Patent Publication Number: US-11661126-B2

Title: Method and apparatus for transporting and steering a heavy load

Description:
RELATED APPLICATION DATA 
     This application is a nonprovisional of and claims the benefit under 35 U.S.C. § 119(e) of U.S. Provisional Patent Application No. 62/719,343, filed Aug. 17, 2018, the disclosure of which is incorporated by reference herein in its entirety. 
    
    
     BACKGROUND 
     The field of the present invention is related to a class of transportation machines commonly referred to as “walking machines,” which are large, typically non-wheeled, power-driven structures operable for transporting heavy loads (e.g., loads weighing upwards of several thousand tons) over a road or other ground surface. These machines, and the heavy substructures in themselves, are fabricated from steel and other high-strength materials and find particular use in carrying and sequentially transporting large structures. For example, a walking machine may be used to transport oil drilling rigs and position them over a drilling well bore in a new field undergoing exploration for oil, or over existing well bores in an old, established field. 
     Instead of using ground-contacting wheels to move the heavy loads, these walking machines typically comprise a plurality of lifting assemblies that use hydraulic lift cylinders to lift the load above the supporting surface and then move the load relative to the supporting surface by transporting the load via rollers or tracks in the walking machines. 
     In order to position the oil rig or other heavy load in a precise position, these walking machines may be provided with a steering mechanism whereby the walking machine unit may be rotated or steered to a desired position. U.S. Pat. No. 6,581,525, the disclosure of which is incorporated by reference herein, provides additional details relating to walking machine systems and methods for moving heavy loads. The &#39;525 patent also discloses a steering system for a walking machine in which a substructure of the walking unit may be disengaged and rotated relative to its upper structure thus repositioning the substructure for travel at a desired steered angle. U.S. Published Application No. 2017/0022765 discloses a walking machine unit with an improved steering system. The present inventor has recognized that these steering systems have room for improvement. 
     SUMMARY 
     The present disclosure is directed to apparatus and methods for transporting heavy machinery, equipment or other heavy load from one location to another, whereby the apparatus is constructed to transport the load in multiple directions in order to move the load in a desired path to a set position. An example embodiment is directed to a walking machine comprising a plurality of lifting assemblies operative to lift the load above the supporting surface and then move the load relative to the supporting surface (e.g., the road or other ground surface) by transporting the load via rollers or tracks in the walking machines. In one embodiment, the lifting assembly may include transport mechanisms operative for transporting the load in multiple directions—in one example both a first direction (e.g., longitudinally) and a second direction (e.g., laterally)—so that lifting assemblies may be driven or steered in a desired walking direction or along a desired directional path. In another example embodiment, a walking machine is provided with an improved re-centering system whereby the bad being transported can be quickly and efficiently re-centered after each movement to ensure that the load is properly centered and stabilized before the load is subsequently moved. Additional aspects and advantages will be apparent from the following detailed description of example embodiments, which proceeds with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a diagrammatic view of an example walking machine system for moving a large support structure, such as an oil rig. 
         FIG.  2    is a partial view of the walking machine system of  FIG.  1    with two walking machine units in position underneath and connected to the oil rig. 
         FIGS.  3 - 7    are partial views of the walking machine system of  FIG.  1    illustrating an example operation of the walking machine units. 
         FIG.  8    is a top plan view of a walking machine system according to an example embodiment, with four walking machine units, one disposed at each of the four corners of the oil rig. 
         FIGS.  9 - 12    are each a top plan view of one side of the walking machine system of  FIG.  8   , illustrating two walking units. In  FIG.  9   , the walking units are in a first longitudinal position and central lateral position; in  FIG.  10   , the walking units are in a forward extended position and central lateral position; in  FIG.  11   , the walking units are in the first (rearward) longitudinal position and right side lateral position; in  FIG.  12   , the walking units are in the first (rearward) longitudinal position and left side lateral position. 
         FIG.  13    is a top isometric view of the walking machine units of  FIG.  9   . 
         FIGS.  14  and  15    are top right and left rear isometric views of a walking machine unit according to one embodiment. 
         FIG.  16    is a partially exploded isometric view of the walking machine unit of  FIGS.  14  and  15   . 
         FIG.  17    is a top isometric view of a roller assembly of the walking machine unit of  FIG.  14   . 
         FIG.  18    is a cross-section view illustrating internal components of the roller assembly. 
         FIGS.  19 A,  19 B, and  19 C  are partially exploded views of a walking machine unit according to another embodiment. 
         FIGS.  20 A,  20 B, and  20 C  illustrate views of an embodiment of a centering fixture or frame. 
         FIGS.  21 A,  21 B, and  22    illustrate an embodiment of a centering pivot arm according to one embodiment. 
         FIG.  23    illustrates an embodiment of a walking machine unit according to one embodiment. 
         FIGS.  24 A and  24 B  are schematic illustrations representing an example operation of the centering pivot arm of  FIG.  21    for realigning a foot section of the walking machine unit of  FIG.  23   . 
         FIGS.  25 A,  25 B,  25 C,  25 D,  25 E,  25 F, and  25 G  collectively illustrate a walking cycle of the walking machine unit in accordance with one embodiment. 
         FIG.  26    illustrates a perspective view of a walking machine unit according to another embodiment. 
         FIG.  27    is a partially exploded view of the walking machine unit of  FIG.  26   . 
         FIG.  28    illustrates an embodiment of a centering fixture or frame of the walking machine unit of  FIG.  26   . 
         FIG.  29    illustrates an example embodiment of an alignment plate of the walking machine unit of  FIG.  26   . 
         FIG.  30    is a top perspective view of a walking machine system according to an example embodiment, with four walking machine units, one disposed at each of the four corners of a rig structure. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     With reference to the drawings, this section describes particular example embodiments and their detailed construction and operation. To facilitate description, any element numeral representing an element in one figure will be used to represent the same element when used in any other figure. The embodiments described herein are set forth by way of illustration only and not limitation. It should be recognized in light of the teachings herein that there is a range of equivalents to the example embodiments described herein. Notably, other embodiments are possible, variations can be made to the embodiments described herein and there may be equivalents to the components, parts, or steps that make up or augment the described embodiments. 
