knee contact forces. The first method produced highly inaccurate contact force predictions and infeasible solutions for most time frames. The second approach produced accurate medial contact force predictions (average R2 = 0.89, average RMS error = 107 N) but inaccurate lateral predictions (average R2 = -1.77, average RMS error = 297 N). The third approach produced accurate testing predictions for both medial (average R2 = 0.91, average RMS error = 96 N) and lateral (average R2 = 0.76, average RMS error = 84 N) contact force. These results reveal that when knee contact force data are available, a single set of model parameter values can be successfully calibrated to predict medial and lateral knee contact force accurately over multiple walking cycles. They also reveal that when knee contact force data are not available (the most common situation), a simple calibration method based on muscle operating ranges on their normalized force-length curves may be sufficient to produce accurate medial but not lateral knee contact force predictions.
This paper presents a method to carry out the analysis of acquired gait motions through a control-based forward dynamic approach. Unlike some well-established control-based methods that consider inputs for all the system degrees of freedom, the current work proposes the more realistic alternative of having inputs at joint level only, thus leading to an underactuated system. The ground reactions come from a foot-ground contact model which is built in a pre-processing stage. Different sets of outputs to be tracked by the joint controllers are evaluated. It is observed that choosing as outputs the weighted trajectories of all the system degrees of freedom yields satisfactory results, and that including the weighted ground reactions provides only marginal improvement.
El cos humà és un sistema multisòlid sobreactuat, ja que cada grau de llibertat pot estar controlat per més d'un múscul. Per resoldre el problema d'indeterminació en el càlcul de les forces musculars, es sol utilitzar un mètode d'optimització. Consisteix en distribuir els moments articulars resultants entre els diferents músculs que actuen a l'articulació, i per tant, estimar la força que aquests realitzen.La reducció de la indeterminació en el càlcul de les forces musculars es pot aconseguir de diferents maneres. Malgrat que l'estratègia que fa servir el sistema nerviós central (SNC) per activar els músculs no es coneix amb exactitud, una de les hipòtesis més utilitzades per solucionar la indeterminació és el fet de considerar que el SNC minimitza una variable fisiològica. El primer estudi presentat en aquesta tesi tractava de resoldre el problema del repartiment muscular minimitzant la suma de les forces musculars normalitzades al quadrat. Per a tal fi, es va utilitzar una funció de cost ponderada per avaluar quins músculs es penalitzen més en la marxa d'un subjecte amb el lligament creuat anterior trencat. Els resultats mostren que la funció de cost que millor aproximava les activacions musculars amb el senyal d'EMG mesurat no tractava tots els músculs per igual.Una altra manera de reduir la indeterminació en el càlcul de les forces muscular és utilitzar la idea que els músculs s'activen sinèrgicament quan l'ésser humà realitza un moviment. En el segon estudi, es presenta una anàlisi de les sinergies musculars que compara la informació de les activacions a dos nivells: en els patrons d'activació-desactivació i en els components de les sinergies musculars d¿una mostra de 18 subjectes amb ruptura del lligament creuat i una mostra de 10 subjectes sans. Es van observar diferències als dos nivells, el qual suggereix que els subjectes amb ruptura al lligament creuat alteren les activacions musculars de la seva cama lesionada per tal d'estabilitzar l'articulació lesionada, en aquest cas el genoll.
The human body is an over-actuated multibody system, as each joint degree of freedom can be controlled by more than one muscle. Usually, optimization techniques are used to solve the muscle force sharing problem, that is, finding out how the resultant joint torque is shared among the muscles spanning that joint.
The reduction of muscle force redundancy can be achieved in several ways. Although the strategy followed by the central nervous system (CNS) to activate the muscles is not completely clear, one of the most used hypotheses to overcome this redundancy is to consider that the CNS minimizes a physiological variable. In the first study presented in this thesis, the solution to the muscle force sharing problem was approached by minimizing the sum of squared normalized muscle forces. For this purpose, a weighted cost function was designed to evaluate which muscles were more penalized in a subject with anterior cruciate ligament (ACL) deficiency during walking. The results showed that the cost function that best fitted normalized electromyography signals with muscle activations did not treat all muscles equally.
