Auto-steering apparatus and method

A vehicular guidance method involves providing a user interface using which data can be input to establish a contour for a vehicle to follow, the user interface further configured to receive information from a differential global positioning system (DGPS), determining cross track and offset data using information received from the DGPS, generating control values, using at least vehicular kinematics, the cross track, and the offset data, and providing an output to control steering of the vehicle, using the control values, in a direction to follow the established contour while attempting to minimize the cross track and the offset data.

TECHNICAL FIELD

The invention generally relates to robotics. More particularly, it relates to automated steering apparatus and methodologies for vehicles, such as farm vehicles and other vehicles.

BACKGROUND OF THE INVENTION

Robots are used to cost-effectively perform complex, hazardous, and repetitive tasks not preferred by humans. Robots play an important role in reducing cost, improving worker health and safety, augmenting product quality, and increasing overall productivity. In agriculture, the opportunities for robot-enhanced productivity are immense—and the robots are appearing on farms in various guises and in increasing numbers. Precision agriculture calls for highly developed systems to perform traditional farming tasks. Current systems provide an operator with assisted navigation via a satellite position signal. This assistance is accomplished using a device such as a lightbar to indicate a direction the operator should drive to maintain a straight line to travel.

The lightbar includes a row of lights or light emitting diodes (LEDs) which interface to a GPS receiver to provide parallel swath guidance. The lightbar consisting of a row of LEDs denotes the vehicle's deviation to the left or right of the swath by respectively illuminating a proportional number of LEDs to the left or right of a central on-course LED. The lightbar's internal guidance computer receives the serial GPS position data and displays a steering indicator to indicate whether or not the vehicle is close to an imaginary A-B line the driver is attempting to drive down, thereby allowing the driver to determine correct steering adjustments. One such lightbar system is model number Starlink LB-3 sold by Starlink Inc., Austin, Tex.

The transfer of global positioning system (GPS) technologies to civilian industry has greatly assisted in meeting the challenges presented by today's precision agricultural needs. Using GPS systems, accurate and highly reliable satellite-based positioning information, which typically achieves less than one meter accuracy by utilizing differential GPS position corrections transmitted from fixed base stations, is provided to operators, for example though moving map displays. Such information allows for precise navigation and guidance. Systems utilizing GPS technology have been used in the past to assist in the aerial and terrestrial application of fertilizers, herbicides and pesticides, etc. However, such systems have generally been limited in their capabilities.

Current navigation systems fail to have an ability to automatically control the vehicle with equipment mounted thereon. During peak operations, the operator may be required to oversee a plurality of tasks including operating the vehicle. Assisted steering systems were used in the past to relieve an operator from driving related tasks. The capability to perform parallel contour swathing while minimizing “skip”, and “overlap” is preferred for cost-effective crop management within precision agriculture. The complexity of operating heavy equipment coupled with other tasks including steering the vehicle to a light bar indicator may be overwhelming to an operator. In a known navigation system, heading correction data is used to guide to, or maintain a vehicle on, a predetermined course.

It is difficult to approximate human steering. For example, a human will sometimes turn a steering wheel rapidly and sometimes slowly for the same turn depending on vehicle kinematics, such as speed.

It would be desirable to retrofit an automatic steering system to an existing vehicle without the need to tap in to or modify the vehicle's hydraulic systems.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In one aspect, a vehicular guidance method involves providing a user interface using which data can be input to establish a contour for a vehicle to follow, the user interface further configured to receive information from a differential global positioning system (GPS), determining cross track and offset data using information from the DGPS, generating control values, using at least vehicular kinematics, the cross track and the offset data, and providing an output to control steering of the vehicle, using the control values, in a direction to follow the established contour while attempting to minimize the cross track and the offset data.

