OPERATIONS SCHEDULING AND SEQUENCING

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OM
CHAPTER 14
OPERATIONS SCHEDULING AND SEQUENCING
DAVID A. COLLIER AND JAMES R. EVANS
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Chapter 14 Learning Outcomes

l e a r n i n g o u t c o m e s

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.
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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 couldnt 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?
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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
Scheduling and sequencing are fundamental to all
three levels of aggregation and disaggregation
planning. Level 3 decisions (explained in
Chapter 13 and Exhibit 13.1) require detailed
resource scheduling (trucks, labor, equipment,
computers, and jobs), sequencing, and day-to-day
execution.
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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.

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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
• Accurately forecasting demand and translating it
  into the quantity and timing of work to be done
• Determining the staffing required to perform the
  work by time period
• Determining the personnel available and the full-
  and part-time mix
• 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
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Exhibit 14.2
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
• Determine the appointment time intervals.
• Determine the length of each workday and time
  off-duty.
• Decide how to handle overbooking.
• Develop customer appointment rules that maximize
  customer satisfaction.

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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
  service-provider 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.

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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
14.1

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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

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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

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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.

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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-come-first-served sequencing is applied.
• Using Earliest Due Date (EDD), the maximum job
  tardiness and lateness are minimized.

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Comparison of Three Ways (By-the Numbers, SPT,
and EDD)to Sequence the Five Jobs
Exhibit 14.3
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Chapter 14 Solved Problem T.R. Accounting
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 Processing Time (days) Due
Date 1 7 11 2 3 10 3 5 8 4 2
5 5 6 17

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Chapter 14 Solved Problem T.R. Accounting

• Solution
• The SPT sequence is 4-2-3-5-1.
• Due Lateness Tardiness
• Job Flow (Fi) Date (Di) (Li) (Max
  (0, Li)
• 4 2 5 - 3 0
• 2 2 3 5 10 - 5 0
• 3 5 5 10 8 2 2
• 5 10 6 16 17 - 1
  0
• 1 16 7 23 11 12 12
• Average 11.2 1.0
  2.8

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Chapter 14 Solved Problem T.R. Accounting
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.

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Chapter 14 Operations Scheduling and Sequencing

• Two-Resource Sequencing Problem (often called
  Johnsons 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.

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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.
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Gantt Job Sequence Chart for Hirsch Product
Sequence 5-1-4-3-2 Using Johnsons Rule
Exhibit 14.5
Johnsons 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!
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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.

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Exhibit 14.6
Gantt Chart Example for Monitoring Schedule
Progress