US2750178A - Picking type mining apparatus - Google Patents

Description

June 12, 1956 R. A. MCCALLUM 2,750,178

PICKING TYPE MINING APPARATUS Filed March 6. 1952 5 Sheets-Sheet l June 12, 1956 R. A. MCCALLUM PICKING TYPE MINING APPARATUS 5 Sheets-Sheet 2 Filed March 6. 1952 June l2, 1956 R. A. MccALLUM PICKING TYPE MINING APPARATUS 5 Sheets-Sheet 3 Filed March 6, 1952 f y N @N @N NNN NNN QSA SN Q. a NQN y w @QN M WIIIIIIA- 0 @N QN ha @A d m w NN 1 @n SAN Nw, Nw n mw @A S l/ .w mwN w RN NDA 51 m&\ rn %NN\ www. \.M\\ E IIH Y mmmmmML-Lov .L n @n no NM. i mwdm. wUNDOm Rumi -d u H im A .A f ma. NNKN f A Aww@ was .w ad? n .NUBNAB Q"WNN n ul "IHM .A mmmQi- NNN @QN QQMWNAWWQN MWNN QWNNQNNN June 12, 1956 R. A. MccALLUM PICKING TYPE MINING APPARATUS 5 Sheets-Shea?l 4 Filed March 6, 1952 w, i M v 6%. w M a NNN k bQNN MYN NN N a \\NN A7 l. l 4 A u Y A o :Mmm: E @s w p W ,M a W KQN L QN n wwx A E wm, w www n y Mwx me Il a n 1I 1 MMMNNMWNvmNWI IWNN. QNN NN R a .MMM @Qs MN I www QN www www A .QN N mwN vmN AMW vm \%N Q E June 12, 1956 R. A. MCCALLUM Plcxmc TYPE MINING APPARATUS 5 Sheets-Sheet 5 Filed March 6. 1952 M, WW MW RIN WWMQ'NQW k Nm m1. ok Wm, wk

l and 2 consists of a plate 27 formed to underlie the gathering head 16 and the receiving end of the flight conveyor 22. The receiving trough 26 has vertical sides 28 which fair inward as at 29 toward the vertical walls 23 of the conveyor trough 24.

As seen in Fig. 1 the flight conveyor 22 conveys material gathered by the gathering head 16 upwardly over the frame 12 and towards the rear thereof. The machine 11 may be provided with a discharge boom, not shown, which may be articulated with respect to conveyor trough 24 so that the material may be discharged off to the rear and one side or another of the machine 11 into a shuttle car, belt conveyor or the like.

A pair of piston and ram assemblies 31 are joined at their ramming end adjacent the seam 20 by a cross head 32 having spaced picking members 33 thereon which engage the working face of the seam 20. Each end of the crosshead 32 is pin connected as at 34 to a ram member 36 which is a part of the ram and piston assembly 31, the details of which assembly will be described in more detail as this specification proceeds.

Each ram piston assembly 31 is provided with a pair of rearwardly extending trunnion members 37 having trunnion stub shafts 38 which extend laterally and outwardly therefrom. Said shafts extend through laterally spaced trunnion supports 39 which extend upward from the frame 12 and flank the ram and piston assemblies 31.

Each piston and ram assembly 31 is adapted to swivel in a vertical plane on the stub shafts 38, and means for raising and lowering the piston and ram assemblies in such manner will now be described. Each piston and ram assembly 31 is mounted on a support plate 41 having lateral extensions 42 on each side of the piston and ram assembly 31. Each end of such extension 42 is provided with a free swivelling connection 43 to a piston rod 44 of a hydraulic cylinder 46 also having a swivel connection 47 to the top of the main frame.