In another aspect, a vehicular guidance system configured to removably attach to a vehicle is described. The vehicular guidance system includes a user interface configured to establish a contour for a vehicle to follow. The user interface is further configured to receive information from a differential global positioning system (DGPS), a computer system configured to receive input from the user interface to generate cross track and offset data. The vehicular guidance system also includes a master controller configured to generate control values, using at least the cross track and the offset data, in order to control the vehicle to follow the established contour, a second controller configured to interface with the master controller and a steering control system. The second controller is configured to receive commands from the master controller to control the steering control system in order to control steering of the vehicle to follow the established contour while attempting to minimize the cross track and the offset data.

In a further aspect, the present invention provides a vehicle guidance system having a computer system having a user interface, the computer system configured to receive data from a differential global positioning system (DGPS) and reference vehicular contour information from a user. The computer system is further configured to generate cross track and offset data. The vehicle guidance system also includes a control system configured to removably attach to a vehicle, the control system configured to receive at least vehicular velocity, the cross track and the offset data to generate commands issued to a steering control system to control steering of the vehicle, to follow the reference vehicular contour.

FIG. 1shows a high-level schematic of an auto-steering system100in accordance with one embodiment of the present invention. In one embodiment, the steering system is used in a vehicle for parallel contour swathing. The auto-steering system100includes a differential Global Positioning System (DGPS)102, a computer system104having one or more application programs, configured to perform lightbar functions, loaded in the computer system. The one or more application programs are further configured to display an interface106(hereinafter “lightbar interface”) to a user on a display device. The system100includes a user interface108that enables the user to setup parameters. For example, such parameters include parameters for establishing a distance for a vehicle to travel, between starting and ending points. Further details of establishing starting and ending points (A-B line) will be described below in connection withFIG. 3. The auto-steering system100is adaptable and may be retrofitted to various vehicles.

As is well known, differential GPS (DGPS) functions by observing the difference between pseudo range measurements determined from the received GPS signals with the actual range as determined from the known reference station point. The DGPS reference station determines systematic range corrections for all the satellites in view based upon the observed differences. The systematic corrections are subsequently broadcast to interested users having appropriate DGPS receivers. The corrections enable the user to increase the accuracy of their GPS determined position. DGPS systems are much less expensive than real-time kinematic DGPS systems. The inventors have determined that DGPS provides sufficient accuracy for various applications including farming applications. Using DGPS strikes a good balance between cost and accuracy.

The lightbar interface106is configured to accept input data from the DGPS102and also from the user interface108. In one embodiment, the lightbar interface106and the user interface108may be configured as an integrated interface109, in a common housing. Alternatively, they may be configured as distinct interface units. In one embodiment, such an integrated interface109is shown inFIG. 5. Exemplary input data from the user interface108may include the A-B line data described atFIG. 3. The DGPS102functions by determining a present position, ground track, and ground speed of a vehicle on which system100is installed. The DGPS102also receives heading information from a magnetic compass (not shown). The heading information may also be calculated from vehicle position history. The lightbar interface106receives such information from the DGPS102together with information from the user interface108and computes deviations from the desired ground track or A-B line. The deviations include heading error (hereinafter “cross track”) and distance from a predetermined A-B line (hereinafter “offset”) values.

The system100further includes a master controller110that, in operation, receives the cross track and offset values as well as vehicle kinematics information such as, for example, vehicular velocity, and computes control values for correcting cross track and offset errors. The system100further includes a low-level controller112that, in operation, receives the control values generated by the master controller110and issues commands. The system100further includes a steering control system114coupled to the controller112. The controller112issues commands to the steering control system114to steer the vehicle along the predetermined track/contour while overcoming the cross track and offset errors. In one embodiment, the master controller110and the low-level controller112may be implemented as software, hardware, or firmware. It will be appreciated that the master controller and the low-level controller may also be implemented, for example, in a programmable logic device, or an application specific integrated circuit.

In one embodiment, the low-level controller112upon sensing a counteracting force on the steering control system114applied by the user, exceeding a predetermined threshold, disables automatic steering, thereby enabling the user to manually steer the vehicle. The master controller and the low-level controller are together depicted as control system116inFIG. 1and alternatively referred as such.

