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Chap016st - Chapter 16 Scheduling CHAPTER 16 SCHEDULING...

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Chapter 16 - Scheduling CHAPTER 16: SCHEDULING Answers to Discussion and Review Questions 1. Job shops are intended to handle a wide range of processing requirements; jobs tend to follow many different paths through the shop, and often differ significantly with respect to processing times. In addition, rush orders, changes in specs, and short planning horizons must be contended with. Consequently, scheduling can be exceedingly complex. Conversely, in continuous systems there is a high degree of uniformity which presents much less difficulty in terms of scheduling. 2. The main decision areas of job shop scheduling concern loading and sequencing. 3. Gantt charts are visual aids used by managers to plan and adjust facility and equipment loading. Advantages of Gantt charts include ease of manipulation, the fact that they provide a visual model of loading, and the ability to assist in trial and error changes. Disadvantages include the need to repeatedly update the chart, the inability to reveal costs associated with different alternatives and the inability to include other details (e.g., processing items which are dependent on the equipment being used rather than the same regardless of the equipment being used). 4. The assignment model assumes a one-for-one matching is possible, that costs for each combination are known and fixed, and that in general, each machine is capable of handling each job. (The last assumption is not strict, however. For example, certain combinations may be “undesirable” because certain jobs cannot be processed on certain pieces of equipment.) 5. a. FCFS: process jobs in order of arrival. b. SPT: process jobs according to processing times, shortest ones first. c. DD: process jobs by due date, earliest due dates first. d. S/O: takes into account remaining processing time on all remaining operations for each job. Jobs with lowest slack per remaining operations are scheduled first. 6. Priority rules allow for the fact that jobs are not equally important: different processing sequences will have different consequences for the organization. Priority rules enable an organization to emphasize those measures of effectiveness deemed most important. 7. Service systems must usually contend with random arrivals and variations in service times. Because of these factors, service systems loads tend to be uneven, making scheduling less effective. 8. Forward scheduling is when scheduling starts with a specific date and moves forward; backward scheduling starts at a specific end date and moves backward. Forward scheduling shows the earliest finish date; backward scheduling shows the latest start date. 16-1
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Chapter 16 - Scheduling 9. To the extent that scheduling efforts can achieve a balance in facility or equipment loading, the amount of output for a given amount of input will be higher than it otherwise would, and hence, productivity will be higher than otherwise. Conversely, poor scheduling will adversely affect productivity because it will not enable maximum use of resources.
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