Patent Publication Number: US-2017355398-A1

Title: System and method for vehicle steering calibration

Description:
BACKGROUND 
     The invention relates generally to a steering calibration of vehicles. 
     Certain vehicles may operate via control systems that direct the steering of vehicles. For example, certain agricultural tractors may include automatic steering systems suitable for steering the agricultural tractors in fields having a variety of soil conditions and obstacles. Generally, the vehicle, such as the agricultural tractor, may be provided a map that may be used by the vehicle to follow certain paths and to avoid certain terrain features. Accordingly, a control system, such as an electronic control system, may be used to control and/or otherwise steer the autonomous vehicle. The agricultural tractor may thus be steered through a field. It would be beneficial to improve on steering of the vehicle. As a result of improved steering, the vehicle may improve drive times and enhance operational efficiency. 
     BRIEF DESCRIPTION 
     In one embodiment a vehicle system includes a spatial location system configured to derive a geographic position of an autonomous vehicle. The vehicle system further includes a computing device communicatively coupled to the spatial location system, the computing device comprising a processor. The processor is configured select a calibration mode via a user input. The processor is also configured to execute an automatic steering calibration based on the calibration mode to update one or more steering parameters, wherein executing the automatic steering calibration comprises driving the vehicle via autoguidance to spatially follow a desired path segment. 
     In another embodiment, a method includes spatially locating an autonomous vehicle location via a spatial location system. The method also includes selecting a calibration mode via a processor receiving user input. The method further includes executing, via the processor, an automatic steering calibration based on the calibration mode to update one or more steering parameters, wherein executing the automatic steering calibration comprises driving the vehicle via autoguidance to spatially follow a desired path segment. 
     In a further embodiment, a non-transitory, computer readable medium comprises instructions that when executed by a processor cause the processor to spatially locate a vehicle location via a spatial location system. The instructions further cause the processor to select a calibration mode via a processor. The instructions also cause the processor to execute, via the processor, a steering calibration based on the calibration mode to update one or more steering parameters, wherein executing the steering calibration comprises driving the vehicle via autoguidance to spatially follow a desired path segment. 
    
    
     
       DRAWINGS 
       These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein: 
         FIG. 1  is a schematic diagram of an embodiment of an vehicle operating within an agricultural field; 
         FIG. 2  is a block diagram of an embodiment of computing systems for the agricultural vehicle of  FIG. 1 , and for a base station; 
         FIG. 3  is a flowchart of an embodiment of a process suitable for automatically calibrating a steering of the vehicle of  FIG. 1 ; and 
         FIG. 4  is a flowchart of an embodiment of a process suitable for selecting various modes and calibrating a steering of the vehicle of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     Certain agricultural and other operations (mining, construction, and the like) may use an unmanned and/or manned vehicle such as a tractor or other vehicle. For agricultural operations, the vehicle may tow or include an agricultural implement such as a planter, seeder, fertilizer, and so on. In operations, the vehicle uses a map suitable for defining field boundaries, driving paths, and the like. The vehicle may operate in unmanned modes based on map data, and/or a human may operate the vehicle based on the map data. The vehicles described herein may include automatic steering system calibration, in addition to autoguidance (e.g., automatic steering system). In autoguidance, a vehicle may use GPS to follow a desired path automatically without human intervention. However, in certain embodiments, a human may work on the vehicle&#39;s cab to apply throttle inputs (e.g., speed control) and breaking. The human may also take over steering, if desired. A manual calibration process for a steering system may be tedious and not as accurate. An improved automatic and/or semi-automatic system and method for steering calibration is described herein, that may include multiple modes of operation with various levels of steering calibration. For example, a first calibration mode may calibrate all or substantially all steering system parameters of the vehicle. A second calibration mode may calibrate any subset of full calibration and may target calculating one or more steering system parameters. The first and second calibration modes may include multiple modes (e.g., submodes) each. 
