US3344610A - Self-traveling propping apparatus - Google Patents

Description

G. DOMMANN ETAL l SELF-TRAVELING PROPPING APPARATUS Filed April 13, 1965 Oct. 3, 1967 United States Patent G 1o claims. (l. 61-45) ABSTRACT F THE DISCLOSURE This speciiication is directed to a mine roof propping apparatus which comprises a pair of parallelly-disposed propping member assemblies which are adapted to operate such that either assembly can be propelled in a plane substantially parallel to the other assembly while maintaining the mine roof in a propped condition. Thus, the two propping assemblies are adapted to operate in simultaneous or alternate manner. Each of the assemblies comprises a pair of substantially parallel propping members which are joined together in a generally parallelogram length, which length is defined by a pair of shackle members/ connected to the bottom portion of each propping column and a pair of parallel bar members pivotally connected to the shackle members. By this construction, each propping assembly can be moved as a unit and maintained during each movement in spaced parallel relationship with the other propping assembly.

This invention relates in general to mine roof propping equipment, and more particularly to a self-traveling mine roof propping apparatus which is adapted to move along a mine oor and follow the progress of a'mineral Winning machine.

Self-advancing roof propping systems are being used in increasing extent in the long wall coal mining operations to provide both roof support for mine roof areas adjacent to advancing coal winning machines which cut progressively into the working face of the coal seam. Such prior art propping systems, like the propping apparatus according to the invention, are hydraulically or pneumatically driven, preferably via automatically controlled hydraulic or pneumatic power systems which enable the propping system to perform its roof supporting and self-advancing functions in a selected sequence and at a rate suiiicient to accompany the advancement of the coal winning machinery into the working face.

' The roof propping apparatus of the invention, like the roof propping systems of the prior art, have column-like propping members which are extendable and contractable, and can be constructed in the form of telescopically arranged piston and cylinder hydraulic actuators. These propping members are provided with cap members and shoe members which are respectively connected to the roof support and floor bearing ends of the individual prop columns for respective engagement with the mine roof and oor.

When the propping members are extended, their cap and shoe members forceably bear against the roof and oor to support the roof and to transmit the roof support icc load from the cap members through the prop columns and shoe members into the iloor.

In the apparatus according to the invention, four propping members are connected in pairs by parallelogram linkages to form a pair of roof propping frames arranged in parallel side by side relation. The hydraulically operated prop columns of each frame are disposed in spaced apart relation to each other in a plane parallel to their line of travel. Both prop columns in each frame a-re extended in unison for supporting the roof, and when the frame is to be immobilized to permit the other frame to be moved along the mine floor by means of an actuator.

When the prop columns of either frame are extended into roof supporting engagement, the frame is immobilized by reason of the high friction between the shoe members and iloor, which results from the high normal load component of the roof support forces transmitted through the shoes. By retractingrthe prop columns in either frame, this normal load and hence the friction resistance to shoe member sliding can be reduced to zero, or to the extent where that frame can be slidably moved on its shoe members along the mine oor by means of an actuator which is connected by cross members to the parallelogram linkages ofthe two frames.

This advancing actuator, which is preferably constructed with one or more parallelly connected hydraulic piston and cylinder linear actuators, has its cylinder members connected together by a cross member to the parallelogram linkage of one frame, and its piston'members connected together by another cross member to the parallelogram linkage of the other frame. Y

Thus, when one frame is released, and the other frame is immobilized, the advancing actuator moves the released frame along a line parallel to the plane of the immobilized frame. When the released frame has lbeen displaced to a selected position either forward or backward in relation to the immobilized frame, such as a position which corresponds to the limit extension of the advancing actuator, the released frame can then be extended and immobilized, and the formerly immobilized frame can be released for movement by the actuator into line with the frame which has been advanced. By repeating this sequence of propping frame shifting, the propping apparatus of the invention can be made to travel under the influence of its actuator in a step by step walking manner so as to follow the progress of a coal winning machine cutting into the working face.

