Different Forms of Drum Buffer Rope Part 1

In this series of posts, I'm going to lay out the basics of the Theory of Constraint's scheduling tool known as Drum Buffer Rope.  I will start with the traditional version of Drum Buffer Rope and then introduce different versions of it.

In his book The Goal, Eliyahu Goldratt effectively uses a story written in a novel format to walk the reader through the steps necessary to move a manufacturing organization from the traditional manufacturing concepts to a facility managed using the concepts of Drum-Buffer-Rope (DBR).  This nontraditional approach through logical thinking is masterminded by a character named Jonah.  Jonah is able to help Alex Rogo understand the invalid thinking and assumptions being used to manage his plant and the negative consequences associated with that type of thinking.  By helping Alex focus his thinking on how the plant is being managed, Jonah helps Alex logically discover a new and better way. And Drum-Buffer-Rope (DBR) is the centerpiece of this process. 

 The thinking behind DBR is really quite simple, but mostly just logical.  Thinking logically is nothing new, but it is not the way most people think.  The fundamental view of DBR is to focus on the system as a whole rather than only a single segment of the system—at least until you have clearly identified the constraint.  This idea of looking at the global system is a major shift in the way systems have previously been viewed and managed.  Prior to global-systems thinking, the pervasive point of view was (and still is) that any systems improvement, at any location, would improve the overall system.  The idea being that the sum total of several isolated improvements would somehow equal an improved to the overall system.  But such is not the case.  The effects of employing the “shotgun” approach to systems management can cause a series of devastating systemic effects.

A system can be defined as a sequence of steps or processes that are linked together to produce something as an end result.  With that definition in mind, it’s easy to understand how virtually everything can be linked to some kind of a system.

Engineering organizations have systems, banks have systems and grocery stores have systems.  Almost anything you can think of is the product of a system.  By design, a system can be as small and unique as two processes linked together, where the output of one process becomes the input for the next process. Or systems can be very complex, with many processes linked together, maybe even hundreds or more.  Just because a system is complex does not mean it can’t be improved—it just means it’s complex, and that’s OK.  Even in a system as simple as two linked processes, one of those two processes will constrain the other.  It’s just the nature of how things work.  If a systems constraint did not exist, then the system should, at least theoretically, be able to produce at infinite capacity.  But infinite capacity is not a level that is ever achieved from a system.  All systems are restricted, at some point in time, by some type of output limitation.  This limitation is usually determined by the presence of some kind of system-capacity limit.  No matter how good the system is, there is still only so much it can do.  Sooner or later whatever kind of system is being analyzed, it is will reach its maximum system capacity and be unable to produce more.  If higher system outputs are required beyond the current capacity, then the system must be changed.

In my next post we will discuss the impact of variation.

Bob Sproull