FIG. 2illustrates a schematic of a vehicle200with the auto-steering system100shown inFIG. 1installed on the vehicle. Also shown inFIG. 2are various components of the auto-steering system100along with various subsystems of the vehicle. For example, as described above with respect toFIG. 1, the control system116, having a master controller110and low-level controller112, interfaces with and issues steering commands to the steering control system114. Steering actuators208appropriately steer the vehicle200upon receiving further commands from the steering control system114. The control system116also receives information from steering sensors206for fine tuning steering of the vehicle200. The control system116may be retrofit to the vehicle200to accomplish auto-steering tasks without tapping into or disturbing hydraulic steering components of the vehicle.

The steering control system114includes a drive motor assembly having a timing belt202, and a drive motor204, for controlling steering of the vehicle. Steering actuators208steer the vehicle in a desired direction of travel. In one embodiment, the drive motor is a D.C. motor biased to steer the vehicle in a manner that approximates a human response. As described above, upon sensing a counteracting force produced by a user by way of manually holding the steering, the controller116disables auto-steering action, thereby enabling the user to manually control steering of the vehicle.

In one embodiment, the master controller110computes the control values in accordance with the following equations:

Vehicular velocity is determined from the DGPS102;
Vehicular turn=Rk*((cross track−RG1)−(offset*RG2))/velocity,where Rk, RG1, and RG2are gains based upon velocity, cross track, and offset.
Turn desired=vehicular turn*Axle—AD+Axle_mid, whereAxle_AD is a conversion constant;Axle_mid is a calibrated value where the vehicle drives straight;Axle_POT is a read axle position;Current is a current read from the D.C. motorMotor output is Gain * (turn desired−Axle_POT)

Referring toFIG. 3A, there is shown an exemplary approach for establishing an A-B line used as a reference for performing parallel swathing. Upon retrofitting the auto-steering system100to a vehicle, the user selects an arbitrary location in a field as a starting point A for which a GPS reading is obtained and logged in the computer system104(FIG. 1). As the user drives to the end of the field or some other predetermined location (endpoint B), GPS reading is obtained and logged for such location. An A-B line is thus established and the auto-steering system100steers a vehicle in a straight line with the A-B line as a reference.

FIG. 3Bshows a detailed diagram of a computer system in accordance with one embodiment of the present invention shown inFIG. 1. The computer system104is loaded with software that interacts with other components of auto-steering system100via a variety of communication protocols. In one embodiment, the control system116may be implemented as a software application loaded in the computer system104. In another embodiment, the control system116may be implemented in another computer independent of the computer system104. Although a variety of computer systems can be used with the present invention, an exemplary general purpose computer is shown inFIG. 3B.

With reference still toFIG. 3B, computer system104includes a memory302, one or more processors (CPUs)304for processing information, a storage device306for storing information therein, an input/output (I/O) device308configured to interact with the DGPS system102and a display device310for displaying information. The display device310is configured to display an interface109for enabling a user to input information into computer system104.

FIG. 4shows a detailed schematic of the auto-steering system shown inFIG. 1disclosing exemplary details of the steering control system114with a feedback used in a closed-loop control system. In one embodiment, the steering control system114includes a steering motor402and an encoder404. The steering motor402, in operation, receives control commands from the low-level controller112to steer the vehicle in a desired travel direction on which system100is installed. The low-level controller112, in operation, monitors steering of the vehicle via a feedback loop, using the encoder404, and issues commands to the steering motor402to attempt to minimize steering errors.

Referring toFIG. 5, there is shown a screen shot of the interface109which includes the lightbar interface106and the user interface108illustrated inFIG. 1. Interface109includes various menus displaying, for example, swath properties506for establishing a reference A-B line—as described in detail in connection withFIG. 3. Interface109is further configured to receive GPS input from the DGPS102and to compute cross track and offset errors as explained atFIG. 1. Lightbar interface106illustrated inFIG. 5may be comparable to a physical lightbar device of the type having a plurality of light emitting diodes. As a vehicle with system100installed thereon is driven to follow a predesignated contour, any deviations from the predesignated contour are displayed by highlighting, changing the color of, or illuminating a proportional number of boxes within interface106. For example, if the vehicle deviates to the left of the predesignated contour, such deviation would be represented by highlighting or displaying a tick mark in box510displayed to the left of a center point511. Likewise, if the vehicle deviates to the right, such deviation would be displayed in box512.

