Patent Publication Number: US-7904226-B2

Title: Correction in position with hitch position sensor

Description:
This divisional application claims priority under 35 U.S.C. §120 from U.S. patent application Ser. No. 11/025,395 filed Dec. 29, 2004 now U.S. Pat. No. 7,580,783 by Peter J. Dix with the same title, the full disclosure of which is hereby incorporated by reference. 
    
    
     FIELD OF THE INVENTION 
     The invention relates generally to agricultural vehicles, and more particularly to tractors or work vehicles that tow implements. The invention calculates a towed implement position based on a towing vehicle position and uses a device indicating relative position of the towed implement. 
     BACKGROUND OF THE INVENTION 
     Tractors and other off-road work vehicles in the agricultural, mining and construction industries have typically operated with manual steering by the operator. Recent changes in control systems and the development of satellite navigation systems (e.g global positioning systems or GPS) have allowed tractors to operate in a semi-automatic or fully automatic steering mode. Combining satellite navigation and ground-based navigation input signals regarding vehicle position and speed with a sophisticated on-board vehicle electronic control system allow the tractor to steer itself with a high degree of accuracy when traversing terrain. 
     To provide this control, the prior art teaches using satellite navigation system information by an on-board vehicle electronic control system to accurately determine and control a vehicle&#39;s position while operating in the field. The operator will typically enter the planned route of the tractor, or let the control system determine the most efficient route. The control methods are well known in the art, and may involve multiple position transmitters or receivers, with various signals signifying location and speed. However these methods do not control a towed implement accurately, as the towed implement does not follow the same path as the towing vehicle. 
     Tractors do not generally to agricultural work directly. Instead, they tow implements that have several ground engaging tools. If the tractor guides itself with a high degree of accuracy, and the implement is rigidly attached to tractor, the implements can follow the ground and their tools can engage the ground with a high degree of accuracy (assuming the tractor is guided with a high degree of accuracy). Not all implements are rigidly attached to the tractor, however. Many are pivotally attached to tractor, like a trailer towed behind an automobile. Because of this pivotal coupling with respect to the tractor, controlling the tractor&#39;s position with a high degree of accuracy does not guarantee that the implement position is going to be similarly controlled. 
     To solve this problem, the prior art teaches the addition of one or more GPS receivers on the towed implement. This method gives a more accurate location for the towed implement, but requires a GPS for each implement. Typically agricultural operations will require several different towed implements to affect the field during the growing cycle of a crop. This would require several GPS receivers, or the removal and reattachment of GPS receivers to each successive implement, in order to allow each towed implement to be tracked accurately according to a planned implement path in the field. 
     Another proposed solution has been to provide the towed implement with a discrete control system that lets the implement determine its position and steer itself with respect to the tractor. The drawback of the system is the addition of a discrete control system as well as steering actuators and position sensors for every implement. 
     What is needed is a more accurate and inexpensive method of determining and controlling the path of a towed implement, using the steering actuator of the tractor itself. What is also needed is a relative position sensor that can be used with a variety of implements, and does not need to be removed and reinstalled, or duplicated for each towed implement. What is further needed is a guidance system that allows the operator to input the geometry of a towed implement, and then uses the vehicle position and towed implement geometry and relative position to accurately control the implement path by actuating the tractor steering mechanism. 
     SUMMARY OF THE INVENTION 
     In accordance with a first aspect of the invention, a computer-implemented method for steering an agricultural vehicle towing an implement is provided, comprising the steps of receiving satellite navigation data indicating a vehicle location and direction of movement, receiving data indicative of a position of the implement relative to the vehicle, calculating a steering command based at least upon the satellite data and the data indicative, and steering the vehicle with the steering command. 
     The data indicative may include data indicative of an angle between the vehicle and the implement. The step of receiving data indicative may include the step of measuring the angle between the vehicle and the implement, wherein the angle is horizontal and taken at a coupling between the vehicle and the implement. The steering method may include the step of receiving a yaw rate signal, and the step of calculating a steering command may include the step of calculating the steering command based upon the yaw rate signal. The step of calculating a steering command may include calculating a steering command configured for forward travel and a steering command configured for reverse travel. The step of calculating a steering command may include calculating an estimated vehicle heading based upon a yaw rate signal and the vehicle location. The step of calculating a steering command may include calculating an estimated implement position and an estimated implement heading based upon the estimated vehicle heading and the data indicative. The step of calculating a steering command may include calculating a desired vehicle steering angle based on the estimated implement position and the estimated implement heading and the data indicative. The steering command may be a valve command, and the step of calculating a steering command may include a step of calculating a steering valve command based upon the desired vehicle steering angle and the actual vehicle steering angle. 
