Abstract:
An irrigation system with an alignment detector uses a plurality of discrete sensors to detect and measure each irrigator span&#39;s misalignment when moving in either direction. In particular, this sensor alignment detector utilizes a first sensor for the forward movement direction and a second sensor for the reverse movement direction, which provides a significant improvement in alignment optimization and sensitivity.

Description:
RELATED APPLICATION 
       [0001]    The present application is based on and claims priority to the Applicant&#39;s U.S. Provisional Patent Application 62/324,682, entitled “Irrigation System With Dual Alignment Sensors,” filed on Apr. 19, 2016. 
     
    
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
       [0002]    The present invention relates to an irrigation system for conveying a fluid from a fluid source through interconnected spans wherein an alignment mechanism maintains alignment of the respective spans. 
       Statement of the Problem 
       [0003]    The present invention involves an irrigation system having a series of irrigator spans having conduits for conveying an applicant such as water. The present invention relates to various types of irrigation systems including linear and lateral move irrigation systems, however, the primary type of irrigation system used for this purpose is called a center pivot irrigation system. Such systems include a center pivot tower about which the entire system rotates. The center pivot tower is connected to the water source for supplying water to the irrigation system. The irrigation system further includes a series of irrigator spans having conduits for conveying the water. Each irrigator span is connected to the adjacent irrigator span in an end-to-end manner at a joint that may include an external ball and socket connection, an external gimbal ring assembly, an external tongue and pin assembly, or an internal hook and receiver assembly. A flexible coupling, such as a flexible hose or boot, is used to connect the conduits of adjoining irrigator spans such that each conduit is in fluid communication with the next. The conduit of the irrigator span positioned adjacent to the center pivot tower is connected to the center pivot tower and the water source. Water is pumped from the water source through the center pivot tower and to the conduits of each irrigator span and is applied to the field through discharge nozzles mounted to the conduits. The irrigation system may include a plurality of irrigator spans, typically 100 feet to 200 feet in length, capable of reaching a few acres or hundreds of acres of the field. The irrigator spans are each moved about the center pivot tower by a drive system located at each intermediate tower structure and at an end tower structure. Each irrigator span includes its own drive system for moving the irrigator span radially about the center pivot tower. In prior art irrigation systems, an alignment mechanism interconnects each pair of connected irrigator spans near the flexible joint to maintain radial alignment between the irrigator spans within a predetermined limit. 
         [0004]    The prior art in this field includes span alignment systems that provide an on-and-off signal to a reversible, constant-speed drive motor to maintain the irrigator spans in substantial radial alignment in both a forward movement direction and a reverse movement direction. U.S. Pat. No. 4,034,778 (Sage et al.), U.S. Pat. No. 3,823,730 (Sandstrom et al.) and U.S. Pat. No. 3,807,436 (Pringle) disclose a means of alignment dependent on cycling drive motors on and off to maintain alignment within defined parameters. For the past forty-five years, the on-and-off cycling of constant-speed drive motors has been the conventional means of maintaining alignment among the plurality of irrigator spans of center pivot irrigation systems. Such on and off cycling of constant-speed drive motors results in excessive wear on drive components and on the drive motor. 
         [0005]    To mitigate the excessive ware on drive components and drive motors, more recent prior art discloses alignment systems that use sensors to detect degrees of misalignment between adjacent irrigator spans and in turn signal variable-speed drive motors to operate continuously but at varied speeds or RPM (revolutions per minute) rather than simply turn on at a constant speed (e.g., 1,750 RPM) and then turn off as needed to maintain alignment within a predetermined limit. 
         [0006]    U.S. Pat. No. 6,755,362 (Krieger et al.) and U.S. Pat. No. 8,948,979 (Malsam) disclose the use of a sensor at each drive tower to detect misalignment between adjacent irrigator spans and vary drive motor speeds to maintain alignment, rather than cycling motors on and off to maintain alignment. These variable-speed alignment systems take advantage of technologies that employ variable-speed drive motors with continuous movement, in lieu of constant-speed drive motors with on and off movement. 
         [0007]    In particular, Krieger discloses an irrigation system, such as a center pivot irrigation system, that includes an alignment mechanism, i.e., alignment detector, to measure the degree of misalignment between two adjacent irrigator spans. This irrigation system has a variable-speed drive system that uses a sensor, described as a potentiometer, to signal a degree of misalignment of an irrigator span of an irrigation system in relation to an adjacent irrigator span. Krieger further discloses that such sensor can be any of a number of types of sensors such as dual wiper or dual directional potentiometers, rotary potentiometers, and so on. In application, such use of a single sensor to measure misalignment, as disclosed by Krieger, limits the sensitivity of misalignment detection because of differing mechanical hysteresis of the irrigator span structural and alignment components in a forward movement direction as compared to a reverse movement direction and also because of potential electrical variations in the elements used to vary the speed of movement of the irrigator spans in a forward movement direction as compared to a reverse movement direction. 