Referring now particularly to Figs. 4 and 4A, each 1 ram and piston assembly 31 comprises a cylinder sleeve 51 having la piston 52 movable therein. The cylinder sleeve 51 has an extended skirt 53 welded to an annular ring 54 which in turn is held by cap screws 56 to a thickened rib 55 at the end of the cylinder sleeve 51. The end of the skirt 53 remote from the cylinder sleeve 51 has welded thereto a stiener ring 57, and a seal 50 including annular sealing members 58 and 59 with sealing lips 61 and 62 respectively are held to the end of the stiffener ring 57 by means of clamping rings 63, 64 and 66, said rings and sealing members being held in place by a plurality of cap screws 67 threaded into the stiffenel' ring 57.

The piston 52 has a skirt 68 and a skirt tube 69 is tted around the annular piston skirt 68 and is held in place by welding. As seen in Fig. 4A, the exterior of the skirt tube 69 is guided within the sealing rings 58 and 59 and is provided with an end sleeve 71 which bears against and tits within the ram member 36. An annular ring 73 is tted to the outside of the end sleeve 71 and a dust sleeve 74 is welded to the periphery of the annular ring 73, and extends along the outside of the skirt 53 toward the end of the cylinder sleeve 51.

The ram member 36 has a pair of spaced apart jaws 76 and 77, and aligned openings 78 and 79 for receiving the pin 34 holding the cross head 32 in position spanning the pair of piston and ram assemblies 31, as seen more clearly in Fig. 2. The ram member 36 has an arcuate surface 81 which matches a similar arcuate surface 82 on the end of the crosshead 32 so that the thrust of the ram member 36 against the crosshead 32 may be taken along the mating arcuate surfaces 81 and 82.

The cylinder sleeve 51 is also provided with a cylinder head 84 having a flange 86 bearing against the end of the cylinder sleeve 51. A control mechanism housing 87 has a flange 88 which bears against a flange 89 at the end of the cylinder sleeve 51, the cylinder head 84 being thus held in position between the anges 88 and 89 by cap bolts 91.

The piston 52 is bored centrally thereof as at 92 and also counter bored at 93 to receive a nut 94 having a shoulder 96 adapted to fit in the counter bore 93, the nut 94 being held in position in the piston 52 by means of countersunk socket head screws 97. As seen more particularly in Fig. 4, the nut 94 is interiorly threaded to receive a screw shaft 99, which upon rotation in a preferred direction will move the piston S2 toward the cylinder head 84. In the embodiment shown, the screw shaft 99 is of the multiple thread type and has live threads which gives a large amount of translative movement of the piston 52 for each revolution of the screw 99.

In order that rotation of the screw 99 in moving the piston back to the cylinder head 84 will not cause rushing of air past the mating thread surfaces of the screw 99 and the nut 94, a closed sleeve 101 surrounds the free end of the screw 99 and is held to the skirt 68 of the piston 52, being held in position by weldments 102. As seen more clearly in Fig. 3, the volume 100 between the end of the screw 99 and an end wall 103 of the sleeve 101 is so chosen that the pressure in the volume 104 enclosed between the piston 52 and the cylinder head 84 and pressure in volume 100 are substantially equal at all times, so that air will be prevented from moving back and forth past the clearance between the threads of the nut 94 and the threads of the screw 99.

As seen also with reference to Figs. 3 and 4, the screw shaft 99 is rotated to effect compression of the air between the piston 52 and the cylinder head 84, such pressure being etective upon release of the screw shaft 99 to advance the piston 52 and the ram 32 rapidly with the crosshead 32 against the seam of coal 20. As seen more particularly in Fig. 1, the frame 12 affords a support for a drive motor 106 mounted to one side of the trough section 24. The motor 106 has a drive shaft 107 and a universal coupling 108 which is on the line of centers of the stub shafts 38, so that the piston and ram assembly 31 associated therewith may freely swivel about the stub shafts 38 while the motor 106 remains in fixed position on the main frame 12.

A driven shaft 109 having a drive pinion 111 fast thereon is journaled at one end within a needle bearing 112 supported within a driving clutch member 113 splined to the shaft 109. The shaft 109 is supported at its other end and turns within an outer race 114 of an overrunning sprag type brake having an inner race 116 keyed at 115 to the driven shaft 109, the outer race 114 thereof being held against rotation in a drilled shaft support 118 by a key 117, said shaft support 118 being formed integrally with the housing 87.

