slide1
Download
Skip this Video
Download Presentation
Operations Management

Loading in 2 Seconds...

play fullscreen
1 / 79

Operations Management - PowerPoint PPT Presentation


  • 83 Views
  • Uploaded on

Operations Management. Chapter 15 – Short-Term Scheduling. PowerPoint presentation to accompany Heizer/Render Principles of Operations Management, 7e Operations Management, 9e . Outline. Global Company Profile: Delta Air Lines The Strategic Importance of Short-Term Scheduling

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about 'Operations Management' - sarila


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
slide1

Operations Management

Chapter 15 –

Short-Term Scheduling

PowerPoint presentation to accompany

Heizer/Render

Principles of Operations Management, 7e

Operations Management, 9e

outline
Outline
  • Global Company Profile: Delta Air Lines
  • The Strategic Importance of Short-Term Scheduling
  • Scheduling Issues
    • Forward and Backward Scheduling
    • Scheduling Criteria
outline continued
Outline – Continued
  • Scheduling Process-Focused Facilities
  • Loading Jobs
    • Input-Output Control
    • Gantt Charts
    • Assignment Method
outline continued1
Outline – Continued
  • Sequencing Jobs
    • Priority Rules for Dispatching Jobs
    • Critical Ratio
    • Sequencing N Jobs on Two Machines: Johnson’s Rule
    • Limitations of Rule-Based Dispatching Systems
  • Finite Capacity Scheduling (FCS)
outline continued2
Outline – Continued
  • Theory of Constraints
    • Bottlenecks
    • Drum, Buffer, Rope
  • Scheduling Repetitive Facilities
  • Scheduling Services
    • Scheduling Service Employees with Cyclical Scheduling
learning objectives
Learning Objectives

When you complete this chapter you should be able to:

Explain the relationship between short-term scheduling, capacity planning, aggregate planning, and a master schedule

Draw Gantt loading and scheduling charts

Apply the assignment method for loading jobs

learning objectives1
Learning Objectives

When you complete this chapter you should be able to:

Name and describe each of the priority sequencing rules

Use Johnson’s rule

Define finite capacity scheduling

List the steps in the theory of constraints

Use the cyclical scheduling technique

delta airlines
Delta Airlines
  • About 10% of Delta’s flights are disrupted per year, half because of weather
  • Cost is $440 million in lost revenue, overtime pay, food and lodging vouchers
  • The $33 million Operations Control Center adjusts to changes and keeps flights flowing
  • Saves Delta $35 million per year
strategic importance of short term scheduling
Strategic Importance of Short-Term Scheduling
  • Effective and efficient scheduling can be a competitive advantage
    • Faster movement of goods through a facility means better use of assets and lower costs
    • Additional capacity resulting from faster throughput improves customer service through faster delivery
    • Good schedules result in more dependable deliveries
scheduling issues
Scheduling Issues
  • Scheduling deals with the timing of operations
  • The task is the allocation and prioritization of demand
  • Significant issues are
    • The type of scheduling, forward or backward
    • The criteria for priorities
scheduling flow
Scheduling Flow

Figure 15.1

forward and backward scheduling

Due Date

Now

Forward and Backward Scheduling
  • Forward scheduling starts as soon as the requirements are known
  • Produces a feasible schedule though it may not meet due dates
  • Frequently results in buildup of work-in-process inventory
forward and backward scheduling1

Due Date

Now

Forward and Backward Scheduling
  • Backward scheduling begins with the due date and schedules the final operation first
  • Schedule is produced by working backwards though the processes
  • Resources may not be available to accomplish the schedule
forward and backward scheduling2

Due Date

Now

Forward and Backward Scheduling
  • Backward scheduling begins with the due date and schedules the final operation first
  • Schedule is produced by working backwards though the processes
  • Resources may not be available to accomplish the schedule

