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This application is a continuation-in-part of U.S. patent application Ser. No. 10/811,590 filed on Mar. 29, 2004, now U.S. Pat. No. 7,211,314. 

   BACKGROUND 
   Mats have many residential, commercial and industrial uses. Some of the most demanding uses involve factory applications. Mats are commonly placed around industrial machines. There they are subject to heavy traffic, as well as liquid, solid and chemical contamination. 
   Most industrial mats are fabricated from rubber. The rubber must be hard for durability. On the other hand, it should be resilient and compressive for the comfort and health of the user. These two properties are significantly incompatible with each other. A hard mat is not resilient and compressive. A soft mat, while resilient and compressive, is not durable. 
   Most mats are supported by legs. Mats are often placed upon metal gratings surrounding a machine or a work area. The gratings are necessary to receive and contain liquid and solid waste and contaminants. The use of mats with legs on top of metal gratings is problematic because the legs tend to sink into and embed within the gratings. 
   Many mats are fabricated to have surface drain holes to promote liquid and solid drainage. The holes are typically contained within the horizontal top surface of the mat. The problem with such a drain hole configuration is that the holes easily clog. They readily catch and retain foreign objects. A hard object trapped in an upright position within a drain hole often presents a serious safety hazard. The problem could be alleviated by positioning drain holes within a vertical wall on the top mat surface. Unfortunately, vertical wall drain holes are difficult to cost effectively mold into rubber. 
   Another problem with mats is that they are often subject to liquid, oily or slippery environments. Such environments constitute serious safety hazards because of the unsafe footing to which users are subjected. This problem can be alleviated by bonding grit to the top surface of a mat. However, it is often not cost-effective to cover a mat with grit. Further, the compressive forces to which a mat is subjected by users causes flexure of the mat which tends to break the bond holding the grit to the mat. As a result, it is difficult to keep sufficient grit bonded to a mat during the life expectancy of the mat. 
   The manufacturing cost of a grit covered mat could be reduced by only applying grit to selective areas of the mat. This becomes problematic because the adhesives typically used to bond grit to a mat are liquid or semiliquid. The adhesives tend to flow out of any surface area or channel to which they are applied. Further, there are no known methods to easily apply adhesives and grit to selective areas of mats. 
   There is a need for an improved mat which would have one or more of the following features. It could be manufactured from hard rubber for durability, yet feel compressive and resilient when stepped upon. When placed upon a grating it would not sink into or embed within the grating. It would have drain openings which are positioned within vertical surfaces on top of the mat. It would have areas of selectively placed grit bonded onto its top surface. A substantial portion of the selectively placed grit would be below the mat surface. The selectively placed grit would also have support from underneath to inhibit flexure causing the grit to become unbonded. Additionally, a cost-effective method for applying selectively placed grit to the top of the mat is needed. The tendency of a liquid adhesive to flow away from the area where it is initially placed needs to be minimized. 
   Because of the difficulty of cost effectively molding drain holes into vertical wall surfaces on top of a mat, there is also a need for a cost-effective process for creating drain holes within a vertical wall surface on top of a mat. 
   SUMMARY 
   The present invention provides a solution for these problems. One version of the invention is comprised of a mat base, a plurality of long legs, a plurality of short legs, a plurality of ribs, a plurality of channels, a plurality of grit trenches and grit. The mat base has a top surface and a bottom surface. The long legs are perpendicularly attached to the bottom surface of the mat base. This provides resilient support for the mat base. 
   The short legs are also perpendicularly attached to the bottom surface of the mat base. The short legs support the mat base and modify the resiliency of the mat. The long legs and the short legs are adapted to provide a selected mat compression when a load is applied to the top surface of the mat. 
   Each rib connects a pair of legs. The length of each rib, as measured along the dimension perpendicular to the mat when the rib is attached to the legs, is approximately the length of the legs to which it is attached. However, its length is not longer than either of the legs to which it is attached. When the mat is placed on top of a floor grating the rib between the legs tends to prevent the mat from becoming embedded within the grating. 
   The channels subdivide the mat top surface into mat segments. Each channel has a floor and a lateral wall surface. The lateral wall surface is vertically oriented with respect to the top surface of the mat. The lateral wall surface has a drain opening. The drain opening permits drainage from the top surface of the mat to below the bottom surface of the mat. 
