COURSE INDUSTRIAL ENGINEERING LESSON: SEQUENCING
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SEQUENCING Sequencing Problem arise when we are concerned with situations where there is a choice as to the order in which a number of task or jobs can be performed.It is essential to ensure smooth flow of work material and effective utilisation of manpower and machines. Sequencing decision is required for complete design of schedule chart.
ASSUMPTIONS I. 2. 3. 4. One job on one machine at a time. Each job once started on a machine must be completed. Given processing time does not change. Time taken by job from one machine to other is negligible
DIFFERENT TIMES I. Job Flow Time: It is the time for a job from some starting point until that job is completed. 2. Make Span Time: It is the time from when processing begins on first job in the set until the last is completed 3. Tardiness :The tardiness of a job is the amount of time after its due date that the job is completed 4. Average number of jobs in system: For a fixed set of job this will be equal to total flow time for all the jobs divided by make span time.
N JOB --1 MACHINE Rule 1-Shortest ProcessingTime (SPT) Jobs Processing Time Due Date (Days) 15 2 16 14 31 13 In this Rule jobs are sequenced according to increasing order of their processing time. i.e. least time first and longest time last.
N JOB --1 MACHINE Rule 2-Earliest Due Date (EDD): Here sequencing is done in order of increasing due date Rule 3-Critical Ratio Rule(CR): CR = Due Date / Processing Time Here jobs are sequenced in order of increasing critical ratio. Rule 4-SlackTime Remaining Rule (STR) Slack Time Due Date Processing Time In this rule jobs are sequenced in order of increasing slack time remaining.
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