Grippers in Motion - the Fascination of Automated Handling Tasks - Wolf Part 8 pdf

sliding grip a) external sliding grip b) internal sliding grip c) centering grip TCP = tool center p oint a) b) c) TCP TCP 90° Getting To Grips With Handling Tasks 3 For applications requiring very high cycle times the workpiece is preferably picked up on the fly. This type of gripping is characterized by the effort to pick the workpiece up without letting the handling system move into a set position for the pick operation. The type of movement is generated by “overlapping” positions and is possible only if the workpiece has degrees of freedom along the movement direction. As illustrated in figure 3.22, proper gripping strategies can be developed for picking workpieces up safely. By means of these strategies the workpiece can be well positioned within the gripper without having to resort to expensive sensor technology. In addi- tion to using gripper movements to adjust workpieces for the pick operation, specially selected gripper jaws can help centering the workpiece. This type of pick operation requires the workpiece to be positioned at a stop ring which supports positioning with the relative move- ment. The gripper jaws can be used as stop rings as well. Gripping Accuracy Control As detailed above precise presentation of the workpiece and accu- rate gripping during pick operations are essential for reliable place operations. Any errors in a pick operation can only be compensated by appropriate gripper or handling system sensors at a later stage. With smaller tolerances picking errors can be compensated by feed rails. Three reasons for faulty positioning of the workpiece are distinguished: Figure 3.22 Gripping strategies 142 1. faulty positioning of the workpiece before pick operation 2. faulty positioning of the gripper in relation to the workpiece (handling system error) 3. workpiece slipping within the gripper at gripper jaw closing or caused by faulty contact surface combination or gripping forces Faulty positioning of the workpiece might be due to faulty syn- chronization of the gripper in relation to workpiece movement on a conveyor or workpiece support as described above. Other reasons could be faulty clamping devices or hazardous materials between clamping device and workpiece. In any case it is important to pay attention to the degrees of free- dom the workpiece has while being gripped, i .e. if the workpiece is still in the preparatory position when the gripper jaws close or if it is able to move within certain degrees of freedom. If the workpiece cannot be adjusted, faulty positioning of workpieces may cause premature wear or damage of gripper or handling system in the long run. The same applies to faulty positioning of the gripper in relation to the workpiece. Integrating a mechanical collision and overload protection unit between gripper and handling system is one way to avoid strain or damage (see Chapter 4). This protection measure can be applied in case of workpiece tolerances leading to bracings. 