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RobotendeffectorFromWikipedia,thefreeencyclopedia
Inrobotics,anendeffectoristhedeviceattheendofaroboticarm,designedtointeractwiththeenvironment.Theexactnatureofthisdevicedependsontheapplicationoftherobot.
Inthestrictdefinition,whichoriginatesfromserialroboticmanipulators,theendeffectormeansthelastlink(orend)oftherobot.Atthisendpointthetoolsareattached.Inawidersense,anendeffectorcanbeseenasthepartofarobotthatinteractswiththeworkenvironment.Thisdoesnotrefertothewheelsofamobilerobotorthefeetofahumanoidrobotwhicharealsonotendeffectorstheyarepartoftherobot'smobility.
Endeffectorsmayconsistofagripperoratool.Whenreferringtoroboticprehensiontherearefourgeneralcategoriesofrobotgrippers,theseare:[1]
1. Impactivejawsorclawswhichphysicallygraspbydirectimpactupontheobject.2. Ingressivepins,needlesorhackleswhichphysicallypenetratethesurfaceoftheobject(usedin
textile,carbonandglassfibrehandling).3. Astrictivesuctionforcesappliedtotheobjectssurface(whetherbyvacuum,magnetoor
electroadhesion).4. Contigutiverequiringdirectcontactforadhesiontotakeplace(suchasglue,surfacetensionor
freezing).
Theyarebasedondifferentphysicaleffectsusedtoguaranteeastablegraspingbetweenagripperandtheobjecttobegrasped.[2]Industrialgripperscanbemechanical,themostdiffusedinindustry,butalsobasedonsuctionoronthemagneticforce.Vacuumcupsandelectromagnetsdominatetheautomotivefieldandinparticularmetalsheethandling.Bernoulligrippersexploittheairflowbetweenthegripperandthepartthatcausesaliftingforcewhichbringsthegripperandpartcloseeachother(i.e.theBernoulli'sprinciple).Bernulligrippersareatypeofcontactlessgrippers,namelytheobjectremainsconfinedintheforcefiledgeneratedbythegripperwithoutcomingintodirectcontactwithit.BernoulligripperareadoptedinPhotovoltaiccellhandlinginsiliconwaferhandlingbutalsointextileorleatherindustry.Otherprinciplesarelessusedatthemacroscale(partsize>5mm),butinthelasttenyearstheydemonstratedinterestingapplicationsinmicrohandling.Someofthemarereadyofspreadingouttheiroriginalfield.Theotheradoptedprinciplesare:ElectrostaticgrippersandvanderWaalsgrippersbasedonelectrostaticcharges(i.e.vanderWaals'force),capillarygrippersandcryogenicgrippers,basedonliquidmedium,andultrasonicgrippersandlasergrippers,twocontactlessgraspingprinciples.Electrostaticgrippersarebasedonchargedifferencebetweenthegripperandthepart(i.e.electrostaticforce)oftenactivatedbythegripperitself,whilevanderWaalsgrippersarebasedonthelowforce(stillelectrostatic)duetotheatomicattractionbetweenthemoleculesofthegripperandthoseoftheobject.Capillarygrippersusethesurfacetensionofaliquidmeniscusbetweenthegripperandtheparttocenter,alignandgraspthepart,cryogenicgrippersfreezeasmallamountofliquidandtheresultingiceguaranteesthenecessaryforcetoliftandhandletheobject(thisprincipleisusedalsoinfoodhandlingandintextilegrasping).Evenmorecomplexareultrasonicbasedgrippers,wherepressurestandingwavesareusedtoliftupapartandtrapitatacertainlevel(exampleoflevitationarebothatthemicrolevel,inscrewandgaskethandling,andatthemacroscale,insolarcellorsiliconwaferhandling),andlasersourcethatproducesapressureabletotrapandmovemicropartsinaliquidmedium(mainlycells).Thelasergripperareknownalsoaslasertweezers.
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Aparticularcategoryoffriction/jawgripperaretheneedlegrippers:theyarecalledintrusivegrippersandexploitsbothfrictionandformclosureasstandardmechanicalgrippers.
Themostknownmechanicalgrippercanbeoftwo,threeorevenfivefingers.
