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1、IE458CAMComputerAidedManufacturingPart-5RoboticSystemsIndustrialEngineeringDepartmentKingSaudUniversityContentsWhatisanindustrialrobot?ThebasiccomponentsofarobotPowersourcesforrobotsHydraulicdriveElectricdrivePneumaticdriveRobotsensorsThe hand of a robot(end-effector)RobotMovementandPrecisionTherobo
2、tjointsRobotclassificationPhysicalclassificationControlclassificationRobotreachRobotmotionanalysisandcontrolRobotProgrammingandLanguagesRobotSelectionRobotapplicationsRobotE衬塑复合管涂塑复合管钢塑复合管消防涂覆钢管Whatisanindustrialrobot?The word robot is derived from a satiricalfantasy play,Rossums Universal Robots,wr
3、itten by Karel Capek in1921.In his play,Capek used the word to mean,forcedlabor.TheRoboticsIndustriesAssociation(RIA),formerlyknownastheRoboticsInstituteofAmerica,definesrobotinthefollowingway:An industrial robot is a programmable multi-functional manipulator designed to move materials,parts,tools,o
4、r special devices through variable programmedmotionsfortheperformanceofavarietyoftasks.Anindustrialrobotconsistsofanumberof rigid links connected by joints ofdifferenttypes,controlledandmonitoredby a computer.To a large extent,thephysicalconstructionofarobotresembles a human arm.The linkassemblyment
5、ionedaboveisconnectedtothebody,whichisusuallymountedonabase.Thislink assembly is generally referred to as a robot arm.A wrist isattachedtothearm.Tofacilitategrippingorhandling,a handisattachedattheendofthewrist.Inroboticsterminology,thishand is called an end-effector.Thecomplete motion of the end-ef
6、fector isaccomplishedthroughaseriesofmotionsand positions of the links,joints,andwrist.Atypicalindustrialrobotwithsix-degreesoffreedomisshownin.Figure1ThewidespreaduseofCNCinmanufacturingisidealfortheuseofindustrialrobotstoperformrepetitivetasks.Suchtasksmayinvolvehandlingheavyandsometimeshazardousm
7、aterials.SophisticatedCNCmachiningcenterscancontainpalettechangersandspecialinterfacesthatcaneasilyaccommodateindustrialrobots.Specializedrobotscanassistinbothassemblyandinspectionprocesses.Material handling robots are used in many industries.It may besurprisingtofindsuchrobotsusedeveninthefastfoodi
8、ndustry.Thismaterialhandlingrobotisusedinpreparingpalettesforshipping.Repetitivetasksareidealtobeperformedbysuchmachines.ShownisaFanucM-16iRoboticArmusedinaprecisiongrindingprocessonautomotiveparts.Shown is a FanucRobotarmliftingthree heavy boxes atonce.Inusingrobotics,humansafetyfactorsinsuchataska
9、recompletelyeliminated.This alsogreatly reduces therisksofrepetitivestressinjuriestofactoryworkers.HandlingofdangerousmaterialsisanimportanttaskforRobotstoperform.Thesizeandweightofsomeautomotivepartsmaybetoocumbersome and hazardous for humans to manipulate in certainprocesses.Shownisaroboticarmused
10、inconjunctionwithasmallpunchpress.Togetherthesetwomachinescouldcompriseasmallmanufacturingcell.The use of Robotics in such a setup can greatly reduce thechanceofhumanerrorandinjury.It is now commonplace to find automotive manufacturers usingroboticsinmanyphasesoftheautomotiveassemblyline.Hereanautom
11、otivesprayboothutilizesaFanucRobotarmisusedtopreciselydepositpaintonthiscarbody.Theuseofroboticscanimprovethequalityofcertainmanufacturedgoods.Here a Fanuc S-420W material handling robot is used in theelectronicappliancesindustry.Youwillnoteseveralothersinthebackgroundusedinotherstepsofthemanufactur
12、ingprocess.AnotherFanucA-510robotarmusedinthefoodindustry.Improvedproductivity is an important factor in using robotic equipment isrepetitive production line operations.It can greatly reduce thehumanfactorswhichcanleadtoerrorsandriskofinjury.ShownaretwoFanuchRobotarmsemployedtoperformprecisionweldin
13、gtasks.Thistypeofprocesswouldbeextremelydifficulttoachievebyhumans.THE BASIC COMPONENTS OF A ROBOTThebasiccomponentsofarobotincludethemanipulator,thecontroller,and the power supply sources.The types andattributesofthesecomponentsarediscussednext.Power Sources for Robots Animportantelementofarobotist