Often these approaches are combined to develop a trade-off between a feasible schedule and customer due dates

scheduling criteria
Scheduling Criteria

Minimize completion time

Maximize utilization of facilities

Minimize work-in-process (WIP) inventory

Minimize customer waiting time

Optimize the use of resources so that production objectives are met

scheduling process focused facilities
Scheduling Process-Focused Facilities

Schedule incoming orders without violating capacity constraints

Check availability of tools and materials before releasing an order

Establish due dates for each job and check progress

Check work in progress

Provide feedback

Provide work efficiency statistics and monitor times

planning and control files

Planning Files

An item master file contains information about each component

A routing file indicates each component’s flow through the shop

A work-center master file contains information about the work center

Control Files

Track the actual progress made against the plan

Planning and Control Files
loading jobs
Loading Jobs
  • Assign jobs so that costs, idle time, or completion time are minimized
  • Two forms of loading
    • Capacity oriented
    • Assigning specific jobs to work centers
input output control
Input-Output Control
  • Identifies overloading and underloading conditions
  • Prompts managerial action to resolve scheduling problems
  • Can be maintained using ConWIP cards that control the scheduling of batches
input output control example1

Work Center DNC Milling (in standard hours)

Explanation:

250 input,

270 output implies

–20 change

Explanation:

270 input,

270 output implies

0 change

Input-Output Control Example

Figure 15.2

input output control example2
Input-Output Control Example

Options available to operations personnel include:

Correcting performances

Increasing capacity

Increasing or reducing input to the work center

gantt charts
Gantt Charts
  • Load chart shows the loading and idle times of departments, machines, or facilities
  • Displays relative workloads over time
  • Schedule chart monitors jobs in process
  • All Gantt charts need to be updated frequently to account for changes
gantt load chart example

Day

Work Center

Monday

Tuesday

Wednesday

Thursday

Friday

Metalworks

Job 349

Job 350

Mechanical

Job 349

Job 408

Electronics

Job 408

Job 349

Painting

Job 295

Job 408

Job 349

Processing

Unscheduled

Center not available

Gantt Load Chart Example

Figure 15.3

gantt schedule chart example

Start of an activity

End of an activity

Scheduled activity time allowed

Maintenance

Actual work progress

Nonproduction time

Point in time when chart is reviewed

Now

Gantt Schedule Chart Example

Figure 15.4

assignment method
Assignment Method
  • A special class of linear programming models that assign tasks or jobs to resources
  • Objective is to minimize cost or time
  • Only one job (or worker) is assigned to one machine (or project)
assignment method1

Typesetter

Job A B C

R-34 $11 $14 $ 6

S-66 $ 8 $10 $11

T-50 $ 9 $12 $ 7

Assignment Method
  • Build a table of costs or time associated with particular assignments
assignment method2
Assignment Method

Create zero opportunity costs by repeatedly subtracting the lowest costs from each row and column

Draw the minimum number of vertical 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 method3
Assignment Method

Subtract the smallest number not 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.

Optimal assignments are at zero locations in the table. Select one, draw lines through the row and column involved, and continue to the next assignment.

assignment example

Step 1a - Rows

Step 1b - Columns

Typesetter

Typesetter

Typesetter

A B C

Job

R-34 $11 $14 $ 6

S-66 $ 8 $10 $11

T-50 $ 9 $12 $ 7

A B C

Job

R-34 $ 5 $ 8 $ 0

S-66 $ 0 $ 2 $ 3

T-50 $ 2 $ 5 $ 0

A B C

Job

R-34 $ 5 $ 6 $ 0

S-66 $ 0 $ 0 $ 3

T-50 $ 2 $ 3 $ 0

Assignment Example
assignment example1

Step 2 - Lines

Step 3 - Subtraction

Typesetter

Typesetter

A B C

Job

R-34 $ 5 $ 6 $ 0

S-66 $ 0 $ 0 $ 3

T-50 $ 2 $ 3 $ 0

A B C

Job

R-34 $ 3 $ 4 $ 0

S-66 $ 0 $ 0 $ 5

T-50 $ 0 $ 1 $ 0

Assignment Example

The smallest uncovered number is 2 so this is subtracted from all other uncovered numbers and added to numbers at the intersection of lines

Because only two lines are needed to cover all the zeros, the solution is not optimal

assignment example2

Step 2 - Lines

Step 4 - Assignments

Typesetter

Typesetter

A B C

Job

R-34 $ 3 $ 4 $ 0

S-66 $ 0 $ 0 $ 5

T-50 $ 0 $ 1 $ 0

A B C

Job

R-34$ 3 $ 4 $ 0

S-66$ 0 $ 0 $ 5

T-50 $ 0 $ 1 $ 0

Assignment Example

Start by assigning R-34 to worker C as this is the only possible assignment for worker C.

