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UNIT - V
SEMESTER - IV
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Scheduling Operations Companies differentiate based on product volume and product variety
Differentiation affects how the company organizes its operations
Each kind of company operation needs different scheduling techniques
Scheduling has specific definitions for routing, bottleneck, due date, slack and queue
Scheduling DefinitionsRouting: The operations to be performed, their sequence, the work centers, & the timestandards
Bottleneck: A resource whose capacity is less than the demand placed on itDue date: When the job is supposed to be finishedSlack: The time that a job can be delayed & still finish by its due dateQueue: A waiting line
Characteristics of High-Volume Operations
High-volume aka flow operations, like automobiles, bread, gasoline can be repetitive or
continuous
High-volume standard items; discrete or continuous with smaller profit margins Designed for high efficiency and high utilization High volume flow operations with fixed routings
Bottlenecks are easily identified Commonly use line-balancing to design the process around the required tasks
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Gantt Charts - Low-Volume Tool
Developed in the early 1900s by Henry Gantt
Load charts illustrate the workload relative to the capacity of a resource
Shows todays job schedule by employee
Low-volume, job shop operations, are designed for flexibility.
Use more general purpose equipment
Customized products with higher margins Each product or service may have its own routing (scheduling is much more difficult)
Bottlenecks move around depending upon the products being produced at any giventime
Low-Volume Operations
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Gantt Chart continued
Progress charts:
Illustrate the planned schedule compared to actual performance
Brackets show when activity is scheduled to be finished.
Characteristics of GANT Chart:
It is used to represent the Timing of Task required to complete a project. Simple to understand
Easy to construct
Displaying simple Activities / Events Plotted against Time.
Each task takes up one row with date.
The expected time for each task is represented by a horizontal bar.
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Scheduling Work - Work Loading
Infinite loading: Ignores capacity
constraints, but helpsidentify bottlenecks in aproposed schedule toenable proactivemanagement
Finite loading: Allows only as much
work to be assigned ascan be done withavailable capacity butdoesnt prepare forinevitable slippage
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Other Scheduling Techniques
Forward Scheduling starts processing when a job is received
Backward Scheduling begin scheduling the jobs last activity so that the job
is finished on due date
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Monitoring Workflow
Input / Output Control I/O control is a capacity-control technique used to monitor work flow at individual work
centers
Monitors how well available capacity is used and provides insight into process problems
Figure 15-6 Input/output report for work center 101
Input Information (in hours) Period
4 5 6 7 8
Planned Input 800 750 800 820 800
Actual Input 750 780 780 810 810
Deviation -50 30 -20 -10 10
Cumulative deviation 0 -50 -20 -40 -50 -40
Output information (in hours) Period
4 5 6 7 8Planned output 800 800 800 800 800
Actual output 800 750 780 850 825
Deviation 0 -50 -20 50 25
Cumulative deviation 0 0 -50 -70 -20 5
Backlog (in hours) 100 50 80 80 40 25
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Commonly Used Priorities Rules First come, first served (FCFS)
Last come, first served (LCFS)
Earliest due date (EDD)
Shortest processing time (SPT) Longest processing time (LPT)
Critical ratio (CR):
(Time until due date)/(processing time)
Slack per remaining Operations (S/RO)
Slack /(number of remaining operations)
Which of several jobs should be scheduled first?Techniques are available to do short-term planning of jobs based on available capacity &
priorities
Priority rules:
Decision rules: to allocate the relative priority of jobs at a work center
Local priority rules: determines priority based only on jobs at that workstation
Global priority rules: also considers the remaining workstations a job must pass through
How to Sequence Jobs
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Measuring Performance
Job flow time:
Time a job is completed minus the time the job was first available forprocessing; avg. flow time measures responsiveness