         [0008]    Malsam discloses an irrigation system that includes an alignment mechanism, i.e., alignment detector, to measure the degree of misalignment between two adjacent irrigator spans. Again, like Krieger, Malsam discloses a variable-speed drive system that uses a single sensor to detect misalignment, regardless of the direction of travel. Malsam discloses potential sensors to include sensors such as potentiometers, capacitive alignment sensors, laser-based alignment sensors, non-contact proximity sensors, or other devices capable of quantifiably measuring the irrigator span alignment. Like Krieger, Malsam discloses the use of a single sensor to signal a degree of misalignment of an irrigator span of an irrigation system in relation to an adjacent irrigator span. Also, the same as Krieger, Malsam&#39;s use of a single sensor to measure misalignment limits the sensitivity of misalignment detection because of differing mechanical hysteresis of the conventional irrigator span structural and alignment components in a forward movement direction as compared to a reverse movement direction as disclosed above. 
         [0009]    Both Krieger and Malsam disclose the use of a single sensor at each span juncture, i.e., flexible joint, to detect a degree of misalignment between adjacent irrigator spans. Both Krieger and Malsam disclose that in application the single sensor can be any number of types of sensors such as dual wiper or dual directional potentiometers, rotary potentiometers, capacitive alignment sensors, laser-based alignment sensors, non-contact proximity sensors, or other devices capable of quantifiably measuring the irrigator span alignment. Those familiar with the operation of center pivot irrigation systems may know that optimal span alignment in each movement direction, i.e., either a forward movement direction or a reverse movement direction, may result in a slight bow in the direction of movement or travel among the plurality of irrigator spans. This bowed condition may result from the forces at each drive tower supporting each span to project the drive wheels to move tangentially to the circumference of the respective wheel track, such discrete movement being associated, respectively, with both the forward movement direction and the reverse movement direction. In other words, the drive towers are each attempting to progress in a straight line, i.e., tangentially to the circumference of the wheel track, in either a forward movement direction (clockwise) or a reverse movement direction (counter-clockwise); but all drive towers are held and restrained by the center pivot tower, causing the drive tower of each span to pivot in a circular pattern and with varying tension among the plurality of respective irrigator span structures and between corresponding adjacent irrigator spans. 
         [0010]    The dynamic tension forces resulting from a center pivot being operated may be understood from the series of movements that begin with the movement of the last or outermost drive tower that also controls the overall pace of movement of the entire roving pivot arm over the field. The last (outermost) drive tower is positioned to move tangentially to its corresponding circular wheel track, in either a forward movement direction or reverse movement direction. Assume a forward movement direction (clockwise). Once such forward movement commences the last drive tower begins to lead the remaining stationary and aligned intermediate drive towers. Because the entire roving pivot arm is attached to the stationary center pivot tower, the last drive tower is forced to move in a circular pattern about its corresponding wheel track. As the last drive tower pivots about the stationary adjacent intermediate drive tower, i.e., next-to-last drive tower, a corresponding alignment detector, using a sensor, signals the adjacent intermediate drive tower to move forward at a pace that realigns the adjacent intermediate irrigator span with the last irrigator span, even as the last irrigator span is continuously moving at an operator selected ground speed. This adjacent intermediate drive tower is also configured to move tangentially to its corresponding circular wheel track. Just as with the last drive tower, the adjacent intermediate drive tower&#39;s tangential movement is restricted by the center pivot tower, causing both the last drive tower and the next-to-last, intermediate drive tower to move in corresponding circular paths with varying tension among the plurality of respective irrigator span structures and between corresponding adjacent irrigator spans. 
         [0011]    Once such forward movement of the adjacent intermediate drive tower commences, the last drive tower and the adjacent, next-to-last, intermediate drive tower begins to lead any remaining stationary intermediate drive towers. This movement cycle may continue with each corresponding intermediate drive tower to result in a substantially aligned plurality of intermediate irrigator spans, under tension, with a slight leading bow of the last drive tower in the direction of movement. 
         [0012]    The forces created when a roving center pivot arm begins to move, in either a forward movement direction or a reverse movement direction, may result in considerable mechanical hysteresis, causing mechanical stress and movement among the structural components, particularly those flexible components that are part of the irrigator span&#39;s flexible joint structure at each respective drive tower. This hysteresis may be caused by backlash or elastic deformation but is mainly caused by frictional effects among the assembled components of the center pivot structure. Also, variables such as topography underlying the plurality of irrigator spans, may create mechanical hysteresis when a roving center pivot arm moves. Such forces may create mechanical hysteresis having a different signature in a forward movement direction than in the reverse movement direction. For example, at a given point in the field, the wheels of a drive tower of a corresponding irrigator span may be moving uphill in a forward movement direction, but moving downhill in a reverse movement direction. The uphill verses downhill movement may result in very different mechanical hysteresis, even though the only variables may be the direction of movement and the uphill verses downhill topography. In other words, the alignment detector, using a single sensor as disclosed by Krieger and Malsam to detect misalignment, may result in a different alignment result in a forward movement direction as compared to the alignment result from the same alignment detector when moving in a reverse movement direction, and vice versa. 
