US3425229A - Mine roof support - Google Patents

Description

Feb. 4, 1969 K. M. GROETSCHEL 3,425,229

MINE ROOF SUPPORT 4 7 Filed NOV. 12, 1963 37 INVENTOR Karl Moria Groetschel ATTORN EXS K- M. GROETSCHEL Feb. 4, 1969 MINE ROOF SUPPORT Sheet 2 of 5 Filed NOV. 12, 1965 NECTION 46 THREADED 1 76.6 CON INVENTOR Karl Mu ria Grpetschel BYM 7%{5 ATTORNEYS 1969 K. M. GROETSCHEL 3,425,229

MINE ROOF SUPPORT Sheet Q of 3 Filed Nov. 12, 19.65

FIG. IO

FIG. ll

MENTOR Karl Maria Gromschel BY &

FIG. l2

ATTORNEYS United States Patent G 36,367 US. Cl. 61-45 Int. Cl. E21d 11/00; F16m /04 27 Claims ABSTRACT OF THE DISCLOSURE A traveling or walking mine support which can be advanced and which includes a forward assembly and a rearward assembly movably attached together. The assemblies include supports or props for supporting the roof of a mine. The forwardmost assembly includes girders or caps mounted on the prop or props for supporting the roof of a mine in such fashion that the major supporting effect of the caps is provided forwardly of the prop and forwardly of the forward assembly so as to be capable of supporting the roof of the mine in the area where the working face of the mine is located.

The present application is a continuation-in-part of my application Ser. N0. 254,713 filed Jan. 29, 1963, now US. Patent No. 3,320,751.

The present invention relates generally to the mining art, and, more particularly, to an arrangement for sup porting the roof of a mine using travelling supporting assemblies.

A travelling mine support has been proposed in US. patent application Ser. No. 254,713, which may advance close to the working face of a mine but wherein the area near the working face is free of props. This is accomplished by means of mechanically placed and moved roof support devices in which the roof, in the area which is free of props, is secured by girders or beams extending from the roof support devices into the area of the working face of the mine. This solves the task of advancing, into the area of the working face of a mine, an essential part of the support effect of the entire support arrangement, especially an arrangement which has a forward assembly and a rear assembly. Combined with this advancement of the support effect is a purposeful and pliedetermined distribution of the load which may be borne by a group of roof support devices. This distribution may, if desired, be adapted to changes or variations which may result especially because of the changing behavior of the roof in the course of the progressive working of the mine. This purposeful, predetermined distribution of the capacity to bear loads takes place with the use of a single prop and a long girder extending from the working area of the face to the area of the mine filling by placing the prop under the girder at such a location that, on the one hand, the arm extending from the prop to the working area is long enough to fully secure the mining regionif desired, from the prop (or forward region prop, respectively) to the working areabut, on the other hand, the length of the rear arm of the girder exceeds, as much as possible, the length of the long forward arm, By employing this feature, an over-all system can be produced whose effective load capacity (in contrad-istinction to known supports for operations with prop-free working fronts) not only extends from the edge of the mine filling to the immediate area of the forwardmost prop, but also still further into the working area side thereof in the propfree region, if possible up to the working face. This load 3,425,229 Patented Feb. 4, 1969 capacity becomes effective in a magnitude which can reach up to the full load capacity of a prop to be installed at that location.

This task of the girder and therefore also that of its support element has a condition, at a corresponding resistance of the element supporting the girder, that the girder extending far backwards beyond its support location has such a high resistance to bending that it is, by itself, able to absorb the entire support effect of this support element.

According to the present invention, these features of the previously proposed structure are improved and supplemented by various features and this is the main object of the present invention.

Further objects and features of the invention are as follows? (1) In support assemblies including forward and rear partial assemblies, the prop which is to be set, preferably with the highest setting force and which is to be provided with the highest load capacity, belongs to the forward assembly. The prop support effect is transferred to the end areas of the girder which passes through the whole area and which is correspondingly strong, and this prop is set in a region which is per so already sufficiently supported by the rear partial assembly.

(2) The upper portions and, under certain circumstances, if desired, the bottom portionsbe they those of the rear assembly or of the forward assembly-are preferably fashioned as rigid frames with the use of especially suited profiles.

(3) Of the load capacity of the forward assembly end close to the face and which load capacity amounts to a multiple of that of the forward cap boards known today, a portion is transferred to forward cap boards which may be telescoped or are extensible from the forward assembly. This transfer is done for the purpose of immediately securing the roof region respectively made free by the mining machine. These forward cap boards are pushed forward or advanced under high pre-tensioning.

(4) The total assembly formed by a forward and a rear assembly which advances by the so-called dragging method isin order to make it possible to use the assembly also in the case of an uneven, especially dipping floor-provided with a specially fashioned device which makes it possible that the travelling direction of the assemblies may at any time be corrected and/or changed.

(5) In order toprovide for substantially increasing the setting force of the one or the other support, if the necessity exists, especially of the support of the forward assembly, the distribution feature may be used and a device is employed which is suitable for this purpose and which may, in a further development, itself form a supporting element for a roof support device.

The present invention preferably starts with a support assembly which includes two partial assemblies, one assembly being formed of the above-mentioned girder and the element supporting the former-which assembly may be a single or also a double prop and is called a front face assembly or forward assemblyand an assembly which, according to the circumstances under which it is used, is more or less independent, and is located at the mine filling side, and which is called in the following forward support element or elements of the rear as-' sembly, takes place by transferring the prop forming one of the two main parts of the forward assemblythe support element-in as close a proximity as possible to the forwardmost support of the rear assembly. Under certain circumstances this will be into the region of the rear assembly itself and the arm of the girder located in the rear of the support location extends in the vertical center plane of the rear assembly, far backward and if possible up into the end region of the rear assembly on the mine filling side. If a double girder is involved, the arms of this double girder extend far rearwardly along the center plane and if possible up into the end region of the rear assembly on the mine filling side.

The idea of transferring the support effect of the girder into its end region is best realized if the portion of the girder in which the 'girder is supported does not lie against the roof, at least not in a flush manner. This [may be achieved, for example, by using spacing elements, which has already been proposed in my copending application, at selective locations of the end regions of both arms. However, at least one end and preferably the forward arm of the girder is provided with such an element. These spacing elements are preferably displaceable in the longitudinal direction of the girder. These spacing elements may, under circumstances depending upon the condition of the roof, include simple welded-on plates or the like. Sometimes, however, especially in the case of a relatively plastic roof, a simple broadening of the girder end area in the same plane is sufficient for effecting the concentration of the load capacity in the end areas of the :girder. However, preferably spacing elements which are pivotable in all directions with respect to the girder are provided.

The support of the forward assembly is located as close as possible to the fonwardmost support and/or support group of the rear assembly. Therefore, any special securing of that region of the roof lying respectively directly above the area of the girder supported by the prop becomes superfluous, because this roof area is respectively part of the zone already supported by the rear assembly, it being noted that this girder pertains to the forward assembly and does not effectively support this roof region since the girder is effective substantially only in its end region. By means of this arrangement of the prop assigned to the forward assembly, the result is obtained that also, especially in the case where at the same time there is the arrangement of the access path through the mine shaft within the protective region of the rear assembly, a desired shortening of the length of the extent of the total assembly is achieved, as -well as generally a still more favorable distribution of the total pressure upon the various supporting zones of the rear and of the forward assembly.

BRIEF DESCRIPTION OF THE DRAWINGS Additional objects and advantages of the present invention will become apparent upon consideration of the following description when taken in conjunction with the accompanying drawings in which:

FIGURE 1 is a schematic side elevational view of a first embodiment of a support arrangement in accordance with the present invention.

FIGURE 2 is a schematic plan view of FIGURE 1.

FIGURE 3 is a schematic plan View of another arrangement of the present invention.

FIGURE 3a is an enlarged schematic side elevational view of a part of FIGURE 3.

FIGURE 3b is an enlarged schematic sectional view taken generally along the plane defined by reference line 3-3 of FIGURE 3.

FIGURE 30 is an enlarged schematic sectional view illustrating a variation of the structure shown in FIGURE 3b.

FIGURE 4 is a schematic rear elevational view of the structure of FIGURE 3 as seen in the direction of the arrow.

FIGURE 5 is a schematic plan view of another embodiment of the present invention.

FIGURE 5a is a schematic elevational view of modification which may be used in the structures of FIGURES 1, 2, and 5.

FIGURE -6 is a schematic side elevational view, partly in section, of a further embodiment of the present invention.

FIGURE 6a is a schematic sectional view taken substantially along the plane defined by reference line 6-6 of FIGURE 6.

FIGURE 7 is a schematic plan view of the structure illustrated in FIGURE 6.

FIGURE 8 is a schematic plan view of the structure shown in FIGURE 6 but viewed from a lower level than FIGURE 7 and partly in section and with parts broken away for purposes of clarity.

FIGURE 9 is a schematic view on a reduced scale of a variation of the structure shown in FIGURE 8.

FIGURE 10 is a schematic side elevational view of a novel prop structure which can be used in combination with the embodiment illustrated in FIGURE 1.

FIGURE 11 is a schematic side elevational view of a lower frame structure which can be used in combination with the embodiment illustrated in FIGURE 5.

FIGURE 12 is a schematic plan view of the structure illustrated in FIGURE 11.

BRIEF DESCRIPTION OF THE INVENTION Before discussing the drawings in detail it should be noted that it is of special advantage if, according to one of my previous proposals, forward cap boards extend from the head frame of the rear assembly-and this may, for example, be four-legged-along both sides of the girder of the forward assembly. These cap boards are pressed to the roof under great pretensioning. The loads supportable by the ends of these cap boards which are substantially smaller in comparison to those being supportable by the front arm of the girder, are transferred to the forward supports of the rear trestle which thus is employed to aid in securing the front region and yet maintains its independence from the forward assembly.

