Articles de revista
http://hdl.handle.net/2117/4014
20170219T12:13:51Z

Roughness evolution of previously milled samples along a polishing test
http://hdl.handle.net/2117/100585
Roughness evolution of previously milled samples along a polishing test
Buj Corral, Irene; Vivancos Calvet, Joan
In the present work results about roughness evolution along a polishing operation with corundum disks of size Norton 400 are presented. Hardened steel and hardened stainless steel samples were previously subjected to ballend milling or side milling with cylindrical tool at different cutting conditions. Roughness height parameters Ra and Rt, as well as parameters related to the AbbottFirestone curve such as Rk, Rpk, and Rvk, and shape parameters such as Rsk and Rku were studied. It is usually considered that a polishing operation is complete when Ra does not decrease significantly with more polishing time. In the present paper, an alternative method for determining the end of a polishing test is presented. Roughness is measured both in the longitudinal and in the transversal direction with respect to cutting marks, and it is assumed that the polishing operation is finished when longitudinal values equal transversal values, provided that from that moment on roughness values do not decrease significantly. Moreover, it is recommended to measure parameter Rvk in addition to or even instead of Ra, in order to obtain information about the presence of valleys from the previous milling operation.
20170206T11:31:55Z
Buj Corral, Irene
Vivancos Calvet, Joan
In the present work results about roughness evolution along a polishing operation with corundum disks of size Norton 400 are presented. Hardened steel and hardened stainless steel samples were previously subjected to ballend milling or side milling with cylindrical tool at different cutting conditions. Roughness height parameters Ra and Rt, as well as parameters related to the AbbottFirestone curve such as Rk, Rpk, and Rvk, and shape parameters such as Rsk and Rku were studied. It is usually considered that a polishing operation is complete when Ra does not decrease significantly with more polishing time. In the present paper, an alternative method for determining the end of a polishing test is presented. Roughness is measured both in the longitudinal and in the transversal direction with respect to cutting marks, and it is assumed that the polishing operation is finished when longitudinal values equal transversal values, provided that from that moment on roughness values do not decrease significantly. Moreover, it is recommended to measure parameter Rvk in addition to or even instead of Ra, in order to obtain information about the presence of valleys from the previous milling operation.

Residual stresses induced by honing processes on hardened steel cylinders
http://hdl.handle.net/2117/100210
Residual stresses induced by honing processes on hardened steel cylinders
Buj Corral, Irene; Vivancos Calvet, Joan; Setien, Iñaki; San Sebastian Ormazabal, Maria
In the present paper, residual stresses induced by honing processes on hardened steel cylinders were determined. Cubic boron nitride (CBN) abrasives were employed. Both surface measurements and depth profiles were obtained by means of XRD. SEM observations were performed on samples’ surface. Roughness and material removal rate were also measured. Compressive residual stresses, which are known to increase fatigue life of components, were reported both in the axial and in the tangential direction. Shearing stresses were negligible. If only rough honing is taken into account, as a general trend, the lower cutting conditions used, the higher surface stresses are. A similar situation was found when only semifinish or only finish honing is considered. In most cases studied, stress profiles similar to those obtained in grinding processes, in which compressive stresses decrease with depth, were observed. However, in rough honing at hard cutting conditions, a typical hookshaped profile was found with maximum compressive stress at 80µm depth. Such shape is usual in turning processes. In order to obtain high surface stresses a rough, semifinish or finish honing operation with low cutting conditions is recommended. However, if stresses are to be obtained at a certain depth, rough honing at high cutting conditions is to be selected.
20170127T13:04:22Z
Buj Corral, Irene
Vivancos Calvet, Joan
Setien, Iñaki
San Sebastian Ormazabal, Maria
In the present paper, residual stresses induced by honing processes on hardened steel cylinders were determined. Cubic boron nitride (CBN) abrasives were employed. Both surface measurements and depth profiles were obtained by means of XRD. SEM observations were performed on samples’ surface. Roughness and material removal rate were also measured. Compressive residual stresses, which are known to increase fatigue life of components, were reported both in the axial and in the tangential direction. Shearing stresses were negligible. If only rough honing is taken into account, as a general trend, the lower cutting conditions used, the higher surface stresses are. A similar situation was found when only semifinish or only finish honing is considered. In most cases studied, stress profiles similar to those obtained in grinding processes, in which compressive stresses decrease with depth, were observed. However, in rough honing at hard cutting conditions, a typical hookshaped profile was found with maximum compressive stress at 80µm depth. Such shape is usual in turning processes. In order to obtain high surface stresses a rough, semifinish or finish honing operation with low cutting conditions is recommended. However, if stresses are to be obtained at a certain depth, rough honing at high cutting conditions is to be selected.

