Fixed task zone chaining: worker coordination and zone design for inexpensive cross-training in serial CONWIP lines
This work introduces a new canonical model of worker cross-training, called a Fixed Task Zone Chain (FTZC), as a special type of zone-based cross-training and develops a methodology to employ it in U-shaped CONstant Work In Process (CONWIP) lines. The FTZC approach is intended to address lines with more stations than workers in environments where extensive cross-training is prohibitive. It incorporates a two-skill chain to cross-train one skill at each end of each zone; however, tasks at the interior of a zone are not cross-trained. A heuristic dynamic control policy is developed that maximizes the line's throughput given a zone structure. Some useful properties of the optimal policy are provided as a basis for a heuristic control policy that yields high throughput. The performance of an FTZC system is contingent upon the choice of zone structure; therefore, the zone assignment (ZonA) algorithm is created to design the zone structure to achieve high throughput levels. Sufficient conditions which guarantee that the line is balanceable through ZonA are derived. Benchmarking over a test suite supports the effectiveness of the proposed heuristic worker control policy as well as the ZonA algorithm, and its performance is compared with other paradigms.