Patent Publication Number: US-2013253752-A1

Title: Continuous-move irrigation control system

Description:
BACKGROUND 
     1. Field 
     Embodiments of the present invention relate to control systems for irrigation systems. More particularly, embodiments of the present invention relate to control systems to guide irrigation systems with elevated irrigation pipelines in a continuous manner while maintaining the pipelines in an aligned configuration. 
     2. Discussion of Related Art 
     Crops are cultivated throughout the world in a wide variety of climates with different terrains and soils. It is desirable in many of these climates to artificially supplement the climate&#39;s natural precipitation via irrigation systems to ensure crops receive adequate water. Additionally, irrigation systems can be used to deliver fertilizers and chemicals to, among other things, promote healthy crop growth, suppress weeds, and protect crops from frost. 
     Common irrigation systems include center-pivot systems and lateral-move systems, each having an elevated, elongated pipe supported by a plurality of drive towers spaced along the pipe. The pipe includes a plurality of spaced sprinklers that may extend downward toward the crops to enable distribution of water to the crops from above. Center-pivot systems are ideal for use in fields having circular crop areas and generally include a hydrant located in the middle of each circular crop area. In such systems, an elevated, elongated pipe with sprinklers extends from a hydrant to an outer circumference of the circular crop area such that the systems may be driven in a generally circular or semi-circular pattern over the crops to deliver water thereto during rotation. Lateral-move systems are ideal for use in square, rectangular, and irregular-shaped fields. Such systems generally include one or more hydrants located in and/or adjacent to a field and/or one or more ditches located along or through a field that are connected to an elevated, elongated pipe with sprinklers. Unlike the center-pivot system having a pipe with a stationary end, the pipe in a lateral-move system is connected to and extends from a movable cart designed to traverse up and down a cart path. The pipe may be locked at an angle perpendicular to the cart path and pivot at an end at the cart path, which is desirable if the cart path extends down the middle of a field to enable pivoting from one side of the cart path to the other with each pass along the cart path. 
     In both center-pivot and lateral-pivot move systems, each pipe is long, for example, twenty to thirty feet, and heavy, given the length of the pipe, the components mounted to the pipe, and the water carried in the pipe. To move the pipe and the drive towers during an irrigation operation, each of the drive towers includes one or more wheels that are fixed in orientation and driven by a mechanical drive unit. The mechanical drive units may be a series of electric motors or other similar sources of propulsion. In general, the mechanical drive units propel the drive towers and the pipe forward, for example, in a circular or lateral pattern along a field and over crops, to provide crop irrigation. 
     While the pipe and the drive towers are being driven, it is generally desirable to maintain the towers in linear alignment to ensure uniform crop irrigation and prevent kinking or bursting of the pipe if one or more of the drive towers become misaligned. 
     SUMMARY 
     The following brief summary is provided to indicate the nature of the subject matter disclosed herein. While certain aspects of the present invention are described below, the summary is not intended to limit the scope of the present invention. Embodiments of the present invention provide an irrigation control system and method that maintains proper alignment of an elevated, irrigation pipeline and its drive towers, thereby ensuring uniform irrigation of crops and decreasing a likelihood of kinking or bursting of the pipeline. The present invention provides, in its simplest form, an irrigation control system and method to drive at least one drive tower supporting an irrigation pipeline. 
     The aforementioned aspects may be achieved in one aspect of the present invention by providing a control system to guide a plurality of towers that support a linear pipeline of an irrigation system in a continuous manner along a path. The control system may include an antenna coupled to the linear pipeline, a receiver in communication with the antenna, and/or a controller in communication with the receiver. 
     The antenna may be operable to receive signals from at least one external positional information source. The receiver may be operable to process the signals to produce position data corresponding to a current position of the drive tower with respect to the support tower and produce alignment data of the drive tower with respect to the support tower. The controller may be programmed to drive the wheel at a speed corresponding to a difference between the current position of the support tower and a point along the path and adjust the speed of the wheel based on the alignment data. 
