Abstract:
A dual span center pivot irrigation system comprising first and second center pivot span structures pivotally secured at their inner ends to a fixed center pivot structure. Each of the center pivot span structures are independently operable with the movements thereof being coordinated by suitable controls. The center pivot span structures may be operated in at least three different modes, namely: (1) independent wiper; (2) follow the leader; and (3) independent full circle.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a dual span center pivot irrigation system and more particularly to the controls for independently operating and coordinating the movement of each of spans of the center pivot irrigation system relative to one another in at least three different modes. Each of the center pivot span structures is pivotally secured to a fixed center pivot structure and is supported upon one or more self-propelled drive units for pivotally moving the span structure relative to the center pivot structure. 
     2. Description of the Related Art 
     Optimal plant husbandry requires adherence to the art of irrigation with a fair degree of precision. While established plants can tolerate over watering and under watering to a certain degree, seeds and seedlings are not so tolerant. Efficient farming practices demand a very specific seed density with a relatively high germination rate. Improper irrigation results in gaps or irregularities in seed density, and improper watering of the seeds will have a deleterious effect in achieving a proper germination rate. 
     Extremely small seeds, such as carrot seeds, have a very poor germination rate using conventional irrigation techniques. The primary problem associated with the conventional irrigation techniques with respect to small seeds involves controlling the amount of irrigation liquid (e.g., water) and its effect on the seed exposed on a surface for germination. Because the very small seeds are unduly influenced by heavy water application, small seeds will fail to stay in a designated spot and will wash away with the irrigation water, thereby increasing the seed density in one area to the exclusion of other areas 
     There are two basic types of conventional irrigation, Center Pivot and Solid Set. In a conventional center pivot irrigation system, a fixed center pivot structure is provided which includes a vertically disposed water supply pipe supported thereon which is in communication with a source of irrigation water under pressure. The center pivot span structure is pivotally secured at its inner end to the center pivot structure and includes a water delivery pipe supported on one or more self-propelled drive units with the inner end of the water delivery pipe being in fluid communication with the vertically disposed water supply pipe. In operation, the center pivot span structure pivots or rotates in a circle, or portions thereof, about the fixed center pivot structure. Inasmuch as the center pivot span structure rotates in a 360-degree circle, in normal situations, one revolution of the center pivot span structure results in a complete irrigation of the underlying area contained beneath the span structure. One complete revolution of the center pivot span structure normally consumes a considerable amount of time such that successive passes over the same area will not occur frequently enough for small seeds and the seedlings growing therefrom. Thus, the farmer is faced with the difficult choice of applying a relatively fine mist of water to the delicate seeds on an intermittent basis and hoping that a high germination rate results therefrom. Inasmuch as soil can only absorb the irrigation liquid at a certain rate, the farmer is limited with respect to the amount of water that may be dispensed on a single pass versus the amount of time that successive passes can occur with a single center pivot span structure. Thus, the dilemma heretofore faced by the farmer is the delicate balancing of a spray rate per single pass of a single center pivot span structure versus the absorption capability of the underlying soil and the seed size to retain the seed in the desired location while preventing the washing of soil or other matter which will cover up the seeds. 
     In a conventional Solid Set irrigation system, an irrigation pipe network placed above ground throughout the filed is provided which includes evenly space vertical pipes, typically terminated with impact sprinklers place at a height slightly above a mature crop canopy. The irrigation pipe network is in communication with a source of irrigation water under pressure. In operation, a valve is opened allowing water to be distributed though the pipe network and impact sprinklers. Due to the design of impact sprinklers, prior to full water pressure in the pipe, the water distributed through the impact sprinklers floods or “dribbles” onto the field. In a similar manner, as the water pressure is turned off, instead of instantly shutting off the water distribution through the impact sprinklers, the water floods or “dribbles” onto the field as water pressure is lost. The effects of turning water ON and OFF through the impact sprinklers of Solid Set irrigation results in a redistribution of small seedlings know as wash-out. Because the irrigation pipe network is located above ground, this wash-out effect can also be the result of a break in the pipe network. Also associated with a conventional Solid Set irrigation system is the associated labor. Because the irrigation pipe network is located above ground, the network must be assembled and disassembled at various times throughout the growing season to accommodate various cultivation and harvesting equipment. 
