Monitoring of misalignment in low speed geared shafts with acoustic emission sensors

The most common condition monitoring method applied to rotating machines is vibration measurement, although recently it has been proposed that acoustic emission (AE) offers additional advantages in early fault detection and low speed rotation systems. Capturing the AE signals is conditioned by the severe attenuation with distance and the presence of material discontinuities between source and sensor, therefore measurement device placement is more important than in traditional accelerometry. In this study AE signals are measured in gearboxes at misalignment conditions for the revision of signal characteristics from the generated signal due to the interaction of shafts, bearings and gears. For this purpose, several tests are performed using combinations of speed and varying load, considering the effect of lubricating oil temperature. Fixed measurements are taken over the bench supports, and on-board, where the sensors are rotating with the shafts. In parallel to acoustic emission a vibration analysis is done in order to contrast and analyze differences between both technologies at different operation states. Acquired data is processed to obtain statistical parameters from measurements in order to verify the values and tendencies due to transient phenomena related to changes in speed and load. AE provides better results than vibration employing the same time domain condition indicators. On the contrary, vibration recognizes clearly the fault through frequency analysis.This work has been supported by project DPI2017-85390-P funded by the Spanish Ministry of Science and Technology and RM16-XX012 PredictEA project funded by SODERCAN

Aplicación de la sensibilidad a la síntesis óptima de mecanismos planos con restricciones cinemáticas

RESUMEN: En este artículo se presenta un procedimiento de síntesis óptima de mecanismos basado en análisis de sensibilidad. Los coeficientes de sensibilidad obtenidos ofrecen una relación de primer orden entre los parámetros que definen la geometría del mecanismo y sus características cinemáticas. El procedimiento utiliza estos parámetros de sensibilidad para proporcionar la información necesaria de evolución desde el mecanismo inicial hasta la solución optimizada.ABSTRACT: This paper describes a procedure for the optimal synthesis of mechanisms based on sensitivity analysis. The sensitivity coefficients obtained give a first order relationship between geometrical parameters and kinematic characteristics of the mechanism. The procedure uses theses sensitivity parameters in order to obtain the necessary information about the evolution of the mechanism from the initial configuration to the optimal solution

Síntesis de guiado de sólido rígido en mecanismos espaciales mediante coeficientes de sensibilidad relativos

En este artículo se presenta un método para la síntesis dimensional óptima de mecanismos espaciales. Dicho método está basado en el cálculo exacto del gradiente a través de los denominados coeficientes de sensibilidad. La formulación de los mecanismos analizados se hace mediante ecuaciones de restricción en coordenadas esféricas. Una de las principales características del método es que hace posible la definición de un número elevado de posiciones de precisión así como la inclusión de distintos tipos de restricciones cinemáticas adicionales manteniendo unos tiempos de convergencia bajos. Para mostrar sus características se ha aplicado a un mecanismo de suspensión de automóvil del tipo triángulos superpuestos.In this paper a method for dimensional synthesis in spatial linkages is presented. This method is based on the calculus of the exact gradient through the called sensitivity coeficients. The modelling of the mechanisms uses constraint ecuations formulated in spherical coordinates. One of the main advantages of the method is the possibility of definition of a high number of precision poses as well as various types of kinematics constraints with a low convergence time. An automotive suspension mechanism type double wishbone is used to test the abilities of the method.Este trabajo ha sido desarrollado en el marco del Proyecto DPI2002-02043 financiado por el Ministerio de Ciencia y Tecnología del Gobierno de España

