Anomaly detection in today's industrial environments is an ambitious challenge in order to detect possible arising faults/problems, which may turn into severe waste during production, into defects or even into damages of systems components, at an early stage. Data-driven anomaly detection from multi-sensor networks faces challenges in proper data (information) fusion methodologies to establish adequate modeling cycles, whose outcome are models characterizing the anomaly-free reference situation based on which new on-line data are compared with, i.e. how much these deviate from them (pointing to potential faults). In this paper, we propose a new approach which is based on i) causal relation networks (CRNs) representing the inner causes and effects between sensor channels (or sensor nodes) in form of partial sub-relations, which are modeled by non-linear (fuzzy) regression models for characterizing the (local) degree of influences of the single causes on the effects, ii) an advanced analysis of the multi-variate residual signals obtained from the partial relations in the CRNs, which employs independent component analysis (ICA) to characterize hidden structures in the fused residuals (a significant change in these indicates an anomaly) and iii) automatized control limits on the energy content of latent variables obtained through the demixing matrix from ICA. Suppression of possible noise content in residuals ---to decrease the likelihood of false alarms ---, is achieved by performing ICA-based residual analysis solely on the dominant parts. Our approach was successfully evaluated for a real-world manufacturing process in the context of micro-fluidic chip production, where customer complaints arose about the quality of the chips during a specific production cycle $\rightarrow$ our approach could detect the anomaly in the process (leading to the bad quality chips) with negligible delay based on the process data recorded by multiple sensors in two production phases (injection molding and bonding), while it produced lower false alarm rates than several related and well-known state-of-the-art methods for (unsupervised) anomaly detection and while it also caused much lower parametrization efforts (in fact, none at all) to produce reliable results.
Keywordson-line anomaly detection; causal relation networks; advanced multi-variate residual analysis; dominant parts of independent component analysis; automatized control limits; on-line production systems