A drivenclutch member 119 is keyed at 121 to the driven shaft 109 and is supported within bearings 122 held in a bearing support 123 formed integrally with the housing 87. Clutch plates 124 connect the driving clutch member 113 to the driven clutch 119, and a clutch throwout yoke 126 controls the clutching between the driving clutch member 113 and the driven clutch member 119.

The pinion A111 meshes with a gear 127 supported on bearings 128 which in turn are supported on a bearing surface 129 formed as a part of an extension 131 of the screw 99. As seen in Fig. 4 the extension 131 is supported in a bearing 132 held in an annular boss 133 extending inwardly from an end wall 134 of the housing 87. The shaft extension 131 is also supported on a ball bearing held in the cylinder head 84 and between a shaft seal and thrust assembly, indicated generally by the reference numeral 125, and a lock nut 135 threaded to the shaft extension 131.

A multi-disc clutch 136 includes clutch plates 137 externally splined to an internally splined hub 138 extending from the gear 127, and clutch discs 139 splined on the inside diameter thereof to an externally splined hub 141,

which.inuturnissplined to a hubA 142 of theouterrace 143 ofan overrunningclutch 1,44. haying an inside race 146 held by a spline 147 to tite shaft extension 131 of the screw99.

' Iheclutch.lfismaintained in ,clutching position by means of springs 148 held in bores 149 on the exterior of the .cylinder head 84.and bearing against a piston 151 movable within a cylinder 153 held by cap screws 154.V to `the outside .of the ,cylinder head 84. Pressure from the springs lflSagainstthe piston 151 is transmitted by thrust b all bearings .152 .against a pressure disc 155 freely mounted. onthe shaft extension 131. YPressure disc 155 bears, againstpressurepins v154 .passing through bores 156 in the hub fof thedriven gear 127. Pressure to release the clutching .engagement of theclutch discs 136 is aiforded ythrN-l-lh apressure line 157 and acting against a face 15S of the pistonl'landin a drectionopposed to the force of the springs 148, vundenconditions as Will appear as this specification proceeds.

.An auxiliary housing 16d has a circularflange 161 which is held by cap screws.162 to the housing 87. The housing 160 contains a shaft 163 which is splined at 164 tothe end ofthe shaft extensionv llprotrudin g into the housing 160. The .shaft 163. ismade a part of an internal race 166 of an overrunning .sprag type clutch 167 having an outer race '168.,form'ed integrally with a shaft 169 for driving an auxiliary pump '.171-to supply pressure fluid to the ,line 172 extending through the Wall of the housing 161 under conditions Las will appear in moredetail as this description proceeds.

. .Referring nowparticularly to Figs. 5, 6, 7 and 8 ofthe drawings, eachpiston and ram assembly 31 has Welded togthebottom thereof aplate 173 having formed integrally therewith a downward extending boss 174 reduced as at 176 to provide a shoulder 177rfor a flanged bushing 178 which rests upon .the support plate 41 and between thei shoulder '5177. A plate 18)v is held Iby countersunk screwsfljSfS tothe plate'173 and partially encircles the boss 174 alo-ng. an arcuatesurface '19.0 thereof." The plate ltlprovdes additional bearing surfacelfor the piston and ram assembly 31: on the suppnrt'plate 451. The-.portionof reduced diameter 176 of the boss17.4 is also fitted with a angedbushjngl79 which bearsagainst the under .side of the supportplate 4 1, and is heldin positionby a circulalnplatejwljheld to the boss 17,4 by c ap screws 182. The supportjplate 41V. has an arcuate flange 183 which matches an arcuate angedmember'184 held to thev plate 173 yby cap-screws 186. Theboss 174' thus provides aturning .center for thepiston and ram assembly 31 with respect.to thtsuppostrlate@ Such turning, of the piston .ram assembly ,'31, .howeyen isglimitedbya,resilientpad 137 whichisbonded on its underside as; at"1$8jto the upper side ofthe supportplate 41; the upper side of theresilientpadbeingbonded as at 189 to a,. plat.e4 191 which is held inposition to the under- 4side`olf;the`.plate"1734 by cap screws'192. As seenmore jparticularlyinfFigs. 7 andSthe turning .of the ypiston ram rasserrlblyiwith respect to thesupportplatefll is limited by the resistance toshearing afforded b y the resilientpad "18.7.

