Scheduling
Chapter 19
Learning Objectives
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.
1.
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
LO 1
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
LO 1
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
LO 2
Typical Scheduling and Control Functions
Allocating orders, equipment, and
personnel
2. Determining the sequence of order
performance
3. Initiating performance of the scheduled
work
4. Shop-floor control
1.
LO 2
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
LO 2
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)
(Due date - Current date)
CR 
Number of days remaining
Example of Job Sequencing: First-Come
First-Served
Suppose you have the four
jobs to the right arrive for
processing on one machine
Jobs (in order
of arrival)
A
B
C
D
What is the FCFS schedule?
Processing
Due Date
Time (days) (days hence)
4
5
7
10
3
6
1
4
Do all the jobs get done on time?
Answer: FCFS Schedule
Jobs (in order
of arrival)
A
B
C
D
Processing
Time (days)
4
7
3
1
Due Date Flow Time
(days hence)
(days)
5
4
10
11
6
14
4
15
No, Jobs B, C,
and D are
going to be late
Example of Job Sequencing: Shortest
Operating Time
Suppose you have the four
jobs to the right arrive for
processing on one machine
What is the SOT schedule?
Jobs (in order
of arrival)
A
B
C
D
Processing
Time (days)
4
7
3
1
Due Date
(days hence)
5
10
6
4
Do all the jobs get done on time?
Answer: Shortest Operating Time Schedule
Jobs (in order
of arrival)
D
C
A
B
Processing
Time (days)
1
3
4
7
Due Date Flow Time
(days hence)
(days)
4
1
6
4
5
8
10
15
No, Jobs A
and B are
going to be
late
Example of Job Sequencing: Earliest Due
Date First
Suppose you have the four
jobs to the right arrive for
processing on one machine
What is the earliest due date
first schedule?
Jobs (in order
of arrival)
A
B
C
D
Processing
Time (days)
4
7
3
1
Due Date
(days hence)
5
10
6
4
Do all the jobs get done on time?
Answer: Earliest Due Date First
Jobs (in order
of arrival)
D
A
C
B
Processing
Time (days)
1
4
3
7
Due Date Flow Time
(days hence)
(days)
4
1
5
5
6
8
10
15
No, Jobs C
and B are
going to be
late
Example of Job Sequencing: Critical Ratio
Method
Suppose you have the four
jobs to the right arrive for
processing on one machine
What is the CR schedule?
Jobs (in order
of arrival)
A
B
C
D
Processing
Time (days)
4
7
3
1
Due Date
(days hence)
5
10
6
4
Do all the jobs get done 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)
No, but since
there is a
three-way tie,
only the first
job or two will
be 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
LO 2
Steps to Johnson’s Rule
List the operation time for each job
2. Select the shortest operation time
3. If the shortest time is on the first machine, do first
1.


4.
If the shortest time is on the second machine, do the job
last
For ties, do first
Repeat 2-3 for each remaining job
LO 2
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?
Jobs
A
B
C
D
Time in Hours
Stage 1
Stage 2
1.50
1.25
2.00
3.00
2.50
2.00
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.
2.
3.
LO 2
There are n things to be distributed to n destinations
Each thing assigned to one and only one destination
Only one criterion can be used
Example : Assignment Method
Assignment Matrix Showing Machine Processing Costs for Each Job
LO 2
Example Step 1: Row Reduction
LO 2
Example Step 2: Column Reduction
LO 2
Example Step 3: Apply Line Test
LO 2
Example Step 4: Additional Reduction
LO 2
Example Optimal Solution
LO 2
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
LO 2
$17
Personnel Scheduling in Services
 Scheduling consecutive days off
 Scheduling daily work times
 Scheduling hourly work times
LO 4
Any Questions?
SCHEDULING