A comparative study of elastic motions in trajectory tracking of flexible RPR planar manipulators moving with high speed
http://hdl.handle.net/2117/100019
A comparative study of elastic motions in trajectory tracking of flexible RPR planar manipulators moving with high speed
Firoozabadi, Amirhossein Eshaghiyeh; Ebrahimi, Saeed; Font Llagunes, Josep Maria
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 3RPR, 2RPR and 1RPR) with flexible intermediate links is developed based on the assumed mode method. The flexible intermediate links are modeled as EulerBernoulli beams with fixedfree 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 endeffector 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 nRPR 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.
20170125T12:22:51Z
Firoozabadi, Amirhossein Eshaghiyeh
Ebrahimi, Saeed
Font Llagunes, Josep Maria
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 3RPR, 2RPR and 1RPR) with flexible intermediate links is developed based on the assumed mode method. The flexible intermediate links are modeled as EulerBernoulli beams with fixedfree 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 endeffector 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 nRPR 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.

Ceramic macromembrane for tangentoaxial micro and ultrafiltration water systems
http://hdl.handle.net/2117/99841
Ceramic macromembrane for tangentoaxial micro and ultrafiltration water systems
Cusidó Fàbregas, Joan Antoni; Cremades Oliver, Lázaro Vicente; Sitjar Cañellas, Rafael
An innovative proposal of tangentoaxial filtration based on the concept of macromembrane (large size) is presented in the context of micro and ultrafiltration ceramic membranes. The macromembrane is made of Al2O3–TiO2 by slip casting. It includes an internal system for rotating the fluid trough a propeller which enhances the tangentoaxial filtration. This filtration yields better than the crossflow filtration in conventional extruded ceramic tubes of small diameter. The reasons are, first, its larger sizes relative to the extruded tubular filters, and second, that it can work at higher pressures, resulting in better operational performance. Furthermore, costs of industrialscale production could be lower. In this study, the conceptual basis, pilot plant, first experimental results, and proposals for improvement of the system to continue the project are presented.
20170123T11:42:13Z
Cusidó Fàbregas, Joan Antoni
Cremades Oliver, Lázaro Vicente
Sitjar Cañellas, Rafael
An innovative proposal of tangentoaxial filtration based on the concept of macromembrane (large size) is presented in the context of micro and ultrafiltration ceramic membranes. The macromembrane is made of Al2O3–TiO2 by slip casting. It includes an internal system for rotating the fluid trough a propeller which enhances the tangentoaxial filtration. This filtration yields better than the crossflow filtration in conventional extruded ceramic tubes of small diameter. The reasons are, first, its larger sizes relative to the extruded tubular filters, and second, that it can work at higher pressures, resulting in better operational performance. Furthermore, costs of industrialscale production could be lower. In this study, the conceptual basis, pilot plant, first experimental results, and proposals for improvement of the system to continue the project are presented.

Dynamical models of a wire scanner
http://hdl.handle.net/2117/99206
Dynamical models of a wire scanner
Barjau Condomines, Ana; Herranz Álvarez, Juan Francisco; Dehning, Bernd
The accuracy of the beam profile measurements achievable by the current wire scanners at CERN is limited by the vibrations of their mechanical parts. In particular, the vibrations of the carbon wire represent the major source of wire position uncertainty which limits the beam profile measurement accuracy. In the coming years, due to the Large Hadron Collider (LHC) luminosity upgrade, a wire traveling speed up to 20¿m s1 and a position measurement accuracy of the order of 1¿µm will be required. A new wire scanner design based on the understanding of the wire vibration origin is therefore needed. We present the models developed to understand the main causes of the wire vibrations observed in an existing wire scanner. The development and tuning of those models are based on measurements and tests performed on that CERN proton synchrotron (PS) scanner. The final model for the (wire¿+¿fork) system has six degreesoffreedom (DOF). The wire equations contain three different excitation terms: inertia forces associated with the fork rotation, parametric terms associated with the fork tips approaching/separating motion, and terms associated with the wire stiffness (Duffing terms). Though forced, parametric, and Duffing oscillators have been treated in the literature, it is the first time that a model containing all those terms is treated through a purely analytical model. The model has been run for different rotation patterns, and the results show the same trends as the measurements. From the simulations, we conclude that fork flexibility is the main cause of the wire vibration.
20170113T10:18:19Z
Barjau Condomines, Ana
Herranz Álvarez, Juan Francisco
Dehning, Bernd
The accuracy of the beam profile measurements achievable by the current wire scanners at CERN is limited by the vibrations of their mechanical parts. In particular, the vibrations of the carbon wire represent the major source of wire position uncertainty which limits the beam profile measurement accuracy. In the coming years, due to the Large Hadron Collider (LHC) luminosity upgrade, a wire traveling speed up to 20¿m s1 and a position measurement accuracy of the order of 1¿µm will be required. A new wire scanner design based on the understanding of the wire vibration origin is therefore needed. We present the models developed to understand the main causes of the wire vibrations observed in an existing wire scanner. The development and tuning of those models are based on measurements and tests performed on that CERN proton synchrotron (PS) scanner. The final model for the (wire¿+¿fork) system has six degreesoffreedom (DOF). The wire equations contain three different excitation terms: inertia forces associated with the fork rotation, parametric terms associated with the fork tips approaching/separating motion, and terms associated with the wire stiffness (Duffing terms). Though forced, parametric, and Duffing oscillators have been treated in the literature, it is the first time that a model containing all those terms is treated through a purely analytical model. The model has been run for different rotation patterns, and the results show the same trends as the measurements. From the simulations, we conclude that fork flexibility is the main cause of the wire vibration.

