US1642949A - Drilling machine - Google Patents

Description

G. H. GILMAN DRILLING MACHINE mw.. l..

E mm mm,

Sept. 20 1927.

G. H. GILMAN DRILLING MACHINE Patented Sept. 20, 1.927.

UNITED .STATES 1,642,94e PATENT orrica GEORGE H. cinnamon BELMQNT, MASSACHUSETTS.

.mamme MACHrNE.

,Applicar'io'n'fiiea-Juiy.12, 192i. .-seriai No. 484,072.

My invention :relates `to drilling-machines and y more particularly but not exclusively to -a hammer rock drill.

The invention will be best .understood from lthe following description when read in the light of the accompanyingdrawings of a specific embodimentL Vof the rinvention selected for illustrativey purposes, while the scope of 'the invention will be .more particularly pointed out inthe .appended claims.

Fig. l isa lcentral longitudinal sectionof a hammer rock drillembodying .my invention; i

Fig. 2 is a central vlongitudinal section Ona plane at right angles-to that of Fig. l; Figs. 3, 4 and 5 respectively arefsections on the lines 3-3, 4-4 and 5 5 of l.;

Figs. 6, 7v and 8 are diagrainsillustrating the operation of the gear shifting ,mechanism and its controlling valve; and

Fig. 9 is a section on the line .9-9 of Fig. l, with the valve moved to the position illustrated by Fig. 7

Referring to the draw-ings, I Ihave shown a cylinder or'casing for yhoii-singi'the operative parts of the machine. Herein .the cylinder comprises first, ajfront head or chuck casing l which provides both a rotatable support for the sectional chuck .3 and ya casing for the gearing hereinafter described; second, .a main-cylinderpertion '5 which .is provided `with a bore for receivingthe large head 7 ofi-the piston; third, a block 9 Awhich supports a rearwardcylinder section l1 ,providing a bore for receivingthe .shank 13 of vthe piston; fourth, -a motor casing 15,; and fifth, a -rear -cylinder .head 17. These parts of the cylinder or :casing lare .shown zas held in assembled relation by vmea-ns of ithroughbolts 19 of which .I have vshown four, each extending from Ithe :rear :cylinder head .to the flange Q'llof the chuckcasing.

The drill steel 23 herein 'is ,provided Iwith lugs 25, received in recesses k27 linthe chuck,

'y which construction in a Vknow-n manner fpermits insertion of the drill .steel and retains it when inserted, and atthe Sametime .permits a slight longitudinal movement of :the steel relative the chuck and constrains yitfto rotate therewith. For striking .the :.drill steel, ,the hammer `piston `is shown `fas provided vwith a hammer bar '29, which fitsfthe front head l.3l of the. main cylinder portion in a fluid-tightmaniier and .is 'adapted to strike ithe rearward endfofythewsteel atfthe .the passage 37 communicates.

end of the .forward vstroke of the Lhammer piston.

.Herein .motive fluidvis supplied the machine -through a hose connection 33, which conductsthemotive fluid to the. casing of -a throttle valve 35 adapted to supply motive fluidor towinterrupt .such supplyto the intake passage 37 for the hammer. vFor distrbuting the supply, the .bore of the rearward .cylinder .member 1l is-shown as provided near its forward end with an intern-alannular groeve 39 and with this groove Leading rearwardly from lthe annular ,groove is a longitudinal groove 41 formed in the interior wal-l of the bore of the cylinder member '11.1, while in the same plane as the rearward-portion of the groove 41 and diainetrically opposite thereto is y.the port 43 of the passage 45 leading to the forward end of the larger cylinder bore. Further," the shank is shown as provided with a reduced diameter portion v47, whi-le opening into the intermediate portion of the llarger bore of the cylinder is an exhaust passage 49 adapted to be alternately placed in communication with the cylinder chambers at opposite sides of the head 7 bythe reciprocations fof the latter.

