job shop scheduling

JOB SHOP SCHEDULING

Prepared by Res.Asst.Hanife Demiralp

One Machine Scheduling

EXAMPLE: Suppose that 6 employees are to be trained to operate different machines by a single trainer who can train only one person at a time. The time to train each person varies and is given in the table along with due dates and the number of operations involved.

JOB Time Due Date

Number of Operations

Employee 1

Employee 2

Employee 3

Employee 4

Employee 5

Employee 6

3 days

5

4

7

9

2

4

7

13

10

15

5

2

4

1

2

1

3

Solution Screen

Flow time is the time that each job ends

Lateness is the difference between flow time and due

date

The solution of one-machine scheduling: the sequence according to Shortest Processing Time (SPT) is Employee 1, Employee 3, Employee 2, Employee 4 and Employee 5. Because employee 1 has the shortest processing time, then employee 3 has the second shortest processing time etc.

Gantt Chart of Scheduling

Example 2: First Come First Served

JOBDate

Received Time Due Date

Number of Operations

Employee 1

Employee 2

Employee 3

Employee 4

Employee 5

Employee 6

98

87

99

93

82

95

3 days

5

4

7

9

2

104

107

113

110

115

105

2

4

1

2

1

3

Date received must be less than or equal to starting

date.

Solution Screen

Completion time = Flow Time + Starting Day - 1Flow time of job5= 100-82+9=27

Flow Time of job2= 100-87+5+9=27 etc.

The result according to FCFS (First Come First Server); the sequence (schedule) is job 5 is first, then job 2, job 4, job 6, job 1 and last one is job 3. Because the FCFS option selected, the program will schedule the jobs according to the receipt day.

Example 3: Schedule According to SlackSlack is defined as the due date – time required

to process a job. In order to use slack, the due date must be given.

Data Table

Solution Screen

The jobs are scheduled according to increasing order of slack!

Gantt Chart of Schedule