     The external positional information source may be a fixed GPS unit. The controller may include a variable-speed drive motor coupled to the drive tower and operable to drive the wheel of the drive tower at variable speeds. The variable-speed drive motor may drive the wheel continuously throughout an irrigation operation and may be operable to perform a correction during the irrigation operation without ceasing movement of the wheel. The controller may be further programmed to generate a control signal to increase or decrease the speed of the wheel if the alignment data is outside of a range of values. 
     The control signal may maintain a current speed of the wheel if the alignment data indicates that the drive tower is aligned with a vertical plane defined by the end support tower, increase the speed of the wheel if the alignment data indicates that the drive tower is trailing the vertical plane with respect to a forward direction of movement of the drive tower, and/or decrease the speed of the wheel if the alignment data indicates that the drive tower is leading the vertical plane with respect to the forward direction of movement of the drive tower. The controller may be further programmed to transmit a signal to the variable-speed drive motor for adjusting the position of the drive tower with respect to the vertical plane. The controller may be further programmed to generate a control signal to increase or decrease the speed of the wheel if the alignment data is outside of a range of values. 
     The antenna may be further operable to receive global positioning system information. The control may be further programmed to generate a control signal to activate or deactivate an irrigation nozzle mounted on the drive tower. The global positioning system correction information may be a real time kinematic correction factor. The vertical plane may be aligned with a center of a drive line for the linear pipeline. The linear pipeline may be an elevated irrigation pipeline. 
     The aforementioned aspects may also be achieved in an aspect of the present invention by providing a tower to transport a portion of an irrigation system along a path. The tower may include a frame having a wheel, a variable-speed drive motor coupled to the wheel, a portion of an overhead irrigation pipeline supported by the frame, an antenna coupled to the frame and vertically aligned with the portion of the overhead irrigation pipeline, a receiver in communication with the antenna, and a controller in communication with the receiver and the variable-speed drive motor. 
     The variable-speed drive motor may be operable to drive the wheel continuously and at variable speeds to perform correction operations. The antenna may be operable to receive signals from at least one external positional information source. The receiver may be operable to process the signals to produce position data corresponding to a current position of the frame and/or produce alignment data of the frame. The controller may be programmed to drive the wheel at a speed corresponding to a difference between the current position of the frame and a point along the path and/or adjust the speed of the wheel based on the alignment data. The portion of the overhead irrigation pipeline may be positioned at a right angle with respect to a central vertical plane through the wheel. 
     The controller may be further programmed to transmit a control signal to the variable-speed drive motor so that the speed of the wheel is increased or decreased if the alignment data is outside of a range of values, or maintained if the alignment data is within the range of values. The control signal may increase the speed of the wheel if the alignment data is less than a value and decreases the speed of the wheel if the alignment is greater than the value. The antenna may be further operable to receive a real time kinematic correction factor. The tower may further include an irrigation nozzle coupled to the tower and operable to be activated by the controller based on the position data. 
     The aforementioned aspects may also be achieved in an aspect of the present invention by providing a method of driving a tower with an elevated pipeline of an irrigation system in a continuous manner along a path while maintaining alignment of the elevated pipeline. The method may include the steps of acquiring a current position of the tower along the path, acquiring alignment data related to the tower and a portion of the irrigation pipeline coupled to the tower, calculating a point along the path that is a distance from the current position, generating a control signal based on the alignment data and the calculated point along the path, transmitting the control signal to a variable-speed drive motor, driving a wheel coupled to the tower via the variable-speed drive motor to cause the tower to continuously move toward the point at a rate that maintains the alignment data within a range of values, and increasing the rate if the alignment data is less than a value within the range of values, or decreasing the rate if the alignment data is greater than the value or another value within the range of values. The method may further include the step of activating an irrigation nozzle on the tower based on the current position of the tower along the path. 
     Additional aspects, advantages, and utilities of the present invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the present invention are described in detail below with reference to the attached drawing figures, wherein: 
         FIG. 1  is a perspective view of a guidance control system constructed in accordance with various embodiments of the present invention illustrating a lateral move irrigation system with a plurality of drive towers supporting an overhead irrigation pipeline; 
         FIG. 2  is a top plan view of the guidance control system of  FIG. 1 , illustrating one of the drive towers leading a horizontal plane defined by the guidance control system; and 
         FIG. 3  is a flow chart of the guidance control system of  FIG. 1 . 