     The described features, structures, characteristics, and methods of operation may be combined in any suitable manner in one or more embodiments. In view of the disclosure herein, those skilled in the art will recognize that the various embodiments can be practiced without one or more of the specific details or with other methods, components, materials, or the like. In other instances, well-known structures, materials, or methods of operation are not shown or not described in detail to avoid obscuring more pertinent aspects of the embodiments. 
       FIGS.  1 - 7    are a series of schematic drawings illustrating an example walking machine system for moving an oil rig  10  (or other large support structure) along a ground surface  5 . The oil rig  10  is supported at the ground surface  5  by a plurality of support legs  55  attached to the bottom support structure  50 . The walking machine system includes a set of four lifting assemblies (or lifting machine units), with a lifting assembly or unit arranged in position proximate each of the corners of the oil rig  10 . Two lifting assemblies  100 ,  102  are visible in  FIGS.  1 - 7    and the other two lifting assemblies  104 ,  106  are illustrated in  FIG.  8    described below. The lifting assemblies  100 ,  102 ,  104 ,  106  may be supported via a longitudinal beam (as shown) or other configuration such as via a horizontal beam. Though four lifting assemblies are shown, the system may include additional lifting assemblies. 
     Operation of the lifting assemblies  100 ,  102 ,  104 ,  106  is now described with respect to a first lifting assembly  100  with the understanding that the same description applies equally to lifting assemblies  102 ,  104 ,  106 . For initial installation, the lifting assembly  100  is set in position on the ground as in  FIG.  1    with its lifting cylinder retracted and not contacting the oil rig  10 . The lifting cylinder of the lifting assembly  100  is raised partway as in  FIG.  2    to contact the oil rig support beam/structure  50 . The lifting assembly  100  is then connected to the beam/structure  50  via a suitable fastener mechanism (e.g., attachment bolts are visible in  FIG.  2   ) or other suitable attachments. The lifting cylinder is then retracted, thereby lifting the lower structure or jack pad of the lifting assembly  100  off the ground (due to its attachment to the support beam  50  of the oil rig  10 ), and then the lifting assembly lower structure and foot pad are driven forward by a first push-pull mechanism to the forward position as in  FIG.  3   . The lifting cylinder is then partially extended, lowering the lifting assembly lower structure and jack pad to the ground as shown in  FIG.  4   . The lifting cylinder is then raised to the extended position thereby lifting the support structure  50  and support legs  55  of the oil rig  10  off the ground as in  FIG.  5   . Once the oil rig  10  is lifted, the lifting assembly lower structure (the foot) is driven rearward by the first push-pull mechanism to the rearward position, thereby moving the rig  10  forward as in  FIG.  6   . The lifting cylinder is then retracted, lifting the assembly lower structure off the ground as in  FIG.  7   , after which the assembly lower structure may then be driven forward to the position as in  FIG.  3   . The process steps are then repeated. 
     In one embodiment, a second push-pull mechanism, operating separately or in combination with the first (longitudinal) push-pull mechanism, provides for lateral drive motion. In any event, the second (lateral) push-pull mechanism is operable independently from the first (longitudinal) push-pull mechanism enabling for lateral motion with or without longitudinal motion. 
     Further details of the lifting assembly and push-pull mechanisms will now be described.  FIG.  8    illustrates a top plan view of the walking machine system comprised of the four walking machine units  100 ,  102 ,  104 ,  106  with the oil rig  10  removed and showing support structure  50 . The walking machine units  100 ,  102 ,  104 ,  106  in  FIG.  8    are illustrated in a first longitudinal (non-extended) travel position, and laterally centered. 
       FIGS.  9 - 13    illustrate one side of the walking machine system and two of the walking machine units  100 ,  102  in various positions. In  FIGS.  9  and  13   , the walking machine units  100 ,  102  are illustrated in the first longitudinal, non-extended or rearward, travel position, and laterally centered (similar to  FIG.  8   ). The isometric view of  FIG.  13    further illustrates the forward walking machine unit disposed within the cross beams  52 ,  54  of the support structure  50  and also illustrates the rear lifting assembly with cross beams of the support structure  50  removed. In  FIG.  10   , the walking machine units  100 ,  102  are illustrated in the second longitudinal, forward-extended, travel position, and laterally centered. In  FIG.  11   , the walking machine units  100 ,  102  are illustrated in the first longitudinal, non-extended or rearward, travel position, and laterally to the right side. In  FIG.  12    the walking machine units  100 ,  102  are illustrated in the first longitudinal, non-extended or rearward, travel position, and laterally to the left side. Though not shown, the walking machine units may be translated into the second longitudinal, forward-extended, travel position, and laterally translated to the left or right. The following sections describe additional details relating to the walking machines units  100 ,  102 ,  104 ,  106  and their various components for supporting the movement of the overall walking machine system. 
       FIGS.  14 - 16    collectively illustrate details of the walking machine unit  100  according to an embodiment. As noted previously, it should be understood that any description relating to walking machine unit  100  also applies to walking machine units  102 ,  104 ,  106 , or any other walking machine units used in the walking machine system. With general reference to  FIGS.  14 - 16   , the walking machine unit  100  comprises a foot plate assembly or foot section  110 , an upper roller guide assembly  200  (with lateral drive), a longitudinal drive assembly  300 , and a lift assembly  400 . With particular reference to  FIG.  14   , the following provides additional details of the structure and drive system for the lateral translation mechanism according to one embodiment. 
     With reference to  FIG.  14   , the foot section  110  comprises a foot plate  111  that contacts the ground surface during a walking motion of the walking machine unit  100 . The foot section  110  comprises a foot plate  111  of generally rectangular shape that may include slightly curved front and rear ends. In other embodiments, the foot plate  111  may alternatively be another suitable shape such as oblong or circular, the elongated rectangular structure may enable the walking machine unit  100  to have a longer longitudinal travel stroke with a solid/stable footprint. The foot section  110  includes a plurality of retainer bars secured to and arranged about the upper surface of the foot plate  111 , including retainer bars  112   a ,  112   b ,  112   c  on one lateral side (see  FIG.  14   ), retainer bars  112   d ,  112   e ,  112   f  on the opposite side (see  FIG.  15   ), and additional retainer bars on the front and rear sides (not shown) of the foot plate  111 . 
