Axialpositionofthesledgeismeasuredwiththeaidofalinearpotentiometer constructed of0.3-ramthick stainlesssteelwiregivingresistanceapproximately 0-8ohmsoverthemeasuring range.Tomaintain constanttensioninthewirestheyaretensionedwithtwocompression springs. DrillPipes: Thedrillpipes,constructed ofaluminum,arelocatedinapipecarousel.Insidediameterofthepipesis13 mm,outsidediameteris15mm,andthethree-ended helicalfluteoutsidethepipehasa17-ramouter diameter.Couplingsintheendsofpipesaremadeofsteelandpresentthesamedesignasthespindle coupling,butwithoutanysecuringmeans. Connection betweenthepipeshappensbypushingthemtogetheruntilthelockingringsnapsintothe groove.Thethree-ended fluteissymmetricandsothepipescanbeconnected inanyofthethree possibleorientations. Disconnection oftwodrillpipesfromeachotherhappenswhentheclamping mechanism holdsthelowerpipeandspindlepullstheupperpipeapart.Thenthelockingsolenoidinthe spindleisopenedbyacommandandthesledgeisdriventotheupperposition.Duringelevationofthe spindle,amechanical de-coupling mechanism separatesthepipefromthespindle,leavingitinthepipe carousel.Atoolisseparatedfromthepipebyfirstdrivingthetoolintothetoolcarouselandlockingitin there.Thenthepipeispulledwiththeaidofthesledgeapartfromthetool. Forenhancedorspecial sampling actions, twopowerlinesareroutedthrough drillpipecouplings toallow useofpossible activedrillingtoolsintheendofdrillstring.Thesepossible toolsinclude, forexample, percussive toolsandultrasonic tools.Dr.T.C.NgandHolinser Grouphavealready developed adesign forasuitable activepercussive toolinUniversity ofHongKong.Special measuring instruments canbe mounted inthetoolsformeasuring temperature, contact force,etc. Pipecarousel: Thepipesarelocated inapipecarousel, whichhasaskeleton-like appearance withthinvertical barsand slotteddisksatbothends.Thedesign allowsthespindle tobelocated andmoveinsidethecarousel, whichsavesalotofvolume. Thepipesarenotmounted positively tothecarousel, butsitintheslots surrounded bystructures abovetheupperdiskandaround andbelowthelowerdisk.Therotation ofthe carousel isactuated withaMaxond13motorlocated outside thecarousel andagearrimconnected to theupperendofthecarousel. Thecarousel ispositioned tothecorrect angular positions withtwolimit switches andindexpins;oneforeachpipeindexing andoneforabsolute position indicator. Inthebottom ofthecarousel thereisaslotthrough whichthedrillinghappens. Inordertoprevent inadvertent fallingof apipeintotheslot,twospring-loaded pushers addsomefrictionbetween thepipeandpipecarousel. ToolCarousel: Thetools,whichalsodouble assample containers, arestoredinatoolcarousel. Thereare11storage cupsforthetools.Thetoolsaremounted tothecupswithabayonet-like passive mechanism. Thetoolis inserted tothecarousel withcombined andcontrolled feedandtoolrotation. Withtheaidofanaligning pinthetoolfindscorrect position inthecarousel andthreeflatsprings snapoverupperedgeofdrilling bitsholding thetool.Forremoving thetoolitisrotated sothatabulgeinthesideofthetoolliftsthespring abovetheedgeandsetsthetoolfree.Coupling between thetoolandstringissimilar tothepipe connections. Thelocking between thecarousel andthetoolmakesitpossible todisconnect thetoolfrom thestringsimplybypulling. Actuation andposition sensing ofthetoolcarousel issimilartothatofthepipe carousel, exceptthattheMaxondl0motorislocated insidethecarousel support (Figure9). 193