According to a special feature of the invention, which has the aim of further increasing the effectiveness of the forward assembly for securing the roof, after the respective change of location which may take place together with the rear assembly or separately therefrom, the support of this assembly is set with an especially high setting force-which may, if desired, reach the amount of the load capacity (normal load) of the prop per se. As a rule, the setting force of this support is then higher than that of each single member of the rear assembly, but it may also be higher than that of all supports of the rear assembly together.

This can be carried out by suitably fashioning this support as a hydraulic prop and by means of a setting force amplifier which works for example according to the principle that, when setting, pistons having different cross sectional areas become successively effective. Such a setting force amplifier may, for example, be fashioned as a vessel encompassing the foot of the hydraulic prop; such a vessel forms the pressure piston of a further hydraulic cylinder, and this vessel is made to be effective directly when setting the prop, or at a period of time thereafter, and is actuated preferably by the same pressure medium. Preferably, the forward assembly prop is also the prop with the highest load capacity within the total assembly.

Within the scope of the basic idea of the present invention, the rear assembly could, if desired, also be constructed so that the setting force of at least its front props can be increased in order to compensate thereby for the portion of its supporting effect provided to the cap boards which may extend from these props. Then, if desired, the supports at the mine filling side and/or this support group of the rear assembly may be constructed to have less strength as, for securing the roof region assigned to these rear assembly supports, the end of the rear arm of the forward assembly which extends into this zone now contributes to the supporting action.

Considering the special task and the requirements connected therewith which the assembly top portions have to fulfill in the support system according t the invention based on the ideas of my above-mentioned proposal, it has already been proposed therein, in the interest of a purposeful, predetermined load distribution, as a preferred embodiment of a four-prop rear assembly to provide a rigid frame formed of longitudinal and transverse struts for the top portion, instead of the closed-off top elements at first used for such a trestle. These top elements were of similarly large size, but uniformly plane, closed-off and corresponding to the area of the bottom element of the assembly.

The frame construction which, according to my previous proposal is already constructed as a turning frame displaceable on its supports, is open from the inside and is, if desired, only covered by a protective shield. This construction has an effect which is, in comparison with large-area, closed-off top portions, very different with respect to the roof and is, in accordance with the idea of load distribution (if not considering the rarest cases of a fully plane or even roof) substantially more advantageous. If this effect and also the attendant construction details as to how to build the frame are recognized, this can lead to a very substantial further advantage. The frame body which, because of the free space present within its inner boundaries, is effective only at the relatively narrow beam surfaces which are spaced more or less far apart depending upon the size of the frame, can under no circumstances concentrate such a. large total pressure upon one point of its surface, which total pressure may, in the most unfavorable case one can think of, amount to 120 or 160 tons at a 30 or 40 ton normal load of each prop of a four-legged assembly. On the other hand, this pressure can be concentrated when using the overall closed, rectangular or square top portion elements, if such a body meets the apex of a roof projection with its center portion. In the case of the frame-like top portion, however, because of this shape, only at most the total resistance of respectively two or four props of the four-legged trestle may be effective at one point.

Thus, in addition to safely avoiding the possibility of the definitely damaging concentration of a pressure twice as high upon one point of the roof, which would cause damage and/or splitting of the roof, the frame now also does not need to be constructed correspondingly strong for such a load condition, i.e., it does not need to have the correspondingly large weight. In addition to the substantially lesser weight, there is essentially better movability of such a frame which is desired for transport in the narrow f-ace regions.

From this recognition and from the fact that the contact conditions of support assemblies which are extending breadthwise, as, for example, a multi-prop trestle, are not substantially different with respect to the bottom in comparison to the roof, the present invention provided the frame construction also for the rigid bottom structure.

There is a disadvantage of the embodiment of such a rigid frame girder due to its relatively high structural height because the mine areas are limited in height, especially when working narrow seams, where, under certain circumstances, even the saving of one single centimeter may be of decisive importance. According to another feature of the invention this disadvantage is eliminated by making the struts themselves, which form the support elements of the frame, of a frame which is constructed according to the requirement to be as narrow as possible. This frame includes two box profiles or hollow structural beams with two short transverse struts, employing socket-like bodies which lie upon the props and are, as their second function, formed as such transverse struts. Box profiles provided with side openings or chambers are especially suited for the struts of such frame girders because they make it possible not only to weld together the socket-like bodies employed for the formation of short transverse struts in an especially reliable manner by meshing these socket-like bodies into the side chambers, but also to connect the profiles, by arranging them in as close a proximity as possible to one another, which is advantageous for the given purpose of forming a narrow frame.

If desired a frame body of even smaller breadth, a most narrow frame, results if, according to a further feature of the invention, the head of the prop is fashioned as a tapering bearing pin and it is thereby possible to use a bearing shell of correspondingly smaller diameter.

In order now to construct the frame-like girders of these new embodiments displaceable upon the prop or prop pair carrying the girders such short transverse struts which form socket-like bodies and/ or hearing shells, are provided at small distances from one another, if desired, directly side-by-side, in the region to be considered for support.

The capability for such a frame, in which the bearing shells are not under the strut but in a higher plane be tween the partial struts to be turned over, is achieved by using bearing shell pairs, one shell of which opens downwardly and the other one of which opens upwardly, or by having the side-by-side arranged shells alternately open on the bottom and on the top side.

The desire for as low a structural height as possible exists for that of the forward region just as for the abovedescribed rear support assembly. Therefore, the frames, which in this case constitute the girder, are dimensioned to be suitable only for the respective manner of application in basically the same way, as they form, in the first case, only the struts, and they are correspondingly adapted with respect to the local arrangement of bearing shells and transverse struts and thus are usable with the same advantages. Thus, it is proposed to insert such narrow frames as forward assembly girders and, with similar advantages, as girders for two-prop assemblies. In accordance with the present considerations of the load distribution they may be constructed as simple forward assembly girders and/or two-prop assembly girders which can be displaced from one prop to the other or can be turned thereon, or both. In an analogous manner, they can be used as the strut for the bottom and broad frames and/ or bottom structures of two-prop assemblies.

There are cases where the use of two narrow and parallel box profiles for the formation of a sufiiciently strong upper portion of one of the assemblies and/ or a strut thereof is unavoidable, for reasons of lack of space. For instance, if the upper portion of a rear two-prop trestle is laterally encompassed by the prongs of a forkshaped forward assembly girder this will occur. However, in cases where a still further decrease of the girder breadth must be provided, the most suitable embodiment may be one in which the formation of the girder is of profiles which are disposed to lie side-by-side without spaces in between and are connected together and with bearing shells which, in this case can, however, only be placed underneath these profiles. That is especially the case, if additionally, the construction advantage inherent in all such girders and/ or girder frames is to be exploited, i. e., to use such profiles for housing auxiliary means (such as linkage springs, guide springs, advancing caps, hydraulic rubber tubes, or the like).

As at the end of the girder of the forward assembly extending to the working area of the face, a support capacity of not only greater amount but also-thanks to I the particular, planned distribution of the capacity-a vantage of the invention results. That is, the possibility to branch off part of this support capacity and to use the same for securing the roof immediately after the mining machine has gone by, in the areas which have respectively been cleared by the machine but which are not yet encompassed by the support system proper, and this is done by advancing from this girder into the cleared region. For this purpose, it is possible to use means which per se are separate from the girder and which are similar to the usual forward cap boards. However, as this would hardly be suitable from the point of view of the mechanization and safety, the invention proposes according to a further feature thereof, a construction of an auxiliary cap structure which can be advanced from the girder and this construction is of special advantage for fulfilling the mentioned task under the prerequisites given by the new support system. By the use of this novel auxiliary cap structure the desired direct support of the respectively freshly cleared roof region disposed behind the machine is accomplished with great load capacity and therefore in an assuredly effective manner.

This telescopable advancing element which is called the advancing cap" in the following description and which can be pushed forward immediately behind the mining machine, is provided laterally of an, if desired, also underneath, the girder. In the preferred case of a girder of the box profile type, the advancing cap is provided in the hollow space of this profile or, in the case of a profile having lateral chambers, in these lateral chambers.

The advancing cap includes a spring body which is displaceable in the longitudinal direction, preferably a spring unit whose free end extending out of the hollow space of the girder carries a suitably skid or runner-like pressure plate which is pressed against the roof by means of the spring unit through the effect of a pretension. This pretension may be imparted to the spring body because of the special configuration of this spring unit and because of its particular arrangement on the girder. The spring set which is thereby pretensioned is pushed forward as required by means of a suitable advancing device, as, for example, the piston of a pressure cylinder mounted beside the girder, at the girder, or inside of the girder.

With the aim of maintaining the spring tension of such a displaceable spring cap as much without loss as possible, an intermediate element, suitably of elongate form may be arranged beneath this spring cap and is carried along when the spring cap is being telescoped. The height of this intermediate element preferably corresponds to the distance between the upper surface of the pressure plate and the upper edges of the girder.

This measure makes it possible to advance or telescope the advancing cap (if the roof is planar)without decreasing its pressure against the roofby the same length by which the front edge of the last-mentioned spacing element, which itself may also be a spring body or, respectively, the lower-most element of the spring set, is displaced from the lower edge of the open end of the girder in the backward direction.

According to a further feature of the present invention, a considerable distance of the path of the advancing cap which is desired to be kept free of tension losses may be provided by having the lower front edge of the girder project forwardly, for example by cutting the front edge obliquely.

