ES2575745A1 - Method and system for the detection of defects of railway axes in fatigue tests (Machine-translation by Google Translate, not legally binding) - Google Patents
Method and system for the detection of defects of railway axes in fatigue tests (Machine-translation by Google Translate, not legally binding) Download PDFInfo
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- ES2575745A1 ES2575745A1 ES201431966A ES201431966A ES2575745A1 ES 2575745 A1 ES2575745 A1 ES 2575745A1 ES 201431966 A ES201431966 A ES 201431966A ES 201431966 A ES201431966 A ES 201431966A ES 2575745 A1 ES2575745 A1 ES 2575745A1
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
- G01M17/00—Testing of vehicles
- G01M17/08—Railway vehicles
- G01M17/10—Suspensions, axles or wheels
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N3/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N3/32—Investigating strength properties of solid materials by application of mechanical stress by applying repeated or pulsating forces
Abstract
Description
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DESCRIPCIONDESCRIPTION
Metodo y sistema para la deteccion de defectos de ejes ferroviarios en ensayos a fatigaMethod and system for detecting railway axle defects in fatigue tests
Objeto de la invencionObject of the invention
La presente invencion tiene aplicacion en el campo de la defectologia y la prevencion de danos. Mas espedficamente, tiene aplicacion en la deteccion prematura de fisuras durante los ensayos a fatiga de ejes ferroviarios y la posibilidad de establecer asi un criterio de parada en una maquina de ensayo a fatiga.The present invention has application in the field of defectology and the prevention of damages. More specifically, it has application in the premature detection of fissures during fatigue tests of railway axes and the possibility of establishing a stop criterion in a fatigue testing machine.
Antecedentes de la invencionBackground of the invention
Actualmente existen multitud de estandares regulando el diseno, fabrication y mantenimiento de ejes ferroviarios debido a que los ejes son uno de los elementos mas importantes en un veticulo de ferrocarril en terminos de seguridad.Currently there are many standards regulating the design, manufacture and maintenance of railway axles because the axles are one of the most important elements in a railroad vehicle in terms of safety.
Previamente al montaje de un eje en una maquina ferroviaria, este ha sido sometido a estrictos controles que incluyen ensayos a fatiga para verificar si efectivamente los limites de fatiga del eje superan determinados valores especificados en la normativa. Los ensayos a fatiga se pueden realizar en maquinas donde el eje rota, o mas frecuentemente, en maquinas de ensayo de resonancia tipo Sincotec donde las condiciones de entorno estan completamente controladas. Para ambos tipos de maquinas, los ensayos pretenden verificar habitualmente si aparece un defecto en el eje antes de 107 ciclos, por lo que es necesario establecer un criterio de parada por seguridad en caso de que aparezca una grieta durante el test. En el caso de maquinas de ensayo de resonancia, se suele determinar que el eje se ha agrietado cuando la frecuencia del ensayo cae mas de 0,5 Hz.Prior to the assembly of an axle on a railway machine, it has been subjected to strict controls that include fatigue tests to verify if the axle fatigue limits actually exceed certain values specified in the regulations. Fatigue tests can be performed on machines where the axis rotates, or more frequently, on Sincotec type resonance test machines where the surrounding conditions are completely controlled. For both types of machines, the tests usually seek to verify whether a defect appears on the shaft before 107 cycles, so it is necessary to establish a safety stop criterion in case a crack appears during the test. In the case of resonance test machines, it is usually determined that the axis has cracked when the test frequency drops more than 0.5 Hz.
Actualmente, durante un ensayo a fatiga de un eje ferroviario, la deteccion de defectos, o el criterio de parada antes de llegar a los 107 ciclos, se basa en establecer niveles de alarma para el desplazamiento del centro del eje, temperatura y variation de la carga aplicada. Sin embargo, los criterios de parada muestran una baja sensibilidad a las fisuras y cuando la maquina se detiene, los defectos son ya muy grandes.Currently, during a fatigue test of a railway axis, the detection of defects, or the stopping criteria before reaching 107 cycles, is based on establishing alarm levels for the displacement of the axis center, temperature and variation of the applied load However, the stop criteria show a low sensitivity to cracks and when the machine stops, the defects are already very large.