     
    
    
     The drawing figures do not limit the present invention to the specific embodiments disclosed and described herein. The drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the invention. 
     DETAILED DESCRIPTION 
     The following detailed description of the invention references the accompanying drawings that illustrate specific embodiments in which the invention can be practiced. The embodiments are intended to describe aspects of the invention in sufficient detail to enable those skilled in the art to practice the invention. Other embodiments can be utilized and changes can be made without departing from the scope of the present invention. The following detailed description is, therefore, not to be taken in a limiting sense. The scope of the present invention is defined only by the appended claims, along with the full scope of equivalents to which such claims are entitled. 
     In this description, references to “one embodiment”, “an embodiment”, or “embodiments” mean that the feature or features being referred to are included in at least one embodiment of the technology. Separate references to “one embodiment”, “an embodiment”, or “embodiments” in this description do not necessarily refer to the same embodiment and are also not mutually exclusive unless so stated and/or except as will be readily apparent to those skilled in the art from the description. For example, a feature, structure, act, etc. described in one embodiment may also be included in other embodiments, but is not necessarily included. Thus, the present technology can include a variety of combinations and/or integrations of the embodiments described herein. 
     Turning to  FIGS. 1 and 2 , a guidance control system  10  constructed in accordance with various embodiments of the present invention for use with a portion of an irrigation system  12  is illustrated. An example of a complete irrigation system is shown and described in more detail in U.S. patent application Ser. No. 13/042,192 filed Mar. 7, 2011, which is hereby incorporated into the present application by reference in its entirety. The guidance control system  10  broadly includes a plurality of antennas  14 A,  14 B,  14 C,  14 D, a receiver  16 , and a controller  18 . 
     The irrigation system  12  is generally utilized to irrigate crops or other farmland areas and includes an elevated linear pipeline  22  extending from a lateral-move cart with support tower  24  that connects the pipeline  22  to a fluid source. The fluid source may be a tank, a well, a canal, or a similar source that typically has a fixed location proximate to or remote from the pipeline  22 . The system  10  is illustrated with the lateral-move cart with support tower  24  for illustrative purposes only and may be configured with other types of supports without deviating from the scope of the present invention. For example, the irrigation system  12  may be configured with a stationary center-pivot support tower instead of the lateral-move cart with support tower  24 . An example of a lateral-move cart is shown and described in more detail in U.S. Patent Publication No. 2010/0274398 filed Apr. 28, 2009, which is hereby incorporated into the present application by reference in its entirety. 
     The pipeline  22  extends along a centerline vertical axis  28  when the pipeline  22  is in a perfectly straight configuration. The vertical axis  28  is defined by an elbow joint  30  of the lateral-move cart with support tower  24 . The pipeline  22  includes a plurality of fluid-spraying sprinklers affixed to the pipeline  22  along a length thereof to deliver fluid to crops during an irrigation operation. The elbow joint  30  rotatably couples the pipeline  22  to the lateral-move cart with support tower  24 . The pipeline  22  has a plurality of sections  32 A,  32 B,  32 C,  32 D extending from and connected in series to the elbow joint  30 . Although the pipeline  22  is illustrated with four sections  32 A,  32 B,  32 C,  32 D, the pipeline  22  may have any number of sections  32 A,  32 B,  32 C,  32 D without deviating from the scope of the present invention and preferably has at least two sections, for example, a support-tower joining section, such as section  32 A, and an end section such as section  32 D. 
     The sections  32 A,  32 B,  32 C,  32 D of the pipeline  22  are substantially identical to each other and respectively include moveable drive towers  34 A,  34 B,  34 C,  34 D that cooperatively support the sections  32 A,  32 B,  32 C,  32 D in an elevated position. Each of the drive towers  34 A,  34 B,  34 C,  34 D includes a structural framework  37  to increase the structural integrity of the sections  32 A,  32 B,  32 C,  32 D, a mechanical drive unit  38 , and a wheel and tire assembly  40 ,  42  on either end of the drive unit  38 . The drive towers  34 A,  34 B,  34 C,  34 D are operable to independently drive the sections  32 A,  32 B,  32 C,  32 D laterally and along a path  36  in coordination with the lateral-move cart with support tower  24 , which also travels laterally and along the path  36 . The drive towers  34 A,  34 B,  34 C,  34 D are also operable to independently drive the sections  32 A,  32 B,  32 C,  32 D around the lateral-move cart with support tower  24 , for instance, to allow the sections  32 A,  32 B,  32 C,  32 D to travel around a circular portion at an end of the path  36  and/or to an opposite side of the path  36 . 
