Tooth defect detection in planetary gears by the current signature analysis: numerical modelling and experimental measurements

Monitoring transmission systems is a huge scientific focus to prevent any anomaly and malfunctioning damaging the system. Several methods were used to investigate the gears behaviour and mainly its state. And until the last century, vibrations signals were the most performing technique in this field. However, nowadays, other alternatives are considered more accurate and accessible such as controlling the motor current signals to study the behaviour of the mechanical system. Within this context, this paper aims to study the electromechanical interaction between a double stage of planetary gearboxes driven by an asynchronous machine. The model used is based on a Park transformation for modelling the asynchronous machine and a torsional model to describe the dynamic behaviour of the double-stage planetary gearbox. Through this approach, the numerical simulations illustrate the impact of the tooth gear defect on the signature of the motor current. The results obtained from the simulations will be presented in the time domain and the frequency domain using the fast Fourier transform and the Hanning window to highlight the mechanical frequencies in the phase current spectrum. This work will be distinguished by validating the numerical results using experimental measurements, which will be displayed in order to justify the sensitivity of the model developed.The authors would like to acknowledge the help provided by the project “Dynamic behaviour of gear transmissions in nonstationary conditions”, ref. DPI2017-85390-P, funded by the Spanish Ministry of Science and Technology. They would like to thank the University of Cantabria cooperation project for the doctoral training to Sfax University students

Multi-domain model and condition monitoring of gear transmission

RESUMEN: Esta tesis estudia la interacción electromecánica entre un motor asíncrono y una transmisión mecánica mediante la técnica de análisis de la corriente del motor (Motor Current Signature Analysis MSCA). El estudio combina un doble enfoque teórico y experimental. Se han desarrollado modelos teóricos que simulan el comportamiento dinámico de componentes eléctricos y mecánicos con el propósito de conseguir un mejor conocimiento de la relación entre ambos dominios. Se ha utilizado la transformada de Park en la simulación de un motor asíncrono que acciona la transmisión mecánica. Se han modelizado diversos ejemplos de transmisión, tanto ordinarias como planetarias, incorporando la excitación paramétrica debida a la rigidez de engrane variable, así como la presencia de defectos con distintos tamaños y localizaciones. Los modelos desarrollados han sido validados mediante la evaluación de registros experimentales obtenidos en dos bancos de ensayo de laboratorio, comparando las señales procedentes de distintos dominios como corriente eléctrica, vibraciones mecánicas y presión sonora tanto en condiciones normales como en presencia de defectos.ABSTRACT: The ultimate work is focused on the motor current signature analysis (MCSA) technique, which describes the phase current signal in different operating conditions. The current signal was presented simultaneously with Mechanical signals, vibrations and acoustic pressure. The strategy of this thesis is based on investigating the impact of planetary gears behaviour on the phase current signal. First, numerical models were used to define the impact of the gears’ behaviour on the current signal. The theoretical model is composed of the electrical part of the asynchronous motor and a dynamic model of the planetary gears. The motor was modelled using Park transformation that generates a new bi-phased model. For the mechanical system, a one stage spur gears example was used. The objective beyond using this model was to have the hand to gears modelling and to approve the electrical model and to validate the electromechanical coupling. The second mechanical system was a double stage planetary gearbox testbench. In this part a torsional model was used to simulate the planetary test bench. In both cases, the numerical model determines the impact of the load perturbation due to the mechanical system on the motor current. The numerical study was extended study the impact of a local crack on the electrical signal. In order to validate the model, different simulations took place by implementing defects with different sizes, localization, and number. Later, the numerical simulations were followed by an experimental teste. The experiments were elaborated on a double stages’ planetary gearbox. An electrical clamp was used to record the phase current in the asynchronous motor driving the planetary gearbox. Meanwhile, Acoustic pressure and vibrations were taken simultaneously around the whole testbench. Finally, a teeth crack was implemented on the planet gears in the planetary gearbox to study the impact of defects on current signal