This production system is operated in Pull mode based on an inventory level decision-making mechanism.
For one part type, when the order is arriving, the managers will first check the finished product inventory
(be) to determine whether the stock is large enough to provide the quantity ordered. If the order
can be fulfilled, a corresponding quantity of parts will be delivered to the customer. If the order cannot be
filled, the upstream Work-In-Process (WIP) inventory (b7) of the last workstation (W7) will be checked. In
addition, for the last workstation W7, a certain quantity of intermediate products of multiple production
lot-sizes from b7 will be processed to meet the shortage of be. This approach is called a back scheduling
for the production system operation. All of the checking work and production will thus be stopped until a
certain upstream WIP inventory level (bi) of a certain workstation (Wi) can fulfill the shortage of a certain
downstream WIP inventory level (bj) for workstation (Wj) production. Moreover, safety stock s is considered,
and each WIP inventory level should be larger than s after determining the production quantity for
the downstream workstation. Considering the design requirements of the production line and setup-time
reduction, the production quantity for each workstation is multiple production lot-sizes. Figure 4 shows
the logic for this Pull production mode