Shop Floor Planning

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Job Shop Scheduling

Single processor scheduling. One product ata time from the machine / process

Flow shop scheduling. Job contains severaloperations that are to be performed in a specificorder. Operations are carried out in more thanone processor.

General shop scheduling

More than twomachines & two jobs. Flow of work can take anypattern.


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Case Scheduling Procedure

The adjacent tablegives details ofproduction time & duedates of 4 jobs.

Prepare scheduleby SPT & DD method.

Compare thetardiness obtainedfrom these methods.

Job Prod

Time

Due

Date

1 4 6

2 7 9

3 2 19

4 8 17


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(By - DD Method)Job

(a)

Due

Date

(b)

Processing

time

(c)

Completion

time

(d) = cum

of (c)

Tardiness

(d) = +ve

of (d) (b)

1 6 4 4 0

2 9 7 11 2

4 17 8 19 2

3 19 2 21 2


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(Single Machine) (By - SPT Method)Job

(a)

Processing

time

(b)

Due

Date

(c)

Completion

time

(d) = cum of

(b)

Tardiness

(d) = +ve

of (d)

(c)

3 2 19 2 0

1 4 6 6 0

2 7 9 13 4

4 8 17 21 4


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Johnsons Procedure

(Two Machines) Step 1: Determine the minimum processing time on either machine.

Step 2 A: If the minimum processing time occurs on machine 1,place the associated job in the first available position in thesequence.

Step 2 B: If the minimum processing time occurs on machine 2,place the associated job in the last available position in thesequence.

Step 3:

(a) The job sequenced by either step 2A or 2B is removedfrom consideration.

(b) Repeat the process starting from step 1, until all the jobsare sequenced.

(c) Ties can be broken arbitrarily.


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Case Flow Shop Scheduling

There are two machines& five jobs. All the jobsare first processed on

machine 1 & then onmachine 2. Theprocessing time of the

jobs on two machines isgiven in the table.

Design a schedulingprocess to minimize themake-span.

Jobs PT*

Mc-1

PT*

Mc-2

1 4 7

2 6 3

3 2 3

4 7 7

5 8 6

* PT- Processing Time. Mc- Machine


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2 6

1

3

2

1

2

7

M

1 J3 J1 J4 J5 J2

M

2 J3 J1 J4 J5 J2

5

1

3

2

0

2

7

3

0

Schedule Sequence using Johnsons Procedure


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Commonly Employed Rules for

General Job Shop Scheduling Earliest due date ( EDD). Priority is given

to the job with the earliest due date.

First in system first served (FISFS).Priority is given to the job that arrived first.

First come first served (FCFS). Priority

is given to the job that arrived at themachine first.


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Commonly Employed Rules for

General Job Shop Scheduling Least Slack First (LSF). Priority is given to the

processing of the job that has least slack. Slackis the difference between the due date & the

work remaining on the job. Shortest processing time (SPT). Priority is

given to the job with the shortest processing timeon the machine.

Least work remaining (LWR). Priority is givento the job with the least amount of processing tobe done.


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Case General Job Shop Scheduling

6 jobs are to beprocessed on threemachines (A,B,C) as perdetails given in the Table.For example, Job A willtake 3days on machine A,3days on B, & 2days onmachine C. Its due dateis 10 days.

Prepare schedules forgeneral job shop for therules discussed earlier.

Job Sequence &

Processing

Time

Due

Date

1 A(3),B(3),C(2) 10

2 A(5),C(2) 13

3 B(4),A(4),C(3) 124 B(3),C(5),A(2) 18

5 C(5),B(4) 14

6 C(2),A(5),B(5) 15


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EDD Sequencing

Job Sequence &

Processing

Time

Due

Date

1 A(3),B(3),C(2) 10

2 A(5),C(2) 13

3 B(4),A(4),C(3) 12

4 B(3),C(5),A(2) 18

5 C(5),B(4) 14

6 C(2),A(5),B(5) 15

Job EDD

Sequence

Due

Date

1 A(3),B(3),C(2) 10

3 B(4),A(4),C(3) 12

2 A(5),C(2) 13

5 C(5),B(4) 146 C(2),A(5),B(5) 15

4 B(3),C(5),A(2) 18


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Scheduling Rule : EDDTime 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22

Mach A

J-1 J-2 J-3 J-6 Idle J-4

Mach B

J-3 J-1 J-5 J-4 Idle J-6

Mach C

J-5 J-6 J-1 J-2 Idle J-3 J-4 Idle

Jobs

Finished 1

2

5 3

4

6


Gantt Chart


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EDD Sequencing - Tardiness

Job

Schedule

Process

Time &

Sequence

Processing

Time

Due

Date

Tardiness

1 A(3),B(3),C(2) 9 10 0

2 A(5),C(2) 15 13 2

3 B(4),A(4),C(3) 11 12 04 B(3),C(5),A(2) 11 18 0

5 C(5),B(4) 22 14 8

6 C(2),A(5),B(5) 22 15 7


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Gantt Chart

Scheduling Rule : FISFSTime 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22

Mach A

J-1 J-2 J-3 J-6 J-4 Idle

Mach B

J-3 J-1 J-4 J-5 Idle J-6

Mach C

J-5 J-6 J-1 J-2 J-4 J-3 Idle

Jobs

Finished 1 2 5

3

4 6


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FISFS Sequencing - Tardiness

Job

Schedule

Process

Time &

Sequence

Processing

Time

Due

Date

Tardiness

1 A(3),B(3),C(2) 9 10 0

2 A(5),C(2) 11 13 0

3 B(4),A(4),C(3) 19 12 74 B(3),C(5),A(2) 19 18 1

5 C(5),B(4) 14 14 0

6 C(2),A(5),B(5) 22 15 7


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Gantt Chart

Scheduling Rule : FCFSTime 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22

Mach A

J-1 J-2 J-3 J-6 J-4 Idle

Mach B

J-3 J-4 J-1 J-5 Idle J-6

Mach C

J-5 J-6 J-4 J-2 J-1 J-3 Idle

Jobs

Finished

2

5 1

3

4 6


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FCFS Sequencing - Tardiness

Job

Schedule

Process

Time &

Sequence

Processing

Time

Due

Date

Tardiness

1 A(3),B(3),C(2) 16 10 6

2 A(5),C(2) 14 13 1

3 B(4),A(4),C(3) 19 12 74 B(3),C(5),A(2) 19 18 1

5 C(5),B(4) 14 14 0

6 C(2),A(5),B(5) 22 15 7


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Summary of the Performance of

Scheduling Rules

Rule No of Tardy

Jobs

Ti

EDD 3 17FISFS 3 15

FCFS 5 22

Documents

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