hu‐motor integrated hammering mechanism
TRANSCRIPT
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HumotorIntegratedHammeringMechanism
TeamA
KothaBharathKumarReddyED11B021
PaboluSahithipriyaED11B025
ShrutiPandeyED11B035
DiyyalaChaitanyakumarED11B045
SaneethSriramojuED11B053
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Appendix
SINo Topic PageNo
1) Problemstatement 3
2) Motivation 35
3) TargetSpecification 5
4) Assumptions 6
5) TargetCustomers 6
6) Challengesanddifficulties 6
7) Somepossiblesolutionsandtheir
evaluation
712
8) Calculations 1315
9)
Constraints
on
design 15
16
10) Partsandmaterial 16
11) Partsandfinaldimensions 1718
12) CompleteCADmodel 18
13) Scopeofimprovement 19
14) Suggestionsandcritics 19
15) References 19
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ProblemStatement:
Todesignamechanismwhichcanreplacethetraditionalhammering
mechanismto
crush
the
stones,
and
to
improve
the
efficiency
of
worker
and
reduceeffortwhilehammeringthestones.Alsomechanismisdesignedto
integrateitwithHumotor(amechanismdevelopedtoutilizeworkerstimeand
energyinanefficientway)
Motivation:
Themainmotivationistodevelopanalternativehammeringmechanismto
reduceworkereffect.MechanismisdesignedtobeintegratedwithHumotorto
furtherincrease
the
efficiency
of
the
worker.
Intraditionalways,aheavyweighthammerisusedtocrushthestones.
Hammerheadhastobeliftedabovetheshoulderlevelandshouldbedroppedon
thestonestocrushthestones.Liftingheavyweightsrepeatedlyisnotagoodidea
inperspectiveofergonomics.Soifwecancomeupwithaway,sothatworker
willberelaxedtolifttheweights,thenwecanreducemusclefatigue.
Figure1:Atraditionalsledgehammer.
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Imagesource:http://www.blackrocktools.com/media/catalog/product/cache/1/image/9df78eab33525d08d6e5fb8d27136e95/3/1/3103_3
lb._sledge_hammer_tekton_2_.jpg
Figure2:Workerusingsledgehammer
Humotorisamechanismwhichisdevelopedtoreducetheeffortof
workerwhileliftingheavyloads.Insteadofliftingheavyloadsworkerhastodo
pedalingmotiontolifttheheavyloadsusingHumotor.Soifwecanintegrate
hammeringtoHumotorwecangreatlyreducehumaneffort.
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Figure3:
Schematic
of
Hu
motor
Thesolutionsalreadyexisting includecrushingplants.Generallytheseare
heavydutystonecrushingplantsandcantbemovestonewplaces.Theseplants
use a lot of electricity. Cost of these plants is too high and a normal building
constructor cant afford to spend so much. So we want to design a mechanism
which dont use electricity, cheap, not so heavy and uses human energy
efficiently.
TargetSpecifications:
o Atleastasmuchproductivityaswithmanualhammering(eachhitinevery1.75sec)
o Amomentumtransferof35KgN/mpereachhit.o Costbelow10,000/ INR.
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o Longlifeofproduct.Assumptions:
Wemadesomeassumptionsduringtheanalysisanddesignofmechanism
whichsimplifies
the
process.
Assumptions
are
mentions
below.
o Time of impact is same regardless of the mass of hammer head. Time ofimpactmayvaryfromhittohitbutbyassumingthatitisconstant,wejust
needtoworryaboutmomentumtransfer.Whentimeofimpactissame,it
isenoughtotransfersameamountoflinearmomentum.
o Afterhittingtherock,hammerheadmomentarilycomestorest(i.e.,allthemomentumistransfertorock)
o The momentum that needs to be transferred is calculated using a videowhich
is
taken
while
aworker
is
actually
using
hammer.
We
assumed
that
it
isenoughifourmechanismgivesthismuchfinalmomentum.
o Productivityrate isalsocalculatedfromavideo.Althoughproductionratemayvaryfromworkertoworker,weassumedittobeourtargetvalueand
designedmechanismaccordingly.
TargetCustomer:
1. Constructionworkers.2. Mines3. Otherplaceswherestonesneedtobecrushed.
We went and met workers in constructions sites of our institute (near
SharavathihostelandSaraswathihostel).Fromoutinteractionwecametoknow
that, it isveryhardtousesledgehammer for longtimes.Liftingthehammer to
suchheightisadifficulttaskandtheysaidalternativemechanismwillbehelpful.
Wetookavideowhileworkerisusingsledgehammertoanalyzethehammering
process.
ChallengesandDifficulties:
o Liftingthehammerheadupto2metersheight.o Repetitivemotionofhammero Jerkproducedwhenhammerheadhitstherock.o Protectingworkerandcomponentsfromjerk.