Average # jobs in system: Measures amount of work-in-progress; avg. # measures responsiveness
and work-in-process inventory
Makespan: The time it takes to finish a batch of jobs; measure of efficiency
Job lateness: Whether the job is completed ahead of, on, or before schedule;
Job tardiness: How long after the due date a job was completed, measures due date
performance
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Scheduling Performance Calculations
Job A finishes on day 10 Job B finisheson day 13
Job C finisheson day 17
Job D endson day 20
Calculation mean flow time: MFT= (sum job flow times)/ # of jobs
= (10+13+17+20)/4 = 60/4 = 15 days
Calculating average number of jobs in the system:
Average # Jobs =(sum job flow times)/ # days to complete batch= (60)/20 = 3 job
Makespan is the length of time to complete a batch
Makespan = Completion time for Job D minus start time for Job A
= 20 0 = 20 days
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Performance Calculations continued
Lateness and Tardiness are both measures related to customer service
Average tardiness is a more relevant Customer Service measurement asillustrated below
Example 15-5 Calculating job lateness and job tardiness
Completion
Job Date Due Date Lateness Tardiness
A 10 15 -5 0
B 13 15 -2 0C 17 10 7 7
D 20 20 0 0
Average 0 1.75
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Scheduling Bottlenecks In the 1970s Eli Goldratt introduced optimized production technology (OPT)
OPT focused on bottlenecks for scheduling & capacity planning
Definitions:
Throughput: quantity of finished goods that can be sold
Transfer batch: quantity of items moved at the same time from one resource to the
next
Process batch: quantity produced at a resource before switching to another
productOPT Principles
Balance the process rather than the flow
Non-bottleneck usage is driven by some other constraint in the system
Usage and activation of a resource are not the same a hour lost at a bottleneck is lost
forever, but an hour lost at a non-bottleneck is a mirage
Bottleneck determine throughput and inventory in system
The transfer batch does not need to be equal to the process batch
The process batch should be variable
Consider all constraints simultaneously.
Lead times are the result of the schedule and are not predetermined.
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Scheduling for Service Organizations Demand management:
Appointments & reservations
Posted schedules
Delayed services or backlogs (queues)
Scheduling Employees:
Staff for peak demand (if cost isnt prohibitive)
Floating employees or employees on call
Temporary, seasonal, or part-time employees
TOC is an extension of OPT theory is that a systems output is determined by its constraints
1. Identify the bottleneck(s) in the process
2. Exploit (fully utilize) the bottleneck(s)3. Subordinate all other decisions to Step 2 - Schedule non-bottlenecks to support
maximum use of bottleneck activities
4. Elevate the Bottleneck(s)
5. Do not let inertia set in
Theory of Constraints
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Developing a Workforce Schedule: Tibrewala, Philippe, and Brown developed atechnique for scheduling a seven day operation giving each employee two consecutive
days off. This example shows how a staff of six people can be scheduled.
Step 1 Find out the minimum number of employees needed for each day ofthe week
Step 2 Given the above requirements, calculate the number of employeesneeded for each pair of consecutive days
Step 3 - Find the pair of days with the lowest total needed
(1) Day of the week M T W Th F Sa Su
Number of staff needed 4 5 5 3 5 2 3
(1) Pair of Consecutive Days Total of Staff needed
Monday & Tuesday 9 employees
Tuesday & Wednesday 10 employees
Wednesday & Thursday 8 employees
Thursday & Friday 8 employees
Friday & Saturday 7 employees
Saturday & Sunday 5 employees
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Workforce Scheduling Continued
Step 4 Update the number of employees you still need to schedule for
each day
Step 5 Using the updated staffing needs, repeat steps 2 through 4 until
you have satisfied all needs
(2) Day of the week M T W Th F Sa Su
Number of staff needed 3 4 4 2 4 2 3
(2) Pair of Consecutive Days Total of Staff needed
Monday & Tuesday 7 employees
Tuesday & Wednesday 8 employees
Wednesday & Thursday 6 employees
Thursday & Friday 6 employees
Friday & Saturday 6 employees
Saturday & Sunday 5 employees
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Scheduling Continued
