You are an expert at summarizing long articles. Proceed to summarize the following text:

You are an expert at summarizing long articles. Proceed to summarize the following text: 
THE FIELD OF THE INVENTION 
     The present invention relates to a powered support frame, especially in the form of a shield support, with a roof cap, a gob shield and a linking arrangement to join the gob shield to a ground frame, whereby the powered support frame is provided on both sides on its roof cap and on its gob shield with a laterally extensible gap sealing plate element and with at least one gap cylinder, configured as a hydraulic cylinder, to extend the gap sealing plate elements. 
     A powered support frame with the above features is described in DE 28 22 368 A1; the powered support frame has a laterally extensible gap sealing plate arranged both on the roof cap and on the gob shield. In each case a hydraulic positioning cylinder is provided for the lateral extension of the gap sealing element concerned. 
     The gap sealing elements serve not only for the sealing of a gap arising between two support frames, against rock fall from the roof and from breaking out in the case of face equipment, but also for the alignment of the individual support frames normal to the stratification between the roof and the floor on the one hand, and in the direction of face advance to their halt against a face conveyor on the other hand, so that when the face conveyor connected to their advancing mechanisms moves, the support frames can follow on a preferred line. 
     There is the problem, especially in support frames provided for very large seam thicknesses, for instance between 3 meters and 6 meters, that the alignment of the individual support frames is difficult to handle using the individual controls for each positioning cylinder for each gap sealing element. This problem is exacerbated if saddles and troughs occur and/or the floor undulates in the direction of the mining. In difficult mining conditions of this type the adjacent support frames must be aligned on the one hand convergent, and on the other divergent, so that the support frames can have, for instance in the region of their gob shields, a substantially smaller separation from each other than in the region of their roof caps. 
     SUMMARY OF THE INVENTION 
     The present invention therefore has the aim of improving a powered support frame as previously described, such that even with very large seam thicknesses a good alignment of the support frames to the face conveyor is simple to contrive. 
     In accordance with the present invention, double acting gap cylinders of the gap sealing elements are connected to a common pressure feed line and to a common return line and are activated with a uniform working pressure when the gap sealing elements are to be extended, so that all the gap cylinders, joined and communicating with each other, of the gap sealing elements on a support frame for bridging a gap to an adjacent support frame, effect a floating activation of the individual gap sealing elements until they impact on the gap sealing elements of the adjacent support frame. Owing to the connection of all the gap cylinders to a uniform pressure supply with the prescribed working pressure each gap cylinder extends the gap sealing element connected to it as far to the side until, under the prescribed pressure, this abuts the adjacent support frame or its extended gap sealing element. In this manner the work requirement for the alignment of the individual regions of individual support frames is avoided, since the support frames, owing to the floating actuation of their lateral gap sealing elements, automatically assume their optimum positions with respect to each other. 
     In accordance with one embodiment of the invention, in the region of the linking arrangement an additional gap sealing element is provided, so that especially with large seam thicknesses, an additional sealing and alignment facility is provided. 
     Possibly, several gap cylinders are provided, distributed over the extent of each gap sealing element. 
     For very large seam thicknesses, the gaps arising between adjacent support frames can become so large when saddles and troughs occur in the direction along the face, that the working region of an individual hydraulic cylinder of conventional design is insufficient. Therefore, according to one embodiment of the invention, for the extension of each gap sealing element a gap cylinder arrangement is provided comprising two individual cylinders arranged in series with each other, with one inner cylinder and one outer cylinder with respect to the center line of the support frame. The working range of the gap cylinder arrangement is thereby increased in an advantageous manner with respect to the alignment of the support frames to each other and to the face conveyor. Possibly, on the pressure side the inner cylinder is connected to a common pressure feed line and the outer gap cylinder to a further common pressure feed line, and on the return side the inner gap cylinder and the outer gap cylinder are connected to a common return line. 
     With regard to especially difficult deposit conditions, this increase in the working range can also be used to reduce the normal width of an individual support frame, and to configure the working region of the two gap cylinders positioned on either side so that the inner gap cylinders in their extended position first set the normal width of a support frame. Further to this, the possibility still exists of undertaking the necessary alignment of the support frame using the working range of the outer gap cylinder. 
     According to one embodiment of the invention it is proposed that the inner gap cylinder and the outer gap cylinder can be actuated by the working pressure in a time sequence, whereby a non-return valve is arranged between the pressure supply and the first, inner, gap cylinder. Thereby, the inner gap cylinder can first be extended and established in the required extended condition by the non-return valve; following this the alignment of the support frame concerned can be undertaken by controlling the outer gap cylinder by means of a separate valve arrangement. 