     A slide plate  180  (see  FIG.  16   ), which may be constructed of stainless steel, is disposed flat on a substantially central portion of the foot plate  111  nesting between the retainer bars  112 . The slide plate  180  thus remains free-floating, but its lateral and longitudinal position is maintained centrally within and flat against the foot plate  111 . Alternatively the slide plate  180  may be attached to the foot plate  111  such as by welding or connectors (e.g., screws or bolts), but the floating construction may better manage expansion/contraction issues due to different expansion coefficients of the steel types and may also provide for easier construction and/or repair/replacement or allow for expansion of a non-composite plate configuration due to deflection of the foot plate/slide. 
     A low friction plate  190  comprising a flat bushing is disposed underneath the lower surface of the roller guide assembly  200  to provide for a low friction slide surface between the roller guide assembly  200  and the slide plate  180 . The low friction plate  190  may be made of nylon (e.g., a lubricant filled plastic such as Nylatron® plastic available from Quadrant EPP USA, Inc. of Reading, Pa.), PTFE, bronze or other metal, or other suitable plate/sheet material or coated plate. In other embodiments, a lubrication (e.g., grease) may be applied to the slide plate  180 . Alternately, the positions of the slide plate  180  and the low friction plate  190  may be reversed. Alternately, instead of a low friction slide surface configuration, roller bearings or other suitable bearing or roller assembly system may be employed to provide for low friction lateral movement. 
     With collective reference to  FIGS.  14 - 16   , the roller guide assembly  200  comprises a main or bottom plate  210  and first and second roller support sides. The first roller support side comprises a top plate  230  and a vertical wall  234  forming a generally I-beam cross-section with the bottom plate  210 . The top plate  230 , vertical wall  234  and bottom plate  210  collectively form an open channel or track  235 . The top plate  230  is secured to the vertical wall  234  and the bottom plate  210  via a series of eight stiffening ribs, two of which are designated by element numerals  232   a  and  232   b  (see  FIG.  14   ). Similarly, the second roller support side comprises a top plate  220  and a vertical wall  224  forming a generally I-beam cross-section with the bottom plate  210 . The top plate  220 , vertical wall  224  and bottom plate  210  form an open channel or track  225 . The top plate  220  is secured to the vertical wall  224  and the bottom plate  210  via a series of eight stiffening ribs, two of which are designated by element numerals  222   a  and  222   b.    
     Guide tubes  160 ,  170  are attached to the bottom plate  210  on opposite longitudinal sides. The guide tube  160  includes an attachment bracket  164 , and the guide tube  170  includes an attachment bracket  174 . The roller guide assembly  200  is mounted to the foot plate  111  via the guide tubes  160 ,  170  to allow lateral movement. Guide bars  161 ,  171  are disposed on opposite longitudinal sides of the foot plate  111 . Guide bar  161  is secured to the foot plate  111  via brackets  162 ,  166 , and guide bar  171  is secured to the foot plate  111  by brackets  172 ,  176 . Brackets  144 ,  154  are also secured onto the foot plate  111  for attachment to the lateral drive cylinders  140 ,  150 . A cylindrical sleeve or bushing  160   a  of low friction material (e.g., nylon or other suitable material) may be installed within the guide tube  160  and around the guide bar  161 , and a cylindrical sleeve or bushing  170   a  of low friction material is similarly installed within the guide tube  170  and around the guide bar  171 . 
     The lateral drive force is provided by lateral drive cylinders  140 ,  150  attached between the roller guide assembly  200  and the foot plate  111 . The drive cylinder  140  is connected at one end  141  to the bracket  164  via a pin  149 , and at its second end  145  on piston shaft  142  to the bracket  144  on foot plate  111  via pin  146 . Similarly on the other side, the drive cylinder  150  is connected at one end  151  to the bracket  174  via a pin  159 , and at its second end  155  on piston shaft  152  to the bracket  154  on foot plate  111  via pin  156 . Alternate lateral drive force may be provided by any suitable drive mechanism including the piston/cylinder drive (as illustrated), jack screw drive, rack and pinion assembly, chain and sprocket drive, gear drive, electric motor, or other drive systems. 
     The entire lift mechanism  400  and roller guide assembly  200  thus are able to be translated laterally, driven by the hydraulic drive cylinders  140 ,  150 , via the interaction of slide plates  180  and friction plate  190  described previously with reference to  FIG.  16   . Further details relating to the lift assembly  400  and roller guide assembly  200  for accommodating lateral translation movement are described in U.S. Pat. App. No. 2017/00227695, the disclosure of which is incorporated by reference herein. 
     With collective reference to  FIGS.  16 - 18   , the following sections describe details relating to the longitudinal drive assembly  300  for accommodating longitudinal movement of the walking machine. As illustrated in the figures, the longitudinal drive assembly  300  comprises a roller assembly  305  and drive cylinder  310 . With particular reference to the cross-section of  FIG.  18   , the roller assembly  305  includes a roller housing section  322  of generally rectangular box shape formed with two internal channels  331 ,  335  for accommodating the rollers  334 ,  336 . The first internal channel  331  is formed by side walls  326   a ,  326   b , with roller plate  334  attached to the side walls  326   a ,  326   b . The second internal channel  335  is formed by side walls  324   a ,  324   b , with roller plate  336  attached to the side walls  324   a ,  324   b . The rollers  334 ,  336  may comprise chain roller bearings such as available from Hilman Incorporated of Marlboro, N.J. Other low friction or reduced friction systems may be employed for the longitudinal drive assembly  300  in place of the roller assembly  305 , such as other types of bearings, slide surfaces (e.g., a plate bushing), or other suitable construction. 
     With particular reference to  FIG.  17   , the roller assembly  305  includes a drive connection bracket assembly including a U-shaped upper bracket  370  and a U-shaped lower bracket  380 . An attachment bracket  374  is disposed on the end of the upper bracket  370 . A hole  372  is disposed in the end of the upper bracket  370  for connection to the longitudinal drive cylinder  310 . The longitudinal drive cylinder  310  is disposed within a central channel or opening between the (inner) side walls  326   b ,  324   b  and extends into the open inner portion of the U-shaped brackets  370 ,  380 . As illustrated in  FIGS.  15  and  16   , the longitudinal drive cylinder  310  is connected at its shaft end  312  to bracket  240  on the upper roller guide assembly  200  via a pin  313 , and on the other end  314  to upper and lower brackets  370 ,  380  via a pin  315  extending through a hole (not shown) formed in the upper bracket  370  and a corresponding hole (not shown) in the lower bracket  380 . 
