Short-term Scheduling

Transcription

1 Scheduling Importance Short-term Scheduling Operations Management hapter Faster movement of throughput Lower cost etter customer service Faster delivery ependable delivery Realistic commitments Scheduling Issues Forward Scheduling ackward Scheduling Scheduling riteria Minimize completion time Maximize utilization Minimize WIP Minimize customer waiting time Scheduling Process-Focused ctivities ( shops) Forward looking schedules MRP due dates Refined with capacity limitations Planning files Item master file Routing file Work-center master file ontrol files

2 Loading s (work centers) Wyatt s ab Service Input-Output ontrol Tracks work as added and completed onwip cards (constant work-in-process) Gantt harts Visual conceptualization of work schedule ssignment Method Use of linear programming to assign jobs ab Site irport owntown enter us Station istance in Miles Row subtraction olumn subtraction ab Site ab Site irport irport owntown owntown enter us Station enter us Station

3 over ZEROS ab Site irport owntown enter us Station Optimal ssignment irport taxi to customer owntown taxi to customer center taxi to customer us station taxi to customer Total distance traveled = = miles ssignments WJ KG S S ssign production to MXIMIZE total production. What is the total production of your assignments? Preferred schedule WJ KG S S Sequencing s Order in which jobs assigned to work centers Priority Rules FFS (first come, first served) SPT (shortest processing time) E (earliest due date) LPT (longest processing time) ritical Ratio Sequencing N s: Johnson s Rule Limitations

4 Today is day on the company schedule Four jobs on order Rank according to the decision rules Minimize total lateness JO UE TE YS REMINING First come First served (FFS) ue ate ays Total: days late Shortest (SPT) Longest (LPT) ue ate ays ue ate ays Total: days late Total: days late

5 Earliest ue ate (E) ue ate ays Total: days late ue ate Remaining ritical Ratio (-) /=. (-) /=. (-) /=. (-) /=. ue ate ritical Ratio: Sequence ritical Ratio... ays Total: days late Rule comparison- days late best can achieve N/ (Johnson s Rule) Scheduling Rule FFS SPT LPT verage ness. verage Flow... verage # jobs in system.. Scheduling or more jobs on more than one work center ll jobs must be listed Shortest activity time on FIRST machine in process Once scheduled eliminate Move onto remaining jobs as per above E... ritical Ratio..

6 Limitations of Rules Scheduling ynamic on t always recognize constraints or available resources on t look beyond due dates Finite apacity Scheduling (FS) Overcomes rulebased system limitations Graphical interactive scheduling Software packages utilized in well over half of U.S. production facilities Theory of onstraints TO Identify constraints evelop plan Focus resources to create effective plan Reduce constraint effects ontinually reassess ottlenecks rum, uffer, Rope Scheduling Repetitive Facilities Lower inventory levels Faster product throughput Improved quality Improved communication Smoother processes

7 Scheduling Services Focus on staffing levels No inventory for smoothing Labor-intensive and variable demand Restrictions Labor laws Union contracts omplication of schedules Seniority Status