     For example, in certain submodes of calibration, a control system executes a full or subset calibration derivation while automatically steering the vehicle through a series of patterns. In other submodes of calibration the controller executes a full or subset calibration while the operator drives the vehicle manually. In yet another submode of calibration the controller executes full calibration continuously, to periodically update the steering model parameters, for example to adapt the model parameter values as they change over time. Other modes or submodes may only update a steering offset parameter while leaving all the remaining parameters unchanged. Still other modes or submodes may verify whether or not the current calibration parameters are valid and within an acceptable tolerance, and if they are not, full calibration may then be performed. By applying certain steering calibration processes described herein, a more accurate steering may be provided, suitable for more efficient driving and turning. 
     Turning now to  FIG. 1 , the figure is a schematic diagram of an embodiment of a vehicle  10  (autonomous and/or manned tractor) towing an agricultural implement  12  within an agricultural field  14 . The vehicle may additionally include automatic steering (e.g., autoguidance), where a human operator may ride in the cab operating throttle and brakes while the vehicle  10  steers automatically. While in the depicted embodiment, the vehicle  10  is depicted as an agricultural tractor, in other embodiments, the vehicle  10  may be a construction vehicle, a mining vehicle, a passenger vehicle, or the like. The tractor  10  or other prime mover is configured to tow the agricultural implement  12  throughout the field  14  along a direction of travel  16 . In certain embodiments, the tractor  10  is steered (e.g., via an operator or an automated system) to traverse the field along substantially parallel rows  18 . However, it should be appreciated that the tractor  10  may be steered to traverse the field along other routes (e.g., along a spiral paths, curved paths, obstacle avoidance paths, and so on) in alternative embodiments. As will be appreciated, the agricultural implement  12  may be any suitable implement for performing agricultural operations throughout the field  14 . For example, in certain embodiments, the agricultural implement  12  may be a tillage tool, a fertilizer application tool, a seeding or planting tool, or a harvesting tool, among others. While the agricultural implement  12  is towed by the tractor  10  in the illustrated embodiment, it should be appreciated that in alternative embodiments, the agricultural implement may be integrated within the tractor  10 . As described earlier, it should be noted that the techniques describe herein may be used for operations other than agricultural operations. For example, mining operations, construction operations, automotive operations, and so on. 
     As the tractor  10  and the agricultural implement  12  traverse the field, the tractor  10  and the agricultural implement  12  may encounter various field and/or soil conditions, as well as certain structures. Such field and/or soil conditions and structures may be defined as features for purposes of the description herein. For example, the tractor  10  and the agricultural implement  12  may encounter features such as a pond  20 , a tree stand  22 , a building or other standing structure  24 , fencing  26 , and miscellaneous features  28  and so on. The miscellaneous features  28  may include water pumps, above ground fixed or movable equipment (e.g. irrigation equipment, planting equipment), and so on. In certain embodiments, the tractor  10  is configured to operate autonomously (e.g., without an operator present in the cab of the off-road vehicle). Accordingly, a steering system may steer the tractor  10  and agricultural implement  12  throughout the field without direct control by an operator, for example via a map. 
     The map be transmitted and/or included in a base station  30 . The base station  30  may be communicatively coupled to the tractor  10  to provide for updated maps suitable for operating on the field  14 . The map may include a field boundary  32 , as well as the various features in the field, such as the pond  20 , the tree stand  22 , the building or other standing structure  24 , the fencing  26 , wet areas of the field  14  to be avoided, soft areas of the field to be avoided, the miscellaneous features  28 , and so on. As the tractor  10  operates, the steering may go out of adjustment. Accordingly, a steering calibration system may be provided, either included in a vehicle control system, in an external system such as the base station  30 , or in a combination thereof. The steering calibration system may apply certain steering calibration processes (e.g., algorithms) described in more detail below to adjust or otherwise correct the steering to provide for improved driving and control of the tractor  10 , as discussed in detail below, 
     It may be useful to illustrate a system that may be used to both autonomously drive the agricultural vehicle  10  as well as to calibrate steering for the agricultural vehicle  10 . Accordingly, and turning now to  FIG. 2 , the figure is a schematic diagram of an embodiment of a control system  36  that may be employed within the agricultural vehicle  10  of  FIG. 1 . In the illustrated embodiment, a control system  36  includes a spatial location system  38 , which is mounted to the agricultural vehicle  10  and configured to determine a position, and in certain embodiments a velocity, of the agricultural vehicle  10 . As will be appreciated, the spatial location system  38  may include any suitable system configured to measure and/or determine the position of the autonomous agricultural vehicle  10 , such as a global positioning system (GPS) receiver, for example, and/or GLONASS or other similar system. In certain embodiments, the spatial location system  38  may additionally or alternatively be configured to determine the position of the scouting vehicle  10  relative to a fixed point within the field  14  (e.g., via a fixed radio transceiver). Accordingly, the spatial location system  38  may be configured to determine the position of the scouting vehicle  10  relative to a fixed global coordinate system (e.g., via the GPS), a fixed local coordinate system, or a combination thereof. The spatial location system  38  may additionally use real time kinematic (RTK) techniques to enhance positioning accuracy. 