""The resilient pad 187 formingpart of the support 41 thus."alfords Alimited, swiveling movementof each individual'ram andpiston assembly 31 occasioned by variation .in resistanceY encountered by the crosshead 32 thrpughontxitsflength, such variation in somecasescausing-'the crosshead to assume positions where it no longer wouldbe at rightnan'gles to ,the individual piston and ram .assemblies"31. Sinceeach ram and piston assembly lies on a, tixedtu'rning center .there would be involved a degree f swiyelingmoyement of one 0r the otherofsuch piston .andI ram assembliesso V.that there ,would varise ,at ,the saine tirne a .condition of non-.parallelism o f the assemhliesin accommodating lthe Skt-'Wins movement of.-,th.e. `cr.o.sst.1 ntd 32.

Referring now particularly to Fig. 3 of the drawings,

.thereis shown an hydraulic Circuit whchontrqls the L0D- eration of.. the mechanism.. thus fat incriminati-add.- tionally insures the completion of a compressionstrglge offthepiston .52. of each. ram and piston assembly, and frees` the, driving mechanism after such return. 01 Y101,11- presson stroke. for a power stroke, sothat .each pistQnSZ and ram meinber is free to `move rapidly under, .the force of. the compressed air to .advance thecrosshcad 32 rapidly against the coal seam 20.

I t may be noted in describing the piStQnanCl Ltnlas` semblies of Fig. 3, that one of s uch assemblies andthe control mechanism therefor bears reference numerals alone, while the other of such assemblies bears reference numerals having an additional letter a reference character. All references to apparatus bearing only the numeral reference includes also the .numeral and letter. reference. Where necessary, for understanding of theoperation and function, and in cases where the conditionof oneof assemblies is alected by the conditionof the other, reference to the separate assemblies by their appropriate nnmeral designation and their appropriate numeral and letter designation will be made. All apparatus common to both assemblies bears the numeral designation only, by way of example, certain pumps, pressurelines and valve apparatus.

The hydraulic system comprises atank or reservoir 196 connected by a line 197 to a main pump 198. The output from main pump 19S is connected .by a pressure line 199 toY an on-offl spool type valve 201. A pressure line 202 connects on-off valve, 2111 to auxiliary valves 2,03 and V20 3a connected in series, each of which is actuated to open position by a push rod 264,which is shifted axially to the right as seenin Fig. 3 by the movementof piston 52 to position adjacent `the the'cylinder head 84. lThe conjcint opening of thel valves 2,03 passes pressure fluid by Way of a pressure line y206 which branches into pressure lines 157 leading toylinders 153, thepressure rluidbeingoperable to release lclutch 13,6.

Consider theoperation of the mechanism thusfar described for achieving a cocking or compression. stroke of the pistonjZ within the cylinder ,51. The piston ,5.2 will be consi dered at the start of suchstrole in ,an Aextendedposition as shown in Fig. 3. The invention herein comprehends a. master switch .for controlling thepperation ofthe motors 106, which operation also. sta rts the main pump 19s. A shas been explained, .the two screw v shafts 99 are of opposite hand` and must therefore be turned by motors operating in ydifferent directions. The proyisionof. such a design eliminates any whipping torques .Caused by sudden release of load upon each of the motors, as will be explained. It may be understood,,however,. that screw shaft`s99 may be provided with threads of the s arnehand for the Sake 0f nterchanseabilty and. that .thernntor/S 1 06 in such case run in thesame direction.

