Patent Publication Number: US-RE41358-E

Title: Automatic steering system and method

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
     This application is a continuation-in-part of U.S. patent application Ser. No. 10/804,721, filed Mar.  19, 2004, now U.S. Pat. No. 7,437,230  which is incorporated herein by reference  claims the benefit of U.S. provisional application No.  60 / 456 , 130 , filed Mar.  20 ,  2003 . 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to automatic steering, and in particular to a system and method for providing GPS-based guidance for an auxiliary steering system, which is installed in parallel with a primary steering system of a vehicle and utilizes a constant factor, such as the vehicle steering rate, in a control system with a feedback loop. 
     2. Description of the Related Art 
     In the field of vehicle guidance and navigation, the Global Positioning System (GPS) has enabled a wide range of applications. For example, various GPS receivers are available for aviation, marine and terrestrial vehicles. The GPS information provided by such receivers can be processed and used for navigation. In more sophisticated systems, vehicle guidance can be automatically controlled using such information. For example, a predetermined travel or flight path can be programmed into an on-board computer. The vehicle guidance system can automatically maintain appropriate course parameters, such as course, heading, speed, altitude, etc. Control system, feedback theory and signal filtering techniques can be used to interactively anticipate (with higher order systems) and compensate for course deviations and navigation errors. Such sophisticated autopilot and automatic steering systems tend to involve powerful computers and complex flight and steering controls integrated with manual controls. 
     Accurate vehicle and equipment guidance is an important objective in agriculture. For example, tilling, planting, spraying, fertilizing, harvesting and other farming operations typically involve specialized equipment and materials, which are operated and applied by making multiple passes over cultivated fields. Ideally, the equipment is guided through accurately-spaced passes or swaths, the spacing of which is determined by the swatch width of the equipment. Gaps and overlaps can occur when operators deviate from the ideal guide paths, resulting in under-coverage and over-coverage respectively. Such gaps and overlaps are detrimental to agricultural operations and can reduce crop yields. For example, gaps in coverage reduce the effective areas of fields being cultivated and treated. Overall crop production may suffer as a result. Overlaps in coverage tend to be inefficient and wasteful of materials, such as fertilizer, pesticides, herbicides, seed, etc. Another potential problem with overlapping coverage relates to the potentially crop-damaging effects of double applications of certain agricultural chemicals. 
     Previous systems for assisting with the guidance of agricultural equipment include foam markers, which deposit foam along the swatch edges. The foam lines produced by foam markers provide operators with visible reference lines on which subsequent passes can be aligned. However, foam marking systems consume foam-making materials and provide only temporary foam marks. 
     GPS technology advanced the field of agricultural guidance by enabling reliable, accurate systems, which are relatively easy to use. For example, the OUTBACK S™ steering guidance system, which is available from RHS, Inc. of Hiawatha, Kans. and is covered by U.S. Pat. No. 6,539,303 and No. 6,711,501, which are incorporated herein by reference, includes an on-board computer capable of storing various straight-line and curved (“contour”) patterns. An advantage of this system is its ability to retain field-specific cultivating, planting, spraying, fertilizing, harvesting and other patterns in memory. This feature enables operators to accurately retrace such patterns. Another advantage relates to the ability to interrupt operations for subsequent resumption by referring to system-generated logs of previously treated areas. 
     The OUTBACK S™ GPS guidance system provides the equipment operators with real-time visual indications of heading error with a steering guide display and crosstrack error with a current position display. They respectively provide steering correction information and an indication of the equipment position relative to a predetermined course. Operators can accurately drive patterns in various weather and light conditions, including nighttime, by concentrating primarily on such visual displays. Significant improvements in steering accuracy and complete field coverage are possible with this system. However, it lacks the “hands off” capability and inherent advantages of automatic steering, which are addressed by the present invention. 
     Heretofore there has not been available an automatic steering system and method with the advantages and features of the present invention. In particular, there has not been available a system adapted for original equipment or retrofit installations in parallel with various vehicle hydrostatic steering configurations, which system provides automatic steering assistance using a constant factor, such as the vehicle steering rate, in a control system with a feedback loop. 
