George Liberopoulos

Extended kanban control system: combining kanban and base stock

This paper introduces a new mechanism for the coordination of multi-stage manufacturing systems. This mechanism is called the Extended Kanban Control System (EKCS) and depends on two parameters per stage, the number of kanbans and the base stock of finished parts. The EKCS is a combination of the classical Kanban and Base Stock control systems and includes each system as a special case. The dynamics of the EKCS are described, in particular, in relation to the dynamics of the Generalized Kanban Control System (GKCS), a known control mechanism that also includes the Kanban and Base Stock control systems as special cases. Advantages of the EKCS over the GKCS are discussed. Finally, properties of the dynamics of the EKCS are presented. One important property is that the capacity of the EKCS depends only on the number of kanbans but not on the base stock of finished parts.

Perturbation analysis for the design of flexible manufacturing system flow controllers

Dynamic allocation of stochastic capacity among competing activities in a just in time manufacturing environment is addressed by optimal flow control. Optimal policies are characterized by generally intractable Bellman equations. A near-optimal controller design technique is proposed. It provides an approximate numerical solution to the Bellman equation, a tight lower bound for the optimality gap of tractable, near-optimal controller designs, and a building block for improved, near-optimal controller designs that rely on the decomposition of a multiple part-type problem to smaller (two or three part-type) problems. Computational experience is reported for two and three part-type problems.

A unified framework for pull control mechanisms in multi‐stage manufacturing systems

This paper presents a unified framework for pull production control mechanisms in multi‐stage manufacturing systems. A pull production control mechanism in a multi‐stage manufacturing system is a mechanism that coordinates the release of parts into each stage of the system with the arrival of customer demands for final products. Four basic pull production control mechanisms are presented: Base Stock, Kanban, Generalized Kanban, and Extended Kanban. It is argued that on top of any of these basic coordination mechanisms, a local mechanism to control the work‐in‐process in each stage may be superimposed. Several cases of basic stage coordination mechanisms with stage work‐in‐process control are presented, and several production control systems that have appeared in the literature are shown to be equivalent to some of these cases.

The Value of Advance Demand Information in Production/Inventory Systems

Advance demand information, when used effectively, improves the performance of production/inventory systems. In this paper, we investigate the value of advance demand information in production/inventory systems. For a single-stage make-to-stock queue, we assess the value of using advance demand information under a variety of assumptions on the cost of obtaining advance demand information, and the delivery timing requirements. This analysis enables us to identify conditions under which advance demand information may bring significant benefits.

The extended kanban control system for production coordination of assembly manufacturing systems

Abstract In assembly manufacturing systems there are points in the production process where several component parts are put together in areas called assembly cells so as to form more complex parts called subassemblies. In this paper, we present and compare two variants of the Extended Kanban Control System (EKCS) - a recently developed pull production control mechanism that combines base stock and kanban control - for the production coordination of assembly manufacturing systems. In both variants, the production of a new subassembly is authorized only when an assembly kanban is available. Assembly kanbans become available when finished subassemblies are consumed. If an assembly kanban is available, in the first variant, each component part of a subassembly is released into the assembly cell as soon as itis available (independent release). In the second variant, however, it is released only when allother component parts also become available (simultaneous release). In both variants, when a component part is released into the assembly cell, it releases its kanban, thus authorizing the production of a new component part.

Systems analysis speeds up Chipita's food-processing line

Chipita International, Inc., one of Greeces largest manufacturers of bakery products and snacks, makes croissants on seven specialized processing lines in Lamia, Greece. A rise in the demand for croissants over the past years called for an increase in output. We undertook a project to determine cost-effective ways of speeding up the croissant-processing lines. We found that the efficiency of a typical line (the ratio of the effective processing rate to the nominal processing rate) was 86 percent because of equipment failures. To reduce the impact of failures and increase the efficiency of the line, we proposed to modify the line by inserting an in-process buffer-refrigerator having a capacity of 40,000 croissants in the middle of the line and by speeding up the part of the line upstream of the buffer. We found that the efficiency of the modified line would rise to just under 98 percent at a cost of a minor increase in in-process inventory. We estimated that the modified design of the line would bring in extra earnings and savings of

Comparative modelling of multi-stage production-inventory control policies with lot sizing

19,150 per week because of the resulting increase in output, the elimination of the first shift of the week, and the reduction of scrapped material during long failures.

Production/Inventory Control with Advance Demand Information

We propose a unified modelling framework, based on a queuing network representation, for describing, comparing and contrasting classical and new multi-stage production-inventory control policies with lot sizing. The classical policies that we consider are installation stock reorder point policies, echelon stock reorder point policies and classical kanban policies, which we refer to as installation kanban policies. The new policies that we propose are echelon kanban policies and hybrid policies, which combine reorder point and kanban policies. The combination of reorder point and kanban policies can be done in a synchronized or an independent way, leading to synchronized and independent hybrid policies, respectively.

Performance Evaluation of an Automatic Transfer Line with WIP Scrapping During Long Failures

Recent advances in information technology, such as EDI and web-based platforms, have made information exchange between supply chain partners cheaper and more secure. These advances also arrived at a time when the concepts of collaboration and partnership within supply chains are being recognized and developed. The principle premises of such concepts are rather simple and natural: more collaboration and more shared information should lead to better supply chain performance. The details, on the other hand, on how to achieve better performance through increased collaboration and information are not always trivial. This chapter focuses on the following particular issue regarding increased information exchange: how should advance demand information be used to increase performance in production/inventory systems and what is the extent of the performance increase that can be expected?

Dynamics and design of a class of parameterized manufacturing flow controllers

We develop a model of a failure-prone, bufferless, paced, automatic transfer line in which material flows through a number of workstations in series, receiving continuous processing along each workstation. When a workstation fails, it stops operating, and so do all the other workstations upstream of it. The quality of the material trapped in the stopped workstations deteriorates with time. If this material remains immobilized beyond a certain critical time, its quality becomes unacceptable and it must be scrapped. We develop analytical expressions for important system performance measures for two cases. In the first case, the in-process material has no memory of the quality deterioration that it experienced during previous stoppages, whereas in the second case it has. In both cases, we assume that the workstation uptimes and downtimes follow memoryless distributions. We use the analytical expressions to numerically study the effect of system parameters on system performance. To evaluate the memoryless assumption, we compare the performance of the original model to that of a modified model in which the workstation downtimes do not follow memoryless distributions. The performance of the modified model is obtained via simulation.