Automatic Control of Passive, Towed Implements

• US 20100084147A1
• Filed: 10/02/2008
• Published: 04/08/2010
• Est. Priority Date: 10/02/2008
• Status: Active Grant

• Current Assignee: Trimble Navigation Limited (Trimble Inc.)
• Original Assignee: Trimble Navigation Limited (Trimble Inc.)
• Inventors: Aral, Gurcan
• Granted Patent: US 8,112,201 B2
• Time in Patent Office: Days
• US Class Current: 172/1
• CPC Class Codes: A01B 69/004 automatic
• CPC Class Codes: G05D 1/021 specially adapted to land vehicles

Abstract

An automatic control system for passive, towed implements is described. The system provides a strategy for optimal control of a towed implement using a nudge input to an autopilot-controlled tractor. Implement path-tracking error, as measured by a GNSS receiver, is consistently corrected to zero.

Claims

1. A control system for towing a passive implement along a desired path with an autopilot-controlled tractor comprising:

a GNSS receiver mounted on the implement;

a model; and

,

a control module;

wherein,

the implement is connected to the tractor by a hitch,

the GNSS receiver measures position and speed of the implement,

the model estimates immediate implement offset and delayed offset of the tractor-hitch-implement system from the desired path,

the control module sends nudge commands to the autopilot-controlled tractor such that implement offset from the desired path is minimized.

2. The control system of claim 1 wherein the model comprises implement, tractor and hitch elements ordered within the model so that nudge inputs to the model are applied directly to the input of the implement element and the output of the implement element is fed back to the control module.

3. The control system of claim 2 wherein the tractor element of the model includes the tractor wheelbase and a critically damped, second order system characterized by the time, τ

, required for the tractor to respond to a nudge input.

4. The control system of claim 3 wherein T is between 1 and 2 seconds.

5. The control system of claim 2 wherein the hitch element of the model includes the distance from the hitch to the midpoint of the tractor'"'"'s rear axle.

6. The control system of claim 2 wherein the implement element of the model includes the distance from the implement'"'"'s control point to the hitch.

7. The control system of claim 1 wherein the GNSS receiver is a GPS receiver employing SBAS corrections.

8. The control system of claim 7 wherein the SBAS corrections are obtained from the FAA WAAS.

9. The control system of claim 1 wherein the GNSS receiver is a GPS receiver employing RTK positioning.

10. A method for guiding a passive implement along a desired path comprising:

providing an autopilot-controlled tractor having a nudge input;

providing a GNSS receiver fixed to the implement;

towing the implement behind the tractor via a hitch;

using a model of the tractor—

hitch—

implement system to provide feedback to a control system that provides nudge inputs to the autopilot-controlled tractor and to the model;

wherein,

the model estimates the immediate implement offset from the path;

tractor, hitch and implement elements within the model are arranged such that nudge inputs from the control system are applied to the implement element directly; and

,

the control system nudge inputs cause the difference between the actual implement path and desired path to be minimized.

11. The method of claim 10 wherein the tractor element of the model includes the tractor wheelbase and a critically damped, second order system characterized by the time, τ

, required for the tractor to respond to a nudge input.

12. The method of claim 11 wherein T is between 1 and 2 seconds.

13. The method of claim 10 wherein the hitch element of the model includes the distance from the hitch to the midpoint of the tractor'"'"'s rear axle.

14. The method of claim 10 wherein the implement element of the model includes the distance from the implement'"'"'s control point to the hitch.

15. The method of claim 10 wherein the GNSS receiver is a GPS receiver employing SBAS corrections.

16. The method of claim 15 wherein the SBAS corrections are obtained from the FM WAAS.

17. The method of claim 10 wherein the GNSS receiver is a GPS receiver employing RTK positioning.

18. A control system for a passive implement towed by an autopilot-controlled tractor comprising:

an inner feedback loop that uses estimated immediate implement offsets from a desired path to modify the dynamic behavior of the implement;

an outer feedback loop that uses the difference between estimated delayed implement offsets from the path and actual measured implement offsets from the path to compensate for drift and disturbances; and

,

a control module that combines measured implement speed with error signals generated by the inner and outer loops to generate nudge commands that are fed to the tractor'"'"'s autopilot such that the implement offset from the desired path is minimized.

19. The system of claim 18 wherein the nudge commands are fed to a model of the implement as well as to the tractor autopilot.

20. The system of claim 18 wherein the control module comprises an amplifier that amplifies the combined error signal generated by the inner and outer loops in proportion to the distance between the implement'"'"'s hitch point and the location of a GNSS receiver mounted on the implement.

21. The system of claim 18 wherein the control module comprises an integrator that integrates the product of the implement'"'"'s speed as measured by a GNSS receiver and the combined error signal generated by the inner and outer loops.

22. The system of claim 18 wherein the control module comprises proportional and integral elements, the outputs of which are summed to generate the nudge commands.

23. The system of claim 18 further comprising an operator'"'"'s implement nudge input for offsetting the implement from its desired path by a specified distance.

24. A control system for a passive implement towed by an autopilot-controlled tractor comprising:

a GNSS receiver mounted on the implement; and

,

a feedback loop incorporating a Smith predictor, wherein,

nudge commands are sent to the tractor'"'"'s autopilot and to a model of a tractor—

hitch—

implement system,

estimated immediate implement offset (from a desired path) obtained from the model is used to speed up the response of the implement, and,

estimated delayed implement offset obtained from the model is compared to actual implement offset to compensate for process disturbances.

25. The control system of claim 24 further comprising a control module that:

a. amplifies an error signal in the feedback loop in proportion to the distance between the implement'"'"'s hitch point and its GNSS receiver antenna,

b. multiplies the error signal by the speed of the implement and integrates the result over time, and,

c. sums the results of operations (a) and (b) to generate the nudge commands.