Within such a spring unit such as a set of leaf springs which in their entirety form the body of the advancing cap, the leaf spring strength of the individual springs suitably increases from the uppermost to the lowermost and the length of the individual springs is, in a manner known per se, dimensioned to be decreasing in a step-wise manner from the uppermost to the lowermost.

The relatively high pretensioning under which the advancing cap is thereby kept in readiness for advancement into the respectively cleared roof region, at, or, respectively, in the girder, and which, especially in the case of pair-wise or multiple arrangements of the cap, may amount to a magnitude of one ton, is accomplished as follows: In the end phase of telescoping and pressing the girder onto the roof during the respective displacement of the assembly, the pressure disk of the advancing capwhich disk already projects a certain measure beyond the surface level of the girder when the girder is still in the lowered positiontouches the roof earlier than the element carrying this disk. As a consequence, the girder which is further elevated during the continued elescoping of the prop comes into contact with the roof only by overcoming the strong spring resistance of the advancing cap.

According to the invention, the advancing cap can be returned to its position of readiness within or at the girder profile. This is achieved by the fact that, when the forward assembly is advanced, i.e., in the non-elevated position of the girder and of the advancing cap carried by the girder and thereby perforce in the relaxed condition of the spring set, the spring set is prevented from advancing together with the moving girder because it comes into contact with the new face of the mine and thus is pushed back into the girder. The return of the advancing cap may also be carried out by changing the operating direction of the advancing cylinder which may, if desired, be constructed to be effective in two directions.

In addition to the advancing caps arranged at the girder or at the girders, respectively, of the forward assembly, or in place of these caps, auxiliary caps of the same or a similarly effective construction may also be combined with the advancing caps of a rear assembly. Such latter caps may be provided, as mentioned above, as being able to be placed under high pretensioning force with the rear assembly preferably being of trestle form. This may be done especially if they are, according to their preferable construction, built up of a box profile suitable for displaceably accommodating springs and/or spring sets. During the phase in which the pivotable advancing caps of a trestle are brought from their position which they were made to occupy before the moving of the trestlewhich was done automatically according to one of my previous proposals into the upward position after the end of the trestle telescoping operation, the spring caps extending from the advancing caps contact the roof earlier than the caps themselves which are carrying these spring caps in the same manner as the abovementioned spring advancing caps. If, under the pressure of the advancing caps which are still further pivoted upwardly by the great force of hydraulic pistons, or if desired under the pressure of the still further telescoped trestle, the elements carrying such spring caps continue to move upwardly, the spring caps are pressed against the roof, by the resulting tensioning of their springs and with a correspondingly high pretensioning force.

The combining of the rear and the forward assemblies to the combination support device whose main components and/or partial assemblies are effective with respect to the roof independently of one another, may, for example, be accomplished by placing the support element of the forward assembly upon the bottom structure of the rear assembly which is arranged as a trestle or frame. According to another embodiment which may be more advantageous depending upon the conditions in each particular case, the forward assembly may also have its own bottom structure which may be fixedly connected with the rear assembly in as close a proximity as possible to the latter and in a jointed or resilient manner. This bottom structure of the forward assembly may also be independent of the rear assembly.

In the latter case, the partial assemblies are individually moved in a successive manner with the so-called dragging step. In these advancing operations of such combined support devices, known safety measures are exercised in order to keep the partial assemblies in their orderly travelling direction.

The known safety devices for such purposes, as, for example, a profile bar mounted at the forward partial assembly and extending into a central zone of the rear assembly, do not satisfy the practical requirements below ground, at least not in the case of assemblies of the inventive construction. They are not able to guarantee a (faultless, straight travel of the assembly if the floor is uneven, and they do not prevent the assembly from slipping or sliding in the case of dipping seams, particularly of more voluminous seams, and in the case of movement with larger steps. This is so because it has not been recognized before that a very complex problem is involved here, the ditficulties of which are caused especially because of the fact that the force which is effective at the forward connection of the assemblies during the moving process-assuming the rear assembly which slides on the sloping floor or which must be prevented from sliding, respectively, is involvedis effective on a long lever arm as a twisting force at the bottom structure of the forward assembly. This force must be counteracted and, depending upon the degree of the seam dip and the construction and weight of the rear assembly, has a twisting moment of several hundred meterkilograms and, under certain circumstances, even up to over 1 meterton. Furthermore, the fact may not be overlooked that, with increasing seam volume and corresponding vertical extension of the mining area, the assemblies, when travelling, are exposed to the danger of tottering and/ or tilting to an increased degree and this danger must be counteracted just as well as the danger of sliding. According to the invention, measures are proposed by means of which these danger factors and difficulties are eliminated.

As such measures the following are proposed by the invention which incorporates a guide rod known per so which guidingly connects the-two partial assemblies and these measures may be used singly or in combination depending upon prevailing circumstances:

(a) The pressure of the support of the forward assembly is purposely concentrated upon at least two regions of the bottom structure of the forward assembly for each dragging step of the rear assembly. Under certain circumstances this bottom structure will have to be broadened. These two regions are provided at a "distance from the vertical axis of the support. By this means the bottom structure is fixed upon the floor against any possibility of rotating or twisting. If the support of this forward assembly which holds the guide rod is placed only below the normal setting force afiter the respective moving process has been completed, this moving process preceding the dragging of the rear assembly only by a short period of time so that the natural subsidence pressure which later secures the bottom structure against twisting has had no time yet to become effective, a more effective securing of the guide rod in its effective position is achieved and this is secure enough at least for moderate stresses. For supporting this effect, ribs or other projections may be provided in the pressure zone of the bottom structure which increase the adherence to the floor.

(b) In order to satisfy the stricter requirements with respect to guidance in the case of a heavy assembly, especially in greatly dipping seams, the invention proposes as a further and for this case vital measure, to increase that force which is effective as the only one immediately after the end of the respective setting operation of the forward assembly with respect to the bottom structure and therefore immediately with regard to the fixed mounting of the guide rod. That is, the setting force is artificially produced within the prop, in a suitable manner, for example by arranging a setting force amplifier at the prop.

(c) As a further measure and keeping the same aim in mind, it is proposed to employ the girder of the forward partial assembly, which girder is mounted in the upper construction of the rear partial assembly of encompasses this body on both sides--and suitably conforming the lateral intermediate spaces between these two upper structural componentsas a guide element for the displacement of the rear assembly. When moving the partial assemblies this is done by limiting the amount which the girder of the one assembly is lowered when disengaging from the roof to a magnitude which falls short of the height of the profile of the respective girder of the other assembly which stays in touch with the roof and this height is increased in the downward direction in certain cases by projections, as for example pegs, ridges, or the like. Thereby the measures proposed under (a) and (b) which involve securing the guidance along the floor are enhanced by an effective guidance along the roof which prevents any tilting of either of the assemblies, even under the most difiicult conditions.

((1) Finally, it is provided that the measures and means proposed under (a) are correspondingly applied to a girder of the forward assembly employed for guiding the assemblies in a combined manner, if an especially smooth roof requires this, while at the same time the increased setting force measure (b), perforce has an influence upon the mentioned girder.

As a rigid guidance of the partial assemblies together would disadvantageously affect the possibilities of the desired purposeful distribution of the load, according to a special feature of the invention, the guide rod is fashioned resiliently, for example as a broad leaf spring or also as a spring set and is fastened to the forward assembly. It is arranged preferably somewhat elevated above the floor, in a manner permitting limited movements in the vertical plane and it is mounted for example by means of a hooksh-aped bent element or a joint suitably fastened at the edge of the bottom structure of the forward assembly facing the working area of the mine. This edge projects as far as possible and this guide rod extends suitably up into the end region of the main assembly, preferably still beyond this end region into the mine filling zone.

The guide element may, if desired, also be fashioned as a fork whose prongs guide the rear assembly at its outer sides. Instead of extending along the center, as is usual, a single guide rod may be provided along one side of the two assemblies, if desired, which is done especially in the case of lighter assemblies. The single rod is guided in side channels provided along the corresponding outer edge of the rear assembly; also, the forward assembly may be arranged off-center at the end of a centrally extending guide rod.

In order to be able to change and/ or correct the travelling direction of such a drag-advancing combined support device, as desired especially in the case of dipping seams, without having to contend with the disadvantage of having to release or relieve both assemblies from contact with the roof at the same time, a play between the side edges of the guide rod and those of the channel or the like in which the guide rod is guided may be provided according to a further feature of the invention. This play permits a limited transverse shifting and/or lateral pivoting of one of the assemblies with respect to the other. As this play must be capable of being eliminated and limited as desired in order to be able to keep the guide rod in each respective new position, means are further provided for accomplishing this task, as for example eccentrics, toggle levers, wedges, spindles, thrust bolts, stop pins, or the like which are a-ctuatable mechanically or hydraulically and if desired also manually.

Under the assumption that the elongated guide element in the lower zone of the support, as well as the girder of the forward assembly which is under certain circumstances also employed for guiding purposes, are secured against twisting after each respective displacement of this assembly, these guide elements may now also serve as supports for the use of transverse-shifting devices forming a special feature of the invention. For example levers, spindles, pressure pistons, and especially those levers, spindles, and pistons which are effective in two directions and/or are able to change directions may be used to serve as supports at the rear assembly against the forward assembly, or at the forward assembly against the rear assembly.

Such dually effective transverse shifting devices, which are arranged between respectively one simple support or abutment at the rear assembly and a support or abutment engaging the guide rod but permitting movement of this guide rod in its longitudinal direction, make it possible to move the total assembly at right angles to the assembly axis or also obliquely with respect to the travelling direction of the assembly. This may be done in a rhythm which is the same, in principle, as that in which the displacement of a combined support assembly having two successively connected assemblies takes place by means of an advancing cylinder in the travelling direction, i.e., the assembly first to move pushing itself away from the second and still stationary assembly by means of the cylinder and the following latter assembly dragging itself forward by pulling at the advanced former assembly which by then has been fixedly placed again.

