【机器人系列】sensing for robotics and control课件

SensingforRoboticsandControl ME4135R R Lindeke GeneralIdeasaboutSensors Sensoraretrulysystems Sensorssystemsconsistofthreeseparableideas Informationalsources physicallymeasurabledatasources lightbeams audiobeams electricalfields etc Detectorareas DevicesthatreacttochangesintheinformationalsourcesDataInterpreters devices hardorsoftbased thatconvertinformationalchangesintousefulinformation SensorTopics PositionalControlSensingKinesethicSensingResolversAbsoluteEncodersIncrementalEncodersEnvironmentalSensorsContactPointFieldSensorsProximity typicallysinglepointRemoteSinglePointFieldSensors KinesethicSensing Thesesensorsprovidefeedbackinformationtothejoint linkcontrollers servoinformation TheyuseanalogordigitalinformationalresponsesWewillexplore3generallyusedtypes ResolversAbsoluteEncodersIncrementalEncoders Resolvers OperatingprincipleisthatachargedrotatingshaftwillinducevoltageonstationarycoilsSecondaryVoltagesarerelatedtoPrimaryvoltageasSin andCos ratiosoftheprimaryfieldvoltage ResolverIdeas Typicallyweuse2statorsone notshown mountednormaltoanaxisthatis90 awayfromtheonethruWindingA Resolvers cont PositionisdeterminedforcomputingstatorratioWindingAcarriesSin signalWindingBcarriesCos signalA B tan soShaftposition Atan2 B Reading A Reading ofinterest ResolverIssues ThesedevicesaresusceptibletoElectricalNoise mustbehighlyshieldedUsuallyusegearingtoimproveresolutionTypicallyareexpensivebutveryruggedforuseinharsh shockmotion environments OpticalEncoderPositionalSensors BasedonPhotoelectricsource receiverpairsLooksforchangeofstateaschangingreceiversignallevel binaryswitching UsesacarefullydesigneddiskwithclearandopaquepatchestocontrollightfallingonafixedsensorasdiskrotatesCanbemade absolute withseveralpairsofemitters receiversorIncrementalwith2 outofphase photosensors OpticalServoMeasurementSystems AbsoluteEncodersUseGlassDiskmarkedforpositionalresolutionReaddigitalwords 0010111011 atreceivertorepresentshaftpositionCommonlyAvailablewithupto16bitsofinformation 216 toconvertintopositionalresolution OperatingPrinciple Zdcvkpsdjfpsdjfgoipsdjfg oadgn oiardfgnd oikrjghdar okgjnsldkfgknllkknresffzsdfsdfkjfksdf kkjnfllll AbsoluteEncoders opticaldisks AbsoluteEncoderVariations 8bit ComparingNaturalBinarytoGrayCode NaturalBinarygiveactualpositionwhenreadActualpositionisknownw oanalysisGraycodeisdesignedsoonlyonebitchanges atatime WhereBitchangeissubjecttopositionalerrorsaslight bleeds aroundpatchedgesGraycodesare therefore lesserrorprone butrequirean intelligentconverter togiveactualshaftposition UsingAbsoluteEncodersResolution ABSfor 5liner 360 25 360 32 11 25 ToImproveResolution AddGearingtoshaft encodercouplingNewResolutionis Increase ofLines thisincreasescomplexityandcostoftheencoder canbeasignificantcostincrease AbsoluteEncoderfor0 18 Resolution IncrementalEncoders Thisdevicesuse3pairsofEmitter receiversTwoareforpositionalresolution thethirdisa calibrator markingrotationalstartpoint Sinewaveisobservedduetoleakage lightbleeding aroundopaquepatches IncrementalEncoders Thepositionaldetectoruseswhatiscalled Quadrature techniquestolookatthechangingstateofthe2 bitsreportingpositionforeachopaque clearpatchontheopticaldisk IncrementalEncoders Noticethe squarewave quadraturesignalstheyareoffsetby phase Eachpatchresolvesinto22or4positions Withouthardwarechange resolutionisafunctionofthenumberofpatches orlines IncrementalEncoders For500lineInc encoders resolution 18 w ogearing Considera500 Line incrementalencoder ComparingAbsoluteandIncrementalEncorders IncrementalareusuallycheaperforsamelevelofresolutionAbsoluteareabletoprovidepositionalinformationatanytimeunderpowerIncrementalmustbehomedafterpowerlosstorecalibratecountnumbersComparedtoresolvers encodersarefragilesomustbeshockprotectedduringoperation EnvironmentalSensors Thesesensorsprovide codedecisionmaking powertotheManipulatorThesesensorscanbesimpleSinglepointdevices Simpledevicestypicallytriggeryes nodecisionswithswitchchangesThesesensorscanbecomplex2 Darray oreven3 Dfield devicesTypicallythereceiversarecomplexarraysThedatainterpretersaresophisticatedsoftwareandhardwaredevicesTheycanadd