     Alternatively, the inner gap cylinder and the outer gap cylinder can be simultaneously charged with the working pressure. In this case all the gap cylinders of the currently realised gap cylinder arrangements extend over their working range depending on the gap to be bridged, so that thereby even extreme convergences or divergences can be bridged. 
     With regard to relieving the load due to cross forces arising on individual gap cylinders, in accordance with one embodiment of the invention the gap sealing elements are guided by means of bolt guides on an associated component of the support frame. This construction of guidance of a gap sealing element on a component of a support frame carrying it is described in outline in DE 28 53 050 C2. Here, however, a longitudinal boring, carrying the guiding bolts, is arranged in the associated component of the support frame and is thus poorly accessible and difficult to assemble. It is therefore proposed that the gap sealing elements, formed in an angle-shape, have, on arms aligned to the component of the support frame carrying them, sleeving attachments with a longitudinal boring arranged in them, which engages so as to encompass a bolt arranged on the component. Additionally, in the longitudinal boring of the attachment, a pressure spring can be arranged supporting itself between the deepest parts of the longitudinal boring and the component, engaging around the outside of the bolt and guided by the bolt against buckling. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     An embodiment of the invention, which is described below, is shown in the drawings, wherein: 
     FIG. 1 is a section of a face installation comprising several support frames arranged adjacent to each other in a front view as seen from the face; 
     FIG. 2 is an individual support frame in a side view; 
     FIG. 3 is an arrangement of two gap sealing elements on both sides of a support frame in an embodiment on a gob shield; and 
     FIG. 4 is a hydraulic circuit plan in a simplified representation for the control of the gap cylinder arrangement present on a support frame. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The front view, which can be seen in FIG. 1, of a part of a face installation, shows six adjacently arranged support frames  10 , whose ground frames  12  stand in the direction along the face (double arrow  51 ) upon an undulating, i.e. with saddles and troughs, bottom wall  11 . Props  14  are supported on the ground frame  12 , which carry a roof cap  13 . Each support frame  10  is equipped on both sides with gap sealing elements  15 , which can be extended sideways, using individually arranged gap cylinder arrangements  16 , to the adjacent installation, so that an alignment of the support frame  10 , converging and diverging to the roof, can be effected. 
     As is more clearly seen from FIG. 2, a first gap sealing element  15  is arranged in the region of the roof cap  13 , shown formed in several parts in the embodiment depicted; a further gap sealing element  15  is positioned in the region of the gob shield  17 , and finally a gap sealing element  15  is also arranged on the guide bars  19  joining the ground frame  12  to the gob shield  17 . The gap sealing elements  15  are retained on the components  13 ,  17 ,  19  of the support frame  10  carrying them by gap cylinder arrangements  16  and can extend sideways, whereby to relieve the gap cylinder arrangements  16  from cross forces, bolt guides  20  are arranged between each gap sealing element  15  and the associated component  13 ,  17 ,  19  of the support frame  10 , which can be seen in detail in FIG.  3 . 
     On the associated component of the support frame, in this case a gob shield  17 , the gap sealing elements  15 , angularly formed with an upper abutment arm  21  and an alignment arm  22 , are arranged on both sides so as to slide, whereby the alignment arm  22  of the gap sealing element  15  has an attachment  23  extending inside it, and projecting to the gob shield  17 , and having a longitudinal boring  24 , which engages around a bolt  25 , fastened to an intermediate wall  18  of the gob shield  17 , and is guided by positive engagement on it. In the longitudinal boring  24  a pressure spring  26  is arranged, supported against the deepest part of the longitudinal boring  24  at one end and against the intermediate wall  18  at the other end, which is guided on the outer periphery of the bolt  25  and is thereby secured against buckling. As already realised in the gap sealing described in DE 28 53 050 C2, the pressure spring  26  pretensions the individual gap sealing element  15  in its extended position, so that activation of the gap cylinder, comprising double acting cylinders  27 ,  30 , generates the necessary pressure against each other for the active alignment of the support frame  10  in the extending direction, whilst on controlling the gap cylinders  27 ,  30  in the direction of retraction the spring force of the pressure spring  26  has always to be overcome. 
     FIG. 3 shows further detail of the gap cylinder arrangement  16  for extending the associated gap sealing element  15 , which comprises two individual cylinders arranged in series, namely an inner gap cylinder  27  and an outer gap cylinder  30 , which are supported against each other. The piston rod of the inner gap cylinder  27  is attached to a tongue  28  fastened by means of a fastener  29  to the gob shield  17 , whilst the piston rod  31  of the outer gap cylinder  30 , the latter firmly fixed to the inner gap cylinder  27 , is fastened to a tongue  32  on the alignment arm  22  of the gap sealing element  15  by means of a fastener  33 . The right-hand half of FIG. 3 shows the right-hand gap sealing element  15  fully retracted, whilst the left-hand part of FIG. 3 shows a partly extended, that is by means of the outer gap cylinder  30 , gap sealing element  15  of the gob shield  17 . 