14、he drive system.Thedrivesystemsuppliesthepower,whichenablestherobottomove.Thedynamic performance of the robot is determined by the drivesystemadopted,whichdependsmainlyonthetypeofapplicationandthepowerrequirements.The three types of drive systems are generally used for industrial robots:1.Hydraulicd
15、rive2.Electricdrive3.PneumaticdriveHydraulic DriveA hydraulic drive system gives a robot great speed andstrength.Thesesystemscanbedesignedtoactuatelinearorrotationaljoints.Themaindisadvantageofahydraulicsystemisthatitoccupiesfloorspaceinadditiontothatrequiredbytherobot.Problemsofleaks,makingthefloor
16、messy.Because they provide high speed and strength,hydraulicsystemsareadoptedforlargeindustrialrobots.Hydraulicrobotsarepreferredinenvironmentsinwhichtheuseofelectric-driverobotsmaycausefirehazards,forexample,inspraypainting.ElectricDrivesComparedwithahydraulicsystem,Anelectricsystemprovidesarobotwi
17、thlessspeedandstrength.Electricdrivesystemsareadoptedforsmallerrobots.Robotssupportedbyelectricdrivesystemsaremoreaccurate,exhibitbetterrepeatabilityCleanertouse.PneumaticDrivePneumatic drive systems are generally used for smaller robots.These robots,with fewer degrees of freedom,carry out simple pi
18、ck-and-place material-handling operations,such as picking up an object at one location and placing it at another location.These operations are generally simple and have short cycle times.Pneumatic robots are less expensive than electric or hydraulic robots.Most pneumatic robots operate at mechanical
19、ly fixed end points for each axis.A big advantage of such robots is their simple modular construction,using standard commercially available components.This makes it possible for a firm to build its own robots at substantial cost savings for simple tasks such as pick and place,machine loading and unl
20、oading,and so forth.Robotic SensorsThemotionofarobotisobtainedbyprecisemovementsatitsjointsandwrist.Whilethemovementsareobtained,itisimportanttoensurethatthemotionispreciseandsmooth.The drive systems should be controlled by proper means to regulate themotion of the robot.Along with controls,robots a
21、re required to sense some characteristics of their environment.Thesecharacteristicsprovidethefeedbacktoenablethecontrolsystemstoregulatethemanipulatormovementsefficiently.Sensors provide feedback to the control systems and give the robots more flexibility.Sensors such as visual sensors are useful in
22、 the building of more accurate andintelligentrobots.The sensors can be classified in many different ways based on their utility.Inthissectionwediscussafewtypicalsensorsthatarenormallyusedinrobots:Position sensors.Theyareusedtomonitorthepositionofjoints.Range sensors.Rangesensorsmeasuredistancesfroma
23、referencepointtootherpointsofimportance.Velocity sensors.VelocitysensorsareusedtoestimatethespeedwithwhichamanipulatorismovedProximity sensors.ProximitysensorsareusedtosenseandindicatethepresenceofanobjectwithinaspecifieddistanceorspacewithoutanyphysicalcontactThe Hand of a Robot:End-EffectorsTheend
24、-effectors(commonlyknownasrobothand)mountedonthewristenablestherobottoperformspecifiedtasks.Varioustypesofend-effectorsaredesignedforthesamerobottomakeitmoreflexibleandversatile.End-effectors are categorized into two major types:1.Grippers:2.Tools.Grippersaregenerallyusedtograspandholdanobjectandpla
25、ceitatadesiredlocation.Grippers can be classified as:Mechanicalgrippers,Vacuumorsuctioncups,Magneticgrippers,Adhesivegrippers,Hooks,Scoops,Others.Grippersusuallyoperateinjawtypefashionbyhavingfingerswhich either attach to the gripper,or are part of theconstruction,open and close.The attached fingers
26、 can bereplacedwithnewordifferentfingers,allowingforflexibility,seeFigure2.Gripperscanoperatewithtwofingersormore.Figure2Attimes,a robot is required to manipulate a tooltoperformanoperationonaworkpart.Spot-welding tools,arc-welding tools,spray-painting nozzles,and rotating spindles for drilling and
27、grinding are typical examples of tools used as end-effectors.End-effectors-ToolsGripperdesigns:Therearemanyapproaches to gripperdesigns.These Figuresshowsthevariouslinkageswhichresultinpivotingactionforgripping.Robot Movement and PrecisionSpeed of response and stabilityaretwoimportantcharacteristics