In a propping apparatus of this type, it is important that the individual prop columns are maintained in a substantially perpendicular attitude with respect to the mine i-loor. In this way, the propping columns can be utilized to their full load bearing capacity and propping frame stability is assured. This vertical attitude must also be maintained when either frame is being advanced.

In addition, it is highly desirable that this perpendicular attitude is maintained when the prop column shoes pass over irregular contour portions of the iloor.

One of the novel and advantageous features of the propping apparatus according to the invention lies in the use of parallelogram linkages for maintaining the prop columns of each propping frame in positions parallel t0 one another and substantially normal to the floor.

To maintain the propping frames parallel to each other and with their prop columns normal to the oor, parallelogram linkage type cross members are used for connecting the frames to their common advancing actuator.

In a preferred embodiment of the apparatus according to the invention, the advancing actuator is constructed as a composite linear actuator having two piston and cylinder hydraulic actuators disposed in parallel relation to each other, and spaced somewhat closely together for convenience in an arrangement somewhat resembling that of a double-barrel shotgun. These individual actuators are preferably of the double-acting type to permit the sequential stepwise advancement of the propping frames.

Both cylinders are ixedly connected together by any suitable conventional fastening means, or if desired, can be bored into a common block.

Likewise, the two piston rods which pass through both ends of the cylinders are connected together at their ends, by conventional fastening means, `such as for example, double shackles. These shackles are in turn connected to each other by a rigid bar, which can be advantageously shaped into a cover plate to protect the moving parts of the composite advancing actuator. Accordingly, this cover plate extends parallel to the piston rods protected by it.

The piston cover plate is connected at approximately the center of its length by a cross member which serves for connecting said piston cover plate to a pair of superposed parallel bars in the parallelogram linkage of one of the frames.

This cross member is preferably constructed in the form of a U-shaped elastic bar harness which is connected at its closed end to the piston cover plate, and at its two separated ends to the bars of the corresponding frame parallelogram linkage. The connection of this bar harness to the cover plate and parallelogram linkage bars is of a type which precludes rotation at the connection points.

A similar bar harness cross member connects the cylinders of the composite actuator to corresponding similar superposed bars in the parallelogram linkage of the other frame.

By using elastic bars, such as are commonly used in constructing leaf springs, for the propping frame parallelogram linkages, and as parallelogram linkage cross members connecting the frames to the composite actuator, the propping apparatus of the invention is able to perform its propping and self-advancing functions and to maintain a normally directed roof support load transmission into the oor in spite of local irregularities thereon by reason of the elastic deection properties of the bars used in `the frame parallelogram linkages and the cross members.

The U-shaped harnesses can be inserted with their closed ends into pocket-like retainers provided on the cylinders and piston plate cover, and can be secured thereto by means of pin retainers. The free ends of these harnesses can be fastened to the parallel elastic coupling bars of the parallelogram linkages by clamping them to the bars with a spacer inserted between the coupling bars.

For a more secure frame-to-actuator connection, it is preferable to use two U-shaped harnesses disposed parallel to one another and slightly spaced apart for connecting each frame parallelogram linkage to the corresponding piston portion or cylinder portion of the composite actuator.

For the purpose of avoiding unnecessary restriction in the motion of the individual prop columns of each frame, the two superposed coupling bars of its parallelogram linkage are disposed parallel to each other and in spaced apart relation, and are connected at their extremities by pivot pins to the prop columns of the frame. It is advantageous for the prop columns to be provided with releasable shackle members for the connection of the coupling bar ends by the pivot pins. To prevent undesired rotation of the prop columns relative to the shackles which form a part of its parallelogram linkage, said shackles are secured xedly but releasably by means of dowel pins or similar fastening means to their respective prop columns.

