Design of Identification System Based on Machine Tools’ Sounds Using Neural Networks

Recently, deep learning models such as convolutional neural networks (CNNs), convolutional autoencoders (CAEs), CNN-based support vector machines (SVMs), YOLO, fully convolutional networks (FCNs), fully convolutional data descriptions (FCDDs) and so on have been applied to defect detections and anomaly detections of various kinds of industrial products, materials and systems. In those models, downsampled images, including target features, are used for training and testing. On the other hand, although various types of anomaly detection systems based on time series data such as sounds and vibrations are also applied to manufacturing processes, complicated conversions to the frequency domain are basically needed in conventional approaches. This paper addresses an important industrial problem for detecting anomalies in machine tools at low cost using audio data. Intelligent anomaly diagnosis systems for computer numerical control (CNC) machine tools are considered and proposed, in which raw time-series data without the need of conversion to the frequency domain can be directly used for training and testing. As for the NN models for comparison, conventional shallow NN, RNN and 1D CNN are designed and trained using the nine kinds of mechanical sounds. Classification results of test sound block (SB) data by the three models are shown. Then, an autoencoder (AE) is designed and considered for the identifier by training it using only normal SB data of a machine tool. One of the technical needs in dealing with time-series data such as SB data by NNs is how to clearly visualize and understand anomalous regions in concurrence with identification. Finally, we propose the SB data-based FCDD model to meet this need. Basic performance of the SB data-based FCDD model is evaluated in terms of anomaly detection and concurrent visualization of understanding.