Drum, Buffer, Rope and Days of Inventory (DOI) Control

Abstract

The theory of Constraint (Goldratt, The goal: A process of ongoing improvement, 1992) is subordinating the production line input and output material to the line bottleneck/constraint capacity. The line inventory in days (DOI), is optimized by using the TOC rules. The constraint’s daily output, the line’s Drum Beat, defines the amount of raw material which enters the line. Connecting the beginning of the line with a theoretical “rope” to the line’s constraint, with same Drum Beat- the same amount of material, governs the line entrance through the constraint. In order to secure the continuous feeding of the constraint, a buffer, a few days of work in process, is kept a step or two ahead of the constraint.