Abstract:
A linear water feed apparatus for use in agricultural irrigation includes a linear-move machine with a mobile truss assembly supporting a plurality of individual sprinklers and adapted for movement in a specified direction across a field to be irrigated. The truss assembly is oriented transverse to the specified direction, and a supply pipe is arranged in the specified direction along or within the field to be irrigated. The supply pipe mounts a plurality of water supply hydrants at spaced locations along the pipe, each of the hydrants enclosing a water supply valve. A docking station is supported at one end of the truss assembly closest to the supply pipe, and is adapted to engage and open successive ones of the water supply valves in the plurality of hydrants. The docking station assembly includes a docking station that is suspended from a frame for floating movement about at least three mutually perpendicular axes.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     This invention relates to apparatus used for agricultural irrigation, and more specifically, to a linear water feed mechanism that automatically and successively engages and disengages spaced hydrants mounted on a water supply pipe extending alongside or through a field to be irrigated.  
         [0002]     Mobile irrigation systems having elevated boom or truss assemblies carrying multiple sprinklers are typically of the center pivot-type or the linear- (or lateral-) move-type. In a center-pivot machine, the elevated truss assembly pivots about an upright standpipe that supplies water to the sprinklers attached to the truss assembly. In a linear-move machine, the elevated truss assembly is carried on mobile, wheeled towers that move the machine linearly along a path that is perpendicular to the elevated boom or truss. Typically, the linear-move machine travels from one end of a field to the other and back again, and sprinkling typically occurs in both directions.  
         [0003]     While linear-move machines can irrigate more area than center-pivot machines by reason of the resulting rectangularly-shaped irrigation pattern, the linear-move machines have proven to be problematic in several respects. The most significant problem relates to the manner in which water is supplied to the machine. In some cases, the machine travels alongside an open ditch or canal from which water is continuously removed. Ditch water is typically filled with dirt and/or debris that can clog the sprinkler nozzles. In other cases, one or more hoses are dragged by the machine the length of the field, requiring one or more manual attachment/detachment procedures and attendant issues of hose management. In still other cases, complex mechanisms have been proposed for automatic docking with hydrants spaced along the length of a water supply pipe. One of the problems with this arrangement is that the hydrant risers have had to be held firmly in concrete or welded onto steel pipe. Alignment mechanisms have been complex and costly to maintain. As a result, reliable docking under various conditions has proven to be an elusive goal, and we are unaware of any automatic docking mechanisms that have achieved a significant degree of commercial success to date.  
       BRIEF DESCRIPTION OF THE INVENTION  
       [0004]     This invention relates to a unique “floating” docking station assembly that can be added to essentially any new or existing linear-move machine. The docking station assembly is supported and controlled so as to reliably and effectively capture each hydrant, open the hydrant water-supply valve to permit water to be supplied to the sprinklers on the truss assembly, close the valve, and then disengage from the hydrant for movement with the machine to the next hydrant. The “floating” docking station as described herein also minimizes the load placed on the hydrant, thus permitting a simpler main line construction.  
         [0005]     The docking station per se is formed by a pair of housings sandwiched about a hydrant valve actuator. The two housings support multiple pairs of guide wheels adapted to engage a round plate or flange on the hydrants. The housings also support docking stops and related mechanical and electrical hardware for halting the movement of the machine and docking station when properly aligned with the hydrant valve, opening and closing the valve, and subsequently permitting the resumption of machine movement after the allotted sprinkling time has expired. The docking station is resiliently suspended, or hung, from a supporting frame that, in turn, supports related hydraulic and electrical hardware as described in further detail below.  
         [0006]     Two pairs of vertically-oriented, angled guide wings respectively mounted on the front and back of the docking station supporting frame, along with one pair of horizontally-oriented front and back guide wings, assist in “capturing” the hydrants on the water supply pipe. In this regard, the docking station is operable in opposite forward and rearward directions of movement of the linear-move machine, with no change or adjustment in any of the component parts. For purposes of this application, therefore, any use of “front” or “forward,” etc. is intended to refer to the ends of the machine, docking station, etc. that lead in the direction of initial movement of the machine, i.e., along a path P 1  as shown in  FIG. 1 . Use of “back” or “rearward,” etc. is intended to refer to the opposite ends of the machine, docking station, etc. that trail in the movement along path P 1  but that lead in movement in the opposite direction along a path P 2 .  
         [0007]     To ensure consistent and effective hydrant engagement via interaction with the guide wings, the docking station is arranged and supported so as to permit several degrees of movement:  
         [0008]     1. The docking station is resiliently suspended or hung from its supporting frame by elongated coil springs (or equivalents) extending vertically between the docking station and the docking station supporting frame to enable up and down or vertical movement, but also to facilitate front-to-back, side-to-side and compound movements, i.e., tilting and twisting movements.  
         [0009]     2. Spring-loaded, compressible tie rods extend horizontally between the supporting frame and docking station utilizing swivel bushings to enable front-to-back horizontal movement, but also to facilitate the limited vertical, side-to-side and compound movements.  
         [0010]     3. The docking station and its supporting frame are also movable laterally on a carriage or trolley along a pair of rails extending perpendicularly to the path of movement of the machine so as to permit a wide range of lateral adjustment to accommodate a similarly wide range of hydrant misalignment situations.  
         [0011]     In addition to movements that relate to hydrant capture, the docking station trolley is also movable to any number of positions along a rigid side beam secured to one side of a drive tower of the linear-move machine. This allows for manual or automatic adjustment of the water distribution pattern between the forward and return movements of the linear-move machine, or for subsequent forward movements along the path as further described herein.  
         [0012]     In order to facilitate the docking operation, a new hydrant design has been adopted for use with the docking station of the linear-move machine. The hydrant in accordance with an exemplary embodiment includes a standard vertical pipe or riser fixed to the water supply pipe. At the upper end of the riser, a valve housing is attached by any suitable means and incorporates a spring-loaded valve assembly. The upper end of the valve housing is formed with an exterior, round, horizontal flange or plate that cooperates with the docking station during capture of the hydrant. The valve itself projects above the top of the flange to facilitate alignment with the hydrant valve actuator on the docking station. Alternatively, existing hydrant risers with compatible valves may be modified simply to include the round flange or plate to facilitate capture. Another alternative is the use of a conversion kit to render existing hydrants compatible with the docking station.  
         [0013]     The hydrant valve actuator carried by the docking station includes a housing that incorporates a piston/cylinder, the piston portion of which is movable within an enlarged chamber in the actuator housing. “Extend” and “retract” cavities are formed on either side of (i.e., above and below) the piston portion (or simply “piston”) with the assistance of a pair of rolling diaphragms attached between the piston and the actuator housing. Briefly, water under pressure introduced into the “extend” diaphragm cavity will push the piston/cylinder downwardly such that the lower edge of the cylinder will engage the hydrant valve and push it downwardly away from the valve seat to open the valve. Water can then be supplied to the sprinklers on the truss assembly via another conduit connecting the valve actuator to a distribution pipe on the truss assembly. When a pre-programmed sprinkling time has expired, water under pressure introduced into the “retract” cavity will drive the piston/cylinder upwardly and back into the hydrant valve actuator, closing the valve prior to movement to the next hydrant.  
         [0014]     It is another feature of the invention to facilitate different operating modes for the linear-move machine. For example, the machine may be used in a simple start/stop irrigation mode where the docking station is fixed to the side beam at the desired location, and the machine moves from hydrant to hydrant, stopping at each for a pre-programmed period of time for sprinkling. The water supply is cut off by a main control valve while the machine moves to the next hydrant.  
         [0015]     It is also possible to manually adjust the position of the docking station along the side beam to vary the sprinkling pattern, for example, on the return path of the linear-move machine, to thereby provide more uniform application of water in the irrigated field. Alternatively, well-known drive and control devices may be utilized to automatically move the docking station along the side beam from one position to another.  