In the positionof the 4parts shown by Fig. l, motive fluid fis conducted from the supply V,passage37 through the annular groove 39, .the groove 4l, .the port 43 and passage 45 ^tosupply live motive fluid to the cylinderchamber forwardly of the head 7 and as at this @time the cylinder chamber at the rear of the head is placed in communication with the atmosphere bythe kpassage 49, the Vpiston will move rearwardly. Rearward movement of the piston l'closes Ithe port 43 yand near the end of the rearward stroke ,places the `groove 39 in communication with the cylinder chamber at the rea-r ofthe `head 7 'by means .of the reduced diameter/portion 47 of theshank. After the piston opens the passage 49 to the cylinder chamber forwardly of :the head, the air whiohhas been admitted thereto during the rearward stroke is exhausted to the atmosphere. Under these conditions the piston will moveforwardly, .aided by the Huid acting on .the rearward end of :the shank `in `a manner .hereinafter to be described.

' For .rotating Athe chuck l fhave shown a rotary engine, whichv Aengine herein compri-ses a 'centrally located .toothed rotor .51

and the toothed rotary abutments 53 in mesh with the rotor. 'lhe rotor journalled on the exterior ol the reduced diameter portion 55 ot the rearward cylinder section 11, While the abutments are keyed to shafts 57. The motor casing 15 is formed to lit the periphery ol the rotor and abutnients except at the point adjacent their intersection, Where are located the intake passages 59 and opposite these the exhaust passages G1.

As illustrated the rearward cylinder sec tion 11 provided with a cylindrical iange G3 and the rear cylinder head with a cylindrical llange over which flanges lits they central bore oit the motor casing, the smaller bores ol the motor casing litting over the flanges GT ot the bearing blocks G9 supporting the rearward end ot the shafts 5T. `In this manner is 'termed a casing for the rotary engine.

In the contacting surfaces oft the block l) and the rearward cylinder section 11 are shown adjacent interior and exterior annular grooves which provide an annular chamber T1 with Which the exhaust passages G1 oit the motor `connnunicate and which is placed in communication with the atmosphere by means ot the passage 78. `The tlange (i5 hereinbetore referred to is shown as made integral with the sleeve T5, over which sleeve placed the body portion ol the rear cylinder head 1T and which sleeve is carried by the rearn'artfl extremity of the section 11. ln the Atace ot the tlange (Se abutting the body portion is termed an annular iore Ti'. ivith which the intake passages a9 ott' the motor communicate. Motive linid is supplied the groove by Way ot' a suitable valve '79 arranged to throttle or completely interrupt the supply.

For supplying the chuck rotating motor with motive fluid, I herein provide a.' suitable conduit means leading both 'from the motivo tluid supply `connectioior and from the smaller cylinder bore to the motor throttle. 1n the submitted embodiment ot my invention, this conduit means comprises a passage indicated in its entirety by 81 and which opens into the rear cylinder chan'iher and is in permanent communication With the motive liuid supply by way ot a coniinunicating slot S3 l'forined in the valve sleeve 85, other portions ot this conduit means being provided by the rear cylinder chamber and the passage indicated in its entirety by S7 and leading :trom the rear cylinder chamber to the throttle valve '79. The conduitl 81 provides a supply ovll motive fluid lor the rear cylinder chamber and the motor during the 'forward stroke of the piston. During the rearward stroke, the motive lluid admitted to the rear cylinder chamber through the conduit 81 and the groove 4-1 compressed, which cushions the hannner and increases the rotative ellort ol the motor. Any suitable n'xeans lor' preventing' the return ol motive fiuid trom the rear cylinder chamber to the source during the rearward stroke may be provided. In the submitted embodiment oli my invention, such a means takes the term ot the inwardly opening check valve 89 constructed to be operated by fluid in the manner usual with such valves and provided with the spring Slt) to insure its seating. 1t will be noted that in this manner a compressor is provided of which compressor the conduit- E31 is the intake and the conduit 8T the outlet, and by mans olI which intake and outletlive niiotive lluid from the source ol' supply is coml'nesifsed to augment the pressure ol the motive tluid.

As illustrated, on the forward end ot" each shalt 5T are oppositely arranged eecentrics 91 and on the cm'respondging eccentrics ot each shat't are carried the internal toothed .yokes lli-3, which are adapted to surround and mesh with the exteriorly toothed portion Stlot the shiltable sleeve 95 splined to the chuck by means ol cooperating tongues 0T and grooves 00. llihen the motor is in operation, the gear toothed portion of the particular yoke 93 in mesh with the sleeve is caused to roll around the gear toothed portion ot' the sleeve, which rotates the sleeve at a speed proportional to the ditlfen ence in the number ot teeth on that yoke and on the sleeve. One oi the yokes is it'orniod with a slightly different number ot teeth than the other, in order that the torque impressed on the drill steel. or its speed may be varied by shitting the gea r toothed portion ot the sleeve from one yoke to the other. lhe space between the yokes made ot sullicient width to enable the, gear toothed portion ot the sleeve to be placed intermediate the yokes, under which condition the chuck is diseonneeted from the motor.

