Transformer (modifier) design for controlling articulated vehicles smoothly

Abstract

The present invention relates to a practical approach to alleviate or remove the jerky heading change in ArVs. The rate of change of articulation angle in heading kinematics is effectively canceled. This modification (also called as transformer) can be done such that articulated vehicles can change their heading similar to front wheel-steered vehicles.

Claims

1. A method of operating an automated steering system with a control feedback loop for an Articulated Vehicle (ArV) comprising: a. modeling steering performance of a Front Wheel Steered Vehicle (FrV) FrV; and b. modifying the steering control feedback loop in a manner where steering performance of an ArV reacts similar to that of an FrV, wherein the step of modifying comprises creating a modification function which effectively cancels rate of change of articulation angle in the heading kinematics of the ArV, which then affects heading angle rate of change.

2. The method of claim 1 wherein the modification function is in the form of: $M\left(s\right)=\frac{2V}{L}\frac{1}{s+\frac{V}{L_1}}$ where V=velocity L.sub.1=front wheel base for the ArV L.sub.2=rear wheel base for the ArV s=complex variable And it is assumed: L.sub.1=L.sub.2 and articulation angle is relatively small (e.g. <15).

3. The method of claim 2 wherein the modification function is discrete form comprises: $O\left(k+1\right)=e^{\left(-\frac{V}{L_1}T\right)}O\left(k\right)+\frac{2L_1}{L}\left(1-e^{\left(-\frac{V}{L_1}T\right)}\right)I\left(k\right)$ where, O stands for the output I stand for the input T stand for the sampling time, 0.1,s V stands for the velocity L stands for the wheel-base for a specific FrV (e.g. Case 210) L1 stands for the half wheel base for articulated vehicle (e.g. Steiger 400) K stands for discrete time step.

4. The method of claim 1 wherein the control loop includes a PID controller.

5. The method of claim 1 wherein the control loop includes an adjustable time constant.

6. The method of claim 1 wherein the PID controller includes inputs comprising: a. desired turning rate; and b. an adjustable time constant.

7. The method of claim 1 wherein the PID output comprises a steering command to a hydrostatic steering system, which converts the steering command into an actual turning rate.

8. The method of claim 1 wherein the ArV comprises an agricultural tractor.

9. The method of claim 8 wherein the agricultural tractor comprises: a. chassis only articulation; b. front wheel steer and chassis articulation; c. front wheel steer, rear wheel steer, and chassis articulation.

10. An automated steering system for an Articulated Vehicle (ArV) comprising: a. a set of navigation sensors; b. a set of vehicle motion models; c. a navigation planner which provides a steering angle instruction based on position heading data from the navigation sensors and motion status data from the vehicle motion models; d. a steering controller which modifies the steering angle instruction from the navigation planner by a feedback control loop wherein a part of modification comprises: i. modifying the control feedback loop in a manner where steering performance of an ArV reacts similar to that of a Front Wheel Steered Vehicle (FrV), wherein the modifying comprises a modification function which effectively cancels rate of change of articulation angle in the heading kinematics of the ArV, which then affects heading angle rate of change.

11. The automated steering system of claim 10 operatively installed in an ArV.

12. The automated steering system of claim 11 wherein the ArV includes: a. front steerable wheels b. rear steerable wheels, or c. both.

13. The automated steering system of claim 10 wherein the ArV includes a steering mechanism comprising a hydrostatic steering system.

14. An Articulated Vehicle (ArV) ArV comprising: a. a frame; b. a motor on the frame; c. an articulation point in the frame; d. a front wheel base from the articulation point to front wheels; e. a rear wheel base from the articulation point to rear wheels; f. a steering mechanism to control articulation angle of the frame at the articulation point; g. an automated steering system operatively connected to the steering mechanism comprising: i. a set of navigation sensors; ii. a set of vehicle motion models; iii. a navigation planner which provides a steering angle instruction based on position heading data from the navigation sensors and motion status data from the vehicle motion models; iv. a steering controller which modifies the steering angle instruction from the navigation planner by a feedback control loop wherein a part of modification comprises: 1. modifying the control feedback loop in a manner where steering performance of an ArV reacts similar to that of a Front Wheel Steered Vehicle (Frv), wherein the modifying comprises a modification function which effectively cancels rate of change of articulation angle in the heading kinematics of the ArV, which then affects heading angle rate of change.

