Transcript Document

OM2
CHAPTER 14
OPERATIONS SCHEDULING
AND SEQUENCING
DAVID A. COLLIER
AND
JAMES R. EVANS
OM2, Ch. 14 Operations Scheduling and Sequencing
©2010 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or
posted to a publicly accessible website, in whole or in part.
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Chapter 14 Learning Outcomes
learning outcomes
LO1 Explain the concepts of scheduling and
sequencing.
LO2 Describe staff scheduling and appointment
system decisions.
LO3 Explain sequencing performance criteria and
rules.
LO4 Describe how to solve single- and two-resource
sequencing problems.
LO5 Explain the need for monitoring schedules using
Gantt charts.
OM2, Ch. 14 Operations Scheduling and Sequencing
©2010 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or
posted to a publicly accessible website, in whole or in part.
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Chapter 14 Operations Scheduling and Sequencing
ean Rowecamp, clinical coordinator of nursing services, was faced
with a deluge of complaints by her nursing staff about their work
schedules and complaints by floor supervisors about inadequate
staffing. The nurses complained they were having too many shift
changes each month. Supervisors said they had too many nurses
during the days and not enough at night and on the weekends. It
seems that nothing she did would satisfy everyone. The nurses were
unionized, so she couldn’t schedule them more than 7 consecutive
working days and the nurses required at least 16 hours between shift
changes. Nurses were constantly making “special requests” for personal
time off, despite the negotiated procedures for bidding for shifts and
vacation times. Jean lamented that she became an administrator and
longed for the days when she was just a simple caregiver.
What do you think? As a student, how do you schedule your
homework, school projects, and study activities? What criteria do
you use?
OM2, Ch. 14 Operations Scheduling and Sequencing
©2010 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or
posted to a publicly accessible website, in whole or in part.
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Chapter 14 Operations Scheduling and Sequencing
This chapter addresses key issues and methods for
scheduling and sequencing in manufacturing and
service organizations.
•
Scheduling refers to the assignment of start
and completion times to particular jobs,
people, or equipment.
•
Sequencing refers to determining the order in
which jobs or tasks are processed.
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Chapter 14 Operations Scheduling and Sequencing
Telling Umpires Where to Go
Some of the critical factors in developing major league umpire
schedules were to ensure that umpire crews were not assigned to
consecutive series with the same team if possible; that the number
of times a crew was assigned to a team was balanced over the
course of the season; that travel sequences be rational and
realistic; and that a variety of constraints be met. For instance, it
makes more sense to schedule a crew to several consecutive
series out on the East Coast or West Coast and move them to
nearby cities rather than shuttle them back and forth across the
country. Various constraints limited the scheduling possibilities. For
example, one could not schedule a crew for a day game in another
city after working a night game on the previous day. In addition,
crews need time to rest and travel between game assignments. All
these factors needed to be considered in the context of the game
schedule, which was created well in advance.
OM2, Ch. 14 Operations Scheduling and Sequencing
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posted to a publicly accessible website, in whole or in part.
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Chapter 14 Operations Scheduling and Sequencing
Scheduling and Sequencing in the Resource
Management Framework
Scheduling and sequencing are fundamental to all
three levels of aggregation and disaggregation
planning (see Exhibit 13.1).
Level 3 decisions require detailed resource
scheduling (trucks, labor, equipment, computers,
and jobs), sequencing, and day-to-day execution.
OM2, Ch. 14 Operations Scheduling and Sequencing
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Chapter 14 Operations Scheduling and Sequencing
Scheduling in Supply Chains
•
The complexity of many business situations dictates that
effective scheduling systems be computerized.
•
Scheduling and information exchange are at the heart of
managing an efficient and responsive value chain
because the network of processes needs to be
synchronized.
•
Computer-generated schedules and the sharing of
production, purchasing, inventory, delivery, and
customer information among suppliers and buyers in
the value chain enable faster service at lower cost.