While the coupling bars of the parallelogram linkages could be pin-connected directly to the prop columns of the frames, it is advantageous to use such intermediate shackle members because in the event that it becomes necessary to replace individual prop columns in either of the prop frames, such replacement can be performed expediently and economically.

It is therefore, an object of the invention to provide a self-traveling roof propping apparatus for supporting mine seam roofs.

Another object of the invention is to provide a roof propping apparatus as aforesaid which is adaptable for use in mining seams having irregularly contoured oor's.

Another and further object of the invention is to provide a roof propping apparatus as aforesaid wherein the support load is borne by structural members in the apparatus and is transferred to the oor along lines which are substantially perpendicular to the oor surface.

`Other and further objects and advantages of the invention will become apparent from the following detailed description and accompanying drawings in which:

FIG. 1 is a schematic plan view of the bottom portion of a propping apparatus according to a preferred embodiment of the invention, taken from a plane passing normally through its propping columns.

FIG. 2 is a schematic side view of a portion of the apparatus shown by FIG. 1.

FIG. 3 is a schematic sectional view taken along the line 3 3 of FIG. 1.

FIG. 4 is a schematic sectional view of the composite advancing actuator used in the apparatus of FIGS. 1-3, and taken along the line 4--4 of FIG. 1.

Referring now to FIGS. 1 4 of the drawings, the propping apparatus A of the invention comprises a pair of roof propping frams B and C which are connected to an actuating system D for stepwise relative movement one at a time along spaced-apart parallel travel line paths.

Each of the propping frames B and C is adapted to travel along a mine floor F and has a pair of propping column members 11 which are selectively extendable for supporting engagement with the mine roof (not shown) and are retractable for frame B, C movement along the mine floor.

At the upper, or roof supporting ends (not shown) of columns 11 are connected cap members (not shown) which Ibear against the roof when said columns 11 are extended, and transmit the roof support load to the floor F through the columns 11 and shoe members 12 which are pivotally connnected to the bottom end portions of said column 11.

When the columns 11 on either frame B or C, are extended for supporting the roof, that frame B, C is substantially immobilized because of the high friction resistance to the sliding of the shoe member 12 along the oor F.

On the other hand, when the columns 11 on either frame B or C are retracted out of roof supporting engagement, that frame B or C can be slidably moved along the oor F by the actuating system D.

To provide the aforesaid extension and retraction capability in the columns 11, said columns 11 are preferably constructed as telescopically arranged hydraulic piston and cylinder actuators which are connected to a suitable conventional hydraulic power source (not shown) through a hydraulic control system (not shown) of conventional construction.

The propping column members 11 are disposed in spaced-apart parallel relation to each other in a plane parallel to the line of travel of their corresponding frame B, C.

Parallelogram linkages G are provided for maintaining the columns 11 in each of the frames B, C in a mutually parallel spaced relation, with the columns 11 i'n each frame being connected together by a parallelogram linkage G.

As can be seen in greater detail in FIG. 2, each parallelogram linkage G comprises a pair of shackle members 13 mounted to the lower portions of the columns 11, and a pair of parallel spaced-apart bars 15 which are pivotally connected at their ends to the shackles 13 by means of pins 16.

The columns 11 in each of the frames B, C are maintained in parallel relation to each other by the action of the parallelogram linkages G, which because the pivot connection axes established by the pins 16 are perpendicular to the plane of said columns 11, permit only equally an-gular shifting of the columns 11 in said plane. Because of the fixed connection of the shackles 13 to the columns 11, and the arrangementof the relatively at bars 15 with their most -rigid section perpendicular to the plane of the columns 11, substantially no relative twisting movement of the columns 11 in either frame B, C can occur.