         [0016]     In another mode, a second movable side beam may be mounted adjacent the first fixed side beam. The docking station is mounted on the second movable beam (or telescoping arm) for movement from one end of the arm to the other, while the telescoping arm itself is movable from an extended forward position to an extended rearward position relative to the fixed beam. This arrangement allows the docking station to engage a first hydrant, with the docking station at the forward end of the telescoping arm, and the telescoping arm in its extended forward position. As the linear-move machine (and fixed beam) moves forwardly, the telescoping arm slides (relative to the fixed side beam and hence the machine as a whole) to an extended rearward position, causing the docking station to be driven to the rearward end of the telescoping arm. After disengagement from the first hydrant valve, the telescoping arm and docking station are moved to their extended forward positions for engagement with the second hydrant valve. This cycle is repeated as the linear-move machine continues to travel the length of the field.  
         [0017]     In a full automatic mode, additional hardware changes are required. In the exemplary embodiment, parallel inner and outer fixed beams are attached to the end tower of the linear-move machine, and a docking station is mounted for reciprocatory movement on each. Flexible hoses connect each docking station to the distribution pipe on the truss assembly of the linear-move machine. At the same time, the water supply pipe is modified to the extent that alternate hydrants are offset in opposite lateral directions from the supply pipe to permit engagement with the respective inner and outer docking stations. The docking stations are movable along the respective inner and outer fixed beams by any suitable drive mechanism. In an exemplary mode of operation, the outer docking station will be located at the forward end of the outer fixed beam and engage a first outer hydrant. As the linear-move machine moves forward, the outer docking station will remain engaged and the inner docking station will move along the inner fixed beam and into engagement with the first inner hydrant. The outer docking station will disengage the first outer hydrant and move forward on the fixed outer beam, as the linear-move machine continues to move forward. This “leap-frog” process is repeated as the linear-move machine continues to travel along its path. In this way, no periodic shutdowns of the machine are required.  
         [0018]     In all cases, the various operations of the linear-move machine and docking station(s) are controlled by a Programmable Logic Controller (PLC) located on the drive tower of the linear-move machine, operatively connected to a series of solenoids carried by the docking station supporting frame that control the various mechanical movements of the components. The PLC may be electronically “inserted between” the linear-move machine&#39;s PLC and the linear-move machine itself to permit seamless integration of the operation of both the linear-move machine and one or more docking stations.  
         [0019]     Accordingly, in one aspect, the invention relates to a linear water feed apparatus for use in agricultural irrigation comprising a linear-move machine including a mobile truss assembly supporting a plurality of individual sprinklers and adapted for movement in a specified direction across a field to be irrigated, the truss assembly oriented transverse to the specified direction; a supply pipe arranged in the specified direction along or within the field to be irrigated, the supply pipe mounting a plurality of water supply hydrants at spaced locations along the pipe, each of the hydrants enclosing a water supply valve; and a docking station supported at one end of the truss assembly closest to the supply pipe, and adapted to engage and open successive ones of the water supply valves in the plurality of hydrants, the docking station assembly including a docking station suspended from a first frame for floating movement about at least three mutually perpendicular axes.  
         [0020]     In another aspect, the invention relates to a linear water feed for use in agricultural irrigation comprising a linear water feed machine including a wheel-mounted truss assembly supporting a plurality of individual sprinklers and adapted for movement in a specified direction across a field to be irrigated, the truss assembly oriented transverse to the specified direction; a supply pipe arranged in the specified direction along or within the field to be irrigated, the supply pipe mounting a plurality of water supply hydrants at spaced locations along the pipe, each of the hydrants enclosing a water supply valve; and a docking station supported on a first frame that is attached to an end of the truss assembly closest to the supply pipe, adapted to locate, engage and open successive ones of said water supply valves in the plurality of hydrants, the docking station supported for movement on a trolley in a direction substantially transverse to the specified direction, wherein the trolley includes a pair of parallel rails extending beyond the wheeled truss assembly, and further wherein the first frame is provided with plural rollers engaged with each of the parallel rails.  
         [0021]     In another aspect, the invention relates to a linear water feed for use in agricultural irrigation comprising a linear water feed machine including a wheel-mounted truss assembly supporting a plurality of individual sprinklers and adapted for movement in a specified direction across a field to be irrigated, the truss assembly oriented transverse to the specified direction; a supply pipe arranged in the specified direction along or within the field to be irrigated, the supply pipe mounting a plurality of water supply hydrants at spaced locations along the pipe, each of the hydrants enclosing a water supply valve; and a docking station supported on a first frame that is attached to an end of the truss assembly closest to the supply pipe, and adapted to engage and open successive ones of the water supply valves in said plurality of hydrants; wherein said docking station is supported at the one end of the truss assembly by means for allowing the docking station to move in up and down, side-to-side and front to back directions, and for allowing the docking station to simultaneously tilt and swivel relative to the first frame.  
         [0022]     In still another aspect, the invention relates to a linear water feed apparatus for use in agricultural irrigation comprising a linear-move machine including a mobile truss assembly supporting a plurality of individual sprinklers and adapted for movement in a specified direction across a field to be irrigated, the truss assembly oriented transverse to the specified direction; a supply pipe arranged in the specified direction along or within the field to be irrigated, the supply pipe mounting a plurality of water supply hydrants at spaced locations along the pipe, each of the hydrants enclosing a water supply valve; and a fixed side beam mounted on one end of the truss assembly closest to the supply pipe extending substantially parallel to the supply pipe; a telescoping arm mounted on the fixed side beam for movement in two opposite and parallel directions relative to the fixed side beam; a docking station including a support frame mounted on the telescoping arm for movement along the telescoping arm in the two opposite directions; the docking station resiliently suspended from the supporting frame for vertical, horizontal and compound movements.  
         [0023]     In still another aspect, the invention relates to a linear water feed apparatus for use in agricultural irrigation comprising a linear-move machine including a mobile truss assembly supporting a plurality of individual sprinklers and adapted for movement in a specified direction across a field to be irrigated, the truss assembly oriented transverse to the specified direction; a supply pipe arranged in the specified direction along or within the field to be irrigated, the supply pipe mounting a plurality of water supply hydrants at spaced locations along the pipe, the hydrants alternately offset in opposite transverse directions from the supply pipe, each of the hydrants enclosing a water supply valve; and a pair of laterally spaced, inner and outer beams fixed to a side of the truss assembly closest to the water supply pipe; a docking station including a supporting frame mounted on each of the pair of laterally-spaced inner and outer beams, each docking station having a hydrant valve actuator in fluid communication with a distribution pipe in the truss assembly, wherein the docking station on the inner beam is adapted to engage hydrants offset in one direction from the supply pipe, and the docking station on the outer beam adapted to engage hydrants offset in the opposite direction from the supply pipe.  