OM2, Ch. 14 Operations Scheduling and Sequencing
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Chapter 14 Operations Scheduling and Sequencing
Staff Scheduling
Staff scheduling attempts to match available personnel with
the needs of the organization by:
1. Accurately forecasting demand and translating it into
the quantity and timing of work to be done
2. Determining the staffing required to perform the
work by time period
3. Determining the personnel available and the full- and
part-time mix
4. Matching capacity to demand requirements and
developing a work schedule that maximizes service
and minimizes costs
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Exhibit 14.1
Staff Scheduling Procedure for T.R. Accounting Service
T. R. Accounting Service is developing a workforce schedule for three weeks from
now, and has forecast demand and translated it into the following minimum
personnel requirements for the week.
Day
Mon
Tue
Wed
Thur
Fri
Sat
Sun
Min Personnel
8
6
6
6
9
5
3
OM2, Ch. 14 Operations Scheduling and Sequencing
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posted to a publicly accessible website, in whole or in part.
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Exhibit 14.2
OM2, Ch. 14 Operations Scheduling and Sequencing
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posted to a publicly accessible website, in whole or in part.
Final Accountant Schedule
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Chapter 14 Operations Scheduling and Sequencing
Appointment Systems
From an operations’ perspective, appointments can be
viewed as a reservation for service time and capacity.
Four decisions to make regarding designing an
appointment system are:
1. Determine the appointment time intervals.
2. Determine the length of each workday and time
off-duty.
3. Decide how to handle overbooking.
4. Develop customer appointment rules that maximize
customer satisfaction.
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©2010 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or
posted to a publicly accessible website, in whole or in part.
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Chapter 14 Operations Scheduling and Sequencing
Appointment Systems
From an operations’ perspective, appointments can be
viewed as a reservation for service time and capacity.
 Given the perishable nature of professional serviceprovider time and the potential loss of revenue, most
service providers overbook.
 Example: If you book a dentist appointment and do
not reschedule and do not show up, the dentist may
lose forever the revenue he/she could make during
that time.
 Appointment systems are critical to maximizing
revenue and minimizing idle time.
OM2, Ch. 14 Operations Scheduling and Sequencing
©2010 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or
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Chapter 14 Operations Scheduling and Sequencing
Software to Schedule Anywhere
One provider of small business software offers an online
employee scheduling system called Schedule-Anywhere
(ScheduleAnywhere.com). This service allows managers to
schedule employees from any computer with Internet
access, whether at work, at home, or on the road. “With
over 70,000 users, we get a lot of feedback on what
people really need in an employee scheduling system,”
said Jon Forknell, vice president and general manager of
Atlas Business Solutions. “Many of our customers told us
they needed an online solution that was affordable and
easy to use.”
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posted to a publicly accessible website, in whole or in part.
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Chapter 14 Operations Scheduling and Sequencing
ScheduleAnywhere gives users the power to
• schedule employees from any computer with Internet
access
• create schedules by position, department, location, etc.
• view schedule information in a 1-day, 7-day, 14-day, or
28-day format
• enter staffing requirements and view shift coverage
• see who’s scheduled and who’s available
• automatically rotate or copy employee schedules
• pre-schedule time-off requests
• avoid scheduling conflicts
• give employees read/write or read-only access to
schedules
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posted to a publicly accessible website, in whole or in part.
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Chapter 14 Operations Scheduling and Sequencing
Sequencing
Sequencing is required when several activities
must be processed using a common resource.
Example: An insurance claims analyst needs to
process 25 customer medical claims on a
computer (the resource). What claims should be
processed first, second, and last to maximize
customer satisfaction or minimize average claim
lateness?
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Chapter 14 Operations Scheduling and Sequencing
Sequencing
Flow time is the amount of time a job
spent in the shop or factory. Flow time is
computed as follows:
Fi = ∑pij + ∑wij = Ci - Ri
OM2, Ch. 14 Operations Scheduling and Sequencing
©2010 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or
posted to a publicly accessible website, in whole or in part.