Another way to reduce muscle redundancy is using the idea that muscles are activated synergistically when performing a task. In the second study, a muscle synergy analysis was carried out to compare the muscle activation information at two levels: onset-offset activation patterns and muscle synergy components of a sample of 18 ACL-deficient subjects and a sample of 10 healthy subjects. Some differences were found at both levels, what suggests that ACL-deficient subjects alter the muscle activations of their injured leg to stabilize the joint.
Finally, in the third study, muscle synergies were used in a two-step optimization method to predict physiologically consistent muscle and knee contact forces, while calibrating muscle parameters. In the outer level, muscle parameters were calibrated; while, in the inner level, muscle activations were calculated using the current muscle parameters. The results showed that a set of muscle parameters were able to reproduce knee contact forces with high accuracy when knee contact forces were used during the calibration process. This study shows the main differences when these forces are available for calibrating muscle parameters and when they are not. The most important differences in the muscle parameter calibration affected lateral muscles. Therefore, this fact suggests that trials where lateral muscles play a more important role should be used to obtain a better calibration when no contact forces are available.
El cos humà és un sistema multisòlid sobreactuat, ja que cada grau de llibertat pot estar controlat per més d’un múscul. Per resoldre el problema d’indeterminació en el càlcul de les forces musculars, es sol utilitzar un mètode d’optimització. Consisteix en distribuir els moments articulars resultants entre els diferents músculs que actuen a l’articulació, i per tant, estimar la força que aquests realitzen.
La reducció de la indeterminació en el càlcul de les forces musculars es pot aconseguir de diferents maneres. Malgrat que l’estratègia que fa servir el sistema nerviós central (SNC) per activar els músculs no es coneix amb exactitud, una de les hipòtesis més utilitzades per solucionar la indeterminació és el fet de considerar que el SNC minimitza una variable fisiològica. El primer estudi presentat en aquesta tesi tractava de resoldre el problema del repartiment muscular minimitzant la suma de les forces musculars normalitzades al quadrat.
Per a tal fi, es va utilitzar una funció de cost ponderada per avaluar quins músculs es penalitzen més en la marxa d’un subjecte amb el lligament creuat anterior trencat. Els resultats mostren que la funció de cost que millor aproximava les activacions musculars amb el senyal d’EMG mesurat no tractava tots els músculs per igual.
Una altra manera de reduir la indeterminació en el càlcul de les forces muscular és utilitzar la idea que els músculs s’activen sinèrgicament quan l’ésser humà realitza un moviment. En el segon estudi, es presenta una anàlisi de les sinergies musculars que compara la informació de les activacions a dos nivells: en els patrons d’activació-desactivació i en els components de les sinergies musculars d’una mostra de 18 subjectes amb ruptura del lligament creuat i una mostra de 10 subjectes sans. Es van observar diferències als dos nivells, el qual suggereix que els subjectes amb ruptura al lligament creuat alteren les activacions musculars de la seva cama lesionada per tal d’estabilitzar l’articulació lesionada, en aquest cas el genoll.
Per últim, en el tercer estudi, es van utilitzar les sinergies musculars junt amb un problema d’optimització de dues etapes per tal de predir les forces musculars i de contacte al genoll de manera fisiològicament consistent, alhora que es calibren els paràmetres musculars. En el nivell exterior de l’optimització, es calibren els paràmetres musculars, mentre que en el nivell interior, es calculen les activacions musculars amb els corresponents paràmetres musculars. Els resultats indiquen que un conjunt de paràmetres musculars pot predir les forces de contacte al genoll amb alta precisió quan es disposa de les forces experimentals de contacte al genoll durant el procés de calibratge. Aquest estudi presenta les diferències entre
el cas en què s’utilitzen les forces experimentals de contacte al genoll per calibrar els paràmetres i quan no s’utilitzen. A més, suggereix que si s’utilitzessin captures biomecàniques de moviments on els músculs laterals tinguessin un rol més important que en la marxa, el calibratge dels paràmetres seria més acurat. Per tant, es podrien predir les forces de contacte al genoll amb més precisió quan no es disposa d’aquestes.