     In accordance with a second aspect of the invention, a guidance system for a tractor towing an implement is provided, the system comprising means for generating tractor location and direction of movement signals, means for generating an angle signal representing an angle between the tractor and the towed implement, and means for computing an implement heading based upon the tractor location and movement signals, and the angle signal. 
     The tractor location means may include a means for receiving satellite navigation information. The guidance system may include a means for computing a tractor heading based upon the implement heading and the angle signal. 
     In accordance with a third aspect of the invention, an agricultural vehicle is provided, including a tractor, a towed implement, coupled to the tractor, a position sensor configured to indicate the position of the tractor, a relative position sensor configured to provide a signal indicating a relative position of the implement with respect to the tractor, and an electronic control system for calculating a heading of the tractor based on the position of the tractor and the relative position of the implement. 
     The electronic control system may include at least one digital microprocessor and digital memory. The electronic control system may be configured to calculate a steering command for the tractor. The implement may be pivotally coupled to the tractor at an implement hitch, and the relative position sensor may measure an angle between the towed implement and the tractor at the hitch. The electronic control system may include an operator input device, wherein the operator input device is configured to receive a geometry of the towed implement and the digital memory is configured to store the geometry. The electronic control system may be configured to calculate a desired vehicle steering angle based at least upon the geometry and the relative position signal. The electronic control system may be configured to calculate a steering command for the tractor based at least upon the position of the tractor and the relative position signal. The position sensor may include a satellite navigation receiver. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a top view of a work vehicle and towed implement, showing planned implement path and implement angle in accordance with the present invention. 
         FIG. 2  is a schematic of the guidance system. 
         FIG. 3  is a process diagram of the guidance system. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     “Towed” or “towing” refers to an agricultural work vehicle (e.g. a tractor) pulling or pushing an implement (e.g. a plow). Typically, the implement will be towed behind the vehicle, however for some applications, the implement will be pushed ahead of the vehicle. Therefore towing may refer both to implement-in-front or implement-behind configurations. 
       FIG. 1  shows a tractor  100  pivotally coupled to a towed implement  102  via a hitch pin  104 . The tractor  100  includes a chassis  106 , steerable wheels  108 , rear drive wheels  110 , a GPS (global positioning system) receiver  112 , and a hitch  114 . The steerable wheels  108  are located near the front of the tractor and are pivotally and rotatably attached to the chassis  106 . The drive wheels  110  located near the rear of the tractor are rotatably attached to the chassis  106 . The hitch  114  is rigidly attached to the rear of the chassis  106 . The GPS receiver  112  is mounted on the tractor such that reception of satellite signals is maximized. The steerable wheels may be steerable with respect to the frame to which they are mounted, or alternatively they may be mounted on a frame that is itself steerable with respect to another portion of the vehicle, such as wheels that are steered by articulating the frame or chassis of a vehicle. Some vehicles are configured to both steer wheels with respect to a frame to which they are coupled (traditional steering) and also to steer that frame with respect to another frame of the vehicle (articulated steering). Wheels that are steerable by more than one method of steering, such as this traditional steering plus articulated steering, are also considered steerable wheels. 
     The towed implement  102  includes a tongue  116 , a tool bar  118  and a plurality of ground engagement tools  120  distributed along the length of the tool bar. The forward end of the tongue  116  is pivotally coupled to the hitch  114  of the tractor  100 . The tongue typically extends backward away from the tractor, along a longitudinal centerline of the tractor. The tool bar  118  is rigidly attached to the tongue  116 , preferably perpendicularly, and extends laterally away from the tongue. The ground engagement tools  120  depend from or are supported by the tool bar  118 . The tools engage the ground directly by contacting the ground, as in the case of a plow having multiple plowshares. Alternatively, the tools may engage the ground indirectly, as in the case of sprayer implement with multiple sprayer heads. 
     At the beginning of a workcycle, the tractor is typically parked and not coupled to the implement. The farmer backs the tractor  100  up to the implement  102 , aligning the hitch  114  with the tongue  116  such that the hitch pin  104  can be inserted in receiving apertures in the tongue and hitch. After inserting the hitch pin, thereby coupling the implement to the tractor, the farmer drives the tractor to the field to be cultivated, towing the implement behind the tractor. 
       FIG. 1  shows the tractor moving forward, seen in direction of travel arrow “A”, and pulling the towed implement behind the tractor. Some tractors may be operated in reverse, in which case the direction of travel would be opposite the direction of travel “A”, and the tractor would push the implement through the field. Alternatively, the hitch  114  may be mounted on the front of the tractor, allowing the farmer to push the implement through the field while operating in direction of travel “A”. Whether and implement is pushed are pulled, it is considered to be “towed” for purposes of this application. 
