truck set-up scheduling for the elgin, il facility vijay viswanathan, graduate student dr. jaejin...
TRANSCRIPT
Truck set-up scheduling for the Elgin, IL facility
Vijay Viswanathan, Graduate StudentDr. Jaejin Jang, Associate Professor
Department of Industrial Engineering
Overview of Presentation
• Introduction• Detailed Problem Description• Objective of Project• Assumptions• The Scheduling Algorithm• Simulation Input• Summary of Results• Conclusion
Introduction
• Wisconsin Lift Truck corporation sells, rents, services trucking equipment like…– Aerial lift and
construction equipment– Cranes– Lift Trucks – Industrial Cleaning
Equipment– Loaders – Pallet Trucks – Personnel Carriers
Introduction
• They have seven locations in Wisconsin and two locations in Illinois
• Our contact for this project is – Kristine Rauch
• Industrial Engineer, WLT, Brookfield, WI
Receive Truck
Stock Sold to Customer
Inventory WIP
Schedule for Set-Up
Stage
Delivery(Corp run or
Branch truck)
Set-Up(Bay Area)
Problem Description
• Bay has maximum capacity of 25– 5 stations with capacity of 5 trucks each
• 4 are considered WIP • 1 truck is being worked on
• 5 techs available for scheduling– one tech assigned to each of the 5 bays
Problem Description Cont’d
• 4 set-up types• 19-Used Truck Setup
– 3 types of New Truck Setups• 20-N.T SET-UP• 36-NEW RTL SET-UP• 76-I/C NT SETUP
Tech 1
Tech 2
Tech 3
Tech 4
Tech 5
Schematic of the Truck Set-up Bays
Scheduling Objective
• Minimize the time it takes for stock and new customer truck set ups to get from WIP to the delivery area
• Minimize tardiness to ensure timely delivery of trucks to customers as much as possible
Assumptions• There will be no preemption during
setup, once a job is started, it is completed – If we cannot finish a truck without
stopping in the middle of processing, we do not start the truck
• Once a tech has completed a setup they will start the next set up right after
• Both stock and customer trucks are taken together as number of stock trucks is negligible
• 6 hour work day
Receive Truck
Schedule for Set-Up
Truck set for
delivery
Set-Up(Bay Area)
Scope for scheduling
• 2 areas where scheduling can be done– When picking trucks from the infinite
arrival area into one of the 5 WIPs– When selecting one truck for set-up in
each bay station
Raw Data Analysis• Data From: Jan 2005 – May 2006 i.e.; 16
months– Job Type 76 – 515 jobs– Job Type 36 – 43 jobs– Job Type 19 – 97 jobs– Job Type 20 – 449 jobs– Total Significant Jobs: 1104
• % of Job Type 76 – 46.65%• % of Job Type 43 – 3.89%• % of Job Type 19 – 8.79%• % of Job Type 20 – 40.67%• Total No. of Trucks - 1974• No. of Stock Trucks [IMH RENTAL] - 89
[4.5%]• No. of Sold Trucks – 1885 (95.5%)
Simulation Input Data
–Setup times for each job type• Total labor $$ billed on each truck available• Tech billed at $97 per hour
–Distributions for inter-arrival times, by job type
• Used ARENA Input Analyzer module to fit each of these into standard probability distributions
More Simulation Inputs..
• Due dates were assigned as an attribute to every job arriving– Due date distribution also determined
from invoice data
• Results were used to design an ARENA simulation so that different scheduling algorithms could be implemented and their performance evaluated.
Scheduling LOGIC
• Experimented with 4 different hybrid scheduling algorithms.
• Scheduling Algorithms used are a simple combination of standard algorithms with modifications made to suit this problem.– LST and SPT
• Process trucks in both WIP and bay queues in order of lowest value of the sum of Slack time and Processing time.
• In doing so, we anticipate minimizing flowtime as also reducing slack.
– LST OR SPT• A modification of the above algorithm where incoming trucks
are processed as per the least slack time, if (slack >0), else SPT is used to select trucks from the queues.
Scheduling Logic
– EDD With Priority• Modification of the EDD algorithm to incorporate a
priority mechanism for new truck types over old truck types
• Selection rule is – least value of (due date/priority), where priority is “50” for a new truck type and “10” for a used truck type (type 19)
– Shortest Processing Time • Plain ol’ SPT in least order of processing time
Simulation run Parameters
• Replication Length – 180 Days• Hours/day – 6 hrs• Warm up period – 10 Days• Number of Replications -4
Simulation Results [ALL UNITS DAYS]
JOB TYPE 20
RULE Combination Avg. Flowtime Max. Flowtime Avg. Lateness Max. Lateness
LST_SPT 5.33 19.48 517.44 1832
LST_OR_SPT 5.53 31.75 638.97 1681.74
EDD_PRIO 7.34 41.28 393.22 1705.47
SPT 7.09 59.86 422.55 1507.55
JOB TYPE 19 [USED TRUCK]
RULE Combination Avg. Flowtime Max. Flowtime Avg. Lateness Max. Lateness
LST_SPT 2.65 16.14 406.02 1104
LST_OR_SPT 5.84 31.12 466.45 1373.9
EDD_PRIO 7.38 29.55 501.92 1550.34
SPT 4.87 56.84 618.11 1527.85
Conclusion• The combination of LST and SPT works best to
minimize overall flow time (but not tardiness).• If either LST/SPT is used depending on
whether the job is slack or not, this leads to a significant reduction in max. lateness, compared to using LST + SPT in all cases.
• SPT scheduling yields the least max. lateness.• A priority based scheme predictably decreases
the avg. lateness for new truck set-ups. • Future Work Idea
– An Intelligent scheduler that can decide on the right scheduling algorithm based on a reasonable guess of whether incoming jobs will be late or not.
Thank you!
Questions/Comments?