Saxe, J. G. 1873. "The Blind Men and the Elephant" in The Poems of John Godfrey Saxe. Complete Edition. Boston, MA: James R. Osgood and Company, 7778.

Womack, J. P. and Jones, D. T. 1996. Lean Thinking. New York: Free Press.

About the Author.

Since 1986, AGI-Goldratt Institute has enabled organizations to better align the way they operate with what they are trying to achieve-strategic bottom-line results.

AGI is the birthplace of constraint-based techniques and solutions for business success. Many organizations and consultants trace their roots back to AGI not only for TOC, but also for how TOC integrates with other improvement methods.

AGI provides its clients with rapid, bottom-line results with what it calls VELOCITY-a powerful business approach combining speed with direction. VELOCITY consists of three pillars: TOC, the system architecture; TOCLSS, the focused improvement process; and SDAIS, the deployment framework.

SDAIS (Strategy-Design-Activate-Improve-Sustain) begins with creating and then executing the strategic roadmap to ensure that business processes are designed and aligned to achieve the strategy. Once designed, the business processes are activated to allow the organization to operate in a stable, predictable manner with less investment and organizational churn.

Once stable, focused system improvements are applied to increase sustainable bottom-line results. Execution management tools and transfer of knowledge enable each aspect of SDAIS and serve as the foundation for self-sufficiency and sustainment.

AGI has expertise in TOC, TOCLSS, and SDAIS, with years of experience adapting each of these elements to meet the unique needs of its clients, regardless of size or industry.

AGI excels at leading organizations through successful business transformations by providing business assessment, implementation support, execution management tools, training, and mentoring.

We are motivated by making the complex manageable and enabling our clients'selfsustaining success.

SECTION III.

Drum-Buffer-Rope, Buffer Management and Distribution *

CHAPTER 7.

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

CHAPTER 8.

DBR, Buffer Management and VATI Flow Classification

CHAPTER 9.

From DBR to Simplified-DBR for Make-To-Order

CHAPTER 10.

Managing Make-To-Stock and the Concept of Make-To-Availability

CHAPTER 11.

Supply Chain Management

CHAPTER 12.

Integrated Supply Chain *

This section makes clear the fact that Constraints determine the performance of a system. Identifying the constraint, then knowing how to 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 TOC replenishment is reviewed and critiqued. Sixth, some suggested problems within DBR as presented in the academic literature are discussed. After the introductory section, the chapter is organized to follow the outline of the purposes and conclude with a summary and recommendations for future research. Two overarching objectives of this chapter are to provide academics a suggested framework and to provide information so that they and others can build a solid foundation of principles for further simulation and case study research.

Literature on Precursors of TOC and DBR

TOC represents one in a long line of improvements to manufacturing operations, which include interchangeable parts, the moving assembly line, and assembly line balancing.

Historical Developments Preceding TOC

There were a number of key developments preceding TOC. Without attempting a review of the development of the Industrial Revolution and the Information Age, I present here some highlights including the development of interchangeable parts, the creation of the moving assembly line, assembly line balancing, Just-in-time (JIT) planning and control systems, and the Optimized Production Technology (OPT)3

Interchangeable Parts

Eli Whitney, the cotton gin inventor, is usually credited with developing interchangeable parts for his contract to make muskets for the U.S. government in the late 18th century. However, a large number of companies contributed to the development of interchangeable parts. Those who credit Whitney with the innovation note that, as a firm doing business with the U.S. government, Whitney's firm was required to make his innovation available to the armories at Springfield and Harper's Ferry, Virginia. Both of these armories made substantial use of interchangeable parts.

Conti and Warner (1997) quote Boorstin (1965) as describing interchangeable parts as "the greatest skill saving innovation in human history," enabling workers without specialized skills to make complex products. Conti and Warner date the history of interchangeable parts back to the mid-16th century, when the Venetian Arsenal used standardized parts in shipbuilding.

Advantages of Interchangeable Parts Interchangeable parts drove down unit costs and made available a large stock of replacement parts so that a failed unit could easily be repaired.

Disadvantages of Interchangeable Parts Initially, the items made from interchangeable parts lacked variety and thus failed to meet market demand. These finished goods also lacked the flair and uniqueness of a piece made by an artisan. Introducing new products was problematic because of the difficulty of making all new machine tools.