Theendeffectorsthatcanbeusedastoolsservevariouspurposes,suchasspotweldinginanassembly,spraypaintingwhereuniformityofpaintingisnecessary,andforotherpurposeswheretheworkingconditionsaredangerousforhumanbeings.Surgicalrobotshaveendeffectorsthatarespecificallymanufacturedforthepurpose.
Contents
1Mechanismofgripping1.1Shapeofthegrippingsurface1.2Forcerequiredtogriptheobject
2Examples3Seealso4References
Mechanismofgripping
Acommonformofroboticgraspingisforceclosure.[3]
Generally,thegrippingmechanismisdonebythegrippersormechanicalfingers.Generallyonlytwofingergrippersareusedforindustrialrobotsastheytendtobebuiltforspecifictasksandcanthereforebelesscomplex.
Thefingersarealsoreplaceablewhetherornotthegripperitselfisreplaced.Therearetwomechanismsofgrippingtheobjectinbetweenthefingers(forthesakeofsimplicity,thefollowingexplanationsconsideronlytwofingergrippers).
Shapeofthegrippingsurface
Theshapeofthegrippingsurfaceofthefingerscanbechosenaccordingtotheshapeoftheobjectsthataretobemanipulated.Forexample,ifarobotisdesignedtoliftaroundobject,thegrippersurfaceshapecanbeaconcaveimpressionofittomakethegripefficient,orforasquareshapethesurfacecanbeaplane.
Forcerequiredtogriptheobject
Thoughtherearenumerousforcesactingoverthebodythathasbeenliftedbytheroboticarm,themainforceactingthereisthefrictionalforce.Thegrippingsurfacecanbemadeofasoftmaterialwithhighcoefficientoffrictionsothatthesurfaceoftheobjectisnotdamaged.Theroboticgrippermustwithstandnotonlytheweightoftheobjectbutalsoaccelerationandthemotionthatiscausedduetofrequentmovementoftheobject.Tofindouttheforcerequiredtogriptheobject,thefollowingformulaisused
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Anexampleofabasicforceclosureendeffector
Aspotweldingendeffector
Alaserweldingendeffector
where:
istheforcerequiredtogriptheobject,isthecoeffecientoffriction,isthenumberoffingersinthegripperandistheweightoftheobject.
Buttheaboveequationisincomplete.Thedirectionofthemovementalsoplaysanimportantroleoverthegrippingoftheobject.Forexample,whenthebodyismovedupwards,againstthegravitationalforce,theforcerequiredwillbemorethantowardsthegravitationalforce.Hence,anothertermisintroducedandtheformulabecomes:
Here,thevalueof shouldnotbetakenastheaccelerationduetogravity.Infact,here standsformultiplicationfactor.Thevalueof rangesfrom1to3.Whenthebodyismovedinthehorizontaldirectionthenthevalueistakentobe2,whenmovedagainstthegravitationalforcethen3andalongthegravitationalforce,i.e.,downwards,1.
Examples
Theendeffectorofanassemblylinerobotwouldtypicallybeaweldinghead,orapaintspraygun.Asurgicalrobot'sendeffectorcouldbeascalpelorotherstoolsusedinsurgery.Otherpossibleendeffectorsaremachinetools,likeadrillormillingcutters.Theendeffectoronthespaceshuttlesroboticarmusesapatternofwireswhichcloseliketheapertureofacameraaroundahandleorothergraspingpoint.
Examplesofendeffectors
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Arepairandobservationendeffectorinuseinspace(Canadarm2)
Ahighlysophisticatedattemptatreproducingthehumanhandforceclosureendeffector
Seealso
Grapple(tool)TongsShadowHand
References1. 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,Graspingdevicesandmethodsinautomatedproductionprocesses,CIRPAnnalsManufacturingTechnology,Volume63,Issue2,2014,Pages679701,ISSN00078506,http://dx.doi.org/10.1016/j.cirp.2014.05.006.
3. "RoboticsGraspingandForceclosure"(http://ipvs.informatik.unistuttgart.de/mlr/marc/teaching/11Robotics/11grasping.pdf)(PDF).pdf.FUBerlin.Retrieved20140320.
Koren,Y.(1985).Roboticsforengineers.McGrawHill.ISBN0070353999
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Categories: Roboticmanipulation
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