For shitting the sleeve 95, the forward end thereof is shown as provided with an annular groove 101 which receives the lower end ot the shipper bar 103, so that moves ment oit the bar will cause corresponding` movement ot' the sleeve. Herein, the meehanisni tor operating the shipper bar is ear- 1 ried by the chuck casing and comprises both a manually and a fluid operative means. The manually operative means as shown comprises a rod 105, bolted to the shipper bar and provided with a handle member 107 carrying the sln'ing-pressed pin 10D adapted to engage recesses 111 lormed in the surface ot the chuck, exteriorly olE the portion 113 oilf the chuck casing which houses the shipper bar and gearing. The rod 105 is supported by the Walls oi an opening 111- which it tits and is held in adjusted position by engagement ol the pins With the recess 111.

Herein, for operating the shipper bar by Sil message fluid pressure, the upperendof the bar-is attached to a pistonrod 115 'which' in conjunction with the rod 105 acts to'guide the bar and whichis formed-integrally with vthe piston 117. rEh-is piston f-is' reciprocably mounted lin a's1eeve119 fittedy in the bore 121 formed in the enlarged portion 123 of the Achuck casing. As illustrated by F igpl, the sleeve terminates at V`an lintermediate portion of the bore 121 in order/to prov-idea forward cylinder vportionof a diameter larger than that provided bythe sleeve and is provided wit-h a flange 125 which holds it in position when the machine is assembled.

In the forward portion lof the bore is thev annular piston 127 which in a fluid-tight manner lits both'fthe 'rod '115 and the cylindrical surface of the "bore 121.

Rearwardlyfgof the sleeve 119 I zherein provide a tapered bore 128 forreceiving the asthe valvev end of the'passage 133 and lead-- ing from'the bore 129 is `a passage 137 communicating with the rearward end of the 4cylinder for the fpiston l117 a' passage 139 communicating with thev forward-end of the cylinder for the piston v127 and a passage 141 communicating with the adjacent ends of the two cylinders. The valve is provided with a live air-slot '143 with which communicates the radial `passage 145 and' with the latter communicates an eX- terior arcuate groove'147, the slot, passage and groove all beingvin the same plane with the passages 137, 139, 141 and the conduit 133. Formed on the exterior surface o-f the valve is a longitudinalfeXha-ust groove 149 and a wider longitudinal "exhaust groove 151, while interiorly of the casing for the valve isv formed an 'annular groove 159 in permanent communication with the atmosphere through a port 161. The longitudinal exhaust grooves 149 and 151 have one end in the plane ofthe passages leading to the cylinders and the other in the plane of the groove 159 so that when `the exhaust grooves are in com u nication with lthe passages leading'to t-he cylinders, the latter will be placed. in communication with the atmosphere. v

The gear shifting mechanism is shown in its neutral position in Fig. 6, under which conditions `both `yokes-fare 'disconnected rfrom the sleeve 95. Inlthis lposition of parts, motive fluid is supplied 4both the'passages 137 and 139 leading v.to the cylinder ends most remote, while the passage 141 is connected to the atmosphere yby way of the `groove 151, which in :this position of the valve communicates with said passage. This causes both pistons yto approach eachother and be held at adjacent ends of their respective cylinders. 17V hen the valve is moved from the neutral position to the position illustrated by Fig. 7,. motive fluid *isv exhausted through the passages 139 and 141 and is supplied to the passage 137, which causes both pistons to move forwardly the full distance permitted 'by the construction and places the sleeve 95 inmesh with the forwardly located yoke.v IV hen the valve is moved from the neutral' position to that illustrated by Fig. 1, mo-

tive fluid yis exhausted from the rearward end of the smaller cylinder and suppliedtol nular groove 159 while .at its other end it.

terminates in the plane of thepassages leading to the cylinder ends. Movement of the valve in the position illustrated by Fig. 8 closesofl the intake passage .133 and connects all of the passages lea-ding to the cylinder ends to each other and to the-atmosphere by way of the valve passages 143, 145, grooves 163, 159 and passage 161. e It will be observed that the percussive and chuck rotating motors herein described are of the type wherein the motive fluid is substantially continuously admitted and eX- hausted for producing continuous motion of the motor.