         [0024]     The invention will now be described in more detail in connection with the drawings identified below. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0025]      FIG. 1  is a schematic plan view of a linear-move machine incorporating a docking station in accordance with the subject invention;  
         [0026]      FIG. 2  is an enlarged plan view, primarily in schematic form, illustrating the docking station mounted to the side of an end tower of the linear-move machine illustrated in  FIG. 1 ;  
         [0027]      FIG. 3  is a perspective view of the docking station and end tower of the linear-move machine shown in  FIG. 2 ;  
         [0028]      FIG. 4  is a left side elevation of the apparatus shown in  FIG. 2 ;  
         [0029]      FIG. 5  is a front elevation of the apparatus shown in  FIGS. 2-4 ;  
         [0030]      FIG. 6  is an enlarged side elevation of the docking station taken from  FIG. 4 ;  
         [0031]      FIG. 7  is an enlarged detail of the docking station in plan view, as shown in  FIG. 2 ;  
         [0032]      FIG. 8  is a perspective view of one of two docking station housings incorporated in the docking station shown in  FIGS. 1-7 ;  
         [0033]      FIG. 9  is a perspective view taken from the opposite side of the docking station housing shown in  FIG. 8 ;  
         [0034]      FIG. 10  is a perspective view of the hydrant valve actuator incorporated in the docking station in  FIGS. 1-7 ;  
         [0035]      FIG. 11  is a partial perspective view of an upper portion of the docking station shown in  FIGS. 1-7 , including the docking station trolley and supporting frame;  
         [0036]      FIG. 12  is a perspective view similar to  FIG. 11 , but rotated 90°;  
         [0037]      FIG. 13  is a partial simplified side elevation of the docking station when in initial engagement with a hydrant;  
         [0038]      FIG. 14  is a view similar to  FIG. 13  but directionally reversed and with the hydrant fully engaged and aligned within the docking station;  
         [0039]      FIG. 15  is a rear elevation view of the docking station and hydrant as shown in  FIG. 13 , with the hydrant fully engaged within the docking station;  
         [0040]      FIG. 16  is a simplified plan view of the docking station, with vertical and horizontal guide wings and suspension components removed;  
         [0041]      FIG. 17  is a right front perspective view of the docking station and hydrant shown in  FIG. 15 ;  
         [0042]      FIG. 18  is a cross section taken through the hydrant valve and hydrant valve actuator, in a valve closed position and with the hydrant fully engaged within the docking station;  
         [0043]      FIG. 19  is a view similar to  FIG. 18  but with the hydrant valve shown in a valve open position;  
         [0044]      FIG. 20  is a view similar to  FIG. 14  but showing the docking station disengaged and moving away from the hydrant;  
         [0045]      FIG. 21  is a schematic diagram of the control systems for the linear-move machine and docking station;  
         [0046]      FIG. 22  is an overhead schematic illustrating a sprinkling pattern achieved when the docking station is centrally located along the side beam fixed to the end tower of the linear-move machine;  
         [0047]      FIG. 23  is a view similar to that shown in  FIG. 22 , but with the docking station moved toward a forward end of the side beam attached to the linear-move machine;  
         [0048]      FIG. 24  is a view similar to  FIGS. 22 and 23 , but with the docking station located at a rearward end of the side beam attached to the linear-move machine;  
         [0049]      FIG. 25  is an overhead illustrating the different sprinkler patterns that are achievable with the docking station located in the positions shown in  FIGS. 22, 23  and  24 ;  
         [0050]      FIG. 26  is a flow chart illustrating the control sequence for the linear-move machine and docking station in a start/stop mode of operation;  
         [0051]      FIG. 27  is a partial elevation of a linear-move machine incorporating a docking station in accordance with another exemplary embodiment of the invention;  
         [0052]      FIG. 28  is a partial perspective view of the linear-move machine shown in  FIG. 27 ;  
         [0053]      FIG. 29  is a front elevation of the linear-move machine shown in  FIG. 27 ;  
         [0054]      FIG. 30  is an enlarged detail taken from  FIG. 28 ;  
         [0055]      FIG. 31  is an enlarged detail taken from the opposite end of the machine shown in  FIG. 29 ;  
         [0056]      FIG. 32  is a partial side elevation similar to  FIG. 27 , but with the telescoping arm and docking station moved to an extended rearward position; and  
         [0057]      FIG. 33  is a schematic drawing of a continuous docking configuration in accordance with another embodiment of the invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0058]     With reference initially to  FIG. 1 , a typical linear-move irrigation machine  10  includes a main truss assembly  12  supported by several wheeled towers  14  for movement in a forward direction along a linear path P 1 , or in a rearward direction along an opposite path P 2 . These paths extend perpendicularly to the truss assembly  12 , and parallel to a water supply pipe  26 . A drive tower  16  typically supports a generator (not shown) for supplying power to the drive wheels  18 . In an end-feed arrangement, the drive tower is located at one end of the field, and the supply pipe  26  runs along that end of the field. In a center-feed machine, the drive tower is typically located in the center of the field and the supply pipe also runs through the center of the field. Separate electric motors (also not shown) are often attached to the remaining towers  14  for driving the respective wheel pairs  20  as needed to maintain alignment with the end tower  16  and associated drive wheels  18 . Other drive arrangements including the utilization of battery power and/or electric drive motors connected to a power source by a cable could be employed.  
         [0059]     Guide booms  22 ,  24  extend in opposite directions from the end tower  16  (parallel to the paths P 1  and P 2 ), and are engaged in a guide furrow F adjacent and parallel to the supply pipe  26  to thereby guide and maintain the machine in the desired path. Typically, if the guide booms stray laterally from the furrow beyond a predetermined limit, the machine will shut down. Other guide arrangements including the use of electronic and/or optical sensors, wire, GPS, etc. may be utilized as well.  
         [0060]     The water supply pipe  26  is fitted with spaced hydrants  28  that supply water to the machine  10  for distribution through a distribution pipe  27  (see  FIGS. 4 and 5 ) on the truss assembly and ultimately to the sprinklers (one shown at  29  in  FIG. 5 ) suspended from the boom assembly  12 , at spaced locations therealong. The supply pipe  26  is shown above ground, but may be underground, with only the hydrants  28  visible. The linear-move machine  10  as described is generally well-known, and this invention relates primarily to the manner in which the linear-move machine  10  engages and disengages the hydrants  28 .  
         [0061]     In connection with the further description of the docking station and related hardware, the various drawing figures have been simplified via omission of details for the sake of clarity and ease of understanding. For example, in some views, certain structure not necessary for understanding the text relating to these views has been omitted. In addition, wiring and other minor details that would otherwise clutter the drawings, but that are nevertheless well understood by those of ordinary skill in the art, have also been omitted from various figures.  
         [0062]     In an exemplary embodiment, and with specific reference to  FIGS. 2 through 7 , a rigid side beam  30  is bolted or welded (or otherwise suitably secured) to an existing frame  32  of the drive tower  16 , such that the beam extends substantially parallel to the water supply pipe  26 , and to the direction of movement of the linear-move machine. Side beam  30  may be, for example, a solid or hollow box-beam, but in any event, the beam is provided with inverted V-shaped rails  34 ,  36  (best seen in  FIGS. 3, 4  and  5 ) along upper and lower edges of the beam, running substantially the entire length of the beam.  
         [0063]     A docking station assembly in accordance with one embodiment of the invention, includes a trolley, a supporting frame and the docking station itself. The trolley  38  includes a pair of metal plates  40 ,  42  connected by a pair of, e.g., 2 in. dia. pipes  44 ,  46  (or other suitably rigid members) extending laterally away from the side beam  30 . The larger plate  40  is located adjacent the side beam, and mounts an upper pair of rollers  48 ,  50  and a lower pair of rollers  52 ,  54  ( FIGS. 5 and 6 ) that permit the trolley  38  to roll along the rails  34 ,  36  of the side beam  30  to any desired location along the length of the side beam. Simple pins or bolts (not shown) in combination with holes in the beam (or any other suitable mechanical, hydraulic, pneumatic or electric locking device), provide a reliable locking arrangement for securing the trolley, and hence the docking station, at desired locations along the side beam  30 .  
