Patent Publication Number: US-2018030666-A1

Title: Lightweight panel mat with interlocking elements

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. application Nos. 62/368,954 filed Jul. 29, 2016 and 62/402,391 filed Sep. 30, 2016, the entire content of each of which is expressly incorporated herein by reference thereto. 
    
    
     BACKGROUND 
     The present invention relates to a reusable lightweight panel mat system for the construction of equipment support surfaces and temporary walkways and roadways in areas having poor ground integrity characteristics. More particularly, the present invention relates to a reusable system of durable panel mats which are much lighter than wood or wood/steel mats which can be quickly and easily positioned in a single layer to form equipment support surfaces, walkways or roadways and which can thereafter be easily removed and stored until needed again. 
     While conventional wood mats provide useful service at a reasonable cost, the wood core can deteriorate over time due to moisture causing gradual rotting and degradation of the wood material. This causes the mat to be discarded, because unlike some of the other materials that are used on the upper and lower layers of the mat, the core cannot be replaced without essentially making an entirely new mat. 
     Also, wood mats generally require heavy equipment for installation due their weight and bulk. Accordingly, alternatives to wood mats are needed for alternatives for wood mats that need to possess the necessary physical properties to be able to withstand harsh outdoor conditions as well as to support equipment. And of course cost is a factor in determining the selection of alternate materials, as it is not cost-effective to provide a mat that is multiple times more expensive than one that can be made of wood. 
     Thus, there is a need for improvement in these types of mat constructions both to provide longer service lives as well as to conserve natural resources and facilitate installation, and these needs are now satisfied by the panel mats of the present invention. 
     SUMMARY OF THE INVENTION 
     The invention now provides a lightweight universal panel mat made of plastic or elastomeric material and designed to be interlocked with additional panel mats of similar configurations. These panel mats have a first section having an upper surface that forms a top surface of the panel mat and is relatively flat, textured or structured to facilitate movement over the upper surface and a second section having geometry that includes a plurality of cells that are open or wherein some or all of the cells have flat top surfaces with the geometry supporting the first section and providing a plurality of open lower surfaces. These panel mats also include first, second, third and fourth sides wherein: the first side is configured with a plurality of tabular extensions; the second side is located adjacent the first side and is configured with a plurality of tabular extensions; the third side is located opposite the first side and is configured with openings that are unobstructed and configured, dimensioned and arranged to receive therein the plurality of first side tabular extensions; and the fourth side is located opposite the second side and is configured with slots or recesses that are configured, dimensioned and arranged to receive therein the plurality of second side tabular extensions. 
     The tabular extensions on the first side, the second side or on both sides preferably include either a protruding bump or depression, and the openings, slots or recesses of the third or fourth sides have an upper surface that includes a corresponding depression or protruding bump that enables the respective tabular extensions to be snap-lockingly engaged together. Also, the tabular extensions and openings, slots or recesses can be formed on the first section, the second sections, or partially on each section. The upper surface of the first section is generally rectangular of length L and width W where L and W each may be any value between 1 foot and 16 feet; and the first and second sections are welded or bonded together to form a unitary panel mat. 
     The first and second sections may be parts of an integral component that is molded together or the tabular extensions, openings and slots or recesses can be milled or routered in a solid plastic or elastomeric component. If desired, these panel mats may include metal wire, bar or plate reinforcement located within the second section or between the first and second sections. Typical metals for such use would be steel, stainless steel or aluminum. 
     In one embodiment, the first side is configured with at least three tabular extensions; the second side is configured with at least three tabular extensions each having a depression on an upper surface; the third side is located opposite the first side and is configured with openings that are unobstructed and configured, dimensioned and arranged to receive therein the first plurality of tabular extensions; and the fourth side is located opposite the second side and is configured with spaced slots or recesses that are configured, dimensioned and arranged to receive the second tabular extensions therein, wherein the slots or recesses each have an upper surface that includes a protruding bump configured and dimensioned to at least partially engage a depression of the second tabular extension to provide snap-locking of the bumps into the depressions; wherein the tabular extensions and openings, slots or recesses are formed partially on each section. 
     In another embodiment, the first side is configured with at least three tabular extensions, each having a protruding bump on an upper portion thereof; the second side is configured with at least three tabular extensions each having a protruding bump on an upper portion thereof; the third side is located opposite the first side and is configured with openings that are unobstructed and configured, dimensioned and arranged to receive therein the plurality of first side tabular extensions, with the openings having an upper surface that includes a depression therein that is configured and dimensioned to receive a protruding bump of the first side tabular extensions; and the fourth side is located opposite the second side and is configured with spaced slots or recesses that are configured, dimensioned and arranged to receive the plurality of second side tabular extensions therein, wherein the slots or recesses each have an upper surface that includes a depression therein that is configured and dimensioned to receive a protruding bump of the second side tabular extensions. 
     In yet another embodiment, the first side is configured with at least two tabular extensions, each having at least two protruding bumps on an upper portion thereof; the second side is configured with at least two tabular extensions each having at least two protruding bumps on an upper portion thereof; the third side is located opposite the first side and is configured with openings that are unobstructed and configured, dimensioned and arranged to receive therein the first side tabular extensions, with the openings having an upper surface that includes at least two depressions therein that are configured and dimensioned to receive the protruding bumps of the first side tabular extensions; and the fourth side is located opposite the second side and is configured with spaced slots or recesses that are configured, dimensioned and arranged to receive therein the second side tabular extensions, wherein the slots or recesses each have an upper surface that includes at least two depressions therein that are configured and dimensioned to receive the protruding bumps of the second side tabular extensions. 
     Generally, the first and second sections are separate components having peripheral boundaries configured to contact each other for attachment, and the sections are welded, molded, bonded, joined or sealed together where the peripheral boundaries contact each other to prevent water from entering into and between the sections. This also protects any internal steel reinforcement from rusting. 
     Preferably, each slot or recess of the fourth side of the panel has a lower surface that includes a bridge or rail structure forming a lower entry of the slot or recess for initial contact with the lower surface of a second side tabular extension that is to be received therein. Similarly, the second side tabular extensions are configured with an angled bottom portion that allows the forward end of the second side tabular extensions to move away from the upper portion of the slot or recess to allow detachment of the second side tabular members from the slots or recesses. 
     Typically, the protruded bumps and depressions are circular or oval in configuration and the depression has a slightly larger circumference than the protruding bumps. Also, some or all of the openings, slots or recesses include either a cut out end portion, an open bottom or an opening adjacent and behind the bridge or rail structure to allow dirt or water to exit the opening, slot or recess and to facilitate entry of the tabular members therein. 
     In one configuration, the upper surface of the first section is a structured surface that includes a raised pattern of spaced elements in a pattern, such as a herringbone or spaced longitudinal line pattern, or channels that allow water to drain from the mat. These can be molded into the surface of the top section. The channels can easily be achieved by including a plurality of raised islands spaced by and closely arranged near each other to form the channels, with the islands having a polygonal, circular, or elliptical shape. Additionally, the lower surface of the second section can be structured and can include openings or channels to provide a secure footing when the panel mat is placed on wet or muddy ground. These structured lower surface of the second section preferably includes a plurality of cells having a polygonal, circular or elliptical shape forming bottom openings in the lower surface, wherein some or all of the cells have a top surface that extends to and supports the upper surface of the first section to strengthen the panel mat, and wherein some or all of the cells have a flat bottom surface. 
     And the upper surface of the first section may be a structured surface that includes channels that allow water to drain from the mat and a plurality of raised islands spaced by and closely arranged near each other to form the channels, with the islands having a polygonal, circular, or elliptical shape; and wherein the lower surface of the second section is structured and includes a plurality of cells having a polygonal, circular or elliptical shape to provide a secure footing when the panel mat is placed on wet or muddy ground, wherein the cells have a top surface that extends to and supports the upper surface of the first section. The panel mats can be designed with the first section including, at the third and fourth sides of the panel mat, a lip portion that covers edges of the respective first and second sides of adjacently connected similarly configured panel mats and provides channels that assist in allowing drainage of water from the top surface of the panel mat. 
     For any of the embodiments described herein, a preferred embodiment of the invention provides a third section located below and welded, molded, bonded, joined or sealed together to the second section, with the third section configured and dimensioned to close off the plurality of openings of the cells or when applicable to receive flat bottom surfaces of some or all of the cells, and form a bottom surface for the panel mat that is relatively flat, textured or structured. This further strengthens the mat without adding significant weight as it allows the cells to provide better resiliency and compression properties to the panel mat. 
