Scheduling and Sequencing by Johnson Rule

SCHEDULING & SEQUENCING BY JOHNSON’S RULE GROUP MEMBERS  Rajendra kumar  Pratik  Puneet  Pintu

DEFINATION 

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Establishing the timing of the use of equipment, facilities and human activities in an organization Effective scheduling can produce:1) Cost savings 2) Increases in productivity

Scheduling Difficulties 

Variability in    

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Setup times Processing times Interruptions Changes in the set of jobs

No method for identifying optimal schedule Scheduling is not an exact science Ongoing task for a manager

Minimizing Scheduling Difficulties 

Set realistic due dates

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Focus on bottleneck operations

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Consider lot dividing of large jobs

SEQUENCING

JOHNSON’S RULE

SEQUENCING 

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Sequencing: Determine the order in which jobs at a work center will be processed. Workstation: An area where one person works, usually with special equipment, on a specialized job. Priority rules: Simple hierarchy used to select the order in which jobs will be processed. Job time: Time needed for setup and processing of a job. Everything is #1 Priority

Priority Rules 

FCFS - first come, first served

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LTR - Least time required

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LAR/LOR – Least activity required/Fewest operations required

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EDD - earliest due date

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CRS - critical ratio scheduling

Top Priority

JOHNSON’S RULE 

Technique for minimizing completion time for a group of jobs to be processed on two machines or at two work centers.

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Minimizes total idle time

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Several conditions must be satisfied

Johnson’s Rule Conditions 

Job time must be known and constant

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Job times must be independent of sequence

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Jobs must follow same two-step sequence

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Job priorities cannot be used

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All units must be completed at the first work center before moving to second

Example Of Johnson’s Rule (Two Machines) Job No. A B C D E F G H I J

Time on M1

15 17 9 12 14 12 12 13 15 13

Time on M2

11 10 13 15 14 10 14 15 14 13

MC1

MC2

St. Time

St. Time

End Time

0 15 15 32 32 41 41 53 53 67 67 79 79 91 91 104 104 119 119 132

Sequence

End Time

15 26 32 42 42 55 55 70 70 84 84 94 94 108 108 123 123 137 137 150

C G D H E I J A B F

Sequence

MC1

MC2

(By Johnson's Rule)

St. Time

St. Time

C G D H E I J A B F

End Time

0 9 9 21 21 33 33 46 46 60 60 75 75 88 88 103 103 120 120 132

End Time

9 22 22 36 36 51 51 66 66 80 80 94 94 107 107 118 120 130 132 140

So we can say that by using Johnson’s rule of scheduling Time saved in this case is :150 – 140 = 10

Johnson’s Rule for Three Machines 

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Condition:-Largest time on M2 should be less than or equal to smallest time on M1 or M2 or both. If condition satisfied then we calculate:R1 = M1 + M2 R2 = M2 + M3 This whole can be understand by the help of following example:-

Job No. A B C D E F G H TOTAL

Time on M1

16 15 12 13 14 15 13 12

Time on M2

Time on M3

12 11 10 9 11 10 9 12

11 12 13 15 17 16 14 17

84

115

MC1

MC2

St. Time

St. Time

0 16 31 43 56 70 85 98

End Time

16 31 43 56 70 85 98 110

16 31 43 56 70 85 98 110

End Time

28 42 53 65 81 95 107 122

MC3

R1

R2

SEQUENCE

St. Time

M1+M2

M2+M3

(BY JOHNSON'S RULE)

28 42 54 67 82 99 115 129

End Time

39 54 67 82 99 115 129 146

28 26 22 22 25 25 22 24

23 23 23 24 28 26 23 29

C G D H F E A B

Idle time on Machine-2 is:122 – 84 = 38 Idle time on machine-3 is:146 – 115 = 31

SEQUENCE

MC1

MC2

MC3

(BY JOHNSON'S RULE)

St. Time

St. Time

St. Time

C G D H F E A B

0 12 25 38 50 65 79 95

End Time

12 25 38 50 65 79 95 110

12 25 38 50 65 79 95 110

End Time

22 34 47 62 75 90 107 121

22 35 49 64 81 97 114 125

End Time

35 49 64 81 97 114 125 137

Total time saved by Using Johnson’s rule Is:146 – 137 = 06

CONCLUSION 

Thus we can say that by using Johnson’s rule we can do more better sequencing of machines and can save the time of production.