         [0064]     With reference especially to  FIGS. 3, 6 ,  7 ,  11  and  12 , the docking station supporting frame  56  is carried on the trolley  38  and includes a pair of inverted U-shaped subassemblies  58 ,  60  that are connected at their upper ends by frame members  62 ,  64  ( FIGS. 3 and 5 ) and two pairs of roller mounting flanges  66 ,  68  ( FIGS. 3, 6 ,  7  and  12 ), each flange pair mounting two rollers  70  such that the supporting frame  56  is movable laterally, in a direction perpendicular to the paths P 1  and P 2  ( FIG. 1 ), along the trolley pipes or rails  44 ,  46  between plates  40 ,  42 . This arrangement provides a lateral adjustment feature for the docking station  76  relative to the side beam  30  as described further herein. As best seen in  FIGS. 7, 11  and  12 , a pair of horizontally oriented coil springs  71 ,  73  are connected between the outer plate  40  and the inner U-shaped subassembly  60 , while a second pair of horizontally-oriented coil springs  75 ,  77  extend between the inner plate  42  and the outer U-shaped subassembly  58 . This arrangement maintains the docking station  76  (described below) in a generally centered position along the trolley rails  44 ,  46  (between plates  40  and  42 ), but also permits reciprocatory spring-biased movement of the docking station  76  in opposite directions along the rails. Thus, the docking station  76  is able to accommodate various degrees of misalignment of any one or more of the hydrants  28 . Lateral movement of the docking station  76  to enable capture of a misaligned hydrant is also enabled by front and rear pairs of substantially vertical guide wings. Specifically, a forward pair of guide wings  72 ,  74  is fixed to respective forward ends of subassemblies  58 ,  60  and extend forwardly of the docking station  76 , flaring outwardly in the forward direction. A rearward pair of guide wings  78 ,  80  is fixed to respective rearward ends of subassemblies  58 ,  60  and extend rearwardly of the docking station  76 , also flaring outwardly but in the rearward direction. The role played by the guide wings  72 ,  74  and  78 ,  80  in assisting the capture of the hydrant flange is explained further below.  
         [0065]     The docking station itself, indicated at  76 , includes a pair of housings  82 ,  84  (one shown in  FIGS. 8, 9 ) on either side of, i.e., sandwiched about, a hydrant valve actuator assembly  86  ( FIG. 10 ). Since the housings  82 ,  84  are identical to one another, only one need be described in detail. As best seen in  FIG. 8  (exterior side) and  FIG. 9  (interior side), housing  82  includes a main body portion  85  with two pairs of oppositely directed flanges  88 ,  90  and  92 ,  94 , each flange pair supporting between them a respective generally hourglass-shaped V-track roller  96 ,  98  for rotation about a vertical axis defined by pivot pins or bolts  100 ,  102 . The main body portion  85  of housing  82  also supports two pair of vertically aligned guide wheels  104 ,  106  and  108 ,  110  for rotation about horizontal axes indicated by bolt or pivot pin holes  112 ,  114 ,  116  and  118 , respectively. The pairs of guide wheels are supported axially between the V-track rollers  96 ,  98 , on the inner side of the housing  82 . An additional pair of idler rollers  119 ,  121  may be mounted on each housing, but they are merely optional, not required. An open channel member  97  is fixed to the inner side of the housing  82 , vertically centered between the guide wheels  104 ,  106 ,  108  and  110 . The open side of the channel faces inwardly, creating a slot that receives one side of the hydrant flange  122 . A vertically mounted side guide roller  99  is fixed to the housing and partially protrudes through an aperture  101  in the housing for engagement with the flange  122 . Thus, when housings  82 ,  84  are assembled on either side of the valve actuator assembly  86 , a passageway or docking space  120  is defined by the two laterally opposed pairs of V-track rollers  96 ,  98  at the front and back of the docking station, the channel members  97  and the two pairs of laterally opposed guide wheels ( 104 ,  106 ) and ( 108 ,  110 ) located axially between the two pairs of V-track rollers on each housing  82 ,  84 . This passageway  120  (best seen in  FIGS. 5 and 15 ) is located below the hydrant valve actuator  86 , and is sized and shaped to receive the flange  122  ( FIGS. 1, 14 ,  15  and  17 - 20 ) on the hydrant  28  as also described further below.  
         [0066]     Also fixed to the housings  82 ,  84  are a pair of substantially horizontally-oriented guide wings  124 ,  126  ( FIGS. 2, 3 ,  5 ,  6  and  7 ). The guide wings  124  and  126  are secured to the housings  82 ,  84  by means of bolts, welding or any other suitable means. Wing  124  projects outwardly and upwardly in a forward direction, while wing  126  projects outwardly and upwardly in a rearward direction. These wings work in concert with guide wings  72 ,  74  and  78 ,  80  to align the docking station  76  with the hydrants  28 . The vertically-oriented wing pairs  72 ,  74  and  78 ,  80  are designed to be engaged by the hydrant flange  122  when the hydrant is misaligned in a lateral direction, causing the docking station  76  to move laterally along the trolley rails  44 ,  46  in a direction dependent upon which of the guide wings is engaged. The horizontally-oriented wings  124 ,  126  are especially designed to assist in adjustment of the docking station  76  to a hydrant  28  that is slightly higher than a desired optimum height, i.e., when the flange  122  is higher than the passageway or docking space  120 . Thus, when wing  124 , for example, engages a hydrant flange  122 , it will cause the docking station to crawl upwardly over the flange  122  so that the flange can be engaged by one or more of the V-track rollers  96 ,  98 . The V-track rollers  96 ,  98  will also cam the docking station  76  in a direction that brings the docking station to a position where the flange  122  is located in the center of the V-track rollers  96 ,  98  as best seen in  FIGS. 13-15 . Note that the profile at the narrow center of the V-track rollers  96 ,  98  complement the rounded profile of the peripheral edge of the flange.  
         [0067]     With reference especially to  FIGS. 13-16 , the housings  82 ,  84  and valve actuator assembly  86  of the docking station  76  also support a pair of dock stops  128 ,  130  on the forward and rearward ends, respectively, of the docking station. The rearward stop  130  is controlled by a similar linkage and actuator arrangement as forward stop  128 , but is supported on the opposite side of the docking station  76 . Note that the forward and rearward stops and their associated linkage and drives are identical, with an actuator  166  mounted on each side of the docking station  76 , i.e., one actuator  166  is mounted on the housing  82  and the other actuator  166  is mounted on the housing  84 . For convenience and clarity, and with the exception of stops  128 ,  130 , the links, shafts and bearing supports for each stop have the same respective reference numerals. Thus, the description of stop  128  below applies equally as well to stop  130 . In addition, note that the direction of movement in  FIG. 13  is reversed in  FIG. 14  to enable a clear illustration of the stops  128  and  130  in both retracted and extended positions. Note also that in  FIGS. 13, 14  and  20 , one of the open channel members  97  (nearest the viewer) has been omitted to more clearly show the flange  122  within the opposite channel member.  
         [0068]     The forward stop  128  is in the form of a vertically-oriented bar combined with a horizontally-oriented proximity sensor  132  at its lower end. The proximity sensor for stop  130  is indicated at  131 . The stop  128  is pivotally supported by two sets of parallel links  134 ,  134 ′ and  136 ,  136 ′. The upper set  134 ,  134 ′ is pivotally attached at a forward end to the upper end of stop  128  via a pivot pin, and at a rearward end to end  138  of a shaft  140 . The lower set of links  136 ,  136 ′ is pivotally attached at a forward end to the lower end of the stop  128  and at a rearward end to a clevis  142  ( FIG. 10 ) secured to the lower housing  196  of the valve actuator assembly  86 . In this regard, the pivot pin or bolt (not shown) extends through holes  137 ,  137 ′ in the clevis. This parallel linkage arrangement allows the stop  128  to move essentially vertically up and down between raised (go) and lowered (stop) positions upon rotation of shaft  140 , as shown, respectively, in  FIGS. 13 and 14 .  