For-purposesof vdescripticm the ram andpiustpn assemblyand control mechanism therefor in the lower half of the drawing of Fig. 3, andbearing the numeraldecsignation alone,` will be considered, but it is believed t hat theoperation of the mechanismof theupperhalf of Eig. 3. .and bearing both nume-.ral and letter rcfctenceqhaactors, will bereadily understood.

jgThe motor. 1 06 turns shaft 109, clutch members 1,13 and 1,19'being engaged through the medium of therclntsh throwout yoke 1'26which isin the clutch .engagingposi- Ytion bec :a1 1se of the positionof ythepush rod 2tl4 b ei ng shifted to the left underthe urgence ofaspringlll.. Ik@ p ush rod` 204,1,actuates a throwout lever j2t)7 to e ngag e clutch members 113 and 119, thethrQWout lever biel-Dg urged to Suchrosition additionally by ,a-Snring ,208. i 'The pininn 'lllandiheinner facs 111,6., are freefto run Wit-.h respect tothe vny.errnmnittg .Clutch- 114, .116.11m arrow .on .the inner. raceA A116.. indicating the. direction of. 'free- A.doin ,of increment.. Qfthernner .race 1.16.-,with -respect; t9

the outer race 1124.' The pinion 111 drives the gear 127 and since fluid is blocked from the clutch control cylinder 153 by the series connected valves 203, the return spring 148 causes engagement of the clutch 136 thus driving the hub 142 forming the outer race of the sprag or overrunning clutch 144. The inner race 146 of overrunning clutch 144 is adapted to overrun the outer race 142 in the direction of the arrow shown on the inner race 146, and the hub 142 and gear 127 thus drive the screw shaft 131 in a counter-clockwise direction as viewed from the right as seen in Figs. 3 and 4.

Such counterclockwise movement of the screw shaft 99 thus moves the piston 52 and ram member 36 to the right to compress air between piston 52 and cylinder head 84.

The piston skirt 69 and cylinder sleeve S1 define an annular chamber 210 behind the piston 52. This annular chamber 210 communicates by means of a conduit 209 with the confined space 104 between piston 52 and cylinder head 84, so that a differential total force will exist across the piston 52. The conduit 209 is connected by a conduit 211 in series with a valve 212 to a source of compressed makeup air 213.

The counterclockwise movement of screw shaft 99 moves the piston to the end of the push rod 204 extending into the cylinder 51 to move the push rod 204 to the right against the load of the return spring 214. Movement of the push rod 204 in turn moves a linger 216 to actuate and open valve 212 to the supply of make-up air 213. lf the pressure of the air in volume 104 is less than the pressure of the source 213 additional air under pressure moves past a check valve 217 to the confined space 104.

The piston 52 and ram 36 may now be considered to be in a cocked or ready-for-fire position, but before the piston 52 may move in a firing or power stroke, the screwV shaft 99 must be free for turning in the piston 52. The movement of the piston to such cocked position then accomplishes the following operations.

The rst of these is release of the clutching elements 119 and 113 by rocking of the throwout lever 207 in a clockwise direction against the spring 208. Assuming that piston 52 reaches the cocked position before piston 52a, the push rod 204 is effective to open valve 203. Since the valves 203 are connected in series and the valve 203a associated with the other ram and piston assembly 31 is still closed, pressure fluid from pump 198 is effectively blocked thus cutting off the tlow of pressure fluid to the cylinder 153.

A bleed pressure line 218 is connected between each of cylinders 153 and 15311 and tank 196, there being a bleed valve 219 connected therein which regulates the rate at which pressure fluid is released from the cylinders 153 and 153a.

With fluid still released from cylinder 153 clutch 136 remains engaged. The pressure of the compressed air between piston 52 and cylinder head 84 would normally drive piston 52 to the left at the same time effecting clockwise rotation of the screw shaft 99. The sprag clutch 144, however, overruns only when the inner race 146 thereof rotates in a counterclockwise direction with respect to outer race 142. The shaft 131, then, is locked to the outer race 142 tending to turn same in the same direction (clockwise). The tendency of the outer race 142 to turn clockwise is of course restrained by the clutch 136 which locks the outer race 142 to the driven gear 127. The gear 127, however, is restrained against rotation in a clockwise direction by the pinion 111 which now must be driven in a counter-clockwise direction, such tendency of counter-clockwise rotation of the inner race 116 of the sprag clutch 114, 116 associated therewith causing the clutch 114, 116 to lock.