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Por otro lado, en el estudio de las senales vibratorias que se pueden adquirir de un eje bajo analisis, es importante destacar las modernas tecnicas de procesado de senales disponibles hoy en d^a como por ejemplo, la transformada wavelet (WT) y especialmente una de sus evoluciones, la llamada transformada wavelet packet o transformada en paquetes wavelet (WPT), la cual permite la descomposicion discreta de todas las bandas de frecuencia de la senal. Esta herramienta permite descomponer la senal obteniendo information tanto en el dominio del tiempo como de la frecuencia. Debido a esto es especialmente util para detectar fenomenos transitorios y discontinuidades en las senales que otras herramientas, como la transformada rapida de Fourier (FFT) no detectan. En definitiva, esta herramienta es adecuada para trabajar con senales de tipo no estacionario como las que normalmente se obtienen de maquinaria rotativa.On the other hand, in the study of vibratory signals that can be acquired from an axis under analysis, it is important to highlight the modern signal processing techniques available today such as the wavelet transform (WT) and especially a of its evolutions, the so-called wavelet packet transform or transformed into wavelet packets (WPT), which allows the discrete decomposition of all frequency bands of the signal. This tool allows to decompose the signal obtaining information both in the domain of time and frequency. Because of this, it is especially useful for detecting transient phenomena and discontinuities in the signals that other tools, such as the fast Fourier transform (FFT) do not detect. In short, this tool is suitable for working with non-stationary signals such as those normally obtained from rotating machinery.
El estado del arte ofrece algunas soluciones para la detection de defectos en ejes basadas en herramientas clasicas que unicamente trabajan en el dominio de la frecuencia, como la FFT. El analisis de estas senales se reduce al primer y segundo armonico de la velocidad de giro, que son senalados como buenos indicadores de la presencia de un defecto. Sin embargo, estos metodos han mostrado poca efectividad en la practica en trabajos experimentales en determinadas condiciones de carga y velocidad. Quizas tambien por la presencia de otros defectos como desalineamiento o desequilibrio, que tambien afectan a estas frecuencias.The state of the art offers some solutions for the detection of defects in axes based on classic tools that only work in the frequency domain, such as FFT. The analysis of these signals is reduced to the first and second harmonic of the speed of rotation, which are indicated as good indicators of the presence of a defect. However, these methods have shown little effectiveness in practice in experimental work under certain load and speed conditions. Perhaps also by the presence of other defects such as misalignment or imbalance, which also affect these frequencies.
Por otra parte, en los ultimos anos, el interes de la diagnosis de defectos en ejes ha cobrado mucho interes, sin embargo, la mayoria de tecnicas propuestas en los ultimos anos utilizan senales obtenidas de modelos, y raramente se incluye el proceso inverso de identification de defectos, por lo que su aplicacion practica en el terreno experimental es mas que dudosa.On the other hand, in recent years, the interest in the diagnosis of defects in axes has gained a lot of interest, however, most of the techniques proposed in recent years use signals obtained from models, and the reverse identification process is rarely included of defects, so its practical application in the experimental field is more than doubtful.
Segun lo expuesto anteriormente, las invenciones hasta ahora conocidas por el estado de laAs stated above, the inventions hitherto known by the state of the
tecnica para la deteccion de fisuras en ejes no han mostrado efectividad en la practica.technique for detecting fissures in shafts have not shown effectiveness in practice.
Concretamente, dentro de las orientadas a ensayos de fatiga de ejes ferroviarios, existenSpecifically, within those oriented to fatigue tests of railway axes, there are
tecnicas que realizan la funcion del objeto de invention, pero de una manera poco fiable ytechniques that perform the function of the object of the invention, but in an unreliable and
poco eficiente debido a que no logran detectar a su tiempo las grietas que aparecen en uninefficient because they fail to detect the cracks that appear in a time
eje ferroviario, corriendo el riesgo de un fallo catastrofico del eje y la maquina. El estado delrailway axis, running the risk of a catastrophic failure of the axis and the machine. The state of
arte demanda por tanto una evolution en estas tecnicas que permita realizar esta deteccionart therefore demands an evolution in these techniques that allows this detection
de defectos en ejes ferroviarios que, sometidos a un analisis a fatiga como el comentadoof defects in railway axes that, subjected to a fatigue analysis as commented
anteriormente, pueda detectarlos de forma incipiente y reducir asi tanto los gastos depreviously, it can detect them incipiently and thus reduce the expenses of
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tiempo y ene^a, como el riesgo de fallo catastrofico del eje con los posibles dano que puede implicar para la maquina y su entorno.time and jan ^ a, such as the risk of catastrophic failure of the axis with the possible damage that it may imply for the machine and its surroundings.
Descripcion de la invencionDescription of the invention
La presente invencion resuelve los problemas comentados anteriormente proponiendo un metodo que permite la detection de fallos en eje ferroviarios con una antelacion considerable respecto a los metodos tradicionales. Concretamente, la presente invencion se refiere a un metodo para detectar un defecto en un eje ferroviario durante un ensayo a fatiga, que comprende los pasos de:The present invention solves the problems discussed above by proposing a method that allows the detection of rail faults with a considerable advance compared to traditional methods. Specifically, the present invention relates to a method for detecting a defect in a railway axis during a fatigue test, comprising the steps of:
- adquirir, mediante al menos un sensor, una senal de tipo vibratorio del eje ferroviario;- acquire, by at least one sensor, a vibratory type signal of the railway axis;
- medir, en un procesador, la energia de la senal vibratoria adquirida en una cierta banda de frecuencias;- measure, in a processor, the energy of the vibratory signal acquired in a certain frequency band;
- comparar, en el procesador, la energia medida con un umbral de energia establecido previamente;- compare, in the processor, the measured energy with a previously established energy threshold;
- determinar que se ha detectado un defecto en el eje en caso de que la energia medida supere el umbral de energia preestablecido;- determine that a defect in the axis has been detected in case the measured energy exceeds the pre-established energy threshold;
- detener el ensayo a fatiga en funcion de la deteccion de un defecto.- stop the fatigue test based on the detection of a defect.
