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You are an expert at summarizing long articles. Proceed to summarize the following text: 
FIELD OF THE INVENTION 
       [0001]    The present invention pertains to the field of subterranean excavation. More particularly, the present invention pertains to devices used to stabilize material forming the walls, roof, and pillars of a tunnel, room, or other subterranean excavation to prevent collapse of the material into the excavated space. 
       BACKGROUND OF THE INVENTION 
       [0002]    Coal mining in the United States is a major industry, reaching an all-time high in the production in 2008 at 1.17 billion short tons being mined in 25 states. Coal accounts for approximately half of all electricity produced in the United States, and provides 40% of the world&#39;s electricity needs. 
         [0003]    Mining has always been a very dangerous activity, although in recent years improvements in technology have decreased the number of fatalities and accidents. Still, many fatalities and accidents occur due to a collapse of a tunnel roof or the collapse of a tunnel rib. A rib is defined as the side wall of a tunnel. Tunnels are developed in an engineered layout so that sufficiently sized pillars are left in place to support the overall mining system. Roofs have been supported by various means, and to various degrees, for the history of mining. In 2007, areas of the Crandall Canyon Mine in Utah collapsed due to pillar failures. A second collapse ultimately trapped and killed six miners, and a third collapse killed three would-be rescuers. Given the prevalence of mining worldwide, coupled with the desire to reduce mining deaths, further improvements to safety will remain a primary and overarching concern. 
         [0004]    Surface control of the tunnel roof and ribs is an important concern of the mining business during the development of the tunnels and while men and material are transported through these tunnels. Once the mined material is exposed, the surfaces comprising the roof and ribs are commonly referred to as “the skin”. Ideally, the skin of the roof is supported by a primary support system, usually consisting of resin bolts installed on an approved pattern. Secondary systems are also applied when conditions are less than favorable. This secondary supporting system is responsible for controlling local skin failures, defined as mined material and loose rock that slip away from the surface of the rib or roof. This mined material and loose rock that fall from the roof and ribs are responsible for many accidents and deaths. 
         [0005]    Most surface control problems (rib skin failures) of the ribs result from the separation of mined material due to anomalies in the mined material, such as fracture planes, allowing the mined material to fall to the mine floor, possibly injuring anyone near. 
         [0006]    To minimize these skin failures and the associated accidents and issues, several product styles have evolved: Pans (“Mine Safe Draw Rock Shields”), Mesh/Geogrid, Mats, Boards, and Channel. Each product style is designed to help create and aid in the secondary support system. The variety of styles reflect the different and unique properties of the rib and roof to which they are applied, and thus the products styles are neither necessarily interchangeable, nor is selection of a particular product style purely a matter of preference. The different product styles thus reflect differences in equipment, time, and skill required to install the products, the characteristics of the material forming the rib and roof, as well as the cost of the actual product itself. 
         [0007]    Pan systems involve the use of a pan and a plate machine bolted into the skin. The pan system stiffens the skin, and thus helps prevent skin failures. The term pan, as commonly used in the industry, is a bearing plate bolted directly against the skin to stabilize the skin, and is usually used in conjunction with a support plate, which is a smaller plate sandwiched between the pan and the bolt, effectively further stabilizing the through hole of the pan. Pan products are advantageous due to their fast installation, the limited expertise and specialized equipment need for such installation, their relatively small size for ease of handling by installers, and versatility in terms of placement location, resulting in a competitively priced product compared to other systems. A typical pan, such as that detailed in U.S. Pat. No. 7,284,993 B2, features a through hole for receiving a bolt, and a square, planar central surface immediately surrounding the through-hole, with one or more continuous channels circumscribing the through-hole. Another typical pan is the so-called spider plate made by Minova http://www.minovausa.com/pdfs/Products/SpiderPlate.pdf, featuring a plurality of “legs” or channels extending from the center of the pan to the perimeter or outer boundary of the pan. The &#39;933 (Jenmar) pan, as well as other pans, are not fail-proof, and their small design size requires a greater number of pans be used in any given area to create surface control. Given the high cost of skin failures, further improvements in safety products is highly desirable. 