     It should be understood that although the longitudinal drive mechanism is shown for example as a hydraulic drive system comprising the longitudinal drive cylinder  310 , other types of longitudinal drive mechanisms may be employed such as the piston/cylinder drive (as illustrated), jack screw drive, rack and pinion assembly, chain and sprocket drive, gear drive, electric motor, or other drive systems. 
       FIGS.  19 A,  19 B, and  19 C  collectively illustrate another embodiment of a walking machine unit  500  (see  FIG.  19 C ) that can be used in conjunction with the walking machine system. The walking machine unit  500  may include some of the same features and characteristics as the walking machine unit  100  described previously with reference to  FIGS.  14 - 18   . Accordingly, certain features of the walking machine unit  500  may be described briefly herein and other features may not be further discussed in detail to avoid obscuring more pertinent features of the embodiment. The following section provides a brief description of the walking machine unit  500  for ease of reference followed by a more detailed description of particular features of the walking machine unit  500 . 
     Briefly, the walking machine unit  500  includes a foot section  510  with a foot plate  511  that contacts the ground surface during a walking motion of the walking machine unit  500 . Similar to foot plate  111 , the foot plate  511  may have a generally rectangular shape with curved ends, or may have any other suitable shape to support movement of the walking machine unit  500 . The foot section  510  includes a plurality of retainer bars secured to and arranged about the upper surface of the foot plate  511 , including retainer bars  512   a ,  512   b ,  512   c ,  512   d  on one lateral side, retainer bars  512   e ,  512   f ,  512   g ,  512   h  on the opposite side, and additional retainer bars  512   i ,  512   j  on a front foot plate section  511   a , and retainer bars  512   k  (second retainer obscured from view) on a rear foot plate section  511   b.    
     Slide plates  580   a ,  580   b , which may be constructed of stainless steel, are disposed flat on the foot plate  511 , with one slide plate  580   a  positioned against the front foot plate section  511   a , and the other slide plate  580   b  positioned against the rear foot plate section  511   b , where the slide plates  580   a ,  580   b  nest between the respective retainer bars  512   a - 512   k  on the foot plate  511 . The slide plates  580   a ,  580   b  thus remain free-floating, but their respective lateral and longitudinal position is maintained centrally within and flat against the foot plate  511 . Alternatively the slide plates  580   a ,  580   b  may be fixedly attached to the foot plate  511  such as by welding or connectors (e.g., screws or bolts), but the floating construction may better manage expansion/contraction issues due to different expansion coefficients of the steel types and may also provide for easier construction and/or repair/replacement or allow for expansion of a non-composite plate configuration due to deflection of the foot plate/slide. 
     The walking unit  500  includes a set of low friction plates  590   a ,  590   b  each comprising a flat bushing, where the plates  590   a ,  590   b  are disposed underneath the lower surface of the roller guide assembly  600  to provide for a low friction slide surface between the roller guide assembly  600  and the slide plates  580   a ,  580   b . As described previously, the low friction plates  590   a ,  590   b  may be made of nylon (e.g., a lubricant filled plastic such as Nylatron® plastic available from Quadrant EPP USA, Inc. of Reading, Pa.), PTFE, bronze or other metal, or other suitable plate/sheet material or coated plate. In other embodiments, a lubrication (e.g., grease) may be applied to the slide plates  580   a ,  580   b . Alternately, the positions of the slide plates  580   a ,  580   b  and the low friction plates  590   a ,  590   b  may be reversed. Alternately, instead of a low friction slide surface configuration, roller bearings or other suitable bearing or roller assembly system may be employed to provide for low friction lateral movement. 
     The roller guide assembly  600  is similar to the roller guide assembly  200  discussed previously with reference to  FIGS.  14 - 16   . Briefly, the roller guide assembly  600  comprises a main or bottom plate  610 , a first roller support side  620 , and a second roller support side  630 . The roller support sides  620 ,  630  each include vertical walls (not numbered) forming a generally I-beam cross-section with the bottom plate  610 . Similar to the roller guide assembly  200 , the roller guide assembly  600  includes a plurality of stiffening ribs (not numbered) extending from the bottom plate  610  to strengthen the roller support sides  620 ,  630 . 
     Similar to the walking machine unit  100 , the lateral drive force for the walking machine unit  500  is provided by lateral drive cylinders  540 ,  550  (see  FIG.  19 C ) attached between the roller guide assembly  600  and the foot plate  511 . The drive cylinder  540  is connected at one end to the bracket  564  via a pin  549 , and at its second end to the bracket  544  on foot plate  511  via pin  546  (see  FIG.  19 B ). The drive cylinder  550  is connected in a similar arrangement to the brackets  554 ,  574  along the other end of the foot plate  511 . Alternate lateral drive force may be provided by any suitable drive mechanism including the piston/cylinder drive (as illustrated), jack screw drive, rack and pinion assembly, chain and sprocket drive, gear drive, electric motor, or other drive systems. 
     The following sections describe details relating to the longitudinal drive assembly for accommodating longitudinal movement of the walking machine. With particular reference to  FIG.  19 C , the longitudinal drive assembly comprises a roller assembly  705  and a pair of drive cylinders  710 ,  712 . The roller assembly  705  includes a roller housing section  720  of generally rectangular box shape formed with two internal channels (not shown) for accommodating a set of rollers  730  (see  FIG.  19 B ). The rollers  730  may comprise chain roller bearings or other low friction or reduced friction systems such as bearings, slides surfaces, or other suitable construction operable to facilitate movement of the roller assembly  705 . In a similar fashion as the roller assembly  305 , the roller assembly  705  is positioned on the roller guide assembly  600  between the roller support sides  620 ,  630  to accommodate longitudinal movement. 