El eje ferroviario, de acuerdo a una de las realizaciones de la invencion, puede rotar en un banco de pruebas, donde pueden controlarse las condiciones del test comodamente. Alternativamente el eje puede estar sometido a una maquina de resonancia, donde el eje no necesita rotar.The railway axis, according to one of the embodiments of the invention, can rotate in a test bench, where the test conditions can be controlled comfortably. Alternatively, the shaft may be subjected to a resonance machine, where the shaft does not need to rotate.
La deteccion de un fallo implica que se detenga el test de fatiga en curso, ya que se establece un criterio de parada para el test de fatiga en funcion de la deteccion de una grieta. De esta forma, el test puede detenerse con una considerable antelacion comparado con los metodos tradicionales.The detection of a fault implies that the current fatigue test is stopped, since a stop criterion is established for the fatigue test based on the detection of a crack. In this way, the test can be stopped with considerable anticipation compared to traditional methods.
El umbral de energia puede establecerse de acuerdo a unos cambios de energia relativos, respecto al valor de eje sano, detectados para la cierta banda de frecuencias en ejes defectuosos. De esta forma, el analisis de un eje defectuoso revela cambios en la energia medida en una cierta banda de frecuencias, los cuales quedan registrados para establecerThe energy threshold can be set according to relative energy changes, with respect to the sound axis value, detected for the certain frequency band in defective axes. In this way, the analysis of a defective axis reveals changes in the energy measured in a certain frequency band, which are recorded to establish
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as^ un umbral Kmite para los siguientes ejes ferroviarios a estudiar. En concreto un eje defectuoso implica un aumento de ene^a detectable en la cierta banda de frecuencias.as ^ a threshold Kmite for the following railway axes to study. In particular, a defective axis implies an increase in detectable ene in the certain frequency band.
De acuerdo a una de las realizaciones de la invention, se contempla determinar una primera frecuencia critica del eje ferroviario. Adicionalmente, la banda de frecuencias bajo analisis se centra en los subarmonicos de la primera frecuencia critica del eje.According to one of the embodiments of the invention, it is contemplated to determine a first critical frequency of the railway axis. Additionally, the frequency band under analysis focuses on the sub-harmonics of the first critical frequency of the axis.
En una realization de la invencion, el subarmonico en el que se centra en el analisis, consiste en el tercer subarmonico de la primera frecuencia critica del eje. Los resultados experimentales han revelado que es el que mejores resultados ofrece en cuanto a detection prematura de defectos.In an embodiment of the invention, the subharmonic in which it focuses on the analysis, consists of the third subharmonic of the first critical frequency of the axis. Experimental results have revealed that it has the best results in terms of premature defect detection.
Esta frecuencia en concreto es la que ha revelado en las pruebas experimentales ser una evidencia sorprendente para la prediction de defectos. Se puede anticipar la deteccion de un defecto hasta 150.000 ciclos frente a los metodos convencionales, lo que implica considerables beneficios en cuanto a tiempo, energia y reduction del riesgo de fallo catastrofico del eje.This frequency in particular is what has revealed in experimental tests to be surprising evidence for the prediction of defects. It is possible to anticipate the detection of a defect up to 150,000 cycles compared to conventional methods, which implies considerable benefits in terms of time, energy and reduction of the risk of catastrophic axis failure.
De acuerdo a una de las realizaciones de la invencion, se contempla tambien analizar las energias en los armonicos de la velocidad de rotation del eje ferroviario.According to one of the embodiments of the invention, it is also contemplated to analyze the energies in the harmonics of the rotation speed of the railway axis.
La presente invencion contempla aplicar una transformada wavelet en paquetes a la serial adquirida y, posteriormente, calcular la energia de la serial a partir de la transformation aplicada. La energia se distribuye en paquetes que corresponden a distintas bandas de frecuencia de la serial adquirida.The present invention contemplates applying a wavelet transform in packets to the acquired serial and, subsequently, calculating the energy of the serial from the applied transformation. The energy is distributed in packets that correspond to different frequency bands of the acquired serial.
