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"""WidgetPacking.py
Scenario:
In a factory, nProd widget-making machines produce widgets with a weight
widgWeight (uniformly distributed [widgWeight-dWeight..widgWeight+dWeight])
on average every tMake minutes (uniform distribution
[tmake-deltaT..tMake+deltaT]).A widget-packing machine packs widgets in tPack
minutes into packages. Simulate for simTime minutes.
Model 1:
The widget-packer packs nWidgets into a package.
Model 2:
The widget-packer packs widgets into a package with package weight not
to exceed packMax.
"""
from SimPy.Simulation import *
import random
## Experiment data -------------------------
nProd=2 #widget-making machines
widgWeight=20 #kilogrammes
dWeight=3 #kilogrammes
tMake=2 #minutes
deltaT=0.75 #minutes
tPack=0.25 #minutes per idget
initialSeed=1234567 #for random number stream
simTime=100 #minutes
print 'WidgetPacking'
################################################################
#
# Model 1
#
#################################################################
##Data
nWidgets=6 #widgets per package
class Widget:
def __init__(self,weight):
self.weight=weight
class WidgetMakerN(Process):
"""Produces widgets"""
def make(self,buffer):
while True:
yield hold,self,r.uniform(tMake-deltaT,tMake+deltaT)
yield put,self,buffer,1 # buffer 1 widget
class WidgetPackerN(Process):
"""Packs a number of widgets into a package"""
def pack(self,buffer):
while True:
for i in range(nWidgets):
yield get,self,buffer,1 #get widget
yield hold,self,tPack #pack it
print "%s: package completed"%now()
print "Model 1: pack %s widgets per package"%nWidgets
initialize()
r=random.Random()
r.seed(initialSeed)
wBuffer=Level(name="WidgetBuffer",capacity=500)
for i in range(nProd):
wm=WidgetMakerN(name="WidgetMaker%s"%i)
activate(wm,wm.make(wBuffer))
wp=WidgetPackerN(name="WidgetPacker")
activate(wp,wp.pack(wBuffer))
simulate(until=simTime)
################################################################
#
# Model 2
#
#################################################################
##Data
packMax=120 #kilogrammes per package (max)
class WidgetMakerW(Process):
"""Produces widgets"""
def make(self,buffer):
while True:
yield hold,self,r.uniform(tMake-deltaT,tMake+deltaT)
widgetWeight=r.uniform(widgWeight-dWeight,widgWeight+dWeight)
yield put,self,buffer,[Widget(weight=widgetWeight)] #buffer widget
class WidgetPackerW(Process):
"""Packs a number of widgets into a package"""
def pack(self,buffer):
weightLeft=0
while True:
packWeight=weightLeft #pack a widget which did not fit
#into previous package
weightLeft=0
while True:
yield get,self,buffer,1 #get widget
weightReceived=self.got[0].weight
if weightReceived+packWeight<=packMax:
yield hold,self,tPack #pack it
packWeight+=weightReceived
else:
weightLeft=weightReceived #for next package
break
print "%s: package completed. Weight=%6.2f kg"%(now(),packWeight)
print "\nModel 2: pack widget up to max package weight of %s"%packMax
initialize()
r=random.Random()
r.seed(initialSeed)
wBuffer=Store(name="WidgetBuffer",capacity=500)
for i in range(nProd):
wm=WidgetMakerW(name="WidgetMaker%s"%i)
activate(wm,wm.make(wBuffer))
wp=WidgetPackerW(name="WidgetPacker")
activate(wp,wp.pack(wBuffer))
simulate(until=simTime)
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