Implementing Drum-Buffer-Rope in your production planning
Drum-Buffer-Rope (DBR) is one application of the theory of constraints in production planning. Implementing DBR will improve the flow of operations that have an internal constraint or a capacity-restrained resource, making it more efficient.
Put simply, DBR details a work schedule for the constraint (Drum), which buffers the constraint so that it is never starved (Buffer) and sets a release mechanism (Rope) to ensure that work gets released into the system at the right time.
This systematic approach protects the weakest link in the production system against process variation and dependency, which maximizes the system’s overall effectiveness.
Imagine a hospital waiting room. If the time the doctor takes to see each patient is the Drum, then the Buffer can be the receptionist scheduling appointments so there are always two or three patients in the waiting room. The Rope is the nurse calling in each patient once the doctor is ready to see them.
“DBR is the method of managing your constraint process,” says Lalit Bhushan, Senior Business Advisor with BDC Advisory Services.
“Think of it as a way to set clearly articulated rules for your Drum process. It’s one of the many methods to manage your bottleneck by putting rules around it.”
Bottleneck vs. Constraint
A bottleneck is a resource or operation that has more demand placed on it than it can deliver.
A constraint is the element that limits the performance of the system towards achieving its goal.
Although “bottleneck” and “constraint” are sometimes used interchangeably, a bottleneck is usually evidence of the constraint, which could come from equipment, team members or even from a policy.
In a hospital, for example, a bottleneck can form around the work of the doctor, who must take a certain amount of time with each patient. This becomes the constraint on the total number of patients who can be seen and the number of procedures that can be performed.
In this case, hospital team members will support the work of doctors to make them as productive as possible. Imagine a hospital waiting room. If the time the doctor takes to see each patient is the Drum, then the Buffer can be the receptionist scheduling appointments so there are always two or three patients in the waiting room. The Rope is the nurse calling in each patient once the doctor is ready to see them.
This principle can be applied in a manufacturing plant, a construction site or a software company. Workers and processes adapt to help the constraint become as productive as possible to raise the production of the entire company.
Five steps to implement the Theory of Constraints (TOC)
Entrepreneurs can follow these five steps to implement the Drum-Buffer-Rope approach to their bottlenecks to maintain a smooth and reliable flow of work through their operations.
1. Identify the constraint
To implement DBR, first identify all the constraints within your operations. Constraints can be either a physical resource, a process or a policy.
To do this, map out the processes or pathways of your system carefully. Identify places where there is a delay and keep asking yourself ‘why?’ to discover the reason. It could be anything from the lack of availability of a specific skill to a missing piece of equipment.
The clear identification of the constraints is important. Try to look at your system on a granular level: The constraint could be caused by a single person or piece of equipment slowing down your entire process. Ideally, you should have a smooth and continuous flow of work and/or materials through your processes with minimal disruptions.
In DBR, this is how you identify the Drum, or the maximum rhythm at which you can work.
2. Make your constraint as efficient as possible
Once you’ve gained a full understanding of the constraint, your goal should be to eliminate non-value-added activities or sources of variations.
Because your constraint determines the rate at which your system works, it is important to eliminate wasted time. For example, if your constraint is a piece of machinery, then it is important to ensure it is always in use. Again, using process mapping can help.
Keep in mind that once you have optimized one constraint, the bottleneck may move to another part of the system.
3. Subordinate everything else to the constraint
The other elements of your processes must now be adjusted to a "setting" that will allow the constraint to operate at maximum effectiveness.
One way to do this is to have a Buffer of work in front the constraint (Drum) to ensure that the constraint never runs out of work.
The Buffer also gives some flexibility to your schedule. An example of a Buffer could be a flexible shipping date or the completion of non-constraint work while waiting for the constraint to finish. The Rope controls the release of new work. The constraint sets the pace and work should only be released at the rate the constraint can consume it.
Together, the Buffer and the Rope ensure that the constraint is always fed and there is no wasted time.
Returning to the hospital metaphor: in addition to a waiting room system, some doctors might run their clinic with two rooms. The doctor works on one patient in one room and the nurse prepares the second patient in another. The doctor will move between two rooms to optimize the capacity. This way, the doctor always has a patient to see and there is no wasted time.
Once this has been done, the overall system is evaluated to determine if the constraint has shifted to another component. If the constraint has been eliminated, then you can jump to step five.
4. Elevate the constraint
If steps 2 and 3 didn’t work, then you should elevate the constraint by investing resources in it.
"Elevating" the constraint refers to taking whatever action is necessary to eliminate the constraint. Major changes to the existing ways of working are considered at this step, such as hiring a new person or upgrading your machines. This is only necessary if the constraint is a true bottleneck.
5. Return to step one
Do not let inertia settle in. Optimizing your constraint will often result in the creation of new constraints. Your goal should be to continuously improve your processes to limit waste and reduce costs through a process of continuous improvement.
The importance of cooperation for Drum-Buffer-Rope
DBR includes a degree of protection for the unexpected. Any schedule or production plan must be productive, reliable, robust and realistic.
- Productive: It must relate to the market demand while contributing to and being measurable against the organization's goal.
- Reliable and robust: It must reflect the capability of the resources available and stand up to the inevitable disturbances or disruptions that will hit it.
- Realistic: It is capable of being done with the resources available, including material supply.
“The constraint acts as pace-making. Any improvement efforts that are not towards improving the constraint will not increase the system performance,” says Bhushan.
The theorists behind DBR conclude that the true constraint (the Drum) is the market. Therefore, for DBR to work effectively there must be full cooperation and communication between sales and operations. Sales cannot simply take orders and promise delivery with little or no input from operations.