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Unformatted text preview: 1/28/2007 Industrial Data and Systems Analysis 1 Throughput Concepts, Flow Time, and Littles Law Peter L. Jackson Professor School of O.R. and I.E. 1/28/2007 Industrial Data and Systems Analysis 2 Overview Throughput Concepts What is it Worth to Increase Throughput? Flow time and Lead time Littles Law What is it Worth to Reduce Flow Time? 1/28/2007 Industrial Data and Systems Analysis 3 What is Throughput? Activity of a repetitive process Output = input ( throughput), unless... Measure of interest: throughput rate Flights per hour, out-patients per day, gallons per second, messages per hour, etc. 1/28/2007 Industrial Data and Systems Analysis 4 What is Cycle Time? Takt time Inverse of throughput rate Units of time per unit of output Time between successive outputs Toyota System Flow time Time spent in system by single unit (includes queue time) Definition of cycle time is not consistent: even within the same company! 1/28/2007 Industrial Data and Systems Analysis 5 Throughput Detractors Unscheduled time Starved / blocked by production control system Speed loss Quality loss Scrap, rework Breakdowns Setup time Planned downtime partial shifts maintenance meetings, training 1/28/2007 Industrial Data and Systems Analysis 6 The M.F.D. THRUPUT Game 1/28/2007 Industrial Data and Systems Analysis 7 Throughput Targets DGR (daily going rate): units per day required to support final assembly schedule (level schedule) Cycle time (Takt time): time allowed between successive units of output to achieve DGR Takt time = effective daily operating time / DGR Stated as requirement: process must be designed and operated to achieve these targets 1/28/2007 Industrial Data and Systems Analysis 8 Will the Process Achieve Target? Begin with throughput rate achievable under ideal operating conditions Adjust for breakdowns, setups, quality loss, speed loss Ex. Adjust for speed loss: Equipment runs at 100y% speed Throughput rate adjusted for efficiency = unadjusted rate * y Adjust for planned downtime 1/28/2007 Industrial Data and Systems Analysis 9 Adjust for Repair Cycles MTTF: mean time to fail (when running) MTTR: mean time to repair Mean repair cycle length = MTTR+MTTF Fraction of time equipment is operational = MTTF / (MTTR+MTTF) Throughput rate adjusted for repair = Unadjusted rate * MTTF / (MTTR+MTTF) repair repair operational TTR TTF 1/28/2007 Industrial Data and Systems Analysis 10 Adjust for Setup Cycles Run time = average lot size / production rate Setup cycle length = Setup time + run time Fraction of time equipment is running = Run time / (Setup cycle length) Throughput rate adjusted for setups =...
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This note was uploaded on 01/09/2009 for the course ORIE 312 taught by Professor D.ruppert,p.jacks during the Spring '08 term at Cornell University (Engineering School).
- Spring '08