Description

III. BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1A is a diagrammatic view of a hydraulic-assisted autosteer system.

(2) FIG. 1B is a simplified functional diagram of a navigation/autosteer system for a vehicle

(3) FIG. 1C is block diagrams (parts 1 and 2) of a PID controller based autosteer system for a vehicle.

(4) FIG. 1D is a simplified schematic of PID operation.

(5) FIG. 1E is an illustration of one example of an FrV vehicle.

(6) FIG. 1F is an illustration of coordinates of a navigation system for a FrV body fixed frame system on a vehicle in addition to error signals (cross track and heading errors) used in control loops.

(7) FIG. 1G is an illustration of one example of an ArV vehicle (wheeled).

(8) FIG. 1H is an illustration of one example of an ArV vehicle (tracked).

(9) FIG. 1I is an illustration of a top view of an ArV vehicle (tracked), where the vehicle components were illustrated.

(10) FIG. 1J is a schematic of ArV navigation coordinates.

(11) FIG. 2A is an illustration of control loop implementation for an FrV vehicle.

(12) FIG. 2B is an illustration of control loop implementation for an ArV vehicle according to one embodiment of the invention.

(13) FIGS. 3A-D are graphs comparing ArV autosteering with the modification of the invention versus without modification.

(14) FIG. 4 is a schematic similar to FIG. 1C but showing where the modification of the invention would reside.

IV. DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS OF THE INVENTION

(15) A. Overview

(16) For a better understanding of the invention, specific implementations will now be described in detail. It is to be understood that the invention can take many forms and embodiments. The specific examples below are neither inclusive nor exclusive of all forms and embodiment it can take. Variations obvious to those skilled in the art will be included within the invention.

(17) For example, in generalized form, the invention relates to a modified automated steering (autosteer) system for articulated vehicles. The modified automated steering system includes software which utilizes a feedback loop to compensation for error or offset between a planned navigation path and an actual path. The modification causes the heading rate instructions for articulated vehicles (ArV's) to be similar to front steer (FrV's).

(18) As will be appreciated by those skilled in the art, while applicable to agricultural vehicles (e.g. wheeled or tracked ArV's), it is not limited to them. For example, other ArV's are relevant. A few non-limiting examples are in the construction, and transportation areas.

(19) As will be appreciated by those skilled in the art, the specific examples discussed below include some design choices. Those design choices can vary and be applied in analogous ways to other implementations of the invention. For example, in at least some of the specific examples below, comparison of the performance of the new steering control is between the invention applied to a specific ArV (namely, Steiger 400 see FIG. 1G) and a specific FrV (namely, Case 210 see FIG. 1E). The invention can be applied to, compared to, or tested relative other FrV's or ArV's. Additionally, the designer can adjust the performance according to need or desire.

(20) As will also be appreciated by those skilled in the art, the invention can be applied to a variety of different automated steering systems and vehicles, as well as to ancillary functions of the vehicle. A few non-limiting examples for agricultural vehicles include steering an ArV alone, steering an ArV while concurrently performing some agriculture function (e.g. plowing, planting, cultivating, applying chemicals, harvesting), or steering an ArV while it pulls or pushes an implement or trailer.

(21) B. Generalized Example of Methodology

(22) At a generalized level, the invention can be implemented by a transfer function which is discretely implemented in the code. The coding can be relative to the feedback loop for automated steering control. An example of such automated steering control feedback designs before modification can be at Gnss for Vehicle Control (GNSS Technology and Applications which is incorporated by reference herein (https://www.amazon.com/Gnss-Vehicle-Control-Technology-Applications/dp/1596933011).

(23) The transfer function basically modifies the heading rate equation for a ArV. Certain assumptions are made in creating the transfer function. Ultimately, it causes the heading rate of the ArV steering control to be similar to that of an FrV.

(24) This modification basically smoothes out response to steering changes that otherwise would be generated by the PID controller. This reduces the jerkiness of the articulated vehicle, especially at other than low levels beats. It makes the autosteering feel like a front steer. It does not require radical tuning up the gain of the PID controller for the front steer.

(25) Ways in which the transfer function is designed and implemented into an ArV can be shown by specific examples, as will be set forth below.