Un segundo aspecto de la invencion se refiere a un sistema para detectar automaticamente fallos en un eje ferroviario, el sistema esta caracterizado por que comprende:A second aspect of the invention relates to a system for automatically detecting faults in a railway axis, the system is characterized in that it comprises:
- un sensor configurado para adquirir una serial de tipo vibratorio del eje rotatorio;- a sensor configured to acquire a vibratory type serial of the rotary axis;
- un procesador, en comunicacion con el sensor, configurado para obtener medidas de energia de dichas seriales, comparar las energias medidas con un umbral de energia establecido previamente, determinar que se ha detectado un defecto en el eje en caso de que la energia medida supere el umbral de energia preestablecido; y detener el ensayo a fatiga en funcion de la deteccion de un defecto en el eje.- a processor, in communication with the sensor, configured to obtain energy measurements from said series, compare the measured energies with a previously established energy threshold, determine that a defect has been detected in the axis in case the measured energy exceeds the preset energy threshold; and stop the fatigue test based on the detection of a defect in the shaft.
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El sistema de la invention contempla, de acuerdo a una de las realizaciones, un eje que esta siendo sometido a un test de fatiga donde se hace rotar el eje ferroviario en un banco de pruebas.The system of the invention contemplates, according to one of the embodiments, an axis that is being subjected to a fatigue test where the railway axis is rotated in a test bench.
Alternativamente, el sistema de la invencion contempla un eje que esta siendo sometido a un test de fatiga donde el eje esta siendo sometido a una maquina de ensayo de resonancia.Alternatively, the system of the invention contemplates an axis that is being subjected to a fatigue test where the axis is being subjected to a resonance test machine.
El procesador puede estar ademas configurado para detectar aumentos de energia en una banda de frecuencia correspondiente a los subarmonicos de la frecuencia critica del eje y a los armonicos de la velocidad de giro.The processor may also be configured to detect increases in energy in a frequency band corresponding to the sub-harmonics of the critical frequency of the axis and the harmonics of the rotation speed.
En una de las realizaciones de la invencion, se contempla priorizar ciertos subarmonicos donde se ha detectado que los efectos son mas ventajosos, concretamente el tercer subarmonico de la frecuencia critica del eje.In one of the embodiments of the invention, it is contemplated to prioritize certain sub-harmonics where it has been detected that the effects are more advantageous, specifically the third sub-harmonic of the critical frequency of the axis.
Un ultimo aspecto de la invencion se refiere a un programa informatico que comprende medios de codigo de programa adaptados para realizar las etapas del metodo de la invencion, cuando dicho programa se ejecuta en un procesador de proposito general, un procesador de serial digital, una FPGA, un ASIC, un microprocesador, un microcontrolador, o cualquier otra forma de hardware programable.A final aspect of the invention relates to an informatic program comprising program code means adapted to perform the steps of the method of the invention, when said program is executed in a general purpose processor, a digital serial processor, an FPGA , an ASIC, a microprocessor, a microcontroller, or any other form of programmable hardware.
Asi pues, la presente invencion propone por tanto, basandose en resultados experimentales, la detection prematura de defectos en ejes sometidos a test de fatiga mediante la monitorizacion de energia en determinadas bandas de frecuencia relacionadas con armonicos de la velocidad de giro y con frecuencias criticas del eje, las cuales resultan especialmente reveladoras para el tercer subarmonico de la primera frecuencia critica del eje. La monitorizacion de la energia en esta banda de frecuencias permite la deteccion de un defecto aproximadamente 150.000 ciclos antes que los metodos convencionales, ahorrando tiempo, energia y reduciendo riesgos para la maquina y su entorno, lo que supone un avance considerable para su campo tecnico.Thus, the present invention therefore proposes, based on experimental results, the premature detection of defects in axes subjected to fatigue testing by monitoring energy in certain frequency bands related to harmonics of the rotation speed and critical frequencies of the axis, which are especially revealing for the third subharmonic of the first critical frequency of the axis. The energy monitoring in this frequency band allows the detection of a defect approximately 150,000 cycles before conventional methods, saving time, energy and reducing risks for the machine and its surroundings, which represents a considerable advance for its technical field.
Descripcion de los dibujosDescription of the drawings
Para complementar la descripcion que se esta realizando y con objeto de ayudar a unaTo complement the description that is being made and in order to help a
mejor comprension de las caracteristicas del invento, de acuerdo con un ejemplo preferentebetter understanding of the features of the invention, according to a preferred example
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de realization practica del mismo, se acompana como parte integrante de dicha description, un juego de dibujos en donde con caracter ilustrativo y no limitativo, se ha representado lo siguiente:of practical realization of the same, it is accompanied as an integral part of said description, a set of drawings where, with an illustrative and non-limiting nature, the following has been represented:
La figura 1.- Muestra un esquema del procedimiento de descomposicion para la WPT hasta el nivel de descomposicion 3.Figure 1.- Shows a diagram of the decomposition procedure for the WPT up to decomposition level 3.
La figura 2.- Representa la evolution de la ene^a, en funcion del numero de ciclos durante un test de fatiga, del primero armonico de la velocidad de rotation.Figure 2.- Represents the evolution of the Jan ^ a, as a function of the number of cycles during a fatigue test, of the first harmonic of the rotation speed.