     SUMMARY OF THE INVENTION 
     In the practice of an aspect of the present invention, an automatic steering system and an automatic steering method are provided for a vehicle. The vehicle can comprise a motive component, such as a tractor, and a working component connected thereto by a hitch. The system includes a GPS receiver connected to a guidance controller, which includes a microprocessor adapted for storing and processing GPS information. An auxiliary steering subsystem is installed in parallel with the vehicle&#39;s primary hydrostatic steering system, and includes an hydraulic steering valve control block connected to the guidance controller and receiving steering input signals therefrom. The system utilizes a constant steering factor, such as a constant steering rate, which is implemented with “left”, “right” and “none” steering correction signal inputs from the guidance controller to the steering valve control block. The vehicle&#39;s hydraulic steering is thus biased right or left to maintain a predetermined vehicle course. A feedback loop is provided from the vehicle&#39;s primary steering system through a gyroscopic yaw rate correction component to the guidance controller for determining the necessary steering corrections as a function of the desired and actual turning rates. The automatic steering system of the present invention can be installed in a wide variety of agricultural vehicles and equipment. For example, tractors and special-purpose, self-propelled agricultural equipment, such as sprayers and combines, can be equipped with the automatic steering system of the present invention in parallel with the primary hydrostatic steering systems commonly used in modern tractors and other farming equipment. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram of an automatic steering system comprising an aspect of the present invention, shown in a vehicle including a motive component connected to a working component. 
         FIG. 2  is a top plan view of the vehicle, shown following a contour path. 
         FIG. 3  is a schematic diagram showing the automatic steering control logic and a feedback loop. 
         FIG. 4  is a flowchart of an automatic steering method comprising an aspect of the invention. 
         FIG. 5  is a flowchart of an auto-disengage and auto-engage subroutine. 
         FIG. 6  is a flowchart of a subroutine for determining an actual turning rate in a vehicle with an hydraulic piston-and-cylinder unit steering actuator. 
         FIG. 7  is a flowchart of a subroutine for determining an actual turning rate in a track drive vehicle. 
         FIG. 8  is a screen display of a setup menu. 
         FIG. 9  is a diagram showing the major component of the system and their connections to each other and to a vehicle. 
         FIG. 10  is a diagram of the primary hydraulic steering system of a vehicle, such as a tractor. 
         FIG. 11  is a block diagram of a vehicle hydrostatic steering system with a closed-center, load-sensing, non-reactive steering valve control block. 
         FIG. 12  is a block diagram of a vehicle hydrostatic steering system with a closed-center, pressure-compensating, non-reactive steering valve control block. 
         FIG. 13  is a block diagram of a vehicle hydrostatic steering system with an open-center, non-reactive steering valve control block. 
         FIG. 14  is a block diagram of a vehicle hydrostatic steering system with a reactive steering isolation circuit. 
         FIG. 15  is a block diagram of a dual-path hydrostatic steering system for a differential track drive vehicle. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     I. Introduction and Environment 
     As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention, which may be embodied in various forms. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present invention in virtually any appropriately detailed structure. 
     Certain terminology will be used in the following description for convenience in reference only and will not be limiting. For example, up, down, front, back, right and left refer to the invention as oriented in the view being referred to. The words “inwardly” and “outwardly” refer to directions toward and away from, respectively, the geometric center of the embodiment being described and designated parts thereof. Said terminology will include the words specifically mentioned, derivatives thereof and words of similar meaning. 
     Referring to the drawings in more detail, the reference numeral  2  generally designates an automatic steering system according to an aspect of the present invention. Without limitation on the generality of useful applications of the steering system  2 , by way of example, it is shown and described installed on an agricultural vehicle  4  comprising a motive component (e.g., a tractor)  6  connected to a working component  8  by an optional, articulated connection  10 . 
     II. Guidance Module  12   
     The automatic steering system  2  includes a guidance module comprising a guidance controller and path planner  12  and a GPS receiver  14  receiving signals from GPS signal sources  16 , such as the GPS satellite constellation or ground-based reference transmitters, through an antenna  18  mounted on the cab roof or some other suitable location. The receiver  14  is connected to a microprocessor  20 , which provides a graphic display  22  including a heading indicator  24  and a crosstrack error indicator  26 , both of which comprise LED indicator light patterns. The guidance module  12  and its operation are described in U.S. Pat. No. 6,539,303 and No. 6,711,501. 
     An optional hitch module  28  can be provided for controlling an articulated hitch  10 , which shifts the working component  8  laterally in order to compensate for course deviations by the motive component  6 . Such a hitch is shown in U.S. Pat. No. 6,631,916, which is incorporated herein by reference, and is available from RHS, Inc. of Hiawatha, Kans. under the trademark OUTBACK HITCH™. Another optional component comprises a mapping module  32 , which performs mapping functions and provides a graphic display showing field areas treated, current travel paths and other information. For example, the system  2  can calculate the area of a field using the GPS coordinates of the field perimeter, which information can be processed, stored and displayed with the mapping module  32 . A compatible mapping module is available from RHS, Inc. under the trademark OUTBACK 360™. 
     The working component  8  can optionally be equipped with its own GPS receiver  34  and microprocessor  36 , which can be linked to the motive component guidance module  12 . The use of two GPS receivers and microprocessors in this configuration can enhance guidance accuracy by compensating for GPS positioning discrepancies between the components  6 ,  8 . Without limitation on the generality of vehicle steering systems that are compatible with the automatic steering system  2  of the present invention, the vehicle  4  includes a hydrostatic steering system  38  with an hydraulic power supply (e.g., an hydraulic tank and pump)  40 , which is operated by the steering wheel manual steering control  42 . 