(26) C. Specific Example of Methodology

(27) 1. General Method Applied Specifically (Case 210 FrV Vs. Steiger 400 ArV)

(28) In an agricultural automated steering system (e.g. like FIGS. 1A-B), which utilizes one or more PID controllers in a feedback loop (e.g. like FIG. 1C), this embodiment of the invention can be applied to modify the PID programming for an ArV as follows: a. Base the modification on a known FrV. In this example it is a Case 210 (FIG. 1E), where its wheel base between front steer axle and rear axle is indicated by L. b. Base the modification on a known ArV. In this example it is a Steiger 400 (FIG. 1G), where its wheelbase between its center articulation point and the front axle is indicated by L.sub.1, its wheelbase between the center articulation point and the rear axle is indicated by L.sub.2. See FIG. 1J. c. Make the assumption that L.sub.1=L.sub.2 (the front and rear wheelbase have the same length). d. Make the assumption that the maximum range of articulation of the ArV is on the order of <15 degrees. e. Derive a modification function M(s) for the controller to be used when an ArV is selected for steering control according to the following steps: 1. Heading rate equation and the corresponding transfer function for FrV, where L is the wheel base for the Case 210, are:

(29) $\begin{array}{cc}\stackrel{.}{}=\frac{V}{L}\tan \frac{}{}\left(s\right)=\frac{V}{L}\frac{1}{s}& \left(6\right)\end{array}$ 2. Heading rate equation and the corresponding transfer function (using assumptions L.sub.1=L.sub.2, front and rear wheel base have the same length and small articulation angle: <15 deg) for ArV are:

(30) $\begin{array}{cc}\stackrel{.}{}=\frac{V\sin +L_1\stackrel{.}{}}{L_1+L_1\cos }\frac{}{}\left(s\right)=\frac{V+L_{1}s}{2L_1}\frac{1}{s}& \left(7\right)\end{array}$ 3. Modification to the controller for ArV's is as follows:

(31) $\begin{array}{cc}M\left(s\right)=\frac{2V}{L}\frac{1}{s+\frac{V}{L_1}}& \left(8\right)\end{array}$ 4. This modification simply causes the heading rate of ArV to be similar to a FrV as can be seen below:

(32) $\begin{array}{cc}\frac{}{}\left(s\right)=\frac{V+L_{1}s}{2L_1}\frac{1}{s}\frac{2L_1}{V+L_{1}s}\frac{V}{L}=\frac{V}{L}\frac{1}{s}& \left(9\right)\end{array}$ f. To produce the following difference equation from M(s):

(33) 0$\begin{array}{cc}\frac{O}{I}\left(s\right)=M\left(s\right)=\frac{2V}{L}\frac{1}{s+\frac{V}{L_1}}& \left(10\right)\end{array}$ as follows

(34) $\begin{array}{cc}O\left(k+1\right)=e^{\left(-\frac{V}{L_1}T\right)}O\left(k\right)+\frac{2L_1}{L}\left(1-e^{\left(-\frac{V}{L_1}T\right)}\right)I\left(k\right)& \left(11\right)\end{array}$ where, O stands for the output. I stands for the input. T stands for the sampling time, here 0.1 s. V stands for the velocity. L stands for wheel-base for a Case 210. L1 stands for half wheel base for the articulated vehicle. is the vehicle heading angle. is the articulation angle. {dot over ()} is rate of change of the articulation angle. is steering angle for front wheel steered vehicles. S is a complex variable. k is discrete time step

(35) Testing for this specific example validates the modified system. As can be seen in the three graphs below at FIG. 3A-D, using the above-modifier significantly smoothes out steering response (left half of results in each of the three graphs of FIGS. 3A-D). In the graphs, FIGS. 3A and C, the section of graphs between Time 0 and 22.5 have much less deviation in heading error, cross track error, and in steering error (error as used here stands for the difference between actual and target), as compared to non-modified portion (right sections of those graphs between Time 22.5 and 43). The graph (FIG. 3B) shows clearly improvement in steering error. To reveal how much this exemplary embodiment of the invention helps, moderately high gains are selected in the system. In fact, the selected gains are the gains, being used for the CASE 210. FIG. 3D shows the components/contributions of the PID controllers. As seen, in the second part of the test, where the transformer (modifier) is disabled, the jerkiness in steering first yielded oscillation in heading loop, then the oscillation resulted in oscillation in XTE.