         [0013]    Center pivot structures are, by design, built to withstand tension forces created by the irrigator spans trying to move tangentially to the circular path, but being forced to pivot about the center pivot tower that restricts each irrigator span&#39;s movement to a corresponding circular path. Furthermore, center pivot structures are not designed to withstand significant compression among the irrigator spans. Adjusting alignment to result in a corresponding, slight, leading bow in either movement direction provides the needed tension and mitigates unwanted compression among the irrigator spans as the irrigator spans pivot in their corresponding circular paths about the center pivot tower. Use of a single sensor to detect misalignment in both the forward movement direction and the reverse movement direction may result in a sub-optimal alignment result in one or both directions. This is the problem addressed by the present invention. 
       Solution to the Problem 
       [0014]    The present invention employs an alignment detector with dual sensors. Because center pivots operate in both a forward movement direction and a reverse movement direction, alignment of the irrigator spans of a center pivot irrigation system in both a forward movement direction and a reverse movement direction using a single sensor may result in sub-optimal alignment properties. Neither Krieger nor Malsam address this issue and both inventors assume adequate alignment by using one sensor for maintaining alignment among the plurality of irrigator spans, regardless of the direction of movement. The present invention discloses a means to significantly improve on the single sensor method of irrigator span alignment as first disclosed by Krieger and later repeated by Malsam. 
         [0015]    More specifically, the present invention uses two sensors in lieu of one sensor to detect misalignment and maintain proper alignment of each of the plurality of irrigator spans of a center pivot irrigation system. The first sensor signals the alignment status in a forward movement direction and the second sensor signals the alignment status in a reverse movement direction. This addition of a second sensor enables discrete sensing for each movement direction and enables the adjustment of the alignment between adjacent irrigator spans to be optimally and independently set for each movement direction, regardless of varying mechanical hysteresis that may result from a particular movement direction. The prior art disclosed by Krieger and Malsam uses only a single sensor that must serve to provide alignment detection in both directions. The present invention improves span alignment by enabling the achievement of an optimum leading bow that provides tension throughout the plurality of irrigator spans and between adjacent irrigator spans in both movement directions. Using two sensors, one for each movement direction, the corresponding desired leading bows can be achieved independently for the forward movement direction and for the reverse movement direction, thus mitigating the effects of varying mechanical hysteresis resulting from the direction of travel. Using two sensors in lieu of one sensor to detect misalignment and maintain proper alignment of each of the plurality of irrigator spans of a center pivot irrigation system results in a more precise alignment in both movement directions among the plurality of irrigator spans, and, in turn, reduces structural stresses. 
       SUMMARY OF THE INVENTION 
       [0016]    This invention provides an irrigation system with an alignment detector that uses a plurality of discrete sensors to detect and measure each irrigator span&#39;s misalignment. This sensor alignment detector utilizes a first sensor for the forward movement direction and a second sensor for the reverse movement direction. This method makes possible a significant improvement in alignment optimization and sensitivity as compared to the prior art of Krieger and Malsam that both use one sensor for detecting and measuring misalignment among the plurality of irrigator spans, regardless of movement direction. 
         [0017]    These and other advantages, features, and objects of the present invention will be more readily understood in view of the following detailed description and the drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]    The present invention can be more readily understood in conjunction with the accompanying drawings, in which: 
           [0019]      FIG. 1  is a perspective view of an irrigation system  1  embodying the present invention. 
           [0020]      FIG. 2  is a simplified wiring diagram of the dual sensor alignment detector  49  and the major components of an irrigation system  1 . 
           [0021]      FIG. 3  illustrates a variable-speed drive assembly  35  with a variable-speed drive controller  39  signaled by a dual sensor alignment detector  49 . The dual sensor alignment detector  49  includes two sensors  40 ,  41  with two sensor actuator shafts  71 ,  72  connected to a cam  83  by a pivoting pin  74 . 
           [0022]      FIG. 4  is a top view of a flexible joint  3  between two intermediate irrigator spans  12 ,  13  illustrating the limited range of alignment between the intermediate irrigator spans  12 ,  13 . 
           [0023]      FIG. 5  is a top view of an irrigation system  1  with the two intermediate irrigator spans  12 ,  13  aligned and the end irrigator span  14  in a leading bow for the reverse movement direction  55 . 
