November 11 2011 1 Ardavan AsefVaziri Throughput Utilization Bottleneck Effective Capacity Theoretical Capacity and Capacity Leverages Flow Rate Throughput Takt Time and Capacity ID: 422672
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Slide1
Throughput
1
Ardavan Asef-Vaziri
Throughput, Utilization, Bottleneck, Effective Capacity, Theoretical Capacity, and Capacity Leverages.This Lecture is accessed at https://www.youtube.com/watch?v=L5YcxWY66Pg&feature=youtu.beSlide2
Flow Rate, Throughput, Takt Time and Capacity
Throughput
is the
number of flow units per unit of time.Observe the process for a number of periods.Measure the number of flow units that are processed per unit of time.Compute the average number of flow units per unit of time.Throughput = Average Flow RateCapacity is the maximum sustainable flow rate. In periods of heavy congestion, throughput is equal to capacity. In a synchronized operation: Throughput = Demand < Capacity Process Flow Analytics, Throughput Analysis, A. Asef-Vaziri
2Slide3
Flow Rate, Throughput, Takt Time and Capacity
Cycle Time is defined in terms of Capacity.
Cycle time = 1/CapacityCapacity = 15/hour
Cycle Time = 1/15 hourCycle Time = 4 minutesTakt time derived from the German word “pace”. Takt Time is defined in relation to Demand or Throughput.Demand = 12/hour Throughput = 12/ hour Takt Time = 1/Demand = 1/(Throughput) = 1/RTakt Time = 1/12 hourTakt Time = 5 minutes3
Process Flow Analytics, Throughput Analysis, A. Asef-Vaziri Slide4
Flow Rate, Throughput, Takt Time and Capacity
R= Ra
Takt time = 1/RaAverage inter-arrival time = Ta = 1/Ra = 1/R = Average inter- exit timeIt is not uncommon for managers to state that their machines have takt time of five minutes (1/12 hour). It is wrong. Takt time is a measure of external demand, it has nothing to do with the internal measure of machine capacity. In a synchronized system, Takt time is the time each station has to send one flow unit out to the next station.Chapter 4 was on flow time minimization. Chapter 5 is on throughput maximization. Chapter 4 and 5 are both “time” minimizations. Why?
4
Process Flow Analytics, Throughput Analysis, A. Asef-Vaziri Slide5
Activity Time, Unit Load, Total Unit Load
Operation
B
Activity Time =
10
min
Operation
A
Activity Time = 5 min
If both are done on
Recourse (1)
then the
T
heoretical
U
nit
L
oad of Resource(1) is 10+5 = 15 min.
If Capacity waste factor in both stations is 25% then the total unit load 15/(1-0.25) = 20 min. We refer to this as Tp.
It is not important to memorize the theoretical unit load and the unit load. What is important is if we do not consider Capacity Waste Factor then we are talking about the theoretical capacity. If we consider, then we are talking effective capacity or simply capacity.
Process Flow Analytics, Throughput Analysis, A. Asef-Vaziri Slide6
Resources, Resource Pools and Resource Pooling
Unit Load of a Resource Unit (
Tp) – The amount of time the resource works to process each flow unit. This includes a share of all distractions such as maintenance, repair, setup, etc. It is a
effective unit load not the theoretical unit load. 6
Process Flow Analytics, Throughput Analysis, A. Asef-Vaziri Slide7
Effective Capacity
Effective Capacity of a Resource Unit
Rp= 1/unit load = 1/ Tp
Effective Capacity of a Resource Pool = Rp=c/TpBottleneck – The resource pool with the minimum effective capacity. Effective capacity of a process: Effective capacity of the bottleneck. Cross train Claims Supervisor to help Mailroom clerk Increase Capacity.
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Process Flow Analytics, Throughput Analysis, A. Asef-Vaziri Slide8
100% Utilization is a High Risk
Imagine a a freeway where all the cars are driving exactly 65 and the distance between pairs of cars in 1 inch. As long as every one has a speed of exactly 65 that is fine. But can they do that?
What happens if one hits the break? How long does it take to clean the freeway. Do cars pass freeway easier when utilization is 1 and they are moving bumper to bumper, or when 50% of the freeway is empty, U = 0.5, or when U = 0.25. How long it takes to clean up accidents in these situations?
Never make U of all the sub-processes or activities, and not even a single sub-process = 18
Process Flow Analytics, Throughput Analysis, A. Asef-Vaziri Slide9
Capacity Utilization
Capacity utilization of a resource pool
U
p = Throughput/Effective capacity of a resource pool = R/RpCapacity utilization of the processU = Throughput/Effective capacity of the bottleneck resource pool R = 400 per day.
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Process Flow Analytics, Throughput Analysis, A. Asef-Vaziri Slide10
Cycle Time, Takt Time, Flow Time
Day = 480 minutes.Rp = 480 per day
Cycle time = 1/RpCT = 1/480 day
CT = 480(1/480) = 1 minuteWe already knew CT = 1 min.10
R = 400 per day
Takt
Time = 1/R
TT = 1/400 day
TT=480(1/400) = 1.2 minute
Flow Time = 1+5+8+2.5
FT = 16.5
Process Flow Analytics, Throughput Analysis, A. Asef-Vaziri Slide11
Unit Load for a Product Mix
Billing: Physician claims 60%, Hospital claims 40%
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Throughput is 400 units per day.
Process utilization: U =100%
Process Flow Analytics, Throughput Analysis, A. Asef-Vaziri