Fault identification and estimation is an important and necessary step in Condition Based Maintenance. In general, there are two prevalent methods that are used for this purpose, data driven techniques and model based techniques. Data driven techniques use data collected from experiments, learn about the system and then use this knowledge to infer the system’s current state of health. Model based techniques use models to derive the knowledge that can be used to determine the machine’s condition. Each of these methods has its own limitations and strengths. This research proposes a novel approach that integrates the information from both data and models in an optimal fashion to provide accurate diagnostic information about the health condition of machinery. Specifically, rotor-bearing systems are used as test cases to develop these methods.
Figure 1 shows the basic steps involved in any diagnostic methodology. Sensors are used to record various signals from the machine but these signals cannot be directly used as such signals are often very large in size and noisy. Signal processing techniques are hence used to derive useful and compact information about the system from these measurements. These information packets are called features and the process is called feature extraction.
Typically the tasks of a diagnostic and prognostic methodology are as follows.
These duties need to be performed in a sequence. Figure 2 shows the typical sequence of operations to be performed as the degradation in system increases.
It should be noted that model and data integration is achieved in two ways. First, features are developed by combining data and models (model based features). Second, integration is also achieved by smart fusion of model and data based features in a hybrid feature set.
Referring to Figure 3, two machines belonging to a same class have certain similarities; these similarities are captured in the physics-based models. Further, each machine based on its environment has a certain individuality; this individuality is captured in the data. Thus, using both models and data could increase the efficiency and accuracy in performing diagnostics and prognostics. The current research aims at integrating the models and data to better predict the performance of the machine. Also models generalize the system so that efficient algorithms based on models can be applied to various systems with minor modifications.
This new idea of integration of information has been developed and validated to detect, and to identify type and severity of localized defects in rolling element bearings. Rolling element bearings have been chosen for this study as they are the load carrying elements in many high speed machinery, one of the primary sources of nonlinearity and often the cause of failure.