     The farmer typically processes the field in long swaths, turning at the end of a swath and returning back to the starting end of the field. If the farmer processes the field topographically (contour plowing), he will follow a curved path for each swath. 
     When the tractor drives in a straight line, the towed implement centerline will tend to follow the tractor centerline. In this case, the relative position of the implement  102  is directly behind the tractor  100 ; or, in other words, a hitch angle  122  measured on a vertical axis at the hitch pin  104  describing the angle between the hitch  114  and the tongue  116  will be 180 degrees. However, when the tractor drives in a curved path, or when the implement encounters an obstruction such as a boulder in the field, the towed implement centerline will not follow the tractor centerline. In this case, the hitch angle  122  is more or less than 180 degrees, signifying that the implement is not directly behind the tractor. The hitch angle  122  serves as an indicator of the relative position and orientation of the implement with respect to the tractor at all times. 
     Alternatively, hitch  114  may allow the implement to rotate in horizontal, vertical and longitudinal axes simultaneously. In this case, the hitch angle  122  would have three components: horizontal, vertical and longitudinal. In the preferred embodiment, shown here, the relative position sensor (e.g. the hitch angle sensor  203 ) senses the angle of the hitch with respect to the tractor about a vertical axis. In alternative configurations, and for more precision, a relative position sensor can include hitch angle sensors that sense the implement&#39;s rotation about the other two axes with respect to the vehicle. 
     As they move through the field, the tractor and the implement will describe distinct paths through the field. While the farmer directly controls the direction and movement of the tractor, he is more concerned with implement path  124  than with the path of the tractor, since the implement performs the work on the crops. 
     While driving the tractor, the farmer will frequently look back at the towed implement and correct the heading of the tractor to keep the tools on the towed implement aligned with the crop rows. The farmer changes the tractor&#39;s heading by pivoting the front steerable wheels  108  until the tools  120  are in proper alignment with the crop rows. 
     An automatic guidance system  200 , seen schematically in  FIG. 2 , is located on or in the tractor  100  and simplifies the task of driving the tractor. The guidance system  200  includes an electronic control system  202 , GPS receiver  112 , hitch angle sensor  203 , steering valves  204  and a steering actuator  206 . The electronic control system  202  is communicatively connected to the valves  204 , the GPS receiver  112  and the hitch angle sensor  203 . The valves are preferably proportional or directional control valves and are hydraulically connected to the steering actuator  206 . The steering actuator is coupled to and steers the steerable wheels ( FIG. 1 ), changing their steering angle. The electronic control system continually calculates a vehicle steering heading, and sends it to the valves, which in turn move the steering actuator, thereby causing the steerable wheels to pivot, changing the vehicle heading. 
     The electronic control system  202  is located on or in the tractor  100 , and includes a vehicle yaw rate sensor  210 , a vehicle steering angle sensor  212 , an operator input device  214 , one or more microprocessors  216 , and digital memory circuit  218 . The yaw rate sensor  210 , steering angle sensor  212 , operator input device  214  and digital memory  218  are communicatively coupled to the microprocessor  216 . The microprocessor is communicatively coupled to the valves  204 . 
     The relative position sensor, here shown as hitch angle sensor  203 , sends a signal indicative of the relative position of the implement (in this case a continuous hitch angle signal  209 ) to the microprocessor  216 . The hitch angle signal tells the microprocessor the position and alignment of the implement with respect to the tractor. The hitch angle sensor  203  is preferably an optical encoder mounted on the tractor hitch  114  coaxially with the hitch pin  104 . An alternative hitch angle sensor is a potentiometer or variable resistor. Alternatively, the hitch angle sensor may be any device that measures relative implement position without necessarily measuring the hitch angle. The hitch angle sensor  203  need not be the located right at the hitch. It may be disposed a short distance away and be coupled to the hitch by a mechanical linkage. 
     The vehicle yaw rate sensor  210  provides a continual yaw rate signal  211  to the microprocessor  216 , telling the microprocessor the rate at which the vehicle is changing its heading. The yaw rate sensor may be a laser gyro or other rate gyro. Alternatively, the vehicle yaw rate sensor may be a microprocessor circuit programmed to calculate the yaw rate from incoming signals or estimated or calculated values. 
