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RobotendeffectorWikipedia,thefreeencyclopedia

Robotendeffector
FromWikipedia,thefreeencyclopedia

Inrobotics,anendeffectoristhedeviceattheendofaroboticarm,designedtointeractwiththe
environment.Theexactnatureofthisdevicedependsontheapplicationoftherobot.
Inthestrictdefinition,whichoriginatesfromserialroboticmanipulators,theendeffectormeansthelast
link(orend)oftherobot.Atthisendpointthetoolsareattached.Inawidersense,anendeffectorcanbe
seenasthepartofarobotthatinteractswiththeworkenvironment.Thisdoesnotrefertothewheelsofa
mobilerobotorthefeetofahumanoidrobotwhicharealsonotendeffectorstheyarepartoftherobot's
mobility.
Endeffectorsmayconsistofagripperoratool.Whenreferringtoroboticprehensiontherearefourgeneral
categoriesofrobotgrippers,theseare:[1]
1. Impactivejawsorclawswhichphysicallygraspbydirectimpactupontheobject.
2. Ingressivepins,needlesorhackleswhichphysicallypenetratethesurfaceoftheobject(usedin
textile,carbonandglassfibrehandling).
3. Astrictivesuctionforcesappliedtotheobjectssurface(whetherbyvacuum,magnetoor
electroadhesion).
4. Contigutiverequiringdirectcontactforadhesiontotakeplace(suchasglue,surfacetensionor
freezing).
Theyarebasedondifferentphysicaleffectsusedtoguaranteeastablegraspingbetweenagripperandthe
objecttobegrasped.[2]Industrialgripperscanbemechanical,themostdiffusedinindustry,butalsobased
onsuctionoronthemagneticforce.Vacuumcupsandelectromagnetsdominatetheautomotivefieldandin
particularmetalsheethandling.Bernoulligrippersexploittheairflowbetweenthegripperandthepartthat
causesaliftingforcewhichbringsthegripperandpartcloseeachother(i.e.theBernoulli'sprinciple).
Bernulligrippersareatypeofcontactlessgrippers,namelytheobjectremainsconfinedintheforcefiled
generatedbythegripperwithoutcomingintodirectcontactwithit.Bernoulligripperareadoptedin
Photovoltaiccellhandlinginsiliconwaferhandlingbutalsointextileorleatherindustry.Otherprinciples
arelessusedatthemacroscale(partsize>5mm),butinthelasttenyearstheydemonstratedinteresting
applicationsinmicrohandling.Someofthemarereadyofspreadingouttheiroriginalfield.Theother
adoptedprinciplesare:ElectrostaticgrippersandvanderWaalsgrippersbasedonelectrostaticcharges(i.e.
vanderWaals'force),capillarygrippersandcryogenicgrippers,basedonliquidmedium,andultrasonic
grippersandlasergrippers,twocontactlessgraspingprinciples.Electrostaticgrippersarebasedoncharge
differencebetweenthegripperandthepart(i.e.electrostaticforce)oftenactivatedbythegripperitself,
whilevanderWaalsgrippersarebasedonthelowforce(stillelectrostatic)duetotheatomicattraction
betweenthemoleculesofthegripperandthoseoftheobject.Capillarygrippersusethesurfacetensionofa
liquidmeniscusbetweenthegripperandtheparttocenter,alignandgraspthepart,cryogenicgrippers
freezeasmallamountofliquidandtheresultingiceguaranteesthenecessaryforcetoliftandhandlethe
object(thisprincipleisusedalsoinfoodhandlingandintextilegrasping).Evenmorecomplexare
ultrasonicbasedgrippers,wherepressurestandingwavesareusedtoliftupapartandtrapitatacertain
level(exampleoflevitationarebothatthemicrolevel,inscrewandgaskethandling,andatthemacro
scale,insolarcellorsiliconwaferhandling),andlasersourcethatproducesapressureabletotrapand
movemicropartsinaliquidmedium(mainlycells).Thelasergripperareknownalsoaslasertweezers.

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Aparticularcategoryoffriction/jawgripperaretheneedlegrippers:theyarecalledintrusivegrippersand
exploitsbothfrictionandformclosureasstandardmechanicalgrippers.
Themostknownmechanicalgrippercanbeoftwo,threeorevenfivefingers.
Theendeffectorsthatcanbeusedastoolsservevariouspurposes,suchasspotweldinginanassembly,
spraypaintingwhereuniformityofpaintingisnecessary,andforotherpurposeswheretheworking
conditionsaredangerousforhumanbeings.Surgicalrobotshaveendeffectorsthatarespecifically
manufacturedforthepurpose.