     It is also possible for the upper surface of the first section to relatively flat and when the third section is a relatively flat plate, the bottom surface of the third section is also relatively flat. This type of construction is ideal for placement of the panel mats for temporarily protecting gym flooring or athletic fields from events such as graduations, concerts, of other large gatherings. It is also very helpful to evenly distribute any loads on the mats and prevents any edges of the open cells from cutting into soft surfaces such as grass or filling up with much or dirt. 
     Alternatively, when the top surface of the first section is structured, the bottom surface of the third section can be structured in a similar fashion to provide better engagement with the ground or to allow the mats to be used with either side facing upwards and away from the ground. 
     The panel mats of the invention are typically rectangular wherein W=2 L or square wherein W=L, and wherein L is preferably 2.5, 3, 3.5, 4, 4.5, 5, 6, 7, or 8 feet and W is preferably 2.5, 3, 3.5, 4, 4.5, 5, 6, 7, 8, 9, 10, 12, 14 or 16 feet. When the panel mat is square, it includes two or three each of the first tabular members, second tabular members, openings and slots or recesses or and when rectangular it includes four or six first tabular members, four or six openings, two or three second tabular members and two or three slots or recesses. These panel mats generally weigh between about 10 and 125 pounds making them easily movable manually by one or two workers without the use for heavy equipment. These panel mats are able to withstand point loads of between 300 and 500 psi and spread loadings of 40,000 to 50,000 pounds per square foot. 
     Each side of the panel mats advantageously includes multiple tabular members and multiple openings. Typically, between 2 and 8 tabular members and openings are provided on the first and second sides of the mat but in some designs those numbers of members and openings can be provided on each side of the mat for more secure connection between conjoined mats. 
     The panel mats of the invention may also include one, two, three or four lifting elements that are affixed to the mats to allow lifting and installation or reclamation. These lifting elements include (a) a ring or U or D shaped member that is movable between first and second positions, wherein the first position is one where the member resides below the surface of the mat and the second position is an operative position where the ring or U- or D-shaped member is exposed for engagement with lifting equipment, and (b) a structure that secures the ring or U- or D-shaped member to the mat. Preferably, the structure that secures the ring or U- or D-shaped member to the mat includes a plate that engages the surface of the mat opposite the surface from which the member extends, and a post that extends through the mat for engagement with the ring or U- or D-shaped member either directly or through a connecting element. 
     Thus, the mats of the present invention can be assembled to easily provide a temporary support surface, deck, walkway or roadway using a plurality of connected panel mats as disclosed herein. Generally, the first side tabular extensions of a first mat engage the third side openings of one or more adjacent similarly configured panel mats and the second side tubular extensions of the first mat engage the slots or recesses of the fourth side of one or more adjacent similarly configured panel mats. The mats can be joined together in a manner that allows the ends to be aligned or not. A staggered configuration is generally preferable as it avoids generating long seams between rows of joined mats where the seam can separate more easily during use of the temporary flooring. Therefore, it is preferred that the tabular members and openings are arranged on the sides of the mat in a configuration that allows the mats to be joined in an offset or staggered manner so that the ends of the mat are not aligned when installed. 
     The installation of the panel mats can proceed by a number of ways depending upon what is desired. For a smaller installation, smaller size mats that are easily lifted and installed by one or two workers are preferable, while the larger size mats facilitate a faster construction because more area is covered by each mat. The lifting elements assist in allowing these larger mats to be lifted and installed or reclaimed by equipment. And often, combinations of the different mats would be utilized so that the temporary flooring best covers the entire space to be protected by the mats. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING FIGURES 
       The invention is more fully appreciated upon a review of the appended drawing figures which illustrate the most preferred embodiments of the invention and wherein: 
         FIG. 1  is a perspective view of a panel mat according to the present invention showing the top surface of the first section; 
         FIG. 2  is a perspective view of the mat of  FIG. 1  showing a lower surface of the second section; 
         FIG. 3  is an exploded view of the mat of  FIG. 1 ; 
         FIG. 4  is an exploded view of the mat of  FIG. 2 ; 
         FIG. 5  is an illustration of five mats that are interconnected with the light areas illustrating the top surfaces of the connected mats and the dark areas illustrating the bottom surfaces of the connected mats; 
         FIG. 6  is a cross-sectional detail of the snap-locking engagement of the male members and depressions of adjacently connected mats; 
         FIG. 7  is a cross-sectional detail of the mat to show a lip portion that forms with an adjacently connected mat a channel for removal of water; 
         FIG. 8  is a perspective view of another panel mat according to the present invention, showing the top surface thereof; 
         FIG. 9  is a perspective view of the panel mat of  FIG. 8  showing the bottom surface thereof; 
         FIG. 10  is an exploded view of the panel mat of  FIG. 8  looking down from the top surface; 
         FIG. 11  is an exploded view of the panel mat of  FIG. 9  looking up from the bottom surface; 
         FIGS. 12A to 12C  are cross-sectional views of the panel mat of  FIG. 8  with  FIG. 12A  showing a cross section across the entire panel mat,  FIG. 12B  illustrating a cross-section of the extension tab and  FIG. 12C  illustrating a cross-sectional view of the tab receiving opening; 
         FIGS. 13A and 13B  illustrate the joining of three panel mats according to  FIG. 8 , with  FIG. 13A  showing the joined panel mats from a top view thereof and  FIG. 13B  showing the joined mats from a bottom view thereof; 
         FIG. 14  is a perspective view of yet another panel mat according to the present invention when viewed from the top surface thereof; 
         FIG. 15  is a perspective view of the panel mat of  FIG. 14  when viewed from the bottom surface thereof; 
         FIG. 16  is an exploded view of the panel mat of  FIG. 14 ; 
         FIG. 17  is a detail view of the interlocking of four panel mats according to  FIG. 14 ; 
         FIG. 18  illustrates a mat that has a structured upper surface in the form of a herringbone pattern; 
         FIG. 19  illustrates the bottom surface of a mat that has linear channels provided therein; 
         FIG. 20  illustrates a mat having four lifting elements; 
         FIGS. 21A and 21B  illustrate the mat of  FIG. 20  with the lifting elements in an operative position in  FIG. 21A  and in a retracted position in  FIG. 21B ; 
         FIG. 22  illustrates a particular construction for the lifting element shown in  FIG. 20 ; 
         FIG. 23  illustrates the bottom surface of the mat of  FIG. 20 ; and 
         FIGS. 24A, 24B and 24C  illustrates an alternative construction for a lifting element wherein  FIG. 24A  illustrates how the lifting element is inserted into the mat, while  FIG. 24B  illustrates the ring of the lifting element in an operative position and  FIG. 24C  illustrates the ring pivoted for placement in the retracted position in the mat. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Certain terms that are used herein are defined hereinbelow to assist in the understanding of the invention. 
     The terms “substantially” and “relatively” are used for their ordinary meanings to indicate that the dimensions or configurations are not precise or exact. A skilled artisan can readily determine what tolerances are acceptable to provide a surface that is considered to be flat based upon the size of the panel mats and the type of service that the panel mats are expected to provide. Typically, the terms “substantially” or “relatively” will mean that a surface can vary by as much as an inch or two although in the more preferred embodiments the variance is less than 1 inch. 
     Additionally, all dimensions recited herein are approximate and can vary by as much as ±10% to in some case ±25%. In some situations, the term “about” is used to indicate this tolerance. And when the term “about” is used before reciting a range, it is understood that the term is applicable to each recited value in the range. Often, the craftsmanship and engineering procedures that are followed in construction of these mats minimize these tolerances as much as possible or industrially practical. 
     The invention relates to a rectangular panel mat that is preferably square and that is made of plastic or elastomeric material. The panel mat can be made of first and second sections (for two layer mats) or with an additional third section (for three layer mats) which are part of an integral component that is molded to have the desired configuration and features. Typically, the first and second sections are molded together in one operation while the third section is later joined to the mat formed from the first and second sections. Alternatively, a two layer mat can be made from a solid integral plastic or elastomeric component wherein the tabular extensions, openings and slots or recesses are milled or routered into the component top provide the configurations and features. The third section can then be added to the formed mat. Preferably, however, the first and second sections are separately molded and then combined in the desired configurations disclosed herein. To form the panel, the molded first and second sections may be are joined together by welding, an adhesive, molding, bonding, or by joining via an interlocking structure. Having each section heated and joined together in a press is another and more preferred joining option. 
