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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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