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TECHNICAL FIELD 
       [0001]    This invention relates to large irrigation machines of the type utilized in watering crops in the field and, more particularly, to a way of preventing such machines from becoming stuck in the water and mud in deep wheel tracks created when the machine repeatedly passes through soft spots and depressions in the field. 
       BACKGROUND AND SUMMARY 
       [0002]    Center pivot and lateral move irrigation machines have been plagued for many years with the problem of deep wheel tracks caused by repeated passes of tower drive wheels over the same path of travel again and again. While the tracks may be shallow at first, they may become progressively deeper with each pass, and in those areas of the field where drainage is a problem, the wheel tracks may collect water and become so deep that the wheels literally get stuck in the mud. This problem can occur at any of the towers on the machine and at any place in the field such that it takes only one stuck tower to shut down the entire machine. Getting the tower unstuck can be a time-consuming and difficult process, and consequential irrigation delays during critical watering schedules may become costly in terms of potential crop yield losses. 
         [0003]    The present invention provides a method and apparatus for preventing this problem. In its broadest aspects, the invention contemplates preparing a foundation in potentially problematic wheel tracks that the tower wheels can ride upon as the tower traverses the problem area. It is recognized that the majority of any particular wheel track will not pose a problem; however, after a number of passes by a machine, certain areas of the track may begin to deepen and collect water to such an extent that it becomes apparent this particular area is going cause problems. At that time, a foundation member in accordance with the present invention may be inserted into the track and laid at the bottom thereof in position to be engaged by the tower wheels on their next pass. One preferred approach contemplates inserting foundation members immediately behind the lead wheel of a two-wheeled tower such that the foundation members are in position to be engaged and pushed down into final position by the trailing wheel of the tower. With the foundation members in place, the weight of the tower is borne by the foundation members as the wheel passes over, and further deepening of the wheel track is substantially eliminated. 
         [0004]    One embodiment has individual foundation members in the nature of a generally rectangular pad, preferably constructed of high density Polyethylene or the like. Each pad has a width that is slightly less than the nominal width of the wheel track, so that when the pad is placed within the track, the sides of the track confine the pad and keep it from moving out of place. Each pad is preferably provided with interlock structure at its opposite ends so that an appropriate number of pads can be interlocked end-to-end in a series of sufficient length as to provide adequate foundation through the troublesome area. 
         [0005]    In another embodiment, the foundation material may be somewhat thinner and take the form of a ribbon that can be laid down in the track and cut to the desired length. Preferably, the ribbon is sufficiently flexible as to permit storage in the form of a coil for convenient transport and dispensing. It is further contemplated that the mobile tower itself may be utilized to carry the supply of foundation members to the trouble site. 
         [0006]    In a further embodiment, the foundation material is similar in thickness to the separate pad embodiment, but each pad is interconnected with additional such pads in a series by hinging lines of weakness. The continuous string of pads may be conveniently stored in a somewhat flat-sided coil as permitted by the lines of weakness. A string of pads of any desired length may be severed from the rest of the supply at an appropriate line of weakness and laid down in the wheel track to support the wheels. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIG. 1  is a fragmentary perspective view of a center pivot irrigation system with which the principles of the present invention may be utilized; 
           [0008]      FIG. 2  is a top isometric view of one embodiment of foundation member in accordance with the present invention wherein the member is in the nature of a foundation pad; 
           [0009]      FIG. 3  is a bottom isometric view of the foundation pad of  FIG. 2 ; 
           [0010]      FIG. 4  is an enlarged, longitudinal cross-sectional view through the foundation pad of  FIG. 2 ; 
           [0011]      FIG. 5  is an isometric view illustrating the manner in which a pair of foundation pads may be interlocked end-to-end, the pads being illustrated in the initial stage of interlock; 
           [0012]      FIG. 6  is an enlarged, fragmentary longitudinal cross-sectional view through the interlocking structure of a pair of the pads in the condition of  FIG. 5 ; 
           [0013]      FIG. 7  is an isometric view of the two foundation pads with the interlock process partially completed; 
           [0014]      FIG. 8  is an enlarged, fragmentary longitudinal cross-sectional view of the interlocking structure when the parts are in a condition corresponding to  FIG. 7 ; 
           [0015]      FIG. 9  is an isometric view illustrating three of the foundation pads fully interlocked to create a series of the pads; 
           [0016]      FIG. 10  is a fragmentary, enlarged, longitudinal cross-sectional view through one of the interlocking structures corresponding to the fully interlocked condition of the pads in  FIG. 9 ; 
