Abstract:
An insulated foot pad for a tripod has an insulated block sandwiched between two plates. The plates are made of a material that is a poor conductor of heat. Tripod legs placed on the foot pads will not sink into the snow on sunny days nor into warm asphalt on hot days.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefits of U.S. Provisional Application No. 61/289,926, filed Dec. 23, 2009, the disclosure of which is hereby incorporated by reference in its entirety including all figures, tables and drawings. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not applicable 
     REFERENCE TO SEQUENCE LISTING, A TABLE, OR A COMPUTER PROGRAM LISTING COMPACT DISC APPENDIX 
     Not applicable 
     BACKGROUND OF THE INVENTION 
     In the last several years land survey equipment has changed dramatically. Changes in technology have allowed this equipment to provide levels of accuracy never before achieved. Though survey equipment has changed, it is still mounted, as survey equipment has been for ages, on a tripod. It is still necessary that the tripod hold survey equipment steady and level to achieve accurate readings. This can be a difficult task since surveys are conducted in the field under temperature extremes. Most field survey tripods have spiked feet to hold the ground. Problems occur when these tripods are set on snow or ice. Within minutes the feet melt through the snow causing instrument position to change. Similar problems occur when a tripod is placed on asphalt on a warm day. The tripod legs sink into the soft asphalt. Many types of tripod feet are available. The tripod feet are designed to grip different surfaces. These various feet however do not prevent the tripod from shifting as the feet melt through the surface on which they are placed. Some insulated foot pads have been designed for machinery but they are designed primarily to dampen vibration from the machine (see U.S. Pat. No. 2,921,760). 
     A need remains for means to prevent tripod feet from melting into a surface on which they are placed. Such a means would allow surveys to be conducted with more accuracy, for less cost, and in less time since the surveyor is not constantly resetting the tripod. 
     All patents, patent applications, provisional patent applications and publications referred to or cited herein, are incorporated by reference in their entirety to the extent they are not inconsistent with the teachings of the specification. 
     BRIEF SUMMARY OF THE INVENTION 
     The subject invention involves an insulated foot pad for a tripod foot or instrument foot. Each pad has two rigid plates which sandwich a piece of insulating foam. The plates provide the pad surface area and are constructed for minimal heat conductivity. For example, the plates are made from plastic, which conducts heat poorly, and are preferably a light color to reflect the suns rays. Pins on the outside of one plate snap into hollow conduits in another plate to keep heat transfer to a minimum when the plates are connected. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
         FIG. 1  is a top exploded perspective view of a preferred embodiment of the insulated foot pad of the subject invention. 
         FIG. 2  is a bottom exploded perspective view of a preferred embodiment of the insulated foot pad of the subject invention. 
         FIG. 3  is a top perspective view of a preferred embodiment of the insulated foot pad of the subject invention supporting a tripod foot. 
         FIG. 4  is a cross-sectional view along line  4 - 4  of  FIG. 1  of a preferred embodiment of the insulated foot pad of the subject invention. 
         FIG. 5  is a cross-sectional view along line  4 - 4  of  FIG. 1  of a preferred embodiment of the insulated foot pad of the subject invention to which a rubberized pad is attached. 
         FIG. 6  is a bottom perspective view of a preferred embodiment of a bottom plate of the insulated foot pad of the subject invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The invention involves an insulated foot pad for feet of an instrument. A block of insulating material is sandwiched between two plates that conduct heat poorly. 
     A preferred embodiment of the subject insulated foot pad  10  is shown in the appended figures. In an exemplified embodiment, the insulated foot pad is used to support a tripod foot on a surface. In the exemplified embodiment an insulating block of foam is sandwiched between two plastic plates. A top plate  12  having an top surface  13  and a bottom surface  15  contacts the foot of the tripod while a bottom plate  14  having an upper surface  17  and a lower surface  19  contacts the ground. The feet of a tripod for a field survey are most often spiked to anchor the tripod in soft ground. These often black spikes rapidly melt through ice and snow. The plates of the pad of the subject invention provide surface area for the tripod foot. The plates can be any shape or size. In the exemplified embodiment the plates are rectangular and are of sufficient size to offer surface area but are not too large to be cumbersome when carrying them in the field. In a particularly preferred embodiment, the top plate  12  has a recess  16  to capture the spike of a tripod foot. 