143 'ETTING4O'RIPS7ITH(ANDLING4ASKS  'RIPPING4AKES4IME !UTOMATEDSYSTEMSAREEITHERDESIGNEDASSELFSUPPORTINGSYSTEMS ORWITHADIRECTLINKTOEXISTINGPRODUCTIONFACILITIES)NTHISRESPECT THEYARENOTDIRECTLYINTEGRATEDINTOTHEMATERIALSmOW )FDIRECTLINKAGETOPREORPOSTOPERATINGFACILITIESISSELECTEDEACH WORKPIECEFEDINTOTHEHANDLINGPROCESSISDUEFORFURTHERUSE ORPROCESSING4HEDISTANCEBETWEENPICKANDPLACESTATIONIS EFFECTEDWITHONEORSEVERALWORKPIECESWITHINAGRIPPER %ACHWORKPIECEDELIVEREDINTHEDESIREDQUALITYANDCORRECTORDER STATUSISSUPPOSEDTOBEMOVED&ORTHESESITUATIONSHANDLINGTIME PERWORKPIECEISESSENTIAL+INETICDEVICESWITHTHEIRCHARACTERISTICS INTERMSOFWORKSPACEANDVELOCITYSEE#HAPTERAREOFGREAT IMPORTANCEOPENINGANDCLOSINGTIMESOFGRIPPERSALSOMATTERFOR CYCLETIME &IGURE$IRECTLINKAGEOFWORKPIECEINPUTWITHWORKPIECEOUTPUTINAPLACEPOSITION                 3ELFSUPPORTINGSYSTEMSORINDIRECTLINKAGESAREDECOUPLEDFROM MATERIALSmOWBYBUFFERSORMAGAZINES4HEWORKPIECESARETAKEN FROMSTORAGETOAPROCESSINGSTATIONWHERETHEYAREMANIPULATEDOR REORIENTEDANDSUBSEQUENTLYPLACEDFORSTORAGEAGAIN4HEMATERI ALSmOWMUSTBEDISTINGUISHEDINASFARASCYCLETIMESARESELECTED WITHTHERESULTTHATTHEHANDLINGOPERATIONMUSTWAITFORTHEPRO CESSINGMACHINE3WIVELUNITSAREFREQUENTLYEMPLOYEDTOAVOID IDLINGDURINGWORKPIECECHANGEINTHEPROCESSINGMACHINE +INETICDEVICESWHICHCARRYTHEGRIPPERSAREUSUALLYHIGHTECHCOM PONENTSWHICHAREMUCHMOREEXPENSIVETHANTHEGRIPPERS!SIX AXISROBOTFOREXAMPLECOSTSFARMORETHANTHEGRIPPERPERFORMING THEPICKOPERATION&ORMOSTINVESTMENTSINAUTOMATIONPROlTABILITY CALCULATIONINCLUDESHANDLINGOUTPUTPERMINUTEIEAROBOTWILL ONLYPAYIFITISABLETOMOVEAMINIMUMNUMBEROFWORKPIECESPER MINUTE4HESEECONOMICCONCERNSLEADSFROMTHEPRINCIPLEOFSINGLE GRIPPINGTOTHEPRINCIPLEOFMULTIPLEGRIPPINGTOREDUCECYCLETIME PERWORKPIECE /NEBENElTOFSINGLEGRIPPINGISTHATGRIPPERDESIGNDOESNOTNEED TOBEVERYSOPHISTICATED!TWOlNGERORTHREElNGERGRIPPERWILLBE SUFlCIENT#OMBINEDWITHAMULTIAXISROBOTTHEGRIPPERCANmEXIBLY ENCLOSEWORKPIECESBECAUSEGRIPPERPOSITIONINGCANBECOMBINED WITHMOSTDIVERSEWORKPIECEORIENTATIONS)NTERMSOFWORKPIECE POSITIONINGINTHEWORKSPACETHEROBOTCANMAKEFULLUSEOFITS mEXIBILITY7ORKPIECEORIENTATIONISNOTIMPORTANTFORRELIABLEPICK OPERATIONSINTHISCASE &IGURE-ATERIALSmOWFORSELFSUPPORTINGSYSTEMWITHOUTSWIVELUNIT         'ETTING4O'RIPS7ITH(ANDLING4ASKS  4HESAMEAPPLIESTOPLACEOPERATIONS0ROGRAMMINGANDPUTTING SYSTEMSINTOOPERATIONISSTREAMLINED)NTERFERINGEDGESARE REDUCEDBYCOMPACTGRIPPERCONSTRUCTIONANDLOWNUMBEROF GRIPPERlNGERS 4HEDISADVANTAGEOFTHESINGLEGRIPPERISTHATPERFORMANCEIS DIRECTLYCOUPLEDWITHCYCLETIMEOFTHEAXESINUSE$URINGONE CYCLEFROMPICKTOPLACEPOSITIONJUSTONEWORKPIECECANBETRANS  PORTEDATATIME!CCORDINGTOWORKPIECETYPEANDAPPLICATIONIE WORKSPACEANDNUMBEROFORIENTATIONSTODAY{SROBOTKINEMATICS OPERATEATAREGULARCYCLETIMEBETWEENTWOANDTENSECONDSPER WORKPIECE6ERYFEWSPECIALKINETICDEVICESDESIGNEDFORHIGHSPEED ANDLOWWEIGHTHANDLINGTASKSCOPEWITHCYCLETIMESFARBELOW THESERATES5SINGPARALLELKINEMATICSROBOTSEQUIPPEDWITHCARBON lBREARMSFOREXAMPLEAREABLETOREACHUPTOGACCELERATION WHICHEQUALSATENFOLDACCELERATIONOFTHEEARTHANDTHUSKEEP CYCLETIMESPOSSIBLYUNDERSECONDSPERWORKPIECE 4HEPRINCIPLEOFMULTIPLEGRIPPINGBOOSTSTHEPERFORMANCEOF AKINETICDEVICE&IGURESHOWSTHATADUALGRIPPERALREADY REDUCESCYCLETIMEBYPERCENTCOMPAREDTOTHESINGLEGRIPPERAT IDENTICALPICKINGANDPLACINGTIMES  &IGURE%FlCIENCYINCREASEBYTHEPRINCIPLEOFMULTIPLEGRIPPING   'ETTING4O'RIPS7ITH(ANDLING4ASKS  4HISBENElTPAYSBECAUSETHENUMBEROFKINETICDEVICESANDTHEIR