     In the illustrated embodiment, the control system  36  includes a steering control system  46  configured to control a direction of movement of the agricultural vehicle  10 , and a speed control system  48  configured to control a speed of the agricultural vehicle  10 . In addition, the control system  36  includes a controller  49 , which is communicatively coupled to the spatial locating device  38 , to the steering control system  46 , and to the speed control system  48 . The controller  49  is configured to automatically control the agricultural vehicle during certain phases of agricultural operations (e.g., without operator input, with limited operator input, etc.). 
     In certain embodiments, the controller  49  is an electronic controller having electrical circuitry configured to process data from the spatial locating device  38  and/or other components of the control system  36 . In the illustrated embodiment, the controller  49  includes a processor, such as the illustrated microprocessor  50 , and a memory device  52 . The controller  49  may also include one or more storage devices and/or other suitable components. The processor  50  may be used to execute software, such as software for controlling the agricultural vehicle, software for determining vehicle orientation, software to perform steering calibration, and so forth. Moreover, the processor  50  may include multiple microprocessors, one or more “general-purpose” microprocessors, one or more special-purpose microprocessors, and/or one or more application specific integrated circuits (ASICS), or some combination thereof. For example, the processor  50  may include one or more reduced instruction set (RISC) processors. 
     The memory device  52  may include a volatile memory, such as random access memory (RAM), and/or a nonvolatile memory, such as read-only memory (ROM). The memory device  52  may store a variety of information and may be used for various purposes. For example, the memory device  52  may store processor-executable instructions (e.g., firmware or software) for the processor  50  to execute, such as instructions for controlling the agricultural vehicle, instructions for determining vehicle orientation, and so forth. The storage device(s) (e.g., nonvolatile storage) may include ROM, flash memory, a hard drive, or any other suitable optical, magnetic, or solid-state storage medium, or a combination thereof. The storage device(s) may store data (e.g., position data, vehicle geometry data, etc.), instructions (e.g., software or firmware for controlling the agricultural vehicle, etc.), and any other suitable data. 
     In certain embodiments, the steering control system  46  may include a wheel angle control system, a differential braking system, a torque vectoring system, or a combination thereof. The wheel angle control system may automatically rotate one or more wheels and/or tracks of the agricultural vehicle (e.g., via hydraulic actuators) to steer the agricultural vehicle along a desired route (e.g., along the guidance swath, along the swath acquisition path, etc.). By way of example, the wheel angle control system may rotate front wheels/tracks, rear wheels/tracks, and/or intermediate wheels/tracks of the agricultural vehicle, either individually or in groups. The differential braking system may independently vary the braking force on each lateral side of the agricultural vehicle to direct the agricultural vehicle along a path. Similarly, the torque vectoring system may differentially apply torque from an engine to wheels and/or tracks on each lateral side of the agricultural vehicle, thereby directing the agricultural vehicle along a path. In further embodiments, the steering control system may include other and/or additional systems to facilitate directing the agricultural vehicle along a path through the field. 
     In certain embodiments, the speed control system  48  may include an engine output control system, a transmission control system, a braking control system, or a combination thereof. The engine output control system may vary the output of the engine to control the speed of the agricultural vehicle. For example, the engine output control system may vary a throttle setting of the engine, a fuel/air mixture of the engine, a timing of the engine, other suitable engine parameters to control engine output, or a combination thereof. In addition, the transmission control system may adjust gear selection within a transmission to control the speed of the agricultural vehicle. Furthermore, the braking control system may adjust braking force, thereby controlling the speed of the agricultural vehicle. In further embodiments, the speed control system may include other and/or additional systems to facilitate adjusting the speed of the agricultural vehicle. 