The shoes 12 are articulately connected to the bottom end portions of the columns 11 by means of pivot pins P, and are of such length and breadth as to be capable of spanning irregular portions of the floor F. As will be apparent to those skilled in the art, by providing pivotally connected shoes 12 of appropriate lateral dimensions on each column 11, the propping apparatus A can be adapted to travel along mine floors F having any normal range of irregularity in elevation contour, and at any location on said iloor F, the propping frames B and C of said apparatus A can be extended for supporting the roof with the columns 11 being maintained substantial-1y perpendicular to the average local floor contour.

The actuating system D includes a pair of co-extensive superposed hydraulic actuators H disposed in parallel relation to each other and having cylinders 17 and pistons 18 which are respectively connected together for operation in unison.

The connection of the cylinders 17 is preferably achieved by boring into a common casting block, but any other suitable fastening means (not shown) can be substituted for iixedly connecting said cylinders 17 together.

The piston rods 18 which extend beyond the ends of the cylinders 17 and are xedly connected together at their ends by means of double shackle 19. These shackles 19 are in lturn xedly connected to a cover bar 20v which also serves for protecting the working parts of the actuators H from damage, and the operating personnel from injury by contact with said actuators H.

The cover bar 20 extends in parallel spaced-apart relation to the piston rods 18 and cylinders 17, and along the length thereof.

To utilize the relative motion of the pistons 18 and cylinders 17 in the actuating system D for moving the frames B and C relative to each other, parallelogram type cross members K are used for operatively connecting the cylinders 17 to the parallelogram linkage G of one of the frames B, C, and for operatively connecting the pistons 18 via their attached cover bar 20 to the parallelogram linkage G of thelother of said frames B, C.

The cross members K also serve to maintain the frames B and C in laterally spaced-apart relation to each other, so that they travel along parallel paths of constant spacing when driven by the actuating system D.

For this purpose, the cross member K arrangement is preferably constructed with pairs of oppositely disposed U-shaped harness members 21, which can be constructed of at bar stock bent into a U-shape, wtih one of said harness members 21 in each pair being connected at its closed end portion to the pi-ston cover bar 20, and the other harness member 21 in each of said pairs being connected at its closed end portion to the integral cylinder block 30. The free ends of the harness members 21 are connected to the bars 15 of the parallelogram linkages G on corresponding propping frames B and C.

To accommodate the securing of the closed end portions of the harness members 21, the cover bar 20 and cylinder block 30 are preferably provided with shackle members 24 which are ixedly attached as by welding thereto. Each of the shackles 24 is provided with a pair of retainer pins 23 for securing the closed end portions of the harness member 21 passed through the slotted pocket openings between the pins 23, shackles 24 and the cover bar 20 or cylinder block 30 to which said shackles 24 are mounted. The pins 23 are inserted into the shackle 24 lugs which extend from the cover bar 20 and cylinder block 30 and are oriented substantially parallel to the direction of piston 18 and cylinder 17 motion. In this manner, a harness member 21 to actuating system D fastening is achieved in both a simple and expedient manner that substantially precludes relative rotation between the harness members 21 and actuator system D about any axis other than those of the pins 23.

The free end portions 25 of the harness members 21 are connected to the two s-uperposed coupling bars 15 on each propping frame B and C by means of clamping bolts 26 which clamp said end portions 25 between spacers 27 and the inwardly facing surfaces of the bars 15.

In-the propping apparatus A thus far described, the propping frames B and C are similarly constructed for interchangeability, and to permit said frames B and C, and the actuating system D to be transported as separate units which can be assembled at the work site in the mine.

As shown by way of example in FIGS. l and 2, four harness members 21 (two pairs) are used in the cross member K to provide a more stable structural connection between the actuating system D and the frames B and C. If desired, additional pairs of similarly connected harness members 21 can be provided, or a single pair of harness members 21 of greater Width, but bent into the same type of U-shape can be substituted for the two pairs of narrower harness members 21 shown.

At the work site, the four U-shaped harnesses 21 are assembled to the actuating system D by inserting the pins 23. Then the propping frames B and C are coupled to the actuating system D by means of the cross member K by inserting and tightening the clamping bolts 26.