(3) Pair of Consecutive Days Total of Staff needed
Monday & Tuesday 5 employees
Tuesday & Wednesday 6 employees
Wednesday & Thursday 4 employeesThursday & Friday 4 employees
Friday & Saturday 5 employees
Saturday & Sunday 5 employees
(4) Pair of Consecutive Days Total of Staff needed
Monday & Tuesday 3 employees
Tuesday & Wednesday 5 employees
Wednesday & Thursday 4 employeesThursday & Friday 3 employees
Friday & Saturday 3 employees
Saturday & Sunday 5 employees
(3) Day of the week M T W Th F Sa Su
Number of staff needed 2 3 3 1 3 2 3(4) Day of the week M T W Th F Sa Su
Number of staff needed 1 2 3 1 2 1 2
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Schedule Continued
(5) Day of the week M T W Th F Sa Su
Number of staff needed 0 1 2 0 1 1 2
(6) Pair of Consecutive Days Total of Staff needed
Monday & Tuesday 1 employees
Tuesday & Wednesday 2 employees
Wednesday & Thursday 1 employees
Thursday & Friday 0 employeesFriday & Saturday 0 employees
Saturday & Sunday 1 employees
(5) Pair of Consecutive Days Total of Staff needed
Monday & Tuesday 1 employees
Tuesday & Wednesday 3 employees
Wednesday & Thursday 2 employees
Thursday & Friday 1 employeesFriday & Saturday 2 employees
Saturday & Sunday 3 employees
(6) Day of the week M T W Th F Sa Su
Number of staff needed 0 1 1 0 0 0 1
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Final Schedule
(7) Day of the week M T W Th F Sa Su
Number of staff needed 0 0 0 0 0 0 0
Employees M T W Th F Sa Su
1 x x x x x off off
2 x x x x x off off
3 x x off off x x x4 x x x x x off off
5 off off x x x x x
6 x x x x off off x
This technique gives a
work schedule for each
employee to satisfy
minimum daily staffing
requirements
Next step is to replace
numbers with
employee names
Manager can give
senior employees firstchoice and proceed
until all employees
have a schedule
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Scheduling Across the Organization
Scheduling executes a companys strategic business
plan and affects functional areas throughout thecompany
Accounting relies on schedule information and completionof customer orders to develop revenue projections
Marketing uses schedule effectiveness measurement todetermine whether the company is using lead times forcompetitive advantage
Information systems maintains the scheduling database
Operations uses the schedule to maintain its priorities andto provide customer service by finishing jobs on time
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A system that consists of numerous programmable
machine tools connected by an automated material handlingsystem
FMS first proposed in England in 1960s
System 24 operates 24 hours a day
Automation is main purpose in beginning
History of FMS
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Flexible Automation
Ability to adapt to engineering changes in parts
Increase in number of similar parts produced on the system
Ability to accommodate routing changes
Ability to rapidly change production set up
Flexible automation is used when the product mix requires a combination of
different parts and products to be manufactured from the same system.
To reduce set up and queue times
Improve efficiency
Reduce time for product completion
Utilize human workers better Improve product routing
Produce a variety of Items under one roof
Improve product quality
Serve a variety of vendors simultaneously
Produce more product more quickly
How Can Use FMS
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Components of Flexible Manufacturing Systems / Technology
NC - Numerically Controlled Machine
NC Machines or numerically controlled machines are controlled by
punched tape.
CNC - Computer Controlled Machine
Computer Numerical Controlled (CNC) automatically adjusts and is
controlled by an attached computer.
DNC - Direct Numerical Controlled
Direct Numerical Controlled Machines (DNC) is controlled by several NC
machines that are controlled by a single computer.
AGV - Automated Guided Vehicle
ASRS - Automated Storage and Retrieval System
Robotics and
Conveyors
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FMS Layouts Progressive Layout:
Best for producing a variety of parts
Closed Loop Layout: Parts can skip stations for flexibility
Used for large part sizes
Best for long process times
Ladder Layout: Allows two machines to work on product at the same time
Parts can be sent to any machine in any sequence
Parts not limited to particular part families
Open Field Layout: Enables material to move along the machine centers in any particular order
necessary.
