Hierarchical management of a heterarchical manufacturing grid

Automated manufacturing systems are traditionally hierarchically controlled by a centralized control system. This makes the system deterministic and therefore easier to be optimized for efficient manufacturing of a large number of one single product. However, in modern manufacturing the demand for customization and high-mix, low-volume production is growing. This move is strengthened by the acceptation of 3D printers for industrial products and new technologies that make it easier to reconfigure manufacturing systems. Hence, new paradigms like agile manufacturing, which focuses on a shorter time to market, and flexibility are becoming more important to industry. One of these paradigms is grid manufacturing, which uses a group (grid) of autonomous manufacturing systems that can be controlled as a heterarchy (where every system is autonomous and equal to each other). In this paper the goal is to determine, by simulation, if it is useful to develop a hierarchical entity to reserve some of these systems to partly break the heterarchy. This way it would be easier to optimize performance of manufacturing batch products. To fully utilize a grid it would be of interest to be able to use both hierarchical control, where a hierarchical entity reserves specific manufacturing systems, and heterarchical control, where a product can negotiate with any manufacturing system to complete the next step. Since both hierarchical and heterarchical control have advantages this paper investigates the possibility to dynamically choose one of both strategies, depending on the current demand.