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IntroductionToRobotics-Lecture14Instructor(OussamaKhatib):Okay.Okay.Let’sgetstarted.Sotoday’svideosegmentisabouttactilesensing.Now,Iwonderwhatisdifficultaboutbuildingtactilesensors;anyonehasanidea?Sowhatistheproblemwithbuildingatactilesensor?Oh,youusedtoseethevideofirst,okay.So,yeah.Student:Doyouneedfunctionstobeableto,Imean,doyouneedaperturbationtobeabletoseewhatyou’retouchingsometimes?Instructor(OussamaKhatib):Well,yeah,sometimesyou,Imean,ahuman–tactilesensingisamazing.Soyouhavethestaticinformation,soifyougrabsomething,nowthewholesurfaceisincontact,andyoucandeterminetheshape,right?Sowhatdoesitmeanintermof,like,designingatactilesensor,justifyouthinkaboutthestaticcase?Student:It’ssoft,malleable.Instructor(OussamaKhatib):Well,youneedsomesoftnessinthethingyouareputting.Thenyouneedtotakethiswholeinformation,whatkindofresolutiondoyouneed,ifyouaretouchingtofeeltheedge?Youneedalotofpixels,right?Sohowcanyoutakethisinformationand–firstofall,howyoudeterminethatinformation;whatkindofproceduredoyou–yes?Student:Well,there’sanelementofpressure,like,howhardyou’re–theaverage–howareyoutouchingonallthesedifferentthings.Instructor(OussamaKhatib):Okay.Soyoucanimagine,maybe,asortofresistiveorcapacitivesensorthatwilldeflectalittlebitandgiveyouthatinformation.Howmanyofthoseyouwouldneed?Youneed,sortof,anarray,right?Sohowlarge,like,let’ssaythisistheendoffactor.I’mtryingtoseeifyoudidthatproblem–you’regoingtohavealotofinformationhere,andyouneedtotakeitback,andyouhavealotofwires;youhaveamatrix,andyou’regoingtohavealotof,basically,informationtotransmit.So,thedesignoftactilesensorsbeingthisproblemofhowwecanputenoughsensors,andhowwecanextractthisinformationandtakeitback.Sotheseguyscameupwithaninterestingidea;hereitis.Thelight,please.[Video]:Anoveltactilesensorusingopticalphenomenonwasdeveloped.Inthetactilesensorsshownhere,lightisinjectedattheedgeofanopticalwaveguidemadeoftransparentmaterialandcoveredbyanelasticrubbercover.Thereisclearancebetweenthecoverandthewaveguide.Theinjectedlightmaintainstotalinternalreflectionatthesurfaceofthewaveguideandisenclosedwithinit.Whenanobjectmakescontactwithit,therubbercoverdepressesandtouchesthewaveguide.Scatteredlightarisesatthepointofcontactduetothechangeofthereflectioncondition.Suchtactileinformationcanbeconvertedintoavisualimage.Usingthisprinciple,aprototypefinger-shapedtactilesensorwithahemisphericalsurfacewasdeveloped.ACCDcameraisinstalledinsidethewaveguidetodetectscatteredlightarisingatthecontactlocationonthesensor’ssurface.TheimagefromtheCCDcameraissenttothecomputer,andthelocationofthescatteredlightisdeterminedbytheimageprocessingsoftware.Usingthisinformation,theobject’spointofcontactonthesensor’ssurfacecanbecalculated.Toimprovethesizeandtheoperationalspeedofthesensor,aminiaturizedversionwasdeveloped.Thehemisphericalwaveguidewithcover,thelightsourceinfraredLED’s,aposition-sensitivedetectorforconvertingthelocationoftheopticalinputintoanelectricsignal,andtheamplifiercircuitwereintegratedinthesensorbody.Thescatteredlightarisingatthepointofcontactistransmittedtothedetectorthroughabundleofopticalfibers.Byprocessingthedetector’selectricsignalbycomputer,itispossibletodeterminethecontactlocationonthesensor’ssurfacein1.5milliseconds.Throughfurtherminiaturization,afingertipdiameterof20millimetershasbeenachievedinthelatestversionofthetactilesensor.Itiscurrentlyplannedtoinstallthistactilesensorinarobotichandwiththeaimofimprovingitsdexterity.Instructor(OussamaKhatib):Okay.Acoolidea,right?Becausenowyou’retakingthisinformation,andtakingitintoavisualimage,andtransmittingtheimage,and,infact,thiswasdonealongtimeago.IbelievetheemperorofJapanwasvisitingthatlaboratory,andhesawthis,andhewasquiteimpressed.Beforestartingthelecture,justwantedtoremindyouthatwearegoingtohavetworeviewsessionsonTuesdayandWednesdaynextweek,andwewill,again,signupfortwogroups.IhopewewillhaveabalancebetweenthosewhoarecomingonTuesdayandWednesday.WewilldothesigningupnextMonday,sothosewhoarenotheretoday,besuretocomeonMondaytosignup,allright?Okay.Lastlecturewediscussedthecontrolledstructure.Weweretalkingstillaboutonedegreeoffreedom,andwearegoingtopursuethatdiscussionwithonedegreeoffreedom.Sowearelookingatthedynamicmodelofamassmovingatsomeacceleration,Xdoubledot,andcontrolledbyaforce,F.SothecontrolofthisrobotisdonethroughthisproportionalderivativecontrollerinvolvingminusKP,XdesiredandminusKV,Xdot.SotheKPisyourpositiongain,andtheKVisyourvelocitygain.Now,ifwetakethisbluecontrollerandmoveittotheleft,theclosedloopbehaviorisgoingtobewrittenasthissecondorderequation,andinthisequation,wecanseethatwehave,sortof,mass,string,dampersystemwhoserestpositionisatthedesiredXDposition.SoKVisyourvelocitygain,andKPisthepositiongain.Now,ifwerewritethisequationbydividingitbyM,wearegoingtobeabletoseewhatclosedloopfrequencywehaveandwhatdampingratiowehave,andeverytime,thelecturetime,thisfinishes.Sowhatisyourclosedloopfrequency?KPisequalto10,andthemassisequalto1;whatistheclosedloopfrequency?Student:Squarerootof10.Instructor(OussamaKhatib):Squarerootof10,andwhatisthedampingr