The dynamics of multibody systems with contacts
and Coulomb friction is discussed following a general approach.
In addition, a new friction cone is introduced, the equation
of which is derived and analyzed. This novel geometrical tool
makes it possible to assess the solvability of the dynamic
equations qualitatively, and also to obtain the values of the
friction coefficient that can make the dynamic formulation
Peiret, A.; Kövecses, J.; Font-Llagunes, J.M. ASME International Design Engineering Technical Conferences and Computers and Information in Engineering Conference p. 1-7 DOI: 10.1115/DETC2017-67988 Data de presentació: 2017-08-07 Presentació treball a congrés
The dynamics of multibody systems with many contacts are frequently formulated as a Linear Complementarity Problem (LCP), for which several direct or iterative algorithms are available to solve it efficiently. These formulations rely on discretized friction models that approximate the friction cone of the Coulomb model to a pyramid. However, they produce rank-deficient LCPs even though the physical problem does not have constraint redundancy and has a unique solution. Here, a new discretized friction model is presented which results in an LCP formulation with a full-rank lead matrix. This model relies on an inertial term to couple the equations of the model, which behaves as close to the Coulomb model as the other discretized models. Moreover, it is shown through some simulations that some algorithms can be used with this formulation, which could not be used with the other rank-deficient LCP formulations.
Swing motion has a potential for exercise, and
particularly rehabilitation, due to the involvement of
neuromuscular function during the movement without
the need of supporting the subject’s weight through the
limbs. An in-depth understanding of the biomechanics
of swing motion is needed to objectively assess the
effects of this therapy. The physics of swing motion
using simple mathematical models has previously been
studied by other authors . The aim of the current
work is to develop a multi-segment biomechanical
model for the computational analysis of the swing
motion dynamics. A prototype mechanical swing has been developed and, as a first step, the physiological response to exercise using the swing in a sample of healthy subjects has been measured. This paper presents preliminary findings.
Hidalgo, M.B.; Pàmies-Vilà, R.; Febrer, M.; Pajares, I.; Muñoz-Farré, A.; Medina, J.; Font-Llagunes, J.M. Congress of the European Society of Biomechanics p. 1 Data de presentació: 2017-07-03 Presentació treball a congrés
Symmetry is an important gait feature that is measured
and reported frequently, particularly in patients with
hemiparesis. For many rehabilitation professionals, a
goal of gait re-education is the achievement of symmetry during locomotion [1, 2]. The objective of this work is to examine changes in gait symmetry when using an audio feedback device in paediatric patients with hemiparesis that follow a training plan.
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.
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.
Font-Llagunes, J.M.; Clos, D.; Lugrís, U.; Romero, F.; Pàmies-Vilà, R.; Alonso, F.J.; Cuadrado, J. Congreso Nacional de Ingeniería Mecánica p. 1-6 Data de presentació: 2016-11-09 Presentació treball a congrés
Robotic gait training after spinal cord injury is of high priority to maximize independence and improve the living conditions of the patients. Current rehabilitation robots are expensive and heavy, and are generally found only in the clinical environment. To overcome these issues, we present the design of a low-cost, low-weight and personalized robotic orthosis for incomplete spinal cord injured subjects. The paper also presents a preliminary experimental evaluation of the assistive device on one subject with spinal cord injury that can control hip flexion to a certain extent, but lacks control of knee and ankle muscles. Results show that gait velocity, stride length and cadence
of walking increased (24,11%, 7,41% and 15,56%, respectively) when wearing active orthoses compared to the case when the subject used the usual passive orthoses.
Font-Llagunes, J.M.; Lugrís, U.; Febrer, M.; Romero, F.; Pàmies-Vilà, R.; Alonso, F.J.; Cuadrado, J. Reunión del Capítulo Español de la Sociedad Europea de Biomecánica p. 1-2 Data de presentació: 2016-10-24 Presentació treball a congrés
Muñoz-Farré, A.; Febrer, M.; Pajares, I.; Febrer, A.; Pàmies-Vilà, R.; Font-Llagunes, J.M. Reunión del Capítulo Español de la Sociedad Europea de Biomecánica p. 1-2 Data de presentació: 2016-10-24 Presentació treball a congrés
Font-Llagunes, J.M.; Clos, D.; Lugrís, U.; Alonso, F.J.; Cuadrado, J. International Workshop on Wearable Robotics p. 281-285 DOI: 10.1007/978-3-319-46532-6_46 Data de presentació: 2016-10-21 Presentació treball a congrés
Robotic gait training after spinal cord injury (SCI) is of high priority to maximize independence and improve the living conditions of these patients. Current rehabilitation robots are expensive and heavy, and are generally found only in the clinic. To overcome these issues, we present the design of a low-cost, low-weight robotic orthosis for subjects with SCI. The paper also presents a preliminary experimental evaluation of the assistive device on a subject with SCI. Results show that gait velocity, stride length and cadence of walking increased (24.11, 7.41 and 15.56 %, respectively) when wearing active orthoses compared to the case with standard passive orthoses.