Romero, F.; Alonso, F.J.; Charneco, J.M.; Lugrís, U.; Font-Llagunes, J.M. Reunión del Capítulo Español de la Sociedad Europea de Biomecánica p. 1 Data de presentació: 2014-11-21 Presentació treball a congrés
The aim of this paper is to present a computational benchmark for gait analysis that has been developed in order to share real data captured in a biomechanics laboratory and the results of the inverse dynamic analysis. This work belongs to the library of computational multibody benchmark problems that the Technical Committee for Multibody Dynamics of the International Federation for the Promotion of Mechanism and Machine Science (IFToMM) is developing. The work presents the kinematic and dynamic study of human motion by means of multibody system dynamics techniques. The subject selected to perform the experiments walks on a walkway that encloses two force plates. The motion is captured by 12 optical cameras that acquire the position of 37 passive markers. The inverse dynamic analysis (IDA) is carried out using a 12-segment 2D model with 14 degrees of freedom. Displacement signals are filtered using an algorithm based on Singular Spectrum Analysis (SSA) and the natural coordinates of the model are calculated using algebraic relations among the marker positions.
Afterwards, a procedure ensures the kinematic consistency and the data processing continues with the approximation of the position histories using B-spline curves. The velocity and acceleration values are then obtained by analytical derivation. The double support indeterminacy is solved using the Corrected Force Plate (CFP) sharing method. The IDA provides the joint drive torques that the musculoskeletal system generates during human locomotion from acquired kinematic data, foot-ground contact forces and estimated body segment parameters (BSP). All this information is available online in http://iftomm-multibody.org/benchmark. Therefore, it can be viewed by other researchers, which can submit their own results using the same input data and proposing new solutions.
—This paper presents the main design steps in the
development of an active knee-ankle-foot orthosis (KAFO)
conceived to assist the gait of incomplete spinal cord injured
(SCI) subjects. The design approach is based on the idea of
modifying the available passive orthoses by adding
adaptable mechatronic modules at the joints. This approach
has resulted in a prototype that has been tested on SCI
patients. The design and control problems found and their
adopted solutions are thoroughly described.
Serrancoli, G.; Font-Llagunes, J.M.; Barjau, A. Proceedings of the Institution of Mechanical Engineers. Part K, journal of multi-body dynamics Vol. 228, num. 3, p. 241-11 DOI: 10.1177/1464419314530110 Data de publicació: 2014-09-01 Article en revista
The human body is an over-actuated multi-body system, as each joint degree of freedom can be controlled by more than one muscle. Solving the force-sharing problem (i.e. finding out how the resultant joint torque is shared among the muscles actuating that joint) calls for an optimization process where a cost function, representing the strategy followed by the central nervous system to activate muscles, is minimized. The main contribution of the present study has been the particular formulation of that cost function for the case of the pathological gait of a single subject suffering from anterior cruciate ligament rupture. Our hypothesis was that the central nervous system does not weight equally the muscles when trying to compensate for a lower limb injury during gait (in contrast to what is the usual practice for healthy gait where all muscles are weighted equally). This hypothesis is supported by the fact that muscle activity in injured individuals differs from that of healthy subjects. Different functions were tested until we finally came out with a cost function that was consistent with experimental electromyography measurements and inverse dynamics results for a subject suffering this particular pathology.