     The drive cylinders  710 ,  712  are attached to the roller support sides  620 ,  630  of the roller guide assembly  600  and also attached to the roller assembly  705  to drive the walking machine unit  500  in a longitudinal direction. With reference to  FIG.  19 A , the drive cylinder  710  is attached along one end to the roller support sides  630  via opening  714  formed thereon, and the drive cylinder  712  is attached along one end to the roller support sides  620  via opening  716  formed thereon. The drive cylinder  710  is also attached along another end to an opening  718  formed on a flange  722  of the roller housing section  720 , and the drive cylinder  712  is also attached along another end to an opening  724  formed on the flange  722  of the roller housing section  720 . It should be understood that although the longitudinal drive mechanism is shown for example as a hydraulic drive system comprising the longitudinal drive cylinders  710 ,  712 , other types of longitudinal drive mechanisms may be employed such as the piston/cylinder drive (as illustrated), jack screw drive, rack and pinion assembly, chain and sprocket drive, gear drive, electric motor, or other drive systems. 
     With particular reference to  FIGS.  20 - 24   , the following sections collectively describe components of the walking machine unit  500  designed to center or accommodate for misalignment during the drive operation when moving a load using the walking machine system.  FIGS.  20 A,  20 B, and  20 C  collectively illustrate an embodiment of a centering fixture (or frame)  800  of the walking unit  500 . With reference to  FIGS.  20 A,  20 B, and  20 C , the centering fixture  800  includes a first support arm  802  and an opposite second support arm  804 . The fixture  800  further includes a second pair of support arms  806 ,  808  each extending transversely across from the first support arm  802  to the second support arm  804  along top and bottom ends to form a generally square-shaped or rectangular-shaped structure for the centering fixture  800 . It should be understood that in other embodiments, the fixture  800  may have a profile other than a square or rectangular shape. 
     The fixture  800  includes a first mounting plate  810  positioned between the first and second support arms  802 ,  804  and adjacent the arm  806 , where the first mounting plate  810  is coupled to the arms  802 ,  804 ,  806 . Similarly, the fixture  800  includes a second mounting plate  812  is positioned between the first and second arms  802 ,  804  and adjacent the arm  808  and coupled thereto. The mounting plates  810 ,  812  each include one or more fastener openings  814  (e.g., bolt holes) for receiving bolts  816  (see  FIG.  19 C ) therethrough to attach the centering fixture  800  to the roller assembly  705  when the walking machine unit  500  is assembled. With reference to  FIG.  20 B , the centering fixture  800  includes an opening  818  disposed between the mounting plates  810 ,  812  and bounded between the support arms  802 ,  804 . The opening  818  aligns with an opening  735  formed on the roller assembly  705  (see  FIG.  19 B ) to accommodate the lift cylinder  520  when the walking machine unit  500  is fully assembled. 
     With reference to  FIG.  20 A , the centering fixture  800  further includes one or more centering members or strike plates  820  supported thereon, the strike plates  820  each providing a contact area for an alignment or centering pivot arm  828  of the walking machine unit  500  as further described in detail below with reference to  FIGS.  21 - 24   . Turning back to  FIG.  20 A , the strike plate  820  is substantially an L-shaped bracket having a first surface  822  and a second surface  824  arranged generally orthogonally to the first surface  822 . In some embodiments, the centering fixture  800  may include four strike plates  820 , with one strike plate  820  coupled to the arms  802 ,  806 ; one strike plate  820  coupled to the arms  804 ,  806 ; one strike plate  820  coupled to the arms  802 ,  808 ; and one strike plate  820  coupled to the arms  804 ,  808 , as illustrated in  FIG.  20 B . In such embodiments, the first surface  822  of the strike plate  820  is arranged along a horizontal plane of the centering fixture  800  and the second surface  824  arranged along a vertical plane of the centering fixture  800 , such that the strike plates  820  each generally wrap around either the first and second support arms  802 ,  804 . In other embodiments, the centering fixture  800  may include only two strike plates, such as where the two strike plates  820  supported on arm  806  are formed as a single, integral unit, and the two strike plates  820  supported on arm  808  are formed as a single, integral unit. 
     In some embodiments, the centering fixture  800  may be made of a welded steel construction. Due to its weight, the centering fixture  800  may be difficult to lift manually during the assembly process. Accordingly, in some embodiments, the centering fixture  800  may include a lift ring  826  (e.g., a D-ring assembly) coupled to one or both arms  806 ,  808  to aid in lifting the centering fixture  800 . 
       FIGS.  21 A and  21 B  are a side elevation and top plan view, respectively, of a centering pivot arm  828  of the walking machine unit  500 , and  FIG.  22    is an exploded view of the centering pivot arm  828 . With collective reference to these figures, the centering pivot arm  828  includes a first pivot arm side plate  830  and a second pivot arm side plate  832 , each having a generally S-shaped curve construction. The centering pivot arm  828  includes a jacking block  834  coupled along one end between the pivot arm side plates  830 ,  832 , and further includes an adjustable bearing block  836  coupled along an opposite end between the side plates  830 ,  832 . In addition, a stainless steel pin  838  extends between the side plates  830 ,  832  and provides an attachment point of the centering pivot arm  828  to the hood assembly  900  (see  FIG.  23   ). 
     With particular reference to  FIGS.  21 A and  21 B , the adjustable bearing block  836  includes at least one contact surface  840 . Preferably, the contact surface  840  is generally flat/planar to reduce bearing pressure in comparison to a round contact surface, but the surface can have any suitable profile. Briefly, the adjustable bearing block  836  corrects for rotational misalignment of the foot, while the foot level contact surface  842  helps ensure the foot is level and parallel to the ground. Additional information on the functionality of the centering pivot arms  828 , adjustable bearing block  836 , and foot leveling contact surface  842  is described in further detail with particular reference to  FIGS.  23 - 25   . In some embodiments, the adjustable bearing block  836  may be made of an ultra-high molecular weight plastic or nylon material to provide some sliding contact and minimize wear. In other embodiments, the adjustable bearing block  836  may instead be a steel block (or other suitable metal), or may be formed from a metal structure and include a plastic contact surface. 