Estimation of muscular forces from SSA smoothed sEMG signals calibrated by inverse dynamicsbased physiological static optimization
http://hdl.handle.net/2117/99092
Estimation of muscular forces from SSA smoothed sEMG signals calibrated by inverse dynamicsbased physiological static optimization
Romero Sánchez, Francisco; Alonso Sánchez, Francisco Javier; Gragera, C.; Lugrís Armesto, Urbano; Font Llagunes, Josep Maria
The estimation of muscular forces is useful in several areas such as biomedical or rehabilitation engineering. As muscular forces cannot be measured in vivo noninvasively 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 leastsquares 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.
20170112T12:53:35Z
Romero Sánchez, Francisco
Alonso Sánchez, Francisco Javier
Gragera, C.
Lugrís Armesto, Urbano
Font Llagunes, Josep Maria
The estimation of muscular forces is useful in several areas such as biomedical or rehabilitation engineering. As muscular forces cannot be measured in vivo noninvasively 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 leastsquares 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.

Traumatic brain injury in pedestrian–vehicle collisions: Convexity and suitability of some functionals used as injury metrics
http://hdl.handle.net/2117/98620
Traumatic brain injury in pedestrian–vehicle collisions: Convexity and suitability of some functionals used as injury metrics
Sánchez Molina, David; Arregui Dalmases, Carlos; Velázquez Ameijide, Juan; Angelini, Massimo; Kerrigan, Jason; Crandall, Jeff R.
Background and Objective:
Abrupt accelerations or decelerations can cause large strain in brain tissues and, consequently, different forms of Traumatic Brain Injury (TBI). In order to predict the effect of the accelerations upon the soft tissues of the brain, many different injury metrics have been proposed (typically, an injury metric is a real valued functional of the accelerations). The objective of this article is to make a formal and empirical comparison, in order to identify general criteria for reasonable injury metrics, and propose a general guideline to avoid illproposed injury metrics.
Methods:
A mediumsize sample of vehiclepedestrian collisions, from Post Mortem Human Subject (PMHS) tests, is analyzed. A statistical study has been conducted in order to determine the discriminant power of the usual metrics. We use Principal Component Analysis to reduce dimensionality and to check consistency among the different metrics. In addition, this article compares the mathematical properties of some of these functionals, trying to identify the desirable properties that any of those functionals needs to fulfill in order to be useful for optimization.
Results: We have found a pairwise consistency of all the currently used metrics (any two injury metrics are always positively related). In addition, we observed that two independent principal factors explain about 72.5% of the observed variance among all collision tests. This is remarkable because it indicates that despite high number of different injury metrics, a reduced number of variables can explain the results of all these metrics. With regard to the formal properties, we found that essentially all injury mechanisms can be accounted by means of scalable, differentiable and convex functionals (we propose to call minimization suitable injury metric to any metric having these three formal properties). In addition three useful functionals, usable as injury metrics, are identified on the basis of the empirical comparisons.
Conclusions: The commonly used metrics are highly consistent, but also highly redundant. Formal minimal conditions of a reasonable injury metric have been identified. Future proposals of injury metrics can benefit from the results of this study.
20161220T12:21:19Z
Sánchez Molina, David
Arregui Dalmases, Carlos
Velázquez Ameijide, Juan
Angelini, Massimo
Kerrigan, Jason
Crandall, Jeff R.
Background and Objective:
Abrupt accelerations or decelerations can cause large strain in brain tissues and, consequently, different forms of Traumatic Brain Injury (TBI). In order to predict the effect of the accelerations upon the soft tissues of the brain, many different injury metrics have been proposed (typically, an injury metric is a real valued functional of the accelerations). The objective of this article is to make a formal and empirical comparison, in order to identify general criteria for reasonable injury metrics, and propose a general guideline to avoid illproposed injury metrics.
Methods:
A mediumsize sample of vehiclepedestrian collisions, from Post Mortem Human Subject (PMHS) tests, is analyzed. A statistical study has been conducted in order to determine the discriminant power of the usual metrics. We use Principal Component Analysis to reduce dimensionality and to check consistency among the different metrics. In addition, this article compares the mathematical properties of some of these functionals, trying to identify the desirable properties that any of those functionals needs to fulfill in order to be useful for optimization.
Results: We have found a pairwise consistency of all the currently used metrics (any two injury metrics are always positively related). In addition, we observed that two independent principal factors explain about 72.5% of the observed variance among all collision tests. This is remarkable because it indicates that despite high number of different injury metrics, a reduced number of variables can explain the results of all these metrics. With regard to the formal properties, we found that essentially all injury mechanisms can be accounted by means of scalable, differentiable and convex functionals (we propose to call minimization suitable injury metric to any metric having these three formal properties). In addition three useful functionals, usable as injury metrics, are identified on the basis of the empirical comparisons.
Conclusions: The commonly used metrics are highly consistent, but also highly redundant. Formal minimal conditions of a reasonable injury metric have been identified. Future proposals of injury metrics can benefit from the results of this study.