Since the actuating system D is constructed as a double cylinder actuator, and is fastened via coupling bars '15 to the propping frames B and C and by the two spacedapart pairs of U-shaped harnesses 21, said coupling bars 15 and harness members 21 being relatively elastic, in a manner similar to steel `leaf springs with regard to loading in directions parallel to the columns 11 (i.e. perpendicular to the floor F), and relatively stiff as regards loading in planes perpendicular to the columns 11 and parallel to the floor F, the apparatus A is provided with the necessary structural rigidity to maintain its propping frames B and C in their intended spaced-apart parallel positions for stepwise travel along parallel line paths and yet have sufficient yielding capability for adaptation to the mine floor F contour irregularities. This elastic yielding is assured not only by the elastic material and arrangement of the harnesses 21 and coupling bars 15, but also by the pins 16 which connect said coupling bars 15 with the columns 11, said pins 16 being in spaced-apart relation to each other and arranged in mutually parallel relation.

In the operation of the apparatus A, only one of the proppin-g frames B or C is moved at a time. For example, if it is desired to move the frame B, the frame C is extended for roof supporting engagement and thereby immobilized, with the frame B being retracted so as to be slidable along the oor F. This is necessary because one movable member, either the cylinder block 30 or the piston bar 20 of the actuating system D must be connected to the fixed frame C, and the other movable member must be connected to the frame B that is to be moved. For example, the cylinder block 30 is connected for movement with the frame B, with the piston bar 20 being connected for movement with the frame C.

The actuating system D is then energized to move the frame B along its line of travel for a selected distance relative to either end of the fixed frame C, up to the extension capability of the actuators H. With frame B thus advanced, it can be extended and thereby immobilized to serve as the fixed frame for advancing the frame C, which is then released from its previous roof supporting engagement.

To advance frame C relative to and in line with the frame B, the actuating system D is again energized, but in this case the cylinder block 30 is held fixed along with the frame -B and the piston bar 20 is moved with the frame C.

Thus, by repeating the aforementioned sequence of operations, the propping apparatus A can be moved either backwards or forwards along the mine oor F by sequential stepwise movement of its frames B and C in a manner similar to walking, except that the frames B and C are not lifted up from the oor F when moved, but rather slide along said oor F upon their shoes 12.

As will be apparent to those skilled in the art, the control of the propping apparatus A movement can be simply accomplished by means of a conventional hydraulic control system (not shown) which is connected to a hydraulic power source (not shown) and to the actuating system D for controllably energizing same to perform the desired frame B, C shifting movements.

The same hydraulic power source used for extending and retracting the propping columns 11 can be used for operating the actuating system D, if desired. Likewise, the hydraulic controls for the actuating system D can be integrated with those used for controlling the columns 11.

It is advantageous to provide such an integrated control system with interlocked control means to prevent attempted movement of an extended and thus locked frame B, C, since normally, both frames B and C will be extended for supporting the roof prior to any movement of the apparatus A.

As can be appreciated by the artisan, there are numerous apparent variations and modifications which can be implemented into the apparatus A according to the invention to adapt said apparatus A for expedient operation in a particular application.

What is claimed is:

1. A self-traveling mine roof-propping apparatus which comprises:

(a) a first roof-propping frame which is adapted to travel along a mine floor and is extendable for supporting engagement with the roof, said frame being substantially immobile when extended .for roofsupporting engagement, said frame having a pair of propping column members disposed in spaced-apart parallel relation to each other in a plane parallel to their line of travel;

(b) a first parallelogram linkage; comprising a pair of shackle members, each of which being xedly connected to the fbottom portion of a propping column in the frame, and a pair of superposed parallel bar members of substantially equal length disposed in spaced-apart relation and pivotally connected at their ends to said shackle members, whereby said parallelogram is defined by a pair of oppositely disposed parallel bar members and a pair of oppositely disposed parallel shackle prop column members; connecting the propping columns of said first Iframe to each other in mutually spaced parallel relationship;