     In certain embodiments, the control system  36  may also control operation of the agricultural implement  12  coupled to the agricultural vehicle  10 . For example, the control system  36  may include an implement control system/implement controller configured to control a steering angle of the implement  12  (e.g., via an implement steering control system having a wheel angle control system and/or a differential braking system) and/or a speed of the agricultural vehicle/implement system  12  (e.g., via an implement speed control system having a braking control system). In such embodiments, the control system  36  may be communicatively coupled to the implement control system/controller on the implement  12  via a communication network, such as a controller area network (CAN bus). 
     In the illustrated embodiment, the control system  36  includes a user interface  54  communicatively coupled to the controller  49 . The user interface  54  is configured to enable an operator (e.g., standing proximate to the agricultural vehicle) to control certain parameter associated with operation of the agricultural vehicle. For example, the user interface  54  may include a switch that enables the operator to configure the agricultural vehicle for or manual operation. In addition, the user interface  54  may include a battery cut-off switch, an engine ignition switch, a stop button, or a combination thereof, among other controls. In certain embodiments, the user interface  54  includes a display  56  configured to present information to the operator, such as a graphical representation of a guidance swath, a visual representation of certain parameter(s) associated with operation of the agricultural vehicle (e.g., fuel level, oil pressure, water temperature, etc.), a visual representation of certain parameter(s) associated with operation of an implement coupled to the agricultural vehicle (e.g., seed level, penetration depth of ground engaging tools, orientation(s)/position(s) of certain components of the implement, etc.), or a combination thereof, steering calibration information, among other information. In certain embodiments, the display  56  may include a touch screen interface that enables the operator to control certain parameters associated with operation of the agricultural vehicle and/or the implement. 
     In the illustrated embodiment, the control system  36  may include manual controls configured to enable an operator to control the agricultural vehicle while automatic control is disengaged (e.g., while unloading the agricultural vehicle from a trailer, during certain steering calibration modes, etc.). The manual controls may include manual steering control, manual transmission control, manual braking control, or a combination thereof, among other controls. In the illustrated embodiment, the manual controls are communicatively coupled to the controller  49 . The controller  49  is configured to disengage automatic control of the agricultural vehicle upon receiving a signal indicative of manual control of the agricultural vehicle. Accordingly, if an operator controls the agricultural vehicle manually, the automatic control terminates, thereby enabling the operator to control the agricultural vehicle. 
     In the illustrated embodiment, the control system  36  includes a communications system  60  communicatively coupled to the controller  44 . In certain embodiments, the communications system  60  is configured to establish a communication link with a corresponding communications system  61  of the base station  30 , thereby facilitating communication between the base station  30  and the control system  36  of the autonomous agricultural vehicle. For example, the base station  30  may include a control system  63  having a user interface  62  having a display  64  that enables a remote operator to provide instructions to a controller  66  (e.g., instructions to initiate control of the agricultural vehicle  10 , instructions to direct the agricultural vehicle along a path, instructions to command the steering control  46  and/or speed control  48 , instructions to transmit mapping data, etc.). 
     In certain embodiments, the controller  66  of the control system  63  is an electronic controller having electrical circuitry configured to process data from a mapping system  68  having a map  70 . In the illustrated embodiment, the controller  66  includes a processor, such as the illustrated microprocessor  72 , and a memory device  74 . The controller  66  may also include one or more storage devices and/or other suitable components. The processor  72  may be used to execute software, such as software for controlling the agricultural vehicle, software for determining vehicle orientation, software to perform steering calibration, and so forth. Moreover, the processor  72  may include multiple microprocessors, one or more “general-purpose” microprocessors, one or more special-purpose microprocessors, and/or one or more application specific integrated circuits (ASICS), or some combination thereof. For example, the processor  50  may include one or more reduced instruction set (RISC) processors. 
