Tonight I am starting a 2 part series contrasting the Theory of Constraints with Lean Manufacturing. Specifically, I want to discuss the differences between a TOC “bottleneck” and a Lean Manufacturing “pacemaker.” I have seen TOC proponents and Lean Manufacturing proponents go to blows over this topic. I hope to explain the differences (yes, they are different) while explaining how I believe we as continuous improvement practitioners should move forward leveraging the strengths of both concepts.
The first part of the series (tonight) will be all about TOC. Tomorrow night I will cover the Lean side of things.
Theory of Constraints Overview
Theory of Constraints (TOC) is a management philosophy developed by Dr. Eliyahu Goldratt, a physicist. TOC popularized after the release of the 1984 best seller “The Goal.” To this day this book is one of my all time favorites. I even have it on mp3 and listen to it in my car from time to time… yes I know, I have issues.
In “The Goal” we meet Herbie who is an overweight child who holds up the rest of his friends during a hike through the woods. The boys formed a human chain so the leader could keep track of them all. Herbie, poor lad, was in the middle of the pack which soon created some issues for all involved. The faster kids in front of Herbie ended up way ahead of the pack while all the kids stuck behind Herbie were frustrated as they had to wait on him. The scout leader (and plant manager), Alex Rogo, fixed the situation by moving Herbie to the front of the line which set the “pace” for the rest of the kids. Soon after moving him there they removed all kinds of junk from Herbie’s back pack. This helped Herbie go faster which made the whole system (boys) move faster. This story summarizes the main ideas behind TOC. Specifically, you can also explain TOC this way:
- Identify the constraint (your bottleneck or the thing slowing you down)
- Decide how to exploit the constraint (make sure the constraint is only working on the things it needs to do and not other stuff)
- Subordinate all other processes to the constraint (don’t let any other process work ahead of the constraint)
- Elevate the constraint (speed the constraint up, i.e take the junk out of Herbie’s back pack)
- If the constraint moves, which it often does, return to Step 1 and repeat.
TOC teaches a concept called drum, buffer, rope (DBR). The main premise behind DBR is that the drum is the constraint or bottleneck in the system. It sets the pace for all other processes. The buffer is inventory that is used to protect the drum. Dr. Goldratt often speaks of “Murphy” (Murphy’s Law) who likes to strike at the worst time messing everything up. Thus, buffers are used to ensure our constraints and other key areas are never starved for work, even if Murphy strikes. Lastly, the rope is the scheduling or work release mechanism that gets everything moving.
If DBR sounds similar to some concepts Mr. Ohno taught 50+ years ago you are correct. However, there are some differences when you look into the fine print which we will discuss tomorrow night!
Other TOC Resources
Dr. Goldratt has written many other books which explain additional TOC concepts. If you are interested just Google it and you will see what I mean. His book “Critical Chain” is a super Project Management book.