elevator scheduling lingfeng luo zhao han. elevator scheduling problem elevator as a control system...
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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 Comparison
FCFS SSTF SCAN
Avg Waiting Time
FCFS SSTF SCAN240
245
250
255
260
265
270
275
Total Average Waiting Time
Thank you!
Questions