     The automatic steering module  44  is connected to the guidance module  12  and receives GPS-based navigation signals as input therefrom, which are used to generate output to a steering valve control block  46 , which in turn provides steering direction hydraulic output to the vehicle hydrostatic steering system corresponding to “right”, “left” and “none” directional changes. The automatic steering system  2  utilizes a constant factor, such as the steering rate, which is adjustable as an input to the steering valve control block  46 . As described below, this value normally remains constant after an initial adjustment by the operator to accommodate particular equipment configurations and operating conditions. The vehicle hydrostatic steering system  38  is affected by external disturbances, such as those associated with the operation of the vehicle  4 . The automatic steering control logic accommodates and compensates for such external disturbances. 
       FIG. 3  shows the automatic steering control logic in a feedback loop with the vehicle steering system  38 . Utilizing position/speed input from the GPS receiver  14  and smooth heading feedback input from a yaw rate filter  48 , the guidance controller and path planner  12  produces a desired turning rate for comparison to a feedback actual turning rate at a summer  50 , the resulting error value from which is input to a proportional integral derivative (PID) compensator  52 , with gain adjustments G 1 , G 2  and G 3 . A deadband filter  54  defaults to a “none” steering command until predetermined signal thresholds are reached, which cause “left” or “right” steering command outputs to the vehicle steering system  38 . Significant advantages in simplicity of construction, programming and operation are achieved by limiting the available steering commands to left/right/none, as opposed to more complex solutions involving proportional steering correction commands. For example, the steering valve control block  46  can be constructed with relatively simple, solenoid-activated, on-off hydraulic valves, thus avoiding the hardware and software complexities associated with proportional steering correction. 
     Actual turning rate (typically °/sec.) is a function of the steering command signal, the preset steering speed constant, vehicle speed and external disturbances associated with operation of the vehicle  2 . This value is fed back to an inertial based yaw rate gyro  56  and is further filtered by a low pass frequency cutoff noise filter  58  to provide an output corresponding to an observed turning rate for combining with the desired turning rate at the summer  50 . The filter  58  has a first-order control variable comprising an adjustable time constant Γ (tau). The inertial based yaw rate gyro  56  also provides input to the yaw rate filter  48  for combining with a differential heading from the GPS receiver  14  to provide a smooth heading input to the guidance controller and path planner  12 . 
     III. Automatic Steering Method 
       FIG. 4  is a flowchart showing an automatic steering method according to the present invention. The automatic steering method accommodates both straight-line (i.e. “A-B”) and contour guidance. The system  2  can be switched between each operating modes while operating. The system  2  is programmed to automatically disengage and engage the steering function upon encountering certain predetermined conditions, as indicated by the auto-disengage decision step, which initiates the auto-disengage and auto-engage subroutine.  FIG. 5  shows the auto-disengage and auto-engage subroutine. Without limitation on the various engage/disengage conditions that the system  2  can accommodate, examples of include: excessive current position error, which would be triggered by the driver leaving the area of the agricultural operation; ground speed too slow or too fast for effective automatic steering; excessive turning rate; manual steering control corresponding to the operator taking over steering function; and a “deadman switch” operator absent condition. Various other events and conditions can be programmed to activate the auto-disengage subroutine. Upon disengagement, the system  2  will automatically reengage if the disengage condition is removed within a certain time period. For example, the operator may return to the area of previous guidance and resume an agricultural operation within the prescribed time limit. If the time limit for automatic resumption is exceeded, the auto-steer function can be manually reengaged. 
       FIG. 6  is a flowchart of the subroutine for determining actual turning rate. A value Q(desired) is input and manually adjusted with a manual steering rate control valve  70 , such as a needle valve, as discussed in more detail below. Hydraulic system disturbances, such as hydraulic pressure demands from other equipment on the vehicle  4 , also affect the output Q(actual). Left/right/none directional instructions are input to the directional control and output to an hydraulic piston-and-cylinder steering unit  68 , the displacement of which provides a feedback variable (l/s) and determines the steering angle, which in turn provides the actual turning rate as a function of ground speed and external disturbance.  FIG. 7  is a similar flowchart for determining actual turning rate in a track drive vehicle utilizing the operating variables corresponding to hydraulic pressure (P) and gain (G). 