   The grit trenches are embedded within the top surface of the mat. Each trench has two ends. Each end has a retention lip. The retention lip forms a dam for retaining adhesive and grit. The grit is bonded into the trenches by an adhesive. In order to reduce flexure within the trenches at least one trench is supported by some of the long legs perpendicularly attached to the bottom surface of the mat. 
   The preferred improved mat is constructed with all of the described features. An improved mat may also be constructed with less than all of the described features. 
   The invention includes a process for fabricating lateral drain openings into the top surface of a mat. The first step of the process is to mold a mat. The mat has a top surface and a bottom surface. Channels subdivide the mat top surface into mat segments. The channels have a floor and a lateral wall surface. The mat is also constructed to have a rib perpendicularly molded into the bottom surface of the mat below each channel. 
   The next step of the process is to remove material from the floor of at least one channel, at least one of its lateral wall surfaces and its underlying rib. The material is removed to a depth which is below the bottom surface of the mat base. The removal of the material will cause the formation of a drain opening within the lateral wall of the channel. The material can be removed with a grooving tool such as a tire groover. 
   Preferably, a programmable cartesian robot is used to remove the material. A grooving tool, such as a tire groover is attached to the programmable cartesian robot. The grooving tool has a heated blade. The programmable cartesian robot is programmed to remove the material from the floor of each channel and its underlying rib. The mat is secured onto the workbed of the programmable cartesian robot. The programmable cartesian robot and the attached grooving tool are then used to remove the material from the floor of at least one channel, at least one of its lateral wall surfaces and its underlying rib. 
   Preferably, a programmable cartesian robot is also used to bond grit into the trenches embedded within the top surface of the mat. An adhesive dispenser is attached to the programmable cartesian robot. The robot is programmed to fill the trenches with adhesive. The mat is secured onto the workbed of the robot. The robot then fills the trenches with adhesive. After the adhesive is placed, grit is spread over the top surface of the mat. Finally, the excess, non bonded, grit is removed. This may be done by shaking the grit off of the mat. 

   
     DRAWINGS 
     These and other features, aspects, and advantages of the present invention will become better understood with regard to the following description, appended claims, and accompanying drawings where: 
       FIG. 1  is a perspective view of a mat segment of an improved mat. 
       FIG. 2  is a bottom plan view of an improved mat. 
       FIG. 3  is a side elevation sectional view of a section of the improved mat of  FIG. 2 . 
       FIG. 4  is a another side elevation sectional view of a section of the improved mat of  FIG. 2 . 
       FIGS. 5   a,    5   b  and  5   c  are side elevation sectional views of a section of the improved mat of  FIG. 2  showing the compression of short legs and long legs of the mat when a compressive load is applied to the top surface of the mat. 
       FIG. 6  is a perspective view of the mat segment of  FIG. 1  after grit has been bonded into the grit trenches of the mat segment. 
       FIGS. 6   a,    6   b  and  6   c  are sectional views of a channel of an improved mat showing the process for creating a drain opening within the lateral walls of the channel. 
       FIG. 7  is a bottom plan view of an improved mat showing drainage paths. 
       FIG. 8  is a top plan fragmentary view of the mat segment of  FIG. 1  showing the application of adhesive to a grit trench. 
       FIG. 9  is a top plan fragmentary view of the mat segment of  FIG. 1  showing the application of grit to a grit trench. 
       FIG. 10  is a side elevation sectional view of the mat segment of  FIG. 9  showing grit bonded by an adhesive into the grit trench of the mat segment. 
   

   DESCRIPTION 
   The preferred embodiment of the improved mat  30  and methods for fabricating it are shown in  FIGS. 1 through 10 . Preferably, the mat  30  is molded from a hard rubber. This will promote durability. The mat  30  is comprised of a mat base  32 , long legs  38 , short legs  40 , ribs  44 , channels  52 , grit trenches  64 , adhesive  72  and grit  70 . The mat base  32  has a top surface  34  and a bottom surface  36 . 
