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The ability to handle unpredictable dynamic events is becoming more important in pursuing agile and flexible production scheduling. At the same time, the cyber-physical convergence in production system creates massive amounts of industrial data that needs to be mined and analysed in real-time. To facilitate such real-time control, this research proposes a hierarchical and distributed architecture to solve the dynamic flexible job shop scheduling problem. Double Deep Q-Network algorithm is used to train the scheduling agents, to capture the relationship between production information and scheduling objectives, and make real-time scheduling decisions for a flexible job shop with constant job arrivals. Specialised state and action representations are proposed to handle the variable specification of the problem in dynamic scheduling. Additionally, a surrogate reward-shaping technique to improve learning efficiency and scheduling effectiveness is developed. A simulation study is carried out to validate the performance of the proposed approach under different scenarios. Numerical results show that not only does the proposed approach deliver superior performance as compared to existing scheduling strategies, its advantages persist even if the manufacturing system configuration changes. [ABSTRACT FROM AUTHOR]

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.ejor.2005.06.066 Byline: Rajesh Piplani (a), Dennis Wetjens (b) Keywords: Flexible manufacturing systems; Dispatching; Entropic measures of flexibility; Routing flexibility Abstract: Traditionally, part dispatching has been done using static rules, rules that fail to take advantage of the dynamic nature of today's manufacturing systems. In modern manufacturing systems, machines carry multiple tools so parts have the option of being machined at more than one machine. This flexibility, termed routing flexibility in the literature, opens up new possibilities for shop floor planners for the scheduling and dispatching of parts. In this paper, we give some background of manufacturing system flexibility, including its measurements. We also present quantifiable measures of flexibility and discuss part dispatching based on entropic measures of part routing flexibilities. Two rules for parts dispatching, namely 'least reduction in entropy' and 'least relative reduction in entropy' are presented. It is proposed that to take advantage of system flexibility, parts dispatching rules based on flexibility measures should be used, especially in systems with high breakdown rates. An extensive simulation study is conducted to evaluate the performance of the dispatching rules. The simulation study confirms that entropy-based dispatching rules out-perform traditional dispatching. Author Affiliation: (a) Center for Supply Chain Management, School of Mechanical and Aerospace Engineering, Nanyang Technology University, 50 Nanyang Avenue, Singapore 639798, Singapore (b) Eindhoven University of Technology, Eindhoven, The Netherlands Article History: Received 13 July 2004; Accepted 30 June 2005

Kanban control systems have been around for decades and have been used to control work-in-process of manufacturing systems. Lately many variations of the basic control system have been developed; however, much of the work in the development and comparison of control systems has focused on a single-stage manufacturing system producing a single product type. In this research, we present procedures for optimising multiple product kanban control systems, namely Base Stock, Traditional Kanban Control System and Extended Kanban Control System (both dedicated and shared type). We then conduct a detailed simulation study to compare the performance of the systems using a common total cost measure. Numerical results show that the dedicated and shared-extended kanban control systems outperform the other two systems. The study also shows that in spite of their different schematics and contrary to conventional wisdom, the performance of dedicated and shared-extended kanban control systems doesn’t differ much. [ABSTRACT FROM AUTHOR]

The evaluation approach specifically focusing on the supply-side collaboration on inventory decisions between a supplier and a distributor in a two-echelon supply chain are presented. The numerical experiments prove that the supply-side collaboration has the ability to improve the supply chain performance in terms of better stabilizing effect and service level.

In this paper we discuss a typical service network of a company providing repair and refurbishment services for its products. To optimise the network we propose a mixed-integer linear programming (MILP) model that minimises the total cost subject to flow balance and logical constraints. The solution of the model determines which facilities are to be used in the network and the associated flows. The model is validated against data obtained from a computer manufacturer and real-life sources. The optimal network configuration depends on several factors such as the number of products returned, percent of faulty products and warranty fraction of modules, which are uncertain in nature. We also address the issue of identifying these uncertain parameters, and their levels to be considered. A min-max robust optimisation model is then developed and solved to address these uncertainties. [ABSTRACT FROM PUBLISHER]

We investigate the value of various information exchange mechanisms in a four-echelon supply chain under a material requirements planning framework. In the absence of any information sharing, each echelon would develop its own forecasts and plan its inventories based on the history of actual demand from its downstream customer (or echelon). Through a simulation study, we compare this policy with policies where each echelon has access to (i) the end-user demand history and (ii) the planned order schedule of the downstream echelon. Among all the demand information exchange mechanisms, planning inventories based on the planned downstream order schedules resulted in the lowest average inventory level for the entire supply chain. However, use of end-user demand history to forecast and plan inventories at all echelons resulted in the lowest total cost. In addition to the information exchange mechanisms, a simple synchronized replenishment system was considered and evaluated in the study. In the synchronized system, the retailer determines a fixed order interval and the upper echelons replenish only at integer multiples of this interval. The study found that synchronized inventory replenishments among the echelons, even without any exchange of demand information, can bring about more benefits and cost reduction than any of the information exchange mechanisms. [ABSTRACT FROM AUTHOR]

We consider an inventory system under continuous review with two demand classes that are different in terms of service level required (or penalty cost incurred for backordering of demand). Prior literature has proposed the critical level rationing ( CLR) policy under which the demand from the lower priority class is backordered once inventory falls below the critical level. While this reduces the penalty cost for the higher demand class, the fill rate achieved for the lower priority demand class gets compromised. In this study, we propose a new class of two-bin (2B) policy for the problem. The proposed 2B policy assigns separate bins of inventory for the two demand classes. The demand for each class is fulfilled from its assigned bin. However, when the bin intended for the higher demand class is empty, the demand from the higher class can still be fulfilled with the inventory from the other bin. The advantage of the 2B policy is that better fill rates are achieved, especially for the lower demand class. Computational results show that the proposed policy is able to provide a much higher service level for the lower priority class demand without increasing the total cost too much and without affecting the service level for the higher priority class. When a service level constrained optimization problem is considered, the 2B policy dominates the CLR policy when the service level difference for the two classes is not too high or the service levels required for both the classes are relatively lower. [ABSTRACT FROM AUTHOR]

Research is presented concerning the development of a model for the analysis of coordinated inventories of supply chains through the utilization of common time periods or replenishment epochs.