Most complex FMS layout
Includes several support stations
Nuts and Bolts of FMS
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Robots
Robots: Programmable Manipulators
Can tolerate hostile environments
Can work much longer hours than humans
Can perform redundant jobs more consistently
Common Uses of Robots
Loading and unloading
Spray painting Welding
Material handling
Inspection
Machine Assembly
Robots in the beginning were used mainly for spray painting and welding, now
they are also being used for investigative purposes.
By having robots conduct these often times repetitive tasks we have seen a
reduction in job injuries related to these tasks. Robots have made production
much quicker and easier on human beings.
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Computer Integrated Manufacturing
CIM: The Integration of the total manufacturing enterprise through the use ofintegrated systems and data communications coupled with new managerial
philosophies that improve organizational and personnel efficiency.
Components of CIM
CAD - Computer Aided Design
CAM - Computer Aided Manufacturing
CAE - Computer Aided Engineering
CAD uses computer software to manipulate and change products while in the design stage.
CAM uses computer programs to control the automated manufacturing process.
CAE links the functional design to the CAD form design.
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Challenges with FMS Determining if FMS the best production system for your company
(economically and socially)
Possible expansion costs associated with implementing FMS
Day to day maintenance of FMS operations
FMS
ManufacturingTechnology
CIM Robotics
Integration of FMS
By employing the components and concepts from Manufacturing Technology,
Computer Aided Manufacturing and Robotics, it is possible to develop a
Flexible Manufacturing System that will work well in your organization.
These are three main areas making up FMS.
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What is project management
The application of a collection of tools and techniques to direct the use of diverseresources towards the accomplishment of a unique, complex, one time task withintime, cost and quality constraints.
Its origins lie in World War II, when the military authorities used the techniques ofoperational research to plan the optimum use of resources.
One of these techniques was the use of networks to represent a system of related
activities
1. Microsoft Project (Microsoft Corp.)2. MacProject (Claris Corp.)
3. PowerProject (ASTA Development Inc.)
4. Primavera Project Planner (Primavera)
5. Project Scheduler (Scitor Corp.)
6. Project Workbench (ABT Corp.)
Computer Software for Project Management
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Project Management Process Project team
made up of individuals from various areas and departments within a company
Matrix organization
a team structure with members from functional areas, depending on skills
required
Project Manager
most important member of project team
Scope statement a document that provides an understanding, justification, and expected
result of a project
Statement of work
written description of objectives of a project
Organizational Breakdown Structure
a chart that shows which organizational units are responsible for work
items
Responsibility Assignment Matrix
shows who is responsible for work in a project
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Project scheduling by PERT-CPM
1. Scheduling:
i) Identify various tasks or work elements to be performed
in the project.
ii) Determine requirement of resources, such as men,
materials, and machines, for carrying out activities listed
above.
iii) Estimate costs and time for various activities.
iv) Specify the inter-relationship among various activities.
v) Develop a network diagram showing the sequential inter-
relationships between the various activities
2. Scheduling: The various steps involved:
1. Estimate the durations of activities.
2. Based on the above time estimates, prepare a time chart
showing the start and finish times for each activity.
3. Project Control: Project control refers to
comparing the actual progress against the
estimated schedule
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Graph or bar chart with a bar for each project activity that shows passage of time
Provides visual display of project schedule
Gantt Chart
1. Gantt Chart
2. Critical Path Method (CPM)
3. Program Evaluation and Review Technique (PERT)
Project Scheduling and Control Techniques
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History of CPM/PERT
Critical Path Method (CPM)
E I Du Pont de Nemours & Co. (1957) for construction of new chemicalplant and maintenance shut-down
Deterministic task times
Activity-on-node network construction
Repetitive nature of jobs
Project Evaluation and Review Technique (PERT)
U S Navy (1958) used for the POLARIS missile program
Estimates Multiple task time (probabilistic nature)
Activity-on-arrow network construction
Non-repetitive jobs (R & D work)
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Project Network Network analysis is the general name given to certain specific techniques which can be
used for the planning, management and control of projects
Use of nodes and arrows
Arrows An arrow leads from tail to headdirectionally
Indicate ACTIVITY, a time consuming effort that isrequired to perform a part of the work.
