The name Drum-Buffer-Rope (DBR) was given to the TOC solution for managing production environment that has a bottleneck or a severe CCR – Capacity Constraint Resource).
The name was given in the 1980s for describing scheduling the production shop floor as per the OPT – Optimized Production Technology software. The concepts of DBR were first presented in Dr. Goldratt’s book The Goal and the solution was presented in The Race and The Haystack Syndrome.
The solution is based on the fact that there is at least one overloaded resource (Capacity Constraint Resource, CCR) which does not have enough capacity to fulfill the market demand in the required delivery dates. As such a detailed plan is built for the CCR as per the customers’ orders while considering the capacity of the CCR. This plan is called The Drum.
Every Work Order (WO) that goes through the CCR is given two Time Buffers – the Shipping Buffer and the CCR Buffer.
Shipping Buffer is the elapsed time given to the Work Order to flow from the moment the last part leaves the CCR to the completion of the whole WO. The expected time of WO completion (dispatch) is calculated by adding the length of the Shipping Buffer to the moment when the WO leaves the CCR. This is an IDD – Internal Due Date when the order is ready to be shipped. The IDD can serve as the base for the Shipping Schedule.
When production has a CCR or a bottleneck – the calculated realistic shipping date is likely to be later than the original date the customer requested for delivery.
CCR Buffer is the elapsed time given to the WO to flow from the permitted time of material release until the CCR is planned to start the work on the first part in this WO. The CCR Buffer is used to determine the time to release the WO to production. The release time for the WO is calculated by subtracting the CCR Buffer from the time the WO is scheduled to start on the CCR.
Material should be released Not Earlier Than the time calculated by using the CCR Buffer. This concept is called – The Rope – which means chocking the release according to the planned time.
Source: Oded Cohen and Jelena Fedurko, Theory of Constraints Fundamentals, 2012