Un modelo del comportamiento dinámico de una caja de engranajes multietapa

RESUMEN: En este trabajo se aborda el desarrollo de un modelo teórico de una caja de engranajes compuesta por múltiples etapas. Para ello se incorporan las particularidades de cada uno de los elementos individuales que forman parte de este tipo de sistemas. Se plantea un modelo de contacto para engranajes helicoidales considerando una variación periódica de la rigidez como consecuencia del proceso de engrane así como la presencia de irregularidades superficiales. El comportamiento dinámico de los rodamientos se ha considerado incorporando su correspondiente matriz rigidez obtenida a partir de los distintos contactos Hertzianos entre los elementos rodantes y las pistas exterior e interior. Este planteamiento requiere el desarrollo de un proceso iterativo para determinar la posición de operación en función del par resistente. Finalmente las ecuaciones dinámicas se integran directamente obteniendo la respuesta de cada una de las etapas de la caja así como las fuerzas actuantes sobre cada elemento.ABSTRACT: This work focuses on the development of a multistage gearbox theoretical model. The model takes into account the performances of each element involved in this kind of machines. A model for the contact between helical gears is developed including the periodical meshing stiffness and profile errors. Roller bearings are also included by their stiffness matrix obtained taking into account the Hertzian contacts between the rolling elements and the inner and outer race. Bearing stiffness calculation requires an iterative process due the non-linear relationship between forces and displacements. This iterative process provides the shaft centre location as a function of the milling torque. Under the assumption of small displacements around this stationary position a linear stiffness matrix is calculated for each bearing. Finally the dynamic equations are directly integrated obtaining the response for each stage as well as the acting forces on each element

Síntesis óptima del mecanismo de suspensión independiente para autobuses

En este trabajo se presenta una metodología para la síntesis de un mecanismo de suspensión delantera independiente tipo doble triángulo, que se ha aplicado al caso del eje delantero de un autobús urbano de piso bajo. La síntesis del mecanismo de suspensión que representa el modelo de doble triángulo se ha realizado en dos etapas: síntesis de un mecanismo plano equivalente, y síntesis del mecanismo tridimensional. El primer paso consiste en un problema de guiado de biela que se ha resuelto minimizando una función objetivo que representa el error estructural del mecanismo. En este proceso se han tenido en cuenta las restricciones impuestas al mecanismo, relativas a dimensiones de los brazos y la mangueta, ángulo de salida, radio de pivotamiento, etc. El método de síntesis empleado no incluye los efectos derivados de la elastocinemática del mecanismo de suspensión. En el ejemplo presentado se muestra la validez del método propuesto.In this work a methodology for the synthesis of an independent double-wishbone front suspension mechanism is presented. It has been applied to the front gear of a low platform urban bus. The process for the suspension mechanism synthesis of the double wishbone has been done in a two steps: an equivalent planar mechanisms synthesis, and the 3D mechanism synthesis. The first step is a rigid body guidance synthesis problem. It has been solved minimizing an objective function representing the mechanisms synthesis error. In this process it has been taken into account the restrictions imposed to the mechanism as arm dimensions, swivel pin angle, offset radio, etc. The used synthesis method does not include the effects of the suspension mechanisms elasto-kinematics. The validity of the method is shown in the example.Los autores desean expresar su agradecimiento al Ministerio de Ciencia y Tecnología por la financiación del proyecto del Plan Nacional de Automoción de Ref. FIT-110300-2003-3 “Desarrollo de sistemas de suspensión aplicables a nuevas alternativas de vehículos de transporte de pasajeros”

Identification of nonlinear anti-vibration isolator properties

Vibrations are classified among the major problems for engineering structures. Anti-vibration isolators are used to absorb vibration energy and minimise transmitted force which can cause damage. The isolator is modelled as a parallel combination of stiffness and damping elements. The main purpose of the model is to enable designers to predict the dynamic response of systems under different structural excitations and boundary conditions. A nonlinear identification method, discussed in this paper, aims to provide a tool for engineers to extract information about the nonlinear dynamic behaviour using measured data from experiments. The proposed method is demonstrated and validated with numerical simulations. Thus, this technique is applied to determine the nonlinear parameters of a commercial metal mesh isolator. Nonlinear stiffness and nonlinear damping can decrease with the increase in the amplitude of the base excitation. The softening behaviour of the mesh isolator is clearly visible

