Modelling hybrid production systems through the ACD specification: a case study in the fibre-glass industry

This paper is aimed at formalizing a model for hybrid production systems where the interactions between the continuous process parts and the manufacturing subsystems are given by minor stoppages. The proposal is to represent the effects of the continuous process dynamics on discrete manufacturing sub-systems using Autoregressive Conditional Duration (ACD) models originally conceived to treat high-frequency and irregularly spaced financial transaction data. The proposed methodology has been tested on a real-life fibre-glass production plant exploiting simulation techniques. The physical model of the furnace and spooling-bushing department has been run in two different conditions: (i) the fibre-glass breakings, i.e. minor stoppages, on the spooling-bushing machines are generated according to the proposed approach; (ii) historical fibre-glass breakings data are used. The comparison between the simulation results shows that for three spooling-bushing machines only out of 24, the daily throughput of completed spools and the empirical distributions for the uncompleted spools weight are dissimilar under the two different conditions. Therefore, the ACD-based model proved useful for representing the occurrence of fibre-glass breakings on the spooling-bushing machines and, in more general terms, for the logical modelling of the hybrid production systems, where the relationships between continuous and discrete parts are given by minor stoppages.