An example worksheet with the pull tree structure shown is
below. The example has the same structure as at the left. The
operations have been assigned the letters A, B, C, D and E,
corresponding to the indices 1, 2, 3, 4 and 5. As described
for the Line example, the data defining the operations and their
parameters are in rows 1 through 11. The lot size variables
are in rows 12 through 14. We have entered data to represent
a possible manufacturing system. The batch process, operation
C, has a high setup cost, so we are using a large processing
lot size for that operation. The Delay operation does not use
all the parameters as suggested by the x in some cells.
Rows 21 through 26 define the tree structure and compute the
operation flows. Line 21 assigns indices to the operations and
line 22 repeats their names. The values of the flows pulled
from the operations are in line 23. In addition to the flow
of 100 pulled from operation E, we pull an additional 50 units
from operation C. Row 24 shows the precedence ordering defining
the tree. Each operation has a unique following operation, specified
by the index in row 24. Operation E has the index 0 indicating
that it has no follower. Row 25 holds the proportions transferred
from each operation to its following operation. For the pull
tree this proportion is relative to the flow passing through
the following operation. For the example, operation C receives
70% of its input from A and 30% from B. Operation 5 receives
one unit from each of operations C and D for every unit produced.
This information is placed in row 25. Row 26 holds the computed
flows through each operation. This information is transferred
to row 4 for analysis purposes.
cells in the output lot size row, row 14, indicate that the
output lot size of an operation is automatically set equal to
the input lot size of its unique following operation. An exception
is the output lot size at operation E, the lot size that flows
to the customers.
Rows 15 through 19 show the results for each operation. The
queue operation requires 4 servers to handle the flow.
The system results in column G have one important change from
the Line structure case. As before, the System WIP is the sum
of the operation WIP's. The cycle time for the system is not
the sum of the cycle times for the operations. Rather it is
the system WIP divided by the total output flow that appears
in G23, 150. We cannot the sum of operation cycle times because
flow varies between the operations.