It is further possible to provide a transverse moving device which is the same and equally effective in principle also at the upper components of the two assemblies by employing the required, above-mentioned play. This playas has been explained abovecontributes to the guidance of the two partial assemblies together.

According to another feature of the present invention, there are provided hydraulic pressure cylinders to change direction as a transverse travel device for advancing and simultaneously transversely moving connected partial assemblies of the entire support assembly, which assemblies are movable by themselves. The pressure chambere of the hydraulic advancing cylinder effecting the advancement of the two partial assemblies is connected with the pressure chambers of the hydraulic transverse device elfecting the transverse movement of the partial assembly, and the pressure chambers which effect the downward movement of advancing cap boards are connected. Under certain circumstances these are arranged at the assembly and the lever thereof is actuated by a pressure cylinder able to change direction. This connecting is done in such a manner that all of these pressure chambers are put under pressure simultaneously by opening one single valve in the pressure medium supply line.

DETAILED DESCRIPTION OF THE INVENTION FIGURES 1 and 2 With more particular reference to the drawings, FIG- URES 1 and 2 show a two-prop trestle forming the rear assembly which comprises a bottom structure 1 having prop accommodating bases 2, and props 3 and 4 which are spaced at a sufiicient distance from each other to provide for the access path 14, i.e., a path, which permits the personnel to move between the props and perform the necessary control operations. The upper structure 5 is in the form of a cap which rests in semispherical bearings 6 on the props. The construction of this upper structure 5 includes box profiles connected directly to each other by means of welding and without spaces between them, as well as of bearings 6 which are used for support purposes. This construction can be seen more clearly from FIGURE 4, wherein the upper structure of a two-prop trestle encompassed by the narrow-pronged rear fork (cf. FIG- URES 2 and 3) of a forward assembly girder requires a low and yet narrow construction sufficiently capable of bearing loads.

As can further be seen from FIGURES l and 2, the prop 26 of the forward assembly is provided with a load amplifier 28 Prop 26 is placed on an extension of the bottom structure 1 in such proximity to the prop 3 of the rear assembly that the region of the girder which is not effective with respect to the roof, although it is directly supported by prop 26, is placed in a Zone in which the roof is still sufficiently secured by the effect of the rear assembly and especially by the front end of the upper structure 5 of the rear assembly or the prop 3 supporting this girder, respectively. This region of the girder does not contact the roof because of spacing elements or pads 50a, 50b, 51a, 51b arranged on both ends of the assembly partial girders 41a, 41b.

As can further be seen from FIGURES 1 and 2, the girders 41a, 41b, are of the same length, but may also be of unequal lengths depending upon the load distribution arrangement of the total assembly in each individual case. These girders are mounted to be displaceable in the longitudinal direction and each is universally mounted by means of bearing shells 33a, 33b, on the lateral arms 32a, 32b of a traverse member 31 which, according to copending application Ser. No. 254,713, is dome-shaped and thus enables the partial girders mentioned above to be spaced closely together. This traverse member, in turn, is likewise pivotable in all directions and is carried by the prop 26. A further member in the form of a yoke is provided in front of the bearing shell 6 and supports the girders 41a and 41]) at the rear ends thereof while resting on the prop head. It may be readily understood that such distribution of the support capacity of a prop upon four predetermined effective regions can contribute in an equally diversified manner to the desired gentle treatment of the roof. This distribution is effectively ensured by the universally movable arrangement of at least the partial girders. As used in this specification and in the appended claims the term universally mounted means an arrangement whereby relative rotative movement in all directions within certain limits may take place.

In FIGURE 1 and partially also in FIGURE 2, it is shown how the support assembly may be moved in a onestep operation, by means of advancing cylinder 15 with piston 16 and connection element 17. By this means the advancing device is connected with the conveyor 19 which is disposed at the working face of the mine. The neighboring assemblies of this basic construction may be connected by the corresponding known structure and drive means and may be moved forward in a pendulous type movement.

FIGURES 3, 3a, 3b, 3c, and 4 If special conditions such as a steep seam position require the use of a more compact upper structure rather than universally movable partial girders, then the same or similar partial girders are connected to the abovementioncd narrow frame. This is done in a most advantageous manner as shown in FIGURES 3, 3a, 3b, 3c and 5, by using a socket- like body 37a, and 42a, 42b, as the transverse strut which forms the support for the frame upon the prop and replaces the above-mentioned dome-like traverse member 31.

As can be seen particularly from FIGURES 3b and 3c, the welding of the bearing body to the longitudinal beams is carried out by fitting or meshing the bearing in side chambers provided in the box-shaped strut profiles 34a, 34b, 43a, 43b.

With the same effect, all profiles which are basically suitable for serving as the longitudinal strut on assembly girders may be used (43a, 43b), as long as these are provided with at least one chamber-like construction at its side. The box profiles of the embodiment shown in FIGURE 3b (34a, 34b) or box profiles of an essentially equivalent or similar construction are basically the most advantageous if the above considerations are kept in mind.

The possibility of making an extremely narrow frame of f.e. 1 foot width which is even narrower when compared to this above-mentioned narrow frame, can be provided with the structure illustrated in FIGURE 30, i.e., to use smaller lateral dimensions for the bearing body forming the transverse strut of the frame and to use a prop with a tapering head 45 as support for the girder. The choice of a transverse strut which is formed from shells 42a, 42b, which are pro-vided to open in opposite directions and are disposed one above the other, makes it possible for the frame to be repositioned upon the 13 prop immediately after each 180 turning or reversing operation. In case higher load bearing shells are chosen,

as shown in FIGURE 311, it is also possible to provide them opening in opposite directions, but they can only be positioned side-by-side (cf. 37a, 37b) in FIGURE 5.

One feature which may be very advantageous under certain circumstances is to make a turnable or reversible assembly girder even more adapted to the support system disclosed in U.S. patent application Ser. No. 254,713, which has a variable, planned pressure or load distribution. This is accomplished by constructing the turnable assembly girder to be assymetrical as is shown only in an exemplary manner with reference to the partial girders 41a, 41b, which are mounted turnably on the supports 32a, 32b of the dome-shaped transverse member 31 (see FIGURE 2). This assymetrical construction is done in such a way that, in one turned position, the girder may provide the roof with a different supporting area from the one provided to the roof in the other turned position thereof. The difference is that the different supporting area is distributed to be effective differently.

To explain this idea in connection with a further example, a frame-like forward assembly girder like the one according to FIGURES 6 and 7, whose longitudinal struts are provided with a long lower flange and a short upper flange, would also result in a girder which is usable on both sides but which is effective differently with respect to the roof depending on its turned position. This is possible if, in place of only unilaterally usable bearing shells 37a, 37b, transverse struts of the kind which can be used on both sides (42a, 42b) are welded to the structure (this kind being illustrated for example in FIGURE 30).

The mounting of such an element which thus has been converted to a reversible girder is done especially in cases in which such a girder is not simultaneously used as the supporting element of advancing elements of a type which will be described below in connection with FIGURES 6 and 7. In the case of frame girders which may be provided only with an offset bent rear transverse strut 39 for the purpose of detaching from the roof when moving the assemblies and/or partial assemblies and which detachment takes place independently, as for example the forward assembly girders 34a, 34b in FIG- URES 3 and 4, or the frame girders of the four-prop trestle according to FIGURES 6 and 7 having only an offset forward transverse strut 13, such offset struts are no obstacle to using the frames as reversible girders. In such cases, as indicated for example at 46 in FIGURE 6, they are mounted by a threaded connection or the like at the longitudinal struts, thus being mounted in a removable and thereby exchangeable manner.

The embodiment of a support assembly according to FIGURES 3 and 4, especially a construction using girder elements which are as narrow as possible and which are preferably in the shape of a frame, is especially advantageous when adding other members to the assembly. This feature comprises supplementing the total assembly including the forward assembly and two-prop rear assembly with the aim of a load distribution in the dipping direction by adding a second rear assembly to the one forward assembly. That is, this additional structure may be disposed above or below the already present two-prop partial assembly, suitably on a common bottom plate, so that in principle a total support assembly with a fourprop trestle is provided.

This type is only generally shown in the arrangement according to FIGURE 5, but with the structural difference that the fork-shaped frame girder of the forward assembly does notas in FIGURE cooperate with both of the longitudinal struts of the rear assembly but as would be the case in FIG. 3 only with one of these, either the lower or the upper longitudinal strut, encompassing the latter. Thus, the possibility results that the second longitudinal strut of the newly created four-prop trestle may, according to requirements, be provided with various devices having any desired kind of support elements. For example, a hydraulically pivotable cap may be provided having a spring set of a simple or a telescopable construction, or with an auxiliary cap actuatable by hand. Many other similar devices may be used in order to thereby influence the total load distribution in a planned manner and/or to secure the space in the mining area in front of the second rear assembly.

It is also possible, with the aim of planned load distribution, to construct the second additional two-prop frame in such a manner that its forward prop is placed in a straight line with the forward prop 26 in which event the bottom plate and the upper structure 5 have to be extended correspondingly.

FIGURE 5 In the embodiment of FIGURE 5, the rear assembly includes a four-prop trestle whose front prop pair is designated 3a, 3b and whose rear prop pair, which is spaced from the former prop pair by the breadth of the access path 14, is designated 4a, 4b. The upper structure of the trestle is a frame formed from the two longitudinal struts 11a, 11b and the two transverse struts 12 and 13. This trestle is provided, as has been customary up to now, with a bottom structure which is in the form of a housing and which in an unyieldable manner absorbs the loads through the multiprop group. This bottom structure has an entirely plane bottom surface and is provided with support chamber elements or bases.