     A typical panel mat has a 42″ square configuration as this facilitates molding of the first and second sections and results in a lightweight panel mat that can be easily installed manually. The sections are typically molded to a thickness of between about 1/16″ to ⅕″ depending upon the plastic or elastomeric material that is used to make the panel. The panels can range in size from 1′×1′ to 16′×16′. They can be square of any size at or it within those values and of any particular feet, inches or inch fractions. Alternatively, the panels can be rectangular, e.g., 1′×2′, 2′×6′, 3′×8′, 4′×8′, 4′×10′, 6′×9′, 6′×12′, 8′×12′, 8′×16″ and even 12′×16′. The 42 inch square panel would have a weight of approximately 40 pounds when molded from upper and lower halves of high density polyethylene each having a skin thickness of 0.2 inches. The preferred panels have sizes of 2.5′×2.5′, 3′×3′, 3.5′×3.5′ or 4′×4′ as these are relatively easy to be moved because they would have a weight of about 100 pounds or less so that they can be lifted and installed by manual labor rather than heavy equipment. The larger size panels are heavier but the temporary flooring can be installed more quickly given the greater area that these mats cover. 
     Also, rectangular mats can be used wherein the length dimension is double the size of the width dimension. So for example in the preferred embodiments, one side of the mat would have three tabular extensions while the adjacent side would have six tabular extensions. Thus, along the length of one mat, two additional similarly configured mats would be joined thereto whereas the width dimension would be joined to half of the length of an adjacent mat. And if desired, combinations of square and rectangular mats can be joined together to form any particular shape decking or temporary roadway or walkway. As an example, a 42 inch square panel mat can also be joined to a rectangular panel mat that is 42″×7′ long. And if desired, rectangular or square mats can be made. The only limitation is the way that these mats are shipped with widths up to about 8 feet being preferred so that the mats can be shipped by conventional tractor trailers. 
     The larger size square or rectangular mats that weight more than 100 pounds are provided with lifting elements as disclosed herein. And while the lifting elements are very useful and possibly necessary when provided on the larger, heavier mats, they also are useful when applied to any size mats. For example, this would allow multiple smaller mats to be lifted together by such elements to expedite loading of the mats onto a truck or even for installation or reclamation of such mats in connection with the forming or breakdown of the temporary flooring. 
     As noted, the overall size (length, width) should be maximized for loading the panel mats into standard ISO containers and more importantly for concise packing into trucks, tractor trailers or rail cars for shipping. Also the thickness of the panel mats should be between about 1 and 3″ and typically between 1.5″ to 1.75″ thick. The mats are constructed to withstand repeated traffic from shop forklifts carrying loads, semi-truck and trailer travel, and stage point loads all while being rigid enough to protect the surface from damage and prevent any rutting of the subgrade. Point loads of between 300 and 500 psi are provided as point loadings while spread loadings of 40,000 to 50,000 pounds per square foot are provided. The highest loadings are achieved with the three section constructions described herein and with the most dense array of geometrical cells therein. Particularly preferred materials for these panel mats are HDPE or Polypropylene. The panel mat should not have any external fasteners as the tabs and openings, slots or recesses are incorporated into the mat structure itself to facilitate interlocking during installation. 
     When a third section is desired to seal off the cells, it can be provided in the form of a plate or solid flat structure that is bonded, adhered, welded or otherwise joined to the other sections. It also can provide a relatively flat bottom surface for the panel mat when desired, such as when the panel mats are to be installed on a flat surface such as a floor. 
     The panel mats can be molded of many different materials, including any conventional polymeric or copolymeric thermoplastic materials, thermosetting materials, or even fiberboard materials made of recycled plastic or polymeric materials from used carpets, plastic packaging and the like. Mixtures or combined blends of plastic materials may also be used. The panels may also be made of elastomeric materials which can be thermosets (requiring vulcanization) or thermoplastic. 
     A wide range of thermoplastic or polymeric materials can be used for the sections of the panel mats of this invention. These materials would be molded or cast to the desired size and thickness of the mat. Useful materials include:
         Acrylonitrile butadiene styrene (ABS)   Acrylic (PMA)   Celluloid   Cellulose acetate   Cyclo olefin Copolymer (COC)   Ethylene-Vinyl Acetate (EVA)   Ethylene vinyl alcohol (EVOH)   Fluoroplastics (PTFE, alongside with FEP, PFA, CTFE, ECTFE, ETFE)   lonomers   Kydex, a trademarked acrylic/PVC alloy   Liquid Crystal Polymer (LCP)   Polyacetal (POM or Acetal)   Polyacrylates (Acrylic)   Polyacrylonitrile (PAN or Acrylonitrile)   Polyamide (PA or Nylon)   Polyamide-imide (PAI)   Polyaryletherketone (PAEK or Ketone)   Polybutadiene (PBD)   Polybutylene (PB)   Polybutylene terephthalate (PBT)   Polycaprolactone (PCI)   Polychlorotrifluoroethylene (PCTFE)   Polyethylene terephthalate (PET)   Polycyclohexylene dimethylene terephthalate (PC (PC)T)   Polycarbonate   Polyhydroxyalkanoates (PHAs)   Polyketone (PK)   Polyethylene (PE)   Polyetheretherketone (PEEK)   Polyetherketoneketone (PEKK)   Polyetherimide (PEI)   Polyethersulfone (PES)—see Polysulfone   Polyethylenechlorinates (PEC)   Polyimide (PI)   Polylactic acid (PLA)   Polymethylpentene (PMP)   Polyphenylene oxide (PPO)   Polyphenylene sulfide (PPS)   Polyphthalamide (PPA)   Polypropylene (PP)   Polystyrene (PS)   Polysulfone (PSU)   Polytrimethylene terephthalate (PTT)   Polyurethane (PU)   Polysulfone (PSU)   Polytrimethylene terephthalate (PTT)   Polyvinyl chloride (PVC)   Polyvinylidene chloride (PVDC)   Styrene-acrylonitrile (SAN)       

     It is also possible to utilize fiberboard as the elongated members or sheets that form the core structure. The fiberboard material is made of recycled plastic or polymeric materials from used carpets, plastic packaging, rice hulls and the like. They can be provided in the desired sizes for use as the core structure of the mats of this invention. They can be combined with other plastic materials as is generally known. In addition to being environmentally resistant due to their plastic content, these fiberboard/recycled materials are environmentally friendly by allowing recycling of used plastics or polymeric materials. 
     The top and bottom sections may also be made of an elastomeric material. The elastomers are usually thermosets (requiring vulcanization) but may also be thermoplastic. Typical elastomers include: 
     Unsaturated rubbers that can be cured by sulfur vulcanization—these are preferred from a strength and hardness standpoint:
         Natural polyisoprene: cis-1,4-polyisoprene natural rubber and trans-1,4 polyisoprene gutta-percha;   Synthetic polyisoprene;   Polybutadiene;   Chloroprene rubber, i.e., polychloroprene;   Butyl rubber (i.e., copolymer of isobutylene and isoprene) including halogenated butyl rubbers (chloro butyl rubber; bromo butyl rubber);   Styrene-butadiene Rubber (copolymer of styrene and butadiene); and   Nitrile rubber (copolymer of butadiene and acrylonitrile).   Saturated (i.e., non-vulcanizable) rubbers include:   Ethylene propylene rubber (EPM);   Ethylene propylene diene rubber (EPDM);   Epichlorohydrin rubber;   Polyacrylic rubber;   Silicone rubber;   Fluorosilicone Rubber;   Fluoroelastomers;   Perfluoroelastomers;   Polyether block amides; and   Chlorosulfonated polyethylene.       

     The elastomeric, thermoplastic or thermosetting materials disclosed herein can also be provided with conventional fillers to increase weight and hardness. They also can be reinforced with particulates, fibers such as glass, fabric or metal screening or scrim to reduce elongation and provide greater rigidity. 
     Regarding the configuration of the panels, the sections are separately molded with peripheral boundaries that are configured to match each other. The first and second sections can be blow-molded or compression molded to the desired sizes. Then, the sections are joined together where the boundaries are in contact by welding, adhesives, heating, or interlocking connections or combinations thereof. It is desirable for the sections to be joined together to form a waterproof structure so that any openings existing between the sections do not fill up with mud, dirt or water during use. Typically, the first and second sections are sealed by welding or adhesives at a peripheral seam. To facilitate an adhesive or weld the joint, the peripheral boundaries can be provided with a minimum flange detailed to provide additional surface area for sealing. The third section can then be joined to the other two to form a three ply mat. As noted, the third section provides additional compression and strength to the panel mat by holding the cells in position where they cannot move laterally. 