         [0069]     Shaft  140  is supported within a journal bearing  141  in an extended side  144  of the clevis  142 , and in a bearing stand  146  on the housing  82 . The free end of the shaft  140  adjacent the stand  146  mounts a clevis  148  for pivoting movement upon rotation of the shaft. A forward end of an adjustable link arm  150  is pivotally mounted within the free end of the clevis  148 . The rearward end of the link arm  150  is pinned to a forward end of a second link arm  152  via pin  154  ( FIGS. 14 and 17 ). The rearward end of the second link arm  152  is pivotally mounted in a clevis  156  (via pin  158 ) also supported on the housing. Adjacent the forward end of the second link arm (i.e., adjacent pin  154 ), a right angle arm  160  ( FIG. 14 ) is pivotally attached to a rigid connecting link  162  fixed to an output shaft  164  of one of the hydraulic actuators  166 . When the shaft  164  is extended, link  152  will pivot in a counter-clockwise direction, thereby pulling the first link  150  upwardly and rearwardly. This movement causes the clevis  148  and thus shaft  140  to rotate in a counter-clockwise direction. As a result, the parallel linkage comprised of link sets  134 ,  134 ′ and  136 ,  136 ′ will also rotate in the same direction, raising the stop  128  (or  130 ) to a retracted or “go” position. Retraction of actuator shaft  164  will have the opposite effect, i.e., lowering the stop  128  (or stop  130 ) to an extended or “stop” position.  
         [0070]     The docking station  76  itself is suspended or hung from the supporting frame  56  so as to allow the docking station to “float” to a limited extent in essentially any direction to facilitate capture of the hydrant. Specifically, and with reference again to  FIGS. 4-6 , the docking station  76  is resiliently suspended from its supporting frame  56  by means of four coil springs (three shown at  168 ,  170  and  172  in  FIGS. 4-6 ) extending vertically between eyebolts (or other suitable points of attachment) secured to the inside surfaces of the horizontal members  174  of the inverted U-shaped subassemblies  58 ,  60  and eyebolts (or similar)  176  on respective upper surfaces of housings  82  and  84 . In the exemplary embodiment, one pair of springs is attached to the top of housing  82 , and the other pair of springs is attached to the top of housing  84 , such that the four coil springs are arranged in a generally rectangular pattern. These springs permit spring-biased up and down movement of the docking station, and also permit limited side-to-side, front-to-back, and compound movements, i.e., tilting and twisting movements.  
         [0071]     A first pair of spring-loaded, compressible tie rods  178 ,  180  ( FIG. 6 ) is secured substantially horizontally between the rearward vertical member  182  of the U-frame subassembly  58 , and the housing  82  via mounting bushings  184 ,  186  (see also  FIG. 9 ) and  188 ,  190 , while a second pair of similar tie rods (one shown at  179 ) is secured in a similar orientation between the rearward vertical member  192  ( FIG. 3 ) of the other U-frame subassembly  60  and housing  84 , utilizing similar bushings (not shown). For each tie rod, and as best seen in  FIG. 6 , a “piston”  194  is movable within the tie rod against a bias established by an internal spring. Such tie rods are well-known to those skilled in the art. The use of swivel mountings or universal bushings  184 ,  186  and  188 ,  190  with the tie rods, permits some degree of side-by-side, up and down and compound movements, in concert with the vertically-oriented springs  168 ,  170 ,  172  and  174 . Note also that the compressible tie rods also serve as shock absorbers in that they accommodate a limited degree of “over travel” by the linear-move machine during docking.  
         [0072]     With this arrangement, the docking station  76  “floats” relative to its supporting frame  56  for movement in at least three mutually perpendicular directions, i.e., vertical, horizontal front-to-back (and vice versa), and horizontal side-to-side. In addition, limited compound movements, i.e., tilting, swiveling and combinations thereof, are also possible by reason of the flexible nature of the vertically-oriented springs in combination with the tie-rod universal mounting arrangements. These multiple degrees of freedom of movement, in combination with the lateral adjustment enabled by the trolley  38 , permit reliable and accurate docking with hydrants  28  even when the latter are out of alignment relative to the docking station.  
         [0073]     The hydrant valve actuator assembly  86  ( FIG. 10 ) includes a lower housing  196  provided with a pair of attachment flanges  198 ,  200  by which the valve actuator assembly  86  is secured between the housings  82 ,  84 . Specifically, the valve actuator assembly  86  is attached to housing  82  via bolts extending through holes  214 ,  216  in attachment flange  198  and holes  112 ,  116  in guide wheels  104 ,  108  that extend into the housing  82 . Dowel pins extending between holes  210  and  212  (provided in respective angled ribs or bosses  202 ,  204 ) and holes  206 ,  208  on attachment flange  198  may be used to align the attachment flange  198  with the housing  82 . Assembly  86  is attached to the other docking station housing  84  in a similar manner.  
         [0074]     The valve actuator assembly  86  also includes intermediate and upper housing portions  218 ,  220  that, combined with lower housing  196 , enclose the valve actuator, as also described further below. A flexible hose  221  (see  FIGS. 3-5 ) connects the actuator assembly  86  to the distribution pipe  27  of the truss assembly.  
         [0075]     With reference now to  FIGS. 11 and 12 , an additional upper box frame  222  is mounted on the supporting frame  56  above the trolley rails  44 ,  46 . This upper frame supports a pair of pressurized tanks or pressure accumulators  224 ,  226  and a junction box  228 . Pressure accumulators  224 ,  226  are used to supply water under pressure to the valve actuator  86 , and may be of any suitable design such as, for example, Teel Model No. 3P676C. External power may be supplied to the junction box  228  via cables  230 ,  232 . A pair of batteries (for example, two 12-volt batteries, not shown but indicated as the power supply at  233  in  FIG. 21 ) may also be supported on the drive tower of the linear-move machine  222  to provide supplemental power to the docking station PLC  336  and associated solenoids when the linear-move machine  10  is stopped and its own power generator shut off. This arrangement also utilizes the linear-move machine power generator to charge the batteries. As best seen in  FIG. 12 , a solenoid bank is located below the junction box  228  and is supported on a cross member of the upper frame  222 . A plurality of solenoids  234 ,  236 ,  238 ,  240  and  242  are supported below and connected electrically to the junction box  228 . The solenoids are also hydraulically connected to various controlled components. More specifically, solenoids  234  and  236  control the flow of water to and from the valve actuator  86 . Solenoids  238  and  240  control the movements of the dock stops  128 ,  130  and solenoid  242  controls the main water control valve  357 .  
         [0076]     Turning now to  FIGS. 18 and 19 , a hydrant or water supply valve  28  is shown extending upwardly from the supply pipe  26 . One or more riser footings  244  may be used to stabilize the hydrant. The hydrant includes a vertical riser  246  on which a valve housing  248  including the integral docking flange  122  is secured in telescoping relationship. The valve housing  248  encloses and supports a water supply valve assembly  250  in a generally vertical orientation. The valve housing  248  is formed with a lower opening  252  with an adjacent, interior shoulder  254  by which the housing  248  is supported on the upper edge  256  of the riser  246 . The manner in which the valve housing  248  is secured is within the skill of the art and may include threaded attachment, welding or other suitable means.  
