Computation Section
Subunit Inventory Analysis
 Systems - Pull Network




A worksheet with the pull tree structure shown is below. For the example, we propose a manufacturing system. The system uses two raw materials. RM 1 enters at operation 1 and RM 2 enters at operation 2. Operation 1 represents the process of obtaining RM 1 and storing it for use by the system. Its parameters are shown on the worksheet below. The setup time represents the time a lot must be retained after arrival before being released to the shop. Similarly, operation 2 represents the process of obtaining and storing RM 2.

Operation 3 produces part 1. Part 1 requires five units of RM 1 and two units of RM 2. Operation 4 produces part 2. Part 2 requires three units of RM 2.

Operation 5 assembles parts 1 and 2 with one unit of each required for a finished product. Some of the finished items must be recycled into operation 4. For every unit passing through operation 4, 0.2 units will come from operation 5. For illustrative purposes, we are stretching logic a bit with this example because its hard to imagine that the finished item is transferred into a part for subsequent assembly into a finished item.

The system is to produce 1000 units per week of the finished product. In addition, 200 units of part 1 and 400 units of part 2 are to manufactured.

The worksheet below shows the parameter and variable assignments for the example. The replenishment lot sizes for the raw materials are 10,000 and 6,000 units. Operation 3 is a batch process with a lot size of 1,000. Most of the other lot sizes are set to 1000. The finished good is packaged into lots of 100.

Discussion about the network is below the illustration.


The interconnections between the components are described by the Transfer In matrix. A column of this matrix explains the inputs to an operation. Part 1 requires five units of RM 1 and two units of RM 2 as shown in column 3. Column 4 indicates that for each unit passing through operation 4, three units must be withdrawn from the inventory of RM 2 and 0.2 units come from the finished good assembly process. Column 5 explains that the assembly process requires one unit each of parts 1 and 2.

The matrix must be composed entirely of nonnegative numbers that describe the system. Some numbers make the augmented matrix singular. This implies that the system defined is not logically possible.


Return to Top

tree roots

Operations Management / Industrial Engineering
by Paul A. Jensen
Copyright 2004 - All rights reserved