   The long legs  38  are perpendicularly attached to the bottom surface  36  of the mat base  32 . This will provide resilient support for the mat base  32 . The short legs  40  are perpendicularly attached to the bottom surface of the mat base  32 . The long legs  38  and the short legs  40  are adapted to provide a selected mat compression when a load is applied to the top surface  34  of the mat base  32 . The combination of long legs  38  and short legs  40  causes the mat  30  which is constructed from hard rubber to feel and function as if it were constructed from a softer, more compressive rubber. 
   This function is shown in  FIGS. 5   a,    5   b  and  5   c.  There, a compressive force  42  is applied to the top surface  34  of the mat base  32 . Before the compressive force  42  is applied the long leg  38  is in contact with the ground. The short legs  40  are raised above the ground. The compressive force  42  causes the long leg  38  to compress thereby bringing the short legs  40  closer to the ground. Finally, in  FIG. 5   c,  the short legs  40  contact the ground and begin to compress. The result is a mat  30  constructed from hard rubber which compresses as if it were constructed from a softer material. We have found that when using a configuration similar to that depicted in  FIG. 2  to fabricate an 18 inch by 18 inch by three-quarter inch mat, the combination of 504 long legs and 144 short legs  40  provides the preferred compression of the mat. 
   The molded mat  30  contains a number of different rib  44  styles. Shorts support ribs  45  are used to provide structural integrity, especially near the drain openings  58  described below. Long ribs  48  are used to connect legs  38 ,  40 . Each long rib  48  is approximately the length of the legs  38 ,  40  to which it is to be attached. However, the long ribs  48  do not exceed the length of the legs  38 ,  40  to which they are attached. A plurality of long ribs  48  are each connected to a pair of legs  38 ,  40 . The long ribs  48  will thereby prevent the mat  30  from sinking into and becoming embedded into a grating upon which it is placed. The mat  30 , may also be used on top of a solid floor. If only long ribs  48  were used to connect the legs  38 ,  40 , drainage from the top of the mat  30  to the exterior of the mat  30  and air circulation within the mat  30  may be inhibited. Therefore, a plurality of short ribs  46  are used, instead of long ribs  48 , to interconnect some legs  38 ,  40 . This will result in expanded gapping between the floor and the short ribs  46 , thereby promoting drainage and circulation, as shown by the drain paths  60  in  FIG. 7 . 
   The channels subdivide the mat top surface  34  into mat segments  62 , as shown in  FIG. 1 . Each channel  52  has a floor  54  and a lateral wall surface  56 . Most channels  52  have two lateral wall surfaces  56 . Preferably, the lateral wall surfaces  56  contain drain openings  58 . Such drain openings  58  are positioned upon a vertical lateral wall surface  56  rather than horizontally oriented, as in current mats. Because the drain openings  58  are on vertically oriented surfaces the drain openings are less likely to become clogged by contaminants. The drain openings  58  are also much less likely to trap hard and dangerous objects resulting in safety hazards. Liquids and other contaminants drain through the drain openings  58  to the bottom of the mat  30  and to the exterior of the mat  30  by way of the drain paths  60 . 
   The grit trenches  64  are embedded within the top surface  34  of the mat base  32 . The grit trenches  64  are intended to hold grit  70 . Each grit trench  64  has two ends  66 . Each end  66  has a retention lip  68  forming a dam for retaining adhesive  72  and grit  70 . The retention lip  68  prevents the adhesive  72  from flowing out of the grit trench  64 , while the adhesive  72  is in a liquid form. This enhances the ability to selectively place grit  70  upon the top surface  34  of the mat  30 . 
   Grit  70  is securely bonded into the grit trenches  64  with the adhesive  72 . The preferred grit  70  is silicon carbide. The preferred adhesive  72  is cyanoacrylate. In order to minimize the likelihood of mat  30  flexure causing the grit  70  to become unbonded, the grit  70  and adhesive  72  are placed substantially below the top surface  34  of the mat  30 , as shown in  FIG. 10 . However, some of the grit  70  must protrude above the top surface  34  of the mat base  32  in order for the grit  70  to increase the coefficient of friction of the top surface  34  of the mat base  32 . To further reduce unbonding of grit  70  by flexure, long legs  38  are perpendicularly attached to the bottom surface  36  of the mat base  32  below the grit trenches  64  in order to provide support for the grit trenches  64 . Because the grit  70  and adhesive  72  are substantially below the top surface  34  of the mat base  32  and because the grit trenches  64  are supported by long legs  38  grit  70  may be selectively placed upon the top surface  34  without significant unbonding being caused by flexure. 
