Drum-Buffer-Rope

Drum-Buffer-Rope is a production theory derived by Dr. Eli Goldratt in his book, The Goal. In it, he advocates production according to the pace set by a single machine (the drum) with linked production (the rope). He also promotes keeping a buffer in front of the machine that acts as the constraint on the system.

Drum-Buffer-Rope is part of Dr. Goldratt’s Theory of Constraints. This production philosophy closely mirrors the philosophy behind Lean.

Drum=Takt Time

Most students of Lean know that takt time is the pace of production required to meet customer demand. But what happens when the system cannot keep up with that pace?

With a little bit of legwork and a few stopwatches, a team can identify the constraint of that system. There is always a slowest machine. (Caveat: Sometimes, with sporadic problems, the constraint will move around, but that is a different problem.)

Once that slowest machine is identified, it is used as the pacer for the production system. In effect, that beat of that “drum” sets the pace for the entire operation.

Buffer=Buffer

While there is a common perception that Lean operations should have no excess inventory, in reality, small buffers are useful. They just have to be controlled and standardized. The most common is a finished goods inventory that is used to support level production. You may also see inventory if one operation runs a night shift to keep up with the demand of the rest of the facility.

The Theory of Constraints, similarly, promotes using a buffer to prevent starving the constraints. If a machine is a bottleneck, it has no catchup capacity. It should never stop because of a lack of material. The buffer prevents upstream non-constraints from starving the constraint.

Rope=Pull

The rope in Drum-Buffer-Rope is the process of making the entire operation work at the pace of the constraint. Dr. Goldratt likens this to tying a rope between a group of hikers so that they all move at the pace of the slowest member of the group.

In Lean production, this is accomplished with pull. Without a production signal, a process is not allowed to produce any more product.