PERIPHERIESISREDUCEDANDWORKSPACESAVED4HESECOSTSAVINGS HOWEVERAREPARTLYOFFSETBYCONSIDERABLEEXPENSESFORPICKAND PLACESTATIONS3UBSTANTIALPREPARATIONANDIMPLEMENTATIONCOSTS MUSTBEACCOUNTEDFORBECAUSETHEWORKPIECESNEEDTOBEALIGNED INGROUPSFORMULTIPLEGRIPPING 4HEPROCESSOFALIGNINGTHEWORKPIECEINGROUPSFORAMULTIPLE GRIPPERREQUIRESSUBSTANTIALINVESTMENTINTOTHEPERIPHERYOFKINETIC DEVICES!SILLUSTRATEDTHEWORKPIECESMUSTlRSTBEALIGNEDINAROW WITHTHEAPPROPRIATEDISTANCETOEACHOTHERTOBEREADYFORTHEPICK OPERATION 3OMETIMESTHETASKISNOTLIMITEDTOMEREREPOSITIONINGOFTHE WORKPIECES4HEALIGNMENTPATTERNFORPLACINGTHEWORKPIECESMAY BEDIFFERENTTOTHEONEATTHEPICKSTATIONWHICHMAKESMULTIPLE GRIPPINGMOREDIFlCULT&ORMANYAPPLICATIONSANOPTIONTOCHANGE THEDISTANCEBETWEENWORKPIECESWITHINTHEGRIPPERWORKSWELL 4HISCHANGINGOPTIONISFREQUENTLYUSEDFORGRIPPERSINTHEPACKAG INGINDUSTRYTOTAKESEVERALWORKPIECESATATIMEFROMAPREPARATORY PICKPOSITIONTOADIFFERENTPLACEPOSITIONINACARDBOARDBOX %XEMPLARYALIGNMENTOFWORKPIECES BEFOREANDAFTERGRIPPING 7ORKPIECESWHICHMUSTBEROTATEDINTOAVERTICAL POSITIONMAKETHEHANDLINGTASKFARMORECOMPLICATED  4HEWORKPIECESINTHEEXAMPLEMUSTBEROTATEDDEGREEBEFORE THEYCANBEPICKEDUPBYTHEMULTIPLEGRIPPER 3UCHSUPPOSEDLYEASYCHANGESOFWORKPIECEORIENTATIONCANNOTBE PERFORMEDEFlCIENTLYBYMULTIPLEGRIPPERSINPRACTICE4HEEXPENDI TUREFORPROCESSRELIABILITYANDPERIPHERALADJUSTMENTISSUBSTANTIAL COMPAREDTOTHESINGLEGRIPPERWHICHOFTENPAYSBETTERDESPITE HIGHERCOSTFORTHEHANDLINGDEVICE 4HEPRINCIPLEOFMULTIPLEGRIPPINGDESCRIBEDSOFARISBASEDONTHE ASSUMPTIONTHATALLWORKPIECESAREPICKEDUPBYTHEGRIPPERATTHE SAMETIMEANDSUBSEQUENTLYPLACEDATTHESAMETIME 4HEPRINCIPLEOFSTACKGRIPPERSWHICHHASlRSTBEENINTRODUCEDAT THE!54/-!4)#!IN-UNICH'ERMANYFUNCTIONSACCORDING TOTHESINGLEGRIPPERCONCEPTBUTISABLETOSTORESEVERALWORKPIECES WITHINTHEGRIPPER$EPENDINGONWORKPIECEDIMENSIONTHEGRIPPER OFFERSASAVINGCAPACITYOFMINIMUMTWOWORKPIECESANDEXTREMELY SHORTOPENINGANDCLOSINGTIMES&OREFlCIENCYREASONSTHETIME FORPICKINGAWORKPIECEUPANDSTORINGITWITHINTHESTACKGRIPPER MUSTBESHORTERTHANTHETIMEFORTHEHANDLINGMOVEMENTTRANSPORT PERFORMEDBYTHEROBOTORAXISSYSTEM 3EVERALSUCCESSIVEPICKANDPLACEOPERATIONSPERFORMEDBYTHE STACKGRIPPERMAKECYCLETIMESHORTERTHANSINGLEPICKANDPLACE OPERATIONSACCORDINGTOTHECLASSICPRINCIPLEOFSINGLEGRIPPING  4HESTACKGRIPPERCOMBINESATLEASTPARTOFTHEBENElTSOFTHE SINGLEGRIPPERWITHTHOSEOFTHEMULTIPLEGRIPPER-OREOVERTHIS GRIPPERHASASOCALLEDDUALSTROKEOPTION4HELATTERREDUCESCYCLE TIMEISREDUCEDBECAUSETHEGRIPPERISABLETOPICKWORKPIECESONE AFTERTHEOTHERINSEQUENCEANDRELEASETHEMALLATTHESAMETIME PARALLELATTHEPLACESTATION !LIGNMENTPATTERNFORPLACEOPERATIONS REQUIRESROTATINGWORKPIECESDEGREE 4ASKINCLUDESPICKOPERATIONFROM ACONVEYOROPTIMIZEDFORBLEND ANDPLACEOPERATIONFORPACKAGING 0LACINGINSTACKSDEGREEROTATIONOF STACK  Getting To Grips With Handling Tasks 3 In addition to placing them in stacks the workpieces can be placed in rows if the gripper is first turned into a horizontal position by a rotary unit or by the kinematics. Although this principle of stack gripping cannot be compared to the performance of a parallel gripper it does perform much better than a regular single gripper. The advantages of performance have been identified for parallel kinematics, also called delta kinematics, in tables 3.22 to 3.26. A higher workpiece weight