Patent Publication Number: US-6221445-B1

Title: Composite artificial turf structure with shock absorption and drainage

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to artificial turf construction and methods, and, more particularly, to an artificial sports turf which is easy to install and simulates the action of natural playing turf by providing proper shock absorption, improved stability, and reduced turf deflection and irregularities. 
     With increased leisure time, artificial turf systems for indoor and/or outdoor sports surfaces such as golf greens, golf tee pads, playing fields, golf cart paths and walkways, and other sports surfaces have become more widely used and needed. Natural golf greens typically include a sand base of about 18″ in which natural grass grows. The grass is cut to a height of about ⅛-{fraction (3/16)} of an inch to provide a proper playing surface. The sand provides the proper cushioning and drainage, and the grass root system stabilizes the sand. 
     Previously, various constructions have been provided for artificial turf. For example, U.S. Pat. No. 3,795,180 discloses an artificial surface for a ballfield, patio, and the like which utilizes a plastic extruded net for drainage. U.S. Pat. No. 4,913,596 discloses a composite structure for an athletic field having a series of drain tiles covered with pea gravel which overlay a subgrade which includes a ditch for drainage. U.S. Pat. No. 4,462,184 discloses a system for improving synthetic surfaces such as artificial turf and rubberized asphalt which includes a base drainage system. U.S. Pat. Nos. 5,823,711, 5,752,784, and 5,064,308 disclose various drainage systems for athletic fields and the like. 
     While the above systems and structures may be suitable for their intended applications, the prior art has not provided a suitable composite structure for an artificial turf surface with low impact properties so that excessive deflections of the surface do not occur, and suitable drainage to remove water from the surface is provided. With increased demand, artificial golf turf is needed which can be easily installed and maintained. 
     Typically artificial golf course turf has been provided by laying artificial grass on a proper base wherein the grass has a pile range of ¾″-2  filled with sand so that about {fraction (1/8+L )} to {fraction (3/16+L )} inches of the grass tips are exposed. This closely simulates a natural grass golf green which is typically maintained at about {fraction (1/8+L )}″. Thus, the artificial green has a softness, deflection, and stability which provides a playing action much like a natural grass surface. In the past, crushed stone bases or concrete bases have been used below the artificial turf. However, this type of artificial construction requires installation by professional installers so that the construction and installation techniques have not been suitable for ordinary or less skilled workers to perform. Several different construction problems need to be considered if artificial golf surfaces are to be constructed using ordinary workers and lay persons as is necessary to meet the increased needs for artificial golf courses. 
     Basically there have been two types of artificial turf systems used in the golf industry or the sporting industry; a polypropylene fiber system and a nylon fiber system, each having different characteristics for play and, primarily, for durability. The polypropylene grasses have been used primarily as soft, shock absorbent putting greens by sweeping a specialized top dressing blend of sand into the fibers to provide the softness of the green. However, the specification has to be followed very closely in order to provide the required softness. By using a specification of an extended pile height of turf grasses, up to approximately 2″, filled with sand, the desired softness that is needed can be provided. However, the problem occurs that the turf has to be filled with the sand until the actual finished turf tips are achieved. The top dressing procedure of the polypropylene grass is labor intensive, and about two to five days are required, depending on size, to construct the green using a very intensive top dressing technique which includes adding the sand gently while the fibers are brushed upright as the sand is added. Many sequential, repetitive steps of adding a light sand layer to the grass and brushing the sand are required in order to achieve the proper fill, taking considerable time, effort, and expertise. 
     It has not been possible to use short pile turf grasses successfully because of the firmness resulting from their short pile. Different pad arrangements have been tried underneath the short pile turfs, such as rubber, foam pads, and geotextile materials, but these arrangements have not been found to provide the shock absorbing resilience needed, and the specifications and techniques required do not lend themselves to construction by lay persons or ordinary construction workers. In order to meet the demands for artificial sports turfs, it must be possible to use lay persons to construct the turf across the country without undue supervision. 
     To allow someone with less experience to construct artificial turf, local, easily accessible materials, such as sand, need to be utilized in the construction. However, a particular need arises when trying to make a sporting surface base structure or, in this case, a putting green system with loose sand particles in order to keep them stable and firm. Footprints in the surface, or other soft spots would create an imperfect golf ball roll. 
     Accordingly, an object of the present invention is to provide a composite artificial turf structure which is simple to construct and install yet has the proper softness or shock absorption properties to simulate a natural golf green. 
     Another object of the present invention is to provide an artificial sports turf which does not have to be installed according to detailed, precise specifications, but may be installed by lay personnel. 
     Another object of the present invention is to provide an improved artificial turf structure for sports turf having increased drainage for water removal and low impact flexibility that decreases deflection of the surface to provide a natural playing action. 
     Yet another object of the invention is to provide a base locking grid system which provides stability for subbase construction of artificial turf systems for artificial turf and the like where stability, softness and ease of installation is important. 
