Drum Buffer Rope Part 1

In this series of blog posts, I’m going to discuss a key component of the Theory of Constraints known as Drum Buffer Rope (DBR). Drum Buffer Rope is the Theory of Constraints scheduling process which focuses on improving flow by first, identifying the system constraint and then leveraging it.  The important assumption of DBR is that within any plant there is one or a limited number of scarce resources which control the overall output of processes within any facility.  And while many writings have associated DBR with manufacturing, the assumptions and principles even apply to service industries such as hospitals.  In fact, later on in this series, I will lay out examples of two very important service examples.

In his book The Goal, Dr. Eliyahu Goldratt effectively uses a story written in a business 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 in nature.  Thinking logically is really nothing new, but it’s not the way most people think in today’s world.  The fundamental understanding 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 your system constraint.  This idea of looking at the total system is a major shift in the way systems have previously been viewed and managed.  Prior to total systems thinking, the prevalent point of view was, and pretty much 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. 

So, just what is a system?  Typically, a system is a set of interacting or interdependent components a system that are somehow 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, in some way, to some kind of a system.  In a nut-shell, a system is a collection of elements or components that are organized for a common purpose.

Engineering organizations have systems, banks have systems and even 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.  It’s important to understand that just because a system is complex doesn’t mean it can’t be improved.  The key point when considering systems is that even in a system as simple as two linked processes, one of those two processes will typically constrain the other one.  It’s just the nature of how things work.

If a systems constraint didn’t exist, then the system should theoretically, be able to produce at infinite capacity.  But infinite capacity is not a level that is ever achieved from any 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 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 continue our discussion on Drum Buffer Rope will continue by looking at the impact of variation on the system.