Transcript 19-1 Scheduling CHAPTER Scheduling McGraw-Hill/Irwin Operations Management, Eighth Edition, by William J. Stevenson Copyright © 2005 by The McGraw-Hill Companies, Inc.

19-1
Scheduling
CHAPTER
22
Scheduling
McGraw-Hill/Irwin
Operations Management, Eighth Edition, by William J. Stevenson
Copyright © 2005 by The McGraw-Hill Companies, Inc. All rights reserved.
19-2
Scheduling
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
19-3
Scheduling
Scheduling

Scheduling: Establishing the timing of the
use of equipment, facilities and human
activities in an organization

Effective scheduling can yield
Cost
savings
Increases
in productivity
19-4
Scheduling
Typical Scheduling and Control Functions
 Allocating
orders, equipment, and
personnel
 Determining
the sequence of order
performance
 Initiating
performance of the
scheduled work
 Shop-floor
control
19-5
Scheduling

High-Volume Systems
Flow system: High-volume system with
Standardized equipment and activities

Flow-shop scheduling: Scheduling for highvolume flow system
Work Center #1
Work Center #2
Output
19-6
Scheduling
High-Volume Success Factors

Process and product design

Preventive maintenance

Rapid repair when breakdown occurs

Optimal product mixes

Minimization of quality problems

Reliability and timing of supplies
19-7
Scheduling
Scheduling Low-Volume Systems

Loading - assignment of jobs to
process centers
 Sequencing - determining the order in
which jobs will be processed
 Job-shop scheduling
Scheduling
for low-volume systems with
many variations
in requirements
19-8
Scheduling
Sequencing

Sequencing: Determine the order in which
jobs at a work center will be processed.

Workstation: An area where one person
works, usually with special equipment, on
a specialized job.
19-9
Scheduling
Two Work Center Sequencing

Johnson’s Rule: technique for minimizing
completion time for a group of jobs to be
processed on two machines or at two work
centers in a common sequence.

Minimizes Total Idle Time and Flow Time.

Several Conditions Must Be Satisfied
19-10 Scheduling
Johnson’s Rule Conditions

Job time must be known and constant

Job times must be independent of
sequence

Jobs must follow same two-step sequence

Job priorities cannot be used

All units must be completed at the first
work center before moving to second
19-11 Scheduling
Johnson’s
Rule
Optimum
Sequence
1. List the jobs
and their
times at each
work center
2.
Select the job with the shortest time
1.
2.
3.
3.
4.
If the shortest time is on the first center, Do the
job First;
If it is on the 2nd center, Do the job Last.
In case of tie, do the job on the first machine.
Eliminate the job from further consideration
Repeat steps 2 and 3 until all jobs have been
scheduled
19-12 Scheduling
Johnson’s Rule (n Jobs on 2 Centers)
Processing Time (Hours)
Jobs
A
B
C
D
E
F
Work Center 1
1.50
4.00
0.75
1.00
2.00
1.80
Work Center 2
0.50
1.00
2.25
3.00
4.00
2.20
19-13 Scheduling

Sequencing
Priority rules: Simple heuristics
used to select the order in
which jobs will be processed.
Everything is
#1 Priority

Job time: Time needed for
setup and processing of a job.
19-14 Scheduling
Priority Rules

FCFS - first come, first served

SOT - shortest processing time

EDD - earliest due date

LCFS - Last come, first served

STR - slack time remaining

Rush - emergency
Top Priority
19-15 Scheduling
The setup
of jobs is known
Assumptions
of Priority Rules
 Setup time is independent of processing sequence
 Setup time is deterministic
 There will be no interruptions in processing such
as:

Machine
breakdowns
Accidents
Worker illness
19-16 Scheduling
Example 2
Rule
Total
Flow Time
(days)
Average
Flow Time
(days)
Average
Tardiness
(days)
FCFS
50.00
10.00
4.6
SOT
36.00
7.20
2.4
EDD
39.00
7.80
2.4
STR
43.00
8.60
3.2
19-17 Scheduling

Scheduling
Difficulties
Variability
in
Setup
times
Processing times
Interruptions
Changes in the set of jobs

No method for identifying optimal schedule
 Scheduling is not an exact science
 Ongoing task for a manager
19-18 Scheduling
Minimizing
Scheduling
Difficulties
Set realistic due
dates


Focus on bottleneck operations

Consider lot splitting of large jobs
19-19 Scheduling
Scheduling Service Operations

Appointment systems
Controls

customer arrivals for service
Reservation systems
Estimates

Scheduling the workforce
Manages

demand for service
capacity for service
Scheduling multiple resources
Coordinates
resource
use of more than one
19-20 Scheduling
Cyclical
Scheduling
Hospitals,
police/fire
departments, restaurants,
supermarkets
 Rotating schedules

Set
a scheduling horizon
Identify the work pattern
Develop a basic employee schedule
Assign employees to the schedule
19-21 Scheduling
Service Operation Problems

Cannot store or inventory services
 Customer service requests are random
 Scheduling service involves
Customers
Workforce
Equipment