28、ofrobotmovement.Speed defineshowquicklytherobotarmmovesfromonepointtoanother.Stability refers to robot motion with the least amount ofoscillation.Agoodrobotisonethatisfastenoughbutatthesametimehasgoodstability.The precision of robot movement is defined by three basic features:1.high resolution2.Accu
29、racy 3.Repeatability1.Spatial ResolutionThe spatial resolution of a robot is the smallest increment of movement into which the robot can divide its work volume.It depends on:thesystems control resolution and the robots mechanical inaccuracies.Thecontrolresolutionisdeterminedbytherobotspositioncontro
30、l system and its feedback measurement system.Thecontrollerdividesthetotalrangeofmovementsforanyparticularjointintoindividualincrementsthatcanbeaddressedinthecontroller.The bit storage capacity of the control memory defines this ability to divide the total range into increments.For a particular axis,
31、the number of separate increments is given by Numberofincrements=2nwherenisthenumberofbitsinthecontrolmemory.EXAMPLE Arobotscontrolmemoryhas8-bitstoragecapacity.Ithastwo rotational joints and one linear joint Determine thecontrolresolutionforeachjoint,ifthelinearlinkcanvaryitslengthfromasshortas0.2m
32、toaslongas1.2m.Solution Control memory=8bitFromtheequationabove,numberofincrements=28=256(a)Totalrangeforrotationaljoints=360Controlresolutionforeachrotationaljoint=360/256=1.40625(b)Totalrangeforlinearjoint=1.2-0.2=1.0mControlresolutionforlinearjoint=1/256=0.003906m=3.906mm2.AccuracyAccuracycanbede
33、finedastheabilityofarobottopositionitswristendatadesiredtargetpointwithinitsreach.Intermsofcontrolresolution,the accuracy can be defined as one-half of the control resolution.3.RepeatabilityRepeatability refers to the robots ability to position its end-effectorsatapointthathadpreviouslybeentaughttot
34、herobot.TherepeatabilityerrordiffersfromaccuracyasdescribedbelowLet point A be the target point as shown in Figure a.Because of thelimitations ofspatial resolution andtherefore accuracy,the programmedpointbecomespointB.The distance between points A and B is a result of the robots limited accuracy du
35、e to the spatial resolution.WhentherobotisinstructedtoreturntotheprogrammedpointB,itreturnstopointC instead.ThedistancebetweenpointsBandCistheresultoflimitationsontherobotsrepeatability.However,therobotdoesnotalwaysgotopointCeverytimeitisaskedtoreturntotheprogrammedpointB.Instead,itformsa cluster of
36、 points.This gives rise to a random phenomenon ofrepeatability errors.Therepeatabilityerrorsaregenerallyassumed to be normally distributed.If the mean error is large,wesaythattheaccuracyispoor.However,if the standard deviation of the error is low,wesaythattherepeatabilityishigh.Wepictoriallyrepresen
37、ttheconceptoflowandhighrepeatabilityaswellasaccuracyinFigureb,c,d,ande.Considerthecenterofthetwoconcentriccircles as the desired target point.The diameter of the inner circlerepresentsthelimitsuptowhichtherobotend-effectorcanbepositionedandconsideredtobeofhighaccuracy.Any point outside the inner cir
38、cle is considered to be of poor or low accuracy.Agroupofcloselyclusteredpointsimplieshighrepeatability,whereasasparselydistributedclusterofpointsindicateslowrepeatability.Figurea.Figure(a)Accuracyandrepeatability;(b),highaccuracyandhighrepeatability;(c)high accuracy and low repeatability;(d)lowaccur
39、acy and high repeatability;(e)low accuracy and lowrepeatability.THE ROBOTIC JOINTSA robot joint is a mechanism that permits relative movement between parts of a robot arm.Thejointsofarobotaredesignedtoenabletherobottomoveitsend-effectorsalongapathfromonepositiontoanotherasdesired.Thebasicmovementsre
40、quiredforthedesiredmotionofmostindustrialrobotsare:Rotational movement.-Thisenablestherobottoplaceitsarminanydirectiononahorizontalplane.Radial movement.Thisenablestherobottomoveitsend-effectorsradiallytoreachdistantpoints.Vertical movement.Thisenablestherobottotakeitsend-effectortodifferentheights.