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o Minimizingtheenergylossesduetofrictionetc.o Longlifeofproduct.o Lowcost.
Somepossible
solutions
and
their
evaluation:
Weconsideredsomepossiblemechanismstotheproblem.Theyare listed
below.
Mechanism1:
Figure4:Schematicofsolutionusingcams
We considered using two cams and attaching hammer head to one cam
usinginextensiblerope.Herewehaveproblemsoffriction.Surfacedamagemay
occur because of the friction between two cams.And also cams may have very
highinertia.
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Mechanism2:
Figure5:Schematicofsolutionusingfourbarmechanism
Anothersolutionistousefourbarmechanismandattachinghammerhead
tooneofthefourlinks.Butherewewillhavetheproblemofjerk.Linkinfourbar
mechanism cant sustain thejerk produced when hammer head hits rock. As a
resultlinkswillbedamagedeasilyandlifetimeofproductwillbeveryless.
Mechanism3:In thismechanism,aroller is attached to a rotating link. One endof long
stringis
attached
to
afixed
point
and
to
the
other
end
hammer
head
is
attached.
While rotating, roller which is attached to the link will lift the string and so
hammer head rises. After some time hammer head reaches its maximum point
and start to fall on to rock. Here the main problems is that, to create same
momentumnecessarylinkhastorotatewithhighvelocityforsometimeandfor
while lifting the hammer it need to move slowly so as to reduce human effort.
Thoseveryhighvelocitiesareabigtroublewiththismechanism.
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Figure6:Schematicofsolutionusingpulleysandrotatinglink.
Mechanism4:
Figure7:Aschematicusingpulleysandcams.
Becauseofthefrictionbetweenpulleyandsemicircleshapedcam,when
camrotateshammerheadwillraise.Andwewillhavefreefallwhencamleaves
contactwithpulley.Eventhoughsolutionseemstobeworking,wemayface
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problemswhileimplementingthismechanism.Weneedaninterferencefit
betweencamandpulley,becauseoftheneedofhighfrictionbetweenthese.So
whenevercamstartstocomeintocontactwithpulley,theseinterferencewill
causealotoftroubles.Andalsowhenhammerheadfallsonstones,jerk
developedwill
cause
damage
to
the
rope.
Mechanism5:
Figure8:Schematicusingpulley,rollersandlinks.
Thisisanothermechanismusingcams.Rollerisusedtoeliminatefriction
between
cam
and
links.
Mechanism
is
protected
from
jerk
by
the
design
of
cam.
Whenhammerheadmakescontactwithstone,therewontbeanycontact
betweenrollerandcam.Alsothecenterofrotationofhammerheadiscenterof
percussionaboutwhichtherewontbeanynetmomentortorque.
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Belowprosandconsofmechanismsconsideredabovearetabulated.
Mechanism Pros Cons
Mechanism1
Easyto
design
Jerkwontaffectcamsand
otherparts
Surfacefailure
Frictionatsurface
Difficulttofabricatecams
Mechanism2 Veryaccuraterepeated
movement
Welldeveloped
mathematical
solutions
Easytofabricate
Cantaccommodatejerk
developed
Lesslife
time.
Mechanism3 Easytofabricate
Lowcost
Partscanbereplacedeasily
Difficulttogetenoughimpact
Ropemightneedtobechanged
frequently.
Mechanism4
Easyto
manufacture.
Highproductivitycanbe
obtained.
Difficultto
generate
friction
betweenpulleyandcam
Failureofropeduetoimpact
Mechanism5 Uniformliftofhammerhead.
Verylessfriction
Jerkswont
affect
the
system
Difficulttomanufacture
Table1:Comparingadvantagesanddisadvantagesofdifferentmechanisms
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Intheabovemodels,firstfourarehavingsomeproblemswhichcause
troublestofunctioningofmechanism.Eventhoughfifthmechanismseemstobe
workingwell,itisverydifficulttomanufacturesuchacam.Butwehave
advantageofconstantliftofhammerheadwiththiscam.Wedecidetochange
theshape
of
cam,
so
that
manufacturing
will
be
easy,
at
the
cost
of
constant
force
toliftthehammerhead.
Figure9:Initialdesignofcam Figure10:Redesignedcam
Herewecomparedthesetwocamsintermsoffunctionality.
Initiallydesignedcam Redesignedcam
Difficulttomanufacture Comparativelyeasytomanufacture
Almostconstantforcesareinvolved
whileliftingthehammerhead
Varyingforcesareinvolvedwhilelifting
thehammerhead
Nonconvexshapedperimeter Convexshapedperimeter
Table2:Comparingfunctionalitiesoftwocams
Fortheabovereasonswedecidedtogowiththeredesigncameventhough
forcesinvolvedarenotconstantthroughoutthemechanism.
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Calculations:
Tocalculateimpulseneededtobreakthestonewevisitedaconstructionsite,
wherewe
took
the
video
of
the
worker
working
with
the
hammer.
