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SchedulingChapter 19
Learning Objectives
1. Know what a Manufacturing Execution System production activity control is.
2. Understand typical priority scheduling rules and the impact they have on scheduling performance measures.
3. Recognize a simple job allocation procedure.
4. Explain the issues considered in employee scheduling.
Manufacturing Execution Systems
Manufacturing execution system (MES): an information system that schedules, dispatches, tracks, monitors, and controls production Real-time linkage to:
MRP Product and process planning Systems that extend beyond the factory
Service execution system (SES): an information system that links schedules, dispatches, tracks, monitors, and controls the customer’s encounters with the service organization
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Work Center
A work center is an area in a business in which productive resources are organized and work is completed
Can be a single machine, a group of machines, or an area where a particular type of work is done
Loading
Infinite loading: work is assigned to a work center based on what is needed No consideration to capacity
Finite loading: schedules each resource using the setup and run time required for each order Determines exactly what will be done by each
resource at every moment during the day
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Scheduling
Forward scheduling: the system takes an order and schedules each operation that must be completed forward in time Can tell the earliest date an order can be completed
Backward scheduling: starts with due date and schedules the required operations in reverse sequence Can tell when an order must be started in order to be
done by a specific date
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Typical Scheduling and Control Functions
1. Allocating orders, equipment, and personnel
2. Determining the sequence of order performance
3. Initiating performance of the scheduled work
4. Shop-floor control
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Work-Center Scheduling Objectives
Meet due dates
Minimize lead time
Minimize setup time or cost
Minimize work-in-process inventory
Maximize machine utilization
Job Sequencing
Sequencing: the process of determining the job order on machines or work centers Also known as priority sequencing
Priority rules: the rules used in obtaining a job sequence Can be simple or complex Can use one or more pieces of information Common rules shown on next slide
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Priority Rules for Job Sequencing 1. First-come, first-served (FCFS)
2. Shortest operating time (SOT)
3. Earliest due date first (DDate)
4. Slack time remaining (STR) first
Priority Rules for Job Sequencing (Continued)
5. Critical ratio (CR)
remaining days of Number
date) Current-date (DueCR
Example of Job Sequencing: First-Come First-Served
Jobs (in order Processing Due Date Flow Timeof arrival) Time (days) (days hence) (days)
A 4 5 4B 7 10 11C 3 6 14D 1 4 15
Answer: FCFS Schedule
Jobs (in order Processing Due Dateof arrival) Time (days) (days hence)
A 4 5B 7 10C 3 6D 1 4
Suppose you have the four jobs to the right arrive for processing on one machine
Suppose you have the four jobs to the right arrive for processing on one machine
What is the FCFS schedule?What is the FCFS schedule?
No, Jobs B, C, and D are going to be late
No, Jobs B, C, and D are going to be late
Do all the jobs get done on time?Do all the jobs get done on time?
Example of Job Sequencing: Shortest Operating Time
Jobs (in order Processing Due Dateof arrival) Time (days) (days hence)
A 4 5B 7 10C 3 6D 1 4
Answer: Shortest Operating Time Schedule
Jobs (in order Processing Due Date Flow Timeof arrival) Time (days) (days hence) (days)
D 1 4 1C 3 6 4A 4 5 8B 7 10 15
Suppose you have the four jobs to the right arrive for processing on one machine
Suppose you have the four jobs to the right arrive for processing on one machine
What is the SOT schedule?What is the SOT schedule?
No, Jobs A and B are going to be late
No, Jobs A and B are going to be late
Do all the jobs get done on time?Do all the jobs get done on time?
Example of Job Sequencing: Earliest Due Date First
Jobs (in order Processing Due Dateof arrival) Time (days) (days hence)
A 4 5B 7 10C 3 6D 1 4
Answer: Earliest Due Date First
Jobs (in order Processing Due Date Flow Timeof arrival) Time (days) (days hence) (days)
D 1 4 1A 4 5 5C 3 6 8B 7 10 15
Suppose you have the four jobs to the right arrive for processing on one machine
Suppose you have the four jobs to the right arrive for processing on one machine
What is the earliest due date first schedule?
What is the earliest due date first schedule?
No, Jobs C and B are going to be late
No, Jobs C and B are going to be late
Do all the jobs get done on time?Do all the jobs get done on time?
Example of Job Sequencing: Critical Ratio Method
Jobs (in order Processing Due Dateof arrival) Time (days) (days hence)
A 4 5B 7 10C 3 6D 1 4
Suppose you have the four jobs to the right arrive for processing on one machine
Suppose you have the four jobs to the right arrive for processing on one machine
What is the CR schedule?What is the CR schedule?
No, but since there is a three-way tie, only the first job or two will be on time
No, but since there is a three-way tie, only the first job or two will be on time
In order to do this schedule the CR’s have be calculated for each job. If we let today be Day 1 and allow a total of 15 days to do the work. The resulting CR’s and order schedule are:CR(A)=(5-4)/15=0.06 (Do this job last)CR(B)=(10-7)/15=0.20 (Do this job first, tied with C and D)CR(C)=(6-3)/15=0.20 (Do this job first, tied with B and D)CR(D)=(4-1)/15=0.20 (Do this job first, tied with B and C)
Do all the jobs get done on time?Do all the jobs get done on time?
Scheduling n Jobs on Two Machines
Two or more jobs must be processed on two machines in a common sequence
Wish to minimize the flow time from the beginning of the first job to the finish of the last job
Use Johnson’s rule
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Steps to Johnson’s Rule
1. List the operation time for each job2. Select the shortest operation time3. If the shortest time is on the first machine,
do first If the shortest time is on the second machine, do
the job last For ties, do first
4. Repeat 2-3 for each remaining job
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Example of Job Sequencing: Johnson’s Rule
Suppose you have the following five jobs with time requirements in two stages of production. What is the job sequence using Johnson’s Rule?
Suppose you have the following five jobs with time requirements in two stages of production. What is the job sequence using Johnson’s Rule?
Time in HoursJobs Stage 1 Stage 2 A 1.50 1.25 B 2.00 3.00 C 2.50 2.00 D 1.00 2.00
Scheduling a Set Number of Jobs on the Same Number of Machines
Some work centers have enough machines to start all the jobs
Here the issue is the particular assignment of individual jobs to individual machines
Assignment method: a special case of the transportation method of linear programming
1. There are n things to be distributed to n destinations2. Each thing assigned to one and only one destination3. Only one criterion can be used
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Example : Assignment Method
Assignment Matrix Showing Machine Processing Costs for Each JobAssignment Matrix Showing Machine Processing Costs for Each Job
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Example Step 1: Row Reduction
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Example Step 2: Column Reduction
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Example Step 3: Apply Line Test
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Example Step 4: Additional Reduction
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Example Optimal Solution
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Example Optimal Assignment and Their Costs
Job I to Machine E $3
Job II to Machine B 4
Job III to Machine C 2
Job IV to Machine D 5
Job V to Machine A 3
Total Cost $17
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Personnel Scheduling in Services
Scheduling consecutive days offScheduling daily work timesScheduling hourly work times
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SCHEDULING
Any Questions?
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