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 optimization
Pàmies-Vilà, R.; Font-Llagunes, J.M.; Lugrís, U.; Cuadrado, J. Joint International Conference on Multibody System Dynamics and Asian Conference on Multibody Dynamics Data de presentació: 2014-07-02 Presentació treball a congrés
Pàmies-Vilà, R.; Font-Llagunes, J.M.; Lugrís, U.; Cuadrado, J. Mechanism and machine theory Vol. 75, p. 107-116 DOI: 10.1016/j.mechmachtheory.2014.01.010 Data de publicació: 2014-05-01 Article en revista
A new parameter identification method for a three-dimensional foot-ground contact model is presented. The model is used to reproduce the relationship between the contact forces and the relative foot-ground displacements and velocities. The parameters of the contact model are estimated using the optimization method known as covariance matrix adaptation evolution strategy. An extended Kalman filter is implemented as a controller to compute a forward dynamic analysis of the foot motion using body segment parameters and the ankle joint wrench as input data. The aim of this work is to adjust the position and size of the contact elements (spheres) and the model parameters in order to obtain both, a predicted motion provided by forward dynamics as faithful as possible to the captured motion and a resultant foot-ground wrench (obtained through the foot-ground contact model) as close as possible to the measured foot-ground reactions. The results show that the obtained motion is really similar to the captured one and, moreover, the vertical force and the moments in the horizontal plane are in agreement with the experimental mesurments. However, the bristle friction model used for tangential forces provides lower level of agreement with the experimental data. (C) 2014 Elsevier Ltd. All rights reserved.
This article proposes a simple linear-by-part approach for perfectly elastic 3D multiple-point impacts in multibody systems with perfect constraints and no friction, applicable both to nonredundant and redundant cases (where the normal velocities of the contact points are not independent). The approach is based on a vibrational dynamical model, and uses the so called "independent contact space." Two different time and space scales are used. At the macroscale, the impact interval is negligible, and the overall system configuration is assumed to be constant. Consequently, the inertia and Jacobian matrices appearing in the formulation are also constant. The dynamics at the contact points is simulated through stiff springs undergoing very small deformations and generating system vibrations at the microscale. The total impact interval is split into phases, each corresponding to a constant set of compressed springs responsible for an elastic potential energy. For each phase, a reduced inertia matrix associated with a set of contact points, and a reduced stiffness matrix obtained from the potential energy (associated with all contact points undergoing compression) are introduced. From these matrices, a modal analysis is performed yielding an all-analytical solution within each phase. The main difference between the redundant and nonredundant cases concerns the inertia and stiffness matrices for modal analysis. While in the former case, both are related to the total set of contact points (total contact space), in the latter one they are related to two subsets: a subset of independent points for the inertia matrix (independent contact space), and the total set for the stiffness matrix. A second difference concerns the calculation of the normal impulses generated at each contact point. For the nonredundant case, they can be directly obtained from the total incremental normal velocities of the contact points through the inertia and stiffness matrices. For the redundant one, they can be obtained by adding up their incremental values at each impact phase. This requires an updating of a new effective stiffness matrix depending on the contact points undergoing compression at each phase. Four planar application cases are presented involving a single body and a multibody system colliding with a smooth ground.
Lobo-Prat, J.; Font-Llagunes, J.M.; Gómez-Pérez, C.; Medina-Casanovas, J.; Angulo-Barroso, R.M. Computer methods in biomechanics and biomedical engineering Vol. 17, num. 10, p. 1144-1156 DOI: 10.1080/10255842.2012.738199 Data de publicació: 2014 Article en revista
Cervical spinal cord injury and acquired brain injury commonly imply a reduction in the upper extremity function which complicates, or even constrains, the performance of basic activities of daily living. Neurological rehabilitation in specialised hospitals is a common treatment for patients with neurological disorders. This study presents a practical methodology for the objective and quantitative evaluation of the upper extremity motion during an activity of daily living of those subjects. A new biomechanical model (with 10 rigid segments and 20 degrees of freedom) was defined to carry out kinematic, dynamic and energetic analyses of the upper extremity motion during a reaching task through data acquired by an optoelectronic system. In contrast to previous upper extremity models, the present model includes the analysis of the grasp motion, which is considered as crucial by clinicians. In addition to the model, we describe a processing and analysis methodology designed to present relevant summaries of biomechanical information to rehabilitation specialists. As an application case, the method was tested on a total of four subjects: three healthy subjects and one pathological subject suffering from cervical spinal cord injury. The dedicated kinematic, dynamic and energetic analyses for this particular case are presented. The resulting set of biomechanical measurements provides valuable information for clinicians to achieve a thorough understanding of the upper extremity motion, and allows comparing the motion of healthy and pathological cases.