MODELS OF HEIJUNKA-LEVELLED KANBAN-SYSTEMS

Heijunka is a key-element of the Toyota production system. It is used to level the release of production kanbans in order to achieve an even production program over all possible types of products thus reducing or eliminating the bullwhip effect. In this paper the depen-dencies between the parameters of the levelling process and the requirements in finished goods stocks are derived, resulting in an instrument for the sizing of heijunka controlled kanban loops. 2. PROBLEM DESCRIPTION Queueing networks have been extensively used to model and study control policies for production systems. Especially prominent are the works about CONWIP- and kanban sys-tems. Both keep the level of production and the work-in-process constant. While CONWIP keeps the WIP constant by releasing a new production order when one production order is finished, kanban also takes into account the demand process, releasing a new job when demand has occurred and the number of jobs in process has not reached its upper limit. Extensive work is available about models of these two control systems