         [0008]    What is needed is a pan that overcomes deficiencies in the prior art pan category of skin controlling products, specifically a pan that allows a mine operator or others performing subterranean excavation, the flexibility of placement, simple installation, and increased skin stabilization per installed pan. 
       DISCLOSURE OF INVENTION 
       [0009]    Accordingly, the invention provides for an oval bearing plate or pan having a largely convex central portion existing in a first horizontal plane, and a planar peripheral portion or edge portion existing in a second horizontal plane below the first horizontal plane, the convex central portion joined to the peripheral portion by an outermost edge of the central portion angling downwards from the central portion to meet the innermost edge of the peripheral portion. The central portion further includes a plurality of parallel rib members held in spaced apart relationship, the rib members configured as a series of concave channels oriented so as to span the narrowest width of the oval pan. The invention further provides for an oval pan comprised of either galvanized metal or plastic. The invention still further provides for a pan system in which the installed pan becomes largely concave in shape. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    The features and advantages of the invention will become apparent from a consideration of the subsequent detailed description presented in connection with accompanying drawings, in which: 
           [0011]      FIG. 1  is a top view of the pan according to the invention. 
           [0012]      FIG. 2   a  is a cross-sectional side elevational view of the pan shown in  FIG. 1  cut along lines A-A, showing the convex shape of the central portion and the concave profile of the rib members. 
           [0013]      FIG. 2   b  is a cross-sectional side elevational view of the pan shown in  FIG. 1 , cut through the narrowest diameter of the pan parallel with the rib members, showing the convex shape of the central portion. 
           [0014]      FIG. 2   c  is a cross-sectional side elevational view of a rib member shown in  FIG. 2   a  at circle  2   c.    
           [0015]      FIG. 3  is a perspective view of a pan system according to the invention, showing the pan, a support plate, and a bolt in a typical installation on a rib or roof, and a perspective view of a prior art pan system as installed adjacent to the pan system according to the invention. 
           [0016]      FIG. 4   a  is a top view of one side of the pan according to the invention. 
           [0017]      FIG. 4   b  is a partial view of  FIG. 4   a  taken at circle  4   b,  showing the outermost edge of the central portion and the peripheral portion. 
           [0018]      FIGS. 4   c - ce  show embodiments of the pan according to the invention. 
           [0019]      FIG. 5   a  is a cross-sectional, side elevational view of the pan according to the invention, in a typical installation on a rib or roof, showing the concave shape of the installed pan. 
           [0020]      FIG. 5   b  is a perspective view of the pan according to the invention, showing the generally convex shape of the unistalled pan. 
           [0021]      FIG. 6  is a perspective view of two different sized pans according to the invention, showing optional through bores or apertures in addition to the through bore located in the center of the pan, and additionally highlighting the varying number and spacing of the rib members. 
       
    
    
     DRAWINGS LIST OF REFERENCE NUMERALS 
       [0022]    The features and advantages of the invention will become apparent from a consideration of the subsequent detailed description presented in connection with accompanying drawings, in which:
     10  bearing plate or pan     12  through-bore     12   a  first aperture     12   b  second aperture     14  pan edge portion or peripheral portion     14   a  innermost edge of peripheral portion     14   b  second edge of peripheral portion     16  transition point     18  rib member     18   a  length of first rib member     18   b  length of second rib member     18   c  length of third rib member     18   d  length of fourth rib member     18   e  diameter of through-bore     18   f  width of rib member     18   g  angle or rise of rib member     18   h  height of rib member     18   j  width of pan edge     18   k  radius of pan edge     18   l  true radius of pan edge     18   m  width of rib crest     20  central portion     20   a  outermost edge of central portion     20   b  first diameter of central portion     20   c  second diameter of central portion     30  support plate     40  bolt     50  skin (roof and/or rib)     60  prior art pan system     100  pan system   
 
       DETAILED DESCRIPTION 
       [0053]    Now referring to  FIGS. 1-6 , a bearing plate or pan  10  according to the invention is comprised an oval shaped, single piece of embossed or stamped metal, or alternatively, out of plastic, such as thermo-plastic. The pan  10  is comprised of a standard sized 1⅜ inch through-bore  12  cut into the center of a central portion  20  of the pan  10 , the through-bore  12  sized and shaped to receive a bolt  40  (as shown in  FIGS. 3 and 5 ). The central portion  20  includes a first diameter  20   b  and a second diameter  20   c,  the first diameter spanning the shortest width of the oval shaped central portion  20  and existing in a first horizontal plane. The first diameter  20   b  ranges from about 14 inches to about 18 inches. The second diameter  20   c  ranges from about 20 inches to 24 inches. The central portion  20  is defined by an outermost edge  20   a  curving downwards below the first horizontal plane in which the central portion  20  lies. Two additional apertures  12   a    12   b  in spaced apart relation and on opposite sides of the through-bore  12  are formed in the central portion  20 , and may be used to further secure the pan to a skin (rib and/or roof)  50  by each aperture receiving one bolt  40 , as necessary when a typical installation using the central through-bore  12  is not possible, or as desired, in lieu of or in addition to installation using the central through-bore  12  (see  FIG. 6 ). 