is calculated for a multiple gripper because the number of workpieces stacked within the gripper increase the overall weight (table 3.22). Compared to a regular single gripper a stack gripper can be expected to improve performance by nearly 20 percent if four workpieces are stored within the gripper (table 3.23). The same stack gripper with a storing capacity of eight workpieces will increase performance by about 30 percent (table 3.24). If the entire stack is placed at once performance can even be raised by 75 percent if the stack gripper holds four workpieces (table 3.25). Pick- and place performance can be more than doubled by about 116 percent if the stack gripper can store eight workpieces and place them at the same time (table 3.26). Workpieces stored within a stack gripper Pick operation of stack gripper 150 $ELTAKINEMATICSSINGLEGRIPPER SINGLEGRIPPER XPICKXPLACE AMBIENTCONDITIONS WIDTHCONVEYOR MM DISTANCECONVEYORPLACE POSITION MM AVERAGEPATH MM GRIPPERWEIGHTX70MAX G RESULT CYCLE PPMPARTS PERMINUTE $ELTAKINEMATICSMULTIPLEGRIPPER QUADRUPLEGRIPPER XPICKXPLACE AMBIENTCONDITIONS WIDTHCONVEYOR MM DISTANCECONVEYORPLACE POSITION MM AVERAGEPATH MM GRIPPERWEIGHTX70SMAX G RESULT CYCLE PPMPARTS PERMINUTE $ELTAKINEMATICSMULTIPLEGRIPPER QUADRUPLEGRIPPER XPICKXPLACE !MBIENTCONDITIONS CONVEYORWIDTH MM DISTANCECONVEYORPLACE POSITION MM AVERAGEPATH MM GRIPPERWEIGHTX70SMAX G RESULT CYCLE PPMPARTS PERMINUTE $ELTAKINEMATICSMULTIPLEGRIPPER OCTUPLEGRIPPER XPICKXPLACE AMBIENTCONDITIONS WIDTHCONVEYOR MM DISTANCECONVEYORPLACE POSITION MM AVERAGEPATH MM GRIPPERWEIGHTX70SMAX G RESULT CYCLE PPMPARTS PERMINUTE $ELTAKINEMATICSMULTIPLEGRIPPER OCTUPLEGRIPPER XPICKXPLACE AMBIENTCONDITIONS CONVEYORWIDTH MM DISTANCECONVEYORPLACE POSITION MM AVERAGEPATH MM GRIPPERWEIGHTX70SMAX G RESULT CYCLE PPMPARTS PERMINUTE 4ABLE0ICKANDPLACEWORKPIECES70SONEBYONEPERFOR MANCEINCREASECOMPAREDTOSINGLEGRIP 4ABLE0ICKWORKPIECES70SONEBYONEANDPLACETHEMINONE STACKPERFORMANCEINCREASECOMPAREDTOSINGLEGRIP 0ICKWITHSINGLEGRIPAND PLACEINSTACKS 4ABLE0ICKANDPLACEONEWORKPIECE70WITHSINGLEGRIP SOURCEROBOMOTION 4ABLE0ICKANDPLACEWORKPIECES70SONEBYONEPERFOR MANCEINCREASECOMPAREDTOSINGLEGRIP 4ABLE0ICKWORKPIECES70SONEBYONEANDPLACETHEMINONE STACKPERFORMANCEINCREASECOMPAREDTOSINGLEGRIP  [...]...Getting To Grips With Handling Tasks 3.5 Safe Gripping Losing our grip on a coffee-cup or accidentally letting a jar of mixed pickles slip from our hands in the supermarket does not do great harm Losing the grip on workpieces during handling, however, may lead to major financial damage For example, a workpiece accidentally lost in a processing machine may cause serious mechanical defect after re-start... imagine a workpiece within the gripper of a robot rotating with an action radius of three feet at full speed turning into a kind of projectile, even more dangerous at a robot payload up to 1,100 pounds High-grade workpieces require maximum protection against loss or damage, too 3 Risk of workpiece loss or damage is evaluated with the help of the Failure Mode Effect Analysis (FMEA) which has become part. .. and parcel of a methodical handling task approach Risk evaluation is a future-oriented method for analyzing potential hazards and the