     The memory device  74  may include a volatile memory, such as random access memory (RAM), and/or a nonvolatile memory, such as read-only memory (ROM). The memory device  74  may store a variety of information and may be used for various purposes. For example, the memory device  74  may store processor-executable instructions (e.g., firmware or software) for the processor  72  to execute, such as instructions for controlling the agricultural vehicle, instructions for determining vehicle orientation, and so forth. The storage device(s) (e.g., nonvolatile storage) may include ROM, flash memory, a hard drive, or any other suitable optical, magnetic, or solid-state storage medium, or a combination thereof. The storage device(s) may store data (e.g., position data, vehicle geometry data, etc.), instructions (e.g., software or firmware for controlling the agricultural vehicle, mapping software or firmware, etc.), and any other suitable data. 
     The communication systems  60 ,  61  may operate at any suitable frequency range within the electromagnetic spectrum. For example, in certain embodiments, the communication systems  60 ,  61  may broadcast and receive radio waves within a frequency range of about 1 GHz to about 10 GHz. In addition, the communication systems  60 ,  61  may utilize any suitable communication protocol, such as a standard protocol (e.g., Wi-Fi, Bluetooth, etc.) or a proprietary protocol. 
     A steering calibration system  76  is provided in the control system  36 , suitable for adjusting one or more steering tables  78 , for example, which may be used by the steering control system  46  to steer the vehicle  10 . The steering tables  78  may include polynomial coefficients or other coefficients describing certain curves, and such coefficients may be adjusted by the steering calibration system  76  using a process described in more detail below with respect to  FIG. 3 . The automatic steering calibration system  76  may include multiple modes of operation with various levels of steering calibration. For example, a first calibration mode may calibrate all or substantially all steering system parameters of the vehicle  10 . A second calibration mode may calibrate any subset of full calibration and may target calculating one or more steering system parameters. The first and second calibration modes may include multiple modes (e.g., submodes) each. It is to be understood that the tables  80  may be stored in the vehicle  10  and/or in the base station  30 . For example, the base station  30  may include, in some embodiments, its own steering calibration system  82 . 
     In certain submodes of calibration, the steering calibration system  76  and/or  82  may execute a full or subset calibration derivation while automatically steering the vehicle through a series of patterns. In other submodes of calibration, the steering calibration system  76  and/or  82  may execute a full or subset calibration while the operator drives the vehicle manually. In yet another submode of calibration the steering calibration system  76  and/or  82  may execute full calibration continuously during driving, to periodically update the steering model parameters, for example to adapt the model parameter values as they change over time. In other modes or submodes, the steering calibration system  76  and/or  82  may only update a steering offset parameter while leaving all the remaining parameters unchanged. In still other modes or submodes, the steering calibration system  76  and/or  82  may verify whether or not the current calibration parameters are valid and within an acceptable tolerance, and if they are not, a full calibration may then be performed. Accordingly, the vehicle  10  may be more precisely steered, resulting in more optimal fuel use and increased crop yields. 
       FIG. 3  illustrates a flowchart of an embodiment of a process  100  suitable for automatically calibrating a steering of the vehicle  10 . The process  100  may be implemented as computer instructions or code executable via the processors  50 ,  72  and stored in the memories  52 ,  74 . In the depicted embodiment, the process  100  may generate (block  102 ) one or more path segments, each path segment having a velocity. A path segment may include geometric curve(s) or other shape that the vehicle  10  should follow during steering calibration at the desired velocity. In certain embodiments, the path segment generation (block  102 ) may be executed via an external system (e.g., external to the vehicle  10 ), such as an external computing system (e.g., workstation, personal computer, laptop, notebook, tablet, base station  30 , and so on). In other embodiments, the path segment generation (block  102 ) may be executed via the controller  49 . 
     The process  100  may then generate (block  104 ) a curvature command suitable for commanding the vehicle  10  to follow a desired curvature, for example, a command to turn a steering wheel. To generate (block  104 ) the curvature command, the process  100  may use the path segment(s) generated via block  102  and a vehicle state. The vehicle state may include a current vehicle velocity and a current vehicle yaw rate. In one embodiment, the curvature command (block  104 ) is generated via computing system (e.g., controllers  49  and/or  66 ). In other embodiments, a human driver issues the curvature command (block  104 ). The curvature command block  104  may incorporate certain steering coefficients, such as coefficients A, B, C, D for when a third order polynomial is used. The third order polynomial may take the form y=A+Bx+Cx 2 +Dx 3  where y is the steer angle. Thus, given A, B, C, D and a value for x, the steer angle may be found. In one embodiment, x is representative of a Cartesian axis, thus, the third order polynomial equation is representative of a curvature. The curvature command may then get translated (block  106 ) into a desired steer angle via steer mapping. Block  106  may use the equation form y=A+Bx+Cx 2 +Dx 3  where y is the steer angle to derive the desired steer angle. It is to be understood that while a third order equation is described, other embodiments may use a fourth, fifth, sixth or higher order polynomial. 
