Bài giảng Operations Management - Chapter 16: Scheduling

SchedulingMcGraw-Hill/Irwin Copyright © 2012 by The McGraw-Hill Companies, Inc. All rights reserved.You should be able to:Explain what scheduling involves and the importance of good schedulingDescribe scheduling needs in high-volume and intermediate-volume systemsDescribe scheduling needs in job shopsUse and interpret Gantt charts, and use the assignment method for loadingGive examples of commonly used priority rulesSummarize some of the unique problems encountered in service systems, and describe some of the approaches used for scheduling service systems16-*Student SlidesScheduling: Establishing the timing of the use of equipment, facilities and human activities in an organizationEffective scheduling can yieldCost savingsIncreases in productivityOther benefits16-*Student SlidesFlow SystemHigh-volume system in which all jobs follow the same sequenceFlow system schedulingScheduling for flow systemsThe goal is to achieve a smooth rate of flow of goods or customers through the system in order to get high utilization of labor and equipment16-*Student SlidesOutputs fall between the standardized type of output of high-volume systems and the make-to-order output of job shopsOutput rates are insufficient to warrant continuous productionRather, it is more economical to produce intermittentlyWork centers periodically shift from one product to anotherStudent Slides16-*Job shop schedulingScheduling for low-volume systems with many variations in requirementsMake-to-order productsProcessing requirementsMaterial requirementsProcessing timeProcessing sequence and stepsA complex scheduling environmentIt is impossible to establish firm schedules until actual job orders are received16-*Student SlidesLoadingthe assignment of jobs to processing centersGantt chartUsed as a visual aid for loading and scheduling purposesPurpose of the Gantt chart is to organize and visually display the actual or intended use of resources in a time frameworkManagers may use the charts for trial-and-error schedule development to get an idea of what different arrangements would involve16-*Student SlidesAssignment modelA linear programming model for optimal assignment of tasks and resourcesHungarian methodMethod of assigning jobs by a one-for-one matching to identify the lowest cost solution16-*Student SlidesSequencingDetermine the order in which jobs at a work center will be processedPriority rules Simple heuristics used to select the order in which jobs will be processedThe rules generally assume that job setup cost and time are independent of processing sequenceJob timeTime needed for setup and processing of a jobStudent Slides16-*Local priority rules:Focus on information pertaining to a single workstation when establishing a job sequenceGlobal priority rules:Incorporate information from multiple workstations when establishing a job sequence16-*Student SlidesJohnson’s RuleTechnique for minimizing makespan for a group of jobs to be processed on two machines or at two work centers.Minimizes total idle timeSeveral conditions must be satisfied16-*Student SlidesList the jobs and their times at each work centerSelect the job with the shortest timeIf the shortest time is at the first work center, schedule that job firstIf the shortest time is at the second work center, schedule the job last.Break ties arbitrarilyEliminate the job from further considerationRepeat steps 2 and 3, working toward the center of the sequence, until all jobs have been scheduled16-*Student SlidesTheory of constraintsProduction planning approach that emphasizes balancing flow throughout a system, and pursues a perpetual five-step improvement process centered around the system’s currently most restrictive constraint.Bottleneck operations limit system outputTherefore, schedule bottleneck operations in a way that minimizes their idle timesDrum-buffer-ropeDrum = the scheduleBuffer = potentially constraining resources outside of the bottleneckRope = represents synchronizing the sequence of operations to ensure effective use of the bottleneck operations16-*Student SlidesVarying batch sizes to achieve greatest output of bottleneck operationsProcess batchThe economical quantity to produce upon the activation of a given operationTransfer batchThe quantity to be transported from one operation to another, assumed to be smaller than the first operation’s process batch16-*Student SlidesIf scheduling is done well:Goods and services can be made or delivered in a timely mannerResources can be used to best advantageCustomers will be satisfiedIt is important to not overlook the importance of scheduling to strategy and competitive advantageStudent Slides16-*