This bottom structure may also, like its counterpart, i.e., the upper structure of the trestle, be constructed as a frame body for the same static reasons and with almost the same advantages as the construction of the upper structure as a frame. This is another special feature of the invention which has already been mentioned above. The same profiles may be used when constructing the bottom structure as a frame, and this bottom structure then carries suitable means for providing pressure plates, runners, etc., on its underside. In this construction, all the frame embodiments suggested by the invention for the upper structure may, in principally the same manner, be used for providing the bottom structure as a frame. Limitations are imposed only in those cases where consideration has to be given to suitably arranging the necessary mechanical assembly components, as for example advancing cylinders and the like. The elements necessary for supporting the props (as for example prop chamber element or base 2) may also be mounted on such frame-like assembly bottom structures.

According to FIGURE 5, the area lying above the prop 26, which area is ineffective with respect to supporting the roof and which area pertains to the frame girder of the forward assembly, is located even more deeply in the supporting or load bearing region of the rear assembly than was the case in the embodiment according to FIGURES l and 2. The frame girder mentioned above is here provided with the pressure plateshaped spacing element 52 lying upon the front arms 35a, 35b of its caps 34a, 34b, which front arms are bent toward each other. As can be seen, the prop 26, located as in the case of FIGURES 1 and 2 upon an extension of the bottom structure, is in a position which brings it in close proximity to the props 3a, 3b of the trestle. In addition, the frame struts 11a, 1111 are placed forward so that their forward ends are in a common straight line with the prop 26.

Further, it can be seen from FIGURES 1 to 5 that a substantially larger portion of the setting force of the prop of the forward assembly can be effective from the shorter lever arms of the caps 34a, 34b, on the face side of the mine up to the working area of the face, via the pressure plates 50a, 50b, 52. FIGURES 1 to 5 also show how this is done. This displacement of the force is done, according to the embodiment of FIGURES 1 and 2 and also that of FIGURE approximately in the proportion of 2:3. In figures this mean that with a setting force of the prop 26 of, for example, 20 tons, each cap transfers tons, and thus, at the working area (6+6) 12 tons are effective against the roof, while at the rear (4+4) 8 tons are effective on the roof. In the embodiment according to FIGURES 6 and 7 which will be described below, the proportion is 1:2 and accordingly with a setting force of, for example, 24 tons, 16 tons are effective at the working area and 8 tons are effective at the rear.

If, then, additionally the already described special feature of the invention is used according to which the forward end area of the cap which concentrates the load upon itself is fashioned as a sufficiently strong body which is shiftable and/or movable by itself in the longitudinal direction of the cap, the effective relationship of the cap arm lengths to each other may also be varied to a finer degree, in a most simple manner. This is done by means of a cap extension member which is suitably longitudinally shiftable in a telescopic manner, in a continuous manner, or in small stages. This extension member may be a suitably profiled or also a straight-walled insert or a suitable socket-type sleeve. This cap extension member may, if desired, also be a two or multi-pronged fork which may be capable of clamping onto the cap by itself or which may be easily mountable by means of bolts or the like. This extension member is preferably provided with mountings for pressure plates or the like.

The setting load amplifier 28 such as is disclosed in US. patent application Ser. No. 279,168, now Patent No. 3,145,964, essentially comprises, as illustrated in FIGURE 1 by means of a dashed lines, a short stroke cylinder 29 and a pot-shaped piston 30 on whose bottom the foot of the outer portion of prop 26, rests.

The effect of this load amplifier stems from the fact that its piston body encompassing the prop footas already mentioned abovehas a substantially larger pres sure area than the piston body of the inner prop. Consequently, when using the same pressure of the pressure medium, the prop may be set under a setting force which, for example, is three times as great in case the piston 30 of the load amplifier has an area which is three times as large as the area of the piston of the inner prop. By correspondingly choosing the proportions of the piston areas of prop and load amplifier and, under certain circumstances, by additionally increasing the pressure of the pressure medium in the load amplifier, the setting force may be increased by degrees which may be selected as desired. The setting force amounts to, for example 5 tons, in the case of a pressure medium under 100 atmospheres with a piston area of the prop of 50 cm. and increases at the same pressure medium pressure and an effective piston area of the load amplifier of 200 cm. to 20 tons, of which then up to about three quarters, in the case of the example thus tons, are made effective in the forward zone. This depends on the one hand upon the possible proportions of the cap arm lengths which depend upon the structural length of the rear assembly in which the longer, hindward, rear arm is engaging, and, on the other hand, upon the length of the girder fore arm which is possible with prevailing space considerations.

FIGURES 6, 6a and 7 The maximal prop resistance against the roof pressure in the forward zone is effective with, respectively, the same proportion as the setting force. In order to increase the absolute value of this proportion when required, if possible to the value of the load bearing capacity of a prop intended to be placed at the working area of the face, an especially strong prop 27, as provided in FIG- URES 6 through 8, is mounted and it has a load bearing capacity which makes it possible that the above-mentioned purpose is fulfilled. This is, as already mentioned above, a special feature for securing the roof in the front region of the face. It is of great importance as far as its consequences for the total area of the face are concerned, but is, as yet, not of decisive importance. As the prop of the forward assembly, the props of the rear assembly, such as the prop at the face area, may be placed at an increased setting force by means of the described load amplifier. This is of special advantage when additionally using tiltable caps, which will now be described and which are advanced from rear assemblies.

This embodiment is illustrated in FIGURES 6 and 7. The four-prop trestle shown in these figures as the rear assembly is connected with the forward assembly only by a guide element which will be described further below and which ensures the independent movement of each of the two assemblies. The only prop 27 of the forward assembly is provided with the load bearing force amplifier 28 and is mounted on its own bottom structure 40 close to an imaginary straight line between the two trestle props 3a, 3b

The hydraulically actuated advancing caps 21a, 21b which are lowered and again elevated and pressed to the roof with great pressure by pressure cylinders 23a, 2312 or by pivoting pins 24a, 24b actuated by the pressure cylinders, extend from the longitudinal struts 11a, 11b. (FIGS. 6 and 7). These struts are shaped as a frame which is open on the inside and at most is closed off by a protective shield (not shown) which is resiliently mounted and which deflects stones toward the mine filling. This frame is made up of the rear transverse strut 12 and the downwardly bent transverse strut 13 extending at a distance beneath the forward assembly girders 34a, 34b. These advancing caps carry pressure plates 54a, 54b in the form of elements which are tiltable around pivot pins.

The girder sections 34a, 34b of the forward assembly are connected by means of a common pressure plate 53 and, in the region of the prop support, are connected by two socket bearings 37a, 37b for the prop support and these socket bearings form transverse struts in conjunction with transverse bars 38. The arrangement of two neighboring bearings makes it possible to displace the frame by one bearing breadth.

As a supplement, according to the invention, a connection element may be provided at the rear end of such a displaceable girder of the forward assembly. This connection element must be made effective together with the advancement of the girder and must be brought to its ineffective position when the girder is returned. This is similar to the device for finer adjustment of the proportion of the girder arm lengths for the front ends of the girder which was suggested and described above.

FIGURES 6 and 7 furthermore show an illustration of the principle of the device described in detail in the general description, for carrying out the method for support ing the region of the roof which has just been cleared by the mining machine. This method may be most effectively employed, if on the basis of the above-mentioned measures of the invention, a really high supporting capacity is available.

As can be seen from the above-mentioned figures, advancing caps 60a, 60b are provided in the box-shaped hollow profiles of the two girders 34a, 341), which are provided in a twin arrangement in this embodiment. These advancing caps include spring units or sets. The ends of these spring sets are, in the pretensioned condition which is reached in a manner described above, bent downwardlycf. FIGURE 6so that the pressure plate 55 is at about the same level with the pressure plate 53 connecting the girders 34a, 34b. In the relaxed condition of the spring sets, the pressure plate 55 takes the position illustrated by the dot-dash line. This position lies above the level of the plate 53. The springs are staggered in a stepwise manner. The uppermost springs of the two spring sets extend the furthest forward and are provided with eyelets 61a, 61b through which a common transverse rod 62 extends. The piston 63 of a pressure cylinder attached to the eyelet 64 engages this rod. This piston pushes the two spring sets forward a corresponding distance as soon as the mining machine has passed the support assembly and has cleared a new roof zone. During this operation, the pressure plate 55, which is common to both advancing caps 60a, 60b, slides along the roof, overcoming friction. This is made possible by the edge 56 which is bent for this purpose.

FIGURE 6 shows, at 65, an arrangement of the lowermost and preferably especially strongly constructed leaf of the spring set as a spacing element which is positioned as far back as possible from the girder edge 66 which is, because of the oblique cut of the girder end, positioned as far to the front as possible. This arrangement makes it possible that the pretensioning imparted to the spring set is maintained undiminished along a great portion of its possible extension path. Approximately the same effect can be achieved if the spacing element is formed of two parts, one of which constitutes the front edge 66 of the girder which is then thickened, while the rearwardly arranged part, which is carried along by the extending spring set, is arranged on the spring set. The return of such forward cap boards to their original position has already been described above.