In the meantime the motor 106a of the ram and piston assembly 31a will have retracted its piston 52a, the operation of motor 106a being in a counter-clockwise direction as shown. When the piston 52a is retracted, valve 203e will open thus completing the path for passage of pressure fluid from main pump 198 to cylinders 153 and 153a, the pressure applied to said cylinders being effective to release their respective associated clutches 136 and 136g.

In the case of the ram and piston assembly 31 the release of clutch 136 will cause shaft 131 to rotate in a clockwise direction (as seen from the right), and since outer race 142 is locked to the inner race 146 in that direction, the two rotate together as a unit with shaft 131. When the side of the cross-head driven by piston 52 strikes the mine face, the piston may rebound back ward, initially faster than the screw 99 would move it. An important function of the overrunning clutch 142-146 is that, in such case, it overruns in the direction to permit the rebound to run its course without transmission of shock loads to the supporting sleeve 51. As soon as the rebound slows down to the normal retracting speed of the screw, it will be picked up smoothly by the latter and moved on back to its cocked position.

Means are provided to maintain the clutch 136 open until the firing stroke of piston 52 is completed, and during the firing stroke when the shaft 131 is turning in a clockwise direction, shaft 163 which is splined to shaft 131 also moves in a clockwise direction. During the cocking stroke of piston 52, when shaft 131 is turning in a counterclockwise direction, shaft 163 also turns in a counterclockwise direction, but in such direction of rotation of the shaft 163, the inner race 166 of sprag clutch 167 overruns outer race 168. On the other hand, clockwise rotation of shaft 163 causes sprag clutch 167 to lock thereby driving auxiliary pump 171.

A uid line 221 connects tank 196 to the pump 171, and pumped fluid therefrom passes by way of pressure line 172 past a check valve 222 to join pressure line 218 to continue to supply pressure fluid to clutch operating cylinder 153.

The firing stroke of piston 52 and ram 36 is continued by the air trapped between piston 52 and cylinder head 84, the power stroke being carried to completion until the ram 36 and its cross head 32 strikes immovable material or until the pressure of the air trapped in space 210 equals the pressure of the air between piston 52 and cylinder head 84.

Upon completion of movement of the piston 52 the turning movement of screw 99 stops, giving rise to the commencement of a similar set of sequences as described above. In the meantime, however, push rod 204 is returned to its original or start position by the return spring 214. Such movement of the push rod closes valve 203, which would normally cut olf the supply of pressure tluid to cylinder 153 but for the operation of auxiliary pump 171, which insures that clutch 136 remains open until the screw shaft 99, 131 stops turning. Only when valve 203 is closed and pump 171 is no longer delivering pressure uid will clutch 136 be re-engaged.

Concomitantly with the closing of valve 203 clutch 119, 113 is closed, thus making the motor 106 effective once more to repeat the sequence of operations described for its associated ram and piston assembly.

Referring again particularly to Figs. l and 2 of the drawings, the improved machine 11 is operated by first causing the gathering head 16 to sump into a seam of coal 20. The piston and ram assemblies 31 and 31a are lowered by the cylinders 46 into position just above the kerf which has been cut by the sumping operation of the gathering head 16. The operator of the machine starts the motors 106 and 106:1 and also actuates the start valve 201 to start the percussive action of the ram and piston assemblies 31 and 31a and the crosshead 32 connecting them together, the picker members 33 thereon fragmenting the coal from the seam 20.

It may be noted that the vertical side plates 28 aord clearance for the ram and piston assemblies so that they may be lowered about their trunnion shafts 38 into position immediately above the gathering head 16.