La figura 3.- Representa la evolucion de la energia, en funcion del numero de ciclos durante un test de fatiga, del tercer subarmonico de la primera frecuencia de resonancia.Figure 3.- Represents the evolution of energy, as a function of the number of cycles during a fatigue test, of the third subharmonic of the first resonance frequency.
La figura 4.- Muestra un vista ampliada de la figura 3, donde puede apreciarse mas en detalle la zona de interes.Figure 4.- Shows an enlarged view of Figure 3, where the area of interest can be seen in more detail.
Descripcion detallada de la invencionDetailed description of the invention
Para el desarrollo de la presente invencion, es importante comenzar mencionando las pruebas experimentales que la motivan. Puede observarse como de acuerdo a una de las posibles realizaciones, se plantea en primer lugar un test de fatiga convencional al que se someten los ejes ferroviarios bajo estudio que, en este caso particular, son tres ejes ferroviarios huecos hechos de acero. A continuation, se determinan las frecuencias criticas del eje realizando un analisis modal experimental, por ejemplo mediante acelerometria y un martillo dinamometrico, y para este caso se obtienen las frecuencias criticas segun la siguiente tabla:For the development of the present invention, it is important to start by mentioning the experimental tests that motivate it. It can be observed that according to one of the possible embodiments, a conventional fatigue test is first proposed to which the railway axes are subjected to study which, in this particular case, are three hollow railway axes made of steel. Then, the critical frequencies of the axis are determined by performing an experimental modal analysis, for example by accelerometry and a dynamical hammer, and for this case the critical frequencies are obtained according to the following table:
Frecuencia de resonancia (N) Frequency (Hz)Resonance frequency (N) Frequency (Hz)
- 1 one
- 194.2 194.2
- 2 2
- 485.2 485.2
- 3 3
- 886.0 886.0
- 4 4
- 1335.5 1335.5
- 5 5
- 1857.2 1857.2
Una vez se pone en marcha un test convencional, los principales criterios de parada para elOnce a conventional test is launched, the main stop criteria for the
test son, por un lado, si el numero de ciclos alcanza un valor de 107 y por otro lado, si setests are, on the one hand, if the number of cycles reaches a value of 107 and on the other hand, if
detecta un defecto antes de que se alcance el numero final de ciclos. Estableciendo ladetects a defect before the final number of cycles is reached. Setting the
detection de un defecto en funcion de si determinados parametros superan un valor umbralDetection of a defect depending on whether certain parameters exceed a threshold value
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previamente establecido para el desplazamiento del centro del eje, temperatura y variation en la carga aplicada.previously established for the displacement of the center of the axis, temperature and variation in the applied load.
Para este caso concreto, en el que se han sometido al test los tres ejes comentados anteriormente, se obtiene como resultado que dos de ellos se han roto, debido a que no han superado la carga aplicada, en concreto el test 1 y el 3. La siguiente tabla refleja las condiciones de los test:For this specific case, in which the three axes discussed above have been submitted to the test, it is obtained as a result that two of them have been broken, because they have not exceeded the applied load, specifically test 1 and 3. The following table reflects the test conditions:
- Test Test
- Velocidad (RPM) Carga (kN) Criterio de parada Numero de ciclos Speed (RPM) Load (kN) Stop criteria Number of cycles
- 1 one
- 509 240 valor umbral alcanzado 1688594 509 240 threshold value reached 1688594
- 2 2
- 509 216 maximo numero de ciclos 10000000 509 216 maximum number of cycles 10000000
- 3 3
- 509 240 valor umbral alcanzado 1467172 509 240 threshold value reached 1467172
Los resultados confirmados completamente mediante ultrasonidos y particulas magneticas, para corroborar que efectivamente se tratan de ejes defectuosos que han de ser retirados, ya que no cumplen los requisitos de resistencia a fatiga necesarios como para ser montados en una maquina ferroviaria. En el momento de la parada de la prueba se comprueba a simple vista la aparicion de grietas en el eje, lo que demuestra la baja sensibilidad de estos metodos tradicionales.The results are fully confirmed by ultrasound and magnetic particles, to corroborate that they are indeed defective axes that have to be removed, since they do not meet the requirements of fatigue resistance necessary to be mounted on a railway machine. At the time of the test stop, the appearance of cracks in the axis is checked with the naked eye, which demonstrates the low sensitivity of these traditional methods.