         [0054]    A plurality of parallel rib members  18 , in spaced apart relation, are embossed or stamped onto the central portion  20 , each rib member  18  further comprising a concave channel spanning the first diameter  20   b  of the central portion  20 . The central portion  20  is largely convex in shape, with the area upon which the rib members  18  are embossed lying in the first horizontal plane, parallel to the first diameter  20   b  and to one another. The rib members  18  have at least two and in some embodiments, three different lengths. In a typical embodiment, shown in  FIG. 1 , a pair of first rib member lengths  18   a  are about 8 inches long each, each one of four second rib member lengths  18   b  is about 12 inches long, and each one of four third rib member length  18   c  is about 14.5 inches long. 
         [0055]    The central portion&#39;s outermost edge  20   a  meets an innermost edge  14   a  of a pan edge portion or peripheral portion  14  at a transition point  16 , the peripheral portion  14  and the transition point  16  lying in a second horizontal plane, as shown more clearly in  FIGS. 2   a  and  2   b . The uninstalled pan  10  is thus largely convex in shape, as shown more clearly in  FIG. 5   b , with the peripheral portion  14  being flat, the entire pan  10  somewhat resembling a flattened bowler hat resting on its brim. The peripheral portion  14  is thus defined by the innermost edge  14   a  and a second edge  14   b,  the second edge  14   b  being the perimeter or outermost limit around the pan  10 . 
         [0056]    The pan  10  according to the invention, in a typical embodiment as shown in  FIGS. 1-6 , features a surface area of approximately 24×18 inches, when compared to the prior art pans results in a larger surface area of the pan  10  contacting the skin  50  when the pan is part of an installed pan system  100 . The pan  10  has about 30% greater surface area than the 18×18 inch and 17×17 inch square prior art pans, allowing an operator of a coal mine greater flexibility in its roof and rib plan, and importantly, better safety due to the larger surface area controlled by the pan system  100 , as shown more clearly in  FIG. 3 , where a prior art pan system  60  is comprised of a square prior art pan and support plate bolted to a rib, and the pan system  100  including the pan  10  according to the invention bolted to the same rib and adjacent to the prior art pan system  60 . The single most critical characteristic of a skin control product such as the pan  10  is its ability to contact the surface of the mining tunnel skin with adequate stiffness characteristics which help eliminate progressive roof and rib failures. The oval shape of the pan  10  as well as the large, planar peripheral portion  14  allows for easier handling of the pan  10  during installation (no sharp edges or points), as well as superior strength derived from the oval and generally convex shape of the pan. 
         [0057]    When the pan  10  is used in the pan system  100  and installed on the skin  50 , as shown more clearly in  FIGS. 3 and 5   a , the convex central portion  20  is pushed towards the skin  50  by a support plate  30  and the bolt  40 , causing the central portion  20  to dimple and become concave in shape, pushing the pan  10  tightly against the skin  50 . When the pan system  100  is installed, pressure from the bolting machine transfers load energy to the transition point  16  causing a “riveting” process to occur. This energy “pops” the pan  10  tightly into place. Further, the planar peripheral portion  14  has a greater surface area for better load strength and allows the installed pan  10  to more tightly grip the skin throughout the life of the pan. 