       FIG. 8  is a setup menu, which can be displayed by the guidance module  12 , for example when the system  2  commences operation. The steering adjustment step utilizes the manual steering control rate needle valve  70  for adjusting the output of the steering valve control block  46 , which in turn controls the steering speed. The down and up arrows of the guidance module  12  enable positioning the piston and cylinder steering unit  68  at its extreme left and extreme right steering angles respectively. By timing the end-to-end travel time, the operator can determine if the steering control rate valve  70  requires adjustment. For example, 25 seconds of end-to-end travel time is generally suitable for an initial steering control rate valve  70  calibration, subject to further adjustments according to operator preferences, equipment configurations and operating conditions. Opening the steering control rate valve  70  increases the steering control rate and results in more aggressive steering corrections and reduced guidance tracking error. However, if the steering control rate is too high, unstable steering corrections and larger errors can occur. Decreasing the steering control rate by closing the valve  70  generally provides greater stability and smoother response, although an excessively low rate can cause sluggish steering corrections and large tracking errors. Accordingly, the valve  70  should be fine-adjusted for smooth response and minimum tracking errors. 
     The sensitivity adjustment controls the deadband filter  54 . Increasing the deadband width reduces sensitivity and vice versa. Excessive sensitivity tends to result in overreaction by the system  2 , whereas insufficient sensitivity can cause excessive steering errors. Upon successfully adjusting the steering and system sensitivity as described above, the system  2  will generally require little, if any, further adjustment unless equipment configurations and operating conditions change. The auto-engage subroutine ( FIG. 5 ) can be selectively enabled. The diagnostics feature facilitates troubleshooting the system  2  and its operation. For example, the inertial based yaw rate gyro  56  measures and stores sensor data corresponding to negative values for left-hand turns, positive values for right-hand turns and near-zero values for straight-line travel. Such values can provide useful diagnostic information concerning the operation of the system  2 . 
       FIG. 9  shows the major vehicle-mounted components of the system  2  in a typical installation for an agricultural vehicle, such as a tractor. The guidance module  12  is attached to a vehicle surface, such as the inside of the windshield for convenient viewing, by a mounting bracket  72 , which can be secured in place by a suction cup  74 . An optional mapping module  32  can also be secured in a conveniently viewable location by a similar bracket  72  and suction cup  74 . The guidance, mapping and automatic steering modules  12 ,  32  and  44  are interconnected by a suitable wiring harness of CAN cables  76 , which also connect to an electrical power source, such as the vehicle&#39;s electrical system. The optional hitch module  28  is likewise adapted for mounting in the vehicle cab and can be connected to the other modules. A cable  78  extends from the automatic steering module  44  to the steering valve control block  46 , which is connected to the vehicle steering cylinder  68  by block-to-cylinder hydraulic lines  80 . Additional hydraulic lines  82 ,  84  and  86  are connected to the tank and pump of the hydraulic power supply  40  and a load sensing device. 
     The vehicle&#39;s primary steering system  38  is shown in FIG.  10  and includes a primary steering orbital hydraulic valve  88  connected to the steering wheel  90  and to both ends of the piston-and-cylinder steering unit  68  by hydraulic lines  92 . The primary hydraulic steering orbital valve  88  is also connected to the control block  46  by the hydraulic lines  82 ,  84  and  86 . 
       FIG. 11  is a schematic diagram of the system  2  installed in parallel with a vehicle primary hydrostatic steering system  38 A and a steering valve control block  46 A, which has a closed-center, load-sensing, non-reactive configuration (Case A). A variable-displacement, hydraulic pump  94 A provides a source of variable flow, variable pressure hydraulic fluid, as required by the greatest load placed on the hydraulic systems of the vehicle  4 .  FIG. 12  shows the system  2  installed in parallel with a closed-center, pressure-compensating, non-reactive vehicle primary hydrostatic steering system  38 B (Case B) and a steering valve control block  46 B, which utilizes hydraulic fluid at a constant pressure and a variable flow.  FIG. 13  shows the system  2  installed in parallel with an open-center, non-reactive vehicle primary hydrostatic steering system  38 C (Case C) and a steering valve control block  46 C. 
       FIG. 14  shows a reactive steering isolation circuit  96  installed in the hydraulic lines  92  in a steering system  38 A,  38 B or  38 C between the primary steering orbital  88  and the tractor piston-and-cylinder steering unit  68 . Reactive steering systems, which are found on some vehicles, have an hydraulic force feedback into the primary steering orbital  88  from the piston-and-cylinder steering unit  68 . The isolation circuit  96  effectively converts the reactive system to a non-reactive steering system. 
       FIG. 15  shows a vehicle primary hydrostatic steering system  38 D for a track-type vehicle with a differential track drive  98  including a differential hydraulic motor  100  (Case D) and a steering valve control block  46 D. A primary hydraulic control valve  102  is connected to the differential hydraulic motor  100  and is controlled by inputs from a steering wheel  104 . The steering valve control block  46 D is adapted for automatically steering the tracked vehicle by selectively directing pressurized hydraulic fluid to the differential track drive motor  100 . 
     It is to be understood that the invention can be embodied in various forms, and is not to be limited to the examples discussed above. Other components and configurations can be utilized in the practice of the present invention.