Job T-50 must go to worker A as worker C is already assigned. This leaves S-66 for worker B.

Because three lines are needed, the solution is optimal and assignments can be made

assignment example3

From the original cost table

Minimum cost = $6 + $10 + $9 = $25

Step 4 - Assignments

Typesetter

Typesetter

A B C

Job

R-34$ 3 $ 4 $ 0

S-66$ 0 $ 0 $ 5

T-50 $ 0 $ 1 $ 0

A B C

Job

R-34 $11 $14 $ 6

S-66 $ 8 $10 $11

T-50 $ 9 $12 $ 7

Assignment Example
sequencing jobs
Sequencing Jobs
  • Specifies the order in which jobs should be performed at work centers
  • Priority rules are used to dispatch or sequence jobs
    • FCFS: First come, first served
    • SPT: Shortest processing time
    • EDD: Earliest due date
    • LPT: Longest processing time
sequencing example
Sequencing Example

Apply the four popular sequencing rules to these five jobs

sequencing example1
Sequencing Example

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

sequencing example2

Sum of total flow time

Number of jobs

Average completion time = = 77/5 = 15.4 days

Total job work time

Sum of total flow time

Utilization = = 28/77 = 36.4%

Sum of total flow time

Total job work time

Average number of jobs in the system

= = 77/28 = 2.75 jobs

Total late days

Number of jobs

Average job lateness = = 11/5 = 2.2 days

Sequencing Example

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

sequencing example3
Sequencing Example

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

sequencing example4

Sum of total flow time

Number of jobs

Average completion time = = 65/5 = 13 days

Total job work time

Sum of total flow time

Utilization = = 28/65 = 43.1%

Sum of total flow time

Total job work time

Average number of jobs in the system

= = 65/28 = 2.32 jobs

Total late days

Number of jobs

Average job lateness = = 9/5 = 1.8 days

Sequencing Example

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

sequencing example5
Sequencing Example

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

sequencing example6

Sum of total flow time

Number of jobs

Average completion time = = 68/5 = 13.6 days

Total job work time

Sum of total flow time

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

Total late days

Number of jobs

Average job lateness = = 6/5 = 1.2 days

Sequencing Example

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

sequencing example7
Sequencing Example

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

sequencing example8

Sum of total flow time

Number of jobs

Average completion time = = 103/5 = 20.6 days

Total job work time

Sum of total flow time

Utilization = = 28/103 = 27.2%

Sum of total flow time

Total job work time

Average number of jobs in the system

= = 103/28 = 3.68 jobs

Total late days

Number of jobs

Average job lateness = = 48/5 = 9.6 days

Sequencing Example

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

sequencing example9
Sequencing Example

Summary of Rules

comparison of sequencing rules
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

Workdays remaining

Due date - Today’s date

Work (lead) time remaining

CR = =

Critical Ratio (CR)
  • An index number found by dividing the time remaining until the due date by the work time remaining on the job
  • Jobs with low critical ratios are scheduled ahead of jobs with higher critical ratios
  • Performs well on average job lateness criteria
critical ratio example
Critical Ratio Example

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
Critical Ratio Technique

Helps determine the status of specific jobs

Establishes relative priorities among jobs on a common basis

Relates both stock and make-to-order jobs on a common basis

Adjusts priorities automatically for changes in both demand and job progress

Dynamically tracks job progress

sequencing n jobs on two machines johnson s rule
Sequencing N Jobs on Two Machines: Johnson’s Rule
  • Works with two or more jobs that pass through the same two machines or work centers
  • Minimizes total production time and idle time
johnson s rule
Johnson’s Rule

List all jobs and times for each work center

Choose the job with the shortest activity 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.