     Each of the drive units  38  is mounted to a lateral bar  48  of the drive towers  34 A,  34 B,  34 C,  34 D that extends substantially perpendicular to the vertical axis  28 , and includes an electric variable-frequency drive VFD motor operable to drive the plurality of wheel and tire assemblies  38 ,  40  at variable speeds. The drive units  38  are each operable to independently communicate with the controller  18  of the guidance control system  10  so that the controller  18  is operable to independently control each of the drive units  38 . The drive units  38  may include linkages, gears, gear boxes, batteries, and other components and communication equipment to allow the wheel and tire assemblies  40 ,  42  to be driven or rotated in forward and reverse directions along the path  36  as controlled by the controller  18 . 
     The wheel and tire assemblies  40 ,  42  are mounted to and spaced from each other along the lateral bar  48  in a fixed orientation to generally define a direction of travel of the wheel and tire assemblies  40 ,  42  along the path  36 . The drive units  38  and the wheel and tire assemblies  40 ,  42  cooperatively permit independent movement of each of the drive towers  34 A,  34 B,  34 C,  34 D along the path  36  at equal or variable speeds relative to each other, as determined by the controller  18 . 
     Each one of the plurality of antennas  14 A,  14 B,  14 C,  14 D of the guidance control system  10  is rigidly coupled to one section  32 A,  32 B,  32 C,  32 D along the pipeline  22 . When the pipeline  22  is in the straight configuration, the plurality of antennas  14 A,  14 B,  14 C,  14 D extend along the vertical axis  28  defined by the elbow joint  30  of the lateral-move cart with support tower  24 . It is foreseen, however, that each of the plurality of antennas  14 A,  14 B,  14 C,  14 D may be positioned at a known fixed distance offset to the vertical axis  28 , for instance, on another part of the irrigation system  12 , without deviating from the scope of the present invention. 
     Each of the plurality of antennas  14 A,  14 B,  14 C,  14 D extends in an upward direction that is roughly perpendicular to the path  36 . Thus, the longitudinal axis of each of the plurality of antennas  14 A,  14 B,  14 C,  14 D always maintains a right angle relative to the direction of travel of the wheel and tire assemblies  40 ,  42 . In the exemplary embodiment, the plurality of antennas  14 A,  14 B,  14 C,  14 D cooperatively operate as a network with each of the plurality of antennas  14 A,  14 B,  14 C,  14 D corresponding to one of the sections  32 A,  32 B,  32 C,  32 D. It is foreseen, however, that the guidance control system  10  may utilize any number of antennas and as few as a single antenna without deviating from the scope of the present invention. 
     Each of the plurality of antennas  14 A,  14 B,  14 C,  14 D is operable to independently receive a signal containing positional information from a GPS source  15 , such as the Global Positioning System satellite navigation system, one or more satellite sources, and/or one or more terrestrial sources. The positional information relates to a position of one or more of the plurality of antennas  14 A,  14 B,  14 C,  14 D, such as latitude and/or longitude coordinates of one or more of the plurality of antennas  14 A,  14 B,  14 C,  14 D as well as heading and altitude information of one or more of the plurality of antennas  14 A,  14 B,  14 C,  14 D. The positional information may be received in a continuous, real-time fashion as is typically determined and controlled by the external systems such as the Global Positioning System and an RTK or similar system. Each of the plurality of antennas  14 A,  14 B,  14 C,  14 D is operable to communicate the signals to the receiver  16  as they are received. It is foreseen that the guidance control system  10  may operate with as few as one of the plurality of antennas  14 A,  14 B,  14 C,  14 D. For example, antennas  14 A,  14 B may be removed at the sections  32 A,  32 B without deviating from the scope of the present invention. 