     With reference to  FIGS.  23  and  24   , the following section provides a high-level description of the functionality of the centering pivot arms  828 . Although reference in the following description is made only to one centering pivot arm  828 , it should be understood that the walking machine unit  500  typically includes four pivot arms  828  (two on each of a front side and a rear side of the machine walking unit  500 ) each operating in the same general fashion. Accordingly, it should be understood that the ensuing description applies equally to all such pivot arms. 
     With collective reference to  FIGS.  23  and  24   , the pivot arms  828  are used to re-align the foot section  510  relative to the hood assembly  900  between movements of the load to maintain proper weight distribution of the load being moved. As illustrated in  FIG.  23   , to properly align the foot section  510 , the foot leveling contact surface  842  of the centering pivot arm  828  rests against the first surface  822  of the strike plate  820  (supported on the centering fixture  800 ) to ensure that the foot section  510  is parallel to the ground when the foot section  510  is raised. In addition, the adjustable bearing block  836  on the end of the centering pivot arm  828  rests against the second surface  824  of the strike plate  820  to correct any rotational misalignment of the foot section  510 . 
     For example, with particular reference to  FIG.  24 A , when the foot section  510  is rotated in a counter-clockwise direction relative to a central axis A extending through the centering fixture  800 , the adjustable bearing block  836   a  of a first centering pivot arm  828   a  and the adjustable bearing block  836   b  of a second centering pivot arm  828   b  each contact the corresponding strike plates  820   a ,  820   b  (along the second surfaces  824 ) to force a clockwise rotation of the foot section  510  to correct the misalignment. Similarly, with particular reference to  FIG.  24 B , when the foot section  510  is rotated in a clockwise direction relative to a central axis A extending through the centering fixture  800 , the adjustable bearing block  836   c  of a third centering pivot arm  828   c  and the adjustable bearing block  836   d  of a fourth centering pivot arm  828   d  each contact the corresponding strike plate  820   c ,  820   d  (also along the second surfaces  824 ) to force a counter-clockwise rotation of the foot section  510  to correct the misalignment. 
       FIGS.  25 A,  25 B,  25 C,  25 D,  25 E,  25 F, and  25 G  collectively illustrate an embodiment of the walking machine unit  500  during a series of movements. With reference to these figures, the following provides a brief step-by-step illustration of the functionality of the centering pivot arms  828  in conjunction with the centering fixture  800  for realigning the foot section  510  during a movement phase of the walking machine unit  500 . 
     With reference to  FIG.  25 A , in step  1 , the lift cylinder  520  is in a fully retracted position to lift the foot section  510  off the ground. In this position, the centering pivot arms  828  rest against the strike plate  820  on the centering fixture  800  to maintain the foot section  510  properly aligned, with the foot leveling contact surface  842  resting against the first surface  822  of the strike plate  820 , and the adjustable bearing block  836  rests against the second surface  824  of the strike plate  820  (see  FIGS.  20 - 21   ). 
     With reference to  FIG.  25 B , in step  2 , the lift cylinder  520  is extended from its initial position in step  1  (in this embodiment, the lift cylinder extends approximately three inches). In this configuration, the adjustable bearing block  836  is no longer in contact with the strike plate  820 , as the lift cylinder  520  moves and causes the centering pivot arms  828  to pivot away from the edges of the centering fixture  800 . The foot leveling contact surface  842  (see  FIG.  21 A ) of the centering pivot arms  828  remains in contact with the strike plate  820  due to articulation of the centering pivoting arms  828 . In some embodiments, the pivoting movement of the centering pivot arms  828  may be due to gravitational forces, or may be urged by a spring, actuator or air cylinder, a linkage, or other suitable methods. In step  2 , rotation of the foot section  510  may begin (or be completed) if the walking machine unit  500  is being used to rotate the load being carried. In a given walking cycle, the walking machine unit  500  may be able to rotate the foot section  510  (and the load being carried) by about 5° from its initial position. 
     With reference to  FIG.  25 C , in step  3 , the lift cylinder  520  is extended another three inches for a total of six inches of extension. In this configuration, the adjustable bearing block  836  remains out of contact with the strike plate  820  and a smaller surface of the centering pivot arms  828  (as compared to step  2 ) remains contacting the strike plate  820 . As the lift cylinder  520  is extended, the load carried by the walking machine unit  500  begins to be lifted off the ground. 
     With reference to  FIG.  25 D , in step  4 , the lift cylinder  520  is extended another three inches for a total of nine inches of extension. In this configuration, there is no contact between the centering pivot arms  828  and the centering fixture  800 , as the foot section  510  fully contacts the ground surface. In some embodiments, the lift cylinder  520  may not need to be fully extended to nine inches (e.g., six-inch extension as shown in step  3  is sufficient) to lift the load. The nine-inch extension of the lift cylinder  520  may be used to provide additional clearance for the load to accommodate a walking cycle. For example, if one of the legs  55  of the oil rig  10  (see  FIG.  1   ) required additional clearance to avoid rocks or other debris, then the lift cylinder  520  may be extended to nine inches if the six-inch extension was insufficient. 
     With reference to  FIG.  25 E , in step  5 , the lift cylinder  520  is retracted three inches such that the lift cylinder  520  returns to a six-inch extension. When the lift cylinder  520  retracts, the centering pivot arms  828  again contacts the strike plate  820 , where the strike plate  820  assists in articulation of the centering pivot arms  828 . 
     With reference to  FIG.  25 F , in step  6 , the lift cylinder  520  is retracted another three inches such that the lift cylinder  520  returns to a three-inch extension. In this configuration, while the foot section  510  continues being lifted away from the ground, the foot leveling contact surface  842  of the centering pivot arms  828  contacts the strike plate  820  and begins to reduce the capture area to begin the realignment action. 
     Finally, with reference to  FIG.  25 G , in step  7 , the lift cylinder  520  is fully retracted, thereby pulling the foot section  510  off the ground. In this configuration, the adjustable bearing block  836  contacts the strike plate  820  to realign the foot section  510  against any rotational movement. With the centering pivot arms  828  arranged back to their initial position (as illustrated in step  1 ), the walking cycle begin again with step  1  and so on until the walking machine system has reached its final destination. 
