A machine-learning based solution for chatter prediction in heavy-dutymilling machines

The main productivity constraints of milling operations are self-induced vibrations, especially regenerative chatter vibrations. Two key parameters are linked to these vibrations: the depth of cut achievable without vibrations and the chatter frequency. Both parameters are linked to the dynamics of machine component excitation and the milling operation parameters. Their identification in any cutting direction in milling machine operations requires complex analytical models and mechatronic simulations, usually only applied to identify the worst cutting conditions in operating machines. This work proposes the use of machine learning techniques with no need to calculate the two above-mentioned parameters by means of a 3-step strategy. The strategy combines: 1) experimental frequency responses collected at the tool center point; 2) analytical calculations of both parameters; and, 3) different machine learning techniques. The results of these calculations can then be used to predict chatter under different combinations of milling directions and machine positions. This strategy is validated with real experiments on a bridge milling machine performing concordance roughing operations on AISI 1045 steel with a 125 mm diameter mill fitted with nine cutters at 45°, the results of which have confirmed the high variability of both parameters along the working volume. The following regression techniques are tested: artificial neural networks, regression trees and Random Forest. The results show that Random Forest ensembles provided the highest accuracy with a statistical advantage over the other machine learning models; they achieved a final accuracy of 0.95 mm for the critical depth and 7.3 Hz for the chatter frequency (RMSE) in the whole working volume and in all feed directions, applying a 10 × 10 cross validation scheme. These RMSE values are acceptable from the industrial point of view, taking into account that the critical depth of this range varies between 0.68 mm and 19.20 mm and the chatter frequency between 1.14 Hz and 65.25 Hz. Besides, Random Forest ensembles are more easily optimized than artificial neural networks (1 parameter configuration versus 210 MLPs). Additionally, tools that incorporate regression trees are interesting and highly accurate, providing immediately accessible and useful information in visual formats on critical machine performance for the design engineer.Hidrodamp Project (IDI-20110453) of the Centre for Industrial Technological Development (CDTI

Introducción al Análisis y Diseño Orientado a Objetos

La construcción de un sistema software, con independencia de su tamaño, de sus características funcionales y de la tecnología elegida, consta de una serie de fases que abarcan desde su concepción hasta su retirada, definiendo un espacio temporal que recibe el nombre de ciclo de vida del software. Existen diferentes modelos de ciclo de vida, cada uno con sus propias peculiaridades, adaptándose unos mejor que otros a los distintos paradigmas o estilos de programación. Pero, lo que sí se puede afirmar es que en ninguno de estos modelos de desarrollo se comienza un proyecto software por la fase de implementación

El Principio Abierto/Cerrado

El principio abierto/cerrado es, sin duda alguna, una de las referencias más importantes para realizar un buen Diseño Orientado a Objetos, de forma que las clases diseñadas para un determinado software puedan ser extendidas en otros desarrollos, pero sin modificar el código fuente de dichas clases, aprovechando de esta forma las facilidades de extensión y reutilización que ofrece la orientación a objeto

UML 1.1. Un lenguaje de modelado estándar para los métodos de ADOO

Desde la aparición en escena de UML (Unified Modeling Language-Lenguaje Unificado de Modelado), el interés de las empresas de desarrollo de software orientado al objeto por los métodos de análisis y diseño orientados al objeto (ADOO) se ha visto de nuevo incentivado. UML representa la apuesta de tres de los más prestigiosos expertos en metodologías orientadas al objeto, Grady Booch, James Rumbaugh e Ivar Jacobson, por el control de la parc ela del ADOO dentro de la tecnología de objetos bajo la idea de la unificación. Pero UML no es más que una pieza dentro del complejo engranaje que se está construyendo entorno a la idea de la convergencia de los métodos orientados al objeto, y que intentaremos desgranar en el presente artículo

Diagramas de Clase en UML 1.1.

El diagrama de clases es una técnica central y ampliamente difundida en los distintos métodos orientados a objeto. Cada método incluye sus propias variantes a esta técnica, pero en el presente artículo nos vamos a centrar en la visión que se encuentra implementada dentro del lenguaje estándar de modelado UML 1.1

Guía para padres. Ayudándoles a evitar riesgos

Peer reviewe

Seguimiento de la actividad y abandono en Moodle mediante la aplicación UBUMonitor

Teaching with online learning platforms should simplify the monitoring of students’ activity, particularly when evaluating student dropout. Popular learning environments such as Moodle should implement visual analytic tools that facilitate such tasks, nevertheless, institutions are usually reluctant to incorporate them. This paper presents UBUMonitor, a desktop application that allows the visualization of student’s activity data, extended as a proof of concept with a module for dropout tracking. Therefore, by using UBUMonitor, teachers will be able to easily visualize their students’ engagement with their subject, which can facilitate early action to prevent students from dropping out more effectivel

Percentile Study of chi Distribution. Application to Response Time Data.