     SUMMARY OF THE INVENTION 
     The above objectives are accomplished according to the present invention by providing an artificial sports turf comprised of a base surface, a deflection layer disposed above the base surface, and a layer of artificial grass overlying the deflection layer providing a generally level playing surface. The deflection layer is comprised of an open layer of upstanding resilient strands having a prescribed height or thickness. A filling of loose particles is spread into the deflection layer generally up to a prescribed level to provide stability so that the deflection layer deflects upon the artificial grass being impacted to absorb foot traffic and/or ball play yet rebound to maintain a generally uniform play action for the playing surface of the artificial grass. In a preferred embodiment, the base surface may comprise a flexible grid system having a plurality of individual cells interconnected to provide flexibility to the overall grid system to conform to a compacted subbase surface such as soil. If desired, an underlayment may be disposed below the grid system which is porous or non-porous to facilitate water drainage through or by passing the structure. The underlayment may include a geotextile fabric disposed on the compacted subbase. 
     The subbase may include soil, gravel, stone, concrete, asphalt, or existing poor performing artificial grass. Advantageously, the cells include individual round cells and the grid systems includes universal flex joints connecting the round cells together providing relative flexing between the round cells. Preferably, the cells include an interior filling of sand for additional stability. The flex joints include a connector connected between adjacent cells to flexibly join the adjacent cells to provide 360 degrees of flexibility between the adjacent cells. 
     It is possible for a lay person to construct the shock absorption system of the present invention and finish it with a short pile grass surface on top with relative ease. A small amount of fine top dressing sand is deposited into the surface of the grass which is designed to provide the look of natural grass and the smoothness and speed of the roll. For simplified building, the deflection layer has a prescribed thickness or height which is filled with sand whereby the sand and layer are stabilized. Once the deflection layer is filled with sand complete stabilization of that base is provided, and a nice finished top surface can be more easily provided. The process is not labor intensive because the short pile turf requires notably less sand and time to fill. The fine sand or material can be poured into the turf and generally without brushing into the turf because the fine sand goes readily into the turf and is actually pushed into it rather than sweeping after each layer. Installation time has been reduced significantly over conventional means of compacting crushed stone or finishing hard surfaces as concrete or asphalt. 
     The deflection layer designed into the system has two purposes. First, to stabilize the loose particles whether it be sand, rubber, Styrofoam particles, or other loose particles, easily shippable and containing properties that would be loose formed and difficult to compact. The second purpose is to provide a strata beneath the artificial turf to accommodate a non-uniform or imperfect base surface, such as a flexible grid system according to the invention, or an earth compacted base. In either case, the deflection layer provides a leveling course and bridges any imperfections in that base. A true smooth playing surface is provided once the artificial turf layer is finished. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     The construction designed to carry out the invention will hereinafter be described, together with other features thereof. 
     The invention will be more readily understood from a reading of the following specification and by reference to the accompanying drawings forming a part thereof, wherein an example of the invention is shown and wherein: 
     FIG. 1 is a perspective view of an artificial turf construction according to the invention with parts cut away to show the various composite construction; 
     FIG. 2 is a sectional view of a composite artificial turf structure constructed according to the invention taken along line  2 — 2  of FIG. 1; 
     FIG. 3 is a top plan view of a flexible grid base system according to the invention; 
     FIG. 4 is a top plan view of a deflection layer for artificial turf according to the invention; 
     FIG. 5 is a partial perspective view of the deflection layer of FIG. 4; 
     FIG. 6 is a perspective view of the flexible grid system in a flexed state according to the invention; and 
     FIG. 7 is a perspective view of individual geo cells and universal joint according to the invention. 
    
    
     DESCRIPTION OF A PREFERRED EMBODIMENT 
     Referring now in more detail to the drawings, the invention will be described in more detail. 
     FIG. 1 is a perspective view of an artificial sports turf, designated generally as A, illustrated in the form of a golf green  10  constructed according to the invention. As can best be seen in the enlarged sectional view of FIG. 2, the artificial turf has a composite construction which includes an outer layer, designated generally as B, which is artificial turf. The artificial turf may be any conventional artificial grass such as that manufactured by Controlled Products, Inc. of Dalton, Ga. Preferably the artificial turf is specified to have a pile height of {fraction (1/4+L )}″ to {fraction (3/4+L )}″, with {fraction (1/2+L )}″ to {fraction (5/8+L )}″ being preferred. The artificial turf is filled with sand, approximately 3.5 lb./ft 2 , to fill the turf up to {fraction (1/8+L )}″ to {fraction (3/16+L )}″ of the fiber pile height. This stabilizes the grass fibers  11  leaving {fraction (1/8+L )}″ to {fraction (3/16+L )}″ of their tips  11   a  exposed, and the grass fibers stabilize and hold the sand “S” in place. Next, there is a deflection layer, designated generally as C, which provides a drainage material, cushioning for green softness, and eliminates excessive deflection of the artificial turf. Below the deflection layer is a base in the form of a lower grid system, designated generally as D. Flexible base grid system D stabilizes the upper artificial turf and deflection layers B, C. Artificial grass B, deflection layer C, and grid D each include a filling of sand “S.” Next, an underlayment  12  may be provided which may be a suitable geotextile material to prevent the grid system from sinking into the subbase ground soil  14 . A suitable geotextile material may be provided by non-woven or woven form of polypropylene. The subbase may be provided by compacted soil or other subbase surface. 