     The first section can be configured with an appropriate top surface that may be relatively flat, textured or structured to facilitate movement over the panel mat. While a completely smooth top surface may be used, it is preferred that the top surface at least include some texture or channels that facilitate the drainage of moisture and provide a more secure footing for movement across the panels. The channels can be formed by texturing or spaced raised islands or other structures that are provided in the top surface. The top surface can also include raised or embossed patterns or designs that indicate the supplier or owner of the mats. When a flat or relatively flat surface is provided for the top surface, grit or particles can be included to assist in providing better traction when the surface becomes wet. The panels are configured to be oriented with the top section being the surface which is traversed by personal or equipment while the lower portion of the second section faces the ground. 
     The bottom surface of the panel mats may also configured with a flat, textured or structured surface. Preferably, the bottom surface is textured, structured or is provided with openings so that the panel mat can be securely placed on wet or muddy ground. For the latter feature, the bottom surface can be provided with closed holes that are of essentially the same configuration as the islands of the top section and that are sufficient tall to extend to the islands to provide further support to the upper surface of the top section. If desired, the holes can be configured as cells or cups that have the same configuration as the islands so that the top surfaces of the holes or cups fit into the islands. This provides reinforcement of the upper surface to movement or articles that contact that surface, If desired, the holes and islands can be joined together by welding, adhesives, bonding, heating or by snap-locking. 
     The third section can be provided as a flat plate if desired so that the bottom surface of the panel mat is relatively flat. Of course, the third section can also be provided with cells or can be in the form of a grating or other structure that has openings, channels or indentations. As the second section provides some of this the third section is typically used to provide a flat bottom surface and to hold the cells of the second section in position between the first and third sections. And in some embodiments, the bottom surface can also include a textured surface or a raised or embossed patterns or designs that indicate the supplier or owner of the mats so that it appears the same as to top surface of the mat or to provide better gripping or more secure placement on the ground. 
     Generally, the ground is prepared to be relatively flat to receive the bottom surfaces of the panel mats, but the panel mats can also be placed on a previously prepared flat cement or asphalt surface to provide temporary protection of such surfaces. Typically, however, the panel mats are placed on earth, grass, or similar terrain to provide better footing and support for personnel or light equipment traffic. The textured or structure bottom surface facilitate a more secure placement on gravel or wet or muddy ground. 
     One advantageous structure for the upper surface of the first section is one that includes raised circular or polygonal islands, or combinations thereof, with the islands spaced and arranged closely together near each other. This forms channels between and around the islands that are typically between 0.25 and 1 inch wide. When polygonal islands are used, the spacing can be somewhat uniform but it also can be random. The islands can be oriented along a horizontal or vertical direction if desired. The only restrictions would be that the islands not be too high (more than 1 inch tall) or spaced too far apart (more than 2 inches) so that a person&#39;s foot can get caught or twisted between the islands. A preferred hexagonal structure is illustrated in the drawings, but other structures that include squares, rectangles, triangles, octagons, pentagons or other shapes including circles or ovals can be used. A surface texture that mimics spaced boards or tire thread designs are also suitable. 
     An advantageous structure for the lower surface of the second section can be described as a honeycomb or open cell structure. The term “honeycomb structure” refers to a structure that has openings or open cells therein which extend to the bottom surface of the bottom section. The shape of the cells can be hexagonal, square, rectangular, or of another polygonal shape, or they can even be round or oval provided that the top surfaces or configurations of the cells match the configuration and arrangement of the islands of the top section. Some or all of the cells have a top surface which extend up to and into the islands through the lower surface of the top section. As noted, the top surfaces of these cells are joined to the lower surfaces of the islands by a press fit, snap-locking, adhesives or spot welding. The flat tops of the cells can also support a flat lower surface of the top section. With this construction, the strength of the panel can be further increased as each cell acts as a separate support for the upper surface of the top section. 
     Typically, the honeycomb pattern of geometrical cells includes those that have a top surface having a perimeter of 3 to 12 inches. This includes round top surfaces of about 1″ to about 4″ diameter and square or rectangular trapezoids having side of about 1″ to about 4″. As noted, the tops of the cells can be open or some or all of them can be closed. The same is true of the bottoms of the cells, which again can be open or where some or all of the cells terminate in closed flat surfaces. Similar perimeters would be provided for other shapes (i.e., oval, pentagonal, hexagonal, octagonal, etc.). For greater compressive strengths, more dense (i.e., smaller size) cells may be provided. A skilled artisan can design the cell configuration for any particular compressive strength requirements based on the overall size of the mat and number of sections that are to be included. 
     The sidewalls of the cells are also configured to impart strength to the mat. These are typically provided at an angles with regard to the top or bottom surfaces of the mat rather than being perpendicular. Angles of between 45 and 90 degrees are preferred with 60 to 89 degrees being optimal. 
     The cells can be spaced apart or can be placed with at least part of their sidewalls in contact. The number of cells and their spacing and arrangement can vary but a skilled artisan can easily determine any optimum arrangements based on the anticipated loading that will be applied to the mats. It is also possible to have some, typically half, of the cells face upward and others, again typically half, facing downward. This allows half of the cells to include flat surfaces facing the first section and half of the cells to have flat bottom surfaces facing the third section. The flat surfaces can be placed within recesses in the top and/or bottom plates or the can support a flat surface of the top and/or bottom plates that face the cells. Of course, other arrangements are possible including from 10% to all of the cells having flat top surfaces, as well as from 10% to all of the cells having flat bottom surfaces. The half and half arrangement provides better support for the upper and lower surfaces of the mat when the first and third sections are provided as plates. 
     The panel mats are carefully designed so that they can interlock with adjacent, similarly sized and configured panel mats to form a temporary surface or substrate upon which people or light equipment can be placed thereon or moved across much like the a building floor. This interlocking is achieved by a unique design of tabular members and corresponding recesses. A first side of the panel has spaced tabular members arranged along that side. These tabular members can have a trapezoidal, rectangular, square, half oval or half round shape. For example on a square 42 inch panel, three tabular members would be provided, typically on 1 foot centers. More or less tabular members can be included depending upon the actual dimensions of the panel mat and the size of the tabular members. One preferred arrangement disclosed herein includes two tabular members on each side of a square panel mat and more can be used on the longitudinal sides of the mat when it is rectangular rather than square. For example, a 42″ by 84″ rectangular mat could 4 to 6 tabular members on the longitudinal sides and 2 to 3 tabular members on the shorter sides. For larger mats, as many as 8 to 12 tabular members per side can be used. The tabular members can also be formed on either the top or bottom section of the panel mat on a first side thereof, or with a portion of each tabular member part provided on each section. Preferably each section provides about 25 to 75% of the tabular member, with typically about 50% formed on each section. When about half of the tabular member is provided on each section, the halves can be joined together the welding or adhesive used to provide the seal at the periphery boundary of the panel mat. 
     The opposite side of the panel mats from the first tabular members would be configured with corresponding openings configured and dimensioned to receive the tabular members. The opening can be a full opening into which the tabular member extends, or it can be a slot formed between the top and bottom sections. In an alternative and preferred embodiment, the openings are made in the lower half of the panel while the upper half of the panel provides a continuous surface above the opening. This arrangement facilitates cleanout of the openings if mud or other debris is caught in them. Neither the first tabular members nor the openings include any means for joining or connecting the first tabular members to the openings in any temporary or permanent way. This allows the tabular members to simply slide into and out of the openings for a smooth and fast installation or removal of the panel mats. 
     An arrangement of additional or second tabular members is provided on a second side of the panel mat that is adjacent to the first side that includes the first tabular members. These second tabular members include a central depression on a top surface thereof. The depression may be a cell that may be cylindrical, oval, rectangular or square with rounded edge openings. These additional tabular members also preferably include a bottom surface that is angled so that the forwardmost end of the tabular member is located at a higher position than the rearwardmost end. This configuration facilitates interlocking and disengagement of the tabular members. 
     The opposite side of the panel from the additional tabular members includes slots or recesses that are configured and dimensioned to receive the additional tabular members therein. An opening is provided on the lower surface of the slot or recess to allow for drainage of water, dirt, rocks or other debris that may enter therein. The opening is located sufficiently inwardly from the end of the slot so that a bridge or rail structure is provided at the entry for initial contact with the lower surface of the additional tabular members and for providing support to the tabular member when it is present in the slot or recess. The upper surface of the slot or recess includes a male member for interlocking with the depression of the additional tabular member of an adjacent panel. These male members are configured and dimensioned to only partially engage the apertures of the additional tabular members to receive only part of the male members to provide a snap-locking connection between the slots or recesses with the additional tabular members of an adjacent panel when installing the panels on a properly graded or flat surface. The depression is configured with a rounded opening to facilitate movement of the male member into and out of the depression to facilitate installation and subsequent withdrawal of the tabular member from the slot or recess. The angled bottom portion of the additional tabular members assists in the removal of the male member from the depression as it allows the forward ends of the tabular member to move away from the male members when the opposite end of the panel mat is lifted for detachment of the interlocked male members and apertures during removal of the panel mats. 