From
the
video
wecalculatedImpulse,Numberofhitspersecond,Angularvelocityandrelevant
parameters.
Hammerarmlength=90cms
Timetakenforeachhit=1.75seconds
Angularvelocity=7.85rad/seconds
Impulse
calculated
=
32.325
kg
m/sec
Assume
the
link
1(1
)
makes
an
equal
angle
on
both
sides
of
the
horizontal
axis
LettheHeightthroughwhichitmovesbe
Sofromthefigure
sin
21
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Impulsemomentumtheorem
Energyconservationprinciple
2 2
Fromaboveequationsweget
19.6
Tosetthevaluesofmass,lengthsangleaCcodewithconsiderationslike
o Torqueshouldbeuniformandtorquevariationshouldbeminimum(
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Mass(M) Height(H) Length(l1) Angle(rad) Torque(Nm) Torque
variation
13 0.414 0.607 0.348 77.357 4.64
14.2 0.347 0.373 0.483 51.99 5.95
15.1
0.307 0.453 0.3454 67.1 3.9617.2 0.236 0.518 0.23 87.37 2.30
Highlightedvaluesarethesetofselectedvalues.
Aslink1andlink2aretworigidpartsofalink,when1rotatesthelink2alsorotatesbysameangle.
Timetakentodropthehammerhead
2
Thisturnsouttobe0.25seconds.So,ittakes1.750.25secondstomovethe
hammerup.Matchingtheangletotheriseofthehammerwecangetbase
dimensionsofcam,angularaccelerationandtorque.
ConstraintsonDesign:
1) Ifmassofthehammerisincreased,thenwedontneedtoliftittothesame
height
to
create
same
impulse,
so
we
can
have
smaller
link
lengths.
Butatthesametime,wewillbehavingproblemsforfeedingtherockin
andalsoinputtorqueincreases.
2)Ifweincreasethelengthofthelink1,wedontneedtoturnittoomuch
aboutpivottoraiseittothesameheight,butatthesametimeweneedto
applymoretorquetorotatethemass.Linklengthandtorquearelinearly
related.
3)Ifwechangethepivotposition,alltheassemblywillgetaffected.
Hammermay
not
rise
to
the
complete
height
required
or
it
may
rise
more
thanrequired,somecomponentsmaygetstuckwhilemoving.Soweneed
exactpositionforpivotforgoodimpulsegeneration.
4)Rotationangleatpivotisalsoveryimportant.Ifitistoolarge,camsize
willincreasedramaticallyandtherewillbealotoftorquevariationswhile
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rotatingcam.Ifitistoosmall,weneedtohavelargelinksthusby
increasingtorques.
5)Iflengthofsecondlink(onewhichisincontactwithcam)ismore,we
willneedlargercamandifitistoosmalllargerforceswillbegeneratedat
camand
link
contact
which
damages
components.
6)Ifcambaseradiusistoosmall,pressureanglewillbehigh,whichcauses
morestressatcambearingcontact.Ifitistoolargewewillneedalotof
materialwhichincreasesthecostofassembly.Alsoifwehavelargemass,
wewillneedtoputinmoreenergytostartorstopthemechanism(Itacts
likeflywheel)
MassVs.
Torque
variation
*dissameas
PartsandMaterials:
PART MATERIAL
Cam Ductilecastiron
Links Hotrolledplaincarbonsteel
Supportshafts
Ductile
cast
iron
Hammerhead Mediumcarbonsteel
CamsupportandLinksupport Ductilecastiron
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PartsandfinalDimensions:
CAM LINKS
CAMSUPPORT
LINK
SUPPORT
LINK
SUPPORTSHAFT
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BASE CAMSUPPORTSHAFTHAMMERHEAD
CompleteCADmodeloftheMechanism(IncludingFeedingmechanism):
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SCOPEOFIMPROVEMENT:
o DesignofCam:Improveddesignofcamtomaketheforcesinvolvedinliftingthehammerheadconstant
oProductivity:
Productivity
can
be
increased
by
increasing
the
size
of
product
sothatitcanaccommodatemorenumberofcamsandhammerheadsto
increasethenumberofstonescrushingataninstant
o FeedingMechanism:Implementingthefeedingmechanism(AsshowninCADmodel)
SUGGESTIONSANDCRITICS:
o Multipleuseofproductwithmodificationindesignbyreplacinghammerwithaxeforwoodcutting.
o Manufacturingcouldhavebeendoneinbetterway.o AttachmentofCamtoshaftcouldhavebeendonethroughakeyrather
thanwelding.
o IntegrationwithHumotorandincorporatingfeedingmechanism.
REFERENCES:
1. https://www.youtube.com/watch?v=gD6d4hyLNNs2. MachineDesignbyRobertL.Norton3. http://www.efunda.com/materials/alloys/alloy_home/steels_properties.cf
m