Operation management 10e heizer render chapter 15

Sequencing ExampleJob Job Work Processing Time Days Job Due Date Days Apply the four popular sequencing rules to these five jobs... Sequencing ExampleJob Sequence Job Work Processing T

Delta Air Lines

Short-Term Scheduling

Outline – Continued

Machines: Johnson’s Rule

Dispatching Systems

Outline – Continued

Cyclical Scheduling

Learning Objectives

When you complete this chapter you

should be able to:

short-term scheduling, capacity planning, aggregate planning, and a master schedule

charts

loading jobs

Learning Objectives

When you complete this chapter you

should be able to:

sequencing rules

constraints

Delta Airlines

disrupted per year, half because of weather

overtime pay, food and lodging vouchers

Center adjusts to changes and keeps flights flowing

Strategic Importance of Short-Term Scheduling

can be a competitive advantage

facility means better use of assets and lower costs

faster throughput improves customer service through faster delivery

backward

Scheduling Decisions

Organization Managers Must Schedule the Following Arnold Palmer

Hospital Operating room use Patient admissions

Nursing, security, maintenance staffs Outpatient treatments

University of

Missouri Classrooms and audiovisual equipment Student and instructor schedules

Graduate and undergraduate courses Lockheed Martin

factory Production of goods Purchases of materials

Workers Hard Rock Cafe Chef, waiters, bartenders

Delivery of fresh foods Entertainers

Opening of dining areas Delta Air Lines Maintenance of aircraft

Departure timetables

Figure 15.1

Scheduling Flow

Forward and Backward

Scheduling

as the requirements are known

though it may not meet due dates

buildup of process inventory

work-in-Due

Forward and Backward

Scheduling

the due date and schedules the final operation first

backwards though the processes

be available to accomplish the

Forward and Backward

Scheduling

the due date and schedules the final operation first

backwards though the processes

Different Processes/

Different Approaches

Process-focused

facilities Forward-looking schedules MRP due dates

Finite capacity scheduling Work cells Forward-looking schedules

MRP due dates Detailed schedule done using work cell priority rules

Repetitive facilities Forward-looking schedule with a

balanced line Pull techniques for scheduling

Product-focused

facilities Forward-looking schedule with stable demand and fixed capacity

Capacity, set-up, and run times known Capacity limited by long-term capital investment

Table 15.2

Scheduling Criteria

inventory

Optimize the use of resources so that production objectives are met

Scheduling Focused Facilities

violating capacity constraints

before releasing an order

Planning and Control Files

1 An item master file contains information about

each component

2 A routing file indicates each component’s flow

through the shop

3 A work-center master file contains information

about the work center

Planning Files

Control Files

Track the actual progress made against the plan

Loading Jobs

time, or completion time are minimized

centers

Input-Output Control

underloading conditions

resolve scheduling problems

cards that control the scheduling

of batches

the work center

Gantt Charts

idle times of departments, machines,

frequently to account for changes

Gantt Load Chart Example

Job 295

Gantt Schedule Chart

Actual work progress

Nonproduction time

Point in time when chart is reviewed

Assignment Method

programming models that assign tasks or jobs to resources

time

assigned to one machine (or project)

Assignment Method

associated with particular assignments

Typesetter Job A B C R-34 $11 $14 $ 6

S-66 $ 8 $10 $11

T-50 $ 9 $12 $ 7

Assignment Method

repeatedly subtracting the lowest costs from each row and column

and horizontal lines necessary to cover all the zeros in the table If the number

of lines equals either the number of rows or the number of columns,

proceed to step 4 Otherwise proceed to step 3.

Assignment Method

covered by a line from all other uncovered numbers Add the same number to any number at the

intersection of two lines Return to step 2.

locations in the table Select one, draw lines through the row and column

involved, and continue to the next assignment.

Assignment Example

Job R-34 $11 $14 $ 6

S-66 $ 0 $ 0 $ 3

T-50 $ 2 $ 3 $ 0

Typesetter

Step 1b - Columns

Because only two lines

are needed to cover all

the zeros, the solution

is not optimal

Step 3 - Subtraction

Job R-34 $ 3 $ 4 $ 0

Assignment Example

Because three lines are

needed, the solution is

Sequencing Jobs

should be performed at work centers

sequence jobs

Sequencing Example

Job

Job Work (Processing) Time

(Days)

Job Due Date (Days)

Apply the four popular sequencing rules

to these five jobs

Sequencing Example

Job Sequence

Job Work (Processing)

Time Time Flow Job Due Date Lateness Job

Sequencing Example

Job Sequence

Job Work (Processing)

Time Time Flow Job Due Date Lateness Job

jobs in the system = = 77/28 = 2.75 jobs Sum of total flow time Total job work time

Average job lateness = = 11/5 = 2.2 days Number of jobs Total late days

Sequencing Example

Job Sequence

Job Work (Processing)

Time Time Flow Job Due Date Lateness Job

Sequencing Example

Job Sequence

Job Work (Processing)

Time Time Flow Job Due Date Lateness Job

jobs in the system = = 65/28 = 2.32 jobs Sum of total flow time Total job work time

Average job lateness = = 9/5 = 1.8 days Number of jobs Total late days

Sequencing Example

Job Sequence

Job Work (Processing)