intelligence fordecision makingbythemanipulator ContactSensors ForceandDeflectionSensing ForceSensors Measurepressureforgripping directorindirectMeasuredeflectionduringcontact typicalofindirectcontactsensing ContactSensing IndirectcontactsensorsuseStrainGages andHooke sLaw Stress E Strain Thestraingageisaresistivedevicethatexhibitsachangeinresistanceduetochangesinshape lengthorwidth TheStrainGageismountedintoacarefullybuilt andcalibrated Wheatstonebridgesmallchangestothestraingagesresistance observedwhileusingahighlylinearvoltagesource arecalibratedagainstobserveddeflectionThis bar deflectionisstrainandmultiplyingthestraintimesthebar smodulusofelasticityyieldsstressandhenceappliedforce Stress Force Areabar ContactSensing Othercontactsensorare DirectReading Thesedevicesusethepiezoelectricprinciple effect ofthesensormaterialPiezoelectriceffectstatesthatincertainmaterial quartzandsomesilicates appliedforces dynamically willcauseaminute butmeasurable flowofelectronsalongthesurfaceofthecrystalbasedondi polardisruptionduetoshapechangeThisflowismeasureasa Nano current TheCurrentislinearized amplifiedandmeasuredagainstacalibratedforce ContactSensing Asecondgeneraltypewouldbetheclassof Micro Switches LikeattheendoftheConveyorintheS100cellTypically appliedforcesdirectlymoveacommoncontactbetweenNCandNOcontactpoints ExamplesofMicro Switches OneDirectionalReedSwitch Omni DirectionalReedSwitch RollerContactSwitch Etc etc etc TactileSensors feelerarrays PotentialAdvantagesofTactileSensors Theygeneratefarfewerdatabits comparedtovisualarrays leadingtosimplerinterpretationanalysisCollectionismorereadilycontrolled wecompletelycontrolbackgroundandcontrastThepropertieswemeasureareverycloseto exactly thepropertieswedesire Definingthe Ideal TactileSensor Theymustberuggedandcomplianttofaultsinthemanufacturing operating environmentTheyshouldbe Smart ThatisabletoprocessmostofthedataintoinformationfordecisionmakinglocallytheysendonlyresultstothemaincontrollerResolutionshouldbeontheorderofabout100mils about10 4inch Sensorsshouldrespondtoforcesontheorderofabout5 10gmforce 0 1Nor0 022lbf TactileArrays MachineEquivalentofHumanSkinsUsearraysofmicro sizedswitchesorothermethodstodetectshapesandsizesduetocontactimagesof made Switches TactileArrays Thisdevice measures shapesandsizesbydeterminingwhichofanarrayoftargetpointshavebeenchargedTargetsare charged throughcontactwiththeconductiveElastomerskinandthePC board targets TactileArrays Inthisdevice aseriesofthinrodsarepushedintoanobjectA positive imageoftheobjectisproducedbythedisplacedrodsInmodernsensors displacementofeachrodismeasuredbythedetector interpretersystem thismightbeavisionsystemlocatednormaltothedirectionofcontactapplicationoranLVDTunitateach rod TactileArrays TheAnisotropicconductiverubbersensorTheACRandgoldcontactsurfaceisseparatedwhenunloadedAsloadisappliedcontactpatchesgrowindicatingshapeandsizeofexternalobjectandforcebeingapplied ProximitySensors Devices includingPhotocells CapacitancesensorsandInductivesensors thatcanbeusedinareasthatareneartobutnotdirectlycontactinganobjecttobesensedLikeallsensorstheyusestructuredsignalsources receivechangesofstateintheirenergy sensing fieldsandinterpretthesechangeswithsignalchangestothe outside PhotoSensors Themodernphotosensor intheproximityrange emitsmodulatedlight atinfraredornear infraredwavelengths TheemittersareLED Thereceivers phototransistors are tuned tobesensitivetothewavelengthofthesourceemitterduringthe on stepsinthemodulatedoutputstreamTheinterpretersare typically transistorsthatswitchthepower orground sourceontotheoutputlead DiffuseModePhotosensor Inproximitymode thedeviceislookingforitsownemittedbeamreflectedbacktoitspairedreceiverTheleveloflightfallingonthereceivertotriggerpositiveresponsecanbe tuned tothetaskThesensorscanbetunedto Light Operate or Dark Operate LightoperatemeanspositiveoutputwhenreflectivelightissensedDarkoperatemeanspositiveoutputwhenNOreflectivelightissensed Retro ReflectivePhotosensors Thesedevicesrelyon brokenbeams todetectTheyare typically darkoperate t