41、Thesedegreesoffreedom,independentlyorincombinationwithothers,define the complete motion of the end-effector.Thesemotionsareaccomplishedbymovementsofindividualjointsofthe robot aim.The joint movements are basically the same asrelativemotionofadjoininglinks.Dependingonthenatureofthisrelativemotion,the
42、jointsareclassifiedasprismaticorrevolute.Prismaticjointsarealsoknownasslidingaswellaslinearjoints.Theyarecalledprismaticbecausethecrosssectionofthejointisconsideredasageneralizedprism.Theypermitlinkstomoveinalinearrelationship.Revolutejointspermitonlyangularmotionbetweenlinks.Thefivejointtypesare:1.
43、Linear joint(L).Therelativemovementbetweentheinputlinkandtheoutputlinkisalinearslidingmotion,withtheaxesofthetwolinksbeingparallel.2.Orthogonal joint(O).Thisisalsoalinearslidingmotion,buttheinputandoutputlinksareperpendiculartoeachotherduringthemove.3.Rotational joint(R).Thistypeprovidesarotationalr
44、elativemotionofthejoints,withtheaxisofrotationperpendiculartotheaxesoftheinputandoutputlinks.4.Twisting joint(T).Thisjointalsoinvolvesarotarymotion,buttheaxisofrotationisparalleltotheaxesofthetwolinks.5.Revolving joint(V).INthisjointtype,theaxisoftheinputlinkisparalleltotheaxisofrotationofthejoint,a
45、ndtheaxisoftheoutputlinkisperpendiculartotheaxisofrotation.(a)twoformsoflinearjoint-typeL;(b)two forms of orthogonaljoint-typeO;(c)rotationaljoint-typeR;(d)twistingjoint-typeT;(e)revolvingjoint-typeV.Example:A typical robot manipulator can be divided into two sections:Abody-and-armassembly,andAwrist
46、assembly.Thereareusually3degreesoffreedomassociatedwiththebody-and-arm,andeither2or3degreesoffreedomusuallyassociatedwiththewrist.Attheendofthemanipulatorswristisanobjectthatisrelatedtothetaskthatmustbeaccomplishedbytherobot.Forexample,theobjectmightbeaworkpartthatistobeloadedintoamachine,oratooltha
47、tismanipulatedtoperformsomeprocess.Thebody-and-armoftherobotisusedtopositiontheobjectandtherobotswristisusedtoorienttheobject.Toestablishthepositionoftheobject,thebody-and-armmustbecapableofmovingtheobjectinanyofthefollowingthreedirections:1.Verticalmotion(z-axismotion)2.Radialmotion(in-and-outory-a
48、xismotion)3.Right-to-leftmotion(x-axismotionorswivelaboutaverticalaxisonthebase)YawToestablishtheorientationoftheobject,wecandefine3degreesoffreedomforthe robots wrist.The following is one possible configuration for a 3.wristassembly:Roll.This.canbeaccomplishedbyaT-typejointtorotatetheobjectaboutthe
49、armaxis.Pitch.Thisinvolvestheup-and-downrotationoftheobject,typicallydonebymeansofatype Rjoint.Yaw.This involvesright-to-leftrotationof the object,alsoaccomplishedtypicallyusinganR-typejoint.ThesedefinitionsareillustratedinthefollowingTypicalconfigurationofa3-degree-of-freedomwristassemblyshowingrol
50、l,pitch,andyaw.ROBOT CLASSIEFICATION AND ROBOT REACHNormally robots are classified on the basis of their physicalconfigurations.Robots are also classified on the basis of thecontrolsystemsadopted.Classification Based on Physical Configurations Fourbasicconfigurationsareidentified:1.Cartesianconfigur