probability of such hazards Beyond mere damage repair this method is a significant step towards far-sighted and safe gripper design and construction systematically avoid potential errors continuous improvements consequently avoid recurrent errors permanently eliminate detected... systematically avoid potential errors continuous improvements consequently avoid recurrent errors permanently eliminate detected errors avoid errors past future problem analysis Grafik 3.25 Evaluating risks and eliminating defects 152 risk analysis  . 143 'ETTING4O'RIPS7ITH(ANDLING4ASKS  'RIPPING4AKES4IME !UTOMATEDSYSTEMSAREEITHERDESIGNEDASSELFSUPPORTINGSYSTEMS ORWITHADIRECTLINKTOEXISTINGPRODUCTIONFACILITIES)NTHISRESPECT THEYARENOTDIRECTLYINTEGRATEDINTO THE MATERIALSmOW )FDIRECTLINKAGETOPREORPOSTOPERATINGFACILITIESISSELECTEDEACH WORKPIECEFEDINTO THE HANDLING PROCESSISDUEFORFURTHERUSE ORPROCESSING4HEDISTANCEBETWEENPICKANDPLACESTATIONIS EFFECTEDWITHONEORSEVERALWORKPIECESWITHINAGRIPPER %ACHWORKPIECEDELIVERED IN THE DESIREDQUALITYANDCORRECTORDER STATUSISSUPPOSEDTOBEMOVED&ORTHESESITUATIONS HANDLING TIME PERWORKPIECEISESSENTIAL+INETICDEVICESWITHTHEIRCHARACTERISTICS IN TERMS OF WORKSPACEANDVELOCITYSEE#HAPTERARE OF GREAT IMPORTANCEOPENINGANDCLOSINGTIMES OF GRIPPERS ALSOMATTERFOR CYCLETIME &IGURE$IRECTLINKAGE OF WORKPIECEINPUTWITHWORKPIECEOUTPUT IN APLACEPOSITION                 3ELFSUPPORTINGSYSTEMSORINDIRECTLINKAGESAREDECOUPLEDFROM MATERIALSmOWBYBUFFERSORMAGAZINES4HEWORKPIECESARETAKEN FROMSTORAGETOAPROCESSINGSTATIONWHERETHEYAREMANIPULATEDOR REORIENTEDANDSUBSEQUENTLYPLACEDFORSTORAGEAGAIN4HEMATERI ALSmOWMUSTBEDISTINGUISHED IN ASFARASCYCLETIMESARESELECTED WITH THE RESULTTHAT THE HANDLING OPERATIONMUSTWAITFOR THE PRO CESSINGMACHINE3WIVELUNITSAREFREQUENTLYEMPLOYEDTOAVOID IDLINGDURINGWORKPIECECHANGE IN THE PROCESSINGMACHINE +INETICDEVICESWHICHCARRY THE GRIPPERS AREUSUALLYHIGHTECHCOM PONENTSWHICHAREMUCHMOREEXPENSIVETHAN THE GRIPPERS !SIX AXISROBOTFOREXAMPLECOSTSFARMORETHAN THE GRIPPERPERFORMING THE PICKOPERATION&ORMOSTINVESTMENTS IN AUTOMATIONPROlTABILITY CALCULATIONINCLUDES HANDLING OUTPUTPERMINUTEIEAROBOTWILL ONLYPAYIFITISABLETOMOVEAMINIMUMNUMBER OF WORKPIECESPER MINUTE4HESEECONOMICCONCERNSLEADSFROM THE PRINCIPLE OF SINGLE GRIPPINGTO THE PRINCIPLE OF MULTIPLEGRIPPINGTOREDUCECYCLETIME PERWORKPIECE /NEBENElT OF SINGLEGRIPPINGISTHATGRIPPERDESIGNDOESNOTNEED TOBEVERYSOPHISTICATED!TWOlNGERORTHREElNGERGRIPPERWILLBE SUFlCIENT#OMBINEDWITHAMULTIAXISROBOT THE GRIPPERCANmEXIBLY ENCLOSEWORKPIECESBECAUSEGRIPPERPOSITIONINGCANBECOMBINED WITHMOSTDIVERSEWORKPIECEORIENTATIONS)NTERMS OF WORKPIECE POSITIONING IN THE WORKSPACE THE ROBOTCANMAKEFULLUSE OF ITS mEXIBILITY7ORKPIECEORIENTATIONISNOTIMPORTANTFORRELIABLEPICK OPERATIONS IN THISCASE &IGURE-ATERIALSmOWFORSELFSUPPORTINGSYSTEMWITHOUTSWIVELUNIT         'ETTING4O'RIPS7ITH(ANDLING4ASKS  4HESAMEAPPLIESTOPLACEOPERATIONS0ROGRAMMINGANDPUTTING SYSTEMSINTOOPERATIONISSTREAMLINED)NTERFERINGEDGESARE REDUCEDBYCOMPACTGRIPPERCONSTRUCTIONANDLOWNUMBER OF GRIPPERlNGERS 4HEDISADVANTAGE OF THE SINGLEGRIPPERISTHATPERFORMANCEIS DIRECTLYCOUPLEDWITHCYCLETIME OF THE AXES IN USE$URINGONE CYCLEFROMPICKTOPLACEPOSITIONJUSTONEWORKPIECECANBETRANS  PORTEDATATIME!CCORDINGTOWORKPIECETYPEANDAPPLICATIONIE