The Schaller Company example used to illustrate constrained optimization also can
be used to provide a specific illustration of the DBR system. Recall that there are three
sequential processes: grinding, drilling, and polishing. Each of these processes has a limited
amount of resources. Demand for each type of machine part produced is also limited.
However, from Exhibit 21-9 we know that the only binding constraints are the
drilling and polishing constraints. We also know that the optimal mix consists of 30
units of Part X and 30 units of Part Y (per week). This is the most that the drilling and
polishing processes can handle. Since the drilling process feeds the polishing process,
we can define the drilling constraint as the drummer for the plant. Assume that the demand
for each part is uniformly spread out over the week. This means that the production
rate should be six per day of each part (for a 5-day work week). A 2-day time
buffer would require 24 completed parts from the grinding process: 12 for Part X and
12 for Part Y. To ensure that the time buffer does not increase at a rate greater than
six per day for each part, materials should be released to the grinding process such that
only six of each part can be produced each day. (This is the rope—tying the release of
materials to the production rate of the drummer constraint.) Exhibit 21-11, on page
952, summarizes the specific DBR details for the Schaller Company