[14.1]
16
Chapter 14 Operations Scheduling and Sequencing
Sequencing
Makespan is the time needed to process a given
set of jobs. A short makespan aims to achieve
high equipment utilization.
M= C-S
[14.2]
where
M = makespan of a group of jobs
C = completion time of last job in the group
S = start time of first job in the group
OM2, Ch. 14 Operations Scheduling and Sequencing
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Chapter 14 Operations Scheduling and Sequencing
Sequencing
Lateness and tardiness measure performance related to
customer-focused due-date criteria.
• Lateness is the difference between the completion time
•
and the due date (either positive or negative).
Tardiness is the amount of time by which the completion
time exceeds the due date. (Tardiness is defined as zero if
the job is completed before the due date, and therefore no
credit is given for completing a job early).
Li = Ci - Di
[14.3]
Ti = Max (0, Li)
[14.4]
where Li = lateness of job i
Ti = tardiness of job i
Di = due date of job i
OM2, Ch. 14 Operations Scheduling and Sequencing
©2010 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or
posted to a publicly accessible website, in whole or in part.
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Chapter 14 Operations Scheduling and Sequencing
Sequencing
Two of the most popular sequencing rules for prioritizing
jobs are:
Shortest Processing Time (SPT)
With different processing times, SPT sequencing
maximizes resource utilization and minimizes average
flow time and work-in-process inventory.
Earliest Due Date (EDD)
Using Earliest Due Date (EDD), the maximum job
tardiness and lateness are minimized.
OM2, Ch. 14 Operations Scheduling and Sequencing
©2010 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or
posted to a publicly accessible website, in whole or in part.
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Chapter 14 Operations Scheduling and Sequencing
Single-Resource Sequencing Problem
•
In a serial manufacturing process, a bottleneck
workstation controls the output of the entire process.
Therefore, it is critical to schedule it efficiently.
•
With different processing times, SPT sequencing
maximizes workstation utilization and minimizes average
job flow time.
•
When processing times are relatively equal, first-comefirst-served sequencing is applied.
•
Using Earliest Due Date (EDD), the maximum job
tardiness and lateness are minimized.
OM2, Ch. 14 Operations Scheduling and Sequencing
©2010 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or
posted to a publicly accessible website, in whole or in part.
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Exhibit 14.3
Comparison of Three Ways (By-the Numbers, SPT, and EDD)
to Sequence the Five Jobs
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posted to a publicly accessible website, in whole or in part.
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Chapter 14 Operations Scheduling and Sequencing
Solved Problem
Five tax analysis jobs are waiting to be processed by Martha at
T.R. Accounting Service. Use the shortest processing time
(SPT) and earliest due date (EDD) sequencing rules to
sequence the jobs. Compute the flow time, tardiness, and
lateness for each job, and the average flow time, average
tardiness, and average lateness for all jobs. Which rule do you
recommend? Why?
Job
1
2
3
4
5
Processing Time (days) Due Date
7
11
3
10
5
8
2
5
6
17
OM2, Ch. 14 Operations Scheduling and Sequencing
©2010 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or
posted to a publicly accessible website, in whole or in part.
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Chapter 14 Operations Scheduling and Sequencing
Solution
The SPT sequence is 4-2-3-5-1.
Job
4
2
3
5
1
Flow (Fi)
2
2+3=5
5 + 5 = 10
10 + 6 = 16
16 + 7 = 23
Average
Due
Lateness
Date (Di)
(Li)
5
-3
10
-5
8
2
17
-1
11
12
11.2
+ 1.0
OM2, Ch. 14 Operations Scheduling and Sequencing
©2010 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or
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Tardiness
(Max (0, Li)
0
0
2
0
12
2.8
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Chapter 14 Operations Scheduling and Sequencing
Solution
The EDD sequence is 4-3-2-1-5.