     The plates should be made of a material that conducts heat poorly. In the exemplified embodiment, the plates are molded of plastic. Plate thickness should be kept as thin as possible to prevent heat accumulation. Plates however need to be durable, and strong enough to support the survey equipment. The exemplified molded plates are thin but have reinforcing ribs  18  for strength. The ribs prevent full contact between the plate and the insulating material to further reduce heat transfer. 
     The plates enclose insulating material  20 . In the exemplified embodiment, the insulating material is closed cell foam. The foam is resistant to the elements and will not foul if wet. The foam further adds structure and strength to the pad. One skilled in the art would realize that other insulating materials can be used successfully in the pad of the subject invention, including air. 
     The two plates of the exemplified embodiment sandwich the insulating material to form a single foot pad unit  10 . The plates can be affixed to the foam by, for example, an adhesive. Alternatively, the plates can be attached to one another capturing the insulating material. It is important however that the means to connect the plates to one another should not conduct heat from one plate to the other. In the exemplified embodiment, pins  22  snap through apertures  24  in one plate and into hollow conduits  26  molded into the other plate. The hollow conduits  26  transfer less heat than a solid peg might. Bores  27  are cut into the insulating material to allow the hollow conduits or hollow pipes  26  to pass through the closed cell foam of the exemplified embodiment. On skilled in the art would recognize there are several ways to connect the plates to one another through hollow conduits. It is only necessary that the conduits are secured to each plate. In the exemplified embodiment, four conduits are used to secure the rectangular plates. Fewer or more points of connection may be needed to secure plates of different shapes. It is preferred that the least number of connection points be used to minimize the possibility of heat transfer. 
     The insulating foot pad shown in the figures was designed for use with a tripod for land and construction survey. The plate size provides sufficient surface area to support a tripod and its equipment. The recess  16  holds a typical spike type tripod foot  36 . It is noted that in order to keep the convex edge of the recess from contacting the foam and perhaps transferring heat a hole  28  is cut into the foam beneath the recess. The rugged plastic construction will not shatter in cold weather. The plates are white to reflect the sun&#39;s rays. The foam core will not break down with exposure to sun, heat, or water. The pad has a handle  30  so that it can be easily grabbed, removed, and carried when the tripod needs to be moved. 
     In a particularly preferred embodiment, the bottom plate of the pad has spikes  32  to grip the ground ( FIG. 4 ). The spikes allow the pad to grip ice and snow. The number, depth and configuration of the spikes on the bottom of the pad can vary to meet different surface environments. In another particularly preferred embodiment, the bottom plate of the pad is rubberized to grip smooth surfaces ( FIG. 6 ). The rubberized facing of the plate can be a pad  34  applied to the bottom of the plate which covers the entire bottom or can be strips or buttons of rubberized material on the bottom surface of the plate. Alternatively, the rubberized facing can be integral with the bottom plate. 
     To use the subject pads, chose a location for the tripod. On frozen ground, snow, mud or gravel, put a pad in the spot where each leg will go. Firmly push each pad down with your foot. On slick ice, and hard surfaces, rough up the area or chip out a spot for each pad to insure the pads will not slip. Place each foot of the tripod in the center of the recess on each pad. The tripod legs should not be pushed into the pad. The tripod erected on the subject pads should stay level for at least  15  minutes even on the sunniest days. When measurements are complete, remove the tripod and pull the pads up by their handles, loop them together and move on to the next location. 
     Applicants note that the subject device can be configured in different ways for different purposes. The pads of the subject invention can be attached to, or integrated into, the tripod legs. For example, a hinged bracket can be used to affix the pads to the tripod legs so they can be swung beneath the tripod feet. Likewise, tripods can be provided where the tripod feet are the insulated foot pads. Additionally, a different choice of insulating materials may not require the pad to have two plates. It is only important that there be minimal heat transfer to the material contacting the ground so that the portion of the pad contacting the ground will slow the melt of underlying snow and reduce further softening of asphalt. 
     It is understood that the foregoing examples are merely illustrative of the present invention. Certain modifications of the articles and/or methods may be made and still achieve the objectives of the invention. Such modifications are contemplated as within the scope of the claimed invention.