(C) a Second roof-propping frame, similar to the rst, disposed in laterally spaced-apart parallel relation thereto for travel along a line parallel to the line of travel of said first frame;

(d) a second parallelogram linkage; comprising a pair of shackle members, each of which being iixedly connected to the bottom portion of a propping column in the frame, and a pair of superposed parallel bar members of substantially equal length disposed in spacedapart relation and pivotally connected at their ends to said shackle members whereby said parallelogram is defined by a pair of oppositely disposed parallel bar members and -a pair of oppositely disposed parallel shackle prop column members; connecting the propping columns of said second `frame to each other in mutually-spaced parallel relationship;

(e) linear actuating means for sequentially moving said first and second propping frames relative to each other and in side by side relation along parallel line paths; and

(f) cross member means connecting said actuating means to said first and second parallelogram linkage means whereby said rst and second frame members can be moved one at a time along their respective parallel travel lines, with one of said frames being extended in roof-supporting engagement and thereby immobilized while the other frame is moved relative thereto by said actuating means.

2. The apparatus according to claim 1 including means for rigidly fastening the cross member means to the actuating means and to each parallelogram linkage means to prevent rotation of the propping frames relative to each other.

3. The apparatus according to claim 1 including an individual shoe member articulately connected to the bottom portion of each propping column to facilitate the movement of the propping frames upon said shoe members along the floor.

4. The apparatus according to claim 1 wherein the parallel bar members are pivotally connected to the shackle members with pivot connection axes that are perpendicular to the plane of the propping columns in corresponding propping frames.

5. The apparatus according to claim 1 wherein the linear actuating means includes a pair of coextensive superposed piston and cylinder hydraulic actuators disposed in parallel relation to each other, fastening means connecting the pistons of said actuators together, and fastening means connecting the cylinders of said actuators together for operation in unison.

6. The apparatus according to claim S wherein the piston and cylinder hydraulic actuators are both double acting linear actuators having piston rods projecting beyond both ends of their corresponding cylinders, with the ends of said piston rods being tixedly connected t0 a cover =bar by shackle connector means, said cover bar extending in parallel spaced-apart relation to said piston rods, and being connected to the cross member means for transmission of piston rod motion to a propping frame.

7. The apparatus according to claim 6 wherein the cross member means includes at least one pair of oppositely disposed U-shaped harness members, one of said harness members in each pair being connected at its closed end portion to the actuator piston cover bar, and the other of said harness members in each pair being connected to the actuator cylinders, with the open end portions of said harness members being connected to the parallelogram linkages on corresponding propping frames.

8. The apparatus according to claim 7 wherein the open end portions of the harness members are secured by clamping to the parallel barred members of the parallelogram linkages, and including spacer means disposed between said parallel bar members at the clamping points of the harness members for maintaining a selected bar spacing thereat.

9. The apparatus according to claim 7 wherein the closed end portions of the harness members are secured to the cylinders and the piston cover bar by means of shackle members fastened thereto and pin members extending through said shackle members, with the closed end portions of said harness members being passed between corresponding pin members Iand shackle members.

10. The apparatus according to claim 7 wherein two pairs of oppositely disposed harness members are provided for connecting the piston cover bar and cylinders to corresponding parallelogram linkages, said pairs of harness members being connected to said cover bar, cylinders and parallelogram linkages in parallel spaced-apart relation to each other.

1 il References Cited UNITED STATES PATENTS 10/1963 Barall et al. 6145.2 7/19'65 Herrmann et al 61-452 ERNEST R. PURSER, Primary Examiner.

