Abstract:
A system for controlling the position of an agricultural implement coupled to an agricultural vehicle comprises a control unit connected to a field topography database containing three-dimensional data of the topography of a field, a location signal generation arrangement providing location data of the position of the vehicle and/or the implement in the field, an implement position sensor arranged to sense the position of the implement with respect to the ground and to a positioning arrangement configured to move the implement in response to position control signals from the control unit. The control unit is operable to provide the control signals based upon a combination of actual position data received from the implement position sensor and expected required position change data that are derived from elevation data recalled from the field topography database based upon the location data.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a system for controlling the position of an agricultural implement coupled to an agricultural vehicle. 
     BACKGROUND OF THE INVENTION 
     A number of agricultural implements need to be moved during work in a position relatively close to the ground of a field. However, in order to avoid damage, a contact between the implement and the ground needs to be avoided. 
     A typical example is a header for a self-propelled harvesting machine like a combine harvester or a forage harvester. Such headers include grain cutting platforms, corn pickers and corn cutting machines. In the prior art, mechanical ground height sensors have been used for an automatic header height control. These ground height sensors are pivotally mounted below the frame of the header such that they pivot around an axis extending horizontally and transversely to the forward direction and have a surface in mechanical contact with the ground. A potentiometer is coupled to the sensor and submits ground height information to a ground height controller. The latter controls an actuator for adjusting the height of the header with respect to the self propelled harvesting machine such that the height of the header above the ground corresponds to a predefined value, which is usually input by an operator. Often, at least two ground height sensors are distributed over the width of the header, in order to automatically maintain a lateral orientation of the header parallel to the ground. The ground height controller then also controls an actuator moving the header with respect to the self propelled harvesting machine around a horizontal axis extending in the forward direction. It has also been proposed to have contact-less sensors on the header that measure the distance to the ground with electromagnetic or ultrasonic waves. 
     One disadvantage of these sensors mounted to the header and interacting with the ground below the header, even if they are mounted at the forward end of the header, as on a divider tip (see, for example, U.S. Pat. No. 6,813,873), is that they are not able to cause a sufficiently fast lifting of the header when the header is approaching sharp rises in the ground topography. Due to the position of the sensor and the reaction time of the actuator, collisions with the ground cannot always be avoided, causing severe and expensive damage to the header. Additionally, debris such as rocks can be collected and damage parts of the header and of the harvesting machine. This problem is greater with the relatively high ground speeds of actual harvesting machines, since the required reaction time is shorter. 
     U.S. Pat. No. 6,615,570 discloses mounting an optical sensor to a self-propelled harvesting machine. The sensor submits electromagnetic waves towards the ground or a crop area in a distance ahead of the header and determines the flight time of the reflected waves. The elevation of the ground ahead of the harvesting machine is thus determined and used for automatically controlling the position of the header prior to the header reaching the crop area. This improves the response of the header and reduces incidences of improper header position resulting from rapidly changing contours, but requires a relatively expensive optical sensor. 
     U.S. Pat. No. 5,666,793 proposes driving over a field with a harvesting machine and recording the yield and the header height dependent on the position of the harvesting machine. The header height is manually selected by the operator during recording. When the harvesting machine travels over an adjacent path or (in the next harvest season) over the same path, the geo-referenced recorded header heights are used as position dependent nominal values for an automatic header height control. In this manner, the header height can be adjusted to reflect changes in the ground. Since the header height depends on manual input of the operator, at least during the first path, it is required that the latter carefully supervises the header height above the ground, especially when ground contours are rapidly changing. Further, using the header height from a previous path adjacent the actual path involves the risk of ground collisions when ground contours in the adjacent paths are significantly different. 
     U.S. Pat. No. 5,961,573 proposes to record the position of obstructions on a field, like rocks, by visual detection during a scouting operation or while the field is being worked or by storing information after a rock is hit by an implement such as a plow. The header of the harvesting machine is subsequently automatically lifted based upon the geo-referenced obstruction position data to avoid incidences in sufficient time before the obstruction is hit. Due to the fact that the obstruction position data is to be collected manually, this procedure is feasible only for fields with a small number of obstructions, but not for fields with rapidly changing ground contours. 
