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Elevator SchedulingLingfeng Luo

Zhao Han

Elevator Scheduling Problem

Elevator as a control System Behavior depends on programmed algorithms Different solution depending on building type

and number of elevators working together

Assignment of job External elevator request Internal floor request

The Building

Setting:15 floor building2 elevators

Goal: Simulate and analyze three major elevator scheduling algorithms by JAVA

Use simulation results to find optimal algorithm.

Tools we used

Use JAVA to program different elevator scheduling algorithms.

Use Excel to analyze simulated results and plot chart.

Algorithm A

FCFS ( First come first serve)

Elevators work depends on the order of every request. The first one who sends the request can take the elevator first.

Algorithm B

SSTF- Shortest Seek time first

It will find out which floor is the closest to the elevator. Then, the elevator goes to that floor, and search the next requested floor according to their distance.

Algorithm C

Scan SCAN makes

elevators moving from top to the bottom. Elevators turn back when they reach the top or the bottom.

Performance Metrics

We will evaluate these metrics below for simulated outcome of 3 different elevator scheduling algorithms.

Waiting time of a client: the time in between the client makes a outer request till he gets to the destination floor

C: Total passenger carried in given time interval.

Results – Original Data (FCFS)

Imperfections of the program

and things need to improve

1. the arrival rate is the same for day and night, hour to hour.

2. requested rate is the same on every floor 3. the client is always patient 4. no interface

Limitation of each Strategies

FCFS: not efficient, slows down the process for accessing the floor than it must

SCAN: takes longer for the average request, (won’t starve the process for the sake of others

SSTF: leave some request for very long time

Result Pattern

1 4 7 10 13 16 19 22 25 28 31 34 37 40 43 46 49 52 55 58 61 64 67 70 73 76 79 82 85 88 91 94

3 Algorithm ComparisonFCFS SSTF SCAN

Avg Waiting Time

FCFS SSTF SCAN240

245

250

255

260

265

270

275

Total Average Waiting Time

Thank you!

Questions