           [0024]      FIG. 6  is a top view of an irrigation system  1  with the two intermediate irrigator spans  12 ,  13  aligned and the end irrigator span  14  in a leading bow for the forward movement direction  54 . 
           [0025]      FIG. 7  is a top view of an irrigation system  1  with the intermediate irrigator spans in a leading bow for the forward movement direction  54 . 
           [0026]      FIG. 8  is a top view of an irrigation system  1  with the intermediate irrigator spans in a leading bow for the reverse movement direction  55 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0027]    Irrigation systems, such as linear and lateral move irrigation systems and center pivot irrigation systems, generally include fixed-speed drive assemblies at each of the intermediate tower structures to propel the irrigation systems over a respective ground surface, cultivation area or field. Such irrigation systems rely on span motors with fixed-rate speeds, RPM, of the central shafts of the rotors of such span motors due to their relative simplicity and robustness. Such systems, however, can only maintain the relative alignment of various irrigator spans by repeated on-and-off control cycling of the corresponding span motors as roving irrigator spans change states of alignment in either a forward movement direction or a reverse movement direction. This method of maintaining substantial alignment among the plurality of irrigation spans results in each intermediate tower structure coming to a complete stop and then requiring a large impulse of power to the corresponding fixed-speed span motor to start the intermediate tower structure moving again. These strenuous and repetitive start-and-stop movements that result from repeated on-and-off control cycling of the corresponding span motors may result in excessive stress on structures, e.g., transitions from tension to compression among adjacent irrigator spans, excessive wear on components, and unintended downtime of the irrigation system. The irregular, start and stop motion caused by these strenuous and repetitive start-and-stop movements in order to maintain a substantial straight alignment of the irrigator spans can also cause uneven application of irrigation water and/or chemicals to the field. This may result in waste of both water and chemicals. The irregular motion may also cause deviations in alignment or errors in determining the position of the end tower structure of the machine. This can result in errors in operations based on pivot arm position as determined at the center pivot tower structure. 
         [0028]    Accordingly, irrigation systems have been proposed that provide variable-speed drive assemblies. Both Krieger (U.S. Pat. No. 6,755,362) and Malsam (U.S. Pat. No. 8,948,979) have disclosed using a single sensor, such sensors being any number of types of sensors, to signal the degree of misalignment to a variable-speed drive controller of a variable-speed drive assembly to maintain a substantial straight alignment among a plurality of adjacent irrigator spans. This contrasts with the irregular motion caused by the strenuous and repetitive start-and-stop movements of the legacy alignment systems using limit switches, wherein corresponding span motors are repeatedly control cycled between span motor on and span motor off as described above. In an implementation of Krieger and Malsam, an irrigation system includes multiple interconnected irrigator spans that are supported by multiple tower structures. Each intermediate tower structure may include a variable-speed drive assembly that may include a variable-speed drive controller that varies aspects of the supply power furnished to the corresponding span motor to vary the speed of movement of the respective variable-speed drive assembly in either a forward movement direction or a reverse movement direction. As disclosed by Krieger and Malsam, such variable-speed drive controllers may each receive signals from a sensor, such signals used by the variable-speed drive controller to adjust the speed of the corresponding span motor to maintain irrigator span alignment. Both Krieger and Malsam also disclose that in application such single sensor can be any number of types of sensors such as dual wiper or dual directional potentiometers, rotary potentiometers, capacitive alignment sensors, laser-based alignment sensors, non-contact proximity sensors, or other devices capable of quantifiably measuring the irrigator span alignment. 
         [0029]    In the variable-speed drive controllers disclosed by Krieger and Malsam, each variable-speed drive assembly of the intermediate irrigator spans of the irrigation system may include an alignment detector that may include a single sensor, e.g., a potentiometer, a capacitive alignment sensor, a GPS (global positioning system)-based alignment sensor, a laser-based alignment sensor, a non-contact proximity sensor, or any other device capable of signaling varying states of alignment, and the like, configured to detect and output varying states of misalignment. Within each variable-speed drive assembly, the alignment detector is in communication with a corresponding variable-speed drive controller. Each variable-speed drive controller is configured to monitor and process the output of the corresponding alignment detector, that includes a single sensor, and, based on the output of the alignment detector, the variable-speed drive controller may be configured to control the irrigator span motor to increase or decrease speed so as to maintain the interconnected irrigator spans in a substantially linear orientation to the respective longitudinal axes of the irrigator spans, i.e., maintain substantial straight alignment of the irrigator spans with respect to each other. The single sensor included in each alignment detector of each variable-speed drive assembly signals varying degrees of misalignment of the irrigator spans in both the forward movement direction and the reverse movement direction. Such single sensor detects movement, and, thereby, degrees of misalignment, in the variable-speed drive assembly&#39;s mechanical components at each intermediate tower structure as the corresponding irrigator span moves in either a forward movement direction or a reverse movement direction. In contrast to both Krieger and Malsam, the present invention discloses the use of dual alignment sensors, one alignment sensor for the forward movement direction and a second alignment sensor for the reverse movement direction. 
