Page 206 - ExtendSim User Guide
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180 Processing
Processing in parallel
serial processing is an assembly line, where several processes are performed on one part prior to shipment.
Serial Processing model
Since there are many machines in series without buffering queues between them, it is possible that items will be not be able to leave one machine because the next machine will still be busy; this is known as blocking (as discussed in “Blocking” on page 143. Serial processes can cause the entire operation to be slowed to the speed of the slowest activity. This will cause utilization to increase by the amount of time that the item is blocked. If this doesn’t accurately represent your process, put a queue in front of each machine to represent a holding area, as shown in “Select Item Out dialog” on page 162.
Processing in parallel
It is common in industrial and commercial systems for there to be multiple activities working in parallel, each representing the same task being performed. For example, you might have five machines that can each process parts arriving from the stockroom. Or three bank tellers who are available to wait on customers. With the blocks in the Item library, there are many ways to route items to parallel activities.
Remember that, unless items are purposefully duplicated in the model, they can only follow one path at a time.
Parallel processing using one block
When you do not need to show each activity as a separate block, you can choose that the Activ- ity block represent several operations that occur in parallel. This is accomplished by entering a number greater than one for the Maximum items in activity field in the block’s Process tab.
The Activity block can take in items (up to the specified maximum) and process them for a specified time starting from when they arrive. The item with the shortest time in the block (based on the item’s arrival time and how long it takes to process) is passed out first. For exam- ple, you could use the Activity block to represent a supermarket where customers arrive at dif- ferent times and take varying amounts of time to shop. Customers who arrive early or who only shop a little will leave first; customers who arrive later or shop a long time will leave later.
Simple parallel connections
You can also use multiple Activity blocks in a model, each of which represents a process that can accept items in parallel with the other Activity blocks. The simplest way to hand out items to separate parallel activities is by creating connections between the output of the collection point and the inputs of each Activity. This causes ExtendSim to pass items to the first available Activity block. However, if more than one block is free when an item is ready, it is not obvious
Discrete Event

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