This application discloses improvements of Vthe inventions disclosed iny my `pending applications Serial No. 437,664, .filed January 17, 1921, Serial No. 421,743, filed November v4, .1920, and ASerial No. 76,410, filed December19, 1925, the last mentioned lbeing a division of-said application Serial No. 421,748.

Although I Yhave described one specific embodiment of my invention for purposes of illustration, it is kto be understood that wide deviations from the same may be'made without departing from the spirit of my invention.

Claims:

1. A drilling machine having, in combinati-on, fiuid pressure operated motor means for actuating a drilling tool, said motor means .of the type wherein motive fluid is substantially continuously admitted and eX- hausted for producing continuous motion of the motor, means forming .a compressor,

lill

While supplying the compressed motive fluid to said fluid pressure actuated motor means.

2. A drilling machine having, in combination, fluid pressure operated motor means for actuating a drilling tool, said motor means of the type wherein motive fluid is substantially continuously admitted and eX- hausted for producing continuous motion of the motor.l means forming a motor operated compressor, a. motive fluid supply connection, means for supplying said compressor with live motive fluid for actuation thereof and for supplying the compression chamber of said compressor with live motive fluid whereby the latter is compressed, and means permitting the escape of said compressed live motive fluid from said chamber substantially solely by Way of said motor.

3, In a drilling machine, a fluid pressure operated motor for actuating` a drilling tool, said motor of the type wherein motive fluid substantially continuously admitted and exhausted for Inoducing continuous motion of said motor, means providing a motor operated single acting compressor comprising a compressor cylinder' and piston, a motive fluid supply connection, conduit means supplying said compressor With motive fluid from said connection for actuation of said compressor', conduit means supplying said motor with motive fluid from said connection by Way of said compressor cylinder whereby said motor is operated and said cylinder charged with live motive fluid on the expansion stroke of said compressor, and means acting substantially completely to interrupt communication between said cylinder and connection on the compression stroke of said compressor whereby said motor is then supplied with compressed live fluid.

4;. In a drilling machine, a Huid operated motor for actuating a drilling tool, a hammer independent of said motor for actuating said tool, a cylinder for said hammer which with said hammer forms an expansible chamber, an inlet to said expansible chamber having a check valve for automatically permitting' flow of fluid to said chamber and preventing flou7 therefrom, and an outlet from said chamber for con ducting actuating fluid to said motor,

Iii a drilling machine, fluid operated percussive means for actuating a drilling tool, means for substantially completely trapping live motive fluid and for causing said fluid to be compressed by energy imparted by said percussive means, fluid operated motor means for actuating said tool other than said percussive means, said motor means of the type wherein motive fluid is substantially continuously admitted and eX- hausted for producing continuous motion of the motor, and means for supplying the last mentioned motor means with such compressed fluid.

G. In a drilling machine, a Huid operated percussive means for actuating a drilling tool,` a motive fluid supply connection, means for taking a charge of live motive fluid from said connection and for compressing it by energy imparted by said percussive means While preventing return of said charge to said connection, fluid operated motor means for actuating said tool other than said percussive means, said motor means of the type wherein motive fluid is substantially continuously admitted and eX- hausted for producing continuous motion of the motor, and conduit means for supplying the compressed charge to said fluid operated motor means.

7. In a drilling machine, a fluid operated percussive means for actuating a drilling tool, a motive fluid supply connection, means for taking a charge of live motive fluid from said connection and for compressing it by energy imparted by said percussive means while preventing return of said charge to said connection, a motor for giving angular movement to said tool, and conduit means for supplying the compressed charge to said motor.

8. In a drilling machine, a fluid operated percussive means for actuating a` drilling tool, a motive fluid supply connection, means for taking a charge of live motive fluid from said connection and for compressing it by energy imparted by said percussive means While preventing return of said charge to said connection, a rotary engine for rotating said tool, and conduit means for 'supplying the compressed charge to said engine.