     The vehicle steering angle sensor  212  sends a continual steering angle signal  213  to the microprocessor  216 . The steering angle signal tells the microprocessor the current angle of the steerable wheels. The steering angle sensor may be an encoder mounted on the tractor  100 , or may be a microprocessor circuit programmed to calculate steering angle based upon incoming signals and values stored in digital memory  218 . Alternatively, it may include a Hall effect device, potentiometer, variable resistor, linear position transducer, or any other sensor in or on the steering actuator, the wheel, the wheel hub, or steering joint that senses wheel steering or relative movement or position of the wheel with respect to another part of the vehicle, such as wheel rotation about a steering kingpin, or alternatively senses the displacement or movement of the steering actuator or other linkage coupled thereto. If the vehicle is an articulated vehicle, the steering angle sensor can also be disposed to detect the angle between the two or more vehicle frames are subframes that move or steer with respect to each other in order to turn the vehicle. 
     The operator input device  214  is configured to receive information about the field to be processed from the operator, and to transmit the information to the microprocessor  216 . This information may include data such as the size of the field, the operations to be performed, the implements to be used to engage the ground while processing the field, and the geometry  215  of each implement  102 . The geometry  215  describes the ground engagement points of the tools  120  with respect to the location of the hitch pin  104  when the implement  102  is coupled to the tractor  100 . 
     The operator input device  214  is preferably mounted inside the operator compartment of the tractor  100 , to be easily accessible to the operator. The input device preferably includes a display and a keyboard. The microprocessor  216  receives process variables from the keyboard, and displays the current status of the vehicle (location, direction, etc.) on the display. 
     Data entered by the operator on the input device  214  are stored in digital memory  218  by the microprocessor  216 . 
     Memory  218  stores microprocessor instructions and data. The instructions configure the microprocessor to perform the guidance functions indicated in  FIG. 3 . The memory also stores process data calculated or estimated by the microprocessor and entered by the operator using the operator input device  214 . 
     The GPS receiver  112  continually receives information about the absolute position of the vehicle and forwards a vehicle position signal  219  to the microprocessor  216  that indicates this absolute position. The GPS receiver  112  is a satellite navigation system typically mounted on the outside of the tractor  100 , with a clear line of sight to the satellites. Alternatively, the GPS receiver may include an antenna mounted outside the tractor, while the receiver is mounted inside the tractor. Alternatives to a GPS receiver are differential global positioning systems (DGPS), land-based position receivers or dual-frequency real time kinematics (RTK) receivers using inertial navigation system (INS) sensors. 
       FIG. 3  shows the process of calculating the vehicle heading and corresponding steering command. The GPS receiver  112  transmits the vehicle position signal  219  to the microprocessor  216 , and the yaw rate sensor  210  transmits the vehicle yaw rate signal  211  (rate of change of vehicle heading or direction of travel) to the microprocessor. The microprocessor is programmed with a heading estimator algorithm  300  that uses these signals and calculates an estimated heading  302  for the vehicle based thereon. 
     The hitch angle sensor  203  transmits the hitch angle signal  209  to the microprocessor  216 . The microprocessor is programmed with an implement position and heading estimator algorithm  304  that uses the hitch angle signal and estimated vehicle heading  302 , and calculates an estimated position and heading  305  for the implement based thereon. 
     The farmer enters the geometry  215  on the operator input device  214 , along with other information regarding the field to be processed. The operator input device transmits this data to the microprocessor  216 . The microprocessor is programmed with an implement path calculation algorithm  306  that uses the geometry and field information and calculates a desired implement path  124  to be followed by the implement  102  based thereon. 
     The microprocessor is programmed with a steering angle calculation algorithm  308  that uses the hitch angle signal  209 , estimated implement position and heading  305  and desired implement path  124  and calculates a desired vehicle steering angle  310  based thereon. 
     The vehicle steering angle sensor  212  transmits the measured vehicle steering angle signal  213  to the microprocessor  216 . The microprocessor is programmed with a steering wheel angle control algorithm  312  that uses the desired vehicle steering angle  310  and the measured vehicle steering angle signal  213  and calculates the steering commands  314  that the microprocessor sends to the valves  204  based thereon. 
     There are alternative approaches to the preferred embodiments. The implement angle may be about the horizontal or longitudinal axes, or a combination of the horizontal, longitudinal and vertical axes, in order to determine the relative position in three dimensions of the towed implement. The yaw rate signal may be obtained by a combination of other signals such as the vehicle speed and steering angle. 
     It will be understood that changes in the details, materials, steps, and arrangements of parts which have been described and illustrated to explain the nature of the invention will occur to and may be made by those skilled in the art upon a reading of this disclosure within the principles and scope of the invention. The foregoing description illustrates the preferred embodiment of the invention; however, concepts, as based upon the description, may be employed in other embodiments without departing from the scope of the invention. Accordingly, the following claims are intended to protect the invention broadly as well as in the specific form shown.