Management of worksharing systems

Worksharing occurs in serial manufacturing when machines are not uniquely assigned to workers. For example, two workers can operate three machines by alternating usage of the middle one. In some other worksharing systems operators move down the line carrying an item (or batch) with them, working on it at each machine until they are met by another worker who is coming back upstream. The work is then handed off even if the operation is underway. ‘Bucket Brigade’ and ‘TSS’ are worksharing systems based on this idea. This paper examines worksharing in a variety of situations, including unequal work content across machines, uncertain processing times, unequal workers, handoffs with and without preemption, and a range of machine-to-worker ratios. Some systems restrict workers to ‘zones’ of machines. Work zones must overlap if sharing is to occur. The appropriate size of the overlap is shown to depend on the circumstances. Inventory-based rules to control access to shared machines are demonstrated to incease productivity when processing times vary. Worker sequence is found to be quite important; Slowest-to-Fastest is recommended for some situations, but is shown to perform poorly in others. Finally, the issue of whether or not to allow preemption is shown to have a large impact on productivity if inventory is not allowed, and to strongly affect the choice of designs when inventory is allowed. With and without preemption, proper combinations of worker sequence, zone size, and production control rules are shown to nearly eliminate idle time.