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Scheduling Activities 2 model
As an alternative to the preceding example, you could have used the C connector on the Activ- ity block to control its capacity, simulating the opening of the second dining section.
Scheduling Activities 2 model
Each dining section has the capacity to serve five customers at once. By doubling the capacity of one Activity block during the period between 11 AM and 2 PM you can model both dining sections being open. This is accomplished by connecting the value output of a Create block, set to Create values by schedule, to the C input on the Activity. In the model, the portion of the Create block that controls the capacity of the Activity is cloned onto the model worksheet.
Shift block used to schedule
Yet another approach to scheduling an Activity would be to use a Shift block to control it. For instance, the Shift block could contain the same information as the Create block that is con- nected to the C input on the Activity in the Scheduling Activities 2 model, above.
For more information, see the section titled “The Shift block” on page 232.
Controlling the flow of items to an activity
As discussed in “Scheduling activities” on page 187 you can have an activity start based on the time of day. Some methods of adding an additional activity to a model can cause the new activ- ity to cycle on and off frequently. You may not want this to occur, as it can result in higher start up costs, increased machine wear and scrap production, and excess energy consumption. Instead, you can add some hysteresis and have the activity stay on to process a number of items, or stay on for a period of time.
When bringing a system on-line, there are two main ways to control the flow of items to an activity:
• Specify the number of items that will be processed
• Specify the amount of time the activity will be on-line
☞ You can view and report the item contents of Activity blocks at any time. Please see “Item Contents of queues and activities” on page 716.
Fixed number of items
Instead of having a system cycle on and off, you may want to keep the optional activity run- ning. For instance, you can keep a machine on to process a particular number of items, even if the waiting line for the other machines is below the threshold that originally activated it. This reduces the number of times the machine turns on and off.
Processing 189
Controlling the flow of items to an activity
Discrete Event

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