       FIGS.  26 - 30    collectively illustrate another embodiment of a walking machine unit  1000  designed to center and accommodate for load misalignment during the drive operation when moving a load using the walking machine system. The following description of  FIGS.  26 - 30    focuses on aspects of the walking machine unit  1000  relating particularly to managing load alignment. Accordingly, further details regarding other features of the walking machine system (such as longitudinal or lateral drive assemblies) may not be further discussed in detail to avoid obscuring more pertinent features of the embodiment. The following section provides a brief description of the walking machine unit  1000  for ease of reference followed by a more detailed description of particular features of the walking machine unit  1000  designed for load alignment management. 
       FIG.  26    illustrates an example embodiment of the walking machine unit  1000  attached to a rig structure  1400 , and  FIG.  27    is an exploded view of the walking machine unit  1000 . With particular reference to  FIG.  27   , the following provides a brief description of various components of the walking machine unit  1000 . As illustrated in  FIG.  27   , the walking machine unit  1000  includes a foot section  1010  having a foot plate  1011  that contacts the ground surface during a walking motion of the walking machine unit  1000 . Similar to the foot plates  111 ,  511  described previously, the foot plate  1011  may have a generally rectangular shape with curved ends, or may have any other suitable shape to support movement of the walking machine unit  1000 . The foot section  1010  supports one or more slide plates  1020 , which may be laid flat against the foot plate  1011  and nested between various retainer bars  1030  of the foot section  1010  to facilitate movement of the walking machine unit  1000  in a similar fashion as described with reference to previous embodiments. 
     The walking machine unit  1000  further includes a roller guide assembly  1040  for accommodating lateral movement of the walking machine, the roller guide assembly  1040  having similar features as the roller guide assemblies  200 ,  600  described previously. Similar to the previous embodiments, the lateral drive force for the walking machine unit  1000  is provided by lateral drive cylinders  1050 ,  1060  attached along front and rear ends of the foot plate  1011 . An alternate lateral drive force may be provided by any suitable drive mechanism including the piston/cylinder drive (as illustrated), jack screw drive, rack and pinion assembly, chain and sprocket drive, gear drive, electric motor, or other drive systems. 
     The walking machine unit  1000  further includes a longitudinal drive assembly having similar features as the longitudinal drive assemblies described previously. Briefly, the assembly includes a roller assembly  1070  and a pair of drive cylinders  1080 ,  1090  attached to the roller assembly  1070  to drive the walking machine unit  1000  in a longitudinal direction. The roller assembly  1070  may include the same or similar components as described previously with respect to roller assembly  705 , including longitudinal drive cylinders  1080 ,  1090  arranged in a similar fashion as described previously. It should be understood that although the longitudinal drive mechanism is shown for example as a hydraulic drive system comprising the longitudinal drive cylinders  1080 ,  1090 , other types of longitudinal drive mechanisms may be employed such as the piston/cylinder drive (as illustrated), jack screw drive, rack and pinion assembly, chain and sprocket drive, gear drive, electric motor, or other drive systems. 
     With general reference to  FIGS.  26 - 29   , the following sections collectively describe components of the walking machine unit  1000  designed to center or accommodate for load misalignment during the drive operation of the walking machine system.  FIG.  28    illustrates an embodiment of a centering fixture (or frame)  1100  of the walking unit  1000 , and  FIG.  29    illustrates an embodiment of an alignment plate  1220  that operates in conjunction with the centering fixture  1100  to ensure the load is properly aligned during movement of the walking machine. With reference to  FIG.  28   , the centering fixture  1100  includes a first arm  1102  and an opposite second arm  1104  offset from one another, each of which extending along a longitudinal axis. A first plate  1106  is attached along an end of the first arm  1102  and along an end of the second arm  1104 , where the plate  1106  extends transversely across the first and second arms  1102 ,  1104 . Similarly, the fixture  1100  includes a second plate  1108  extending across from the first arm  1102  to the second arm  1104 , the first and second plates  1106 ,  1108  being offset from one another and extending along a horizontal axis. In this configuration, the arms  1102 ,  1104  and plates  1106 ,  1108  form a generally square-shaped or rectangular-shaped structure for the centering fixture  1100 . It should be understood that in other embodiments, the fixture  1100  may have a profile other than a square or rectangular shape. 
     The fixture  1100  further includes a mounting plate  1110  disposed between the arms  1102 ,  1104  and the plates  1106 ,  1108 . The mounting plate  1110  includes one or more fastener openings  1120  (e.g., bolt holes) extending therethrough for receiving bolts  1130  (see  FIG.  27   ) to attach the centering fixture  1100  to the roller assembly  1070  when the walking machine unit  1000  is assembled. As illustrated in  FIG.  28   , the centering fixture  1100  includes an opening  1140  disposed along a central portion of the mounting plate  1110 . In an assembled configuration, the opening  1110  aligns with an opening  1150  formed on the roller assembly  1070  (see  FIG.  27   ) to accommodate a lifting cylinder  1160  when the walking machine unit  1000  is fully assembled. As described in previous embodiments, the lifting cylinder  1160  is used to create a lifting force needed to operate the walking machine and transport the load. 
     Returning to  FIG.  28   , the fixture  1100  further includes a plurality of alignment posts  1170 ,  1180 ,  1190 ,  1200 , each of which extending outwardly relative to the plates  1106 ,  1108 . In one embodiment, the fixture  1100  may include four alignment posts, with a pair of alignment posts  1170 ,  1180  aligned along a common axis extending through the first arm  1102  such that the alignment post  1170  is positioned adjacent a first end of the first arm  1102  and the alignment post  1180  is positioned adjacent an opposite second end of the first arm  1102 . Similarly, the second pair of alignment posts  1190 ,  1200  are aligned along a common axis extending through the second arm  1104  in a similar arrangement as described previously with respect to the alignment posts  1170 ,  1180 . 
     The configuration of the alignment posts  1170 ,  1180 ,  1190 ,  1200  described above can be achieved in any one of various suitable designs. For example, in one embodiment, the alignment posts may be formed as integral components of the respective arms  1102 ,  1104 . In one such embodiment, the arms  1102 ,  1104  may be sufficiently long such that a portion of the arm shaft extends outwardly and beyond the mounting plates  1106 ,  1108  when coupled, thereby forming the adjustment posts described previously. To accommodate this design, the mounting plates  1106 ,  1108  may each include openings (not shown) through which the arms  1102 ,  1104  receive the mounting plates  1106 ,  1108 . Once the mounting plates  1106 ,  1108  are secured, a portion of the arms  1102 ,  1104  extends through the openings and protrudes beyond the mounting plates  1106 ,  1108 , thereby forming the alignment posts illustrated in  FIG.  28   . 
