Unit - V - Industial Scheduling Systems

7/28/2019 Unit - V - Industial Scheduling Systems

1/58

UNIT - V

SEMESTER - IV


2/58

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


3/58

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


4/58

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.


5/58

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


6/58

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


7/58

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


8/58

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


9/58

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


10/58

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


11/58

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


12/58

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.


13/58

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


14/58

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


15/58

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







Thursday & Friday 6 employees




16/58

Scheduling Continued




Wednesday & Thursday 4 employeesThursday & Friday 4 employees






Wednesday & Thursday 4 employeesThursday & Friday 3 employees




Number of staff needed 2 3 3 1 3 2 3(4) Day of the week M T W Th F Sa Su



17/58

Schedule Continued







Thursday & Friday 0 employeesFriday & Saturday 0 employees






Thursday & Friday 1 employeesFriday & Saturday 2 employees





18/58

Final Schedule



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


19/58

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


20/58

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


21/58

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


22/58

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


23/58

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


24/58

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.


25/58

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.


26/58

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.


27/58

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


28/58

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


29/58

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


30/58

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


31/58

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)


32/58

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


33/58

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


34/58

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


35/58

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


36/58

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


37/58

Critical Path Mapping - By Steven Bonacorsi


38/58


39/58

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 ?


40/58

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


41/58

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


42/58

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


43/58

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


44/58

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


45/58

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


46/58

CPM Example:

CPM Network

a, 6

f, 15

b, 8

c, 5

e, 9

d, 13

g, 17 h, 9

i, 6

j, 12


47/58

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


48/58

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


49/58

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


50/58

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


51/58

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


52/58

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


53/58

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


54/58

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


55/58

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


56/58

PERT Example

A

D

C

B

F

E

G

I

H

K

J

PERT Network

Benefits of CPM/PERT


57/58

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


58/58

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.

Documents

Unit - V - Industial Scheduling Systems