Aplicación de la emisión acústica como método para anticipar el fallo de tejidos colaginosos (1ª parte)
http://hdl.handle.net/2117/98617
Aplicación de la emisión acústica como método para anticipar el fallo de tejidos colaginosos (1ª parte)
García Vilana, Silvia; Martínez González, Eva; Sánchez Molina, David; Arregui Dalmases, Carlos; Velázquez Ameijide, Juan; Llumà Fuentes, Jordi; Rebollo Soria, María Carmen
Se usa un montaje experimental basado en Emisión Acústica (EA) para detectar la energía elástica liberada durante el proceso de tracción y rotura de tejidos colaginosos. Se localizan las señales y se cuenta el número de microrroturas detectadas por unidad de tiempo. Se demuestra así que la EA puede usarse para detectar microrroturas en el interior de tejidos blandos colaginosos. En dichos tejidos, la resistencia se debe, fundamentalmente, a las fibras de colágeno
(siendo menor la contribución de la elastina). La disposición de las fibras no es totalmente azarosa,
sino, sólo parcialmente, aleatoria en la que distinguen algunas direcciones preferentes. Esta aleatoriedad dificulta hacer predicciones deterministas sobre el inicio del proceso de rotura de fibras. Inicialmente las fibras no están completamente rectas, por lo que al someterlas a tracción se alinean hasta que entran en tensión y empiezan a deformarse. A partir de cierto nivel de tensión, algunas de las fibras alcanzan su máxima resistencia a tracción y se rompen, mientras que otras permanecen sin tensión (éstas otras fibras sólo alcanzarán tensiones mayores una vez se hayan roto las fibras en situación más desfavorable). En este artículo se analiza una muestra de esófago humano, que se tracciona rompiendo algunas fibras hasta alcanzar la rotura completa del tejido. Los resultados se comparan con otras dos muestras de tejido colaginoso porcino procedentes de vejigas urinarias con el objeto de ver similaridades y diferencias. Los datos se analizan, estadísticamente, para ser comparados con un modelo de rotura estocástico que relaciona el nivel de tensión en el tejido con la probabilidad de rotura, dado el número de roturas previas detectadas, es decir, el deterioro previo del tejido. Se ha encontrado que la probabilidad de rotura puede ser representada adecuadamente por un proceso de Márkov (no homogéneo en el tiempo), a partir del cual se propone un modelo estocástico que parece adecuarse a los dos tipos de tejidos colagionosos estudiados. Además se prueba que la tensión final de rotura sigue una distribución de Fréchet (que es uno de los tres tipos posibles de distribución de valor extremo).
20161220T12:13:01Z
García Vilana, Silvia
Martínez González, Eva
Sánchez Molina, David
Arregui Dalmases, Carlos
Velázquez Ameijide, Juan
Llumà Fuentes, Jordi
Rebollo Soria, María Carmen
Se usa un montaje experimental basado en Emisión Acústica (EA) para detectar la energía elástica liberada durante el proceso de tracción y rotura de tejidos colaginosos. Se localizan las señales y se cuenta el número de microrroturas detectadas por unidad de tiempo. Se demuestra así que la EA puede usarse para detectar microrroturas en el interior de tejidos blandos colaginosos. En dichos tejidos, la resistencia se debe, fundamentalmente, a las fibras de colágeno
(siendo menor la contribución de la elastina). La disposición de las fibras no es totalmente azarosa,
sino, sólo parcialmente, aleatoria en la que distinguen algunas direcciones preferentes. Esta aleatoriedad dificulta hacer predicciones deterministas sobre el inicio del proceso de rotura de fibras. Inicialmente las fibras no están completamente rectas, por lo que al someterlas a tracción se alinean hasta que entran en tensión y empiezan a deformarse. A partir de cierto nivel de tensión, algunas de las fibras alcanzan su máxima resistencia a tracción y se rompen, mientras que otras permanecen sin tensión (éstas otras fibras sólo alcanzarán tensiones mayores una vez se hayan roto las fibras en situación más desfavorable). En este artículo se analiza una muestra de esófago humano, que se tracciona rompiendo algunas fibras hasta alcanzar la rotura completa del tejido. Los resultados se comparan con otras dos muestras de tejido colaginoso porcino procedentes de vejigas urinarias con el objeto de ver similaridades y diferencias. Los datos se analizan, estadísticamente, para ser comparados con un modelo de rotura estocástico que relaciona el nivel de tensión en el tejido con la probabilidad de rotura, dado el número de roturas previas detectadas, es decir, el deterioro previo del tejido. Se ha encontrado que la probabilidad de rotura puede ser representada adecuadamente por un proceso de Márkov (no homogéneo en el tiempo), a partir del cual se propone un modelo estocástico que parece adecuarse a los dos tipos de tejidos colagionosos estudiados. Además se prueba que la tensión final de rotura sigue una distribución de Fréchet (que es uno de los tres tipos posibles de distribución de valor extremo).