     U.S. Pat. No. 6,073,070 proposes to determine a terrain model of a field using sensors mounted to a header of a combine measuring the height of the header over the ground. This terrain model is subsequently used for a new treatment of the field with an available agricultural vehicle. It is not described in which manner the terrain model is used for controlling the implement position during the new treatment. 
     Another example of an agricultural implement with variable height adjustment is a sprayer boom. Generally, the boom is maintained by suitable actuators in a predetermined height above the ground, controlled manually or automatically based upon e.g., roughness of the ground, which is measured by detecting movement of a spring suspended front wheel frame of a tractor ( see, for example, Japanese patent JP 02 021 959 A). This detection suffers also from the disadvantage that uneven ground is detected too late to avoid ground contacts of the boom. 
     Thus, there is a need for a simple and reliable system for controlling the position of an agricultural implement coupled to an agricultural vehicle to control the position of the implement in a manner to avoid ground incidences at rapidly changing ground contours, independently from an operator. 
     It is an object of the present invention to provide a simple, reliable, and responsive system for controlling the position of an agricultural implement coupled to an agricultural vehicle. 
     SUMMARY OF THE INVENTION 
     A system for controlling the position of an agricultural implement coupled to an agricultural vehicle comprises a control unit connected to a field topography database containing three-dimensional data of the topography of a field, a location signal generation arrangement providing location data of the position of the vehicle and/or the implement in the field, an implement position sensor sensing the position of the implement with respect to the ground, and an electro-hydraulic valve structure that controls one or more hydraulic systems (e.q., header tilt system or lift system) configured to move the implement (e.q., header) in response to position control signals from the control unit. The control unit uses a combination of actual position data received from the implement position sensor and expected or predictive required position change data that are derived from elevation data of the field topography database to determine the position control signals. 
     The implement position is thus automatically controlled based upon the actually measured position over the ground and a predictive value is taken from the pre-recorded three-dimensional topography of the field in a manner such that a pre-determined or desired vertical distance between the surface of the ground and the implement is continuously maintained. When the ground in front of the implement has a steep incline, the implement can accordingly be raised before the implement hits the incline. Analogously, the implement can be lowered when the ground ahead of the implement comprises a steep decline. 
     Since the actual position of the implement is also considered by incorporating the data from the implement position sensor, possible absolute errors in the elevation data do not influence the implement position. Further, if the profile of the field has changed since the data in the topography database has been collected, this is recognized by the implement position sensor, such that unintended position errors of the implement (and damage thereto) can be avoided. Another possible source of error, moist ground or other environmental influences leading to wheels of the vehicle penetrating the ground further than expected, is thus avoided. 
     It is an advantage of the present invention that the position control signals for the implement are provided in a simple and reliable manner, since a location signal generation arrangement like a Global Positioning System (GPS) reception antenna is provided on many agricultural vehicles, and the three-dimensional topographic database does not involve significant additional expense. The operator can operate the implement close to the ground at a relatively high speed without a risk of ground incidents even when a rapid slope change is encountered. 
     The expected or predictive required position change data can be recalled from the field topography database based upon heading data that contains information about the forward direction (seen in a horizontal plane, e.g. an angle measured with respect to the south-north direction) and preferably about the speed of the vehicle. This heading data can be obtained by subtracting two subsequent positions from the location signal generation arrangement and/or using data differences from two spaced location signal generation arrangements mounted to the vehicle and/or using a signal from a compass and/or using a signal from an inertial navigation system and/or by using a signal from a steering system of the vehicle. 
     The control unit can alter the height of the implement with respect to the vehicle based upon the difference between the elevation of the ground below the implement and the elevation of the ground in a forward direction ahead of the implement. 
