斯坦福大学网络视频课程之机器人学

[斯坦福大学网络视频课程之机器人学]Instructor(OussamaKhatib):Okay,let’sgetstarted.Sotoday’smoviesegmentisaboutaspecialactuator.Probablyyousawthisonthefirstlecture,butwewillseesomemoredetails.SothisisaflexibleactuatorthatcomesfromToshiba,andthiswasdevelopedintheearly’90s.Itwaspresentedat1991videoproceedings.[Video]:Thisnewactuatorismadeoffiberre-enforcedrubberandisdrivenpneumaticallyorhydraulically.Ithas3degreesoffreedom;pitch,[inaudible],andstretch,whichareadequateforrobotmechanismssuchasfingers,armsorlegs.Theactuatorhasthreeinternalchambers,andthepressureineachcanbecontrolledindependentlythoughflexibletubes.Therubberiscircularlyre-enforcedwithfibertoreducedeformationintheradialdirection.Theactuatorcanbeflexedineverydirectionbycontrollingthepressureineachchamber.[Inaudible]developedactuatorsranginginsizefrom1millimeterto20millimetersindiameter.Thisistheformulameteractuator.Thedesigniseasilyminiaturizedbecauseofitssimplestructure.Thisisamodifiedversion.Therubberisreinforcedspirallywithfibersothatrotationalmovementispossible.Wecanapplytheseflexiblemicro-actuatorstominiaturerobotmanipulators.Byconnectingthemserially,wegetanarmwithmanydegreesoffreedomandsnakelikemovements.Thisisaprototypeconsistingoftwoactuatorsandaminigripper.Ithas7degreesoffreedomincludingthegripper.Itcanaccomplishdelicatetasks,whichcouldbehandledonlywithgreatdifficultybyconventionalrobots.Constructingminiaturerobotmanipulatorsiseasybecausetheactuatorsalsoactastherobotstructure.Ontheotherhad,combiningtheactuatorsinparallelresultsinamultifingeredrobothand.Theyformadexteroushandwithadelicatetouch.Thisprototypeconsistsoffouractuators,each12millimetersindiameter,andithas12degreesoffreedom.It’sabletohandlefragileandcomplicatedworkwithease,becausetheactuator’sdeformedtosuittheshapeoftheworkpieceitself.Theboltiseasilytightenedwithonlyroughsettingsofthepositionandorientationofthehandbecausetheactuatorshavesuchgoodcompliance.Miniaturerobotswithasofttouchandnoconventionallinkscanbecreatedusingtheseactuators.Peopleseetheuseofflexiblemicro-actuators–Instructor(OussamaKhatib):So,whatdoyouthink?Whatwouldbetheadvantagesofusingpneumaticinthisway?Yes?Student:Probablysaferforalotmoreobjects.Instructor(OussamaKhatib):Safer,yousaid?Sosafetyisavery,veryimportantaspectofthedesignofarobot,especiallyiftherobotisgoingtointeractwithhumans,andyoureallydon’twantthisrobottojustgocrazyandhitandmakealargeimpact.Sosoftactuationusingpneumaticisverygoodbecauseitbasically–it’scompliant,right.Nowanotherimplicationofthefactthatyouareusingpneumaticisthestructureoftherobotisgoingtobelighter,becauseifyouthinkaboutoperatingthesefingerswiththemotorsor[inaudible]Ithinkaboutanarmwithmotors.Youneedtocarrythemotors,youneedtoputgears,youneedalotofstructuretohandleit,sodefinitelythisislighter,safer,moreflexible,compliant,allofthat.Anydisadvantageyoucansee?Yes?Student:Hardertocontrol?Instructor(OussamaKhatib):Yeah.Basically–well,Imean,itdependswhatyouwanttoachieve,butyoucannotexpecttoachievethetasks.Whatkindoftasksyoucannotcontrolwiththistypeofactuation?Student:[Inaudible]motion?Instructor(OussamaKhatib):[Inaudible]motionorfastdynamicsifyouwanttochangedirectionsbecause?Whatistheproblemwiththat[inaudible]?Student:[Inaudible]Instructor(OussamaKhatib):Soyeah,Imeanbasicallytheresponseofthisisgoingtobeslowbecauseyouareusingairpressureandyoucannotpushtheairpressuretoapointwhereyoucanreallygetfastdynamics.Welllateroninthequarterwewillseeaconceptthatcombinesthisideaofusingpneumatic,whichislighttocarry,andwouldresultintoanicelightstructure,combineitwithothertypeofactuationtobringhybridactuationinawaythatcombinesboththeadvantagesofthelightstructureandthefastdynamicsthatweneedtoachieveallthedifferenttasksthatwouldrequiretherobottorespondquickly.Yes?Student:Isthereanygoodwayto[inaudible]that,like,youdon’tactuallyknowwhereyou’re[inaudible]?Instructor(OussamaKhatib):Wellthat[inaudible],youwouldseetherobotwasliketurning.Okay,anyonewouldliketoanswerthisquestion?I’msureyouhaveanidea,but,thisisreallynotfundamentaltotherobotdesign.Itismoreonthefactthatwehavenoexternalfeedbackornotouch,orwearenotusingtheinformationaboutthetouchtorealizethatwealreadyleftthatcontact.Butthisisactuallysomethingthatyoucanaddontopofthedesignto–likewould–Whatkindofsensoryyouwoulduse?Student:Pressuresensor?Instructor(OussamaKhatib):Touchsensor,youmeanlikeyouwanttoknowifyouaretouchingornot?Student:Pressurewouldbe[inaudible]toknowexactlylikehowfaryouare,butwithsomethinglikethat,[inaudible].Like[inaudible]putsomethingthatexactlytellsyouthepositionoftheend.Instructor(OussamaKhatib):Sowecanputasensorattheendthatislocalizedatthetipofthefingerandthenwecanfeelwhetherthesensorisonoroff.Thatisjusttouch,butifyouwantmoreinformationaboutthepressure,youneedasensor,[inaudible]sensorthatwouldmeasure.Butthentheproblem–Imean,nowwecomeintoamuchharderproblem,whichisthefactifyou’reholdingsomething–let’simaginewithyourtwofingersyou’reholdingsomething.Andthereisalwaysslip,soyouneedtomeasuretheslipsothatyoucanapplylargerpressure.Andtodothatyouneedthesortofdynamic[inaudible].