           [0017]      FIG. 11  is a fragmentary isometric view illustrating the process of installing an interlocking a pair of the foundation pads within a wheel track; 
           [0018]      FIG. 12  is a fragmentary longitudinal cross-sectional view of the wheel track and interlock process of  FIG. 11 ; 
           [0019]      FIG. 13  is an isometric view similar to  FIG. 11  but further along in the installation process illustrating a series of four of the foundation pads interlocked within the track; 
           [0020]      FIG. 14  is a longitudinal cross-sectional view of the wheel track with the four foundation pads installed as in  FIG. 13 ; 
           [0021]      FIG. 15  is an isometric view similar to  FIGS. 11 and 13  but showing a completely installed string of interlocked foundation pads with the trailing wheel of the irrigation tower riding upon the last few foundation pads in the string; 
           [0022]      FIG. 16  is a cross-sectional view of the wheel track with the foundation pads and the trailing wheel in the same condition as  FIG. 15 ; 
           [0023]      FIG. 17  is a fragmentary, enlarged, transverse cross-sectional view through a typical wheel track with a foundation pad in place and a drive wheel riding on top of the pad to illustrate relationships between the parts under such conditions; and 
           [0024]      FIG. 18  is an isometric view of a second embodiment of foundation member in which the member comprises a ribbon of material that can be stored in a coil and conveniently cut to length before being placed within a problematic wheel track; 
           [0025]      FIG. 19  is an isometric view of a third embodiment of foundation member in which the member comprises a string of pads hingedly interconnected in a continuous string by thinner lines of weakness so the string can be stored in a flat-sided coil and severed from the supply in desired lengths; and 
           [0026]      FIG. 20  is an isometric view illustrating how a string of interconnected pads in accordance with the first embodiment can be easily stripped out of the wheel track at the end of a season of use. 
       
    
    
     DETAILED DESCRIPTION 
       [0027]    The present invention is susceptible of embodiment in many different forms. While the drawings illustrate and the specification describes certain preferred embodiments of the invention, it is to be understood that such disclosure is by way of example only. There is no intent to limit the principles of the present invention to the particular disclosed embodiments. 
         [0028]    For purposes of example, the present invention has been illustrated in the drawings, and will hereinafter be described, in connection with a center pivot irrigation machine. However, it should be apparent to those skilled in the art that the principles of the present invention are not limited to use with a center pivot machine. Indeed, the principles of the present invention may be applied with great benefit to lateral move machines as well. 
         [0029]    The center pivot irrigation machine  10  illustrated in  FIG. 1  has a long, water-carrying conduit  12  that is supported at spaced locations along its length by a plurality of mobile towers  14 . Conduit  12  is adapted to pivot about the upright axis of a supply pipe  16  which is connected to a source of water (not shown) and is supported by a fixed tower  18 . Various of types of sprinklers or emitters (not shown) are typically provided along the length of conduit  12  for directing water onto the ground in the vicinity of machine  10 . 
         [0030]    Each mobile tower  14  has, in the illustrated embodiment, a pair of driven ground wheels  20  and  22  that propel the tower  14  through the field. Ground wheels  20 ,  22  are driven by an electric motor  24  or other suitable means on the tower. Wheels  20 ,  22  are in fore-and-aft alignment with one another such that wheel  22  trails directly behind and in alignment with leading wheel  20 . 
         [0031]    As the towers  14  move through the field in repeated passes, their ground wheels  20 ,  22  leave wheel tracks  26  that can become progressively deeper with each pass. By monitoring the tracks, the farmer can determine which areas in the tracks present potential trouble spots that could benefit from the use of a foundation member in accordance with the present invention. Allowing a wheel track to reach depth of from 8 inches to 12 inches before inserting a foundation member is probably a good idea, as a wheel track of that depth will assist in retaining the foundation member in place, as will hereinafter be described. 
         [0032]    One embodiment of foundation member in accordance with the present invention is illustrated in  FIGS. 2 ,  3  and  4  and is identified by the numeral  28 . In this preferred embodiment, foundation member  28  comprises a generally rectangular body or pad  29  of material having a top  30 , a bottom  32 , a pair of opposite lateral sides  34  and  36 , and a pair of opposite ends  38  and  40 . Preferably, pad  29  is constructed from a suitable synthetic resinous material such as, for example, high density Polyethylene, although a number of other materials may be satisfactory. If pad  29  is constructed from high density Polyethylene, it may advantageously be injection molded. 
         [0033]    Pad  29  has a thickness dimension of such magnitude that pad  29  is fairly rigid. Although some flexibility is permissible, generally speaking pad  29  retains its shape under heavy loading sufficient to keep a number of the pads interlocked with one another in a manner yet-to-be described. As will be seen, however, a second embodiment which does not use interlocking means but is instead essentially of continuous length, can be thinner and thus more flexible without departing from the principles of the present invention. 