         [0077]     The upper end of the housing  248  supports a valve cup  258  formed with an external shoulder  260  that permits the cup  258  to be seated on the valve housing  248 , with a smaller diameter lower portion  262  telescoped into the valve housing. A flexible annular seal  264  is seated in a groove formed in the interior of the cup. The valve assembly or simply “valve”  250  also includes an elongated stem assembly  266  with an annular Buna-Nitrile (or other suitable material) valve seal  268  sandwiched between upper and lower valve seal supports  270 ,  272 . The lower support  272  is counterbored to create a spring recess  274  ( FIG. 19 ). A stem  276  is attached to the upper support  270  by threaded engagement of bolt  278 . The bolt  278  accesses the lower support  270  by means of a bore in the upper support  270 . The stem  276  extends downwardly and through a guide spider  280  fixed near the lower end of the valve housing. A pair of coil springs  282 ,  284  extend between the spring recess  274  and the hub  286  of the guide spider  280 , thereby biasing the valve assembly  250  upwardly to a normally closed position, with valve seal  268  engaged with annular seat  288  at the lower end of cylinder  258 . The upper support  270  is also formed as a spider, with three radial webs  290  (2 partially shown) extending radially outwardly to the interior wall of the cylinder  258 , thus permitting flow out of the hydrant while also providing an engagement interface for the hydrant valve actuator piston/cylinder  302  as described further below.  
         [0078]     As already mentioned, the hydrant valve actuator  86  includes a three-part housing including the upper housing portion  220 , the intermediate housing portion  218  and the lower housing portion  196 , joined together at flanged interfaces  292 ,  294  by bolts or other suitable means. Relatively large diameter portions of the upper and lower housing portions  220 ,  196  in combination with the intermediate portion  218  create an enlarged interior chamber  296  axially between upper and lower smaller-diameter internal, cylindrical bores  298 ,  300 . A unitary piston/cylinder  302  is slidable within the housing, with the piston or flanged portion  304  confined to movement within the enlarged chamber  296 . An upper cylindrical part  306  of the piston/cylinder  302  slides within the upper internal bore  298  while a lower cylindrical part  307  slides within the lower internal bore  300 . A first rolling diaphragm  308  is fixed between the upper end of the piston  304  and radial flanges  310 ,  312  at the interface  292  between the upper and intermediate housing portions  220 ,  218 . Similarly, a second rolling diaphragm  314  is fixed between the lower end of the piston  304  and the radial flanges  316 ,  318  at the interface  294  between the intermediate and lower housing portions  218 ,  196 . This arrangement creates an “extend” cavity  320  above the diaphragm  308  and a “retract” cavity  322  below the diaphragm  314  for fluid acting on opposite sides of the piston  304 . Fluid seals (O-rings or the like)  324 ,  326  are located in respective upper and lower housing portions  220 ,  196  to prevent fluid leakage from chamber  296  along the internal bores  298 ,  300 . A spring  328  is located between an interior shoulder  330  at the lower end of the lower housing section  196  (formed by a counterbore in the lower internal bore  300 ) and the lower side of the piston  304  to normally bias the piston-cylinder  304  in an upward direction, to the retracted position shown in  FIG. 18 . A first port  332  is provided in the upper portion of the housing for introduction/exhaustion of fluid into or from the extend cavity  320  and a second port  334  is provided in the lower housing section  196  for introducing/exhausting fluid into or from the retract cavity  322 . The operation of the hydrant valve actuator  86  will be described further below.  
         [0079]     Before describing the operation of the docking station, a brief description of the docking station control arrangement is in order. With reference to  FIG. 21 , the PLC  336  is located within a panel box on the drive tower  16 . The PLC  336  and associated power supply  233  (two 12-volt batteries) connect to the controller  338  including PLC  340 , for the linear-move machine by means of an interface connector  342 . The controller  340  may be a conventional control module for a linear-move machine with no modification required to interact with the PLC  336  for the docking station. The PLC  336  includes a pre-programmed configuration set-up  344  and receives various user commands from a user interface from an input panel  346  accessible by opening the front face of panel box  228 . The PLC  336  also receives input from the water pressure switch  348 , dock stop proximity switches  350  in the proximity sensors  131  and  132 , and a valve actuator cylinder proximity switch  352 . The PLC  336  provides output commands to the solenoids  234 ,  236 ,  238 ,  240  and  242 .  
         [0080]     The safety mechanisms on the docking module and linear-move machine are also coordinated through the interface connector  342 . The PLC  340  of the linear-move controller  338  communicates with the PLC  336  of the docking station  76  by means of respective interface relays  340 ,  342 . In short, the controls for the docking station  76  are integrated into the controller  338  for the linear-move machine  10 , with no modification required to the controller  338 . While the PLC and associated solenoids may be powered by the linear-move machine engine generator while the linear-move machine  10  is moving, it is preferred to also utilize battery power (e.g., a pair of 12-volt batteries (indicated by reference numeral  233  in  FIG. 21 ) as supplemental power for the docking station  76  when the linear-move machine  10  is shut down during valve actuation and sprinkling.  
         [0081]     The linear-move machine  10  and associated docking station  76  may be programmed to operate in at least five different modes: (1) simple start/stop irrigation; (2) start/stop with manual offset of the docking station  76 ; (3) start/stop with automatic offset of the docking station  76 ; (4) start/stop with one docking station  76  and substantially continuous machine movement; and (5) continuous linear-move machine movement with two docking stations  76 .  
         [0082]     (1) Simple Start/Stop  
         [0083]     In this mode, the docking station  76  is initially located at any desired location along the side beam  30  and locked in place. Generally, for this mode of operation, the docking station  76  will remain in this position throughout the irrigation cycle. With reference to  FIG. 22 , when the docking station  76  is located approximately midway along the side beam  30 , a circular sprinkling pattern  356  will be generated by any one of the sprinklers  29  on the truss assembly  12 .  
         [0084]      FIG. 23  illustrates a circular pattern  358  generated when the docking station  76  is located at the forward end of the side beam  30 , and  FIG. 24  illustrates a third circular pattern  360  generated when the docking station  76  is located at the rearward end of the side beam  30 .  FIG. 25  shows the positions of patterns  356 ,  358  and  360  relative to the truss assembly  12  and drive wheels  18  for appreciation of how the sprinkling pattern locations can be manipulated via location of the docking station  76  along the side beam  30  to achieve greater wetting uniformity in the irrigation cycle.  
         [0085]     As the linear-move machine  10  is driven forward in the direction of path P 1  ( FIG. 1 ), the dock stop  128  (forward) is in the up or go position, while the rearward dock stop  130  is in the lowered or stop position ( FIG. 13 ).  
         [0086]     As the linear-move machine  10  continues to move in a forward direction, the hydrant flange  122  and docking station  76  are initially roughly aligned, if necessary, by the interaction of the flange  122  with the side guide wings  72 ,  74  and front guide wing  124 . Assuming the hydrant flange  122  and docking station  76  are not in substantial alignment during the initial contact, the vertically-oriented front guide wings  72 ,  74  (and/or the horizontally-oriented forward guide wing  124 ) will be engaged by the stationary hydrant flange  122 , causing the docking station  76  to move laterally along the trolley rails  44 ,  46  to an aligned position, while engagement with wing  124  will cause the docking station to move upwardly as the docking station continues to move toward the hydrant. The flange  122  will then be engaged by the forward pair of V-track rollers  96 , the tapered surfaces of which further center the flange  122  relative to the docking station so that the flange is located at the smallest-diameter portion of the V-track rollers, as best seen in  FIG. 15 . In other words, the V-shape of the spinning rollers  96  allows the free-floating docking station  76  to crawl around the hydrant flange  122  until they are aligned. The hydrant flange  122  then slides between guide wheels  104 ,  106  and into the side guide channel members  97  which capture the hydrant flange in the same plane as the docking station.  
         [0087]     In an alternative arrangement, a power-assist feature may be added to facilitate lateral movement of the docking station on the trolley  38  upon engagement of the hydrant flange  122  with one or the other of guide wings  72 ,  74 . This would function similar to power brakes or power steering in a vehicle, and could employ oil hydraulics, water hydraulics, pneumatics, or electric motors to move the docking station along the trolley rails  44 ,  46 .  