AS the coal is `fragmented fromthe seam 201the crosshead32 and piston and ram assemblies 31 and 31a are raised bythe lifting cylinders 46. The means for supply- `ing uid under pressure to the lifting cylinders `46, and the control means therefor, may take any convenient and well known form and are therefore not shown or described. The gathering head 16 then conveys coal fragmented from the seam by the picker members 33` onto the chain flight conveyor 22 for removal onto a shuttle car, belt conveyor or the like.

The operation described is repeated for each particular setting of the picker members 33 until the coal is Ifragmented from the seam up to the top thereof. The machine is then spotted before another part of the seam 20, the sumping operation tirst completed and then the percussive operations begun as described.

'It will be apparent from the foregoing description that there 'has been described a novel and eicient machine for fragmenting minerals from a seam by a continuous operation and without the needof explosives. By mounting each ram and piston assembly for limited swinging movement, thel assemblies may adopt positions of non-parallelism in accordance with the resistance encountered by the crosshead connecting the assemblies. Further, according tothe present invention positive assurance is had of a piston and ram assembly completing a powerl stroke and of simultaneous and conjoint operation in initiating a power stroke.

Whilethe invention has been described in terms of an embodiment which has been preferred'for the purpose of illustrating the novel principles thereof, it is not intended that the scope thereof be limited bythe precise embodiment shown.- nor otherwise than bythe terms of the claims here appended.

I claim:

l. In a mining machine for fragmenting material from a solid seam thereof, a pair of ram assemblies spaced laterally of each other, a crosshead hingedly connected at its ends to said spaced ram assemblies, said crosshead having picking elements thereon adapted to contact said seam, each of said ram assemblies comprising acylinder and a piston therein operatively connected to said crosshead, means for retracting said piston so as to compress elastic uid within said cylinder for subsequent rapid movement by said piston and said crosshead against said seam, said means comprising a threaded member in threading engagement with said piston, means for causing rotation of said threaded member in one direction for retractive movement of said piston and for free rotation of said threaded member in a reverse direction upon movement of said piston by the pressure of said elastic tluid comprising a motor for turning said threaded member in a direction to retract said piston, means drivably connected with said motor for turning said threaded member in a direction to retract said piston, a main clutch operable during retracting movement of said piston to connect said motor with said last named means, a second clutch included with said driving means and operable during retractive movement of said piston, means operable upon the reaching of the retracted position of said piston for disengaging said main clutch and for causing the disengagement of said second clutch for free rotation in an opposite direction of said threaded member upon movement of said piston by said elastic uid, said last named means being operable to prevent the movement of both of said pistons by said elastic uid until both of said pistons have reached their retracted positions.

2. A mining machine according to claim l characterized by means operable upon rotation of said threaded member in said opposite direction for holding said second clutch in disengaged position until said piston has reached a limit of travel.

3. A mining machine according to claim 2 wherein said second clutch is operated by pressure fluid and is oper- LlOA yated only-after both of said-pistons have-reached retracted position.

4. An improved mining machine according to claim` 3 wherein additionaliluid undenpressure is made available to maintain said.second clutches -.in vdisengaged vposition so long aseither 4pistonkhas failed to reach a llimit. of travel.

5. A mining machineaccordng to-clairn lv characterized by a luid pressuresystemjfor operating said second clutch and wherein valvermeans--are operable yby movementfto retractedposition of said piston, and whereyin said valveV means-are connected vin series sothat .fluid .said..threaded member in one direction for retractive movement of .said piston .and for yfreerotationl of said threaded membenin. a reverseldirection upon movement of said pistonbythe.pressureof sid elastic iluid comprising a motor forl turningsaid threaded member in a directionto retract said'piston, means'drivably connected with'said motor for. turningsaid threaded member in a direction to retractsaidrpiston, a main clutch operable during retracting movement vof said piston to` connect said motor withvsaidlast named means, asecond -clutch included with said driving means andope'rable during retractivelmovement "of saidpiston, means operable ,upon the reaching of the retracted position of said piston for disengaging said main clutch and for causing the disengagement of said second clutch for free rotation in an opposite direction of said threaded member upon movement of said piston by said elastic fluid.

