Page 295 - DMGT206_PRODUCTION_AND_OPERATIONS_MANAGEMENT

Production and Operations Management

Notes Total Tardiness =  
Average Tardiness =  
In our example, we assume there are five products waiting for getting processed on a machine.
Their sequence of arrival, processing time and due-date are given in the table on the next page.
We will try to schedule the jobs for the different products, P1, P2, P3, P4, and P5 using the
different scheduling rules, i.e., FCFS, SPT, D Date, LCFS, Random, and STR rules. We will then
compare the results.

Table 14.3: n/1 Scheduling for Job Shop

Job Processing Time = p i Due Date = di
(In Sequence of Arrival) (Days) (i.e., Days From Now)
P1 3 6
P2 3 8
P3 5 8
P4 7 10
P5 4 4

The calculations are shown in Tables below. To make the calculations easier to understand, a
column of ‘sequence’ that reflects the results of the selection criteria, has been inserted before the
calculations of each of the techniques. We can follow the calculations shown in the tables more
clearly, by calculating the flow and tardiness in the case of the First Come First Served rule. The
calculations are shown below:

= 3 + 6 + 11 + 18 + 22 = 60 days
Makespan =  
Mean flow time = 60/5 = 12 days
Total lateness of job = 0 + 0 + 3 + 8 + 18 = 29 days

Average lateness of job = 29/5 = 5.8 days
Similarly, calculations can be made for the other procedures. The calculated values are given in
the two tables that follow.

Table 14.4: Scheduling Parameters for our Example (1)

FCFS SPT D Date
Sequ- Flow Tardi- Sequ- Flow Tardi- Sequ- Flow Tardi-
ence Time ness ence Time ness ence Time ness
P1 3 0 P1 3 0 P5 4 0
P2 6 0 P2 6 0 P1 7 1
P3 11 3 P5 10 0 P2 10 2
P4 18 8 P3 15 7 P3 15 7
P5 22 18 P4 22 12 P4 22 12
Totals 60 29 56 19 58 22

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