     The tabular members can instead include a protruding bump on an upper surface while the openings, slots or recesses include an upper surface that includes a depression for facilitating a snap-locking engagement of the bumps and depressions. Of course, a skilled artisan would readily recognize that the reverse arrangement is also acceptable, namely that the tabular members can include the recesses while the upper surfaces of the openings slots or recesses includes the bumps or other male member protrusions. Combinations can also be made with bumps and/or depressions provided on the tabular members and the corresponding engageable depressions and/or bumps on the openings, slots or recesses. 
     The openings or recesses are configured to be shorter or smaller than the width of the mat. This facilitates the insertion of the tabular members into the recesses or openings. And the bumps and other interlocking structures can be provided on only one of the sides or on both sides as desired. Usually, providing the interlocking structure on the tabular members on one side of the mat is sufficient to achieve good interlocking when the temporary flooring is installed. Alternatively, each opening or recess should also have a portion of the cut out so that there is enough room for the tabular member end to slide in easily without binding. Preferably, this allows the tabular members to be inserted at a 45 degree angle. 
     For even greater connection of the mats, each side of the mat can include multiple tabular members, from 2 to as many as 8 to 12 tabular members being possible, with openings for receiving the provided number of such members arranged between the tabular members. The larger mats would include at least 8 tabular members on two sides. When a rectangular panel is to be made, the longer side would be provided with additional tabs and matching openings or slots or recesses as applicable. As noted as many as 8 to 12 tabular members can be included. This can be done with either the smooth tabular members or the additional tabular members that include the bumps or depressions. 
     These panels are designed for quick and easy installation by one or two workers. The snap-locking feature of the additional tabular members avoids the use of bolting, adding pins or complicated joining configuration which take time and effort resulting in much higher labor costs to install and remove the panels. And the openings or recesses are designed to easily receive the bumps and depressions of the tabular members to allow snap-locking without requiring a large amount of force to lock them together during installation or to disengage them when removing the installation. 
     The configuration of these mats as well as the various sizes that can be used, facilitates a relatively quick and efficient installation of a temporary flooring system. The smaller mats are easily lifted and installed by one or more workers without the use of any connecting hardware. The mats are designed such that the tabular members can easily slide into the openings of an adjacent mat when the additional mat to be installed is held at approximately a 45 degree angle. This enables the tabular members to be smoothly and easily received in the slots or recesses for a quick snap locking of the mats. 
     The configuration of the openings are designed and made either with cutouts or with a shorter or smaller dimension that does not extend to the full width of the mat such that the tabular members can be easily placed therein without binding. In addition when larger panel mats are in use, the lifting elements allows those mats to be simply and easily transported into position. In fact, the flooring installation proceeds in a manner such that after the initial panels are in place, the equipment that is lifting the mats can then move over the previously installed mats such that the field or gymnasium surface is not damaged by the insulation equipment. 
     Turning now to the drawings,  FIG. 1  shows a square panel mat  100  that has three tabular members or tabs  105  on the first side  110  thereof, and three additional tabular members or tabs  115  on the second side  120  thereof. The additional tabs  115  have a depression  125  in the form of an oval opening that has rounded edges and that extends into the tab, the function of which will be described with respect to  FIG. 6 . The upper surface of panel mat  100  also includes a plurality of raised hexagonal islands  160  which are spaced to provide channels therebetween which allow water to drain from the mat. 
     The panel mat  100  also has three openings  130  located on side  135  and three slots or slot-like recesses  140  located on side  145 . Slots  140  also include a male member  150  which extends into the slot, the function of which is also explained with regard to the description of  FIG. 5 . 
       FIG. 2  illustrates the bottom surface of panel mat  100  wherein the same element numbers are used to describe the same components or features shown in  FIG. 1 . Additionally, the lower surface of panel mat  100  includes a plurality of hexagonal shaped holes  155 . 
       FIG. 3  more clearly shows that the panel mat  100  of  FIG. 1  is initially molded in two sections, a top section  200  and a bottom section  300 . The top section  200  includes the upper portions  205  of tabs  105  and upper portions  215  of additional tabs  115 . The upper portions  205 ,  215  of the tabs are integrally formed with the top section  200 . The top section  200  also has a peripheral boundary  225  which is located at the end of the downward facing edges  220  that are provided as well as below the sides of tab portions  205 ,  215 . The bottom section  300  includes the lower portions  305  of the first tabs  105  as well as lower portions  315  of the additional tabs  115  with both portions integrally formed with the bottom section  300 . Bottom section  300  also has upwardly extending edges  320  the ends of which form peripheral boundary  325 . Peripheral boundary  325  also includes the ends of the tab portions  305 ,  315 . 
     When the top and bottom sections of the mat are placed upon each other, the peripheral boundaries  225 ,  325  come into contact with each other and can be joined together by welding or an adhesive. This allows the spaces between the sections to be sealed from the entry of water, dirt or debris. 
       FIG. 3  also illustrates the holes  155  on the bottom surface of the bottom section to show how they are molded into the panel mat. These holes, which in this figure appear as hexagonal cups  355 , have top surfaces  360  that fit beneath and contact the lower surfaces of islands  160  of the top section  200 . Bottom section  300  also shows the bridge or rail structure  370  and adjacent openings  375  that allow dirt or debris that enters into slots  140  to exit rather than to remain in the panel mat. 
       FIG. 4  shows the bottom surface of the bottom section  300  of the panel mat  100  with greater detail of the internal surface of the top section  200 . The same numerals used in  FIG. 3  are used in  FIG. 4  to designate the same components. The internal surface of the top section shows the back sides  260  of the raised islands. Also shown is the bottom of depression  125  which as shown is an oval cell or cup, and male member  150 . These features are more clearly shown in  FIG. 6 . 
       FIG. 5  illustrates a number of connected mats wherein the lighter colors show the upper surfaces of the panel mats and the darker colors illustrate the bottom portions of the panel mats. The first tabs  105  of one panel mat are received in the openings  130  of an adjacent panel mat. Similarly, the additional tabs  115  are received in slots  140  of an adjacent panel mat. The details of these interlocking connections are illustrated in  FIGS. 6 and 7 . 
       FIG. 6  shows that the additional tab  115  is formed by joining upper section  215  to lower section  315  at the point where the peripheral boundaries  225 ,  325  meet. Depression  125  is shown in position after having received male member  150  to provide snap-locking of one panel mat to another.  FIG. 6  also shows the angled bottom portion  380  of additional tab  115  which is provided to disengage the interlocking of male member  15  in depression  125 . This is achieved by lifting the opposite end of the panel mat upward so that the sloped bottom portion  380  moves downward in order to minimize engagement of male member  150  with depression  125 . This along with the curved upper portions of the depression  125  allow the male member to slip out of the depression to disengage the snap-lock connection. 
       FIG. 7  illustrates tab  105  and it&#39;s insertion into opening  130 . Tabular member  105  is also made by joining upper portion  205  to lower portion  305  at the peripheral boundaries  225 ,  325 . As there is no interlocking of tab  105  into opening  130 , the alignment and interconnection of the panel mats are achieved by configuring opening  130  to be of the same shape as but just slightly greater size than tab  105  so that simply sliding the tab  105  into slot  130  provides a tight fit. 
       FIG. 6  also illustrates the lip portion  180  that is provided on the top section  200  along one edge thereof. This contacts the end portion of the adjacent panel mat to provide a longitudinal channel  185  that allows water to drain from between the connected panel mats. Similarly in  FIG. 7 , lip portion  190  that is provided on the top section  200  along one edge thereof to engage the end of an adjacent panel mat to form a similar longitudinal channel  195  that performs the same function of allowing water to drain from between the connected panel mats. 
       FIGS. 3, 6 and 7  also illustrate the angled sidewalls of the cells that provide additional strength to support the upper surface of the first section as well as to provide compression resistance to the mat. While it is possible to use 90 degree cell wall angles, these are harder to mold into the second section and are not preferred for that reason. Instead, an angled sidewall, one that is fully or at least partially angled with respect to the upper and lower mat surfaces, provides greater rebound to the mat after the applied forces are removed. It also allows the cells to slightly compress but as each cell is adjacent another cell, the expansion is limited by the expansion of the adjacent cells. This provides good compression resistance to the mat. And a noted herein, the use of the bottom third section joined to the second section provides additional support for the cells and even more compression strength to the mat. 