         [0030]    The following is an example of an implementation of the present invention using variable-speed drive assemblies.  FIG. 1  illustrates a center pivot irrigation system  1  in accordance with an embodiment of the present invention using variable-speed drive assemblies  35 , each with a variable-speed drive controller  39  using a dual sensor alignment detector  49  with a first sensor  40  and a second sensor  41 . These first and second sensors  40 ,  41  are configured to detect misalignment of each intermediate irrigator span  12 ,  13  and end irrigator span  14 . Each of the sensors  40 ,  41  of the dual sensor alignment detector  49  is dedicated to detecting misalignment in only one of the two movement directions  54 ,  55  of the center pivot irrigation system  1 . For the purpose of this disclosure, the term “sensor” should be construed to include devices for measuring a varying degree of misalignment of the irrigator spans. The sensors  40 ,  41  can provide either an analog or digital output signal quantifying the degree of this misalignment. This contrasts with both the legacy limit switch alignment method that provides only an on/off signal to correct misalignment and the alignment methods that use a single sensor to detect degrees of misalignment in both directions as disclosed by Krieger and Malsam. 
         [0031]    The variable-speed-speed drive assembly  35  may include a dual sensor alignment detector  49  with first and second sensors  40 ,  41 , an irrigator span motor  38 , wheels  36 , and a variable-speed drive controller  39 . The variable-speed drive controller  39  typically used by the present invention may include a dual sensor alignment detector  49  with first and second sensors  40 ,  41  to detect and signal misalignment of the intermediate irrigator spans  12 ,  13  and end irrigator span  14 . In a preferred embodiment, the first sensor  40  detects misalignment in a forward movement direction  54 , and the second sensor  41  detects misalignment in a reverse movement direction  55 . The corresponding signal status of the sensors  40  and  41  signal to the variable-speed controller  39  of the variable-speed drive assembly  35  to enable changes in span motor  36  speed in either a forward movement direction  54 , signaled by the first sensor  40 , or a reverse movement direction  55 , signaled by the second sensor  41 . The output signals of the sensors  40 ,  41  of dual sensor alignment detector  49  are used to achieve and maintain substantial straight alignment with constant tension within and between the plurality of intermediate irrigator spans  12 ,  13  and end irrigator spans  14  in either a forward movement direction  54  or a reverse movement direction  55  while the irrigation system  1  is operating. 
         [0032]      FIGS. 2 and 3  illustrate a variable-speed drive assembly  35  with a variable-speed drive controller  39  configured to modify aspects of 3-phase AC (alternating current) supply power delivered over conductor L 1   68 , conductor L 2   69  and conductor L 3   70  of the incoming span cable  20  in either a forward movement direction  54  or a reverse movement direction  55  ( FIG. 1 ), such direction of movement communicated conventionally to variable-speed drive controller  39  by forward movement direction signal  22  and reverse movement direction signal  23 , respectively. The variable-speed drive controller  39  is also signaled by a first sensor output value  92  and a second sensor output value  93  from the first sensor  40  and second sensor  41 , respectively, of the dual sensor alignment detector  49 . The dual sensor alignment detector  49  including a first sensor  40  and a second sensor  41 , both mounted to a cam  83  by a pivoting pin  74  ( FIGS. 2 and 3 ) and including a first sensor actuator shaft  71  and a second sensor actuator shaft  72 , each configured to detect rotational movement of the cam  83  as the first sensor actuator shaft  71  and second sensor actuator shaft  72  are compressed and uncompressed against a first adjustable set-screw  90  and a second adjustable set screw  91 , respectively, of the stationary back plate  64 . This compressing and uncompressing of the sensor actuator shafts  71  and  72 , respectfully, is caused by rotational movement of the cam  83  driven by the rod  87  moved by a mechanical alignment mechanism of a corresponding flexible joint  3  ( FIG. 4 ) of the intermediate irrigator spans  12 ,  13  and end irrigator span  14  ( FIG. 1 ). The continuous compressing and uncompressing of the sensor actuator shafts  71 , 72  causes two sensor output values  92 ,  93 , respectively, to each be continuously communicated to the variable-speed drive controller  39  over signal wires  94 ,  95 , respectively, through the 5-wire terminal strip  97 . 
         [0033]      FIG. 3  is a three-dimensional view of the dual sensor alignment detector  49  illustrating the connection of the sensors  40 ,  41  to the cam  83  by the pivoting pin  74 . 
