Scheduling example 2, Forward sequencing – Rockwell Automation FactoryTalk Scheduler Users Guide User Manual
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repeats this process until all jobs (and therefore, all operations) have been loaded. Each
operation is loaded on its specified resource at the first available time slot that satisfies the
constraints for that operation.
In a job-at-a-time sequencer, the schedule is controlled by selecting the order in which
the jobs are loaded onto the planning board. Hence, the key to the quality of the schedule
that is generated by the algorithmic sequencer is the rule that is used for selecting the job-
loading order.
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The job-at-a-time scheduling process is shown in the figures below. In this example, we
first load Job A, then Job B, and finally, Job C.
Forward sequencing
There are a number of very simple heuristic rules that can be used to select the order for
loading the jobs on the planning board. One rule that can be used for selecting the job
order is to sort the jobs by a priority value that has been assigned to each job. Other
possible sorting criteria are earliest due date, earliest release date, and smallest remaining
slack time. None of these rules are optimal in a mathematical sense. Each rule represents a
different strategy and focus in planning the jobs. For example, the due-date-related rules
Resource 2
Time
B-10
A-20
5
10
15
Resource 1
Resource 2
Time
A-20
5
10
15
Resource 1
A-10
A-10
Resource 2
Time
A-20
C-20
5
10
15
Resource 1
A-10
C-10
B-20
B-20
B-10