Contents
1Mechanismofgripping
1.1Shapeofthegrippingsurface
1.2Forcerequiredtogriptheobject
2Examples
3Seealso
4References

Mechanismofgripping
Acommonformofroboticgraspingisforceclosure.[3]
Generally,thegrippingmechanismisdonebythegrippersormechanicalfingers.Generallyonlytwo
fingergrippersareusedforindustrialrobotsastheytendtobebuiltforspecifictasksandcanthereforebe
lesscomplex.
Thefingersarealsoreplaceablewhetherornotthegripperitselfisreplaced.Therearetwomechanismsof
grippingtheobjectinbetweenthefingers(forthesakeofsimplicity,thefollowingexplanationsconsider
onlytwofingergrippers).

Shapeofthegrippingsurface
Theshapeofthegrippingsurfaceofthefingerscanbechosenaccordingtotheshapeoftheobjectsthatare
tobemanipulated.Forexample,ifarobotisdesignedtoliftaroundobject,thegrippersurfaceshapecan
beaconcaveimpressionofittomakethegripefficient,orforasquareshapethesurfacecanbeaplane.

Forcerequiredtogriptheobject
Thoughtherearenumerousforcesactingoverthebodythathasbeenliftedbytheroboticarm,themain
forceactingthereisthefrictionalforce.Thegrippingsurfacecanbemadeofasoftmaterialwithhigh
coefficientoffrictionsothatthesurfaceoftheobjectisnotdamaged.Theroboticgrippermustwithstand
notonlytheweightoftheobjectbutalsoaccelerationandthemotionthatiscausedduetofrequent
movementoftheobject.Tofindouttheforcerequiredtogriptheobject,thefollowingformulaisused
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where:
istheforcerequiredtogriptheobject,
isthecoeffecientoffriction,
isthenumberoffingersinthegripperand
istheweightoftheobject.
Buttheaboveequationisincomplete.Thedirectionofthemovementalsoplaysanimportantroleoverthe
grippingoftheobject.Forexample,whenthebodyismovedupwards,againstthegravitationalforce,the
forcerequiredwillbemorethantowardsthegravitationalforce.Hence,anothertermisintroducedandthe
formulabecomes:

Here,thevalueof shouldnotbetakenastheaccelerationduetogravity.Infact,here standsfor

Examples
Theendeffectorofanassemblylinerobotwouldtypicallybeaweldinghead,orapaintspraygun.A
surgicalrobot'sendeffectorcouldbeascalpelorotherstoolsusedinsurgery.Otherpossibleendeffectors
aremachinetools,likeadrillormillingcutters.Theendeffectoronthespaceshuttlesroboticarmusesa
patternofwireswhichcloseliketheapertureofacameraaroundahandleorothergraspingpoint.
Examplesofendeffectors

Anexampleofabasic
forceclosureendeffector

https://en.wikipedia.org/wiki/Robot_end_effector

Aspotweldingend
effector

Alaserweldingend
effector

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Arepairandobservation
endeffectorinusein
space(Canadarm2)

Ahighlysophisticated
attemptatreproducingthe
humanhandforceclosure
endeffector

Seealso
Grapple(tool)
Tongs
ShadowHand

References
1. Monkman,G.J.Hesse,S.Steinmann,R.Schunk,H.(2007).RobotGrippers.WileyVCH.p.62.ISBN978
3527406197.
2. Fantoni,G.,Santochi,M.,Dini,G.,Tracht,K.,ScholzReiter,B.,Fleischer,J.,Lien,T.K.,Seliger,G.,
Reinhart,G.,Franke,J.,Hansen,H.N.,Verl,A.,2014,Graspingdevicesandmethodsinautomatedproduction
processes,CIRPAnnalsManufacturingTechnology,Volume63,Issue2,2014,Pages679701,ISSN0007
8506,http://dx.doi.org/10.1016/j.cirp.2014.05.006.
3. "RoboticsGraspingandForceclosure"(http://ipvs.informatik.unistuttgart.de/mlr/marc/teaching/11Robotics/11
grasping.pdf)(PDF).pdf.FUBerlin.Retrieved20140320.

Koren,Y.(1985).Roboticsforengineers.McGrawHill.ISBN0070353999
Retrievedfrom"https://en.wikipedia.org/w/index.php?title=Robot_end_effector&oldid=667176754"
Categories: Roboticmanipulation
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