Fiabilidad de elementos metálicos en crecimiento de grieta por fatiga aleatoria mediante elementosfinitos probabilistas y modelos B

En este trabajo se plantea un nuevo modelo para la evaluación de la fiabilidad (predicción de la función de distribución de la vida) de elementos estructurales metálicos sometidos a carga cíclica (fatiga) en la fase de crecimiento de grieta. Para ello, y al contrario de los trabajos previosⁿ en los que se enfoca el problema de la fiabilidad en crecimiento de grietas en fatiga aleatoria como un problema de optimización, en este trabajo se considera este caso como un proceso de daño acumulado, discreto en el tiempo y en el espacio, utilizando modelos estadísticos desarrollados por Bogdano y Kozinⁿ, para el estudio de las incertidumbres encontradas en ensayos asociados a procesos físicos de daño acumulado (modelos B). Con ello se evita parte de los problemas concernientes al tratamiento del problema como un problema de optimización detección de un mínimo local en lugar de uno absoluto_ tiempo de computación, etc. Se consideran como variables aleatorias la longitud inicial y final de grieta, el ángulo inicial de propagación de la grieta, la posición inicial de la grieta, los parámetros del material y las cargas aplicadas. No obstante, incertidumbres de otra índole pueden ser incluidas de forma muy simple en el esquema propuesto y en el modulo de programación desarrollado. En este artículo se describen detalladamente las bases del modelo propuesto, el procedimiento de construcción del mismo mediante la utilización de resultados provenientes de un análisis por elementos finitos probabilistas y se presentan sendos ejemplos en modo I puro, y en modo mixto I-II donde se constatan las posibilidades del método así como la precisión del mismo al compararlo con resultados derivados de una simulación de Monte Carlo con 400.000 muestras de uno de los problemas propuestos.Peer Reviewe

Fiabilidad de elementos metálicos en crecimiento de grieta por fatiga aleatoria mediante elementos finitos probabilistas y modelos B

En este trabajo se plantea un nuevo modelo para la evaluación de la fiabilidad (predicción de la función de distribución de la vida) de elementos estructurales metálicos sometidos a carga cíclica (fatiga) en la fase de crecimiento de grieta. Para ello, y al contrario de los trabajos previosⁿ en los que se enfoca el problema de la fiabilidad en crecimiento de grietas en fatiga aleatoria como un problema de optimización, en este trabajo se considera este caso como un proceso de daño acumulado, discreto en el tiempo y en el espacio, utilizando modelos estadísticos desarrollados por Bogdano y Kozinⁿ, para el estudio de las incertidumbres encontradas en ensayos asociados a procesos físicos de daño acumulado (modelos B). Con ello se evita parte de los problemas concernientes al tratamiento del problema como un problema de optimización detección de un mínimo local en lugar de uno absoluto_ tiempo de computación, etc. Se consideran como variables aleatorias la longitud inicial y final de grieta, el ángulo inicial de propagación de la grieta, la posición inicial de la grieta, los parámetros del material y las cargas aplicadas. No obstante, incertidumbres de otra índole pueden ser incluidas de forma muy simple en el esquema propuesto y en el modulo de programación desarrollado. En este artículo se describen detalladamente las bases del modelo propuesto, el procedimiento de construcción del mismo mediante la utilización de resultados provenientes de un análisis por elementos finitos probabilistas y se presentan sendos ejemplos en modo I puro, y en modo mixto I-II donde se constatan las posibilidades del método así como la precisión del mismo al compararlo con resultados derivados de una simulación de Monte Carlo con 400.000 muestras de uno de los problemas propuestos.Peer Reviewe

A path conditioning method with trap avoidance

This work presents a sliding-mode method for robotic path conditioning. The proposal includes a trap avoidance algorithm in order to escape from trap situations, which are analogous to local minima in potential field-based approaches. The sliding-mode algorithm activates when the desired path is about to violate the robot workspace constraints, modifying it as much as necessary in order to fulfill all the constraints and reaching their limit surface at low speed. The proposed path conditioning algorithm can be used on-line, since it does not require a priori knowledge of the desired path, and improves the conventional conservative potential field-based approach in the sense that it fully exploits the robot workspace. The proposed approach can be easily added as an auxiliary supervisory loop to conventional robotic planning algorithms and its implementation is very easy in a few program lines of a microprocessor. The proposed path conditioning is compared through simulation with the conventional potential field-based approach in order to show the benefits of the method. Moreover, the effectiveness of the proposed trap avoidance algorithm is evaluated by simulation for various trap situations.This research is partially supported by DISICOM project PROM-ETEO 2008/088 of Generalitat Valenciana (Spain), research project DPI2011-27845-C02-01 of the Spanish Government (Spain), research project PAID-05-11-2640 of the Technical University of Valencia (Spain), and the Argentinian Government (UNLP 11I127, CONICET PIP 112-200801-0, ANPCyT PICT 2007 00535).Gracia Calandin, LI.; Sala, A.; Garelli, F. (2012). A path conditioning method with trap avoidance. Robotics and Autonomous Systems. 60(6):862-873. https://doi.org/10.1016/j.robot.2012.01.009S86287360