WORKSPACEANDNUMBER OF ORIENTATIONSTODAY{SROBOTKINEMATICS OPERATEATAREGULARCYCLETIMEBETWEENTWOANDTENSECONDSPER WORKPIECE6ERYFEWSPECIALKINETICDEVICESDESIGNEDFORHIGHSPEED ANDLOWWEIGHT HANDLING TASKS COPEWITHCYCLETIMESFARBELOW THESERATES5SINGPARALLELKINEMATICSROBOTSEQUIPPEDWITHCARBON lBREARMSFOREXAMPLEAREABLETOREACHUPTOGACCELERATION WHICHEQUALSATENFOLDACCELERATION OF THE EARTHANDTHUSKEEP CYCLETIMESPOSSIBLYUNDERSECONDSPERWORKPIECE 4HEPRINCIPLE OF MULTIPLEGRIPPINGBOOSTS THE PERFORMANCE OF AKINETICDEVICE&IGURESHOWSTHATADUALGRIPPERALREADY REDUCESCYCLETIMEBYPERCENTCOMPAREDTO THE SINGLEGRIPPERAT IDENTICALPICKINGANDPLACINGTIMES  &IGURE%FlCIENCYINCREASEBY THE PRINCIPLE OF MULTIPLEGRIPPING   'ETTING4O'RIPS7ITH(ANDLING4ASKS  4HISBENElTPAYSBECAUSE THE NUMBER OF KINETICDEVICESANDTHEIR PERIPHERIESISREDUCEDANDWORKSPACESAVED4HESECOSTSAVINGS HOWEVERAREPARTLYOFFSETBYCONSIDERABLEEXPENSESFORPICKAND PLACESTATIONS3UBSTANTIALPREPARATIONANDIMPLEMENTATIONCOSTS MUSTBEACCOUNTEDFORBECAUSE THE WORKPIECESNEEDTOBEALIGNED IN GROUPSFORMULTIPLEGRIPPING 4HEPROCESS OF ALIGNING THE WORKPIECE IN GROUPSFORAMULTIPLE GRIPPERREQUIRESSUBSTANTIALINVESTMENTINTO THE PERIPHERY OF KINETIC DEVICES!SILLUSTRATED THE WORKPIECESMUSTlRSTBEALIGNED IN AROW WITH THE APPROPRIATEDISTANCETOEACHOTHERTOBEREADYFOR THE PICK OPERATION 3OMETIMES THE TASKISNOTLIMITEDTOMEREREPOSITIONING OF THE WORKPIECES4HEALIGNMENTPATTERNFORPLACING THE WORKPIECESMAY BEDIFFERENTTO THE ONEAT THE PICKSTATIONWHICHMAKESMULTIPLE GRIPPINGMOREDIFlCULT&ORMANYAPPLICATIONSANOPTIONTOCHANGE THE DISTANCEBETWEENWORKPIECESWITHIN THE GRIPPERWORKSWELL 4HISCHANGINGOPTIONISFREQUENTLYUSEDFOR GRIPPERS IN THE PACKAG INGINDUSTRYTOTAKESEVERALWORKPIECESATATIMEFROMAPREPARATORY PICKPOSITIONTOADIFFERENTPLACEPOSITION IN ACARDBOARDBOX %XEMPLARYALIGNMENT OF WORKPIECES BEFOREANDAFTERGRIPPING 7ORKPIECESWHICHMUSTBEROTATEDINTOAVERTICAL POSITIONMAKE THE HANDLING TASKFARMORECOMPLICATED  4HEWORKPIECES IN THE EXAMPLEMUSTBEROTATEDDEGREEBEFORE THEYCANBEPICKEDUPBY THE MULTIPLEGRIPPER 3UCHSUPPOSEDLYEASYCHANGES OF WORKPIECEORIENTATIONCANNOTBE PERFORMEDEFlCIENTLYBYMULTIPLE GRIPPERS IN PRACTICE4HEEXPENDI TUREFORPROCESSRELIABILITYANDPERIPHERALADJUSTMENTISSUBSTANTIAL COMPAREDTO THE SINGLEGRIPPERWHICHOFTENPAYSBETTERDESPITE HIGHERCOSTFOR THE HANDLING DEVICE 4HEPRINCIPLE OF MULTIPLEGRIPPINGDESCRIBEDSOFARISBASEDON THE ASSUMPTIONTHATALLWORKPIECESAREPICKEDUPBY THE GRIPPERAT THE SAMETIMEANDSUBSEQUENTLYPLACEDAT THE SAMETIME 4HEPRINCIPLE OF STACK GRIPPERS WHICHHASlRSTBEENINTRODUCEDAT THE !54 /-! 4)#! IN -UNICH'ERMANYFUNCTIONSACCORDING TO THE SINGLEGRIPPERCONCEPTBUTISABLETOSTORESEVERALWORKPIECES WITHIN THE GRIPPER$EPENDINGONWORKPIECEDIMENSION THE GRIPPER OFFERSASAVINGCAPACITY OF MINIMUMTWOWORKPIECESANDEXTREMELY SHORTOPENINGANDCLOSINGTIMES&OREFlCIENCYREASONS THE TIME FORPICKINGAWORKPIECEUPANDSTORINGITWITHIN THE STACKGRIPPER MUSTBESHORTERTHAN THE TIMEFOR THE HANDLING MOVEMENTTRANSPORT PERFORMEDBY THE ROBOTORAXISSYSTEM 3EVERALSUCCESSIVEPICKANDPLACEOPERATIONSPERFORMEDBY THE STACKGRIPPERMAKECYCLETIMESHORTERTHANSINGLEPICKANDPLACE OPERATIONSACCORDINGTO THE CLASSICPRINCIPLE OF SINGLEGRIPPING  4HESTACKGRIPPERCOMBINESATLEAST PART OF THE BENElTS OF THE SINGLEGRIPPERWITHTHOSE OF THE MULTIPLEGRIPPER-OREOVERTHIS