         [0058]      FIG. 2   a  shows a side elevational cross section of the pan  10  according to the invention. The rib members  18  are arranged in parallel, spaced apart relation, each rib member  18  having a concave cross section so as to form a channel in the central portion  20 . Each rib member has a greater depth than the average rib member of the prior art. In a typical embodiment according to the invention, shown in  FIGS. 2   a  and  2   c , each rib is about 0.125 inches deep  18   h,  with a diameter or width  18   f  of about 0.84 inches. Other embodiments of the pan  10  are provided with dimensions for the rib members ranging from depths  18   h  of 0.55 inches to 0.17 inches and diameters  18   f  from 0.75 inches to 0.84 inches. The width of the rib crest  18   m  is about 0.13 inches wide in a typical embodiment. The outermost edge  20   a  has a range of varying dimensions, the width  18   j  of the peripheral portion  14  ranging from about 0.9 inches to about 1 inch, and the radius  18   k  ranging from about 2 inches to 3 inches, with a true radius  181  of about 2.3 inches in a typical embodiment. The angle or rise of the rib member  18   h,  as shown in  FIG. 2   c , in a typical embodiment is about 22 degrees. 
         [0059]    The arrangement and number of rib members  18  per pan  10  provide approximately five times the strength of the prior art pans. The rib members  18  provide strength, and as load-weight is exerted onto the pan  10 , the energy expands onto the convex central portion  20 , the rib members  18  pushing the load energy to the outer edges of the pan, thus aiding in surface tension control.  FIG. 1  shows  10  total rib members  18 , however it should be noted that the number of rib members  18  per central portion  20  may vary, and at least two rib members  18  are needed per pan  10 . 
         [0060]    The pan  10  is typically made of galvanized steel, G-90 and/or G-60 galvanized hot dipped processed steel (see  FIG. 6 ) to resist rust formation and deterioration of the pan. Plastic pans  10  are made of thermo-plastic or other suitable plastic materials. The metal pan  10  is typically stamped, guaranteeing the tolerances of the pan  10  are consistent during the manufacturing process. Plastic pans  10  are created using a thermo forming process using a tool. 
         [0061]    It should be noted that the present invention is not only useful for roof and wall stabilization in mining, but can also be used for any tunneling or other subterranean excavation, such as for placement of utilities beneath the surface. 
         [0062]    Finally, it is to be understood that the above-described arrangements are only illustrative of the application of the principles of the present invention. Numerous modifications and alternative arrangements may be devised by those skilled in the art without departing from the scope of the present invention. For instance, in some embodiments (not shown), two or more pans  10  may be stacked and used together to form a pan system, with or without the use of the support plate  30 , and plastic pans  10  may be used in combination with metal pans  10 , either side by side in a pan system  100  or stacked together. The dimensions and shape of the pan  10  may also be modified to have a rectangular peripheral portion but retaining an oval shaped pan central portion, and the dimensions may be larger or smaller than 24×18 inches, as desired. A square support plate  30  is shown in  FIG. 3 , however any style support plate can be used in the pan system  100  and  FIG. 3  should not be regarded as requiring solely the use of square support plates. Also, use and installation of the pan  10  or of the pan system  100  to the rib or to the roof is identical, and hence references to rib or roof, or rib and roof, or collectively to the skin are not meant to indicate different uses or installations of the pan  10  and/or the pan system  100 . These are just a few possible modifications and alternative arrangements, and the appended claims are intended to cover such modifications and arrangements.

Summary:
A pan ( 10 ) and a pan system ( 100 ) for surface control of wall and/or roof material in a subterranean tunnel or room, the oval pan ( 10 ) having a convex central portion ( 20 ) held at an angle above a horizontal plane and an outermost edge angling downwards and meeting a planar pan edge portion ( 14 ) lying in the horizontal plane, both edges meeting at a transition point ( 16 ). The central portion includes a plurality of parallel concave rib members ( 18 ) arranged to span the shortest width of the pan. In use as a system ( 100 ), a bolt ( 40 ) drilled though a support plate ( 3 ) and the pan secures the pan system to the wall or roof. The force exerted onto the bolt transfers to the pan results in a dimpling of the central portion, allowing for a tighter application of the pan to the wall or roof.