     In other embodiments, the alignment posts  1170 ,  1180 ,  1190 ,  1200  may instead be separate components apart from the arms  1102 ,  1104 . In such embodiments, the alignment posts may be threaded into or otherwise secured to either the mounting plates  1106 ,  1108  or the arms  1102 ,  1104  in various suitable designs. In still other embodiments, the alignment posts  1170 ,  1180 ,  1190 ,  1200  may be formed in different configurations without departing from the principles of the disclosure. 
     In some embodiments, the alignment posts  1170 ,  1180 ,  1190 ,  1200  may be wrapped with a durable, wear resistant cover  1210  (see  FIG.  27   ) or other suitable protective material to increase the durable life of the alignment posts and to facilitate repair when needed. In other embodiments, the alignment posts may not have a cover and instead be made of durable materials themselves. 
       FIG.  29    illustrates an example embodiment of an alignment plate  1220  of the walking machine unit  1000  that operates in conjunction with the alignment posts  1170 ,  1180 ,  1190 ,  1200  to ensure proper load alignment. The ensuing section provides details of the alignment plate  1220 , followed by a brief description of the functionality of the alignment posts  1170 ,  1180 ,  1190 ,  1200  and the alignment plate  1220  within the walking machine unit  1000 . 
     With reference to  FIG.  29   , the alignment plate  1220  is a general planar structure having a header end  1230 , an opposite footer end  1240 , and peripheral sides  1250 ,  1260 . The front and rear surfaces of the alignment plate  1220  include a plurality of openings  1270  extending therethrough, the openings  1270  designed for receiving fasteners  1280  therethrough affix the alignment plate  1220  in position (see  FIG.  26   ). As illustrated in  FIG.  29   , the footer end  1240  of the alignment plate  1220  includes notches  1290 ,  1300  formed thereon. The notches  1290 ,  1300  each include slide surfaces  1310 ,  1320  that lead toward a seat  1330 ,  1340  at the uppermost region of the notches  1290 ,  1300 . Preferably, the seat  1330 ,  1340  has a surface profile designed to correspond with the exterior profile of the adjustment posts  1170 ,  1180 ,  1190 ,  1200 . For example, in the illustrated embodiments, the adjustment posts  1170 ,  1180 ,  1190 ,  1200  are circular, and the seats  1330 ,  1340  are curved with a radius matching that of the circular adjustment posts  1170 ,  1180 ,  1190 ,  1200  to ensure proper engagement. As further described in detail below, the notches  1290 ,  1300  on the alignment plate  1220  and the alignment posts  1170 ,  1180 ,  1190 ,  1200  on the centering fixture  1100  operate together to center and align the load being transported on the walking machine units  1000 . 
     With collective reference to  FIGS.  26  and  29   , the following section provides a description of the functionality of the alignment posts  1170 ,  1180 ,  1190 ,  1200  and the centering fixture  1100  within the walking machine unit  1000 . Although reference in the following description is made to operation of only one pair of adjustment posts  1170 ,  1190 , it should be understood that the walking machine unit  1000  typically includes multiple such posts (e.g., two on each of a front side and a rear side of the machine walking unit  1000 ) each operating in the same general fashion. Accordingly, it should be understood that the ensuing description applies equally to all such adjustment posts. 
     An example operation of a walking machine unit  500  and lifting cylinder  520  was previously discussed with reference to  FIGS.  25 A,  25 B,  25 C,  25 D,  25 E,  25 F, and  25 G . With reference to walking machine unit  1000  of  FIGS.  26 - 29   , the lifting cylinder  1160  and walking foot section  1010  operate in a substantially similar fashion. In other words, the lifting cylinder  1160  cycles through various extended positions to lift the foot section  1010  off the ground and move the load. The following description focuses primarily on the interaction of the alignment posts  1170 ,  1180 ,  1190 ,  1200  and the alignment plate  1220 . 
     During the walking operation, the alignment plate  1220  is raised away from the centering fixture  1100  such that the alignment posts  1170 ,  1190  are not in contact with the notches  1290 ,  1300 . As the walking operation continues, the alignment plate  1220  is brought together toward the centering fixture  1100 . When the load is properly aligned, the alignment posts  1170 ,  1190  of the centering fixture  1100  are seated in the seats  1330 ,  1340  of the respective notches  1290 ,  1300  to maintain the foot section  1010  in a proper, level position.  FIG.  29    illustrates an occasion when the foot section  1010  is not in proper position. With reference to  FIG.  29   , the alignment posts  1170 ,  1190  are positioned against the slide surfaces  1310 ,  1320 , respectively. From this position, the angled slide surfaces  1310 ,  1320  guide the adjustment posts  1170 ,  1190  toward the seats  1330 ,  1340 , thereby shifting the foot section  1010  into proper position. In some embodiments, the centering fixture  1100  and alignment plate  1220  may shift the foot section  1010  by up to 5°. In other embodiments, larger or smaller corrections may be made. With the load centered, the walking operation continues on its next cycle until the load is transported to its desired position. 
       FIG.  30    is a top perspective view of a walking machine system according to an example embodiment, with four walking machine units  1100 , one disposed at each of the four corners of a rig structure  1400 . It should be understood that in other embodiments, more or fewer walking machine units  1100  may be used depending on various factors, such as size and weight of the load. 
     Other embodiments are envisioned. Although the description above contains certain specific details, these details should not be construed as limiting the scope of the invention, but as merely providing illustrations of some embodiments/examples. It should be understood that subject matter disclosed in one portion herein can be combined with the subject matter of one or more of other portions herein as long as such combinations are not mutually exclusive or inoperable. 
     The terms and descriptions used herein are set forth by way of illustration only and not meant as limitations. It will be obvious to those having skill in the art that many changes may be made to the details of the above-described embodiments without departing from the underlying principles of the invention.