Sin embargo, durante estas pruebas convencionales, de acuerdo a una realization de la invention, se instala un acelerometro triaxial en el alojamiento del rodamiento central del eje, un acondicionador de senal y una tarjeta de adquisicion de datos para enviar los datos a un ordenador mediante conexion USB. De esta forma, se pueden adquirir las senales de vibration producidas durante los tests, cuyos parametros se representan a continuation para el caso concreto que estamos describiendo:However, during these conventional tests, according to an embodiment of the invention, a triaxial accelerometer is installed in the central shaft bearing housing, a signal conditioner and a data acquisition card to send the data to a computer by USB connection In this way, you can acquire the vibration signals produced during the tests, whose parameters are represented below for the specific case we are describing:
Frecuencia de muestreo (Hz) Longitud de la senal Almacenamiento de datosSampling frequency (Hz) Signal length Data storage
6000 16384 1 adquisicion cada 3 minutos6000 16384 1 acquisition every 3 minutes
A continuacion, las senales de vibracion se procesan para identificar cambios significativos que puedan asociarse con la presencia de fallos en el eje ferroviario. Particularmente y de acuerdo a la realizacion preferida de la presente invencion, las senales se procesan utilizando la WPT, una variacion de la DWT, que es especialmente eficiente para llevar aNext, the vibration signals are processed to identify significant changes that may be associated with the presence of faults in the railway axis. Particularly and according to the preferred embodiment of the present invention, the signals are processed using the WPT, a variation of the DWT, which is especially efficient for carrying
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cabo analisis locales de senales no estacionarias y permite obtener as^ coeficientes de correlation entre la senal y una wavelet madre.It carries out local analysis of non-stationary signals and allows obtaining correlation coefficients between the signal and a mother wavelet.
La DWT puede se puede implementar utilizando filtros, descomponiendo as^ una senal temporal x(t) mediante dos filtros, un filtro paso bajo y otro filtro paso alto. El filtro paso bajo provee information de las bajas frecuencias, llamada de information de aproximacion (A), mientras que la informacion de altas frecuencias se obtiene utilizando el filtro paso alto y es denominada informacion de detalle (D).DWT can be implemented using filters, thus decomposing a temporary signal x (t) by two filters, a low pass filter and another high pass filter. The low pass filter provides information on the low frequencies, called approximation information (A), while the high frequency information is obtained using the high pass filter and is called detail information (D).
La transformada wavelet en paquetes (WPT) es una variation de la descomposicion DWT, la cual se obtiene aplicando la DWT de una forma recursiva, tal como se muestra en la figura 1, donde W(k; j) representa los coeficientes de la senal en cada paquete, siendo “k” el nivel de descomposicion y “j” la position del paquete dentro del nivel de descomposicion. De esta forma cada vector de correlacion W(k; j) tiene la siguiente estructura:The wavelet packet transform (WPT) is a variation of the DWT decomposition, which is obtained by applying the DWT in a recursive manner, as shown in Figure 1, where W (k; j) represents the signal coefficients in each package, "k" being the decomposition level and "j" the position of the package within the decomposition level. Thus, each correlation vector W (k; j) has the following structure:
W(k, j) = {wi(k; j);...,WN(k; j)} = {wi(k; j)}W (k, j) = {wi (k; j); ..., WN (k; j)} = {wi (k; j)}
El concepto de energia que se utiliza en un analisis WPT es similar a la teona de Fourier. La energia de los paquetes se obtiene de la suma de los cuadrados de los coeficientes de cada paquete, es decir:The concept of energy that is used in a WPT analysis is similar to the Fourier theona. The energy of the packages is obtained from the sum of the squares of the coefficients of each package, that is:
Ekj = Ei(wi(k; j)}2Ekj = Ei (wi (k; j)} 2
El nivel de descomposicion utilizado determina la resolution en frecuencia de cada paquete. Teniendo en cuenta que la senal solo puede ser reconstruida hasta la frecuencia pi, limitada por la frecuencia de muestreo, la resolucion en frecuencia de cada paquete fr, se puede calcular utilizando la siguiente ecuacion:The level of decomposition used determines the frequency resolution of each packet. Taking into account that the signal can only be reconstructed up to the pi frequency, limited by the sampling frequency, the frequency resolution of each fr packet can be calculated using the following equation:
Aplicando estas transformaciones sobre las senales vibratorias adquiridas anteriormente, se analizan los paquetes de energia obtenidos de acuerdo a una wavelet madre "Daubechies 6", la cual es razonable elegir dado que su eficacia ha sido probada en este campo por estudios previos del estado del arte. De acuerdo a una realization de la invention seApplying these transformations on the vibratory signals acquired previously, the energy packages obtained according to a mother wavelet "Daubechies 6" are analyzed, which is reasonable to choose since their effectiveness has been proven in this field by previous studies of the state of the art . According to an embodiment of the invention,
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analizan distintos niveles de descomposicion, en concreto del 5 al 9. Para el nivel de descomposicion 5 se obtienen un total de 32 (25) paquetes, o niveles de energia, para cada senal. Aunque este numero es facilmente manejable para detectar cambios significativos a medida que avanza el numero de ciclos del ensayo a fatiga, cada uno de los paquetes hace referencia a una banda de frecuencias muy ancha (93.8 Hz). Por tanto, una vez que se detectan incrementos en uno de los paquetes con el numero de ciclos, este paquete se descompone a niveles mayores para afinar el valor de frecuencia afectada por el defecto. El maximo valor de nivel de descomposicion elegido en este caso es de 9 para asegurar un equilibrio entre la precision de la frecuencia y un bajo coste computacional, pero de acuerdo a otras realizaciones, este analisis puede plantearse con otros parametros.They analyze different levels of decomposition, specifically from 5 to 9. For decomposition level 5, a total of 32 (25) packages, or energy levels, are obtained for each signal. Although this number is easily manageable to detect significant changes as the number of fatigue test cycles progresses, each of the packages refers to a very wide frequency band (93.8 Hz). Therefore, once increments are detected in one of the packages with the number of cycles, this package is broken down to higher levels to fine tune the frequency value affected by the defect. The maximum decomposition level value chosen in this case is 9 to ensure a balance between the precision of the frequency and a low computational cost, but according to other embodiments, this analysis can be considered with other parameters.
