Drum
This is the element in a company’s operations that prevents
the company from producing additional sales. This is the
company’s constrained capacity resource or bottleneck operation.
It will most likely be a machine or person, though it also might
be a short supply of materials. Because total company results are
constrained by this resource, it beats the cadence for the entire
operation— in essence, it is the corporate drum.
Buffer
The drum operation must operate at maximum efficiency
in order to maximize company sales. However, it is subject to
the vagaries of upstream problems that impact its rate of production.
For example, if the drum is located in the production
department, then if the stream of work-in-process generated by
an upstream work center is stopped, the inflow of parts to the
drum operation will cease, thereby halting sales. To avoid this
problem, it is necessary to build a buffer of inventory in front
of the drum operation to ensure that it will continue operating
even if there are variations in the level of production created by
feeder operations. The size of this buffer will be quite large if the
variability of upstream production is large, and correspondingly
smaller if the upstream production variability is reduced.
Rope
This term refers to the timed release of raw materials into
the production process to ensure that a job reaches the inventory
buffer before the drum operation is scheduled to work on it. In
essence, the rope is the synchronization mechanism driving the
flow of materials to the drum operation. The length of the rope
is the time required to keep the inventory buffer full, plus the
processing time required by all operations upstream of the drum
operation.