Real-time kinematic (RTK) is an even more accurate technique for improving the accuracy of GPS receivers. As is well known, RTK involves the use of two or more GPS receivers which are coupled via a communication link. The GPS receivers are spatially separated and communicate to resolve ambiguities in the carrier phase of the GPS signals transmitted from the GPS satellites. The resulting carrier phase information is used to determine an extremely precise position (e.g., within 2 to 3 centimeters). Thus, RTK DGPS receivers are among the most accurate navigation and surveying instruments available.

FIG. 6shows another embodiment of the auto-steering system for performing parallel contour swathing. The auto-steering system600includes a master processor602which receives and processes command waypoints received from a user. Curvature and velocity profiles for a vehicle (not shown) installed with the auto-steering system600are programmed in device604. Real time kinematic (RTK) DGPS system610determines the position and location information of the vehicle. Device608issues commands to correct vehicular path if the vehicle deviates from a predesignated path of travel. Correction commands from the device608, curvature and velocity profile information from the device604are received in device606, which together with vehicle kinematics information, generates steering commands to a low-level controller112to control the steering control system114. For example, device606provides gain tuning based upon the specific vehicle kinematics associated with each implementation. The system illustrated inFIG. 1can include either DGPS, or the more accurate, yet more complex and more expensive, RTK GPS receivers.

FIG. 7shows a high level flow chart illustrating the steps involved in automatically performing parallel contour swathing in one embodiment of the present invention. Initially, at a step702, cross track and offset information is obtained using a lightbar interface106, user interface108and DGPS102.

At a step704, vehicular velocity is computed using the DGPS. Based on the vehicular velocity, cross track and offset information, control values to correct cross track and offset errors are determined in a master controller110at a step706.

At a step708, steering control system114is adjusted to automatically steer the vehicle, along a predetermined vehicular contour, the steering control system receiving commands from the low-level controller112which in turn receives commands from the master controller110.

At a step710, an inquiry is made to determine if the auto-steering function is to be disabled. If the low-level controller112senses a counteracting force applied by a user to take manual control to steer the vehicle, then the controller112issues commands to the steering control system114to disable auto-steering of the vehicle, thereby enabling the user to take manual control of steering the vehicle as at step712. If the result of the inquiry at step710is false, the process proceeds to step714and auto-steering of the vehicle remains enabled.

FIG. 8is detailed flow chart illustrating the steps involved in automatically performing parallel contour swathing in one embodiment of the present invention. At a step802, the lightbar interface104receives input from the differential GPS. At a step804, the lightbar interface104receives A-B line swath width from the user interface108. Subsequently, at a step806, cross track, offset, velocity, and GPS quality information is determined.

At a step808, an inquiry is made to determine if the user had enabled a hardware switch to enable auto-steering of the vehicle. If false, the process proceeds to a step810, disables automatic steering of the vehicle and notifies the user. Else, the process proceeds to a step812where an inquiry is made to determine if the user wishes to override auto-steering of the vehicle. If true, the process proceeds to step810as described above. Else, the process proceeds to step814to determine whether or not the GPS information received from the DGPS is valid. If the received GPS information is not valid, then the process loops to step810. Else, the process proceeds to step816to determine if the vehicular velocity is greater than a predetermined minimum speed. If not true, then the process proceeds to step810to disable automatic steering and notifying the user. If the vehicular velocity is greater than a predetermined minimum speed, then the process proceeds to step818.

At a step818, control values are calculated in the master controller110to control the steering control system114. At a step820, steering motor commands are issued via a low-level controller to the steering control system114to automatically control vehicular steering.