   Lateral drain openings  58  positioned upon a lateral wall surface  56  are difficult to cost effectively fabricate by molding. Another technique is needed to fabricate the drain openings  58 . First, a mat  30  is molded such that it has a top surface  34  and a bottom surface  36 . It is molded such that channels  52  subdivide the mat top surface  34  into mat segments  62 . As previously described, the channels  52  have a floor  54  and a lateral wall surface  56 . The mat  30  is fabricated such that a rib  48  is perpendicularly molded into the bottom surface  34  of the mat  30  below each channel  52 . 
   Drain openings  58  may be created within the lateral wall surfaces  56  of each channel  52  by removing material from the floor  54 , at least one lateral wall surface  56  and the underlying rib  48 ,  46  of the channel. The material must be removed to a depth which is below the bottom surface  36  of the mat base  32  in order to form a drain opening  58 . 
   The material may be removed with a grooving tool such as a tire groover. The grooving tool has a heated blade  74  for removing rubber. Preferably, the material is removed from the floor  54  of each channel  52  and its underlying rib  48 ,  46  by a process which uses a programmable cartesian robot. The first step of the process is to attach a grooving tool having a heated blade  74  to the robot. Preferably, the grooving tool is a tire groover. The robot is programmed to remove the material from the floor  54  of each channel  56  and its underlying rib  46 ,  48 . After the groover is attached to the robot and the robot is programmed, the mat  30  is secured onto the workbed of the robot. Then, the material is removed from the floor  54  of at least one channel  52 , at least one of its lateral wall surfaces  56  and its underlying rib  46 ,  48  with the robot and the attached groover, thereby forming a drain opening  58 . 
   The robot may also be used to automate the bonding of grit  70  into the trenches  64  embedded within the top surface  34  of a mat  30 . First an adhesive dispenser  76  is attached to the robot. The robot is programmed to fill the trenches  64  with adhesive  72 . The mat  30  is secured onto the workbed of the robot. The robot then fills the trenches  64  with adhesive  72 . Before the adhesive  72  sets grit  70  is spread over it. Finally, the excess grit  70  is removed from the mat  30 . Optionally, the programmable cartesian robot may be equipped with a grit dispenser  78  for selectively spreading grit  70 , as shown in  FIG. 9 . 
   A superior grit  70 —mat  30  bond may be obtained by applying two layers of adhesive  72 . An adhesive dispenser  76  is attached to the robot. The robot is programmed to fill the trenches  64  with adhesive  72 . The mat  30  is secured onto the workbed of the robot. A make coat of adhesive  72  is applied by filling the trenches  64  with adhesive  72 . The robot is used to fill the trenches with adhesive  72 . The grit  70  is bonded to the mat by spreading grit  70  over the top surface of the mat  30 . This bonds the grit  72  to the mat  30 . At this point excess grit  70  should be removed from the mat  30 . Following this, the cartesian robot is used to bond the grit  70  to itself by spreading another layer of adhesive  72  over the grit  70  within the trenches  64 . This is known as the size coat. The preferred adhesive  72  is cyanoacrylate. The preferred grit  70  is silicon carbide. It should be clear, however, that this inventive process may be used with many types of adhesive  72  and grit  70 . 
   Although the invention has been shown and described with reference to certain preferred embodiments, those skilled in the art undoubtedly will find alternative embodiments obvious after reading this disclosure. With this in mind, the following claims are intended to define the scope of protection to be afforded the inventor, and those claims shall be deemed to include equivalent constructions insofar as they do not depart from the spirit and scope of the present invention.

Summary:
An improved mat is disclosed. Long and short legs support the mat and cause it to feel resilient although it is fabricated from hard rubber. The mat has drain holes on vertical surfaces. Ribs prevent the mat from embedding within grating. Grit is selectively placed upon the mat and physically supported. Adhesive for bonding the grit is retained by retention lips. Also disclosed is a process for creating drain holes on vertical surfaces of mats by attaching a grooving tool to a robot and programming the robot to cut through molded mat channels to create the desired drain holes. The claimed process uses the robot to selectively place adhesive upon the mat. An adhesive dispenser is attached to the robot and the robot is appropriately programmed.