     For the second section, a number of different structures can be used to provide support for the upper surface and the first section. In one embodiment, a grid or grating structure can be used where the cells are defined by the openings of the structure, with the cell walls forming polygons or being round or oval in shape with the walls preferably oriented perpendicular to the first section flat bottom surface. Alternatively, the walls can be oriented at an angle to the first section flat bottom surface, with that angle measuring between 45 and 90 degrees and preferably between 60 and 70° with respect to the first section flat bottom surface. The perpendicular orientation provides the greatest compressive strength to the mat while the angled walls provide other benefits with regard to greater cell openings on the bottom sides of the cells and easier manufacture especially to facilitate removal from the mold that forms the cells. It is also contemplated that some or all of the cells could be closed or have flat top surfaces that would contact and support the first section flat bottom surface that is positioned on top of the cells. 
     The cell structure also provides a plurality of open bottom ends of the cells that face away from the first section. Having these cells remain open facilitates installation of the mats on grass surfaces wherein the entire grass surface is not contacted by the mat but only by the perimeters of the open cells. This minimizes damage to the grass during use of the mats. Additionally, the mats can be made of transparent or translucent plastic material so that sunlight can pass through the mats and contact the grass. This facilitates grass growth and health to again reduce damage from coverage by the mats. 
     In some cases, it is desirable for some or all of the bottoms of the cells to have a closed bottom surface. This is desired know when the third section plate is to be included in the mat structure as the closed bottom surfaces of the cells supports the third section plate. A good compromise of open and close cells would be 50:50 for both the top and bottom portions of the second section. 
     It is also desirable to provide a draft angle for the sidewalls of the cells as noted above. In this regard, the top portions of the cells would be smaller than the openings on the bottom of the cells. This structure which is referred to above as angled sidewalls prevents bending and twisting and of the mat when subjected to load bearing forces. And while an angle of 90° is preferred from a strength standpoint, when the second section is molded, that angle can provide difficulty in removing the second section from the mold. Thus, a slightly lesser angle should be used to provide a draft angle that assists in removal of the molded second section from the mold. This can be in the range of 89° to 85°. As noted herein, other angles of as low as 45° can be used if desired for any particular mat configuration or temporary surface installation. 
       FIGS. 8-11  illustrate another panel mat  400  in accordance with the present invention this panel mat includes a first side that has three tabular extensions  405  each with a round protruding bump or disk  410 . The second side of the mat is similarly configured with tab extensions  415  and round protruding discs  420  as shown. The mat has a flat upper surface  425  although it is possible to configure that surface with channels or other irregularities for water removal. For use indoors or in areas that are shielded from the elements (e.g., under a tent), a flat top surface is acceptable. 
     The opposite sides of the panel mat from tabular members are configured to receive such members. A third side of the mat includes three openings  430  each of which includes a central depression  435  which is configured, positioned and dimensioned to receive the circular bumps or disks  410  from a similarly configured panel mat to provide a snap-locking connection therebetween. To facilitate a smooth and easy connection, the depressions have a slightly greater circumference then the circular bumps or disks so that they can be received easily therein. In a preferred embodiment, the sidewall of the bumps is slightly angled so that it creates a tighter connection as it enters into the depression, but an extremely tight or nearly permanent connection is not desired, as the mats are generally used as a temporary flooring which needs to be disengaged and removed after a certain period of use. And preferably, the top surface of the bump or disc contacts the base of the depression to provide further support of that portion of the panel mat. 
     The fourth side of the panel mat includes similarly configured openings  440  with an additional feature of a floor or bridge element  445  which helps secure the tabular members  415  in the recess with the circular disk  420  in snap-locking engagement with the depression  455  that is present in the upper surface of the slot or recess  430 . This depression  455  is best shown in  FIG. 10 . 
       FIGS. 10 and 11  also illustrate the three individual sections  460 ,  470 ,  480  which are joined together to form the panel mat  400 . First or top section  460  includes part of the tabular members  410 ,  415  and the flat surface  425  that forms the top surface of the panel mat. Section  460  is relatively flat although it does include circumferential lip that provides a general recess beneath the top surface to receive the top surfaces of the geometric structures  475  that are present in the second section  470 . These geometric structures  475  are generally cylindrical or trapezoidal in shape and have flat heads that contact and bond to the lower surface of section  460 . 
     Second section  470  include also includes tabular members  485  and circular protruding discs  490  which are configured to be received within the back side of disks  420  of the first section  460 , the back side acting as a depression, so that the tabular members can snap-lock the tabular portions  415 , 485  together. A similar structure is provided for the tabular members  405 , 495  so that they can also snap-lock together. And the disks of the tabular members  485 ,  495  of the second section are designed so that they fit within the depressions of the tabular members  405 ,  415  of the top section  460 . The sidewalls of these disks or bumps  490  can be angled to provide an easy entry into the depression followed by a more secure joint. This is of importance because the second section is adhered to, welded to, or otherwise bonded to the first section to provide an integral panel mat component of the two sections that can be used as is or that can be provided with the third section  480 . While a press-fit is acceptable, the disc and recess are configured so that the top surface of the disc is seated in the bottom surface of the recess to provide further support to the tabular member. 
     Yet another way to join sections  460 ,  470  together would be to heat the sections and press them together in a mold so that the top surfaces of the geometrical elements  475  bond to the bottom surface of section  460 . Similarly, the top surfaces of bumps  490  of tabular members  485  can bond to the recesses behind bumps  420  of tabular members  415 . The same is true for the joining of tabular members  495  and  405 . The resulting structure is an integrally joined together and cannot be easily separated. 
     A most preferred joining technique for the first and second sections is to prepare them in a twin-sheeting operation. This operation, which is also known as twin sheet forming, combines the process disciplines of compression molding, blow molding, and vacuum forming to mold, laminate, and trim multiple layers of materials (substrates with cover stock) in a one step process. The twin sheet molding process forms two sheets of plastic simultaneously through the use of a separate mold on the top platen and a separate mold on the bottom platen. Once the plastic sheets have been vacuum formed, they remain in their respective molds. While both sheets still remain at their forming temperature, the two molds are brought together under high pressures and the two sheets are bonded together. The result is a single product with hollow areas requiring no secondary bonding operations. 
     To provide a flat surface  450  for the mat, third section  480  is provided as a separate flat plate. This plate  450  may be bonded to the lower side of the second section  470  by welding, adhesives or by applying heat and pressure to the components in a mold. Third section  480  includes openings  430  and bridge members  445  which assist in allowing the tabular members to snap-lock with the recesses  455  that are provided in the lower surface of the second section  470 . 
       FIGS. 12A-12C  provide details of how the three sections are joined together. The lower surface of the top section  460  is bonded to the top surfaces of the geometric elements  475  of layer  470 . Between the geometric elements, a lower portion is provided that provides another flat surface that is adhered or bound to the inside surface of lower section  480 . This is best shown in  FIGS. 12B and 12C .  FIG. 12B  also shows the construction of the tabular portion to illustrate how tabular portion  485  and disk  490  fit into the back side of protruding disc  420  of tabular member  415 . Again, the top surface of bump or disk  490  is bonded to the lower surface of the recess provided on the opposite side of bump  420 .  FIGS. 12B and 12C  also illustrate the use of partially angled sidewalls for the cells of the second section. Preferably, at least ⅓ to ½ of the cell height is provided as an angled portion wherein the angle is between 45 and 75 degrees with respect to either the top or bottom surfaces of the mat. 
       FIGS. 13A  and B illustrate how the panel mats can be joined together with  FIG. 13A  a showing a top view and  FIG. 13B  showing a bottom view. It is preferred that the panel mats be joined in a staggered configuration so that all of the joints do not align in the temporary floor that is constructed. Also,  FIGS. 13A and 13B  show two square panels bonded together before a third panel is interlocked thereto in a staggered configuration. Another embodiment of the invention relates to the use of a rectangular panel and the two panels that are joined together in a linear way as shown in  FIGS. 13A and 13B  could instead be configured as a single rectangular panel mat. These larger rectangular panel mats would be use for larger installations as the larger rectangular size would facilitate a faster installation. The construction would be the same as disclosed herein for the square panel mats that are shown. 
       FIGS. 14-16  illustrate yet another panel mat  500  according to the present invention. This panel mat  500  has two tabular extensions on each side, one  505  in a relatively higher position and the other  510  in a relatively lower position. These dual tabular extensions are provided uniformly on each side of the panel mat  500 . 