Nodes A node is represented by a circle- Indicate EVENT, a point in time where one or more
activities start and/or finish.
Activity
A task or a certain amount of work required in
the project
Requires time to complete
Represented by an arrow
Dummy Activity
Indicates only precedence relationships
Does not require any time of effort
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Event
Signals the beginning or ending of an activity
Designates a point in time Represented by a circle (node)
Network
Shows the sequential relationships among activities using nodes and arrows
Activity-on-node (AON)
nodes represent activities,and arrows show precedencerelationships
Activity-on-arrow (AOA)
arrows represent activitiesand nodes are events forpoints in time
Project Network
AOA Project Network for House
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AOA Project Network for House
3
2 0
1
3
1 1
11 2 4 6 7
3
5
Layfoundation
Design houseand obtainfinancing
Order andreceivematerials
Dummy
Finish
work
Selectcarpet
Selectpaint
Build
house
AON Project Network for House
13
22
43
31 5
1
61
71Start
Design houseand obtainfinancing
Order and receivematerials Select paint
Select carpet
Lay foundations Build house
Finish work
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Situations in network diagram
AB
C
A must finish before either B or C can start
A
B
C both A and B must finish before C can start
D
C
B
Aboth A and C must finish before either of B or D canstart
A
C
B
D
Dummy
A must finish before B can start
both A and C must finish before D can start
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Concurrent Activities
2 3
Lay foundation
Order material
(a) Incorrect precedence
relationship
(b) Correct precedence
relationship
3
42
DummyLay
foundation
Order material
1
2 0
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Critical Path Mapping - By Steven Bonacorsi
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Network example
Illustration of network analysis of a minor redesign of a product and its associatedpackaging.
The key question is:How long will it take to complete this project ?
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For clarity, this list is kept to a minimum by specifying only immediaterelationships, that is relationships involving activities that "occur near to each
other in time".
Network example Continued
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Questions to prepare activity network Is this a Start Activity?
Is this a Finish Activity?
What Activity Precedes this? What Activity Follows this?
What Activity is Concurrent with this?
CPM l l i
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CPM calculation
Path
A connected sequence of activities leading from
the starting event to the ending event
Critical Path
The longest path (time); determines the projectduration
Critical Activities
All of the activities that make up the critical path
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Determination of floats Following the determination of the critical path, floats are need to be
computed for the non-critical activities.
For the critical activities this float is zero.
Before showing how floats are determined, it is necessary to define the
below Two times:
1. Latest Start (LS) time
2. Earliest Finish (EF) time
Note: Total float = ES = LF- ES
Free float = Total float - - Head slack
F d P
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Forward Pass Earliest Start Time (ES)
earliest time an activity can start
ES = maximum EF of immediate predecessors
Earliest finish time (EF)
earliest time an activity can finish
earliest start time plus activity time
EF= ES + t
Latest Start Time (LS)
Latest time an activity can start without delaying critical path time
LS= LF - t
Latest finish time (LF)
latest time an activity can be completed without delaying critical path time
LS = minimum LS of immediate predecessors
Backward Pass
CPM anal sis
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CPM analysis
Draw the CPM network
Analyze the paths through the network
Determine the float for each activity
Compute the activitys float
float = LS - ES = LF - EF
Float is the maximum amount of time that this activity can be delay in its
completion before it becomes a critical activity, i.e., delays completion of
the project
Find the critical path is that the sequence of activities and events where
there is no slack i.e.. Zero slack