     Each of the plurality of antennas  14 A,  14 B,  14 C,  14 D may also receive another signal from a correction source or secondary fixed GPS unit  54 , which provides a Real Time Kinematic (RTK) system with correction information about the positional information received by each of the plurality of antennas  14 A,  14 B,  14 C,  14 D to increase the accuracy of the positional information. With the correction information, the position of the pipeline  22  along the path  36  may be determined to within a few centimeters or less. The correction source  54  may be terrestrial-based and may include a dedicated or shared RTK base station plus radios (900 MHz ISM spread spectrum or licensed at approximately 450 MHz) or a public or commercial virtual reference station plus cellular or radio connections, or may be satellite-based such as OmniSTAR® with compatible receiving components. The correction source  54  is located in the path  36  in the exemplary embodiment, but may be located at any known distance that enables communication between the correction source  54  and the antenna  14 . 
     The receiver  16  of the guidance control system  10  is located in a fixed location that is remote from the plurality of antennas  14 A,  14 B,  14 C,  14 D. It is foreseen, however, that the receiver  16  may be located anywhere, for example, on the irrigation system  12 , provided that the receiver  16  is operable to communicate with the plurality of antennas  14 A,  14 B,  14 C,  14 D. The receiver  16  may include crystal oscillators and signal amplifiers as well as other components as are known in the art. The receiver  16  is operable to receive, via a wired or wireless connection, each of the signals from the plurality of antennas  14 A,  14 B,  14 C,  14 D and independently output the signals to the controller  18 . It is foreseen that the receiver  16  may perform one or more processing operations on signals received. In the exemplary embodiment, the receiver  16  assigns a unique identifier to each of the signals received to enable identification of the source from which each of the signals was received, that is, from which of the plurality of antennas  14 A,  14 B,  14 C,  14 D. 
     The controller  18  of the guidance control system  10  is located in a fixed location that is remote from the plurality of antennas  14 A,  14 B,  14 C,  14 D and is preferably adjacently located to the receiver  16  and wired thereto for communication therewith. It is foreseen, however, that the controller  18  may be located anywhere, for example, secured to the irrigation system  12 , provided that the controller  18  is operable to communicate with the receiver  16 , for instance, via at least a wireless connection. 
     The controller  18  is operable to receive and further process the information transmitted from the receiver  16  to determine various factors related to each of the plurality of antennas  14 A,  14 B,  14 C,  14 D. For instance, the factors determinable by the controller  18  based on the information may be the latitude and/or longitude coordinates of one or more of the plurality of antennas  14 A,  14 B,  14 C,  14 D as well as heading and altitude information of one or more of the plurality of antennas  14 A,  14 B,  14 C,  14 D. The controller  18  may then compare the factors of each of the plurality of antennas  14 A,  14 B,  14 C,  14 D to determine whether the pipeline  22  and/or the drive towers  34 A,  34 B,  34 C,  34 D are aligned with each other and/or the vertical axis  28 . The factors may be determined by the controller  18  in a continuous, real-time fashion as the information is transmitted by the receiver  16  and the plurality of antennas  14 A,  14 B,  14 C,  14 D. The controller  18  is further operable to control the speed of the pipeline  22  and drive towers  34 A,  34 B,  34 C,  34 D as they travel along the path  36  based on one or more of the signals. For instance, the controller  18  may set a speed of each of the drive units  38 A,  38 B,  38 C,  38 D to an equal and/or different speeds relative to each other. In the exemplary embodiment, the controller  18  utilizes speeds for each of the drive units  38 A,  38 B,  38 C,  38 D that are slightly different to account for a radial distance of the drive units  38 A,  38 B,  38 C,  38 D from the lateral-move cart with support tower  24 . 
