1. Introduction
The objectives of the Just-In-Time (JIT) manufacturing
approach (see Sugimori, Kusunoki, Cho & Uchikawa,
1977; Ashburn, 1986) are, among others, to reduce the
work-in-process inventory and its #uctuations and hence
reduce production costs. The main principle of the technique
is to produce material only when it is needed. Its
most celebrated component is the so called kanban
method, which many researchers and analysts have adopted
in order to model various types of manufacturing
processes. The main idea behind the kanban method is
the following. A production line is divided into several
stages and at every stage there is a "xed number of tags
(or tickets) called kanban. An arriving job receives a kanban
at the entrance of the stage and maintains possession