Longest path through a network
Find the project duration is minimum project completion time
Total float = ES = LF- ES
Free float = Total float - Head slack
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CPM Example:
CPM Network
a, 6
f, 15
b, 8
c, 5
e, 9
d, 13
g, 17 h, 9
i, 6
j, 12
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CPM Example
ES and EF Times
a, 6
f, 15
b, 8
c, 5
e, 9
d, 13
g, 17 h, 9
i, 6
j, 12
0 6
0 8
0 5
CPM Example
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CPM Example
ES and EF Times
a, 6
f, 15
b, 8
c, 5
e, 9
d, 13
g, 17 h, 9
i, 6
j, 12
0 6
0 8
0 5
5 14
8 2121 33
6 2321 30
23 29
6 21
Projects EF = 33
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CPM Example
LS and LF Times
a, 6
f, 15
b, 8
c, 5
e, 9
d, 13
g, 17
h, 9
i, 6
j, 12
0 6
0 8
0 5
5 14
8 2121 33
6 23
21 30
23 29
6 21
21 33
27 33
24 33
CPM Example
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CPM Example
LS and LF Times
a, 6
f, 15
b, 8
c, 5
e, 9
d, 13
g, 17
h, 9
i, 6
j, 12
0 6
0 8
0 5
5 14
8 2121 33
6 23
21 30
23 29
6 21
4 10
0 8
7 12
12 21
21 33
27 33
8 21
10 27
24 33
18 24
CPM E l
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CPM Example Float
a, 6
f, 15
b, 8
c, 5
e, 9
d, 13
g, 17
h, 9
i, 6
j, 12
0 6
0 8
0 5
5 14
8 21 21 33
6 23
21 30
23 29
6 21
3 9
0 8
7 12
12 21
21 33
27 33
8 21
10 27
24 33
9 24
3 4
3
3
4
0
0
7
7
0
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CPM Example
Critical Path
a, 6
f, 15
b, 8
c, 5
e, 9
d, 13
g, 17 h, 9
i, 6
j, 12
PERT
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PERT
PERT is based on the assumption that an activitys duration follows a probability
distribution instead of being a single value
Three time estimates are required to compute the parameters of an activitys
duration distribution:
pessimistic time (tp ) - the time the activity would take if things did not go well
most likely time (tm ) - the consensus best estimate of the activitys duration
optimistic time (to ) - the time the activity would take if things did go well
Mean (expected time):te =
tp + 4 tm + to6
Variance: Vt =2 = tp - to6
2
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PERT analysis
Draw the network.
Analyze the paths through the network and find the critical path.
The length of the critical path is the mean of the project duration probability
distribution which is assumed to be normal
The standard deviation of the project duration probability distribution is
computed by adding the variances of the critical activities (all of the activities
that make up the critical path) and taking the square root of that sum
Probability computations can now be made using the normal distributiontable.
PERT Example
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PERT Example
Immed. Optimistic Most Likely Pessimistic
Activity Predec. Time (Hr.) Time (Hr.) Time (Hr.)A -- 4 6 8
B -- 1 4.5 5
C A 3 3 3
D A 4 5 6E A 0.5 1 1.5
F B,C 3 4 5
G B,C 1 1.5 5
H E,F 5 6 7
I E,F 2 5 8
J D,H 2.5 2.75 4.5
K G,I 3 5 7
PERT Example
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PERT Example
A
D
C
B
F
E
G
I
H
K
J
PERT Network
Benefits of CPM/PERT
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Useful at many stages of project management
Mathematically simple
Give critical path and slack time
Provide project documentation
Useful in monitoring costs
Clearly defined, independent and stable activities
Specified precedence relationships
Over emphasis on critical paths
Deterministic CPM model
Activity time estimates are subjective and depend on judgment
PERT assumes a beta distribution for these time estimates, but the actual
distribution may be different
PERT consistently underestimates the expected project completion time
due to alternate paths becoming critical
Limitations to CPM/PERT
W ld Cl M f t i
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World Class Manufacturing
Characteristics
Just In Time(JIT) Kanban
Total Quality Management (TQM)
Total Productive Maintenance
Employee Involvement
Simplicity Cellular Manufacturing (GT)
PKE YOKE (Fail Proofing)
Products of High Quality (Zero
Defect)
Products Delivered with shorterlead-time and wide variety.
Flexibility in fulfilling products
demand.
Sources of Non Value Items in the
Organization:
Expediting
Inspection
Over Production (Excess Wip)
Excess Paper Work
Machine Breakdown
Yield Loss
Storage (Excess Inventory)
Material Movement
Setup Time
Waiting
Excess Defects.
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