As a continuation of our previous work, where a Maxwell-Boltzmann distribution was found to model a collective's reaction times, in this work we will carry out a percentile study of the χ distribution for some freedom ranging from k = 2 to k = 10. The most commonly used percentiles in the biomedical and behavioral sciences have been included in the analysis. We seek to provide a look-up table with percentile ratios, taken symmetrically about the median, such that this distribution can be identified in practice in an easy way. We have proven that these ratios do not depend upon the variance chosen for the k generating Gaussians. In general, the χ probability density, generalized to take any value of the variance, represents an ideal gas in a k-dimensional space. We also derive an approximate expression for the median of the generalized χ distribution. In the second part of the results, we will focus on the practical case of k = 3, which represents the ideal gas in physics, and models quite well the reaction times of a human collective. Accurately, we will perform a more detailed scrutiny of the percentiles for the reaction time distribution of a sample of 50 school-aged children (7200 reaction times)

Análisis del perfil sociodemográfico y clínico de personas derivadas a una Unidad de Salud Mental durante el principio de la pandemia por COVID-19 en España

Introduction. The global COVID-19 pandemic has had a negative impact on the mental health of the world's population. Both fear and anxiety have been common factors in all societies. The objective of the study is to analyze the sociodemographic and clinical profile of referrals made from Primary Care (PC) to a Mental Health Unit (MHU) during the first months of the pandemic and confinement in Spain.Material and methods. A cross-sectional descriptive retrospective study was carried out using an ad-hoc questionnaire, administered in 105 subjects, during the months of March and October 2020. The main variable of the study was whether the demand was a consequence of COVID-19 or not. The secondary variables are the sociodemographic profile (gender, age, place of residence, healthy lifestyle, and work situation) and the clinical profile (main, secondary and COVID-19 diagnosis, relapse episode, medical history, substance use and use of psychiatric drugs).Results. Referred patients are mainly diagnosed with anxiety and depression and considered COVID-19 as the main cause of their mental discomfort if they are people who reside in an urban nucleus, if their main diagnosis was hypochondria, or if they did not consume substances.Discussion. The consequences of the COVID-19 pandemic can vary according to the sociodemographic and clinical profile of the population; therefore, they must be studied more thoroughly, especially in patients with previous mental health problems.Introducción. La pandemia mundial del COVID-19 ha generado una repercusión negativa en la salud mental de la población mundial. Tanto el miedo como la ansiedad han resultado factores comunes en todas las sociedades. El objetivo del estudio es el de analizar el perfil sociodemográfico y clínico de las derivaciones realizadas desde Atención Primaria (AP) a una Unidad de Salud Mental (USM) durante los primeros meses de pandemia y confinamiento en España. Material y métodos. Se ha llevado a cabo un estudio retrospectivo descriptivo transversal mediante un cuestionario ad-hoc, de 105 sujetos, durante los meses de marzo y octubre de 2020. La variable principal de estudio fue si la demanda fue consecuencia de la COVID-19 o no. Las variables secundarias son el perfil sociodemográfico (género, edad, lugar de residencia, hábitos de vida saludable y situación laboral) y el perfil clínico (diagnóstico, principal y secundario y de COVID-19, episodio de recidiva, antecedentes médicos, consumo de sustancias y uso de psicofármacos). Resultados. Los pacientes derivados están principalmente diagnosticados de ansiedad y depresión, y consideran la COVID-19 como la principal causante de su malestar mental si son personas que residen en un núcleo urbano, si su diagnóstico principal era hipocondría, o si no consumían sustancias. Discusión. Las consecuencias de la pandemia COVID-19 pueden varias según el perfil sociodemográfico y clínico de la población, por tanto, tienen que ser estudiadas más a fondo, sobre todo en pacientes con problemas de salud mental previos

Direct visualization of pyrrole reactivity by confined oxidation in a Cyclodextrin Metal‐Organic Framework

Metal-organic frameworks can be used as porous templates to exert control over polymerization reactions. Shown here are the possibilities offered by these crystalline, porous nanoreactors to capture highly‐reactive intermediates for a better understanding of the mechanism of polymerization reactions. By using a cyclodextrin framework the polymerization of pyrrole is restricted, capturing the formation of terpyrrole cationic intermediates. Single‐crystal X‐ray diffraction is used to provide definite information on the supramolecular interactions that induce the formation and stabilization of a conductive array of cationic complexes