Scheduling McGraw-Hill/Irwin Copyright 2012 by The McGraw-Hill Companies, Inc. All rights reserved. You should be able to: 1. Explain what scheduling involves and the importance of good scheduling 2. Describe scheduling needs in high-volume and intermediate-volume systems 3. Describe scheduling needs in job shops 4. Use and interpret Gantt charts, and use the assignment method for loading 5. Give examples of commonly used priority rules 6. Summarize some of the unique problems encountered in service systems, and describe some of the approaches used for scheduling service systems 16-2 Student Slides Scheduling: Establishing the timing of the use of equipment, facilities and human activities in an organization Effective scheduling can yield Cost savings Increases in productivity Other benefits 16-3 Student Slides Flow System High-volume system in which all jobs follow the same sequence Flow system scheduling Scheduling for flow systems The 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 equipment Workstation 1 Workstation 2 Output 16-4 Student Slides Outputs fall between the standardized type of output of high-volume systems and the make-to-order output of job shops Output rates are insufficient to warrant continuous production Rather, it is more economical to produce intermittently Work centers periodically shift from one product to another Student Slides 16-5 Job shop scheduling Scheduling for low-volume systems with many variations in requirements Make-to-order products Processing requirements Material requirements Processing time Processing sequence and steps A complex scheduling environment It is impossible to establish firm schedules until actual job orders are received 16-6 Student Slides Loading the assignment of jobs to processing centers Gantt chart Used as a visual aid for loading and scheduling purposes Purpose of the Gantt chart is to organize and visually display the actual or intended use of resources in a time framework Managers may use the charts for trial-and-error schedule development to get an idea of what different arrangements would involve 16-7 Student Slides Assignment model A linear programming model for optimal assignment of tasks and resources Hungarian method Method of assigning jobs by a one-for-one matching to identify the lowest cost solution 16-8 Student Slides Sequencing Determine the order in which jobs at a work center will be processed Priority rules Simple heuristics used to select the order in which jobs will be processed The rules generally assume that job setup cost and time are independent of processing sequence Job time Time needed for setup and processing of a job Student Slides 16-9 Local priority rules: Focus on information pertaining to a single workstation when establishing a job sequence Global priority rules: Incorporate information from multiple workstations when establishing a job sequence Student Slides Johnsons Rule Technique for minimizing makespan for a group of jobs to be processed on two machines or at two work centers. Minimizes total idle time Several conditions must be satisfied Student Slides 1. List the jobs and their times at each work center 2. Select the job with the shortest time a. If the shortest time is at the first work center, schedule that job first b. If the shortest time is at the second work center, schedule the job last. c. Break ties arbitrarily 3. Eliminate the job from further consideration 4. Repeat steps 2 and 3, working toward the center of the sequence, until all jobs have been scheduled Student Slides Theory of constraints Production planning approach that emphasizes balancing flow throughout a system, and pursues a perpetual five-step improvement process centered around the systems currently most restrictive constraint. Bottleneck operations limit system output Therefore, schedule bottleneck operations in a way that minimizes their idle times Drum-buffer-rope Drum = the schedule Buffer = potentially constraining resources outside of the bottleneck Rope = represents synchronizing the sequence of operations to ensure effective use of the bottleneck operations Student Slides Varying batch sizes to achieve greatest output of bottleneck operations Process batch The economical quantity to produce upon the activation of a given operation Transfer batch The quantity to be transported from one operation to another, assumed to be smaller than the first operations process batch Student Slides If scheduling is done well: Goods and services can be made or delivered in a timely manner Resources can be used to best advantage Customers will be satisfied It is important to not overlook the importance of scheduling to strategy and competitive advantage Student Slides 16-15