         [0034]      FIG. 4  is a top view of two intermediate irrigator spans  12 ,  13  and a flexible joint  3  therebetween illustrating predetermined alignment limits between the intermediate irrigator spans  12 ,  13 . 
         [0035]      FIGS. 5 and 6  are illustrations of the respective longitudinal axes of the intermediate irrigator spans  12 ,  13 , with deviations in alignment of the end irrigator span  14  in either a forward movement direction  54  or a reverse movement direction  55 .  FIG. 7  is a top view of an irrigation system  1  with the intermediate irrigator spans  12 , 13  and end irrigator span  14  in a leading bow for the forward movement direction  54 .  FIG. 8  is a top view of an irrigation system  1  with the intermediate irrigator spans  12 , 13  and end irrigator span  14  in a leading bow for the reverse movement direction  55 . 
         [0036]      FIG. 1  illustrates an irrigation system  1  in accordance with the present invention. Examples of irrigation systems  1  include linear or lateral move irrigation systems  1 , center pivot irrigation systems  1 , or the like.  FIG. 1  illustrates an embodiment of the present invention wherein the irrigation system  1  is a center pivot irrigation system  1 , however, it is contemplated that the present invention may be implemented with other types of irrigation systems  1  including linear and lateral move irrigation systems  1 . As shown, the irrigation system  1  may include a center pivot tower structure  2 , a main section assembly  10  coupled or connected to the center pivot tower structure  2 . The center pivot tower structure  2  has access to a water source to furnish water to the irrigation system  1 . 
         [0037]    The main section assembly  10  includes a number of interconnected intermediate irrigator spans  12 ,  13  with applicant conduits  24 ,  25  that are each supported by a truss-type framework structure  6 ,  7  and by one or more intermediate tower structures  30 ,  31  and an interconnected end irrigator span  14  with applicant conduit  26  that is supported by a truss-type framework structure  8  and by an end tower structure  32 . The intermediate tower structures  30 ,  31  and end tower structure  32  are configured to travel about the center pivot tower structure  2  in a circular path that creates wheel tracks  50 ,  51 ,  52 . The intermediate tower structures  30 ,  31  and end tower structure  32  may be any tower configuration known in the art to adequately support the applicant conduits  24 ,  25 ,  26 , e.g., pipes, described herein. It is to be understood that the main section assembly  10  may include any number of intermediate irrigator spans  12 , 13  and end irrigator span  14  and intermediate tower structures  30 ,  31  and end tower structure  32 . The direction of travel for the main section assembly  10  can be either a forward movement direction  54  or a reverse movement direction  55 . 
         [0038]    The intermediate tower structures  30 ,  31  and the end tower structure  32  each may include one or more wheels  36 , to assist in traversing the irrigation system  1  so as to pivot the main section assembly  10  about a ground surface, cultivation area or field in a forward movement direction  54  or a reverse movement direction  55  along wheel tracks  50 ,  51 ,  52 . As shown in  FIG. 1 , each intermediate irrigator span  12 ,  13  and end irrigator span  14  may include applicant conduits  24 ,  25 ,  26  that are configured to carry liquid, e.g., applicant, along the length of the irrigation system  1  to one or more applicant dispersal assemblies (not shown) that are configured to irrigate the cultivation area. Each applicant conduit  24 ,  25 ,  26  may be coupled to one another to allow fluid communication between each applicant conduit  24 ,  25 ,  26 . In an implementation, the applicant conduits  24 ,  25 ,  26  may be supported by truss-type framework structures  6 ,  7 ,  8 . Thus, the main fluid displacement device may be configured to displace applicant through the applicant conduits  24 ,  25 ,  26 . As shown in  FIG. 1 , the irrigation system  1  also may include a cantilevered boom structure  5  that extends outwardly from the end tower structure  32 . 
         [0039]    Both the forward movement direction  54  and the reverse movement direction  55  are dependent on the direction of rotation of the central shafts of the rotors of the irrigator span motors  38 . The wiring configuration of 3-phase AC supply power conductor-L 1   68 , conductor-L 2   69 , and conductor-L 3   70 , included in the incoming span cable  20  and outgoing span cable  21 , may be configured to result in either a clockwise rotation or a counter clockwise rotation of the central shafts of the rotors of the irrigator span motors  38 . Simply reconfiguring two of the three 3-phase AC supply power (i.e., conductor-L 1   68 , conductor-L 2   69 , and conductor-L 3   70 ) results in a reversal of the rotation of the central shafts of the rotors of the irrigator span motors  38 . Thus, in operation, the forward movement direction  54  or reverse movement direction  55  for irrigation system  1  is conventionally changed, both in the prior art and in the system of the present invention, from forward to reverse or reverse to forward using an electromechanical contactor device, controlled by an operator and typically located at a central control panel (not shown), that is typically connected to span cable out  20  at the central control panel (not shown) at a center pivot tower structure  2  (FIG.  1 ). The conventional operation of said electromechanical contactor device configures 3-phase AC supply power consisting of conductor-L 1   68 , conductor-L 2   69 , and conductor-L 3   70  in incoming span cable  20  to provide either a clockwise rotation or a counter clockwise rotation of the central shafts of the rotors of the irrigator span motors  38  that results in the desired forward movement direction  54  or reverse movement direction  55 , as selected by an operator. 
