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manage it and the activities it depends on to maximize constraint performance and thus organization performance is explained. With Drum-Buffer-Rope (DBR), we see how to pace work flows through a system by timing release of new work and buffering system leverage points for statistical fluctuations, all in a way to maximize Throughput and minimize flow time. The newer concept of Simplified Drum-Buffer-Rope is explained in detail as is the framework for a pull material requirements planning (MRP) system based on Theory of Constraints (TOC) and lean concepts. We see how Buffer Management provides clear focus on priorities for expediting to prevent production delays and spotlights the best applications for improvement measures, pointing to specific areas where improvement will do the most good and count toward the bottom line. It thus becomes a centerpiece for implementing a process of ongoing improvement. Buffer Management works in job shops, assembly plants, supply chains, projects, paperwork flows, and many other environments.

CHAPTER 7

A Review of Literature on Drum-Buffer-Rope, Buffer Management and Distribution

John H. Blackstone Jr.

Introduction

This chapter is the lead chapter in a section on the Theory of Constraints (TOC) approach to production and inventory planning and control. The focus is to highlight literature on Drum-Buffer-Rope (DBR) scheduling and execution and control of that schedule through Buffer Management. Today, TOC experts believe that Buffer Management is a necessary condition for an effective Drum-Buffer-Rope system. This scheduling and control mechanism has been extended across supply chains to pull inventory to consumers. This extension of TOC into supply chains is known as Rapid Replenishment.

This chapter reviews articles describing the nature and application of DBR, Buffer Management, and the TOC approach to replenishment.

In the TOCICO Dictionary (Sullivan et al., 2007, 18), drum-buffer-rope is defined as “(t)he TOC method for scheduling and managing operations. Usage: DBR uses the following: (1) The drum, generally the constraint or CCR, which processes work in a specific sequence based on the customer requested due date and the finite capacity of the resource; (2) Time buffers which protect the shipping schedule from variability; and (3) A rope mechanism to choke the release of raw materials to match consumption at the constraint.” (© TOCICO 2007, used by permission, all rights reserved.)

1 The TOCICO Dictionary (Sullivan et al., 2007, 7) defines “capacity constrained resource (CCR)—Any resource that, if its capacity is not carefully managed, is likely to compromise the throughput of the organization ....” (© TOCICO 2007, used by permission, all rights reserved.).

Copyright © 2010 by John H. Blackstone Jr.

The concepts underlying DBR were first laid out by Goldratt2 (1984) in The Goal, although the actual terminology first appeared in Goldratt and Fox (1986), The Race.

DBR is the scheduling and control mechanism used to implement Theory of Constraints in a service or production facility. The term comes from the concept that the slowest station in a facility (or the market if all workstations have extra capacity) must set the pace for all the other stations, or else inventory will grow unchecked at the slower stations. This slowest station (or the market) that sets the pace for the shop is called the drum. The buffer is material (represented as time) upstream of the drum making sure that it is never starved for work. The rope is a signaling mechanism from a buffer to the gateway station pulling material into the shop at the rate the drum completes material.

The purposes of this chapter are sixfold. First, the precursors to TOC scheduling are described. Second, a review and critique of the literature on DBR scheduling is presented. Third, special cases such as free goods (when the market is the constraint), re-entrant flows, and remanufacturing are discussed. Fourth, a review and critique of the literature on Buffer Management are presented. Fifth, the literature on