SChEDuling(调度与规划)

Scheduling Beni Asllani University of Tennessee at Chattanooga Operations Management - 5th Edition Chapter 16 Roberta Russell & Bernard W. Taylor, III Lecture Outline Objectives in Scheduling Loading Sequencing Monitoring Advanced Planning and Scheduling Systems Theory of Constraints Employee Scheduling What is Scheduling? Last stage of planning before production occurs Specifies when labor, equipment, facilities are needed to produce a product or provide a service Scheduled Operations Process Industry Linear programming EOQ with non-instantaneous replenishment Mass Production Assembly line balancing Project Project -scheduling techniques (PERT, CPM) Batch Production Aggregate planning Master scheduling Material requirements planning (MRP) Capacity requirements planning (CRP) Objectives in Scheduling Meet customer due dates Minimize job lateness Minimize response time Minimize completion time Minimize time in the system Minimize overtime Maximize machine or labor utilization Minimize idle time Minimize work-in-process inventory Shop Floor Control Loading Check availability of material, machines and labor Sequencing Release work orders to shop and issue dispatch lists for individual machines Monitoring Maintain progress reports on each job until it is complete Loading Process of assigning work to limited resources Perform work on most efficient resources Use assignment method of linear programming to determine allocation Assignment Method Perform row reductions subtract minimum value in each row from all other row values Perform column reductions subtract minimum value in each column from all other column values Cross out all zeros in matrix use minimum number of horizontal and vertical lines If number of lines equals number of rows in matrix then optimum solution has been found. Make assignments where zeros appear Else modify matrix subtract minimum uncrossed value from all uncrossed values add it to all cells where two lines intersect other values in matrix remain unchanged Repeat steps 3 through 5 until optimum solution is reached Assignment Method: Example 12 Assignment Method: Example (cont.) Project Cost = (5 + 6 + 6 + 4) X $100 = $2,100 12 Sequencing Prioritize jobs assigned to a resource If no order specified use first-come first-served (FCFS) Many other sequencing rules exist Each attempts to achieve to an objective Sequencing Rules FCFS - first-come, first-served LCFS - last come, first served DDATE - earliest due date CUSTPR - highest customer priority SETUP - similar required setups SLACK - smallest slack CR - critical ratio SPT - shortest processing time LPT - longest processing time Critical Ratio Rule Sequencing Jobs Through One Process Flowtime (completion time) Time for a job to flow through the system Makespan Time for a group of jobs to be completed Tardiness Difference between a late job’s due date and its completion time Simple Sequencing Rules Simple Sequencing Rules: FCFS Simple Sequencing Rules: DDATE Simple Sequencing Rules: SLACK Simple Sequencing Rules: CR Simple Sequencing Rules: SPT Simple Sequencing Rules: Summary Sequencing Jobs Through Two Serial Process Johnson’s Rule List time required to process each job at each machine. Set up a one-dimensional matrix to represent desired sequence with # of slots equal to # of jobs. Select smallest processing time at either machine. If that time is on machine 1, put the job as near to beginning of sequence as possible. If smallest time occurs on machine 2, put the job as near to the end of the sequence as possible. Remove job from list. Repeat steps 2-4 until all slots in matrix are filled and all jobs are sequenced. Johnson’s Rule Johnson’s Rule (cont.) A B C D E Completion time = 41 Idle time = 5+1+1+3=10 Guidelines for Selecting a Sequencing Rule SPT most useful when shop is highly congested Use SLACK for periods of normal activity Use DDATE when only small tardiness values can be tolerated Use LPT if subcontracting is anticipated Use FCFS when operating at low-capacity levels Do not use SPT to sequence jobs that have to be assembled with other jobs at a later date Monitoring Work package Shop paperwork that travels with a job Gantt Chart Shows both planned and completed activities against a time scale Input/Output Control Monitors the input and output from each work center Gantt Chart Input/Output Control Input/Output Control (cont.) Advanced Planning and Scheduling Systems Infinite - assumes infinite capacity Loads without regard to capacity Then levels the load and sequences jobs Finite - assumes finite (limited) capacity Sequences jobs as part of the loading decision Resources are never loaded beyond capacity Advanced Planning and Scheduling Systems (cont.) Advanced planning and scheduling (APS) Add-ins to ERP systems Constraint-based programming (CBP) identifies a solution space and evaluates alternatives Genetic algorithms based on natural selection properties of genetics Manufacturing execution system (MES) monitors status, usage, availability, quality Theory of Constraints Not all resources are used evenly Concentrate on the” bottleneck” resource Synchronize flow through the bottleneck Use process and transfer batch sizes to move product through facility Drum-Buffer-Rope Drum Bottleneck, beating to set the pace of production for the rest of the system Buffer Inventory, placed in front of the bottleneck to ensure it is always kept busy Determines output or throughput of the system Rope Communication signal, tells processes upstream when they should begin production TOC Scheduling Procedure Identify bottleneck Schedule job first whose lead time to the bottleneck is less than or equal bottleneck processing time Forward schedule the bottleneck machine Backward schedule the other machines to sustain the bottleneck schedule Transfer in batch sizes smaller than the process batch size Synchronous Manufacturing Synchronous Manufacturing (cont.) Synchronous Manufacturing (cont.) Employee Scheduling Labor is very flexible resource Scheduling workforce is complicated repetitive task Assignment method can be used Heuristics are commonly used Employee Scheduling Heuristic Let N = no. of workers available Di = demand for workers on day i X = day working O = day off Assign the first N - D1 workers day 1 off. Assign the next N - D2 workers day 2 off. Continue in a similar manner until all days are have been scheduled If number of workdays for full time employee < 5, assign remaining workdays so consecutive days off are possible Assign any remaining work to part-time employees If consecutive days off are desired, consider switching schedules among days with the same demand requirements Employee Scheduling Employee Scheduling (cont.) Employee Scheduling (cont.) Automated Scheduling Systems Staff Scheduling Schedule Bidding Schedule Optimization Copyright 2006 John Wiley & Sons, Inc. All rights reserved. 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