         [0040]    With reference to  FIG. 2 , it should also be noted that typically the same electromechanical contactor device, controlled by an operator and typically located at a central control panel (not shown), configures 3-phase AC supply power conductor-L 1   68 , conductor-L 2   69 , and conductor-L 3   70  to set the rotation of the central shafts of the rotors of irrigator span motors  38  to result in either a forward movement direction  54  or a reverse movement direction  55 , also communicates the respective forward movement direction signal  22  or reverse movement direction signal  23  to the variable-speed drive controller  39 . 
         [0041]    Continuing with  FIG. 2 , each variable-speed drive assembly  35  may include a dual sensor alignment detector  49  comprised of a first sensor  40  and a second sensor  41 , a cam  83 , and a rod  87 , an irrigator span motor  38 , wheels  36 , and a variable-speed drive controller  39  that varies aspects of the supply power, i.e., varies the speed, furnished to the corresponding span motor  38 . The forward movement direction signal  22  and reverse movement direction signal  23  are communicated to the variable-speed drive assembly  35  by way of incoming span cable  20  and outgoing span cable  21 . The forward movement direction signal  22  and reverse movement direction signal  23  are each discretely connected by wire or other means to the variable-speed drive controller  39 . 
         [0042]    Continuing with  FIG. 2 , the forward movement direction signal  22  circuit and the reverse movement direction signal  23  circuit are each conventionally connected to the variable-speed drive controller  39  (although in an embodiment this configuration could be different). The dual actuation of both sensors  40 ,  41  may be achieved by cam  83  being rotated by movement of one or more rods  87 . In an implementation of the present invention, one or more intermediate tower structures  30 ,  31  may be controlled by a suitable variable-speed drive assembly  35 , or the like, to assist in traversing the irrigation system  1  over a respective ground surface, cultivation area or field. For example, each intermediate tower structure  30 ,  31  may include a variable-speed drive assembly  35  to propel the respective intermediate tower structure  30 ,  31  over a respective ground surface, cultivation area or field in either a forward movement direction  54  or a reverse movement direction  55 . It should be noted that the present invention does not require a variable-speed drive assembly  35  at the end tower structure  32 . In contrast with intermediate tower structures  30 ,  31  the end tower structure  32  does not require an alignment adjustment and can be controlled using a fixed-speed drive controller (legacy drive), a variable-speed drive controller  39 , or by other means known in the art. 
         [0043]    As described above, the variable-speed drive assembly  35  may incorporate one or more span motors  38  configured to drive the irrigation system  1  in a forward movement direction  54  or a reverse movement direction  55  based on the configuration of 3-phase AC supply power conductor-L 1   68 , conductor-L 2   69 , and conductor-L 3   70 . In either a forward movement direction  54  or a reverse movement direction  55 , the alignment between each intermediate irrigator span  12 ,  13  and between the outermost intermediate irrigator span  13  and end irrigator span  14  of the irrigation system  1  may be maintained by the rotation of one or more cams  83 , rotated by one or more rods  87 , such cams  83  may include a first sensor  40  with a first sensor actuator shaft  71  and a second sensor  41  with a second sensor actuator shaft  72  being compressed and uncompressed, the degree of such compression and decompression controlled by two adjustable set screws  90 ,  91  of back plate  64 ,  FIG. 3 , thereby communicating sensor output values  92 ,  93  to the corresponding variable-speed drive controller  39  to control the speed of irrigator span motor  38  at each intermediate irrigator span  12 ,  13  flexible juncture  3  on the intermediate tower structures  30 ,  31 . The continuous compressing and uncompressing of the sensor actuator shafts  71 ,  72  of sensor one  40  and sensor two  41 , respectfully, against adjustable set screw one  90  and adjustable set screw two  91 , respectively, of stationary back plate  64  causes the sensor output values  92 ,  93  to be continuously communicated to the variable-speed drive controller  39  over signal wires  94 ,  95  through the 5-wire terminal strip  97 . 
         [0044]    Assuming a forward movement direction  54 , the first sensor  40  may be configured to continuously communicate a first sensor output value  92  to result in a discrete speed for the irrigator span motor  38 , such speed being necessary to maintain alignment of intermediate irrigator spans  12 ,  13  in a forward movement direction  54 . Similarly, assuming a reverse movement direction  55 , the second sensor  41  may be configured to continuously communicate a second sensor output value  93  to result in a discrete speed for span motor  38 , such speed being necessary to maintain alignment of intermediate irrigator spans  12 ,  13  in a reverse movement direction  55 . 