Frictional power losses on spur gears with tip reliefs. The load sharing role

The load sharing impact on the efficiency of spur gears with modified profile was assessed in this work. The aim was to analyse the influence of the profile modifications on the load sharing, which also considers the effect of the torque level on the system deflections, and how these load sharing variations affected the system efficiency. Due to the frictional effect importance on power losses, in the operating conditions considered, sliding friction between teeth in presence of lubricant was studied in this proposal. The results established that tip relief improves the efficiency of the system due to the reduction of effective contact ratio. Moreover, there is a tip relief which makes optimal the efficiency in specific operating conditions, corresponding to the unit value of the effective contact ratio. Thus, the main conclusion of this work is that the tip relief which makes optimal the efficiency coincides with the theoretical dynamic optimum of the transmission.The authors would like to acknowledge Project DPI 2013-44860 funded by the Spanish Ministry of Science and Technology and the COST ACTION TU 1105 for supporting this research

Analysis of human-induced vibrations in a lightweight framework

This article analyzes the vibratory behavior of a Material-Composed Sandwich (MCS) framework for residential buildings. It has been observed qualitatively that the use of this kind of framework leads to poor comfort levels. The goal of this study is to find out the sources of this lack of comfort, in order to suggest guidelines that can enhance the performance of the MCS framework, without jeopardizing its advantages with respect to the traditional frameworks. To achieve this objective, an Experimental Modal Analysis (EMA) of a sample MCS framework has been carried out in order to determine the dynamic parameters. Then, a numerical Finite Element (FE) model of said sample MCS framework has been developed and adjusted with the results obtained in the experimental test. Based on this, a real-dimension MCS framework FE model has been built and the resultant behavior compared with that of a commonly used framework made of reinforced concrete. This comparison is finally used to assess the uncomfortable dynamic response of the MCS framework and to draw conclusions on the design guidelines in order to enhance the MCS framework vibratory behaviorThe authors would like to acknowledge Project DPI2013-44860 funded by the Spanish Ministry of Science and Technology and COST ACTION TU 1105 for supporting this research

Enhancement of Mechanical Engineering Degree through student design competition as added value. Considerations and viability

This paper proposes using a student design competition as a learning tool in the Mechanical Engineering Degree for enhancing the general competences and motivation of the students, transferring theoretical knowledge to practical situations and bringing together all courses involved under a common framework. This constitutes an added value that the in-person universities should offer to their students as a consequence of the Bologna process and the raising of open online resources for self-learning. In order to assess the viability of this proposal, a pilot competition design activity (CDA) is presented using project-based learning methods during a Mechanism Theory course for sophomore students. Meanwhile, 27 participants of a 45-student course from a European university took part in the pilot CDA, which consisted of redesigning the motorbike rear suspension used in a student design competition. Participants also completed mid-term and final exams as well as a survey to get their perception of this activity. Based on the success of the pilot CDA, the authors are planning to implement the proposal, including similar CDAs in other Mechanical Engineering courses to use the competition as a link between them and to encourage students to participate on the competition.This work [Project DPI2013-44860] was supported by the Spanish Ministry of Science and Technology and Vicerrector Primero y de Profesorado of the University of Cantabria

Frictional power losses on spur gears with tip reliefs. The friction coefficient role

In this proposal, the effect of the friction coefficient on the efficiency of spur gears with tip reliefs was analysed. For this purpose, the efficiency values using an average friction coefficient along the mesh cycle were compared with those obtained implementing an enhanced friction coefficient formulation, which is based on elastohydrodynamic lubrication fundamentals. In this manner, it can be established the differences between both formulations in the efficiency and friction coefficient values, as well as the advantages of using this enhanced friction coefficient with respect to formulations implemented in traditional approaches of efficiency calculation. In addition to studying the impact of the friction coefficient choice on efficiency, the profile modifications influence on the friction coefficient and efficiency was also assessed. In this regard, three tip relief case studies were set out; pinion tip reliefs, driven wheel tip reliefs and profile modifications in both gears. From the results, it was inferred that the choice of friction coefficient formulation clearly influences the efficiency in gear transmissions with tip reliefs, obtaining discrepancies between both formulations with regard to which tip relief case study provides the lowest efficiency values.The authors would like to acknowledge Project DPI 2013-44860 funded by the Spanish Ministry of Science and Technology