9. In a drilling machine, a hammer piston for actuating a drilling tool, said piston having a pressure surface, a hammer cylinder having a surface opposed to said pressure surface of' said piston, a motor for giving angular movement to said tool. conduit means connecting the space between said surfaces to said motor, a motive fluid supply connection, a conduit connect-ing said connection with the space between said surfaces, a pressure actuated valve for controlling the flow of motive fluid through aid conduit effective to cause motive fluid materially to be compressed between said surfaces,y and means for causing said piston to reciprocate.

l0. In a drilling machine, a hammer piston having a pressure surface. a hammer cylinder having a pressure surface ,opposed to said pressure surface of said piston, a

lllll nem-94o motor' for giving angular movementto lsaid tool, meansonstantly supplying said motor withy motive fluid', said means intermittently completely Vtrapping andi compressing said moti-ve fluid between:` said! pressure surfaces;

11. In' a drilling machine, a motorfor rotating a drillingtool, a motivelfluid supply connection, conduit means connectingV said connection to the atmosphere by way` of said motor, a checkl valve for preventing flow through said conduit means toward said connection, andrmeansfor trapping and compressing live fluid: from said connection betweenE said check valve and: motor and supplying'the compressed fluid tov Vsaid motor.

l2-, En a. drilling machinaalv hammer for actuating a drillingtoohsaid hammer hav'- ing a head and a; shank', a motive fluid supply connection `means' for' intermittently admitting fluid from said: connection to said? cylinder behind said head for' movingl said hammer inone: direction, a conduit meansfor supplying"motivey fluid from said connecti'onitoL thei end' of? said? cylinder fitting said shank, a; motor?y forv actuatingfsaid drill'- ing tooli'hafvingf an intake in communication wifthsaidzconduit' means, and. af valve between said'l intake and? connectionA preventing flow throu'gha` said conduit from said cylinder to vsaid connection..

132. In a drilling machine, ay cylinder having a larger forward bore and a smaller rearward: bore,` ay hammerpiston for actuating a: drillingtool, saidzfhammer` having ahead fitting said larger borey and-a:y shank fitting. said rearward bore,` amotor` for rol lal hammer piston for operating' said*- tool having an: intermittently acting-` 'pressure surfacey and asma-ller; opposed."` pressure surf-ace, a motor for rotating'said tool and means including acylinder for saidpiston and cooperating ports* and. passages for causing said smaller surfacegcompletely to trap. and. compress 'l'ivef pressure fluid in said cylinder and to supply it to said motor for actuation thereof.

15.-1n a drilling machine, a drilling tool, a motive fluid supply connection, a hammer piston having anintermittently acting pressure surface, a shank having a smaller opposed pressure surface, said shank for con* trolling the admission of pressure fluid from said source to said intermittently acting pressure surface, a motor for rotating said tool and having an intake in commiuiication i with the [space behind saidv opposed surface,

ous; communication with said source when said; tool is iny operation, and an inwardly openin'gLcheck valve controlling said passage;

17. In, a percussivetool, a cylinder, a differential pistou therein having a rearwardly facingY continuous pressure surface, a source ofy motive fluid supply, a passage establishing communication between Ysaid source and the cylinder chamber Vfor said continuous pressure surface, said passage beingI in continuous communication with said source when said tool is in operation, and: anv inwardly opening check valve con,- trolling' said passage. Y

138". In a percussivejtooh a piston having a head and a rearward shank, a cylinder hav-ingr portions receiving said head and shank, a source of" motive fluid,` a passage having an inwardly opening check valve connecting` said source withy the cylinder chamber rearwardly ofl said shank, and passages-'controlled by said shank for alternately admitting motivel fluid tothe cylinder chambers onopposite sides ofv saidc'head.

19. Ink ax percussive tool, a. piston providing: a: head: and a rearward shank: having a portion. of'reduced diameter, a cylinder'ha'ving. portions receiving said headand shank, ai motive fluid', supply passage having a port opening into the forward end ofthe cylinder portionreceiving; said shank, a motive fluid supply passage having'a port'. opening into s-aidflast named; cylinder portion rearwardly of said: last named port,na'fluid operated valve` for preventing? return flow through said-last named'passage7` a motive fluid supplyv port opening into saidl'ast named cylinder portion intermediate the other ports, a passage' connectinganV intermediate portion ofthe'cylinder portion receiving said shank with the forwardI end; of the cylinder portion receiving said head, whereby said shank/*may admit fluid toact on. the rear-v ward end of said head during the forward stroke and the rearward end of Said shank may admit fluid to act on the forward end of said head during the rearward stroke.