When especially difiioult roof conditions are encountered not only the two girders 34a, 34b of the forward assembly, but also the two advancing caps 21a, 21b advancing from the head frame of the trestle, are provided with such advancing spring caps. Their construction is basically the same, as are their modes of operation and thus they do not require any special explanation. The combined application of advancing caps mounted at the girder of the forward assembly, as well as cap's arranged at forward cap boards of the rear aggregate under high pressure, is especially advantageous if the two assemblies, as according to their construction shown in FIGURES 6, 7, 8 and 9, can be advanced individually in single steps. In this case, the roof region supported by the advancing caps is secured additionally by the advancing caps of the main assembly during the period of the required removal of the advancing caps of the forward assembly from the roof for the purpose of advancing the forward assembly.

The above-described devices render it possible to obtain faultless guidance of the partial assemblies. According to the embodiment of FIGURES 6, 7 and 8, these assemblies can be individually advanced and such devices also make it possible that the direction can be corrected and also that the assemblies can be shifted in a direction transverse to their longitudinal axis. The above-mentioned figures show in detail that the guide rod 70 which is fixedly connected with the bottom structure 40 of the forward assembly prop 27 slides within a channel 72 provided in the sturdy, housing-like bottom structure of the four-prop main assembly. This guide rod is a broad leaf spring arranged to be somewhat elevated in a suitable manner. It forms a hook 7 1 in the bottom structure 40 and is arranged with its downwardly bent portion laterally rigid. In the vertical plane it is, within limits, resiliently p'ivotable at the plate 40. The guide rod may form an arch supported partially at the bottom of the channel and extends far backwardly. In the example illustrated, the rod extends even beyond the lower edge of the trestle at the area of the mine filling, the end of the rod being bent downwardly.

Under advantageous circumstances, particularly when using the inventive support device in mining operations with a firm, level floor, it may suflice to limit the lateral play between the guide rod and the walls of the guide channel to the small minimum necessary only for the sliding movement of the rod in the travelling direction of the assembly, or to eliminate a larger amount of play which has been provided in the beginning by employing the already mentioned blocking elements.

FIGURES 8 and 9 An exemplary embodiment of the means proposed by the invention by which the much higher requirements can be fulfilled which arise under the unfavorable conditions of a very uneven floor or also an only slightly dipping sea-m with regard to guidance and control of the advancing direction of the support assemblies can be seen from FIGURES 8 and 9. As these figures show, the guide spring 70 is arranged in the sliding channel 72 with a substantial lateral play which permits limited transverse shifts (FIGURE 8) of the two assemblies with regard to each other, as Well as lateral turning movements. This would be done after first assuming that the play eliminating devices, which may be provided, will not have any effect upon the play. In the illustrated example, the rod 70 is encompassed at two locations by sleeve-like elements 73 arranged at the main assembly in a transversely shiftable manner. This is done in such a manner that the rod can still slide in these socket-like elements. The elements 73 replace the channel 72 at those points where they are mounted and are connected with the rear assembly at 75a, 75b by means of respectively one pressure cylinder 74a, 74b which can be made effective in two opposite directions.

The pressure cylinders 74a, 74b, are supported on the trestle which is under pressure due to mine subsidence or under the pressure of the setting force. These cylinders are now able to shift the rod 70 of the forward assembly and thus the latter itself, after it has been sufficiently loosened from thereof by lowering the prop 27. This shifting is within the limits determined by the play or by the stroke of the cylinders. Such shifting is done depending upon which one of the two pressure chambers of one or both of the cylinders are controlled individually or together in the one or in the other transverse direction with respect to the longitudinal axis of the rod. Also, the rod can be brought into a desired oblique direction and with it, the forward assembly.

The for-ward aggregate is fixed in its new position, which does not permit any moving of the assembly, by the setting force of its prop 27. This setting force is capable of being increased sufiiciently in each particular case by means of the load amplifier. By means of the setting operation the forward assembly is also fixedly attached to the guide rod 70. Then, the rear assembly, which has first been deprived of its pressure and has been lowered sufficiently, can be .pulled toward the rod 70 which has been advanced either in parallel position or in a more or less oblique position, as desired. This is done by having the cylinders 74a, 74b change direction to suitably guide the rod 70.

Under certain circumstances, instead of the sleeves, the entire guide channel may be employed as the guiding and driving of the transverse shifting devices. .It may further be suitable to connect the sleeves by rods 76a, 76b so that they form a parallelogram having joints at its corners.

If the circumstances render this necessary, pins may be provided for securing the guide rod in the travelling direction of the assembly although the above-mentioned pressure cylinders are the securing means proper in the usual case. These pins thus would form additional securing means for one of the above-mentioned play-eliminating or limiting means. The pins are insertable in holes or the like, designated 78, which may be provided for this purpose if required, and they are actuated after the respective transverse shifting of the assembly or assemblies, or also at an earlier moment, for the purpose of aiding in the control of this operation. They are kept in the operating position until it is necessary again to change or correct the travelling direction of the entire assembly.

If desired, play eliminating or limiting means may be coupled with the pressure cylinder of the shifting device in a suitable arrangement. Pressure and traction spindles of a dimension and arrangement which are suitable for transversely moving the underground assemblies are, in principle, suitable to fulfill both functions by themselves, i.e., the function of transversely moving the assemblies as well as the function of securing the assemblies in their respective travelling direction and under certain circumstances, it may be especially advantageous to use only these alone.

FIGURE a In FIGURE 5a a possibility is indicated to decrease the structural length of the total assembly in the direction of the strike and thus to further limit the width of the open room between the coal face and the filling area. For this purpose, the forward assembly prop is placed even further backwardly within the zone protected by the rear assembly. This, however, is unsuitable in case of a two-prop rear assembly because the front prop of the rear assembly is located here. The idea is likewise difiicult to realize in the case of a four-prop trestle as the rear assembly, because there is the difliculty of plucing the forward assembly prop into the straight line connecting the two front props of the rear assembly, as any passage from the transport path located within this assembly to the mining area would be made impossible, especially if, in the dipping direction, one assembly follows another assembly, etc., without spacing.

The present invention solves this problem by further developing the element described above as setting load amplifier 28 and comprising the piston 30 which encornpasses the outer prop 26a of the forward assembly prop 26 in a pot-shaped manner and of the pressure cylinder 29 pertaining thereto. This further development is done so that this element is able to serve by itself as independent support above and beyond its function as setting load amplifier. Although the prop located in its hollow piston which is independent per se is maintained within the total support assembly so that, according to requirements, this element can fully replace one or also two of the props standing in the way of carrying out the measure mentioned above of shortening the assembly, be it, for example, the prop 3 in FIGURE 1 or the two props 3a, 3b in FIGURE 5.

For this purpose, the piston 30 and the cylinder 29 of the support element, which up to now was only effective as setting load amplifier, are lengthened in the upward direction to a suitable height, as shown in FIGURE 10, so that the rim of the hollow piston 30 extends above the rim of the cylinder 29. Furthermore, a frame-like yoke 80 is movably arranged at this piston, as can be seen particularly from FIGURE 5a. This yoke is suitably mounted on corresponding holding elements 81 provided at the rim area of the piston 30. This yoke does not prevent the head of the prop resting on the bottom of the hollow piston from projecting upwardly therethrough since this projecting is necessary.

The yoke is constructed to fit into the side supports 82 or it can be constructed to include such brackets. Thereby, this yoke may be a movable support for use with the embodiment according to FIGURES 1 and 2, for the partial girders 41a, 41b, and this support is equivalent to the traverse 31. As illustrated in FIGURE the front end 8 of the girder 5, which thus has now been advanced by the distance which was saved from the length of the assembly shown in FIGURE 1 and which pertains to the rear assembly, now lies on top of the prop 26 resting in the hollow piston 30. This is thus a double support because it is formed of two coaxially connected individual props of which each is provided with an inner and an outer prop and of which each has its own effective region. To use this double support in the embodiment of FIG- URE 5, the prop 26 remains the support of the girder of the forward assembly 34a, 3411 which is fashioned as a narrow frame and this narrow frame construction proves especially advantageous when using such a coaxial double support. However, the hollow piston provided with the above-mentioned yoke, replacing the eliminated two front props 3a, 3b of the rear assembly, now takes over the support of the front ends of the longitudinal struts 11a, 11b. Here, too, the individual structural elements are adapted to one another in their new positions.

20 Such adaptations are minor, but necessary from a constructional point of view.

If, in the former case, the partial girders 41a, 41b supported by the lower props of the double prop which replace the setting load amplifier 28 shall together be effective with 30 tons against the roof, and the end 8 of the girder 5 of the rear assembly which is supported by the upper prop 26 carried by the lower prop of the double prop shall be effective likewise with 30 tons against the roof, the lower prop thus has to be provided with a load bearing capacity of (30+30) 60 tons. correspondingly, with the assembly construction of FIGURE 5, the lower prop of the coaxial double prop carries the end of the longitudinal struts 11a, 11b, via its yoke (see particularly FIGURE 5a) and in this case the double prop must be able to support (2 30+30) tons, if each of the props 3a, 3b which this lower prop replaces of the rear trestle-shaped assembly is arranged to support 30 tons each and if further the inner prop 26, which as before supports the frame 34a, 34b, is dimensioned to have a load bearing capacity of 30 tons.

The embodiments described above in detail for carrying out the inventive idea are in no way exhaustive; rather, changes are possible within the scope of this idea, without departing from the basic idea. Above all, however, the invention is not limited to the simultaneous and combined application of all of these measures, but a number of these measures may be used by themselves and/or in combination with other supporting devices and prop arrangements of the basic type mentioned in the introduction. All in all, the proposed devices may, as is clear from the foregoing, be employed in all known support systems, wherever their application proves to be of advantage.