Las pruebas experimentales reflejan a medida que avanza el numero de ciclos, la evolucion de la energia en las distintas bandas de frecuencia. El analisis de las senales de vibracion de los tres ensayos revela un gran aumento de la energia en varias bandas de frecuencia precisamente para los ensayos que resultaron en la rotura del eje, mientras que este fenomeno no se produce cuando el eje aguanta el test completo sin presentar defecto alguno, es decir, alcanza los 107 ciclos.Experimental tests reflect as the number of cycles progresses, the evolution of energy in the different frequency bands. The analysis of the vibration signals of the three tests reveals a great increase in the energy in several frequency bands precisely for the tests that resulted in the breakage of the axis, while this phenomenon does not occur when the axis endures the complete test without present any defect, that is, it reaches 107 cycles.
Pueden apreciarse cambios significativos en la evolucion de la energia relacionada con armonicos de la velocidad de giro, como por ejemplo en la figura 2, donde se muestra la evolucion de la energia concretamente en la banda de frecuencias 5,9-11,7 Hz, que contiene el primer armonico de la velocidad de giro (8,5 Hz) y en los ultimos 20.000 ciclos del ensayo, antes de que el test se detenga por lo metodos tradicionales, se observa un cambio en la tendencia de la energia motivado por los defectos del eje bajo estudio, que en este caso se trata del test 3.Significant changes in the evolution of the energy related to harmonics of the rotation speed can be seen, as for example in Figure 2, where the evolution of the energy is shown specifically in the frequency band 5.9-11.7 Hz, which contains the first harmonic of the speed of rotation (8.5 Hz) and in the last 20,000 cycles of the test, before the test is stopped by traditional methods, a change in the tendency of the energy motivated by the axis defects under study, which in this case is test 3.
En cambio, lo mas sorprendente ocurre en la observation de los subarmonicos deInstead, the most surprising thing happens in the observation of the subharmonics of
frecuencias criticas del eje, donde tambien se detectan unos cambios significativos,critical axis frequencies, where significant changes are also detected,
espedficamente, en la banda de frecuencias 64,5-70,3 Hz, la cual corresponde al tercerspecifically, in the frequency band 64.5-70.3 Hz, which corresponds to the third
subarmonico de la primera frecuencia critica del eje (que se corresponde segun el ensayosub-harmonic of the first critical frequency of the axis (which corresponds according to the test
experimental de la realization particular bajo estudio con 194,19 Hz, y su tercerexperimental of the particular realization under study with 194.19 Hz, and its third
subarmonico con 64,73 Hz). La figura 3 muestra la evolucion de la energia en esta banda desubharmonic with 64.73 Hz). Figure 3 shows the evolution of energy in this band of
frecuencias en la direction transversal y puede verse que los cambios en la tendencia defrequencies in the transverse direction and it can be seen that changes in the trend of
energia de esta banda de frecuencias se observan antes que los de los armonicos de laenergy of this frequency band are observed before those of the harmonics of the
velocidad de giro. Este efecto sorprendente en la tendencia de la energia es usado por laturning speed. This surprising effect on the energy trend is used by the
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presente invention para detectar ventajosamente los defectos en un eje bajo estudio durante un test de fatiga, ya que, a la vista de las figuras, puede afirmarse que los defectos pueden detectarse con mucha anterioridad y estableciendo un valor umbral para la ene^a, la maquina de pruebas se detendria aproximadamente 150.000 ciclos antes que siguiendo los criterios convencionales de parada, tal y como muestra el area de detection (40) de la figura 4, que corresponde a una vista ampliada de la figura 3 para la zona de interes.present invention to advantageously detect the defects in an axis under study during a fatigue test, since, in view of the figures, it can be affirmed that the defects can be detected much earlier and establishing a threshold value for the jan ^ a, the The test machine would stop approximately 150,000 cycles before following the conventional stop criteria, as shown in the detection area (40) of Figure 4, which corresponds to an enlarged view of Figure 3 for the area of interest.
