production gms
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Production Estimation I
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ProductionEstimation
forLoggingMachines
Machinetime
Productivity
Timestudymethods
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MachineTime
Machine
time
can
be
broken
into
avariety
of
distinctcategories:
ScheduledOperating
ScheduledNonoperating
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MachineTime
Total
Scheduled
Operating
Scheduled
Non-operating
ProductiveMechanical
Delay
Non-mechanical
DelayIdle
Out-of-shift
Repair
Out-of-shift
Service
Out-of-shift
Moving
In-shift
Repair
In-shift
Service
Operational
Lost
Personnel
In-shift
Moving
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UsefulConcepts
ofMachineTime
Scheduledmachinehours(SMH),
Productivemachine
hours
(PMH),
Mechanicalavailability(%MA),and
Utilization(%UT).
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ScheduledMachineHours
Scheduled
machine
hours
include
all
time
the
machineisscheduledtowork.
For
instance,
if
a
logger
planned
to
work
from
6AMto4PMwith30minutesforlunch,his
skidderorfellerbuncherwouldhave9.5SMH
perday.
SMH = 10 0.5 = 9.5 hours
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ProductiveMachine
Hours
Productive
machine
hours
represent
the
time
duringwhichthemachineactuallyperforms
work.
Thisexcludestimelosttobothmechanical
andnonmechanicaldelays.
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ProductiveMachineHours
PMH
=
SMH Mechanical
Delays
NonmechanicalDelays
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ProductiveMachineHours
If
the
skidder
in
the
above
example
spent:
45minuteswaitingfortreestobefelled,
20minutesreplacingahydraulicfitting,and
10minutesmovingtoanotherlanding,
ItsPMHwouldbe:
PMH=9.5(0.75)(0.17)(0.33)=8.25hours
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MechanicalAvailability
Mechanical
availability
represents
the
percentageofscheduledtimeinwhichthe
machineismechanicallyabletoperform
work.
MA SMH Mechanical DelaysSMH
=
100
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MechanicalAvailability
Lower
MA
indicates:
alackofmaintenance,
abuseby
an
operator,
and
needformachineoverhaulorreplacement,
orotherneededactions.
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Utilization
Utilization
measures
the
percentage
of
scheduledtimethatthemachineisactually
productive.
UT
PMH
SMH= 100
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Utilization
LowerlevelofUTforamachinecan
indicate:
anoutofbalancesystemor
lowlevel
of
availability.
Utilization MechanicalAvailability
If
zero
time
lost
to
non
mechanical
delays,
UT
couldequalMA.
However,itcanneverexceedMA.
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Utilization UT MAisimportanttoberemembered.
Itconcisely
expresses
an
important
principle
in
operatingapieceofequipmentefficiently.
Efficientoperations
and
minimum
operating
costsdependuponachievingahighdegreeof
utilizationwithamachine.
Highlevels
of
MA
are
prerequisite
for
obtaining
highutilizationlevels.
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MachineProductivity
Isdefinedasproductionperunittime.
Productionofloggingsystemsisnormally
measured:
in
units
of
volume
(cords,
tons,
cubic
feet,
MBF)
or
intermsofnumberofstems
Commonproductivitymeasuresinclude:
volume/PMH,volume/SMH,
stems/SMH,stems/PMH.
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TimeStudy
Methods
Timestudiesareusedtodeterminethe
potentialproductivity
of
alogging
machine.
Therearethreegeneraltypesoftimestudies:
Gross
time
study
Worksampling
Elementaltimestudy
Weoftencombinemorethanoneofthe
abovetechniqueswhenconductingany
individualstudy.
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GrossTime
Studies
Arequickanddirtywaystogetsome
generalideas
about
what
amachine
can
do.
Thesestudiesoften:
examineashort
time
period
and
/or
lackanystatisticaldesign,thus
provideresults
with
limited
use.
Telluswhathappened,butverylittleabout
whyithappened.
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GrossTime
Studies
Example:measuringproductivityofagrappleskidder
Usingastopwatch
or
our
wristwatch:
Webegintimingwhentheskidderleavesthelandingtothewoodsforanotherloadoflogs.
Weend
after
the
skidder
returns
to
the
landinganddropsthelogs.
Onitsseconddeparturetothewoods,we
recordthe
elapsed
time
as
6.56
minutes.
Wealsomeasuredthelogsskiddedas0.64cords.
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GrossTime
Studies
Example
Productivity=0.64
Cords/6.56/60
=5.85cords/PMH
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GrossTime
Studies
Example
In
reality,
we
should
record
several
skidder
turns,
computingameanandvariability.
Evenwithrepeatedobservationsandsimple
statistics,this
method
offers
relatively
little
information.
For
instance, Howisthetimespentafterleavinglanding?
Whatpercentageoftimeisspentontraveling,
grabbingloads,
and
so
on?
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WorkSampling
Astatisticallybasedprocedure
Observationsofaloggingmachineare
takenatrandomtimes
Ateach
observation
the
current
activity
of
the
machineisrecorded(e.g.functions).
The
percentage
of
time
for
each
activity
is
determinedby:
dividingthenumberofobservationsforeach
activity
by
the
total
number
of
observations
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WorkSampling
Canprovide
agood
estimate
of
the
percentageoftimeforeachactivity.
Does
not
measure
the
amount
of
time
spent
oneachactivity.
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WorkSampling
Example
Activity Obs % of total time
Travel Empty 51 29%
Choking Logs 18 10%Travel Loaded 52 30%
Unchoking Logs 12 7%
Deck Maintenance 9 5%
Mechanical Delays 11 6%
Non-mechanical Delays 22 13%
TOTAL 175 100%
Assume that 175 observations are taken at random over an
eight hour shift for a cable skidder.
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WorkSampling
Anexcellent
methodfor
identifyingtheMA
andUT.
Intheexample,
MA=94%,UT=81%.
Activity Ob
s
% of total time
Travel Empty 51 29%
Choking Logs 18 10%
Travel Loaded 52 30%
Unchoking Logs 12 7%
Deck Maintenance 9 5%
Mechanical Delays 11 6%
Non-mechanical Delays 22 13%
TOTAL 175 100%
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WorkSampling
Productivitycannot
be
measured
since
times
arenotrecoded.
Eithergrosstimestudiesorworksampling
shouldbecombinedwithelementaltime
studiestoestimatetheproductivity.
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WorkSampling
Assume
that
the
following
data
were
collectedfortheaboveexample:
Skiddingcyclesduring8hrshift: 52
Totalvolume
skidded: 30.2 cords
Productivemachinehours=0.81*8
=6.48 PMH
Productivity=30.2/6.48= 4.66cords/PMH
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