     The lower tabular extensions  510  have on their upper surface protruding discs or bumps  515  while the higher tabular extensions  505  have on their lower surfaces, depressions  520  which are configured dimensioned and arranged to receive therein the bumps  515  of the lower tabular extensions  510 . The upper surface of the mat  525  as well as the lower surface of the mat  530  are shown as being relatively flat, but as noted herein, a textured or structured surface can also be provided when these mats are to be used outdoors where they will experience rain, snow or other forms of moisture. 
       FIG. 16  illustrates the three sections of panel mat  500 , namely upper section  540  middle section  550  and lower section  560 . As in the embodiment of  FIGS. 8-11 , the middle section  550  is configured with the plurality of geometric elements, shown in  FIG. 16  as flat-top trapezoidal elements  555  which are designed so that their top surfaces contact the bottom surface of top section  540 . Also, the middle section  550  includes supporting structures for the tabular extensions. As in the other embodiments, the top  540  and middle  550  sections are joined together securely by molding, welding, adhesives or by the application of heat and pressure while in a press in order to securely attach the sections together. Thereafter, the lower or third section  560  can be bonded to the bottom of the second section to seal off all of the geometric elements and form a flat bottom surface for the panel mat  500 . 
       FIG. 17  illustrates how the panel mats can be joined together with the relative positions of tabular members  505 ,  510 , protruding bumps  520 , and mating depressions. As shown, the mat is slightly skewed during installation so that the upper tabular member  505  is slightly above tabular member  510  while the other tabular member  510  is placed below tabular member  505  of an adjacent mat. These tabular members slide easily together and provide snap-locking of the mats together. Also the tabular members are configured so that the joining line of the mats are not straight thus providing greater stability of the installed temporary flooring. 
     As noted, although not necessarily preferred for certain embodiments, the panel mats can be formed of a single piece of plastic or elastomeric material that is cut, drilled, milled or routered to the desired shape and configuration. For example, a solid sheet or molded plastic or rubber can be configured with the taps, slots, openings, and surface features described herein. While this is more expensive, the costs for setting up the machining equipment would be amortized across the large number of mats that would be produced with these features. This can be used to form the first and second sections of the mat while when a flat or closed bottom surface is desired, this would be achieved by the addition of a third section of a flat plate. 
     And as noted, the channels that are linear or random lines or grooves on the top and bottom surfaces of the panel mat allow water to drain from the top surface while also allowing the bottom surface of the mat to be more securely placed on wet or muddy ground. And the bottom surface may include openings as shown herein for the second to partially receive gravel or other prepared ground surfaces to again more securely anchor the panel mat in place. It also can be flat by the addition of a third section. 
       FIGS. 18 and 19  illustrate mats that have alternative structured surfaces.  FIG. 18  illustrates a mat  600  that includes an upper surface in the first section  810  with a herringbone pattern of raised elongated bumps  625 . These bumps are molded into the upper surface of the top section  610  of the mat in order to provide resistance to slipping when operators or equipment move across the mat. The herringbone pattern and elongated bumps  625  provide sufficient open space between them to allow water to drain from the mat in particularly when a worker steps on the mat or a tire or other item moves across the mat when the mat is wet. 
     Alternatively, other designs can be used to provide a structured surface on the mat.  FIG. 19  illustrates a mat  700  that has on the bottom of its third section  710  a plurality of linear channels  725  which are molded into the bottom surface of that section. These channels  725  assist in allowing moisture to drain from the mat when the mat is placed on wet or muddy ground. It also provides a more secure footing for the mat on such ground. 
     And while the panel mats of the present invention are shown with tabs on one side and receiving openings or recesses on an opposite side, it is also possible to include alternating tabs and openings or recesses on any particular side of the mat.  FIG. 20  illustrates a rectangular mat  800  that has six tabular members on the shorter side and  810  members on the longer side. The opposite sides to those would have six or eight openings, respectively, as described hereinabove. Mat  800  also has multiple tabular members on two sides and multiple holes on the other two sides. It is also possible to include such multiple tabs and openings on each side of the mat if desired. In such a configuration, the mats cannot be joined with each mat in an end to end or side to side alignment with an adjacent mat. Instead, these mats would be staggered so that the tabular members can be received in the openings of an adjacent mat. This results in a staggered joining of adjacent mats which is advantageous because the final joined flooring structure would not have aligned mats that would provide linear extended joints across the entire flooring. Such an arrangement is preferred because the mats would tend to remain connected and would resist disengagement compared to mats that are aligned with complete linear joints across the entire flooring installation. 
     When tabs are provided on two sides of the mat and openings on the opposite two sides, it is preferred, however, that tabs and openings or recesses be provided on opposite sides of the mat as this facilitates a more rapid installation. For certain installations, however, especially when larger size panel mats are used, the provision of tabs and recesses on a particular side of the mat assist in aligning multiple panel mats for installation. This is of greater interest when rectangular rather than square panel mats are used. 
     The mats can also be joined to form a temporary flooring installation that is discontinuous, i.e., one that leaves certain openings between joined mats. This allows the mats to be placed around trees, light towers or other obstacles that exist in the area that is to be provided with a temporary flooring of joined mats. In particular, it is relatively easy to leave openings such as by simply omitting one or more mats to provide open space in the floor structure. This can serve a number of purposes, such as allowing the floor structure to be installed around a column, pole, post or other upstanding structure, as well as to leave open space for a light tower, camera tower, video screen support or speaker support tower. Furthermore, in the event that a mat is damaged after installation, it can be unlocked, disconnected and removed for replacement by another similarly sized and configured mat without having to remove all further mats that are connected together in the installation. 
     The third section preferably is used to provide a flat bottom surface for the panel mat. It is possible for the third section to be configures so that it also extends beneath the tabular members to further reinforce those members and help them resist damage during installation when the tabular members are inserted into the openings, slots or recesses, as well as to protect against damage from impact if the panel mats were to be dropped in a way where the tabular members would engage the ground first and bear the force of the weight of the mat. This is typically used on flat or graded surfaces, such as those provide by cement, asphalt or clay. 
     Of course, as noted herein, when the upper surface of the first section is structured, the bottom surface of the third section can be similarly structured in a similar manner or with a different type of structure.  FIGS. 18 and 19  illustrate a preferred combination of different structures wherein  FIG. 18  shows a herringbone pattern on the top surface of the first section while  FIG. 19  illustrates linear channels provided on the bottom surface of the third section. 
       FIG. 20  also illustrates lifting elements  825  four of which are provided on rectangular mat  800 , which would typically have a larger size of about 8′×16′. The lifting elements  825  are shown with a lifting ring  830  which is standing vertically in an operative position to be engaged by lifting equipment. 
       FIGS. 21A and 21B  further illustrate this feature. In  FIG. 21A , the lifting element is shown with ring  830  in the operative position. Also shown is recess  835  which is configured to have the same shape and depth as ring  830 .  FIG. 21B  illustrates the ring  830  pivoted downwardly to fit within recess  835  so that the upper surface of the mat is generally planar. This would avoid workers tripping over the lifting element if it were not retracted into the surface of the mat. 
       FIG. 22  further illustrates lifting element  825 . Also shown is recess  835  which receives lifting ring  830  when pivoted downward into a retracted position so that the surface of the mat is relatively flat. Lifting element  825  includes lifting ring  830  which is mounted on a base member  840  that has a central aperture  845 . On the opposite side of mat  800 , lifting element includes a base plate  850  with an upstanding post  855  that has two legs  860 A and  860 B each of which includes an aperture  865 A and  865 B. The base fits into an elongated opening on the lower surface of the third section  820  so that it is seated therein. Post  855  extends through the mat so that it can align with base member  840  of lifting ring  830 . The base member  840  is joined to the legs of the post by a bolt member  875  that passes through apertures  845 ,  865 A and  865 B. The bolt member is secured in position either by machine threads which are provided in the apertures or by the use of a nut that engages the opposite end of the bolting member  875 . 
       FIG. 23  illustrates base plate  850  in position in the surface of third section  820 . While it is not critical that the plate be seated in the surface of section  820 , by doing so this provides a smooth flat base for the mat  800 . 
       FIGS. 24A, 24B, and 24C  illustrate a variation of lifting element  825 . In these figures, lifting element  880  includes a similar construction with lifting element  885  and with a similar base member and post with leg extensions, but the base plate  890  is configured differently. As shown, base plate  890  is circular and includes two cut out portions  895 . The base plate and cut out portions are received in recess  837  that includes protrusions  838 . The protrusions engage the cut out portions of the base plate so that it can be secured in the recess without rotational movement so that the lifting element can be secured to the mat  800 . 