     Referring now in more detail to flexible grid base system D, as can best be seen from FIG. 3, a preferred embodiment of the system includes a plurality of grid cells  16  which are designed to stand alone or be filled with loose particles  17  or “S” for individual grid support and shock absorption. Adjacent grid cells are interlocked together by flexible universal joints  18  which include a male connector  18   a  received in a socket  18   b  formed in the sidewall  18   c  of the grid cells. While the grid cells are illustrated as circular, other forms may also be utilized. The universal joint provides flexibility in all directions. The grid cells may be joined together to provide a flexible base grid system of any desired area which readily conforms to the compacted base or subbase surface  14 . A sidewall  19 , to which outer cells are attached, may be provided around the completed grid system. The base grid may be manufactured with individual cells and cut in the field, or the individual cells may be joined in the field. 
     The grid cell interiors  16   a , and openings  20  between cells  16 , may be filed with sand, other loose particles  17 . Depending on the desired application, the grid cells may be manufactured to a size that completely supports the synthetic turf top layer so deflection is eliminated. Preferably, the diameter of the cells is no more than about 4 inches, since it has been found that larger diameters allow the deflection layer and/or grass layer to deflect inwardly too much. As noted previously, underlayment  12  is a suitable geotextile material which is placed over already existing compacted base soil, stone material, concrete, asphalt, existing poor performing synthetic turf systems, or other stable base subsystem. 
     The universal joint mechanism of the hub cells allows the adjoining cells to be locked and released as needed and permit flexibility 360° for conforming to undulating or otherwise, less than level subbase surfaces. The locking universal joints may be manufactured as a part of the cell or the cells may be assembled with a double pointed joint apparatus separately, which enables the cells to be joined continuously through receiver holes of a smaller diameter. 
     Deflection layer C is supported by flexible grid system. The deflection layer may comprise a non-woven layer of synthetic fibrous material which is open for containing sand and sufficient water drainage yet has enough resiliency to provide cushioning while maintaining the designed height. The deflection layer also helps in preventing the playing surface from deflecting into the grid cells by settling, upon impact by a golf ball, foot traffic, or other similar impact. In the illustrated embodiment, deflection layer C is constructed of a non-woven, synthetic fibrous material and manufactured to a precise thickness to maintain a baffled layer or membrane which supports the artificial grass layer. The woven deflection layer may also be a multi-layer woven fabric. In addition, the layer may be affixed directly to a geotextile fabric backing  22  such as by weaving, binding, adhesive, thermal, or any other means. This provides additional strength to the deflection layer, and prevents filler sand or loose particles from falling through. Fibrous upstanding yarns  24  of the deflection layer possess sufficient resiliency to maintain the height and loft of the woven fabric to absorb shock from foot traffic or play. In addition, the grid system can be particle filled for additional strength and improved shock absorbent characteristics from impact. The loose fill system also promotes improved drainage of water in outdoor applications. 
     As can best be seen in FIGS. 4 and 5, deflection layer C includes a lower side  26  of mutually entangled heat set plastic yarns  26   a  and an outer side  28  of mutually entangled plastic yarns  28   a  arranged in intersecting diagonal rows  30 ,  32 . Upstanding yarns  24  extend between lower and upper sides  26 ,  28 , and are mutually entangled and heat set therewith. In particular, yarns  24  are spot welded at  24   a  to lower side  26  and are mutually entangled or looped with the upper side yarns. The entire layer is heat set for resiliency. The fibrous yarns are entangled or woven together so as to prevent the disbursement and lateral movement of loose particles when applied within the layer. It has been found that a fibrous strand material with a pile height of about 1″ filled with sand during installation, advantageously stabilizes the construction, i.e. the strands stabilize and anchor the sand particles in place, and provides the needed shock absorption. Preferably, the pile of the deflection layer is filled to the top, 1″. So constructed, the deflection layer is resilient to rebound and assists in preventing permanent deformities and irregularities in the playing surface. A suitable construction according to the above specifications can be manufactured by the Colbond Corporation of Enka, N.C. 
     Thus, it can be seen that an advantageous construction procedure can be had for a composite artificial turf system for sports and the like which can be installed by an ordinary construction worker or laborer having basic mechanical skills, resulting in the desired softness for shock absorption and natural play action, and which accommodates foot traffic while affording proper water drainage. 
     While a preferred embodiment of the invention has been described using specific terms, such description is for illustrative purposes only, and it is to be understood that changes and variations may be made without departing from the spirit or scope of the following claims.