Time Time Flow Job Due Date Lateness Job

Sequencing Example

Job Sequence

Job Work (Processing)

Time Time Flow Job Due Date Lateness Job

EDD: Sequence B-A-D-C-E

Average completion time = = 68/5 = 13.6 days Sum of total flow time

Number of jobs

Utilization = = 28/68 = 41.2% Sum of total flow time Total job work time

Average number of

jobs in the system = = 68/28 = 2.43 jobs Sum of total flow time Total job work time

Average job lateness = = 6/5 = 1.2 days Number of jobs Total late days

Sequencing Example

Job Sequence

Job Work (Processing)

Time Time Flow Job Due Date Lateness Job

Sequencing Example

Job Sequence

Job Work (Processing)

Time Time Flow Job Due Date Lateness Job

jobs in the system = = 103/28 = 3.68 jobs Sum of total flow time Total job work time

Average job lateness = = 48/5 = 9.6 days Number of jobs Total late days

Sequencing Example

Rule

Average Completion Time (Days) Utilization (%)

Average Number

of Jobs in System

Average Lateness (Days)

Comparison of Sequencing Rules

 No one sequencing rule excels on all criteria

 SPT does well on minimizing flow time and

number of jobs in the system

 But SPT moves long jobs to

the end which may result

in dissatisfied customers

 FCFS does not do especially

well (or poorly) on any criteria but is perceived

as fair by customers

 EDD minimizes lateness

Critical Ratio (CR)

time remaining until the due date by the work time remaining on the job

scheduled ahead of jobs with higher critical ratios

criteria

CR = = Due date - Today’s date

Work (lead) time remaining Time remaining

Workdays remaining

Critical Ratio Example

Job Date Due Remaining Workdays Critical Ratio Priority Order

Currently Day 25

With CR < 1, Job B is late Job C is just on schedule

and Job A has some slack time.

Critical Ratio Technique

jobs

jobs on a common basis

jobs on a common basis

changes in both demand and job progress

Sequencing N Jobs on Two

Machines: Johnson’s Rule

pass through the same two machines or work centers

idle time

Johnson’s Rule

center

time If that time is in the first work center, schedule the job first If it is in the second work center, schedule the job last.

from the list

center of the sequence

Johnson’s Rule Example

Job Work Center 1 (Drill Press) Work Center 2 (Lathe)

B E D C A

Johnson’s Rule Example

Job Work Center 1 (Drill Press) Work Center 2 (Lathe)

Johnson’s Rule Example

Job Work Center 1 (Drill Press) Work Center 2 (Lathe)

WC 2

B E D C A

Johnson’s Rule Example

Job Work Center 1 (Drill Press) Work Center 2 (Lathe)

WC 2

B E D C A

Limitations of Rule-Based

Dispatching Systems

need to be revised to adjust to changes

downstream

dates

Finite Capacity Scheduling

systems by providing an interactive, computer-based graphical system

simulation to allow real-time response to system changes

needs and efficiency

Finite Capacity Scheduling

Tooling and other resources

Setups and run time

Interactive Finite Capacity Scheduling

Finite Capacity Scheduling

Theory of Constraints

processed through the facility and sold

faces in achieving its goals

1 Identify the constraints

2 Develop a plan for overcoming the constraints

3 Focus resources on accomplishing the plan

4 Reduce the effects of constraints by

off-loading work or increasing capacity

5 Once successful, return to step 1 and identify

that limit output

 Common occurrence due to frequent changes

 Increasing the capacity of the constraint

 Cross-trained employees and maintenance

 Alternative routings, procedures, or

subcontractors

 Moving inspection and test

 Scheduling throughput to match bottleneck

capacity

Drum, Buffer, Rope

Drum, Buffer, Rope

provides the schedule or pace of production

keep constraints operating at capacity

necessary to pull units through the system

and facilities

Scheduling Repetitive

Facilities

Scheduling Services

Service systems differ from manufacturing

Manufacturing Services Schedules machines

and materials Schedule staff

Inventories used to

smooth demand Seldom maintain inventories

Machine-intensive and

demand may be smooth Labor-intensive and demand may be variable

Scheduling may be bound

by union contracts Legal issues may constrain flexible scheduling Few social or behavioral

issues Social and behavioral issues may be quite

important

Scheduling Services

system to handle complex processes and material requirements

workforce and part-time workers

optimization systems that track sales, transactions, and customer traffic to create work schedules in less time and with improved customer satisfaction

Scheduling Services

union regulations and often use linear programming to develop optimal

schedules

departments, emergency hot lines, and mail order businesses use flexible

workers and variable schedules, often created using computerized systems

feasible, managing capacity through staffing flexibility may be used

Scheduling Service Employees

With Cyclical Scheduling

requirements with the minimum number of workers

keep personnel happy

algorithms to complex linear programming solutions

Cyclical Scheduling Example

lowest total requirements and assign these as days off

subtracting the days worked by the first employee

requirements have been met

Cyclical Scheduling Example

Capacity (Employees)

Excess Capacity

Cyclical Scheduling Example

Cyclical Scheduling Example

Cyclical Scheduling Example

Cyclical Scheduling Example

Cyclical Scheduling Example

Cyclical Scheduling Example

Cyclical Scheduling Example