     Further, the lateral inclination of the implement can be altered by the control unit based upon the difference between the lateral inclination of the ground below the implement and the lateral inclination of the ground in a forward direction ahead of the implement. 
     Preferably, the position control signals are provided to the position altering arrangement sufficiently early before the implement reaches the predefined area ahead of the vehicle, such that the desired position of the implement is achieved when the predefined area is reached. 
     The invention can be used on any type of agricultural vehicles and corresponding implements. Examples are harvesting machines like combines, forage harvesters and cotton harvesters with corresponding headers, tractors with ground working, seeding or tillage implements and tractors with spraying booms or self propelled spraying vehicles with spraying booms. All these implements can be moved with the proposed system in a predetermined height above (or below, like the ground working, seeding or tillage implements) the ground. 
     These and other objects, features and advantages of the present invention will become apparent to one skilled in the art upon reading the following detailed description in view of the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side view of a vehicle with an implement position control system. 
         FIG. 2  is a schematic representation of an implement position control system utilized with the vehicle of FIG;  1 . 
         FIG. 3  is a flow diagram according to which the control unit adjusts the implement height. 
         FIG. 4  is a flow diagram according to which the control unit adjusts the lateral inclination of the implement. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to  FIG. 1 , therein is shown an agricultural vehicle in the form of a harvester or combine  10  comprising a main frame  12  having wheel structure  13  including front and rear ground engaging wheels  14  and  15  supporting the main frame  12  for forward movement over a field of crop to be harvested. Although wheels  14  and  15  are shown, the wheel structure  13  could include or be composed of ground engaging tracks. In the following, references to directions (like forward) are cited with respect to the forward direction of combine  10  that is directed to the left in  FIG. 1  as shown by the arrow. 
     An implement in the form of a header or harvesting platform  16  is used for harvesting a crop and directing it to a feederhouse  18 . The feederhouse  18  is pivotally connected to the frame  12  around a horizontal axis extending transversely to the forward direction such that the platform  16  is vertically adjustable. The feederhouse  18  includes a conveyor (not shown) for conveying the harvested crop to threshing and separating mechanisms(not shown) in the harvester or combine  10 . The operation of the combine  10  is controlled from an operator&#39;s cab  35 . Although the harvester  10  is shown as a combine  10  for harvesting grain, it is to be understood that the present invention may also be utilized with other types of harvesters having vertically controlled headers. 
     The height of the header  16  is controlled by a hydraulic lift system indicated generally at  60 , and a header tilt system indicated generally at  61  may also be provided to maintain the header generally parallel to the surface of the ground. Feelers  62  or other conventional height sensing devices such as acoustic sensors supported from transversely spaced locations on the header  16  provide an indication of header height. A feederhouse transducer  64  provides an indication of the angle of the feederhouse  18  relative to the frame  12 . 
     As shown in  FIG. 2 , the signals from the devices  62  and  64  are connected via lines  62   a  and  64   a  to a control unit  86 , which is connected to an electro hydraulic valve structure  67  to control hydraulic fluid flow to and from one or two lift cylinders  68  connected between the feederhouse  18  and the frame  12  to operate the lift system  60  to maintain the header  16  within a desirable operating height range. The valve structure  67  also controls extension and retraction of a tilt cylinder  69  to rotate the header  16  about a fore-and-aft extending axis for operation parallel to the ground surface. 