         [0088]     As the hydrant flange  122  is captured by the docking station  76 , the linear-move machine  10  continues forward travel until the hydrant flange  122  touches the rearward docking stop  130 . More specifically, when the docking stop proximity switch  132  (part of the stop) is tripped (for example, when the flange  122  is within a few millimeters of the stop), it signals the PLC in the control panel to stop the forward movement of the linear-move machine. At this point, the linear-move machine “coasts” into engagement with the docking stop  130 . The hydrant flange  122  is now fully captured by the docking station  76 , and the linear-move machine is in position to connect to the water supply valve. Depending on the normal operating speed of the linear-move machine, a second proximity switch may be used “upstream” of the switch  132  for the purpose of effecting a reduction in speed of the linear-move machine as it approaches the hydrant.  
         [0089]     When the docking station is fully aligned with the hydrant water supply valve, only the flange  122  is engaged with the docking station. In other words, the docking station self-aligns with the flange  122 , the alignment determined by the dock stop  130 , the laterally opposed and axially spaced pairs of guide wheels  104 ,  106  and  108 ,  110 , and the opposed, horizontally-oriented channel members  97  and associated side-guide wheels  99  on the interior sides of the housings  82  and  84 . Note that in the fully aligned position, the flange is located between and axially spaced from the forward and rearward V-track rollers.  
         [0090]     The PLC  336  now sends a command to port water from the pressure accumulators  224  and  226  (they are connected in parallel) through the extend on/off control solenoid valve  234  to the extend diaphragm cavity  320  in the actuator assembly  86 . At the same time, the same solenoid vents water in the retract cavity  322 . The water force in the extend cavity  320  overcomes the force of spring  328  and pushes the lower cylinder portion  307  down into the hydrant valve housing  248 . The cylinder  307  eventually travels through the valve cup  258 , and as the cylinder continues its downward movement, the valve seal  268  is pushed off the valve seat  288  to thereby open the valve. After extend on/off control solenoid  234  has been signaled by the PLC, a time delay allows sufficient time for system water pressure to recharge both pressure accumulator tanks  224 ,  226  (as needed). After the time delay, the PLC  336  sends a command to solenoid  242  to open the control valve  357  located where the hose  221  joins the water distribution pipe  27  so that water is then free to flow via the valve through the piston-cylinder  302  through the distribution pipe supported on the truss assembly  12  and to the sprinklers  29 .  
         [0091]     After the sprinklers have run for the programmed amount of time, the PLC  336  sends a command to solenoid  242  to close the control valve  357  to prevent water from draining out of the linear-move machine  10 , via pipe  27 . The PLC  336  then sends a command to vent water from the “extend” cavity  320  through the main water extend on/off control solenoid valve  234  to atmosphere. This removes the downward force on the rolling diaphragm  308 . At the same time, the PLC  336  sends a command to port water to the “retract” cavity  322  through the main water retract on/off control solenoid valve  236 . The spring  328  and diaphragm  314  now push the piston-cylinder  302  back up into the actuator housing to the position shown in  FIG. 18 . As the piston-cylinder  302  retracts, the valve seal assembly  250  is pushed upward by the valve springs  282 ,  284  until the valve seal  268  seats on the valve seat  288  and shuts off water flow. When a proximity switch  352  senses the actuator cylinder  307  is retracted, the PLC  336  initiates forward movement of the linear-move machine  10  to the next hydrant. To initiate such forward movement, water is first ported through the solenoid  240  that operates hydraulic actuator  166 . The hydraulic actuator  166  extends its output shaft  164  to thereby raise the stop  130  out of the path of the flange  122  to the retracted or “go” position. The linear-move machine  10  then begins to drive forward to the next hydrant. When the docking station is disengaged from the hydrant flange, the springs  71 ,  73  and  75 ,  77  will return the docking station to its centered position along trolley rails  44 ,  46 . Following a programmed time delay to ensure that the docking station  76  has cleared the hydrant, the PLC sends a command to solenoid  240  to port water from the hydraulic actuator  166  to atmosphere. The hydraulic actuator rod  164  is forced to retract by an internal spring, rotating the dock stop  130  to its extended or “stop” position. The dock stop  130  is now in position to stop the docking station at the next hydrant. It will be appreciated that dock stop  128  will operate in the same manner when the linear-move machine travels in the opposite direction. Thus, stop  128  is always retracted when the linear-move machine travels along path P 1 , and stop  130  is always in the retracted position when the machine travels along path P 2 .  
         [0092]     In this example, water from the irrigation pipes is used as a hydraulic drive fluid. A closed hydraulic system employing standard hydraulic fluids, a pump, reservoir, and filter could also be employed. A water glycol fluid is currently under consideration. A pneumatic system could also be used employing a compressor, filter and reservoir. An electric jack screw or actuator could also connect to the valve actuator  86  and be used to drive it up and down into the hydrant valve  28 .  
         [0093]     The hydraulic control lines that feed the “extend” and “retract” cavities on the valve actuator assembly  86  can have in-line orifices to provide flow rate control in and out of their respective cavities. This will control how fast the valve will turn on and off. By controlling valve opening and closing speed, water hammer will be kept to a minimum.  
         [0094]     A simple flow chart illustrating operation in this mode is shown in  FIG. 26 . Initially, the system checks to see that all safety criteria have been met. If not, the machine will stop. Similarly, when the linear-move machine is wired to the docking station module, operation is in an “auto” mode. If “manual” is chosen or indicated, the machine will stop. The remaining events are in a simple logic loop form, depending on the direction of movement of the machine.  
         [0095]     (2) Start/Stop with Manual Offset  
         [0096]     This mode is essentially identical to the mode described above, but with the option of manually offsetting the docking station  76  for the next set of moves, for example, from the position shown in  FIG. 22  to the position shown in  FIG. 23 . This would improve the overall systems water distribution efficiency over the course of many applications of water. Offsetting the docking station  76  is accomplished easily by manually moving the trolley  38  along the rail or side beam  30  and pinning it in its new desired position. Otherwise, the operation is as described above for the first mode.  
         [0097]     (3) Start/Stop with Automatic Offset  
         [0098]     This mode is essentially identical to mode (2) but with an automatic offsetting feature, controlled by the PLC  336 . This would allow the linear-move machine  10  to move down the field along path P 1  in a first run with the docking station  76  fixed in the position shown, for example, in  FIG. 21 . The PLC would send a command to automatically apply an offset (as shown in, for example,  FIG. 23 ) at the end of the field, and then return back in a second run along path P 2 , applying water in a pattern  358  offset from the first pattern  356 . The automatic movement of the docking station  76  along side beam  30  can be achieved by any suitable mechanical, electromechanical, hydraulic, pneumatic or other drive means in concert with appropriate programming of the PLC  336  as would be well understood by those skilled in the art.  
         [0099]     (4) Start/Stop Semi-Continuous Mode  
         [0100]     With reference to  FIGS. 27-32 , for this start/stop continuous mode, the support structure for the docking station is modified to include a second beam  362  (also referred to as the “telescoping arm”) movable along the side beam  30 . The rigid, stationary side beam  30  remains fixed to the drive tower  16  as described above. In this embodiment, however, the side beam mounts plural roller brackets  364  (three in the exemplary embodiment). Each roller bracket includes a vertically-oriented plate  366  fixed to the side beam  30  at axially spaced intervals, for example, one adjacent each of the forward and rearward ends of the side beam  30 , and one intermediate the ends. As best seen in  FIG. 32 , each plate  366  supports a first upper pair of rollers  368  mounted for rotation at opposite ends of a roller support rod  370  fixed to the plate  366  by an axially centered pin or bolt  372 . A lower pair of rollers  374  is identically mounted but spaced laterally outwardly of the side beam by a spacer block  376  ( FIG. 29 ).  
