SEQUENCING PROBLEMS INTRODUCTION A Sequence is the order

SEQUENCING PROBLEMS

INTRODUCTION A Sequence is the order in which the jobs are processed. Sequencing problems arises when we are concerned with situation where there is a choice as to the order in which a number of tasks can be performed. A sequence problem could involves. I. Jobs in a manufacturing plant. II. Aircraft waiting for landing and clearance. III. Maintaining scheduling in a factory. IV. Programmes to run on a computers. V. Customers in a bank & so on. Most of these problems are solved automatically. Sometimes the ordering is determined by chance or on ‘first come first serve’ basis. But the solutions may not be appropriate in all these cases.

BASIC TERMS 1. Jobs: The jobs or items or customers or orders are the primary stimulus for sequencing. There should be a certain number of jobs say ‘n’ processed or sequenced. 2. Number of Machines : It refers to the no. of service facilities through which a job must pass before it is assumed to be completed. 3. Processing Order: It refers to the order (sequence) in which given machines are required for completing the job. Processing Time: It indicates the time required by a job on each machine. 4. 5. 6. Total Elapsed Time: It is the time interval between starting the 1 st job and completing the last job including the idle time in a particular order by the given set of machines. Idle time on a machine: It is the time for which a machine does not have a job to process, i. e. idle time from the end of job (i-1) to the start of job i. 7. Processing Time: It indicates the time required by a job on each machine. 8. No passing rule: It refers to the rule of maintaining the order in which jobs are to be processed on given machines.

BASIC ASSUMPTIONS 1) 2) 3) 4) 5) 6) 7) No machine can processed more than one job at a time. The processing time on different machines are independent of the order in which they are processed. The time involved in moving a job from one machine to another is negligibly small. Each job once started on a machine is to be performed upto completion on that machine. All machines are different types. All jobs are completely known and are ready for processing. A job is processed as soon as possible but only in the order specified.

TYPES OF SEQUENCING PROBLEMS 1. 2. 3. 4. Problem with ‘n’ jobs through one machine. Problem with ‘n’ jobs through two machine. Problem with ‘n’ jobs through three machine. Problem with ‘n’ jobs through ‘m’ machine.

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