La presente invencion por tanto, monitoriza las vibraciones emitidas por el eje de forma continua y para la deteccion de defectos se buscan los fenomenos observados durante el analisis dinamico del eje en subarmonicos de la velocidad critica del eje, asi como armonicos de la velocidad de giro.The present invention therefore monitors the vibrations emitted by the axis continuously and for the detection of defects the phenomena observed during the dynamic analysis of the axis in subharmonics of the critical speed of the axis are sought, as well as harmonics of the rotation speed. .
La invencion propuesta, de acuerdo a una realization particular, ofrece un criterio de parada temprana del test de fatiga a partir del estudio de las senales emitidas por el eje ferroviario, ya que durante dicho test se adquieren las senales de tipo vibratorio mediante un sensor, por ejemplo un acelerometro, que son recogidas por un sistema de adquisicion y enviadas a un procesador de senales. Tras procesar las senales y aplicar transformada wavelet en paquetes para obtener una medida de la energia (7) de las senales, se realiza un analisis exhaustivo por bandas de frecuencia y se detectan las diferencias de energia en determinadas franjas que indican la presencia de un defecto. La principal desventaja es que los cambios en las frecuencias naturales son muy pequenos, y pueden ser tapados debido a errores experimentales, pero la presenta invencion propone el analisis de los subarmonicos de la primera frecuencia critica del eje y de los armonicos de la velocidad de giro, siendo especialmente relevante el tercer subarmonico de la frecuencia critica, donde la tendencia de la energia es mas evidente y permite anticipar considerablemente la deteccion de un fallo. Por tanto, se establecen unos patrones de energia para los cuales se determina que el eje es defectuoso y, a dicho umbral de energia se vincula la parada del test, con lo que se garantiza la parada temprana de dicho test en caso de que se produzca la deteccion de un fallo en el eje.The proposed invention, according to a particular embodiment, offers a criterion of early stopping of the fatigue test from the study of the signals emitted by the railway axis, since during said test the vibratory type signals are acquired by means of a sensor, for example an accelerometer, which are collected by an acquisition system and sent to a signal processor. After processing the signals and applying wavelet transform in packages to obtain a measure of the energy (7) of the signals, an exhaustive analysis by frequency bands is performed and the energy differences in certain bands are detected that indicate the presence of a defect . The main disadvantage is that the changes in the natural frequencies are very small, and can be covered due to experimental errors, but the present invention proposes the analysis of the sub-harmonics of the first critical frequency of the axis and the harmonics of the speed of rotation , the third subharmonic of the critical frequency being especially relevant, where the energy trend is more evident and allows the detection of a fault to be anticipated considerably. Therefore, energy standards are established for which it is determined that the axis is defective and, to said energy threshold, the test stop is linked, which guarantees the early stop of said test in the event that it occurs the detection of a fault in the axis.
Los patrones de energia adquiridos durante el analisis previo se almacenan en una memoriaThe energy patterns acquired during the previous analysis are stored in a memory
del procesador y, de acuerdo a una de las realizaciones de la invencion, cuando se someteof the processor and, according to one of the embodiments of the invention, when submitted
un nuevo eje ferroviario a un test de fatiga, se recupera de dicha memoria el patrona new railway axis to a fatigue test, the pattern is recovered from said memory
correspondiente a dicho tipo de eje ferroviario. Se determina que existe un defectocorresponding to said type of railway axis. It is determined that there is a defect
estableciendo un umbral de energia y monitorizando las bandas de frecuencia de interes yaestablishing an energy threshold and monitoring the frequency bands of interest already
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mencionadas, lo que permite establecer un criterio de parada para el ensayo a fatiga en funcion de la deteccion de dichos defectos.mentioned, which allows establishing a stop criterion for the fatigue test based on the detection of said defects.
Claims (13)
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| WO2017103294A1 (en) * | 2015-12-16 | 2017-06-22 | Universidad Carlos Iii De Madrid | Method for detecting defects in railway axles during fatigue tests |
| CN110849753A (en) * | 2019-12-09 | 2020-02-28 | 大连理工大学 | Metal material fatigue strength prediction method based on micro scratches |
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| US6192758B1 (en) * | 1998-12-14 | 2001-02-27 | Kang Huang | Structure safety inspection |
| US20040078160A1 (en) * | 2002-10-11 | 2004-04-22 | Frei Mark G. | Method, computer program, and system for intrinsic timescale decomposition, filtering, and automated analysis of signals of arbitrary origin or timescale |
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| WO2017103294A1 (en) * | 2015-12-16 | 2017-06-22 | Universidad Carlos Iii De Madrid | Method for detecting defects in railway axles during fatigue tests |
| CN110849753A (en) * | 2019-12-09 | 2020-02-28 | 大连理工大学 | Metal material fatigue strength prediction method based on micro scratches |
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