FIGURES 11 and 12 show a lower frame structure which can be used in combination with the upper frame structure shown in FIGURE 5. The bottom beams ll'a and 11b in FIGURES 11 and 12 correspond to the longitudinal struts 11a and 11b in FIGURE 5. The transverse struts 12 and 13 in FIGURES 11 and 12 are offset upwardly to make room for the cylinder 16, which is indicated in dashed lines in FIGURE 12. Prop support elements 2' are provided on beams ll'a and 11']; for props 3a, 3b, 4a, and 4b. The upward offset in transverse struts 12' and 13 in FIGURES 11 and 12 corresponds to the downward offset in the transverse struts 12 and 13 in FIGURE 5.

It will be understood that the above description of the present invention is susceptible to various modifications, changes, and adaptations, and the same are intended to be comprehended within the meaning and range of equivalents of the appended claims.

What is claimed is:

1. A mine roof supporting device providing a propfree mine working area, comprising, in combination:

(a) a rear assembly having front and rear support units for supporting the roof of a mine near the mine filling area thereof; and

(b) a forward assembly connected with said near assembly and including (1) prop means disposed in an area wherein a mine roof will be supported by the front support unit of the rear assembly, and

(2) girder means supported by said prop means and having arms extending forwardly and rear- Wardly respectively from said prop means for supporting a mine roof near the mine working face, and means mounted near the ends of the girder arms and projecting thereabove for concentrating the major portion of the support effect in the region of the girder means at the ends of its arms; and

(6) means connecting said forward and rear assemblies together in spaced relationship with said forward assembly being movable with respect to said rear assembly.

2. A mine roof supporting device providing a propfree mine working area, comprising, in combination:

(a) a rear assembly having front and rear support units for supporting the roof of a mine near the mine filling area thereof;

(b) a forward assermbly connected with said rear assembly and including:

(1) prop means disposed in an area wherein a mine roof will be supported by the front support unit of the rear assembly, and

(2) girder means supported by said prop means and having arms extending forwardly and rearwardly respectively from said prop means for supporting a mine roof near the mine working face as though a prop were disposed at the working face and with at least the major portion of the support effect concentrated in the region of the girder means at the ends of its arms; and

(c) said girder means including a rigid frame having at least two longitudinal struts connected with each other by transverse struts, said frame including means for mounting it for support upon said prop means in one of a plurality of positions with respect to said prop means.

3. A device as defined in claim 2 wherein said longitudinal struts are box profiles having laterally opening side chambers formed therein, and said transverse struts being disposed in said side chambers and being of correspondingly smaller profile.

4. A mine roof supporting device providing a propfree mine working area, comprising, in combination:

(a) a rear assembly having front and rear support units for supporting the roof of a mine near the mine filling area thereof;

(b) a forward assembly connected with said rear assembly and including:

(1) prop means disposed in an area wherein a. mine roof will be supported by the front support unit of the rear assembly, and

(2) girder means supported by said prop means and having arms extending forwardly and rearwardly respectively from said prop means for supporting a mine roof near the mine working face as though a prop were disposed at the working face and with at least the major portion of the support effect concentrated in the region of the girder means at the ends of its arms; and

(c) said girder means including a rigid frame having at least two longitudinal struts connected with each other by transverse struts, at least one of the transverse struts including a bearing shell for engaging the head of said prop, and the head of the prop being tapered to form, in cooperation with said hearing shell, means for mounting the frame for universal movement upon the prop, and said transverse struts being relatively short to provide a narrow girder means.

5. A device as defined in claim 4 wherein at least one of said transverse struts includes a bearing shell on both sides thereof, the bearing shells being disposed symmetrically one on top of the other.

6. A device as defined in claim 4 wherein there are a plurality of bearing shells and the bearing shells are provided in pairs disposed on adjacent transverse struts opening upwardly and downwardly, respectively.

7. A device as defined in claim 4 wherein there are a plurality of bearing shells and the bearing shells are provided in pairs and arranged so that the frame is constructed to be reversible.

fl. A mine roof supporting device providing a propfree mine working area, comprising, in combination:

(a) a rear assembly having front and rear support units for supporting the roof of a mine near the mine filling area thereof;

(b) a forward assembly connected with said rear assembly and including:

(1) prop means disposed in an area wherein a mine roof will be supported by the front support unit of the rear assembly, and

(2) girder means supported by said prop means and having arms extending forwardly and rearwardly respectively from said prop means for supporting a mine roof near the mine working face as though a prop were disposed at the working face and with at least the major portion of the support effect concentrated in the region of the girder means at the ends of its arms; and

(c) said girder means including a rigid frame having at least two longitudinal struts connected to each other by transverse struts, and further comprising at least one offset transverse strut and means for removably connecting the offset transverse strut to the longitudinal struts.

9. A mine roof supporting device providing a propfree mine working area, comprising, in combination:

(a) a rear assembly having front and rear support units for supporting the roof of a mine near the mine filling area thereof;

(b) a forward assembly connected with said rear assembly and including:

(1) prop means disposed in an area wherein a mine roof will be supported by the front support unit of the rear assembly, and

(2) girder means supported by said prop means and having arms extending forwardly and rearwardly respectively from said prop means for supporting a mine roof near the mine working face as though a prop were disposed at the working face and with at least the major portion of the support effect concentrated in the region of the girder means at the ends of its arms; and

(c) said girder means being provided with spacing pads at the ends thereof to adapt it for selective mounting arrangements, said spacing pads having relatively large surface areas and being mounted to be shiftable with respect to the girder and being mounted for tilting movement in two directions.

10. A mine roof supporting device providing a propfree mine working area, com-prising, in combination:

(a) a rear assembly having front and rear support units for supporting the roof of a mine near the mine filling area thereof;

(b) a forward assembly connected with said rear as sembly and including:

(1) prop means disposed in an area wherein a mine roof will be supported by the front support unit of the rear assembly, and

(2) girder means supported by said prop means and having arms extending forwardly and rearwardly respectively from said prop means for supporting a mine roof near the mine working face as though a prop were disposed at the working face and with at least the major portion of the support effect concentrated in the region of the girder means at the ends of its arms; and

(c) telescoping extension means are on the girder means and arranged to be longitudinally extensible in a stepwise manner.

11. A device as defined in claim 10 comprising means for mounting the extension means to the device, and said extension means is constructed in the form of a fork and is provided with mounting devices for connecting pressuge transfer disks thereto.

12. A mine roof supporting device providing a propfree mine working area, comprising, in combination:

(a) a rear assembly having front and rear support units for supporting the roof of a mine near the mine filling area thereof;

(b) a forward assembly connected with said rear assembly and including:

(1) prop means disposed in an area wherein a mine roof will be supported by the front support unit of the rear assembly, and

(2) girder means supported by said prop means and having arms extending forwardly and rearwardly respectively from said prop means for supporting a mine roof near the mine working face as though a prop were disposed at the working face and with at least the major portion of the support effect concentrated in the region of the girder means at the ends of its arms; and

(c) telescoping advancing cap means on the girder means.

13. A travelling mine roof Supporting device providing a prop-free mine working area, comprising, in combination:

(a) a rear assembly having front and rear support units capable of being raised and lowered for supporting the roof of a mine near the mine filling area thereof;

(b) power means connected to said rear assembly and having a forwardly moving element; and

(c) a forward assembly connected with said forwardly moving element to be moved thereby and including:

(1) a prop disposed in an area wherein a mine roof will be supported by the front support unit of the rear assembly, said prop being arranged to be raised and lowered,

(2) girder means supported by said prop at a single location and being placed into a mine roof supporting position when the prop is raised and taken out of this position when the prop is lowered, said girder means having arms extending forwardly and rearwardly respectively from said prop for supporting a mine roof near the mine working face as though a prop were disposed there and with at least the major portion of the support effect concentrated in the region of the girder means at the ends of its arms, and

(3) resilient advancing cap means mounted on said girder means having pressure transfer means in the form of a disk on the end thereof, said disk being arranged to project upwardly above the girder means when the latter is not in roof supporting position and to be pressed against the roof of a mine with considerable pretensioning of the cap means when the girder means is in roof supporting position, pressure actuated means connected to said cap means for moving the cap means forwardly into the freshly cleared area immediately after a mining machine has passed.

14. A mine roof supporting device providing a propfree mine working area, comprising, in combination:

(a) a rear assembly having front and rear support units for supporting the roof of a mine near the mine filling area thereof;

(b) a forward assembly connected with said rear assembly and including:

(1) prop means disposed in an area wherein a mine roof will be supported by the front support unit of the rear assembly, and

(2) girder means supported by said prop means and having arms extending forwardly and rearwardly respectively from said prop means for supporting a mine roof near the mine working face as though a prop were disposed at the working face and with at least the major portion of the support effect concentrated in the region of the girder means at the ends of its arms; and

(c) the rear assembly including a bottom structure and the forward assembly includes a bottom structure, and further comprising means for guiding the two assemblies with respect to each other and connected to the forward assembly and mounted to be longitudinally movable with respect to the bottom structure of the rear assembly.

15. A device as defined in claim 14 wherein said guiding means includes a guide rod mounted to be disposed at a distance from the floor of the mine and being resilient in the upward and downward direction but being laterally rigid, said guide rod extending in the rearward direction at least up to the rear edge of the rear assembly in the vicinity of the mine filling.

16. A device as defined in claim 14 wherein said guiding means connected between the forward and the rear assemblies is arranged so that the assemblies have a certain amount of play with respect to each other, and power means for shifting the forward and rear assemblies in the transverse direction with respect to one another and for, at the same time, maintaining them in the desired travelling direction when the two assemblies move toward each other.