     When the signal from one or more sensors  62  on one side of the axis provides a raise indication while the signal from the opposite side provides a lower indication, the control unit  86  will operate the cylinder  69  to tilt the header about the axis for the proper attitude correction. When sensors on both sides of the axis provide a raise or a lower indication, the cylinder  68  will be extended or retracted accordingly for the necessary height correction to maintain the header in a pre-selected range of operating heights. A nominal or desired height of the header  16  above the ground can be input by the operator via a height input means  66  provided in the cab  35 . The height input means  66  can be one of a variety of means, such as a potentiometer, a rotary encoder, a keyboard, a multi-positional switch, a touch-screen, a microphone with voice recognition software, or other method. The reaction times of the lift system  60  and the tilt system  61 , however, are often too slow to compensate for abrupt changes in the ground surface contour, particularly when the harvester  10  is operating at relatively high speeds. The reaction time may also be too slow to compensate for sudden header position changes relative to the ground that result from one or more of the wheels  14  and  15  of the wheel structure  13  encountering a depression or raised area in the ground contour. The ability to cut a crop a pre-selected distance below the crop heads to limit throughput is also limited. 
     An improved header height and tilt control system includes a ground or crop contour predictive system indicated generally at  70  in  FIG. 2 . The system  70  is mounted on the combine  10  to provide ground contour information. The system  70  includes a location signal generation arrangement  74  located at a central location on the cab  35  for receiving signals from satellites of the GPS or another suitable positioning system like Glonass or Galileo. The location signal generation arrangement  74  is connected to the control unit  86 , such that the latter obtains information about the actual position of the combine  10  within a field. 
     Control unit  86  is further connected to a field topography database  76  that contains three-dimensional data of the topography of the field to be harvested, for example data representing longitude, latitude and elevation of the field surface above sea level. The field can be divided into a grid consisting of rectangular elements with edge lengths (of e.g. 0.5 m) and the three-dimensional topography data can be stored for each of the elements of the field. The three-dimensional data can be recorded during a first harvesting path over the field with the combine  10 , or measured with any other vehicle having a positioning system antenna, or taken from a topographical map. 
     During operation, the control unit  86  of system  70  proceeds according to the flow diagram of  FIG. 3  to control cylinder  68  and thus the height of the platform  16 . After start in step  100 , in step  102  the actual height of platform  16  over the ground is measured with sensors  62 . Due to the automatic lateral inclination control (see  FIG. 4 ), usually both sensors  62  give similar values. If not, the lower one of either sensor values is taken, or an average of both. 
     In the next step  104 , the control unit  86  calculates the elevation of the ground below the platform  16  using the topography database  76 . In this step, the position of the signal generation arrangement  74  is converted into the platform position, by using data concerning the actual forward direction of the combine  10  that can be obtained by subtracting two subsequent position data from the location signal generation arrangement  74  and/or by using difference data from two antennae receiving position signals from satellites and/or by using a signal from a compass and/or an inertia navigation system and/or by using a signal from a steering system of the combine  10 . 
     In step  106 , the elevation of the ground below the platform  16  in a predetermined area ahead of the platform  16  is calculated, assuming that combine  10  has been driving further in the actual steering direction for an amount of time Δt, that may be 1s. The distance between the predefined area and the combine  10  (and hence Δt) preferably depends upon the propelling speed of the combine  10 ; hence speed information can input to the control unit via a line  90  or derived from the data provided by the location signal generation arrangement  74  by subtracting two subsequent position data. In this step, information about the heading of the combine  10  in the horizontal plane is required, that can be derived as described in the preceding paragraph. 
     Then, in step  108  a difference between the elevation of the ground ahead the platform  16  and the elevation of the ground beneath the platform  16  is calculated. Possible errors in the absolute elevation values in the database  76  are not critical, since they cancel during calculation of the difference. Afterwards, in step  110  a required change of the platform height is calculated based upon this difference, the actual platform height from step  102 , and the desired height input via height input means  66 , and this difference is used to calculate a required new position of cylinder  68  in step  112 . 
     It should be noted that in step  110  the forward inclination of the ground below the wheels  14 ,  15  of the combine  10  might be considered, since it can influence the height of the platform  16  when the combine  10  moves ahead, when the ground below the wheels  14 ,  15  is not horizontal in the forward direction. 
     Control unit  86  then controls valve structure  67  in step  114  to move the lift cylinders  68 , such that the signals from the feelers  62  on line  62   a  corresponds to the desired header height when the header  16  has reached the predefined area. 
