Page 258 - ExtendSim User Guide
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Resources and Shifts
The Shift block
The schedule for workers is entered in the dialog of the Create block, as shown at right. The block is set to Cre- ate values by schedule, and its value output is attached to the TR (Total resources) input of a Resource Item block.
☞ This model is set to use Calendar dates. The Simulation Setup dialog and block options (such as selecting calendar format when a Create block is set to schedule its outputs) facilitate the dis- play of times and dates in Calendar for- mat. For more information, see “Calendar dates” on page 606.
In this model the workers are part of a
partially closed system. Some are recy-
cled back to the Resource Item block
through its item input connector, while
other workers are added to or removed from the block through its TR connector.
Scheduling resource items
There are at least four additional ways to schedule resource items in ExtendSim:
1) AResourceItemblockfollowedbyaGatecancontrolwhenresourceitemsarereleased.
2) AResourceItemfollowedbyaSelectItemOutblockcontrolswhereresourceitemsare routed.
3) AcombinationoftheGateandSelectItemOutblockscanbeusedtocontrolbothwhere and when items are scheduled.
4) TheQueueEquationblockisusefulforcontrollingbothwhereandwhenitemsaresched- uled for use when the scheduling logic is more complex. With this block, ModL logic state- ments can intelligently control the scheduling of items based on their properties, information in the ExtendSim database, or even the status of other sections of the model. For more information, see “Sorting items using the Queue Equation block” on page 145.
The Shift block
The Shift block is used to schedule both the magnitude and availability of capacity in other blocks in a model. This is useful for simulating situations where a system’s resources follow a pattern of coming on and off line over time. For example, the Shift block could be used to model workers in a factory following a repeated daily pattern of reporting to work in the morn- ing, taking a break for lunch and going home at some point in the evening.
Each Shift block represents a named shift and its schedule that can be referenced by other Item library blocks. The Shift controls the capacity of the blocks that reference it, based on the schedule that is defined in its dialog table. If a shift schedule is changed, all blocks using that named shift will receive the same modified shift pattern. In addition, shifts may be repeated at regular intervals if the Repeat schedule every checkbox is selected. This is useful for model-
Arrival times for workers
Discrete Event

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