     In the pending provisional application Ser. No. 60/651,011 filed Feb. 8, 2005, and entitled IRRIGATION SYSTEM HAVING TWO OR MORE SPANS EXTENDING FROM A CENTER PIVOT STRUCTURE, several patents were discussed in the Background of the Invention portion of the application. None of/the prior art patents disclosed in the pending application involves the use of two or more center pivot span structures which pivotally extend outwardly from a center pivot structure and which are independently driven. In the provisional application, a disclosure is made of two or more center pivot span structures pivotally secured to a fixed center pivot structure and which extend outwardly therefrom with the span structures being independently driven to achieve the desired irrigation of small seeds or the like. Although the concept of two or more center pivot span structures extending outwardly from a center pivot structure is disclosed in the provisional application, the control means and the operational safeties involved therewith were not disclosed in detail. The subject of this invention is the control means and the safeties associated therewith for operating at least a pair of center pivot span structures which radially extend outwardly from a center pivot structure with the center pivot span structures being operated in various modes such as: (1) independent wiper; (2) follow the leader; and (3) independent full circle. 
     SUMMARY OF THE INVENTION 
     A center pivot irrigation system is disclosed comprising a fixed center pivot structure including a vertically extending water supply pipe having upper and lower ends. The water supply pipe is fluidly connected to a source of irrigating water under pressure. The system also includes at least first and second center pivot span structures having inner and outer ends. The inner end of the first span structure is operably pivotally secured and fluidly connected to the water supply pipe at the upper end thereof with the first span structure including at least one self-propelled drive unit for pivotally moving the first span structure with respect to the center pivot structure. The inner end of the second span structure is also operably pivotally secured and fluidly connected to the water supply pipe below the connection of the first span structure to the water supply pipe. The second span structure also includes at least one self-propelled drive unit for pivotally moving the second span structure with respect to the fixed center pivot structure. The first and second span structures are independently pivotally movable with respect to the center pivot structure. 
     In one operating mode of the system, one of the span structures follows the other span structure based on maintaining a user-defined angle. In another mode of operation of the system, each of the span structures moves in partial circles in an independent wiper manner. In another mode of operation of the system, the span structures are operated in independent full circles. A control means is provided for operating the span structures including operational safeties: (1) maintaining the proper included angle between the span structures; (2) to prevent the systems from coming too close to one another; and (3) to prevent the collision of the span structures. 
     It is therefore a principal object of the invention to provide an improved center pivot irrigation system which includes two or more center pivot span structures extending outwardly from a fixed center pivot structure together with the means for independently operating and controlling the operation of the span structures. 
     Still another object of the invention is to provide a system of the type described wherein irrigating water is not delivered through the water delivery pipe on one of the span structures when that span structure is not moving. 
     Still another object of the invention is to provide a center pivot irrigation system of the type described including a control means having a safety which provides for user defined irrigation control of the two independently moving span structures, ensures that the span structures will be properly spaced from one another during the operation of the same and shuts down the entire system if the span structures move into a position wherein they are too close together. 
     Yet another object of the invention is to provide a center pivot irrigation system of the type described which may be operated in at least three modes, namely: (1) independent wiper; (2) follow the leader; and (3) independent full circle. 
     Yet another object of the invention is to provide a control means for a center pivot irrigation system of the type described which ensures that the seeds being irrigated will not be under watered or over watered, eliminates or reduces “wash-out” and eliminates the labor costs associated with the means of irrigation known as Solid Set. 
     These and other objects will be apparent to those skilled in the art. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a partial perspective view of the dual span center pivot irrigation system of this invention; 
         FIG. 2  is a perspective view of the fixed center pivot structure and the inner ends of the dual spans; 
         FIG. 3  is a partial side view of the upper end of the center pivot structure and the inner ends of the dual spans; 
         FIG. 4  is a partial perspective view of the inner end of one of the span structures; 
         FIG. 5  is a partial plan view of the system operating in the independent full circle mode; 
         FIG. 6  is a view similar to  FIG. 6  except that the system is shown to be operating in the follow the leader mode; 
         FIG. 7  is a view similar to  FIGS. 6 and 7  except that the system is shown as being operated in an independent wiper mode; and 
         FIG. 8  is a top level wiring diagram of the system. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The numeral  10  refers to the center pivot irrigation machine of this invention. Machine  10  includes a center pivot structure  12  which supports a vertically disposed water supply pipe  14  which is in communication with a source of irrigation water under pressure. The upper end of water supply pipe  14  is provided with a plurality of radially spaced openings formed therein such as disclosed in the provisional application. A T-shaped connector  16  comprising a vertically disposed portion  18  and a horizontally extending portion  20  has its vertically disposed portion  18  rotatably embracing the upper end of water supply pipe  14  whereby the interior of the vertically disposed portion  18  is in communication with the radially spaced openings so that water may not only exit the upper end of the vertically disposed portion  18  of T-shaped connector  16  but may also pass outwardly from the outer end of the horizontally extending portion  20  of T-shaped connector  16 . 
