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Kafli 17 í Chase … Verkröðun

Kafli 17 í Chase … Verkröðun. Skilgreiningar Markmið verkröðunar Helstu reglur við verkröðun Úthlutun verka, uppsetningartímar Nokkur heilræði Vaktaskipulag. Vinnustöð Skilgreining. Vinnustöð er svæði eða staður í fyrirtæki þar sem aðföng eru skipulögð og verk unnin.

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Kafli 17 í Chase … Verkröðun

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  1. Kafli 17 í Chase …Verkröðun • Skilgreiningar • Markmið verkröðunar • Helstu reglur við verkröðun • Úthlutun verka, uppsetningartímar • Nokkur heilræði • Vaktaskipulag

  2. VinnustöðSkilgreining • Vinnustöð er svæði eða staður í fyrirtæki þar sem aðföng eru skipulögð og verk unnin. • Getur verið vél, hópur véla, hópur manna, FMS-kerfi, … • Verk geta verið pantanir frá viðskiptavinum eða þörf fyrir nýjar framleiðslulotur (endingatími birgða að verða búinn)

  3. Dæmigerðar ákvarðanir í verkröðun • Ráðstafa pöntunum eða lotum, tækjum og vélum, starfsmönnum, … • Ákvarða forgang verka (pantana, lota) • Ákvarða röð m.t.t. uppsetningatíma (skiptingar, stillingar) • Gangsetning verka • Eftirlit, neyðarákvarðanir

  4. Markmið verkröðunar • Standa við lofaða skilafresti • Lágmarka afhendingartíma • Lágmarka uppsetningartíma eða -kostnað • Lágmarka birgðir í ferlinu (WIP) • Hámarka nýtingu vinnustöðva

  5. Helstu reglur við verkröðun 1. Fyrstur kemur, fyrstur fær (FCFS, FIFO) 2. Stysti vinnslutími fyrst (SOT, SPT) 3. Skilafrestir ráða röð (EDD) 4. Byrjunartímar ráða (due date-lead time) 5. Slakar, “Least slack time remaining” (STR)

  6. Helstu reglur við verkröðun (Framhald) 6. STRO, “Least slack time remaining per operation as opposed to per job” 7. Minnsta “critical ratio” (CR) (due date-current date)/(number of days remaining) 8. Minnsta “queue ratio” (QR) (slack time remaining in schedule)/(planned remaining queue time) 9. Síðastur inn, fyrstur út (LCFS) 10. Hendingar ráða (“random order”)

  7. Mælikvarðar á árangur verkröðunar • Staðið við skilafresti. • Flæðitími sem minnstur (tíminn sem verk er í ferlinu). • Birgðir í ferlinu (WIP) sem minnstar. • Nýting vinnustöðva, iðjuleysi sem minnst.

  8. Answer: FCFS Schedule Dæmi 1: FCFS regla Suppose you have the four jobs to the right arrive for processing on one machine. What is the FCFS schedule? Do all the jobs get done on time? No, Jobs B, C, and D are going to be late.

  9. Answer: Shortest Operating Time Schedule Dæmi 1: SOT regla Suppose you have the four jobs to the right arrive for processing on one machine. What is the SOT schedule? Do all the jobs get done on time? No, Jobs A and B are going to be late.

  10. Answer: Last-Come First-Served Schedule Dæmi 1: LCFS regla Suppose you have the four jobs to the right arrive for processing on one machine. What is the LCFS schedule? Do all the jobs get done on time? No, Jobs B and A are going to be late.

  11. Answer: Earliest Due Date First Dæmi 1: EDD regla Suppose you have the four jobs to the right arrive for processing on one machine. What is the earliest due date first schedule? Do all the jobs get done on time? No, Jobs C and B are going to be late.

  12. Dæmi 1: CR regla Suppose you have the four jobs to the right arrive for processing on one machine. What is the CR schedule? Do all the jobs get done on time? In order to do this schedule the CR’s have be calculated for each job. If we let today be Day 1 and allow a total of 15 days to do the work. The resulting CR’s and order schedule are: CR(A)=(5-4)/15=0.06 (Do this job last) CR(B)=(10-7)/15=0.20 (Do this job first, tied with C and D) CR(C)=(6-3)/15=0.20 (Do this job first, tied with B and D) CR(D)=(4-1)/15=0.20 (Do this job first, tied with B and C) No, but since there is three-way tie, only the first job or two will be on time.

  13. Dæmi 2: Johnson’s regla (hluti 1) Suppose you have the following five jobs with time requirements in two stages of production. What is the job sequence using Johnson’s Rule? Time in Hours Jobs Stage 1 Stage 2 A 1.50 1.25 B 2.00 3.00 C 2.50 2.00 D 1.00 2.00

  14. Dæmi 2: Johnson’s regla (hluti 2) Time in Hours Jobs Stage 1 Stage 2 A 1.50 1.25 B 2.00 3.00 C 2.50 2.00 D 1.00 2.00 First, select the job with the smallest time in either stage. That is Job D with the smallest time in the first stage. Place that job as early as possible in the unfilled job sequence below. Drop D out, select the next smallest time ( Job A), and place it 4th in the job sequence. Drop A out, select the next smallest time. There is a tie in two stages for two different jobs. In this case, place the job with the smallest time in the first stage as early as possible in the unfilled job sequence. Then place the job with the smallest time in the second stage as late as possible in the unfilled sequence. Job Sequence 1 2 3 4 Job Assigned D B C A

  15. Úthlutun verka á vinnustöðvar 1. Gefinn tími eða kostnaður við að vinna hvert verk á hverri vinnustöð. 2. Ákvarða hver á að vinna hvert verk þannig að heildartími eða –kostnaður sé lágmarkaður. 3. Úthlutunarlíkanið (Assignment Model), sértilvik af flutningalíkaninu.

  16. Lágmörkun uppsetningartíma 1. Gefið fylki með uppsetningartímum (skiptitímum) eða -kostnaði milli verka (pantana eða lota) 2. Ákvarða röð verka þannig að heildar uppsetningartími sé lágmarkaður. 3. Hliðstætt “Travelling Salesman Problem” (TSP)

  17. Vaktaskipulag • Skipulagning vakta, frídaga, eða daglegs vinnutíma. • Byggist á greiningu á mönnunarþörfum • Hægt að leysa með Línulegri bestun

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