     The control system  70  can thus lift the header  16  sufficiently early before it incidents upon a steep ground incline. Analogously, the header can be sufficiently early lowered when the combine  10  drives down a hill. 
     The system  70  can also be utilized to complement the operation of the tilt system  61  to predict necessary header angle changes to avoid situations wherein the header  16  is substantially offset from a parallel relationship with the ground. If the one side of the ground surface is rising relative to the opposite side for an area, advance information of the particular tilt necessary for that area can be provided for a timely tilt system response even at relatively high ground speeds. This is described in more detail based upon  FIG. 4 . After start in step  120 , in step  122  the actual height of platform  16  over the ground is measured with sensors  62  and the actual lateral inclination of the platform  16  is calculated. 
     In the next step  124 , the control unit  86  calculates the lateral inclination of the ground below the platform  16  using the topography database  76 . In this step, the position of the signal generation arrangement  74  is converted into the platform position, as described previously. In step  126 , the lateral inclination of the ground below the platform  16  in a predetermined area ahead of the platform  16  is calculated, assuming that combine  10  has been driving further in the actual steering direction for an amount of time Δt, that may be 1s. The distance between the predefined area and the combine  10  (and hence Δt) preferably depends upon the propelling speed of the combine  10 ; hence speed information can input to the control unit via a line  90  or derived from the data provided by the location signal generation arrangement  74  by subtracting two subsequent position data. In this step, information about the heading of the combine  10  in the horizontal plane is required, that can be derived as described above. 
     Then, in step  128  a difference between the lateral inclination of the ground ahead the platform  16  and the lateral inclination of the ground beneath the platform  16  is calculated. Possible errors in the absolute elevation values in the database  76  are not critical, since they cancel during calculation of the inclinations. Afterwards, in step  130  a required change of the lateral platform inclination is calculated based upon this difference and the actual lateral platform inclination from step  102 , and this change is used to calculate a required new position of cylinder  69  in step  132 . 
     It should be noted that in step  120  also the forward inclination of the ground below the wheels  14 ,  15  of the combine  10  might be considered, since it can influence the lateral inclination of the platform  16  when the combine  10  moves ahead, when the ground beneath wheels  14 ,  15  is not horizontal in the lateral direction. 
     Control unit  86  then controls valve structure  67  in step  134  to move the tilt cylinder  69 . Thus, the lateral inclination of platform  16  is automatically controlled in a predictive manner combining values from sensors  62  and from the field topography database  76 . 
     The location signal generation arrangement  74  provides elevation data that can be used for calculating elevation data of the ground using the signals from the feelers  62  or the feederhouse transducer  64  and known vertical and horizontal offsets. These elevation data could be used for improving the accuracy of database  76  and stored in a new topographical database with a high accuracy. Further, combine  10  can be provided with another sensor  88  for detecting the orientation of the vehicle, e.g. for a lateral inclination and/or an inclination in the forward direction. Such sensors are already incorporated into available location signal generation arrangements  74  for deadline reckoning purposes. The values from these sensors can be compared with corresponding nominal values derived from the field topography database  76 , and be used to improve the accuracy of the new topographical database. They can also be used for improving accuracy of the actuator  68 ,  69  of the positioning system, since actual orientation or inclination values of the ground can be derived from those sensors instead of taking those from the field topography database  76 . 
     The control unit  86  can also provide a guidance control signal on line  99  to a steering cylinder controlling the steerable rear wheels  15  of the combine. The guidance control signal depends on the position information from the location signal generation arrangement  74  and a pre-planned path stored in a memory (not shown) connected to control unit  86 . 
     Instead of being mounted on the cab  35 , the location signal generation arrangement  74  could also be directly mounted to the header  16 , to avoid a conversion of the position of arrangement  74  to the position of the platform  16 . 
     Having described the preferred embodiment, it will become apparent that various modifications can be made without departing from the scope of the invention as defined in the accompanying claims.