     The controller  18  is operable to individually communicate with the drive units  38 A,  38 B,  38 C,  38 D by transmitting control signals of varying frequencies that are receivable by the drive units  38 A,  38 B,  38 C,  38 D. The drive units  38 A,  38 B,  38 C,  38 D are each assigned to one or more different frequencies, which, when received by one or more of the drive units  38 A,  38 B,  38 C,  38 D, cause the drive unit  38 A,  38 B,  38 C,  38 D to perform a function. For example, a control signal transmitted by the controller  18  may cause one or more of the drive units  38 A,  38 B,  38 C,  38 D to increase, decrease, and/or maintain its rotational speed of the wheel and tire assemblies  40 ,  42  based on the current position of the pipeline  22  and drive towers  34 A,  34 B,  34 C,  34 D with respect to the vertical axis  28  and the path  36  that the pipeline  22  is supposed to follow. 
     The controller  18  may include processors, microprocessors, microcontrollers, field-programmable gate arrays (FPGAs), similar programmable logic devices, or combinations thereof. The controller  18  may further include data storage components, or memory, such as random-access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM), and the like, as well as hard drives, compact disc ROM (CDROM) drives, digital video disc (DVD) drives, flash drives, or the like, and combinations thereof. The controller  18  may also include data input devices, such as keypads, keyboards, mice, etc., and data output devices, such as monitors, displays, lighted indicators, printers, and the like. The controller  18  may additionally include ports to receive data from external sources such as hard wired ports to receive electrical data over a wire or cable, or radio-frequency (RF) ports to receive data wirelessly. 
     The controller  18  may be configured or programmed to execute instructions or operations which may be implemented in hardware, software, firmware, or combinations thereof. In various embodiments, the instructions may be included in a program which may be stored on a computer-readable medium such as RAM, ROM, EPROM, flash memory, a hard-disk drive, a floppy disk, a CD or CDROM or variations thereof, a DVD, a Blu-ray Disc™ (BD), and the like. 
     Turning to  FIG. 3 , the guidance control system  10  may operate as follows. To begin an irrigation operation, the controller  18  transmits control signals at various frequencies to each of the drive units  38 A,  38 B,  38 C,  38 D, which initiates movement of the pipeline  22  and drive towers  34 A,  34 B,  34 C,  34 D along the path  36  at a predetermined speed. As the drive units  38 A,  38 B,  38 C,  38 D and hence the pipeline  22  move along the path  36 , each of the plurality of antennas  14 A,  14 B,  14 C,  14 D receives the signals from the GPS source  15  and the correction source  54  in a continuous and real-time fashion. The information is transmitted from each of the plurality of antennas  14 A,  14 B,  14 C,  14 D to the receiver  16  for processing as the information is received by the plurality of antennas  14 A,  14 B,  14 C,  14 D. The receiver  16  assigns a unique identifier to the information to enable identification of the source from which the information was received, that is, from which of the plurality of antennas  14 A,  14 B,  14 C,  14 D. The receiver  16  then transmits the information to the controller  18 . 
     The controller  18  processes the information to derive positional, heading, and/or altitude information of each of the plurality of antennas  14 A,  14 B,  14 C,  14 D, and assigns a value to each of the plurality of sections  32 A,  32 B,  32 C,  32 D based on the information that represents a real-time position of each of the plurality of sections  32 A,  32 B,  32 C,  32 D. The controller  18  then compares each value of the plurality of sections  32 A,  32 B,  32 C,  32 D to stored data to determine whether each value corresponds to a correct position along the path  36  for each of the plurality of antennas  14 A,  14 B,  14 C,  14 D. The correct position of the plurality of antennas  14 A,  14 B,  14 C,  14 D corresponds to the vertical axis  28  and, in the exemplary embodiment, is the is the plurality of antennas  14 A,  14 B,  14 C,  14 D aligned along and/or within a predetermined acceptable distance or range of the vertical axis  28 , for instance, one foot from the vertical axis  28 . 
     In the exemplary embodiment, the correct position is derived based on the speed at which the plurality of sections  32 A,  32 B,  32 C,  32 D are traveling, as determined by the controller. In other embodiments, the correct position may be derived based on data stored in the controller  18  about the path  36  that the wheels and tire assemblies  40 ,  42  should follow. In other embodiments, the correct position may be derived based on information received by the controller  18  about the path  36  from an external source. In other embodiments, the correct position may be derived based on sensory data received by the controller  18  from one or more sensors, for instance, sensory data of a real-time position of the elbow joint  30  and the vertical axis  28 . 
