An unsupervised neural network for graphical health index construction and residual life prediction

To better characterize the health status and performing remaining useful life prediction, a composite health index is developed through the fusion of multi-channel signals. However, most of the existing literature limits the data fusion to be linear, which implies that the underlying degradation pattern must follow a linear form. This strong prerequisite of these approaches undermines the effectiveness of existing techniques for capturing the potential nonlinear nature of degradation process. In order to overcome this limitation as well as to improve the predictability, this paper proposes a nonlinear health index construction method achieving by an unsupervised neural network. Specifically, a neural network structure is introduced to approximate the highly nonlinear relationship between signals and health status. Furthermore, we consider the remaining useful life prediction as a binary classification problem, and then propose a maximal classification margin constraint, which is integrated with the monotonicity and minimal variability at the failure time to formulate the novel loss function. To estimate the model parameter, we developed a customized adaptive moment estimation algorithm (Adam). The comprehensive case study is performed based on the benchmark C-MAPSS dataset. As reported in the experiment, the constructed health index can better characterize the underlying degradation process.