20. In a percussive tool, a piston having a head and a rearward shank, a cylinder having portions receiving said head and shank, a source of motive fluid, a passage connecting said source with the cylinder chamber rearwardly of said shank, a fluid operated valve preventing return flow through said passage, and passages controlled by said shank 1to1' alternately admitting motive lluid to the cylinder chambers on opposite sides ot said head.

2l. A. rock drill having, in combination, a rotary chuck Yformed for carrying a drill steel, a fluid operated hammer ior imparting percussion to said steel, a fluid operated motor ior rotatingl said chuck, power transmission means betn'een said motor and chuck means ttor varying the mechanical advantage ot' said transmission, fluid operated mechanism tor controlling said means, and means tor supplying motive fluid from a somfce ot supply to the recited lluid operated instrumentalities includingl means tor controlling the motive fluid supplied to cach whereby the torque impressed on the drill steel may be coordinated vvith the percussion imparted thereto.

22. A rock drill having, in combination, a rotary chuck iormed it'or carrying a drill steel, a i'luid operated hammer for imparting percussion to said steel. a `tlnid operated motor ior rotating' said chuck. variable speed reduction gearing for imparting the effort olf said motor to said chuck; a casing carrying said chuck, motor and reduction gearing, said gearing comprising a pair ot annular gears surrounding the axial line ot said chuck and arranged to mesh with a gear coaxial with and operatively connected to said chuck, and fluid ope ated mechanism carried by said casing for causing one or the other ot said annular gears to mesh with said gear operatively connected to said chuck.

Q3. A, rock drill having, in con'ibination. percussive means 'for a drill steel, a chuck formed tor carryingr said drill steel, a casing in which said chuck is rotatably mounted, a motor for rotating said chuck, power transmission means between said motor and chuck including a change speed shift gearing, and means .'lior coordinating the torque impressed on the drill steel with the percussion imparted thereto including iluid operated mechanism for actuating said shiftgearing.

52st. A rock drill having` in combination, a chuck formed 'tor carrying a drill steel, a motor tor rotating said chuck, means tor rendering said motor operative or inoperative at will to drive said chuck, said means comprising an annular gear surrounding and meshing With a gear on said chuck and mechanism for selectivelyplacing said gears into and out` oi mesh, and fluid operated mechanism for actuating said mechanism.

Q5. A rock drill having, in con'lbination, a chuck 'formed 'for carrying a drill steel, a motor for rotating said chuck, means tor rendering said motor operative or inoperative at will to drive said chuck, said means comprising an annular gear surrounding and meshing with a gear on said chuck and mechanism for selectively1 placing said gears into and out ot' mesh, and manually operated mechanism for actuating said merhaiiism.

2G. A rock drill having, in combination, a hannner cylinder containing a hai'runer for imparting percussion to aI drill steel, a rotatable chuck tormed foncarrying said drill steel, a motor for rotating said chuck, power transmission mechanism between said motor and chuck comprising a pair of spaced annular gyratory gears surrounding said chuck and a gear splined to said chuck adapted to mesh with either of said annular gears. and means for varying the mechanical advantage ot .said transmission for coordinating the torque impressed on the drill steel with the percussion imparted thereto or for renderiim; said motor inoperative to drive said chuck conuirising mechanism for holding said gear on said chuck in mesh with `either of said cyratory gears or out oi mesh with both ot them.

2T. A rock drill having, in combination, a hammer cylinder containing a hammer for imparting percussion to a drill steel, a rotatable chuck formed for carrying said drill steel, a motor for rotating said chuck. power transn'iission mechanism between said motor and chuck comprising three gears each with a different number of teeth. gear shitting means 'for causing one ot said gears to `mesh with either of the other oi said gears or to be held out of mesh with both of them for coordinating the torque impressed on the drill steel with the percussion imparted thereto or tor rendering saidmotor inoperative to drive said chuck, one of said gearsbeing driven by said motor and surrounding said chuck and being mounted ilor gyratory movement and another of said gears being mounted on said chuck.

In testimony whereof,` I have signed my name to this specification. t

GEORGE H. GILMAN.

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