       FIG. 24B  illustrates that this lifting ring  885  maybe positioned to sit in a slot  839  so that the ring can be held in the operative position. After the mat  800  has been lifted or installed, ring  885  can be rotated so that it can retreat back into opening  835  as in the preceding embodiment to provide a relatively flat working surface on the mat. 
     And while these lifting elements  825 ,  880  are preferred for use with the panel mats of the invention, a number of other designs for such lifting elements can be used. Instead of the circular lifting ring, a D- or U-shaped member can be used with the remaining structure and recesses adjusted accordingly. So long as the lifting element includes an engagement opening that is securely attached to the mat, skilled artisans can configure many different particular arrangements that would provide the necessary performance. 
     The plastic and elastomeric materials disclosed herein generally have sufficient strength for many applications, but their strength and rigidity can be enhanced by reinforcing the material with appropriate fillers or other materials, such a glass fibers, other particular matter as is generally known in the art. The additional placement of a metal wire, bar, rod or plate into the mold that is used to prepare the sections or in between the sections before they are sealed together can provide further strengthening of the panel mats. 
     In some embodiments, the panel mats can be made translucent. When these panel mats are to be used outdoors and the mat materials are not sufficiently resistant to withstand long term exposure to sunlight, appropriate additives to improve the UV resistance of the material can be included. 
     The panel mats can be provided in different sizes, but generally, square mats or rectangular mats having longitudinal sides that are twice as long as the mat width are preferred. The thickness of the mat can vary depending upon the intended use of the mat. As noted herein, the thickness also determines the size of the side ramp angled portion. Also, the thickness is determined based on the thickness of each of the first, second and third sections. These can be varied as desired for the intended application, with thicker first and third sections and perpendicular cell walls in the second section being used for heavier load bearing installations. 
     The panel mats can be made with different materials and reinforcements for different applications. As the outer surfaces of the mats may be very similar in appearance, it is not readily observable as to which panel mat has a particular construction. For this reason, another aspect of the invention relates to the providing of each mat with identification means that indicates the material, reinforcement and construction of the panel mat. Thus, when a number of different panel mats are maintained in an inventory, the identification means enables operators to readily determine which mats have the particular materials and properties needed for a particular end use, so that the correct mats can be selected and provided to a jobsite for use by the customer. This would be necessary whether the mats are being purchased by the customer or whether the mats are being leased for use. 
     There are a number of ways to identify the different materials and properties of a mat depending upon the specific type of identification means that are applied to the mat. The preferred types of identification means include an external color code, a radio frequency identification (RFID) tag, or an alphanumeric indicator applied to an outer surface of the mat or that is provided upon a plate that is applied to an outer surface of the mat. The simplest identification means to use is an external color code that is placed upon the mat, preferably in an area that does not receive much abrasion or wear. Different colors or strips or color combinations can be used to identify different materials. And it is highly useful to apply the color code to the same relative positions on each mat for easy identification. For example, placing the external color code along a longitudinal side of each mat allows the color coding to be visible when the mats are stacked upon each other. This simple visual confirmation can be used to make sure that the proper mats are selected: even when the mats are just stacked in the work yard, one can see which ones have the correct color code for the desired core construction. 
     Another use of color can be to identify certain panel mats that are to be used only by a particular customer. This would assist in making sure that the mats are properly collected and delivered. This color can be an additional color beyond that which is used to identify the mat core, or the mats can have a single unique color or color pattern (e.g., stripes, dots etc.) that identifies both the customer and the mat core. And further, the color can be provided in a particular location or area to confirm who the customer is to assist in quality control regarding the correct shipping and delivery of the mats. 
     A simpler type of identification means is one that comprises an external alphanumeric indicator that is applied to an outer surface of the mat or that is provided upon a plate that is applied to an outer surface of the mat. These can be carved, burnished or stamped into or onto the mat again is a location that is not expected to experience severe abrasion or wear. This can also be used to identify a particular customer. 
     For installations over a grass field or yard, the mat can be made to be transparent or translucent so that sunlight is able to pass through the mat to help condition the grass. Additionally, no third section is generally provided for such applications as to open bottoms of the cells provide a smaller “footprint” on the grass to minimize compression of the entire grass surface as would occur if a mat having a bottom plate or sheet would be used. These and the other panel mats disclosed herein are useful to provide temporary flooring for concerts, sporting events, commencement and graduation events, and the like that require a smaller footprint than a full football or baseball field. 
     And as noted herein, in addition to the mat identification means, each mat can further be provided with a surface color that indicates a potential use or non-use of the mat. This can assist in allowing personnel to properly operate on the mat and to promote safety. These colors can include, for example, red to indicate that portions of the mat need to be kept free of equipment, yellow for indicating that caution is needed, green to indicate portions of the mat that are designed to accommodate travel or movement by trucks or heavy equipment over the mat. 
     Of course other colors can be used in any of the foregoing embodiments according to a particular code or correspondence of each color to a specific use or prohibited use. These colors can be tailored to the mat user&#39;s particular requirements so that work operations upon or around the mats can be optimized for safety, efficiency and expediency. Coloring can also be used to define certain areas of the worksite or to help the mats blend into surrounding areas, so that the jobsite can look as clean and undisturbed as possible. For these reasons the use of conventional paints and other surface coatings enhance the usefulness of the mats for any particular application. These paints or coatings would need to be compatible to bond with the materials of the mat. If necessary, appropriate primers or other chemicals can be used to assure strong bonding of the paints or coatings to the mats. 
     And in another embodiment, the upper surface of the mat may be provided with a portion of a word or design, such as the name, nickname or abbreviation, mascot or emblem of a school or university. Typically, the desired word or design is incorporated into the material that forms the top section of the mat. This can be done in any one of a number of ways that are known to skilled artisans in the plastic or elastomeric molding field. Thus, after the mats are installed, the word or design can be visible on the temporary flooring. For example, installation on a football field can include the school name or emblem on the temporary flooring in the same location as it would be on the field, so that person observing the installation from the stands can view the name or emblem. This is particularly useful for graduations or other events requiring a large temporary flooring area for chair seating or marching processions wherein the temporary flooring protects the field. 
     Alternatively, for mats that are to be re-used, the portions of the words or designs on a particular mat that makes up the temporary flooring can be painted onto the mat, built into the plastic during molding of the mat, or provided as a wrapping or film that is applied onto the mat. When painted onto the mat surface, a clear protective layer can be provided above the painted surface to protect the design from abrasion due to movement of chairs or people over the mat. 
     Additionally, the words or designs can be logos or artwork applied on top of the mats. These can be provided as a film or sheet that is adhered to the mat surface. Preferably, for outdoor use, the film or sheet would also provide a non-skid surface and would be strong enough to bond and not peel off when exposed to various weather conditions. 
     Of course for any particular word, logo emblem of other design that is to be provided, a specific arrangement of the mats during installation is required. This can be achieved by numbering the mats so that they are installed in the right order and location so that the logo appears properly and correctly. And if the mats are to be used for different installations at different schools, only the mats that contain the emblem or logo need to be changed out and replaced with a different logo or emblem to customize the mat for use at the different school. 
     The preferred sizes of the panel mats of the invention generally range from 1′×1′ to 12′×12′ with rectangular and preferable square arrangements preferred. In certain instances, larger size mats of as large as 8 feet wide by 16 feet long may be provided for a specific end use. These larger size mats will need to be moved and installed by equipment rather than individual workers. For this, they would include lifting elements of the types disclosed herein. They also may require specific vehicles for shipping and transport of the panel mats to and from a job site. For this reason, the smaller sizes of the mats (from 2 by 2 feet to 4 by 4″ square or 2 by 4 to 4 by 8 feet rectangular mats are preferred as being the most versatile for many manually installed applications. In addition to being sufficiently lightweight to be installed by personnel, they also are easy to ship via conventional vehicles such as trucks or tractor trailers. 
     Therefore, in sum, it is to be realized that the optimum dimensional relationships for the parts of the invention can include variations and tolerances in size, materials, shape, form, function and use are deemed readily apparent and obvious to the skilled artisan, and all equivalent relationships to those illustrated in the drawings and described in the specification are intended to be encompassed by the claims appended hereto. 
     Unless defined otherwise, all technical and scientific terms used herein have same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Also, as used herein and in the appended claims, the singular form “a”, “and”, and “the” include plural referents unless the context clearly dictates otherwise. All technical and scientific terms used herein have the same meaning. 
     The foregoing detailed description is considered as illustrative only of the principles of the invention. Further, since numerous modifications and changes will readily be apparent to those having ordinary skill in the art, it is not desired to limit the invention to the exact constructions demonstrated. Accordingly, all suitable modifications and equivalents may be resorted to falling within the scope of the invention.