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Types of short-term scheduling börja lära sig
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Forward scheduling and backward scheduling
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begins the schedule as soon as the requirements are known; often builds up WIP; jobs performed to customer order, schedule can be accomplished even if due date is missed
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begins with the due date of the final operation, schedules jobs in reverse order, used in many manufacturing environments; ex. catering
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Goals of short-term scheduling börja lära sig
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minimize completion time, maximise utilisation, minimise WIP inventory, minimise customer wait time
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process-focused work centres börja lära sig
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high variety, low volume, mate-to-order, different materials and processing for each product, complex production planning and control, production scheduling aspects
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Loading Jobs in Work Centres börja lära sig
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assigning jobs to work centres; approaches: input-output control, Gantt charts, assignment method
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CONWIP - constant WIP; for given average output rate, try to keep L low and constant then W will be short and constant; Little's formula
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shows relative workload in facility, negatives: does not account for unexpected events, must be updated regularly
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occurs in many environments: resources-jobs, planes-gates, course-rooms); type of binary linear programming model
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Priority rules for Dispatching Jobs (sequencing) börja lära sig
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First come first serve; the first job to arrive at a work centre is processed first
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earliest due date; the job with the easiest due date is processed first
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shortest processing time first
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longets processing time first
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critical ratio; the ratio of time remaining to required work time remaining is calculated and jobs are schedules in order of increasing ratio; CR = time remaining/work days remaining -> process jobs with the smallest CR first
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Criteria to evaluate priority rules börja lära sig
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Average Completion Time= Sum of flow times / # jobs; Utilisation = Sum process time / sum flow time; Average number of jobs in system Sum Flow time /Sum processing time; average jobs lateness = sum late times / number of jobs
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