Drum-Buffer-Rope (DBR)

Posted in Operations and Supply Chain Terms, Total Reads: 490
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Definition: Drum-Buffer-Rope (DBR)

Drum-Buffer-Rope is a work scheduling mechanism for the system such that the constraint (drum) is never starved (adequate buffer) by releasing the right amount of work in the system at the right time. (rope)


Let us understand some characteristics of the system to understand the DBR approach properly.

1) Every system has a bottleneck which decides the throughput of the system

2) The throughput of the bottleneck should be maximized through this bottleneck with maximum efficiency while non-bottlenecks should not be optimized to 100% as it would create higher work-in-process inventory ahead of its bottleneck.


Drum buffer rope is a metaphoric example akin to this concept given above.


Here, the bottleneck is called the DRUM which sets the throughput of the system.


There may arise a situation where upstream processes to the bottleneck don’t produce enough and thus starving the bottleneck of the system and reducing throughput of entire system. So, it is suggested that there be a sufficient BUFFER to cater to the DRUM to avoid waiting for the DRUM.


The method by which the DRUM communicates to the system of how much buffer needs to be kept by signalling upstream processes when to slow down, pace up or completely stop so that only the right amount of BUFFER gets accumulated ahead of the DRUM. This is akin to a ROPE which can control it.


Let us take example of a surgery centre which is a service organization. Before the surgery, patients have to undergo a blood test and an X-Ray. Let us assume there are four stations that patients need to go to:

1) Admin

2) Blood lab

3) X-ray room

4) Admin discharge


Let the constrained department be X-ray since there is only one room for it. Thus, a buffer of 3 persons should be established for X-ray room in order to keep X-ray room busy at all times. Hence, X-ray room is the DRUM here and BUFFER is kept ahead of it. The ROPE should be handled such that until there is BUFFER available at X-ray room, Admin should not take in more patients. Only when sufficient buffer of 3 is not available, more patients should be taken in the system.

 

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