Multimodal Hidden Markov Model-Based Approach for Tool Wear Monitoring

In this paper, a novel multimodal hidden Markov model (HMM)-based approach is proposed for tool wear monitoring (TWM). The proposed approach improves the performance of a pre-existing HMM-based approach named physically segmented HMM with continuous output (PSHMCO) by using multiple PSHMCOs in parallel. In this multimodal approach, each PSHMCO captures and emphasizes on a different tool wear regiment. In this paper, three weighting schemes, namely, bounded hindsight, discounted hindsight, and semi-nonparametric hindsight, are proposed, and two switching strategies named soft and hard switching are introduced to combine the outputs from multiple modes into one. As an illustrative example, the proposed approach is applied to TWM in a computer numerically controlled milling machine. The performance of the multimodal approach with various weighting schemes and switching strategies is reported and compared with PSHMCO.