Once a job is scheduled, it is eliminated from the list

Repeat steps 2 and 3 working toward the center of the sequence

johnson s rule example2

B

E

D

C

A

WC 1

B

E

D

C

A

WC 2

Johnson’s Rule Example

Time 0 3 10 20 28 33

johnson s rule example3

B

E

D

C

A

WC 1

B

E

D

C

A

WC 2

B

E

D

C

A

A

B

E

D

C

Johnson’s Rule Example

Time 0 3 10 20 28 33

Time 0 1 3 5 7 9 10 11 12 13 17 19 21 22 23 25 27 29 31 33 35

limitations of rule based dispatching systems
Limitations of Rule-Based Dispatching Systems

Scheduling is dynamic and rules need to be revised to adjust to changes

Rules do not look upstream or downstream

Rules do not look beyond due dates

finite capacity scheduling
Finite Capacity Scheduling
  • Overcomes disadvantages of rule-based systems by providing an interactive, computer-based graphical system
  • May include rules and expert systems or simulation to allow real-time response to system changes
  • Initial data often from an MRP system
  • FCS allows the balancing of delivery needs and efficiency
finite capacity scheduling1

MRP Data

  • Master schedule
  • BOM
  • Inventory
  • Routing files
  • Work center information

Tooling and other resources

Priority rules

  • Expert systems
  • Simulation models

Setups and run time

Finite Capacity Scheduling

Interactive Finite Capacity Scheduling

Figure 15.5

theory of constraints
Theory of Constraints
  • Throughput is the number of units processed through the facility and sold
  • TOC deals with the limits an organization faces in achieving its goals

Identify the constraints

Develop a plan for overcoming the constraints

Focus resources on accomplishing the plan

Reduce the effects of constraints by off-loading work or increasing capacity

Once successful, return to step 1 and identify new constraints

bottlenecks
Bottlenecks
  • Bottleneck work centers are constraints that limit output
    • Common occurrence due to frequent changes
  • Management techniques include:
    • 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
  • The drum is the beat of the system and provides the schedule or pace of production
  • The buffer is the inventory necessary to keep constraints operating at capacity
  • The rope provides the synchronization necessary to pull units through the system
scheduling repetitive facilities
Scheduling Repetitive Facilities
  • Level material use can help repetitive facilities
    • Better satisfy customer demand
    • Lower inventory investment
    • Reduce batch size
    • Better utilize equipment and facilities
scheduling repetitive facilities1
Scheduling Repetitive Facilities
  • Advantages include:
    • Lower inventory levels
    • Faster product throughput
    • Improved component quality
    • Reduced floor-space requirements
    • Improved communications
    • Smoother production process
scheduling services
Scheduling Services

Service systems differ from manufacturing

scheduling services1
Scheduling Services
  • Hospitals have complex scheduling system to handle complex processes and material requirements
  • Banks use a cross-trained and flexible workforce and part-time workers
  • Retail stores use scheduling optimization systems that track sales, transactions, and customer traffic to create work schedules in less time and with improved customer satisfaction
scheduling services2
Scheduling Services
  • Airlines must meet complex FAA and union regulations and often use linear programming to develop optimal schedules
  • 24/7 operations like police/fire departments, emergency hot lines, and mail order businesses use flexible workers and variable schedules, often created using computerized systems
demand management
Demand Management
  • Appointment or reservation systems
  • FCFS sequencing rules
  • Discounts or other promotional schemes
  • When demand management is not feasible, managing capacity through staffing flexibility may be used
scheduling service employees with cyclical scheduling
Scheduling Service Employees With Cyclical Scheduling
  • Objective is to meet staffing requirements with the minimum number of workers
  • Schedules need to be smooth and keep personnel happy
  • Many techniques exist from simple algorithms to complex linear programming solutions
cyclical scheduling example
Cyclical Scheduling Example

Determine the staffing requirements

Identify two consecutive days with the lowest total requirements and assign these as days off

Make a new set of requirements subtracting the days worked by the first employee

Apply step 2 to the new row

Repeat steps 3 and 4 until all requirements have been met

ad