     If the value of one or more of the plurality of sections  32 A,  32 B,  32 C,  32 D is not equal to and/or outside of the predetermined acceptable range of the correct position, then one or more of the plurality of sections  32 A,  32 B,  32 C,  32 D are misaligned. To correct the misalignment, the controller  18  transmits a control signal to one or more of the drive units  38 A,  38 B,  38 C,  38 D to temporarily reduce and/or increase the speed of one or more of the drive towers  34 A,  34 B,  34 C,  34 D until the value of one or more of the plurality of sections  32 A,  32 B,  32 C,  32 D is equal to and/or within the predetermined acceptable range of the correct position. The control signal may by characterized by, for example, a specific frequency. 
     For exemplary purposes,  FIGS. 1 and 2  illustrate drive tower  34 D leading the other drive towers  34 A,  34 B,  34 C and causing the section  32 D of the pipeline  22  to bend and extend horizontally beyond of the vertical axis  28 , which may result in non-uniform irrigation of crops. If the pipeline  22  bends too far beyond the vertical axis  28 , the pipeline  22  may kink or break and require significant maintenance and downtime of the irrigation system  12 . To correct the illustrated bend in the pipeline  22 , the controller  18 , upon a determination by the controller  18  that drive tower  34 D is misaligned via the information transmitted from the antenna  14 D, transmits a control signal with a specific frequency assigned to drive unit  38 D to cause the drive unit  38 D to temporarily decrease speed to a new speed that is less than a speed traveled by the drive towers  34 A,  34 B,  34 C. Because the drive unit  38 D has the VFD motor, the drive unit  38 D is not required to stop to realign the drive tower  34 D with the drive towers  34 A,  34 B,  34 C and may make corrections by simply changing speed. Thus, the present invention provides for a relatively smooth realignment of the drive towers  34 A,  34 B,  34 C,  34 D via one or more speed adjustments without stopping of the tower  34 D, which could result in excessive irrigation of crops under the stopped drive tower  34 D. 
     When the information, as continuously transmitted from the antenna  14 D, indicates that the drive tower  34 D is aligned with drive towers  34 A,  34 B,  34 C, the controller  18  transmits another control signal assigned to drive unit  38 D to cause the drive unit  38 D to increase speed to a speed sufficient to maintain alignment of the drive towers  34 A,  34 B,  34 C,  34 D. It is foreseen that, due to the nature of the path  36 , the drive towers  34 A,  34 B,  34 C,  34 D may travel in slightly different speeds to maintain alignment of the drive towers  34 A,  34 B,  34 C,  34 D. For example, outermost drive tower  34 D may travel faster than innermost drive tower  34 A to maintain alignment of the drive towers  34 A,  34 B,  34 C,  34 D. In this manner, controller  18  is operable to ensure that the pipeline  22  maintains a straight configuration with the plurality of sections  32 A,  32 B,  32 C,  32 D aligned as the pipeline  22  and the drive towers  34 A,  34 B,  34 C,  34 D travel along the path  36 . 
     The information provides additional functionality to the guidance control system  10 . In the exemplary embodiment, the controller  18  controls operation of an end sprinkler gun  50  mounted to the drive tower  34 D at an end  52  of the pipeline  22 . The position of the end sprinkler gun  50  on the drive tower  34 D at the end of the series of drive towers  34 A,  34 B,  34 C,  34 D allows the end sprinkler gun  50  to irrigate one or more portions of the path  36  beyond the end  52  of the pipeline  22 . For instance, if irrigation is desired beyond the end  52  of the pipeline  22  and the drive towers  34 A,  34 B,  34 C,  34 D, the controller may selectively activate the end sprinkler gun  50  when the information indicates that the end sprinkler gun  50  and the pipeline  22  are in a position to irrigate and deactivate the end sprinkler gun  50  and the pipeline  22  have traveled beyond the position. In this manner, the guidance control system  10  is operable to irrigate one or more portions of the path  36  beyond the end  52  of the pipeline  22 . 
     Although the invention has been described with reference to the embodiments illustrated in the attached drawing figures, it is noted that equivalents may be employed and substitutions made herein without departing from the scope of the invention as recited in the claims.