1. Model 4-2: The Enhanced Electronic Assembly and Test System
6th class:
p.120
A Story
Original model shown to production manager
Pointed out that this is only the first shift of a two-shift day — on second shift there are two operators at Rework (the bottleneck station) … 16-hour days (two 8 hr shifts per day)
Pointed out that the Sealer fails sometimes
Uptimes ~ exponential, mean 2 hours
Repair times ~ exponential, mean 4 minutes
Wants to buy racks to hold rework queue
A rack holds 10 parts
How many racks should be bought?
Run for 10 days
Need: Schedules, Resource States, Resource Failures
For our purpose, we will ignore the part of the story with the bullet: “Wants to buy racks to hold rework queue.” Otherwise, to make the simulation model, we modify it according to the “Story” that is told in the above slide.
Start of 6th class
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Chapter 4 – Modeling Basic Operations and Inputs

2. Chapter 4 – Modeling Basic Operations and Inputs
Change Run Conditions
Redefine a “day” to be 16 hours – Run/Setup/Replication Parameters
Change Replication Length to 10 (of these) days
We assume that a “work” day is now 16 hours, and make the modification in the Run pull down menu. We also change the tab on Replication Parameters to 10 days. Be sure to carefully record the time units for Replication Parameters as Days.
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Chapter 4 – Modeling Basic Operations and Inputs

3. Chapter 4 – Modeling Basic Operations and Inputs
Schedules
Vary Capacity (number of units) of a resource over time
In Resource Data module (spreadsheet view)
For Rework Resource, change Type from Fixed Capacity to Based on Schedule
Two new columns – Schedule Name and Schedule Rule
Type in a schedule name (Rework Schedule)
Select a Schedule Rule – details of capacity decrease if the Resource is allocated to an entity
Ignore – Capacity goes down immediately for stat collection, but work goes on until finishes … “break” could be shorter or gone
Wait – Capacity decrease waits until entity releases Resource, and “break” will be full but maybe start/end late
Preempt – Processing is interrupted, resumed at end of “break”
As stated in the slide, simply go the Project Bar for Basic Process and click on the Resource Data module. Make sure you have the split screen (if you don’t, go to View on the pull down menu and check Split Screen), which assures that you will see the spreadsheet that corresponds to the Resource Data module. Go to the row with the name Rework Process, and change Type to Based on Schedule from the pull down menu. You can type in Rework Schedule for Schedule Name, and then select a Schedule Rule. In our problem, the Schedule Rule is Ignore. Ignore assumes that a break is scheduled for an operator in the Rework Process while that operator is still working on an entity (or part), then the operator continues his/her work with the entity into the break until the job on the entity is done. Then the entity releases the operator who can start his/her break. However, the simulation records the operator as being on the break at the time it is scheduled. Can you figure out how this would change if the rule was either Wait or Preempt. The above slide and the packet (on pp ) should help you to explain this.
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Chapter 4 – Modeling Basic Operations and Inputs

4. Chapter 4 – Modeling Basic Operations and Inputs
Schedules (cont’d.)
Define the actual Schedule the Resource will follow – Schedule data module (spreadsheet)
Row already there since we defined Rework Schedule
Click in Durations column, get Graphical Schedule Editor
x-axis is time, y-axis is Resource capacity
Click and drag to define the graph
Options button to control axis scaling, time slots in editor, whether schedule loops or stays at final level for longer runs
Can use Graphical Schedule Editor only if time durations are integers, and there are no Expressions involved
Alternatively, right-click in the row, select Edit via Dialog
Enter schedule name
Enter pairs for Capacity, Duration … as many pairs as needed
If all durations are specified, schedule repeats forever
If any duration is empty, it defaults to infinity (pp in text 3rd ed)
Now we go to the Schedule Data module on the Project Bar. In the spread spreadsheet, you see a row with the name Rework Schedule. Double click where it says 0 Rows under the column Durations, and you get a graphic (the Graphical Schedule Editor). Set the capacity (by dragging the mouse on the graphic) to one for the first eight hours and two for the second eight hours. We will not worry about the bullet that starts with Alternatively, which is simply another way to schedule the resource without the graphic. Again, go carefully through the explanation in the packet (pp ).
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Chapter 4 – Modeling Basic Operations and Inputs

