Synchronisation of inter-arrival times in manufacturing systems with main and side loops

Automated manufacturing systems commonly employ track-bound work piece transport mechanisms and work piece holders. In the systems considered, the track layout comprises one main loop and multiple side loops, following common industrial practice. As soon as work piece holders simultaneously traverse common tracks on multiple routes, e.g. because the main loop serves as a buffer, such manufacturing systems normally show complex, aperiodic inter-arrival times, which may affect performance. A synchronisation method is presented that limits the number of different inter-arrival times and controls the length of inter-arrival time periods without requiring extensive mathematical modelling. It is applied to a simplified model of a manufacturing system, for which allowable parameter tolerances are derived and validated with simulation. Since these tolerances are very narrow, synchronised operation requires continuous control of inter-arrival times. The applicability of the proposed approach is also demonstrated for a larger eight-station assembly model. Since the presented approach limits the number of system states reached, it helps the system designer anticipate and design against state explosions. The presented method clarifies the complexity—flexibility trade-off between system synchronisation and genuinely de-coupled designs that separate tracks for different routes.