     The lower end of a conventional elbow connector  22  is rotatably connected to the upper end of water supply pipe  14  in conventional fashion. The outer end of elbow connector  22  is provided with a flange  24  ( FIG. 3 ) thereon to which is bolted an electrically operated shut-off valve  26 . A conventional pivot flex  28  is bolted to the outer end of the valve  26  and has the inner end of a water delivery pipe  30  bolted thereto and which extends radially outwardly from the center pivot structure  12  in conventional fashion. The water delivery pipe  30  is comprised of a plurality of pipe sections bolted together in an end-to-end relationship to form a first center pivot span structure  32  which includes a plurality of spaced-apart, self-propelled drive units  34  which are adapted to move the first center pivot span structure  32  with respect to the center pivot structure in conventional fashion. The first center pivot span structure  32  includes conventional alignment structure thereon for maintaining the span structure  32  in an aligned condition in conventional fashion. An electrical junction box  50  is at the inner end of span structure  32  for conveying electrical power to the drive units  34  from the center pivot structure  12 . Although the shut-off valve  26  is disclosed as being positioned inwardly of the pivot flex  28 , those positions could be reversed if so desired. 
     The horizontally disposed portion  18  of connector  16  is provided with a flange  38  to which is bolted an electrical water shut-off valve  40 . A pivot flex  42  of conventional design is mounted to the outer end of the valve  40  and has the inner end of a water delivery pipe  44  secured thereto which extends radially outwardly therefrom. Water delivery pipe  44  is comprised of a plurality of pipe sections bolted together in an end-to-end relationship to form a second center pivot span structure  46  which includes a plurality of spaced-apart self-propelled drive units  48  for propelling the second center pivot span structure  46  with respect to the center pivot structure  12 . An electrical junction box  50  is secured to the side of pivot flex  42  for supplying electrical power from the center pivot structure  12  to the second center pivot span structure  46 . The junction box  50  also supplies electrical power and electrical signals to control panels  52  and  54  which are suspended from the inner ends of the span structures  32  and  46 . 
     The numeral  56  refers to a collector ring and resolver assembly positioned above the center pivot structure  12 . Assembly  56  includes a collector ring  57  and resolvers  58  and  60 . Resolver  60  provides the angular position of span structure  32  to control panel  52 . Resolver  58  provides the angular position of span structure  44  to panel  54 . The collector ring and resolver assembly  56  has a horizontally extending tube  62  extending therefrom which has electrical conduit extending therethrough and which is connected to the span structure  46  by a support  64  whereby pivotal movement of the span structure  46  will cause collector ring and resolver assembly  56  to rotatably move. The resolver assembly is designed to function as an angle sensor and senses the angle of the span structure  46  with respect to a user-defined reference zero angle. Similarly, a tube  66  extends from resolver  60  and has a conduit extending therethrough with the tube  66  being secured to the span structure  32  by means of a support  68 . The resolver  60  is designed to function as an angle sensor and senses the angle of the span structure  32  with respect to a user-defined reference zero angle. 
     The control system of this invention is comprised of two control panels, one control panel  54  to control the operations of span structure  46 , and a second control panel  52  to control the operations of span structure  32 . The control system is designed to operate the two spans in the following modes: (1) independent wiper; (2) follow the leader; and (3) independent full circle. These operating modes are achieved by providing constant communications between control panels  52  and  54  via a communications bus, preferably RS485, allowing the transfer of all critical operating parameters and control including, but not limited to, speed, direction and position. During start-up and initialization, one control panel is designated the Primary Control panel and the other is designated the Secondary Control panel. The Primary Control panel is considered the Master Control and can modify or adjust the operating parameters of the secondary control panel to meet the operating requirements of the three operating modes. 
     In the independent wiper mode of  FIG. 7 , both of the spans  32  and  46  operate independently, but in part circles only. A preset safety angle will control how close the spans can come together. More particularly, the requirements of the independent wiper mode are as follows: 1. If a span structure is operating within its sector and the safety angle is reached, meaning the two span structures are too close, the span structure shall set its direction to move away from the other span structure. 2. If both span structures are operating and moving in the same direction and the safety angle is reached, the span structure that is coming from behind will pause. 3. If both span structures are operating but in opposite directions and the safety angle is reached, the span structure that is furthest from its programmed “reverse” or AR position will pause. 4. When a span structure is paused, the water shut-off valve associated therewith is closed to prevent over watering. 