         [0034]    While it may be possible that only a single foundation pad  29  is utilized at any particular trouble spot, it is likely that two or more of the pads may be connected together to form a series in the wheel track. Thus, each pad  29  is provided with interlock structure broadly denoted by the numeral  42  and including one or more male components  44  at one end and a corresponding one or more female components  46  at the opposite end  40 . In a preferred embodiment as illustrated in the figures, a pair of male components  44  and a pair of female components  46  are provided at opposite ends. 
         [0035]    Each male component  44  is in the nature of a hook having a generally outwardly and longitudinally projecting top leg  48  and a downturned tang  50  at the outer end of leg  48 . Top leg  48  is slightly offset upwardly from the remaining body of pad  29  which helps to create an angled recess  52  below leg  48  and rearwardly of tang  50 . In addition, the male component  44  includes a keeper lip  54  that projects axially outwardly from the lower end of tang  50  for use in keeping male component  44  releasably locked within a corresponding female component  46 . 
         [0036]    Each female component  46  includes an opening  56  configured complementally to a male component  44  for the purpose of releasably receiving and retaining component  44  when a pair of the pads  29  are interlocked end-to-end. Thus, each opening  56  includes an undercut portion at its front extremity that defines an overhanging ledge  58 . At its rear end, each opening  56  has a transverse bar  60  that is slightly recessed with respect to the top surface of pad  29 . Thus, as illustrated in  FIG. 10 , when a male part  44  is locked within a corresponding female part  46 , part  44  is hooked over bar  60  as the latter is received by recess  52 . Tang  50  projects downwardly into and through opening  56 , while lip  54  is trapped beneath overhanging ledge  58 . Thus, the two interlocked pads  29  are restrained against axial movement relative to one another by bar  60  and are restrained against vertical displacement relative to one another by overhanging ledge  58 . In effect, ledge  58  and lip  54  keep tang  50  hooked over bar  60 . 
         [0037]    Preferably, each pad  29  is perforated so as to present a plurality of apertures  62 . These allow water and soil to escape from underneath the pad when the pad is laid into a muddy wheel track. Apertures  62  also help keep the pad in place within the wheel track and reduce the tendency for the pad to float up out of the bottom of the track. In one preferred form, each pad  29  is 12 inches wide and 30 inches in length, which width works well in a wheel track made by a standard tire that is 14.9 inches wide. 
         [0038]    Installation and use of the foundation pads  29  is illustrated particularly in  FIGS. 11-17 . As the tower begins to move down into a problem area wherein the machine may get stuck on some future pass, one of the pads  29  is placed on the downslope behind lead wheel  20  as illustrated in  FIG. 11 . In a preferred arrangement, pad  29  is oriented such that the female interlock parts  46  are closest to wheel  20  and male interlock parts  44  are the most remote from wheel  20 . Then, as lead wheel  20  moves on down the slope and space permits, a second pad  29  is connected to the first pad  29  using the vertical insertion/swing down locking technique illustrated in  FIGS. 5-8  (turned 180° from those figures). Additional pads  29  are added from right to left as lead wheel  20  continues to move ahead until an appropriately long string of the pads has been created. 
         [0039]    As illustrated in  FIGS. 13 and 14 , as wheels  20 ,  22  move through a wheel track  26  and enter a deep, muddy portion, the lead wheel  20  tends to push a surge  64  of mud and water ahead of it, which makes it difficult in that instance to place pads  29  in front of lead wheel  20 . Thus, it is generally desirable to carry out the foundation installation process immediately behind lead wheel  20  in a progressive right-to-left pattern as described above. However, installing pads  29  behind, rather than in front of, lead wheel  20  is not a requirement, and in some instances it may be desirable to place pads  29  elsewhere, depending upon the nature of the wheel track  26  and the conditions in front of lead wheel  20 . 
         [0040]      FIGS. 15 and 16  show a long string of installed pads  29 . Any number of pads  29  may be installed, as need be to meet the conditions at hand. Once installed behind lead wheel  20 , the pads of the string are engaged and seated down into place by trailing wheel  22  as it moves down into the problem area of the wheel track and becomes supported by the pads. As illustrated in  FIG. 17 , depending upon the width of each foundation pad  29 , the lateral sides  34 ,  36  are relatively close to sidewalls  66  and  68  of track  26 , and the bottom  32  of pad  29  overlies the bottom  70  of track  26 . This positions pad  29  for use as a solid foundation within the otherwise soft portion of the wheel track and gives firm support to wheels  20 ,  22  the next time they override pad  29 . Hooking the pads together in a string keeps the pads in alignment and allows them to assist one another in maintaining the proper position within the wheel track. 
