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英文原文PoweredsupportsPoweredroofsupportsareusedtosupporttheroofattheface.TheyworkinseveralstepsmostlyintheimmediateforwardsupportIFStypeinordertosupportthenewlyexposedroofassoonaspossible.Innormalsupportingconditionthecanopyofthesupportissettightlyagainsttheroofstrata,bythesupportingresistancesofthehydrauliclegs.Whenthecuttingmachinecutsandpassesseveralsupportunitsbeyondthesupportinquestion,thesupportlegsareloweredandpulledforwardforadistanceequaltothewidthofcutwebbyretractingthehydraulicadvancingram.Theadvancingramactsagainstthefaceconveyorpanline,whosepositionisheldunchangedbytheadvancingrams,forcesofthesupportsthataresetonbothsidesofthesupporttobeadvanced.Assoonasthesupporthasbeenadvancedtothedesignedposition,thesupportisimmediatelyresetagainsttheroof.Finally,theadvancingramofthesupportinquestionisextendedtopushtheconveyorforwardandbecomesreadyforthenextcut.Thesequentialstepsdescribedarefortheadvanceofanindividualsupportinthedirectionperpendiculartothefaceline.Butalongthefacelinedirection,theconveyorcannotbeadvancedinasharpstepimmediatelyaftertheshearerhaspassedit,duetotherigidityofthepanline.Thusthefourthstepisusuallysometimeaftertheshearer,spass,resultinginacurvedorsnakedsection.Duringpaneldevelopmentthepanelentriesareroofboltedasusual.Butinthetailentryoneortworowsofcribsareerectedtosupplementtheroofbolting.Duringretreatingmining,theroofattheheadentryTjunctionareaupto500ft152moutbythefaceisgenerallyreinforcedwithsupportsofsometypetoincreasesupportdensitytocopewiththemovingfrontandsideabutmentpressures.Modernlongwallminingemployshydraulicpoweredsupportsatthefacearea.Thesupportsnotonlyholdsuptheroof,pushesthefacechainconveyorAFC,andadvancesitself,butalsoprovidesasafeenvironmentforallassociatedminingactivities.Thereforeitssuccessfulselectionandapplicationaretheprerequisiteforsuccessfullongwallmining.Furthermore,duetothelargenumberofunitsrequired,thecapitalinvestedforthepowersupportusuallyaccountsformorethanhalfoftheinitialcapitalforalongwallface.Thereforebothfromtechnicalandeconomicpointsofview,thepoweredsupportisaveryimportantpieceofequipmentinalongwallface.ClassificationofpoweredsupportsTheapplicationofmodernpoweredsupportscanbetracedbacktoearly1950s.Sincethen,followingitsadoptionineverypartoftheworld,therehavebeencountlessmodelsdesignandmanufacturedinvariouscountries.Butunfortunately,therestillisnouniformsystemofclassification.Inthissectionasimplifiedclassificationisused.Sinceapoweredsupportconsistsoffourmajorcomponentsi.e,canopy,cavingshield,hydrauliclegsandprops,andbaseplate,thewaysbywhichtheyareinterrelatedareusedforclassification.Inthisrespect,twofactorsaremostimportantapresenceorabsenceofcavingshieldifacavingshieldisincluded,thesupportisashieldtype,otherwise,aframeorachockbnumberandtypeofarrangingthehydrauliclegssincesupportcapacityisgenerallyproportionaltonumberofhydrauliclegs,itisimportanttospecifythenumberofhydrauliclegsthatasupporthas.Furthermore,thewaythehydrauliclegsareinstalledisimportantforexample,averticalinstallationbetweenthebaseandthecanopyhasthecavingshieldhastheleastefficiencyinsupportingtheroof.Basedonthisconcept,therearefourtypesofpoweredsupport,thatis,theframe,chock,shieldandchockshield,inorderofevolutionoftheirdevelopment.However,itmustbenotedthatthetrendofdevelopmentineachtypeissuchthatitbecomeslessdistinguishableintermsofapplication.Thefourtypesofroofsupportscanbeobtainedforeitherlongwallretreatingoradvancingsystems,andtheyareavailableinstandard,onewebback,andimmediateforwardsupportIFSversions.Withthestandardsystem,thewiningmachinetakesacutoraslice,andthearmoredfaceconveyorispushedoverbythehydraulicramsthatarefixedtothesupportunits.Thesupportunitsthenareadvancedsequentiallytotheconveyor.Withtheonewebbacksystem,asupportissetbackfromtheconveyorbyadevicethatautomaticallykeepstheleadingedgeofthesupportatafixdistancefromtheconveyor.Thisallowseasyaccessthoughthefaceandemploysthestandardmethodofadvancingi.e,pushingtheconveyorfirst,andthenadvancingthesupport.WiththeIFSsystem,thesupportunitsisadvancedtotheconveyorimmediatelyafterthecuttingmachinehaspassed,andtheforwardcanopyofthesupportunitsislongenoughtothesupportboththerecentlyandnewlyexposedroofsections.Afterthesupportshavebeenadvanced,theconveyorispushedover.FrameTheframesupportisanextensionofthesinglehydraulicpropsconventionallyusedunderground.Thusitisthefirsttypedevelopedinmodernselfadvancinghydraulicpoweredsupports.Itinvolvessettinguptwohydraulicpropsorlegsverticallyintandemthatareconnectedatthetopbyasingleortwosegmentedcanopies.Thetwosegmentedcanopiescanbehingejointedatanypointbetweenthelegsorinfrontofthefrontleg.Thebaseofthetwohydrauliclegsmaybeacircularsteelshoeweldedatbottomofeachlegorsolidbaseconnectingbothlegs.Generally,aframesupportconsistsoftwoorthreesetsofhydrauliclegs.Thesetmovingfirstisthesecondaryset,thesetmovinglateristheprimaryset.Thereisadoubleactingraminstalledbetweeneachset.Thepistonoftheramisconnectedtothesecondarysetandthecylindertotheprimaryset.Duringsupportadvance,theprimarysetissetagainsttheroofwhilethesecondarysetisloweredandpushedforwardbythepiston.Havingreachedthenewposition,thesecondarysetisagainsttheroofwhiletheprimarysetisloweredandpulledforwardbythecylinder.Thedistanceofeachadvancerangesfrom20to36in.0.500.91mTheframesupportisverysimple,butmoreflexibleorlessstablestructurally.Thereareconsiderableuncoveredspacesbetweenthetwopiecesofcanopywhichallowsbrokenroofrocktofallthrough.Consequently,theframesupportisnotsuitableforaweakroof.Frameshavebecomeseldomusedbecausetheyarelessstableandrequirefrequentmaintenance.ChockInachocksupport,thecanopyisasolidpieceandthebasemaybeeitherasolidorpieceortwoseparatepartsconnectedbysteelbarsattherearand/orthefrontends.Inbothcasesalargeopenspaceisleftatthecenterforlocatingthedoubleactinghydraulicramwhichisusedtopushandpullthechainconveyorandthechockinawholeunit,respectively,adistinctivedifferencefromtheframesupport.Thissetupisalsousedintheshieldsandchockshields.Again,allhydrauliclegsareinstalledverticallybetweenthebaseandthecanopy.Thenumberoflegsrangesfromthreetosix,butthefourlegchocksarebyfarthemostpopularones.Thesixlegchocksaredesignedforthinseamswithtwolegsinthefrontandfourlegsintherear,separatedbyawalkway.Forthesixlegchocks,thecanopyisgenerallyhingejointedabovethewalkway.Mostchockarealsoequippedwithagobwindowhangingattherearendofthecanopy.Thegobwindowconsistsofseveralrectangularsteelplatesconnectedhorizontallyatbothends.Inmostchocksupports,therearehingejointconnectionsbetweenthelegsandthecanopyandbetweenthelegsandthebase.Butinordertoincreasethelongitudinalstability,itisreinforcedmostlywithaboxshapedsteelframebetweenthebaseandeachleg.Alegrestoringdeviceisinstalledaroundeachlegatthetopoftheboxshapedsteelframe.Thechocksaresuitableformediumtohardroof.Whentheroofoverhangswellintothegobandrequiresinducedcaving,thechockscanprovideaccesstothegob.ShieldShields,anewentryintheearlyseventies,arecharacterizedbytheadditionofacavingshieldattherearendbetweenthebaseandthecanopy.Thecavingshields,whichingeneralareinclined,arehingejointedtothecanopyandthebasemakingtheshieldakinematicallystablesupport,amajoradvantageovertheframesandthechocks.Italsocompletelysealsoffthegobandpreventsrockdebrisfromgettingintothefacesideofthesupport.Thustheshieldsupportedfaceisgenerallyclean.Thehydrauliclegsintheshieldsaregenerallyinclinedtoprovidemoreopenspacefortraffic.Becausethecanopy,cavingshield,andbaseareinterconnected,itcanwellresistthehorizontalforcewithoutbendingthelegs.Thus,unlikethesolidconstraintintheframe/chocksupports,thepinconnectionsbetweenthelegsandthecanopy,andbetweenthelegsandthebaseinashieldsupportmakeitpossiblethattheangleofinclinationofthehydrauliclegsvarieswiththeminingheights.Sinceonlytheverticalcomponentofhydrauliclegpressureisavailableforsupportingtheroof,theactualloadingcapacityoftheshieldalsovarieswiththeminingheights.Therearemanyvariationsoftheshieldsupports.Inthefollowing,sixitemsareusedtoclassifytheshields,whichenablesaunifiedterminologytobedevelopedforallkindsofshields.Thetypesofmotionaltracesofthecanopytip,legpositionsandorientation,numberoflegs,canopygeometry,andotheroptionaldesignsanddevicescanbeclearlyspecifiedbytheterminology.Typesofmotionaltracesfortheleadingedgeofthecanopy.Thisisthemostcommonlyrecognizedwayofclassifyingtheshield.Basedonthiscriterion,therearethreetypes,lemniscate,caliper,andellipse.Lemniscate.Thisisthemostpopulartype.Thecavingshieldandthebasearejointedbytwolemniscatebarswhichhaveatotaloffourhinges.Asthehydrauliclegsareraisedandlowered,thedimentionsofthelemniscatebarsareselectedsuchthattheleadingedgeofthecanopymovesupanddownnearlyvertically,thusmaintaininganearlyconstantunsupporteddistancebetweenthefacelineandtheleadingedgeofthecanopy.Thisisafeaturethatiswidelyconsideredmostdesirableforgoodroofcontrol.Thereareclearlimitsofminingheightwithinwhichtheleadingedgeofthecanopymovesnearlyvertically.Theselimitsarestrictlycontrolledbythedimentionalandpositionalarrangementsofthecanopy,cavingshield,lemniscatebars,andthebase.Beyondtheselimits,theedgeswillmoverapidlyawayfromthefacelinecreatingalargeunsupportedarea.Caliper.Inacalipershield,thecavingshieldandthebaseareconnectedbyasinglehinge.Whenthehydrauliclegsareraised,theleadingedgeofthecanopymovesinanarcawayfromtheface,thusincreasingtheunsupportedarea.Thisisconsideredbymost