Reactive Sliding-Mode Algorithm for Collision Avoidance in Robotic Systems

© 2013 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.” Upon publication, authors are asked to include either a link to the abstract of the published article in IEEE Xplore®, or the article’s Digital Object Identifier (DOI).This brief presents a reactive reference conditioning algorithm for robot collision avoidance based on geometric invariance and sliding-mode (SM) ideas. First, constraints are defined in terms of the measurements given by the robot s sensors in order to guarantee that collisions will not occur. Then, a supervisory loop ensures the fulfillment of the constraints modifying the reference trajectory as much as necessary by means of a discontinuous control law. The proposed algorithm activates only when the constraints are about to be violated and, thus, in contrast to conventional SM approaches, there exists no reaching mode to the limit surface of the constraints (sliding surface). The validity and effectiveness of the proposed approach is substantiated by simulation and experimental results using a mobile robot equipped with infrared sensors.This work was supported in part by research under Project DPI2011-27845-C02-01 (Spanish Government), Projects PAID-05-11-2640, and PAID-00-12-SP20120159, (Universitat Politecnica de Valencia, Spain), and Projects ANPCyT PICT-2011-0888, CONICET PIP 112-2011-00361, and UNLP I164 in Argentina. Recommended by Associate Editor M. Zefran.Gracia Calandin, LI.; Garelli, F.; Sala, A. (2013). Reactive Sliding-Mode Algorithm for Collision Avoidance in Robotic Systems. IEEE Transactions on Control Systems Technology. 21(6):2391-2399. https://doi.org/10.1109/TCST.2012.2231866S2391239921

Study of bone remodeling of two models of femoral cementless stems by means of DEXA and finite elements

<p>Abstract</p> <p>Background</p> <p>A hip replacement with a cemented or cementless femoral stem produces an effect on the bone called adaptive remodelling, attributable to mechanical and biological factors. All of the cementless prostheses designs try to achieve an optimal load transfer in order to avoid stress-shielding, which produces an osteopenia.</p> <p>Long-term densitometric studies taken after implanting ABG-I and ABG-II stems confirm that the changes made to the design and alloy of the ABG-II stem help produce less proximal atrophy of the femur. The simulation with FE allowed us to study the biomechanical behaviour of two stems. The aim of this study was, if possible, to correlate the biological and mechanical findings.</p> <p>Methods</p> <p>Both models with prostheses ABG-I and II have been simulated in five different moments of time which coincide with the DEXA measurements: postoperative, 6 months, 1, 3 and 5 years, in addition to the healthy femur as the initial reference. For the complete comparative analysis of both stems, all of the possible combinations of bone mass (group I and group II of pacients in two controlled studies for ABG-I and II stems, respectively), prosthetic geometry (ABG-I and ABG-II) and stem material (Wrought Titanium or TMZF) were simulated.</p> <p>Results and Discussion</p> <p>In both groups of bone mass an increase of stress in the area of the cancellous bone is produced, which coincides with the end of the HA coating, as a consequence of the bottleneck effect which is produced in the transmission of loads, and corresponds to Gruen zones 2 and 6, where no osteopenia can be seen in contrast to zones 1 and 7.</p> <p>Conclusions</p> <p>In this study it is shown that the ABG-II stem is more effective than the ABG-I given that it generates higher tensional values on the bone, due to which proximal bone atrophy diminishes. This biomechanical behaviour with an improved transmission of loads confirmed by means of FE simulation corresponds to the biological findings obtained with Dual-Energy X-Ray Absorptiometry (DEXA).</p

Adaptive Domotic System in Green Buildings

This paper presents an adaptive domotic system in green buildings. In our case, the data of sensor and devices were controlled in CIESOL center. The adaptive domotic system uses a Fuzzy Lattice Reasoning classifier for predicting building energy performance depending on the user condition. Training and testing of classifiers were carried out with temperature condition data acquired for 4 months (February, May, July and November) in the case building called CIESOL. The results show a hihg accuracy rates with a mean absolute error between 0% and 0.21%

Representation of Robots in Matlab

Electronic versíon of an article published as International Journal of Software Engineering and Knowledge Engineering, Volume 29, issue 1, 2019, pp. 23-42. 10.1142/S0218194019500025 © World Scientific Publishing Company[EN] This paper presents a new software tool, namely RoboClass, to include and manage realistic robots and elements of the environment in Matlab simulations. These elements are loaded from CAD models using an STL-file and can be as detailed as desired. All the steps involved in the process are explained in detail. Furthermore, two illustrative examples are considered to show the effectiveness and versatility of the proposed approach: the ABB-IRB120 industrial robot and the CSA research robot. The developed tool is especially useful both for robotics research and teaching.Sanchez, A.; Gracia Calandin, LI.; Morales, R.; Perez-Vidal, C. (2019). Representation of Robots in Matlab. International Journal of Software Engineering and Knowledge Engineering. 29(1):23-42. https://doi.org/10.1142/S0218194019500025S234229

A supervisory loop approach to fulfill workspace constraints in redundant robots

An approach based on geometric invariance and sliding mode ideas is proposed for redundancy resolution in robotic systems to fulfill configuration and workspace constraints caused by robot mechanical limits, collision avoidance, industrial security, etc. Some interesting features of the proposal are that: (1) it can be interpreted as a limit case of the classical potential field-based approach for collision avoidance which requires using variable structure control concepts, (2) it allows reaching the limit surface of the constraints smoothly, depending on a free design parameter, and (3) it can be easily added as a supervisory block to pre-existing redundancy resolution schemes. The algorithm is evaluated in simulation on a 6R planar robot and on the freely accessible 6R robot model PUMA-560, for which the main features of the method are illustrated.Facultad de Ingenierí

Integrated sliding-mode algorithms in robot tracking applications

An integrated solution based on sliding mode ideas is proposed for robotic trajectory tracking. The proposal includes three sliding-mode algorithms for speed auto-regulation, path conditioning and redundancy resolution in order to fulfill velocity, workspace and C-space constraints, respectively. The proposed method only requires a few program lines and simplifies the robot user interface since it directly deals with the fulfillment of the constraints to find a feasible solution for the robot trajectory tracking in a short computation time. The proposed approach is evaluated in simulation on the freely accessible 6R robot model PUMA-560, for which the main features of the method are illustrated.Facultad de Ingenierí