Mouzo, F.; Lugrís, U.; Cuadrado, J.; Font-Llagunes, J.M.; Alonso, F.J. International Conference on NeuroRehabilitation p. 815-819 DOI: 10.1007/978-3-319-46669-9_133 Data de presentació: 2016-10-18 Presentació treball a congrés
Forward dynamic analysis of the acquired gait of subjects assisted by either passive or active knee-ankle-foot orthoses and crutches is used to evaluate the motion and force transmission between orthosis and subject depending on the connecting stiffness. Unlike inverse dynamic analysis, this approach allows to consider the subject’s limbs and the assistive devices as different entities, so that their relative behavior may be studied. The quality of motion transmission and the intensity of interface forces are evaluated for a range of connecting stiffness values, so that those providing the best trade-off between both aspects can be identified.
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
Peiret, A.; Gholami, F.; Kövecses, J.; Font-Llagunes, J.M. ASME International Design Engineering Technical Conferences and Computers and Information in Engineering Conference p. 1-7 DOI: 10.1115/DETC2016-60064 Data de presentació: 2016-08-22 Presentació treball a congrés
Simulation of large-scale multibody systems with unilateral contacts requires formulations with which good computational performance can be achieved. The availability of many solver algorithms for Linear Complementarity Problems (LCP) makes the LCP-based formulations a good candidate for this. However, considering friction in contacts asks for new friction models compatible with this kind of formulations. Here, a new, regularized friction model is presented to approximate the Coulomb model, which allows to formulate the multibody system dynamics as a LCP with bounds. Moreover, a bristle approach is used to approximate the stiction force, so that it improves the numerical behaviour of the system and makes it able to handle redundancy coming from the friction interfaces. Several examples using a 3D wheel model has been carried out, and the proposed friction model shows a better approximation of the Coulomb model compared to other LCP-based formulations.
Serrancoli, G.; Kinney, A.L.; Fregly, B.J.; Font-Llagunes, J.M. Journal of biomechanical engineering. Transactions of the ASME Vol. 138, num. 8, p. 081001-1-081001-11 DOI: 10.1115/1.4033673 Data de publicació: 2016-08-01 Article en revista
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.
This thesis contains contributions to contact simulation and human motion analysis. Effects of the foot and ankle modelling techniques on the foot kinematics and dynamics are investigated. The analyses are carried out based on experimental data obtained using a motion capture system. The appropriateness of modelling the human ankle joint based on a stationary axis of rotation is investigated and a technique is also proposed which is capable of predicting the directional changes of the ankle axis during the foot flexion. Furthermore, two main modelling assumptions related to the number of the foot segments and the dimension of the foot model were the subject of the foot dynamics analyses. Effects of these modelling assumptions on the ankle joint torque and power are determined. A framework was developed which quantifies the gait abnormality of multiple sclerosis (MS) patients using a Kinect camera. The reliability of such a framework in assessing gait parameters in MS patients is evaluated based on captured data by Kinect. Also, a novel set of MS gait indices based on the concept of dynamic time warping is introduced whichcan characterize a patient's gait pattern and quantify the subject's gait deviation from the healthy population. In the second part of the thesis, two algorithms, namely, the accelerated-box and the generalized inverse-based algorithms, were developed for contact dynamics simulation. The accelerated-box algorithm improves the simulation of rigid body contact problems, in particular when the system under consideration has redundant constraints. The mathematical formulation is expressed in terms of a mixed linear complementarity problem (MLCP). The accelerated-box approach is partly motivated by the box friction model which is one of the existing approaches to solve contact problems. The original box friction model suffers from certain drawbacks in the presence of a large number of contact points such as long computational time, divergence problems, and instability. On the other hand, the accelerated-box approach developed in this thesis overcomes such drawbacks by taking advantage of the sparse structure of the lead matrix of the MLCP. This new method reduces the sensitivity of the solution to the constraint relaxation terms and decreases the number of required pivots to obtain the solution, and hence, shorter computational times result. This approach accordingly suggests a more reliable method for real-time simulation of multibody systems. A method based on the use of the Moore-Penrose generalized inverse was developed to deal with systems with redundant contacts. This approach omits the necessity of relaxing the constraints when redundancy exists in the system. To develop such a method, the generalized inverse is incorporated inside the pivoting steps of the MLCP solver. The method is very stable and robust, and its computational time is considerably smaller than the counterpartmethods, specially for highly redundant systems. Finally, a novel complementarity problem formulation is introduced. In…
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.
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