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英文原文POWEREDSUPPORTSPOWEREDROOFSUPPORTSAREUSEDTOSUPPORTTHEROOFATTHEFACETHEYWORKINSEVERALSTEPSMOSTLYINTHEIMMEDIATEFORWARDSUPPORTIFSTYPEINORDERTOSUPPORTTHENEWLYEXPOSEDROOFASSOONASPOSSIBLEINNORMALSUPPORTINGCONDITIONTHECANOPYOFTHESUPPORTISSETTIGHTLYAGAINSTTHEROOFSTRATA,BYTHESUPPORTINGRESISTANCESOFTHEHYDRAULICLEGSWHENTHECUTTINGMACHINECUTSANDPASSESSEVERALSUPPORTUNITSBEYONDTHESUPPORTINQUESTION,THESUPPORTLEGSARELOWEREDANDPULLEDFORWARDFORADISTANCEEQUALTOTHEWIDTHOFCUTWEBBYRETRACTINGTHEHYDRAULICADVANCINGRAMTHEADVANCINGRAMACTSAGAINSTTHEFACECONVEYORPANLINE,WHOSEPOSITIONISHELDUNCHANGEDBYTHEADVANCINGRAMS,FORCESOFTHESUPPORTSTHATARESETONBOTHSIDESOFTHESUPPORTTOBEADVANCEDASSOONASTHESUPPORTHASBEENADVANCEDTOTHEDESIGNEDPOSITION,THESUPPORTISIMMEDIATELYRESETAGAINSTTHEROOFFINALLY,THEADVANCINGRAMOFTHESUPPORTINQUESTIONISEXTENDEDTOPUSHTHECONVEYORFORWARDANDBECOMESREADYFORTHENEXTCUTTHESEQUENTIALSTEPSDESCRIBEDAREFORTHEADVANCEOFANINDIVIDUALSUPPORTINTHEDIRECTIONPERPENDICULARTOTHEFACELINEBUTALONGTHEFACELINEDIRECTION,THECONVEYORCANNOTBEADVANCEDINASHARPSTEPIMMEDIATELYAFTERTHESHEARERHASPASSEDIT,DUETOTHERIGIDITYOFTHEPANLINETHUSTHEFOURTHSTEPISUSUALLYSOMETIMEAFTERTHESHEARER,SPASS,RESULTINGINACURVEDORSNAKEDSECTIONDURINGPANELDEVELOPMENTTHEPANELENTRIESAREROOFBOLTEDASUSUALBUTINTHETAILENTRYONEORTWOROWSOFCRIBSAREERECTEDTOSUPPLEMENTTHEROOFBOLTINGDURINGRETREATINGMINING,THEROOFATTHEHEADENTRYTJUNCTIONAREAUPTO500FT152MOUTBYTHEFACEISGENERALLYREINFORCEDWITHSUPPORTSOFSOMETYPETOINCREASESUPPORTDENSITYTOCOPEWITHTHEMOVINGFRONTANDSIDEABUTMENTPRESSURESMODERNLONGWALLMININGEMPLOYSHYDRAULICPOWEREDSUPPORTSATTHEFACEAREATHESUPPORTSNOTONLYHOLDSUPTHEROOF,PUSHESTHEFACECHAINCONVEYORAFC,ANDADVANCESITSELF,BUTALSOPROVIDESASAFEENVIRONMENTFORALLASSOCIATEDMININGACTIVITIESTHEREFOREITSSUCCESSFULSELECTIONANDAPPLICATIONARETHEPREREQUISITEFORSUCCESSFULLONGWALLMININGFURTHERMORE,DUETOTHELARGENUMBEROFUNITSREQUIRED,THECAPITALINVESTEDFORTHEPOWERSUPPORTUSUALLYACCOUNTSFORMORETHANHALFOFTHEINITIALCAPITALFORALONGWALLFACETHEREFOREBOTHFROMTECHNICALANDECONOMICPOINTSOFVIEW,THEPOWEREDSUPPORTISAVERYIMPORTANTPIECEOFEQUIPMENTINALONGWALLFACECLASSIFICATIONOFPOWEREDSUPPORTSTHEAPPLICATIONOFMODERNPOWEREDSUPPORTSCANBETRACEDBACKTOEARLY1950SSINCETHEN,FOLLOWINGITSADOPTIONINEVERYPARTOFTHEWORLD,THEREHAVEBEENCOUNTLESSMODELSDESIGNANDMANUFACTUREDINVARIOUSCOUNTRIESBUTUNFORTUNATELY,THERESTILLISNOUNIFORMSYSTEMOFCLASSIFICATIONINTHISSECTIONASIMPLIFIEDCLASSIFICATIONISUSEDSINCEAPOWEREDSUPPORTCONSISTSOFFOURMAJORCOMPONENTSIE,CANOPY,CAVINGSHIELD,HYDRAULICLEGSANDPROPS,ANDBASEPLATE,THEWAYSBYWHICHTHEYAREINTERRELATEDAREUSEDFORCLASSIFICATIONINTHISRESPECT,TWOFACTORSAREMOSTIMPORTANTAPRESENCEORABSENCEOFCAVINGSHIELDIFACAVINGSHIELDISINCLUDED,THESUPPORTISA“SHIELD”TYPE,OTHERWISE,AFRAMEORACHOCK；BNUMBERANDTYPEOFARRANGINGTHEHYDRAULICLEGSSINCESUPPORTCAPACITYISGENERALLYPROPORTIONALTONUMBEROFHYDRAULICLEGS,ITISIMPORTANTTOSPECIFYTHENUMBEROFHYDRAULICLEGSTHATASUPPORTHASFURTHERMORE,THEWAYTHEHYDRAULICLEGSAREINSTALLEDISIMPORTANT；FOREXAMPLE,AVERTICALINSTALLATIONBETWEENTHEBASEANDTHECANOPYHASTHECAVINGSHIELDHASTHELEASTEFFICIENCYINSUPPORTINGTHEROOFBASEDONTHISCONCEPT,THEREAREFOURTYPESOFPOWEREDSUPPORT,THATIS,THEFRAME,CHOCK,SHIELDANDCHOCKSHIELD,INORDEROFEVOLUTIONOFTHEIRDEVELOPMENTHOWEVER,ITMUSTBENOTEDTHATTHETRENDOFDEVELOPMENTINEACHTYPEISSUCHTHATITBECOMESLESSDISTINGUISHABLEINTERMSOFAPPLICATIONTHEFOURTYPESOFROOFSUPPORTSCANBEOBTAINEDFOREITHERLONGWALLRETREATINGORADVANCINGSYSTEMS,ANDTHEYAREAVAILABLEINSTANDARD,ONEWEBBACK,ANDIMMEDIATEFORWARDSUPPORTIFSVERSIONSWITHTHESTANDARDSYSTEM,THEWININGMACHINETAKESACUTORASLICE,ANDTHEARMOREDFACECONVEYORISPUSHEDOVERBYTHEHYDRAULICRAMSTHATAREFIXEDTOTHESUPPORTUNITSTHESUPPORTUNITSTHENAREADVANCEDSEQUENTIALLYTOTHECONVEYORWITHTHEONEWEBBACKSYSTEM,ASUPPORTISSETBACKFROMTHECONVEYORBYADEVICETHATAUTOMATICALLYKEEPSTHELEADINGEDGEOFTHESUPPORTATAFIXDISTANCEFROMTHECONVEYORTHISALLOWSEASYACCESSTHOUGHTHEFACEANDEMPLOYSTHESTANDARDMETHODOFADVANCING；IE,PUSHINGTHECONVEYORFIRST,ANDTHENADVANCINGTHESUPPORTWITHTHEIFSSYSTEM,THESUPPORTUNITSISADVANCEDTOTHECONVEYORIMMEDIATELYAFTERTHECUTTINGMACHINEHASPASSED,ANDTHEFORWARDCANOPYOFTHESUPPORTUNITSISLONGENOUGHTOTHESUPPORTBOTHTHERECENTLYANDNEWLYEXPOSEDROOFSECTIONSAFTERTHESUPPORTSHAVEBEENADVANCED,THECONVEYORISPUSHEDOVERFRAMETHEFRAMESUPPORTISANEXTENSIONOFTHESINGLEHYDRAULICPROPSCONVENTIONALLYUSEDUNDERGROUNDTHUSITISTHEFIRSTTYPEDEVELOPEDINMODERNSELFADVANCINGHYDRAULICPOWEREDSUPPORTSITINVOLVESSETTINGUPTWOHYDRAULICPROPSORLEGSVERTICALLYINTANDEMTHATARECONNECTEDATTHETOPBYASINGLEORTWOSEGMENTEDCANOPIESTHETWOSEGMENTEDCANOPIESCANBEHINGEJOINTEDATANYPOINTBETWEENTHELEGSORINFRONTOFTHEFRONTLEGTHEBASEOFTHETWOHYDRAULICLEGSMAYBEACIRCULARSTEELSHOEWELDEDATBOTTOMOFEACHLEGORSOLIDBASECONNECTINGBOTHLEGSGENERALLY,AFRAMESUPPORTCONSISTSOFTWOORTHREESETSOFHYDRAULICLEGSTHESETMOVINGFIRSTISTHESECONDARYSET,THESETMOVINGLATERISTHEPRIMARYSETTHEREISADOUBLEACTINGRAMINSTALLEDBETWEENEACHSETTHEPISTONOFTHERAMISCONNECTEDTOTHESECONDARYSETANDTHECYLINDERTOTHEPRIMARYSETDURINGSUPPORTADVANCE,THEPRIMARYSETISSETAGAINSTTHEROOFWHILETHESECONDARYSETISLOWEREDANDPUSHEDFORWARDBYTHEPISTONHAVINGREACHEDTHENEWPOSITION,THESECONDARYSETISAGAINSTTHEROOFWHILETHEPRIMARYSETISLOWEREDANDPULLEDFORWARDBYTHECYLINDERTHEDISTANCEOFEACHADVANCERANGESFROM20TO36IN050091MTHEFRAMESUPPORTISVERYSIMPLE,BUTMOREFLEXIBLEORLESSSTABLESTRUCTURALLYTHEREARECONSIDERABLEUNCOVEREDSPACESBETWEENTHETWOPIECESOFCANOPYWHICHALLOWSBROKENROOFROCKTOFALLTHROUGHCONSEQUENTLY,THEFRAMESUPPORTISNOTSUITABLEFORAWEAKROOFFRAMESHAVEBECOMESELDOMUSEDBECAUSETHEYARELESSSTABLEANDREQUIREFREQUENTMAINTENANCECHOCKINACHOCKSUPPORT,THECANOPYISASOLIDPIECEANDTHEBASEMAYBEEITHERASOLIDORPIECEORTWOSEPARATEPARTSCONNECTEDBYSTEELBARSATTHEREARAND/ORTHEFRONTENDSINBOTHCASESALARGEOPENSPACEISLEFTATTHECENTERFORLOCATINGTHEDOUBLEACTINGHYDRAULICRAMWHICHISUSEDTOPUSHANDPULLTHECHAINCONVEYORANDTHECHOCKINAWHOLEUNIT,RESPECTIVELY,ADISTINCTIVEDIFFERENCEFROMTHEFRAMESUPPORTTHISSETUPISALSOUSEDINTHESHIELDSANDCHOCKSHIELDSAGAIN,ALLHYDRAULICLEGSAREINSTALLEDVERTICALLYBETWEENTHEBASEANDTHECANOPYTHENUMBEROFLEGSRANGESFROMTHREETOSIX,BUTTHEFOURLEGCHOCKSAREBYFARTHEMOSTPOPULARONESTHESIXLEGCHOCKSAREDESIGNEDFORTHINSEAMSWITHTWOLEGSINTHEFRONTANDFOURLEGSINTHEREAR,SEPARATEDBYAWALKWAYFORTHESIXLEGCHOCKS,THECANOPYISGENERALLYHINGEJOINTEDABOVETHEWALKWAYMOSTCHOCKAREALSOEQUIPPEDWITHAGOBWINDOWHANGINGATTHEREARENDOFTHECANOPYTHEGOBWINDOWCONSISTSOFSEVERALRECTANGULARSTEELPLATESCONNECTEDHORIZONTALLYATBOTHENDSINMOSTCHOCKSUPPORTS,THEREAREHINGEJOINTCONNECTIONSBETWEENTHELEGSANDTHECANOPYANDBETWEENTHELEGSANDTHEBASEBUTINORDERTOINCREASETHELONGITUDINALSTABILITY,ITISREINFORCEDMOSTLYWITHABOXSHAPEDSTEELFRAMEBETWEENTHEBASEANDEACHLEGALEGRESTORINGDEVICEISINSTALLEDAROUNDEACHLEGATTHETOPOFTHEBOXSHAPEDSTEELFRAMETHECHOCKSARESUITABLEFORMEDIUMTOHARDROOFWHENTHEROOFOVERHANGSWELLINTOTHEGOBANDREQUIRESINDUCEDCAVING,THECHOCKSCANPROVIDEACCESSTOTHEGOBSHIELDSHIELDS,ANEWENTRYINTHEEARLYSEVENTIES,ARECHARACTERIZEDBYTHEADDITIONOFACAVINGSHIELDATTHEREARENDBETWEENTHEBASEANDTHECANOPYTHECAVINGSHIELDS,WHICHINGENERALAREINCLINED,AREHINGEJOINTEDTOTHECANOPYANDTHEBASEMAKINGTHESHIELDAKINEMATICALLYSTABLESUPPORT,AMAJORADVANTAGEOVERTHEFRAMESANDTHECHOCKSITALSOCOMPLETELYSEALSOFFTHEGOBANDPREVENTSROCKDEBRISFROMGETTINGINTOTHEFACESIDEOFTHESUPPORTTHUSTHESHIELDSUPPORTEDFACEISGENERALLYCLEANTHEHYDRAULICLEGSINTHESHIELDSAREGENERALLYINCLINEDTOPROVIDEMOREOPENSPACEFORTRAFFICBECAUSETHECANOPY,CAVINGSHIELD,ANDBASEAREINTERCONNECTED,ITCANWELLRESISTTHEHORIZONTALFORCEWITHOUTBENDINGTHELEGSTHUS,UNLIKETHESOLIDCONSTRAINTINTHEFRAME/CHOCKSUPPORTS,THEPINCONNECTIONSBETWEENTHELEGSANDTHECANOPY,ANDBETWEENTHELEGSANDTHEBASEINASHIELDSUPPORTMAKEITPOSSIBLETHATTHEANGLEOFINCLINATIONOFTHEHYDRAULICLEGSVARIESWITHTHEMININGHEIGHTSSINCEONLYTHEVERTICALCOMPONENTOFHYDRAULICLEGPRESSUREISAVAILABLEFORSUPPORTINGTHEROOF,THEACTUALLOADINGCAPACITYOFTHESHIELDALSOVARIESWITHTHEMININGHEIGHTSTHEREAREMANYVARIATIONSOFTHESHIELDSUPPORTSINTHEFOLLOWING,SIXITEMSAREUSEDTOCLASSIFYTHESHIELDS,WHICHENABLESAUNIFIEDTERMINOLOGYTOBEDEVELOPEDFORALLKINDSOFSHIELDSTHETYPESOFMOTIONALTRACESOFTHECANOPYTIP,LEGPOSITIONSANDORIENTATION,NUMBEROFLEGS,CANOPYGEOMETRY,ANDOTHEROPTIONALDESIGNSANDDEVICESCANBECLEARLYSPECIFIEDBYTHETERMINOLOGYTYPESOFMOTIONALTRACESFORTHELEADINGEDGEOFTHECANOPYTHISISTHEMOSTCOMMONLYRECOGNIZEDWAYOFCLASSIFYINGTHESHIELDBASEDONTHISCRITERION,THEREARETHREETYPES,LEMNISCATE,CALIPER,ANDELLIPSELEMNISCATETHISISTHEMOSTPOPULARTYPETHECAVINGSHIELDANDTHEBASEAREJOINTEDBYTWOLEMNISCATEBARSWHICHHAVEATOTALOFFOURHINGESASTHEHYDRAULICLEGSARERAISEDANDLOWERED,THEDIMENTIONSOFTHELEMNISCATEBARSARESELECTEDSUCHTHATTHELEADINGEDGEOFTHECANOPYMOVESUPANDDOWNNEARLYVERTICALLY,THUSMAINTAININGANEARLYCONSTANTUNSUPPORTEDDISTANCEBETWEENTHEFACELINEANDTHELEADINGEDGEOFTHECANOPYTHISISAFEATURETHATISWIDELYCONSIDEREDMOSTDESIRABLEFORGOODROOFCONTROLTHEREARECLEARLIMITSOFMININGHEIGHTWITHINWHICHTHELEADINGEDGEOFTHECANOPYMOVESNEARLYVERTICALLYTHESELIMITSARESTRICTLYCONTROLLEDBYTHEDIMENTIONALANDPOSITIONALARRANGEMENTSOFTHECANOPY,CAVINGSHIELD,LEMNISCATEBARS,ANDTHEBASEBEYONDTHESELIMITS,THEEDGESWILLMOVERAPIDLYAWAYFROMTHEFACELINECREATINGALARGEUNSUPPORTEDAREACALIPERINACALIPERSHIELD,THECAVINGSHIELDANDTHEBASEARECONNECTEDBYASINGLEHINGEWHENTHEHYDRAULICLEGSARERAISED,THELEADINGEDGEOFTHECANOPYMOVESINANARCAWAYFROMTHEFACE,THUSINCREASINGTHEUNSUPPORTEDAREATHISISCONSIDEREDBYMOST