Claims (1)

1. A SELF-TRAVELING MINE ROOF-PROPPING APPARATUS WHICH COMPRISES: (A) A FIRST ROOF-PROPPING FRAME WHICH IS ADAPTED TO TRAVEL ALONG A MINE FLOOR AND IS EXTENDABLE FOR SUPPORTING ENGAGEMENT WITH THE ROOF, SAID FRAME BEING SUBSTANTIALLY IMMOBILE WHEN EXTENDED FOR ROOFSUPPORTING ENGAGEMENT, SAID FRAME HAVING A PAIR OF PROPPING COLUMN MEMBERS DISPOSED IN SPACED-APART PARALLEL RELATION TO EACH OTHER IN A PLACE PARALLEL TO THEIR LINE OF TRAVEL; (B) A FIRST PARALLELOGRAM LINKAGE; COMPRISING A PAIR OF SHACKLE MEMBERS, EACH OF WHICH BEING FIXEDLY CONNECTED TO THE BOTTOM PORTION OF A PROPPING COLUMN IN THE FRAME, AND A PAIR OF SUPERPOSED PARALLEL BAR MEMBERS OF SUBSTANTIALLY EQUAL LENGTH DISPOSED IN SPACED-APART RELATION AND PIVOTALLY CONNECTED AT THEIR ENDS TO SAID SHACKLE MEMBERS, WHEREBY SAID PARALLELOGRAM IS DEFINED BY A PAIR OF OPPOSITELY DISPOSED PARALLEL BAR MEMBERS AND A PAIR OF OPPOSITELY DISPOSED PARALLEL SHACKLE PROP COLUMN MEMBERS; CONNECTING THE PROPPING COLUMNS OF SAID FIRST FRAME TO EACH OTHER IN MUTUALLY SPACED PARALLEL RELATIONSHIP; (C) A SECOND ROOF-PROPPING FRAME, SIMILAR TO THE FIRST, DISPOSED IN LATERALLY SPACED-APART PARALLEL RELATION THERETO FOR TRAVEL ALONG A LINE PARALLEL TO THE LINE OF TRAVEL OF SAID FIRST FRAME; (D) A SECOND PARALLELOGRAM LINKAGE; COMPRISING A PAIR OF SHACKLE MEMBERS, EACH OF WHICH BEING FIXEDLY CONNECTED TO THE BOTTOM PORTION OF A PROPPING COLUMN IN THE FRAME, AND A PAIR OF SUPERPOSED PARALLEL BAR MEMBERS OF SUBSTANTIALLY EQUAL LENGTH DISPOSED IN SPACEDAPART RELATION AND PIVOTALLY CONNECTED AT THEIR ENDS TO SAID SHACKLE MEMBERS WHEREBY SAID PARALLELOGRAM IS DEFINED BY A PAIR OF OPPOSITELY DISPOSED PARALLEL BAR MEMBERS AND A PAIR OF OPPOSITELY DISPOSED PARALLEL SHACKLE PROP COLUMN MEMBERS; CONNECTING THE PROPPING COLUMNS OF SAID SECOND FRAME TO EACH OTHER IN MUTUALLY-SPACED PARALLEL RELATIONSHIP; (E) LINEAR ACTUATING MEANS FOR SEQUENTIALLY MOVING SAID FIRST AND SECOND PROPPING FRAMES RELATIVE TO EACH OTHER AND IN SIDE BY SIDE RELATION ALONG PARALLEL LINE PATHS; AND (F) CROSS MEMBER MEANS CONNECTING SAID ACTUATING MEANS TO SAID FIRST AND SECOND PARALLELOGRAM LINKAGE MEANS WHEREBY SAID FIRST AND SECOND FRAME MEMBERS CAN BE MOVED ONE AT A TIME ALONG THEIR RESPECTIVE PARALLEL TRAVEL LINES, WITH ONE OF SAID FRAMES BEING EXTENDED IN ROOF-SUPPORTING ENGAGEMENT AND THEREBY IMMOBILIZED WHILE THE OTHER FRAME IS MOVED RELATIVE THERETO BY SAID ACTUATING MEANS.

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