運籌管理operationsmanagementch(5)(編輯修改稿)
2025-02-17 22:09 本頁面
【文章內(nèi)容簡介】 g Rules ? SPT Rule A E C B D Processing Promised Flow Job Time Completion Time Lateness A 6 10 6 0 B 8 7 14 7 C 9 8 23 15 D 12 16 35 19 E 14 14 49 35 49 127 76 26 Example: Sequencing Rules ? SPT Rule Performance ? Average flow time: 127/5 = hours ? Average number of jobs in the system: 127/49 = jobs ? Average job lateness: 76/5 = hours 27 Example: Sequencing Rules ? Critical Ratio Rule E C D B A Processing Promised Flow Job Time Completion Time Lateness E (.875) 8 7 8 1 C (.889) 9 8 17 9 D () 14 14 31 17 B () 12 16 43 27 A () 6 10 49 39 49 148 93 28 Example: Sequencing Rules ? Critical Ratio Rule Performance ? Average flow time: 148/5 = hours ? Average number of jobs in the system: 148/49 = jobs ? Average job lateness: 93/5 = hours 29 Example: Sequencing Rules ? Comparison of Rule Performance Average Average Average Flow Number of Jobs Job Rule Time in System Lateness FCFS SPT CR SPT rule was superior for all 3 performance criteria. 30 Controlling Changeover Costs ? Changeover costs costs of changing a processing step in a production system over from one job to another ? Changing machine settings ? Getting job instructions ? Changing material ? Changing tools ? Usually, jobs should be processed in a sequence that minimizes changeover costs 31 Controlling Changeover Costs ? Job Sequencing Heuristic ? First, select the lowest changeover cost among all changeovers (this establishes the first two jobs in the sequence) ? The next job to be selected will have the lowest changeover cost among the remaining jobs that follow the previously selected job 32 Example: Minimizing Changeover Costs Hardtimes Heat Treating Service has 5 jobs waiting to be processed at work center 11. The jobtojob changeover costs are listed below. What should the job sequence be? Jobs That Precede A B C D E A 65 80 50 62 B 95 69 67 65 C 92 71 67 75 D 85 105 65 95 E 125 75 95 105 Jobs That Follow 33 Example: Minimizing Changeover Costs ? Develop a job sequence: A follows D ($50 is the least . cost) C follows A ($92 is the least following . cost) B follows C ($69 is the least following . cost) E follows B (E is the only remaining job) Job sequence is D – A – C – B – E Total changeover cost = $50 + 92 + 69 + 75 = $286 34 Minimizing Total Production Time ? Sequencing n Jobs through Two Work Centers ? When several jobs must be sequenced through two work centers, we may want to select a sequence that must hold for both work centers ? Johnson’s rule can be used to find the sequence that minimizes the total production time through both work centers 35 Johnson’s Rule 1. Select the shortest processing time in either work center 2. If the shortest time is at the first work center, put the job in the first unassigned slot in the schedule. If the shortest time is at the second work center, put the j
教學(xué)課件相關(guān)推薦
鄂ICP備17016276號-1