Model-based diagnosis of gear fault under variable loading condition

A model-based method is proposed to diagnose the gear fault in the gearbox under variable loading condition with the objective to apply it to the wind turbine CMS. A simple test bed is installed to illustrate the approach, which consists of motors and a pair of spur gears. A crack is imbedded at the tooth root of a gear. Tachometer-based order analysis, being independent on the shaft speed, is employed as a signal processing technique to identify the fault, which includes detecting the location and extracting the adequate feature. Lumped parameter dynamic model is used to simulate the operation of the test bed. In the model, the parameter related with the fault is inversely estimated by minimizing the difference between the simulated and measured features. Finally the parameter is used to estimate the crack size based on the regression model made by finite element stiffness analyses of a set of gears with imbedded crack. The results of estimated crack are validated by comparing with the actual ones of seeded crack.