(36) 2. Field Testing (See FIGS. 3A-3D)

(37) In test results indicated at FIGS. 3A-D, the embodiment of the invention functioned as follows. The system starts with the modifier of the invention and, then at time 22.5 s, the modifier was turned off. Operation speed was 4 mph. The vehicle followed a straight line.

(38) It can therefore be seen that this specific example achieves at least one or more the stated objects of the invention.

(39) 3. Specific Example of Hardware Set-Up In this example, the modification is coded discretely into the steering controller. This would be at the location labeled transformer in a typical automated steering system as illustrated diagrammatically in FIG. 4.

(40) While this can involve a modification to the PID control software, this embodiment of the invention is a technology transformation with both overt and subtle real-world beneficial results. As mentioned, and as can be seen in FIGS. 3A-D, steering response as controlled by the autosteer does not result in persistent, and sometimes large magnitude changes or even oscillations; as well as realizes an improvement in XTE. This transforms what otherwise is disruptive autosteer to at least that similar to FrV autosteer. This has practical and physical benefits both for the vehicle operator as well as potentially for any function being accomplished by the vehicle.

(41) As mentioned, this modified control for ArV operation can be used with the ArV alone, in conjunction with a function concurrently performed on the field by the ArV, or relative an implement being pulled, pushed, or otherwise operated with the ArV.

(42) 4. Supplemental Supporting Information

(43) Supporting information can be found in the Appendices attached to U.S. Provisional Application 62/446,009, which is incorporated by reference herein in its entirely. Some of the information found there includes:

(44) a. Similar to FIG. 1I herein, the nomenclature used for an ArV modeled vehicle, as well as key assumptions made in the design include: (1) Wheelbases fore and aft (L.sub.1 and L.sub.2) are assumed to be approximately the same length, i.e. the distance from the front wheels to the middle articulation point and the distance from the rear wheels to the middle articulation point (L.sub.1=L.sub.2). (2) Articulation angles () are assumed to be relatively small (i.e. <<90, specifically very small such as approaching 0, namely on the order of <15 or even <) 10. (3) Case 201 FrV dimensional features are compared to Steiger 400.

(45) b. A comparison of Case 210 FrV and Steiger 400 ArV led to the discovery that at least at low speed the rate of change of articulation angle plays a major role in heading angle change of rate.

(46) c. The transfer functions for articulated vehicles and the corresponding investigations led to how PID control loop can be modified to produce the benefits of the invention.

(47) d. the basic relationships used to produce a modification function (transformer) M(s) that can be programmed into the PID control software based on the foundational discoveries. This transformer was first implemented in computer environment for validation and verification.

(48) e. The starting point is comparing heading rate equation and transfer functions for Case 210 FrV versus Steiger 400 ArV, based on the listed assumptions. The modification function M(s) derived is:

(49) $M\left(s\right)=\frac{2V}{L}\frac{1}{s+\frac{V}{L_1}}$
This function causes heading rate of ArV to be similar to FrV. As further noted, it may not require any other substantial modification of the PID.

(50) f. A computerized simulation of expected autosteer system performance for ArV Steiger 400 with parameters was used in the simulation (note: simulations show closed loop characteristics without noise, which typically would exist at some level).

(51) g. The computerized simulation of expected autosteer performance of an ArV such as Steiger 400, including heading and XTE performance results with the modification function of the invention applied, illustrated smoothness of performance including heading, XTE and other.

(52) h. ArV with modification function behaves similar to FrV in XTE performance.

(53) i. ArV with modification eliminates noisy performance regarding both heading and steering.

(54) D. Options and Alternatives

(55) The foregoing describes generalized and specific forms of the invention. As previously stated, the invention can take many forms and embodiments. Persons of skill in this technical area will appreciate the same.

(56) For example, the invention can be tailored for application to a variety of ArV's. The designer would have to take into consideration the specifics of the particular ArV, but can apply the generalized invention in an analogous way.

(57) By further example, the invention can be installed and operated in a variety of ways. It can be integrated into a control loop of the automated steering system with discrete code. It can also be integrated to modify driver steering input to avoid change in articulation angle in standing still for safety and to provide smoother operation in moving condition.

(58) The assumptions upon which the modification function is based can vary. Examples are the wheel base lengths of the selected front wheel steered and articulated vehicles used.

(59) Other options or alternatives for the designer are to use different sampling time, to use more or less wheel base lengths to smooth out or make the steering more aggressive.