     In the follow the leader mode of  FIG. 6 , the primary span structure will run based on its percent timer setting or based upon a running program. The secondary span structure will follow or lead (based on direction of travel) the primary span structure based on maintaining a user-defined angle. 
     More particularly, the start-up requirements of the follow the leader mode are as follows: 1. When Follow the Leader mode is turned ‘ON’ the other modes will be turned off, so that only one mode can be on at one time. 2. During initial startup of Follow the Leader mode, the primary span structure must pause with the water shut-off valve off while the secondary span structure moves into the trailing position by running at 100% in the appropriate direction. 3. Once the secondary span structure is in the trailing position, if water is to be on, the span structures open both water shut-off valves (open by default). 4. Both span structures will go into waiting, then running once pressurized. 5. Speed and direction of the secondary span structure will be set to match the primary span structure and will be locked out of user control at the secondary span structure. If the user tries to change these, the secondary module will display on the bottom line “PRIMARY PANEL CONTROL ONLY”. 6. The secondary span structure will not have independent start control. It will be started only when the primary panel is started. If the user tries to start the secondary span structure, it will display on the bottom line “PRIMARY PANEL CONTROL ONLY”. 7. The secondary&#39;s main status screen shall display the same percent timer value as is displayed on the primary&#39;s main status screen. This percent timer value will be the percent timer value entered by the user on the primary system. 8. When operating in the forward direction, the secondary span structure shall trail the primary span structure by a user-defined angle. 9. When operating in the reverse direction, the secondary span structure shall lead the primary span structure by a user-defined angle. 10. If the angle between the span structures is less than or equal to the Safety Angle, the span structure that is coming from behind will pause until the span structures are a predefined minimum or “safe” distance apart. 
     The control of the follow the leader mode is achieved as follows: 1. Speed and direction of the secondary module will be set from the primary module and locked out of user control at the secondary module. If the user tries to change these, the secondary module will display on the bottom line “PRIMARY PANEL CONTROL ONLY”. 2. The direction of the secondary span structure will need to match the primary span structure. 3. The software will maintain this trail angle by adjusting the speed of the secondary span structure. 4. Trail angle is the angle between the primary and secondary span structures as provided by collector ring and resolver assembly  56  and by resolver assembly  60 . 
     In the independent full circle mode of  FIG. 5 , both span structures operate independently, however always moving in the same direction. A preset safety angle will control how close the spans can come together. If the secondary span structure comes too close to the primary span structure, the secondary span structure will pause with valve off until the preset “wait” angle is reached. If the primary span structure gets too close to the secondary span structure, the primary span structure will pause with valve OFF until the preset “wait” angle is reached. The same will happen in either direction. 
     The requirements of the independent full circle mode are as follows: 1. When Independent Full Circle mode is turned ‘ON’, the other modes will be turned off, so that only one mode can be on at one time. 2. Direction of the secondary module will be set from the primary module and locked out of user control at the secondary module. If the user tries to change these, the secondary module will display “PRIMARY PANEL CONTROL ONLY”. 3. The direction of the secondary span structure will need to match the primary span structure. 4. If the secondary span structure approaches the primary span structure, the secondary span structure will pause with valve off until the minimum safety angle or minimum distance between the span structure is reached. The primary span structure will continue on. 5. If the primary span structure approaches the secondary span structure, the primary span structure will pause with its water valve off until the minimum safety angle or minimum distance between the span structures is reached. The secondary span structure will continue on. 6. If a span structure is operating and the other span structure is stopped and the Safety Angle is reached, the operating span structure shall stop. 
     A primary control feature of the two span structures is the safety system ( FIG. 8 ) used to ensure the two structures do not collide with each other. The safety system consists of two independent safeties: 
     Safety #1—A software program residing in control panels  54  and  52 . Based on the angular readings from resolvers  58  and  60 , the software programs of control panels  54  and  52  continually pass each other, via a serial communications bus, the position of their span structure. The software programs monitor the position of their span structure relative to the other span structure and shut the system down by removing power should the safety angle or minimum distance between the two span structures be reached. 
     Safety #2—A Stop Box Safety consisting of a position proximity switch  100  is mounted on the lower end of a conventional elbow connector  22 . The actuation device  101  of the Stop Box Safety is located on the upper end of the T-shaped connector  16 , whereby the position proximity switch will shut the system down by removing power should the actuation device  101  activate the Stop Box position proximity switch. 
     It can therefore be seen that the center pivot irrigation system of this invention includes the necessary controls and safeties to ensure that the span structures will be efficiently, safely and precisely controlled to achieve the proper watering of the seeds. 
     Thus it can be seen that the invention accomplishes at least all of its stated objectives.