         [0045]    As shown in  FIG. 2 , each variable-speed drive assembly  35  may include a variable-speed drive controller  39 . A non-limiting list of suitable variable-speed drive controller  39  types includes an AC (alternating current) VFD (variable frequency drive), a variable-torque V/Hz (volts-per-hertz) control VFD, a flux control VFD, a DTC (direct torque control) VFD, a sensorless vector control VFD, a sensored vector control VFD, a brush type DC (direct current) variable-drive control unit, or a DC variable-drive control unit, and the like, all with or without an internal or an external microcontroller or an internal or an external PLC (programmable logic controller). 
         [0046]    While  FIG. 2  illustrates that the variable-speed drive controller  39  can be incorporated inside, e.g., housed within, the variable-speed drive assembly  35 , it is to be understood that the variable-speed drive controller  39  may be a standalone unit. 
         [0047]    As shown in  FIG. 2 , the variable-speed drive controller  39  may be directly connected with the sensors  40 ,  41  (e.g., via a wired connection) of the dual sensor alignment detector  49 . A non-limiting list of suitable sensor  40 ,  41  types includes a potentiometer, a capacitive alignment sensor, a GPS (global positioning system)-based alignment sensor, a laser-based alignment sensor, a non-contact proximity sensor, or any other device capable of signaling varying states of alignment, and the like. The dual sensor alignment detector  49  may result in the sensors  40 ,  41  being actuated by the movement of a cam  83  (similarly shown in  FIGS. 2 and 3 ) on a shaft connected to a corresponding rod  87  associated with a corresponding intermediate irrigator span  12 ,  13 . The sensors  40 ,  41  may be used to communicate sensor output values  92 ,  93  to signal a discrete speed setting for the irrigator span motor  38  in both movement directions  54 ,  55 , respectively. 
         [0048]    Conventionally, selection of either a forward movement direction  54  or a reverse movement direction  55  by operators of irrigation system  1 , using a central control panel (not shown) at center pivot tower structure  2  or a remote control system at one or more intermediate tower structures  30 ,  31  or end tower structure  32 , determines whether the forward movement direction signal  22  or the reverse movement direction signal  23  (as shown in  FIG. 2 ) is present, i.e., carrying either a forward movement direction signal  22  or a reverse movement direction signal  23  to the variable-speed drive controller  39 . 
         [0049]    With reference to  FIG. 2 , the dual sensor alignment detector  49  may include sensors  40 ,  41  actuated by a cam  83 , wherein the cam  83  may already be included and configured in the installed base of existing electric powered irrigation systems  1 . As such, the basic elements and components of the prior art can be readily used with the present invention to signal a lagging state of alignment  56  ( FIG. 7 ), a non-lagging state of alignment  57  ( FIG. 8 ), a leading state of alignment  58  ( FIG. 8 ), or a non-leading state of alignment  59  ( FIG. 7 ) between the corresponding intermediate irrigator spans  12 ,  13  and the end irrigator span  14  for either movement direction  54 ,  55  as illustrated in  FIGS. 6 and 7 . 
         [0050]    Each of the sensor actuator shafts  71 , 72  of the sensors  40 , 41 , respectively, when compressed into adjustable set screws  90 ,  91 , respectively, may be configured to communicate sensor output values  92 ,  93  to the variable-speed drive controller  39  when a respective intermediate irrigator span  12 ,  13  is in a lagging state of alignment  56 , a non-lagging state of alignment  57 , a leading state of alignment  58 , or a non-leading state of alignment  59  ( FIGS. 7 and 8 ). 
         [0051]    Each sensor  40 ,  41  may be in communication with a variable-speed drive controller  39  of a variable-speed drive assembly  35  of the irrigation system  1 . In response to variable-speed drive controller  39  receiving either a forward movement direction signal  22  or a reverse movement direction signal  23  from an incoming span cable  20  ( FIG. 2 ), the variable-speed drive controller  39  uses the sensor output values  92 ,  93  communicated from the first sensor  40 , forward movement direction  54 , or the signal from second sensor  41 , reverse movement direction  55 , to adjust the speed of the irrigator span motor  38 . The variable-speed drive controller  39 , in turn, is configured to monitor and process the sensor output value  92  and sensor output value  93  of the dual sensor alignment detector  49  over signal wires  94 ,  95 , respectively, and to furnish to the corresponding span motor  38  a speed setting that maintains alignment of intermediate irrigator span  12 ,  13  and end irrigator span  14 . 
         [0052]    Although the subject matter has been described in language specific to structural features or process operations, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed as example forms of implementing the claims.