     The circuit plan depicted in FIG. 4 for the control of the gap cylinder arrangements  16  and the individual gap cylinders  27 ,  30  shows the gap cylinder arrangements  16  for the left-hand side  42  of a support frame, and for its right-hand side  43 , with the gap cylinder arrangement  44  for the roof cap  13 , the gap cylinder arrangement  45  for the gob shield  17 , and the gap cylinder arrangement  46  for the region of the guide bars  19 . 
     All the gap cylinder arrangements are supplied from a central pressure feed  34 , which divides in a branching  36  into a pressure feed line  37  for the inner cylinders  27  in each case, and into a pressure feed line  39  for the supply to the outer cylinders  30 , whereby a valve arrangement is connected into the pressure feed line  39 , comprising pilot valves  41  and main valves  40 . 
     A non-return valve  48  and a ball valve  47  are connected into the pressure feed line  37  for the supply to the inner gap cylinders  27 , whereby through a second switch position of the ball valve  47  a connection between the pressure feed line  37  for the inner cylinder  27  and the pressure feed line  39  for the outer cylinder  30  can also be set up to a branching  49  and a branch line  49   a.    
     All the gap cylinders  27 ,  30  of all the gap cylinder arrangements are connected to a common return line  50 , which leads via the valve arrangement  40 ,  41  to the return. The circuit is completed by a pressure limiting valve  52  connected to the pressure feed line  37  for the inner cylinder  27 . 
     The circuit condition illustrated in FIG. 4 shows the starting position, in which the gap cylinders  27 ,  30  are actuated on the pressure side in the retracting direction, so that the gap cylinders  27 ,  30  overcome the force of the pressure springs  26 , which are pre-tensioned in the extending direction of the gap sealing elements  15  and hold the gap sealing elements  15  always in contact with the associated components  13 ,  17 ,  19  of the support frame  10 . To this end the pressure feed  34  is connected via the valve arrangement  40 ,  41  to the line designated return line  50 , so that through this control the side of the piston working in the direction of retraction in the individual gap cylinders  27 ,  30  is impacted with pressure; in this switching condition the lines designated as pressure feed lines  37 ,  39  work as return lines and are connected via the valve arrangements  40 ,  41  to the return  35 . Also shown is the position of the ball valve  47 , which joins the line  37  to the line  39 , so that a common return is effected. 
     If the gap sealing elements  15  are now to be extended, in a first step the ball valve  47  can be switched to the position shown separately in FIG. 4, in which the connection between the inner gap cylinders  27  and the pressure feed line  34  is set up via the ball valve  47  and the non-return valve  48 ; in this control phase the valve arrangement  40 ,  41  still blocks the pressure feed line  39  to the outer gap cylinders  30 . If the inner gap cylinders  27  are extended, then they are locked in their final position by the hydraulic fluid return flow being prevented by the non-return valve  48 . In a second switching step the associated main valve  40 / 1  and  40 / 3  are brought via the pilot valve  41 / 1  and  41 / 3  into that circuit position in which the pressure feed line  39  is switched through to the outer gap cylinders  30 , and in this position the outer gap cylinders  30  are charged with the working pressure, so that they actuate the gap sealing elements correspondingly. At the same time the return line  50  common to all the gap cylinders  27 ,  30  is connected via the main valve  40 / 2  and  40 / 4  to the return  35 . 
     If, during the control effecting the extension of the gap cylinders  27 ,  30 , the position of the ball valve  47  is retained in the position shown in the circuit plan, then the inner gap cylinders  27  and the outer gap cylinders  30  are connected simultaneously and together to the central pressure source  34 , so that in each case alignment of the gap sealing elements  15  is effected by both individual cylinders of the gap cylinder arrangement. In this setting the connection between the pressure feed  34  and the pressure feed line  37  is blocked to the inner gap cylinders  27 , whereby in this setting of the ball valve  47  the pressure feed line  37  is connected to the pressure feed line  39  via the branch line  49   a  and the branching  49 . If now a suitable switching of the main valve  40  onto the pressure feed line  34  is made, then both the inner gap cylinder  27  and the outer gap cylinder  30  lie together and simultaneously on the pressure feed line  34 .

Summary:
It is provide in a powered support frame, for large seam thicknesses with controlled gap sealing, that double acting gap cylinders ( 16, 27, 30 ) of several gap sealing elements ( 15 ) on a powered support frame are connected to a common pressure feed line ( 34, 37, 39 ) and to a common pressure return line ( 50 ) and are impacted with a uniform pressure when the gap sealing elements are to be extended.