GRIPPERHASASOCALLEDDUALSTROKEOPTION4HELATTERREDUCESCYCLE TIMEISREDUCEDBECAUSE THE GRIPPERISABLETOPICKWORKPIECESONE AFTER THE OTHER IN SEQUENCEANDRELEASETHEMALLAT THE SAMETIME PARALLELAT THE PLACESTATION !LIGNMENTPATTERNFORPLACEOPERATIONS REQUIRESROTATINGWORKPIECESDEGREE 4ASKINCLUDESPICKOPERATIONFROM ACONVEYOROPTIMIZEDFORBLEND ANDPLACEOPERATIONFORPACKAGING 0LACING IN STACKSDEGREEROTATION OF STACK  Getting To Grips With Handling Tasks 3 In addition to placing them in stacks the workpieces can be placed in rows if the gripper. Gripping Losing our grip on a coffee-cup or accidentally letting a jar of mixed pickles slip from our hands in the supermarket does not do great harm. Losing the grip on workpieces during handling, . 152 0OTENTIALHAZARDSDUETOWORKPIECELOSSAREEVALUATEDEGONA SCALE OF TO)N THE NEXTSTEP THE PROBABILITY OF OCCURRENCEFOR THESEHAZARDSCANBEASSESSED4HEPROBABILITY OF DETECTINGSUCHA HAZARDISEVALUATEDASWELL)FYOUTHENMULTIPLY THE POTENTIALHAZARD WITHBOTHITSPROBABILITY OF OCCURRENCEANDITSPROBABILITY OF DETECTION YOUGET THE RISKFACTORFOR THE OVERALLRISKASSESSMENT 4HEEXAMPLEFORARISKANALYSIS IN TABLEISBASEDON THE RISK OF WORKPIECELOSSBYAPNEUMATICGRIPPERIE THE WORKPIECESLIDING WITHIN THE GRIPPER'RIPPINGFORCEISSUBSTANTIALLYREDUCEDBYADROP IN PRESSURE OF BARFROMASTANDARDPRESSURE OF BAR!NALYZING THE SITUATIONFOR THE ENTIRESYSTEMMEANSLOOKINGATITSINTERFACES IN RELATIONTOALLOTHERCOMPONENTSNOTJUSTTO THE GRIPPER&OR THE ENTIRESYSTEMAWORKPIECELOSSISEVALUATEDASHIGHLYCRITICAL EGRISK OF PERSONALINJURYORMATERIALDAMAGE4HERISK OF FAULTY POSITIONING OF THE WORKPIECEWITHIN THE GRIPPERISRATEDLOWEG CONCENTRICGRIPPERJAWSDONOTLET THE WORKPIECESLIDEBUTINTOONE DIRECTIONZ.EVERTHELESS THE PROBABILITY OF OCCURRENCEFORSLIDING ISRATEDHIGHERTHANFORTOTALWORKPIECELOSSBECAUSE THE WORKPIECE WOULDlRSTHAVETOSLIDEOUT OF THE GRIPPERJAWSBEFOREITCOULDGET LOST4HEPROBABILITY OF DETECTINGAPRESSUREDROPTOBARISRATED RELATIVELYHIGHDUETO THE PRESSURECONTROLSENSORINSTALLEDWHICH WARNS THE OPERATOR!S THE OPERATORMAYFAILTONOTICETHISWARNING THE RISKANALYSISRESULTISSTILLRATEDAT  DESCRIPTION OF HAZARD  POTENTIAL HAZARD PROBABILITY OF OCCUR RENCE PROBABILITY OF DETECTION  RISKFACTOR  LOSS OF WORKPIECEAT PRESSUREDROPTOBAR  WORKPIECESLIDINGAT PRESSUREDROPTOBAR  'ETTING4O'RIPS7ITH(ANDLING4ASKS  4ABLESHOWSTHATACOMPREHENSIVERISKANALYSISWILLONLYBE FEASIBLEIF THE HAZARDSAREKNOWNFOR THE ENTIRESYSTEM THE GRIPPER OPERATES IN !WORKPIECESLIDINGWITHIN THE GRIPPERMAYRESULT IN SERIOUSDAMAGEFOR THE PERIPHERY OF AN AUTOMATED SOLUTIONAND THE HANDLING UNITASWELLASFOR THE ROBOTITSELF#OLLISIONSWITHAWORK PIECEOUT OF PLACEWITHIN THE GRIPPERAREHIGHLYPROBABLEIFSPACEFOR THE PICKOPERATIONISLIMITED4ABLEISBASEDON THE ASSUMPTION THATAWORKPIECEWHICHISNOTPROPERLYHELDWITHIN THE GRIPPERCAN STILLBEPLACEDWITHOUTCOLLISION 4HISPLAINEXAMPLESHOWSTHATTEAMWORKISINDISPENSABLEFORRISK EVALUATION !PART FROMKNOWHOWABOUT THE BRAKINGEFFECTONA WORKPIECEWITHIN THE GRIPPERITISESSENTIALTOBEAWARE OF THE KINEMATICS IN CASE OF ANEMERGENCYSTOP4HESAMEAPPLIESFOR ROBOTANDCONTROLKNOWHOW 4HECOMPREHENSIVERISKANALYSISHASBEENDEVELOPEDFORTEAMWORK ANDISBASEDONALLSTAFFMEMBERSCONTRIBUTINGTO THE EVALUATIONON THE BASIS OF THEIRSPECIALKNOWHOW4HISIS THE ONLYWAYTOGET ANYWHERENEARTORELIABLEASSESSMENT