     As mentioned earlier, each path segment may include a desired velocity to follow while navigating the path segment. A velocity command based on the velocity may be translated (block  108 ) into a throttle command suitable for moving the vehicle&#39;s  10  throttle to a position that will result in the desired velocity. Given the steer angle and throttle position, the vehicle  10  may then change position, orientation, and/or otherwise move. Measurements may be taken (block  110 ) as the vehicle  10  changes position, orientation, and/or otherwise moves. The measurements may include yaw rate, velocity, new vehicle position, acceleration, current steer angle, and/or rotational rate. 
     In the depicted embodiment, the measurements may be converted (block  112 ) into estimate states. That is, given the recorded measurements, the process  100  may derive (block  112 ) estimated velocity and yaw rate for the vehicle  10 . For example, a physical model of the vehicle  10  may be executed by the processors  50  and/or  72  using the measurements as inputs to derive (block  112 ) the estimated velocity and yaw rate for the vehicle  10 . The current steer angel may be transformed (block  114 ) into an estimate curvature or geometric curve. 
     A comparison between estimated curvature, velocity, and yaw rate, and the desired path segment(s) curvature and velocity (provided by block  102 ) may be made (block  116 ). Deviations between the estimated curvature, velocity, and yaw rate, and the desired path segment(s) curvature and velocity (provided by block  102 ) may then be used to update (block  116 ) the seer parameters A, B, C, and/or D. The updated parameters A, B, C, D may then be stored and provided to blocks  104 ,  106 ,  114 . The process  100  may, in certain modes, be iterative and run continuously. In other modes, the process  100  may be executed when desired, as described in more detail below with respect to  FIG. 4 . 
       FIG. 4  is a flow chart of an embodiment of a process  150  suitable for providing steering calibration for the vehicle  10 . In the depicted embodiment, the process  150  may first select (block  152 ) one or more steering calibration modes  154 . As mentioned earlier, a number of modes  154  may be provided. For example, a first calibration mode may calibrate all or substantially all steering system parameters of the vehicle. A second calibration mode may calibrate any subset of full calibration and may target calculating one or more steering system parameters. The first and second calibration modes may include multiple modes (e.g., submodes) each. 
     For example, in certain submodes of calibration, a control system executes a full or subset calibration derivation while automatically steering the vehicle through a series of patterns. In other submodes of calibration the controller executes a full or subset calibration while the operator drives the vehicle manually. In yet another submode of calibration the controller executes full calibration continuously during driving, to periodically update the steering model parameters, for example to adapt the model parameter values as they change over time. Other modes or submodes may only update a steering offset parameter while leaving all the remaining parameters unchanged. Still other modes or submodes may verify whether or not the current calibration parameters are valid and within an acceptable tolerance, and if they are not, full calibration may then be performed. 
     Once the modes  154  are selected, the process  150  may then execute (block  156 ) steering calibration. In one embodiment, the steering calibration process executed is the process  100  described above with respect to  FIG. 3 . Accordingly, one or more steering coefficients (e.g., A, B, C, D) may be updated as described above, resulting in improved steering and thus more accurate driving and crop yield. The process  150  may then determine (decision  160 ) if further steering calibration is desired. For example, certain of the modes  154  may desire continuous calibration, and thus, the process  150  may iterate to block  156 . Other modes may verify whether or not the current calibration parameters are valid and within an acceptable tolerance. If the current calibration parameters (e.g., A, B, C, D) are not valid or within an acceptable tolerance, the process  150  may then iterate to block  156 . In this manner, a more improved steering calibration is provided. 
     While only certain features of the invention have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.