Page 199 - ExtendSim User Guide
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Routing 173
Items going to several paths
queue lines to be balanced. The Max & Min block (Value library) connected to a Select Item Out block is excellent for this.
Output Line Balancing model: Choosing the shortest queue
In the model, the Max & Min block tells the Select Item Out block which queue line is shortest and thus which queue to hand the next item to. The Min & Max block is set to Output the: minimum value and Top input connector # is: 1. With these settings the block’s top input (L1) is number 1 and the con output reports which of the inputs (L1, L2, or L3) has the lowest value, indicating the shortest queue. The dialog of the Select Item Out block is set to Select output based on: select connector and Top output is selected by select value: 1.
Compared to the Buffering Operations model shown earlier, in this model the number of items in the queues tend to be more balanced. However, the system is not as efficient as it could be since an item often goes to the queue for Machine 1 even though Machine 3 is idle. This hap- pens because if all the queue lengths are equal, the Max & Min block will report the first con- nector as having the shortest queue length. In this case, Queue 1 has first priority for items and the Max & Min block is just looking at the queue lengths and is not considering whether or not the Activity is occupied.
Line Balance with Activities model
The previous model showed how to balance the queues. A more useful model would be to include information about the items being processed when selecting the shortest queue. You can do this by adding the value of an Activity’s F (full) connector to the queue length. The full connector is 1 when the activity is at capacity and 0 otherwise. The resulting model, Line Bal-
Discrete Event

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