17. In a mine roof supporting device, the improvement comprising: girder means arranged to be supported by support units and for contacting a mine roof for supporting the same; and telescoping advancing cap means provided on said girder means, said telescoping advancing cap means being a resilient body in the form of a spring unit which may be pretensioned to aid in supporting a mine roof, the surface thereof at the end zone extending beyond the level of the surface of the girder means carrying this advancing cap means in the relaxed condition of the advancing cap means when it is not pretensioned, and a spacing element provided at a distance from the forward edge of the girder means on which it is supported and disposed below the resilient advancing cap means and connected therewith, said spacing element being the lower leaf of said spring unit.

18. A mine roof supporting device providing a propfree mine working area, comprising, in combination:

(a) a rear assembly having front and rear support units for supporting the roof of a mine near the mine filling area thereof and including a bottom structure;

(b) a forward assembly connected with said rear assembly and having a bottom structure and including 1) a prop disposed in an area wherein a mine roof will be supported by the front support unit of the rear assembly and including setting force amplifier means, and

(2) girder means supported by said prop at a single location and having arms extending forwardly and rearwardly respectively from said prop for supporting a mine roof near the mine working face in a cantilevered manner with at least the major portion of the support effect concentrated in the region of the girder means at the ends of its arms; and

(c) means for guiding the two assemblies with respect to each other and connected to the forward assembly and mounted to be longitudinally movable with respect to the bottom structure of the rear assembly, the bottom structure of the forward assembly being arranged to have the pressure of the support of the forward assembly concentrated on at least two regions of said bottom structure, these regions being arranged at a distance from the vertical axis of the support, the rear assembly having an upper structure and the girder means of the forward assembly laterally encompassing the upper structure of the rear assembly, said girder means being guided along the surfaces of the rear assembly.

19. A mine roof supporting device providing a prop- 75 free mine working area, comprising, in combination:

25 (a) a rear assembly having front and rear support units for supporting the roof of a mine near the mine filling area thereof; (b) a forward assembly connected with said rear assembly and including:

(1) prop means disposed in an area wherein a mine roof will be supported by the front support unit of the rear assembly, and

(2) girder means supported by said prop means and having arms extending forwardly and rearwardly respectively from said prop means for supporting a mine room near the mine working face as though a prop were disposed at the working face and with at least the major portion of the support effect concentrated in the region of the girder means at the ends of its arms; and

(c) said rear assembly comprising upper and lower frames extending respectively between the upper and lower portions of said front and rear support units, said upper and lower frames each comp-rising two longitudinal frame members connected together by means of transverse frame members extending therei-nbetween, the transverse member of the upper frame being offset downwardly, and the transverse members of the lower frame being offset upwardly.

20. In a mine roof supporting device having at least one assembly including a bottom structure, a plurality of upwardly extending props mounted on said bottom structure, and an upper structure carried by the props for supporting a mine roof, the improvement comprising:

(a) a forwardly movable part on said supporting dev1ce;

(b) means for supporting said forwardly movable part for angular movement in a substantially horizontal plane as well as for forward movement relatively to the remainder of said supporting device;

() guide means for determining the direction of movement of said movable part relative to a horizontal longitudinally extending reference axis of the supporting device, such guide means having cooperative surfaces disposed respectively on said forwardly movable part andcon a cooperative part of the supporting device and defining paths diverging respectively to the left and to the right with respect to the reference axis;

(d) traction means for moving said movable part forwardly selectively along a path parallel to the reference axis or along one or the other of said divergent paths;and

(e) power-operated means operatively connected with the guide means for effecting selection of the direction of advancement defined thereby.

21. In a mine roof supporting device having at least one assembly including a bottom structure, a plurality of upwardly extending props mounted on said bottom structure, and an upper structure carried by the props for supporting a mine roof, the improvement comprising:

(a) a forwardly movable part on said supporting device;

-(b) guide means for determining the direction of movement of said movable part relative to a horizontal longitudinally extending reference axis of the supporting device, such guide means having cooperative surfaces disposed respectively on said forwardly movable part and on a cooperative part of the supporting device and defining paths diverging respectively to the left and to the right with respect to the reference axis; and

(o) traction means for moving said movable part forward-1y selectively along a path parallel to the reference axis or along one or the other of said divergent paths,

(d) the supporting device comprising front and rear assemblies each including a bottom structure and each including an upper structure;

(e) one of said assemblies having a guide member extending longt-iudinally of the supporting device into longitudinally overlapped relation with the other of said assemblies; and U (f) said guide member presenting one of said guide surfaces and the other of said guide surfaces being presented by said other of said assemblies.

22. In a mine roof supporting device having at least one assembly including a bottom structure, a plurality of upwardly extending props mounted on said bottom structure, and an upper structure carried by the props for supporting a mine roof, the improvement comprising:

'(a) a forwardly movable part on said supporting device;

(b) guide means for determining the direction of movement of said movable part relative to a horizontal longitudinally extending reference axis of the supporting device, such guide means having cooperative surfaces disposed respectively on said forwardly movable part and on a cooperative part of the supporting device and defining paths diverging respectively to the left and to the right with respect to the reference axis; and

(c) traction means for moving said movable part forwardly selectively along a path parallel to the reference axis or along one or the other of said divergent paths, the supporting device comprising front and rear assemblies each including a bottom structure and each including an upper structure, the upper structures of the front and rear assemblies have respective guide faces cooperating with each other to effect or assist guiding of the front and rear assemblies relative to each other during advancement of the support.

23. In a mine roof supporting device including a bottom structure, a plurality of upwardly extending props mounted on said bottom structure, and an upper structure -carried by the props for supporting the roof, the improvement wherein:

the upper structure includes a frame having laterally spaced, longitudinally extending struts connected together by transverse struts which are spaced apart longitudinally;

at least that one of said transverse struts situated nearest the forward end of said frame is offset down-wardly with respect to the longitudinally extending struts;

the upper structure further includes a girder means having lateral rigidity extending into the aperture defined by said frame and overlying said downwardly offset transverse member thereof;

said girder means includes longitudinally extending girders having laterally inwardly presented side chambers;

said girders are connected by transverse struts of short length to provide a narrow girder means; and

at least one of said transverse struts of short length is situated immediately adjacent to the forward end of said frame and includes a bearing shell for engaging the head of one of said props for supporting said girder means.

24. In a mine roof supporting device including a bottom structure, a plurality of upwardly extending props mounted on said bottom structure, and an upper structure carried by the props for supporting roof, the improvement wherein:

the upper structure includes a frame having laterally spaced, longitudinally extending struts connected together by transverse struts which are spaced apart longitudinally;

at least that one of said transverse struts situated nearest the forward end of said frame is offset downwardly with respect to the longitudinally extending struts;

the upper structure further includes a girder means having lateral rigidity extending into the aperture defined by said frame and overlying said downwardly offset transverse member thereof;

said bottom structure includes laterally spaced longitudinally extending side members connected together by transverse side members extending therebetween, at least one of said transverse members situated nearest the forward end of such bottom structure being offset upwardly from said side members thereof.

25. A mine roof supporting device comprising:

(a) a first assembly including:

(i) a substantially rigid bottom structure of generally rectangular form in plan and defining a longitudinally extending lower guide channel means,

(ii) upwardly extending props carried by said bottom structure in its forward and rearward end regions and spaced apart laterally in at least one of said regions to lie respectively on opposite sides of said lower channel means,

(iii) a substantially rigid upper structure for engaging said roof, said upper structure being carried by said props and including laterally spaced longitudinally extending side portions connected together by transversely extending portions, said portions collectively defining a longitudinally extending upper channel means between said side portions,

(b) a second assembly including:

(i) a bottom structure including a portion disposed in said lower channel means and of a width less than that of said lower channel means to be movable both angularly therein in a horizontal plane and longitudinally thereof,

(ii) an upwardly extending prop carried by said bottom structure,

(iii) an upper structure for engaging said roof, said upper structure being carried by said prop and including a portion disposed in said upper channel means and of a width less than that of said upper structure being carried by said prop 40 angularly therein in a horizontal plane and longitudinally thereof,

(c) traction means operatively connected between said first and second assemblies for effecting relative successive advancement thereof when the upper structure of each is out of load bearing relation with said roof and the upper structure of the other of said assemblies is in load bearing relation with the roof; and

(d) adjustable guide means for controlling the angular position of at least one of said portions of said second assembly in the channel means in which it is disposed tion transversely of said lower channel means,

(b) power energized operating means for moving said guide element.

27. A mine roof supporting device according to claim 25 wherein said adjustable guide means includes:

(a) at least two guide elements spaced apart longitudinally of said lower channel means,

(b) power energized operating means for moving each of said guide elements selectively in one direction or in the opposite direction transversely of said lower channel means.

References Cited UNITED STATES PATENTS 3,174,289 3/1965 Rosenberg 61-45 3,197,966 8/1965 Arnott 61--45.2 3,008,298 1/1961 Wilkenloh et al. 16645.2 3,240,021 3/1966 Meriaux et al 61-45.2

FOREIGN PATENTS 772,868 4/ 1957 Great Britain. 1,278,986 11/1961 France. r 1,119,803 12/1961 Germany. 1,112,480 8/1961 Germany.

866,108 4/ 1961 Great Britain. 882,933 11/1961 Great Britain. 905,312 9/ 1962 Great Britain. 1,312,708 11/1962 France.

975,201 9/ 1961 Germany. 865,922 4/1961 Great Britain.

JACOB SHAPIRO, Primary Examiner. US. 01. X.R.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,425,229 February 4, 1969 Karl Maria Groetschel It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

Column 20, line 58, "near" should read rear Column 25, line 12, "'room" should read roof Signed and sealed this 24th day of February 1970.

(SEAL) Attest:

Edward M. Fletcher, Jr.

Attesting Officer Commissioner of Patents WILLIAM E. SCHUYLER, JR.

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