         [0101]     The telescoping arm  362  is shown substantially square in cross section in the exemplary embodiment, but is not necessarily limited to that shape. The arm is provided with elongated rails  380 ,  382  ( FIG. 29 ) running along the length of the telescoping arm. One rail  380  is located on the upper surface  384  of the telescoping arm  362 , adjacent the inner side (closest to the drive tower) thereof. The second rail  382  is located on the lower surface  386  of the telescoping arm, substantially centered thereon as apparent from  FIG. 29 . The telescoping arm  362  is oriented such that upper rollers  368  on the roller brackets  364  engage the upper rail  380  while the lower rollers  374  engage the lower rail  382 . This arrangement permits the telescoping arm  362  to slide forwardly and rearwardly along the fixed side beam  30  between rearward-extended and forward-extended positions. At the same time, the docking station  76  and its supporting trolley  38  are movable to desired locations along the telescoping arm  362  via upper and lower pairs of rollers  388 ,  390  engaged on additional upper and lower rails  392 ,  394  fixed to the upper and lower surfaces of the telescoping arm, adjacent the outer side wall  396 . The mounting of the docking station  76  to the telescoping arm  362  is substantially identical to the manner in which the docking station is supported on the side beam  30  in the earlier-described embodiments.  
         [0102]     In the exemplary embodiment, the telescoping arm  362  is moved along the fixed side beam  30  by means of a chain drive. Specifically, a group of three sprockets  390 ,  400 ,  402 , best seen in  FIG. 30 , is located at one end of the arm, supported on the lower inner surface  404  for rotation about vertical axes. The middle sprocket  400  serves as a tensioner in that it can be adjusted axially along a slot in the bracket  406  to adjust the chain tension in conventional fashion.  
         [0103]     The opposite end of the lower surface of the telescoping arm is fitted with a pair of sprockets  408 ,  410 , shown in  FIG. 31 . Sprocket  408  is an idler sprocket while sprocket  410  is a drive sprocket, attached to a vertically oriented drive shaft  412 . A first drive chain  414  extends between one side of the docking station trolley plate  40 , around the three sprockets  398 ,  400 ,  402  and along the telescoping arm  362  to an attachment point on one side of roller support bracket  364  in the middle of the fixed side beam  30 . A second drive chain  416  extends between the opposite side of the docking station trolley plate  40 , around the two sprockets  410 ,  408  and along the telescoping arm  362  to an attachment point on the other side of the middle roller support bracket  364 . Accordingly, rotation of the drive shaft  412  in a clockwise direction will cause the telescoping arm  362  to move to the left (relative to the fixed beam) as viewed in  FIG. 27  while rotation in a clockwise direction will cause the telescoping arm  362  to move to the right. Shaft  412  is connected to a suitable motor and clutch arrangement under the control of the docking station PLC.  
         [0104]     More specifically, a neutral position exists when the docking station  76  mounted on the telescoping arm  362  is centered along the length thereof, and when the telescoping arm  362  is itself aligned with and adjacent the fixed beam  30  as shown in  FIG. 27 . Rotating the drive shaft  412  in a counterclockwise direction pulls the telescoping arm  362  forwardly relative to the fixed side beam  30 , while at the same time, moving the docking station  76  to the front of the telescoping arm  362 . This is the position assumed when the first hydrant  28  is engaged at commencement of travel of the linear-move machine  10  along the path P 1 . In other words, the first hydrant  28  engaged by the docking station  76  is forward of the drive tower  16 , i.e., with the telescoping arm  362  extended forwardly to its maximum extent, and the docking station  76  at its forwardmost position on the telescoping arm. With the first hydrant fully engaged and with the hydrant valve open, the linear-move machine  10  begins moving forward. As it does so, the telescoping arm  362  retracts relative to the fixed beam  30  and the linear-move machine. As the linear-move machine continues its forward progress, the telescoping arm  362  continues to retract relative to the fixed side beam  30  and eventually extends rearwardly of the machine. When the telescoping arm  362  approaches its rearwardmost extended position, and with the docking station  76  now at the rearward end of the telescoping arm, as shown in  FIG. 32 , the linear-move machine is halted. The docking station is de-coupled from the first hydrant  26  and the telescoping arm  362  is then again moved forwardly so as to extend beyond the fixed beam  30  and into position for coupling with the next (or second) hydrant. During this movement, the chain drive also moves the docking station  76  from the rearward end to the forward end of the telescoping arm. The docking station  76  is then coupled to the second hydrant and the linear-move machine resumes movement along the path P 1 . This action is repeated as the linear-move machine moves from one end of the field to the other.  
         [0105]     Depending on economics, the telescoping arm  362  could be eliminated and the hydrants  28  along the water supply pipe  26  could be located closer to each other, i.e., with a spacing roughly equal to the travel distance of the docking station  76  along the fixed side beam  30 .  
         [0106]     In order to accommodate movement of the telescoping arm  362  along the fixed side beam  30 , and movement of the docking station  76  along the telescoping arm  362 , hose management hardware is required. In this embodiment, the flexible supply hose  414  connecting the valve actuator on the docking station  76  to the overhead truss assembly  12 , is permitted to seat on a plurality of V-rollers  416  mounted for rotation within an elongated channel member  418  fixed on the upper surface of the telescoping arm  362 . These rollers cooperate with a pair of considerably larger drum wheels  420 ,  422  that are supported on the telescoping arm  362  directly above the rollers  416 . With the hose extending between rollers  416  and drum wheels  420 ,  422  as shown in  FIG. 27 , and then winding back across the tops of the drum wheels  420 ,  422 , it will be appreciated that the hose  414  will move in a controlled manner, as the telescoping arm  362  moves between its extended rearward and extended forward positions, and as the docking station  76  moves simultaneously between rearward and forward positions on the telescoping arm.  
         [0107]     (5) Continuous Mode  
         [0108]     In this mode, two telescoping docking stations are employed. With reference to  FIG. 33 , the linear-move machine  424  is fitted with inner and outer fixed beams  426 ,  428 , respectively, that form a box-like frame  430  attached to the drive tower  16  by one or more connecting beams  432 , as appropriate. A first docking station  434  is mounted for movement along the inner fixed beam  426 , while a second docking station  436  is mounted for movement along the outer fixed beam  428 . The docking stations  434  and  436  are similar to docking station  76 , and the mounting of these docking stations and associated trolleys to the fixed beams  426 ,  428  is also similar to the mounting of the docking station  76  to the beam  30  via trolley  38 . Here, however, the docking stations are driven along the respective beams by chain, cable, belt drive or other suitable means along with a motor and clutch arrangement. In addition, the hydrants  438 ,  440 ,  442 , etc. are offset from supply pipe  444 , in opposite directions, in alternating fashion. This arrangement allows the docking stations  434  and  436  to engage alternate hydrants on opposite sides of the supply pipe. To facilitate this movement, flexible hoses  446 ,  448  connect the docking stations  434 ,  436  to the water distribution pipe  450  on the overhead truss assembly.  
         [0109]     In operation, docking station  434  will engage hydrant  438  while docking station  436  is moved along fixed beam  428  to engage the next hydrant  440  on the opposite side of pipe  444 . After docking station  436  engages hydrant  440 , docking station  434  will disengage hydrant  438  and move forward along inner beam  426  to the next hydrant  442  as the linear-move machine also moves forward. During movement of the machine, it will be apparent that docking station  436  remains stationary relative to hydrant  440  while outer frame  430  moves forward with the machine. This arrangement permits continuous movement of the linear-move machine from one end of the field to the other, without having to stop for engagement with the hydrants along the water supply pipe.  
         [0110]     The above-described docking station configurations provide a reliable and relatively simple solution to the problems normally associated with linear-move machines that incorporate an automatic docking feature.  
         [0111]     While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.