Due Date
Lateness
Tardiness
Job
Flow (Fi)
(Di)
(Li = Ci - Di) (Max (0, Li)
4
2
5
-3
0
3
2+5=7
8
-1
0
2
7 + 3 = 10
10
0
0
1
10 + 7 = 17
11
6
6
5
17 + 6 = 23
17
6
6
Average
11.8
- 1.6
2.4
Given the nature of the data, this is not an easy decision. The SPT rule
minimizes average flow time and average lateness, but Job 5 is extremely
late by 12 days. The EDD rule minimizes the maximum job tardiness and
lateness. Jobs 1 and 5 are tardy by 6 days. If Job 5 is a big client with
significant revenue potential, then the EDD rule is probably best.
OM2, Ch. 14 Operations Scheduling and Sequencing
©2010 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or
posted to a publicly accessible website, in whole or in part.
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Chapter 14 Operations Scheduling and Sequencing
Two-Resource Sequencing Problem (often called Johnson’s
Rule)
•
In the following example, we assume that each job must be
processed first on Resource #1 and then on Resource #2.
•
Hirsch Products manufactures custom parts that first
require a shearing operation (Resource #1) and then a
punch-press operation (Resource #2). Order information is
provided below.
Job
Shear (days)
Punch (days)
1
4
5
2
4
1
3
10
4
4
6
10
5
2
3
OM2, Ch. 14 Operations Scheduling and Sequencing
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posted to a publicly accessible website, in whole or in part.
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Exhibit 14.4
Gantt Job Sequence Chart for Hirsch Product Sequence 1-2-3-4-5
If jobs are completed by order number, the punch press often
experiences idle time awaiting the next job as shown below
(Exhibit 14.4). The makespan is 37 days.
OM2, Ch. 14 Operations Scheduling and Sequencing
©2010 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or
posted to a publicly accessible website, in whole or in part.
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Exhibit 14.5
Gantt Job Sequence Chart for Hirsch Product Sequence 5-1-4-3-2
Using Johnson’s Rule
Johnson’s Rule results in a reduction in makespan from
37 days to 27 days, as shown in the Gantt chart below in
Exhibit 14.5. So, smart scheduling is important for
customer service and process efficiency!
OM2, Ch. 14 Operations Scheduling and Sequencing
©2010 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or
posted to a publicly accessible website, in whole or in part.
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Chapter 14 Operations Scheduling and Sequencing
Schedule Monitoring and Control
•
The scheduling process must be monitored on a
continuing basis to track changes in the status of orders,
input materials, inventory changes, labor turnover, and
sales commitments. Reschedules are a normal part of
scheduling and sequencing.
•
Short-term capacity fluctuations also necessitate
changes in schedules and sequences.
•
Gantt charts are useful tools for monitoring schedules.
Exhibit 14.6 (next slide) shows a Gantt chart for a
variety of jobs. This helps to track jobs that are behind,
on, or ahead of schedule.
OM2, Ch. 14 Operations Scheduling and Sequencing
©2010 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or
posted to a publicly accessible website, in whole or in part.
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Exhibit 14.6
Gantt Chart Example for Monitoring Schedule Progress
OM2, Ch. 14 Operations Scheduling and Sequencing
©2010 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or
posted to a publicly accessible website, in whole or in part.
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Chapter 14 Operations Scheduling and Sequencing
Balloons Aloha Case Study
1. Compute the average flow time, lateness, and tardiness for
this group of jobs using Mr. Sailboat’s sequential order of 1 (fi
rst), 2, 3, 4, 5, and 6 (last).
2. In what order would the jobs be processed using the SPT
rule? Compute the average flow time, lateness, and tardiness
for this group of jobs.
3. Compare the answers in parts 1 and 2.
4. What are your short-term recommendations for this set of six
jobs?
Explain how you arrived at them.
5. What are your long-term recommendations with respect to
sequencing jobs at Balloons Aloha? Explain your reasoning.
OM2, Ch. 14 Operations Scheduling and Sequencing
©2010 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or
posted to a publicly accessible website, in whole or in part.
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