5. Chapter 4 – Modeling Basic Operations and Inputs
Resource Failures
Usually used to model unplanned, random downtimes
Can start definition in Resource or Failure module (Advanced Process panel) … we’ll start in Failure
Attach Advanced Process panel if needed, single-click on Failure, get spreadsheet view
To create new Failure, double-click – add new row
Name the Failure (e.g., such as Sealer Failure)
Type – Time-based, Count-based (we’ll do Time)
Specify Up, Down Time, with Units
Finally, we can account for breakdowns of the sealer machine. This requires that we get Advanced Process into the Project Bar. (If it is not in the Project Bar, go to the File pull down menu and click on Template Panel and click on Attach. When the dialog box appears, simply double click on AdvancedProcess.tpo, and then the Advanced Process will appear in the Project Bar.) Now click on the Failure Data module. A spreadsheet will appear, and rename the default under the Name column with Sealer Failure. For the Type column, use the pull down menu and enter Time. For the Up Time column, use the pull down menu and select EXPO (for exponential distribution) and enter 120 for the mean. Likewise, for the Down Time column, again select EXPO but enter 4 for the mean. Be sure to enter Minutes for the Up and Down Time Units columns.
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Chapter 4 – Modeling Basic Operations and Inputs

6. Resource Failures (cont’d.)
Attach this Failure to the correct Resource
Resource module, Failures column, Sealer row – click
Get pop-up Failures window, pick Failure Name Sealer Failure from pull-down list
Choose Failure Rule from Wait, Ignore, Preempt (as in Schedules)
Can have multiple Failures (separate names)
Now go back to Basic Process in the Project Bar and click on the Resource Data module, since we have to indicate which resource will have the failure. The Failures column for the Sealer row will show 1 rows. Click on the 1 rows and go to the pull down menu for Failure Name, and select Sealer Failure. Go to the Failure Rule pull down menu and select Wait. Note that we could have selected another rule, but we will go with the logic in the packet on p Of course, we could have multiple failures. Hence, adding failures is very simple in Arena once you get the knack on how to do it.
Up to p. 128
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Chapter 4 – Modeling Basic Operations and Inputs

7. Chapter 4 – Modeling Basic Operations and Inputs
Results of Model 4-2
Differ from those of Model 4-1 since this is a longer run; modeling assumptions are different
Prep A/B didn’t change (other than run length and random variation) … need statistical analysis of simulation output to be sure (covered later in the course)
Sealer is more congested (it now can have failures or machine breakdowns)
Rework is less congested (capacity was increased in Model 4-2 when we added the second resource to the second shift of the Rework Process)
Model 4-1 ran for 32 hours, and Model 4-2 ran for 160hours (or ten 16-hour days). In Model 4-2, we also introduced more variation with the schedule by changing the resource capacity at the Rework Process, and permitting failures (i.e., machine breakdowns) in the Sealer Process. Both models kept the preparation of parts A and B the same.
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Chapter 4 – Modeling Basic Operations and Inputs

8. Utilizations – Some Fine Points
Two utilizations reported for each Resource
Utilization is the time-average ratio of the number of units that are busy to the number of units that are available
Scheduled Utilization is the average number busy divided by the average number available – not instantaneous, like Utilization
Identical for fixed-capacity Resource
Can differ for Resources on a variable Schedule
Which to use?
Utilization tracks how well Resource capacity does track time-varying load
Scheduled Utilization indicates how well overall capacity can handle overall load
Utilization >> Scheduled Utilization means you have enough capacity, but poor scheduling of it.
Note from the above slide that Utilization means the same as Instantaneous Utilization on p. 133 of the reading packet. As stated in the packet on p , the Instantaneous Utilization and the Scheduled Utilization are the same if the capacity of the resource stays constant. However, that is not the case for the Rework Process in Model 4-2, which gives us for Instantaneous Utilization and for Scheduled Utilization (see the out files or the table on p. 132 in the packet).
End for 6th class; up to p. 135.
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Chapter 4 – Modeling Basic Operations and Inputs