OF POTENTIALHAZARDSAND RISKS3OFARSTANDARDS$).HAVEBEENSETWHICH REQUIREROBOTPRODUCERSTOEVALUATECERTAINTYPES OF RISKSSUCHAS HYGIENERELATEDRISKS 4ABLE#OMPREHENSIVERISKANALYSIS   ROBOTSWIVELMOVEMENT WITHOUTCONTROLLEDBRAKING MONITOREDSWIVELMOVEMENT OF AROBOTWITHPAYLOAD EMERGENCY STOP 4WOEMERGENCYSTOPSITUATIONSAT THE RISK OF LOSINGGRIPON THE WORKPIECEAREEXPLAINED IN THE FOLLOWING!NYSITUATIONSWHICHMAY OCCURDUETOWORKPIECERANGEWORKPIECETOLERANCESORFRICTION TOLERANCESARENEGLECTED7ORKPIECELOSSMAINLYOCCURSDURING EMERGENCYSTOPANDPOWERFAILURE )NCASE OF ANEMERGENCYSTOPASUDDENBRAKEISPUTON THE ROBOT ARMOR THE KINEMATICS4HISBRAKELEADSTOFORCES OF INERTIAON THE WORKPIECEWHICHARENOTTAKENINTOACCOUNT IN THE REGULARGRIPPING FORCECALCULATIONANDWHICHMAYLEADTOWORKPIECELOSSAT THE WORST 4HEWORKPIECE{SCENTER OF GRAVITYIS THE IDEALGRIPPINGPOINT IN ORDERTOACHIEVEMINIMUMTORQUEDURINGWORKPIECEMOVEMENT )TDEPENDSONWORKPIECEGEOMETRYWHETHERTHISCANBEACHIEVEDOR NOT )F THE ENERGYSUPPLYFOR THE GRIPPERISREDUCEDORCOMPLETELYCUTOFF THE WORKPIECEISMOSTPROBABLYLOSTIF THE RESPECTIVEPROVISIONSFOR GRIPPINGFORCEMAINTENANCEHAVEFAILEDTOBEMADEBEFOREHAND &IGURE"RAKINGMOVEMENT OF AROBOTWITHANUNFAVORABLE WORKPIECEGEOMETRYWITHIN THE GRIPPER &IGURE2OBOTSBEHAVINGDIFFERENTLY IN EMERGENCYSTOPSITUATION  CHECKVALVE WAYVALVE WAYVALVE WITHSPRINGRETURN PNEUMATICDUALCHECKVALVE  THROTTLECHECKVALVE WAYVALVE WAYVALVEWITHSPRING RETURN ACTUATION OF SINGLE GRIPPERS ACTUATION OF DUALGRIP PERS 'ETTING4O'RIPS7ITH(ANDLING4ASKS  4HEUSE OF SPRINGELEMENTSWHICHPRESS THE PISTON OF PNEUMATIC GRIPPERS INTO THE CLOSINGPOSITIONISONEPOSSIBILITYFORMAINTAINING THE GRIPPINGFORCE4HESPRINGSUPPORTS THE CLOSINGFORCEWITHAIR PRESSUREDURINGNORMALOPERATIONANDCLOSES THE GRIPPER &ORGRIPPINGFORCEMAINTENANCETENSIONSPRINGSORCOMPRESSION SPRINGSCANBEUSED(OUSINGRESTRICTIONSEGFORCOMPACT GRIPPERS AREOFTENRESPONSIBLEFOR THE FACTTHATONLY PART OF THE MAXIMUMGRIPPINGFORCECANBESECURED 4HISISANACCEPTABLECOMPROMISEBECAUSEITISSUFlCIENTTOSAFE GUARD THE STATICLOAD OF THE GRIPPERIEHOLDING THE WORKPIECE WITHIN THE GRIPPERWHILEITDOESNOTMOVEASALOSS OF ENERGY USUALLYLEADSTOANEMERGENCYSTOP3PRINGELEMENTSMAINTAINING THE GRIPPINGFORCEAREALSOUSEDFORSECURINGWORKPIECESDURINGLON GERSTANDSTILLSEGOVERWEEKENDSASTHISREDUCESSTARTINGTIMES SPRINGSUPPORTEDGRIPPER  4HEPRESSUREMAINTENANCEVALVEORDUALCHECKVALVEISA SAFEMETHODFORMAINTAINING THE GRIPPINGFORCE OF PNEU MATIC GRIPPERS !SSHOWN IN THE DIAGRAMITISlTTEDAS CLOSEASPOSSIBLETO THE GRIPPER5PONLOSS OF PRESSURE IN THE SUPPLY THE DUALCHECKVALVECLOSESTOPREVENTAIRLEAK AGEFROM THE GRIPPERCYLINDER $UALCHECKVALVESAREEMPLOYEDFORPNEUMATICASWELLASHYDRAULIC GRIPPERS TOMAINTAIN THE GRIPPINGFORCE4HEIRADVANTAGEISTHATTHEY REQUIRENOADDITIONALHOSESWITHIN THE GRIPPER|SIMMEDIATEWORK SPACEANDPERMITmEXIBLElTTING 4HEVALVEMUSTBElTTEDTO THE GRIPPER THE CLOSESTPOSSIBLETO ENABLEFASTREACTIONUPONLOSS OF AIRANDTOKEEP THE PART OF TUBE SUPPLYWHICHCOULDBEAFFECTEDBYALEAKAGEASSMALLASPOSSIBLE 4HEDUALCHECKVALVEISUSEDIFGRIPPINGFORCEMAINTENANCEBY SPRINGFORCEISNOTPOSSIBLEATALLORONLYATUNREASONABLYHIGH EXPENSE4HISIS THE CASEWHEN THE HOUSINGNECESSARYFOR THE SPRINGSSAFEGUARDINGHIGHCLAMPINGFORCESISNOTSUFlCIENT       PRINCIPLE OF FUNCTIONFOR THE DUAL CHECKVALVE  'ETTING4O'RIPS7ITH(ANDLING4ASKS  