7. The invention as dened in claim 6 wherein means are operable upon rotation of said threaded member in said opposite direction for holding said second clutch in disengaged position until said piston has reached a limit of travel.

8. An improved mining machine according to claim 6 characterized by a fluid pressure system for operating said second clutch and wherein uid pressure is made available to operate said second clutch upon reaching of the retracted position by said piston.

9. An improved mining machine according to claim 8 wherein additional tluid under pressure is made available upon rotation of said threaded member in said opposite direction to operate said second clutch until said piston has reached a limit of travel.

10. The invention as defined in claim 6 characterized by a source of elastic iluid under pressure and wherein said means which are operable upon the reaching of the retracted position of said piston are additionally operable to augment the supply of elastic fluid within said cylinder.

1l. In a mining machine for fragmenting material from a solid seam thereof, a ram including a cylinder and a piston therein operatively connected to said ram, means for retracting said piston so as to compress elastic fluid within said cylinder for subsequent rapid movement by said piston with said ram into contact with said seam, said means comprising a threaded member in threading engagement with said piston, a motor for turning said threaded member for retracting said piston, a source of elastic iluid under pressure, and valve means operable upon retraction of said piston to augment from said source the pressure in said cylinder after retracting movement of said piston.

12. In a mining machine for fragmenting material from a solid seam thereof, a ram including a cylinder and a piston therein operatively connected to said ram, means for retracting said piston so as to compress elastic fluid within said cylinder for subsequent rapidv movement by said piston with said ram into contact with said seam, said means comprising a threaded member in threading engagement with said piston, a motor for turning said threaded member for retracting said piston, a source of elastic fluid under pressure, and valve means operable upon retraction of said piston to augment from said source the pressure in said cylinder after retracting move` ment of said piston, and an overrunning clutch interposed between said motor and said threaded member for enabling said piston to move freely after retraction thereof by the pressure of said elastic fluid in a direction to cause said ram to strike said seam.

13. In a mining machine for fragmenting material from a solid seam thereof, a ram including a cylinder and a piston therein operatively connected to said ram, means for retracting said piston so as to compress elastic iiuid within said cylinder for subsequent rapid movement by said piston with said ram into contact with said seam, said means comprising a threaded member in threading engagement with said piston, a motor for turning said threaded member for retracting said piston, a source of elastic fluid under pressure, and valve means operable upon retraction of said piston to augment from said source the pressure in said cylinder after retracting movement of said piston, and an overrunning clutch interposed between said motor and said threaded member for enabling said piston to move freely after retraction thereof by the pres sure of said elastic tluid in a direction to cause said ram to strike said seam, the movement of said piston in a direction toward said seam closing said valve means.

14. In a mining machine for fragmenting material from a solid seam thereof, a pair of ram assemblies spaced 12 laterally of each other, a crosshead hingedly connected at'its ends to said spaced ram assemblies, said crosshead having picking elements thereon ,adapted to contact said seam, Va support foreach of said ram assemblies, a substantially vertical pivot member connecting said support and said ram assembly so as to provide separate pivoting movement of said ram assembly in accordance with the skewing of said crosshead in encountering material of varying resistance throughout its length, and elastic means interposed between said support and said ram assembly for providing limited restraint to pivoting movement of said ram assembly.

15. In a mining machine for fragmenting material from a solid seam thereof, a pair of ram assemblies spaced laterally of each other, a crosshead hingedly connected at its ends to said spaced ram assemblies, said crosshead havingpicking elements thereon adapted to contact said seam, a support for each of said ram assemblies, a substantially vertical pivot member connecting said support References Cited in the lile of this patent UNITED STATES PATENTS 508,856 Zohe Nov. 14, 1893 871,350 Locke Nov. 19, 1907 2,329,875 Cartlidge Sept. 21, 1943 2,562,881 Baldwin et al. Aug. 7, 1951

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