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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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