         [0041]    It will be appreciated that the pads  29  once installed within a wheel track may be left in place permanently or removed at the end of a season as may be necessary or desirable. As illustrated in  FIG. 20 , if removal is desired such operation is quickly and easily accomplished by simply picking up one of the pads at the end of a series and lifting it out of the track, whereupon the other pads connected to the lifted pad will also be stripped out of the track. The individual pads can then be readily disconnected from one another if desired, or left in a connected series. 
         [0042]    It has been found convenient to transport a number of pads to the trouble site using the particular tower whose wheel track is to be fixed. In this respect a lower, horizontally disposed structural pipe  72  on the wheel tower  14  may be utilized to support a container full of the pads  29 , or other arrangements can be made for supporting such a supply of the pads. 
         [0043]    It will be appreciated that pads  29  can be quickly and easily installed, and at a relatively low cost. Moreover, their use as a preventive measure keeps the irrigation machine from becoming stuck and causing the serious problems that are a natural consequence of such negative occurrence. If properly utilized, the pads in accordance with the present invention can prevent the frustrating situation wherein a single isolated trouble spot in only one wheel track can shut down the entire machine. 
       ALTERNATIVE EMBODIMENTS 
       [0044]      FIG. 18  shows a second embodiment of a foundation member in accordance with the present invention, such embodiment being denoted by the numeral  128 . In this embodiment, foundation member  128  takes the form of a continuous ribbon or web  129  of material that may be cut to appropriate length to accommodate the particular trouble spot involved. Preferably, ribbon  129  is constructed from a suitable synthetic resinous material such as high density Polyethylene. 
         [0045]    The foundation ribbon  129  is somewhat thinner than the foundation pad  29  of the first embodiment and thus is not as stiff Preferably, ribbon  29  is of such a thickness that it can be stored in a coil as illustrated in  FIG. 18 . To facilitate such coiling, one side of ribbon  129  may be provided with a series of transversely extending grooves  130  that give increased flexibility to the ribbon. Preferably, ribbon  129  is perforated to present a plurality of apertures  162  for the same reason that apertures  62  are provided in pad  29 . 
         [0046]    Ribbon  129  has opposite straight sides  132  and  134  and is preferably about 12 inches wide. Thus, when a desired length of ribbon  129  is unwound from the coil and cut off, a generally rectangular piece is obtained that will fit down into the problematic wheel track and stay in place. When the severed piece of ribbon  129  is in place within the wheel track, it is retained by the sidewalls of the track in essentially the same manner as illustrated in  FIG. 17  with respect to the foundation pad  29 . 
         [0047]    A third embodiment of a foundation member in accordance with the present invention is illustrated in  FIG. 19  and is denoted by the numeral  228 . In this embodiment, foundation member  228  is blend of the first and second embodiments, taking the form of a series of individual pads  229  interconnected by thinner, hinging lines of weakness  231  to form a continuous strip. Pads  229  are thicker than ribbon  129  of the second embodiment, and are similar in thickness to pads  29  of the first embodiment. Although each pad  229  may be of any suitable length, it is believed that a length of about thirty inches is optimum, with a width of about twelve inches. Preferably, foundation member  228  is molded from a suitable synthetic resinous material such as high density Polyethylene, and each pad  229  is fairly rigid, as in the first embodiment. Lines of weakness  231  permit member  228  to be coiled into a flat-sided coil for storage and transport, as with the second embodiment. Apertures  262  help keep foundation member  228  seated within a wet, muddy track in the same manner as the first and second embodiments. 
         [0048]    To install foundation member  228 , a desired length is unwound from the coil and cut off at the appropriate line of weakness  231 . When the severed length is then inserted down in the problem area of a wheel track, it is retained by opposed sides of the track in the same manner illustrated in  FIG. 17  with respect to the first embodiment. 
         [0049]    The inventor(s) hereby state(s) his/their intent to rely on the Doctrine of Equivalents to determine and assess the reasonably fair scope of his/their invention as pertains to any apparatus not materially departing from but outside the literal scope of the invention as set out in the following claims.

Summary:
To prevent the rut-like wheel tracks of an irrigation machine from becoming so deep that the wheels of an irrigation tower can become stuck in mud and water accumulating in the track, a foundation member is inserted into select, potentially troublesome portions of the wheel track to provide support for the wheels during subsequent passes of the machine. In one embodiment the foundation member comprises a generally rectangular pad constructed from synthetic resinous material and designed to be hooked together with other such pads in a chain-like series to provide the length of foundation required. In another embodiment, the foundation member comprises a thinner web or ribbon of preferably synthetic resinous material that may be wound into a coil for storage and cut to length as required. A third embodiment comprises a series of end-to-end pads hingedly interconnected by thinner lines of weakness that may be severed to provide a desired length of foundation member.