Drum-Buffer-Rope
Drum-Buffer-Rope (DBR) refers to the Theory of Constraints'
scheduling methodology depicted in the ground breaking book          
The Goal by Eli Goldratt.  DBR uses key capacity constrained
workcenters to synchronize and prioritize a factory's operations.  
Synchronizing material release with constraint output creates a
"balanced flow" of material.  These key workcenters also provide
points for management to focus their monitoring activities.
Drum
The capacity limits of a few key workcenters in a manufacturing process determine
the overall output capacity of the entire factory.  Focusing activities to maximize
output on these workcenters will enable a factory to reach its output potential.  TOC
makes the analogy that these key workcenters are like a "drum" that should lead
the entire factory.  The schedules for these workcenters are the "drum beat" that
sets the work pace for all other workcenters to follow.  
Buffer
DBR strategically places time buffers to protect schedules against variability**.  
These buffers are typically in front of drums (Drum Buffers) and also at the end of
the product chain (Shipping Buffer).  Drum Buffers protect the drum from
operational interruptions caused by upstream variability.  This is very important. An
idle drum represents lost capacity for the entire factory.  A shipping buffer protects
the shipping date from variability at work stations after the drum.
Rope
Rope refers to synchronizing all non-constraint workcenters with drums.   Properly
timing the material release for an order's components creates synchronization.  
The material release date for all components is determined by subtracting the
offset directly from the firm drum date.  Material is released according to the pace
of the drums and not the run-rate of non-constraints.
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**
Variability is present in all processes.  It can be created by the statistical fluctuation of the process
itself or by random events like machine "break-downs".  Variability not only impacts the workcenter
where it originates, but in a manufacturing process with sequential, dependent stations its effect can
also be passed along amplifying the variability at later stations.  Excess capacity or additional time
can compensate for variability. Creating feasible schedules requires protection from variability.  
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