Dynamic response of a doubledeck circular tunnel embedded in a fullspace
http://hdl.handle.net/2117/98584
Dynamic response of a doubledeck circular tunnel embedded in a fullspace
Clot Razquin, Arnau; Arcos Villamarín, Robert; Romeu Garbí, Jordi; Pàmies Gómez, Teresa
A threedimensional dynamic model for calculating the groundborne vibrations generated by harmonic loads applied on the interior floor of a doubledeck circular tunnel is developed. The response of the system is obtained coupling the interior floor subsystem and the tunnelsoil subsystem in the wavenumberfrequency domain. The interior floor is modeled as a thin plate of infinite length in the train circulation direction and the tunnelsoil system is described using the Pipe in Pipe model. Some numerical instabilities of the resulting expressions are overcome by using analytic approximations. The results show that the dynamic behavior of the interior floor clearly influences the magnitude of the coupling loads acting on the tunnel structure. The soil response to a harmonic load acting on the doubledeck tunnel is compared to the one obtained for the case of a simple tunnel finding significant differences between them for the whole range of frequencies studied. The proposed model extends the prediction of traininduced vibrations using computationally efficient models to this type of tunnel structure.
© 2016. This version is made available under the CCBYNCND 4.0 license http://creativecommons.org/licenses/byncnd/4.0/
20161219T14:03:12Z
Clot Razquin, Arnau
Arcos Villamarín, Robert
Romeu Garbí, Jordi
Pàmies Gómez, Teresa
A threedimensional dynamic model for calculating the groundborne vibrations generated by harmonic loads applied on the interior floor of a doubledeck circular tunnel is developed. The response of the system is obtained coupling the interior floor subsystem and the tunnelsoil subsystem in the wavenumberfrequency domain. The interior floor is modeled as a thin plate of infinite length in the train circulation direction and the tunnelsoil system is described using the Pipe in Pipe model. Some numerical instabilities of the resulting expressions are overcome by using analytic approximations. The results show that the dynamic behavior of the interior floor clearly influences the magnitude of the coupling loads acting on the tunnel structure. The soil response to a harmonic load acting on the doubledeck tunnel is compared to the one obtained for the case of a simple tunnel finding significant differences between them for the whole range of frequencies studied. The proposed model extends the prediction of traininduced vibrations using computationally efficient models to this type of tunnel structure.

Influence of the controller design on the accuracy of a forward dynamic simulation of human gait
http://hdl.handle.net/2117/97085
Influence of the controller design on the accuracy of a forward dynamic simulation of human gait
Pàmies Vila, Rosa; Pätkau, Olga; Dòria Cerezo, Arnau; Font Llagunes, Josep Maria
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.
20161123T10:08:37Z
Pàmies Vila, Rosa
Pätkau, Olga
Dòria Cerezo, Arnau
Font Llagunes, Josep Maria
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.